XMPP Working Group P. Saint-Andre (ed.) Internet-Draft Jabber Software Foundation Expires: July 6, 2004 January 6, 2004 Extensible Messaging and Presence Protocol (XMPP): Core draft-ietf-xmpp-core-21 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on July 6, 2004. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This memo defines the core features of the Extensible Messaging and Presence Protocol (XMPP), a protocol for streaming Extensible Markup Language (XML) elements in order to exchange structured information in close to real time between any two network endpoints. While XMPP provides a generalized, extensible framework for exchanging XML data, it is used mainly for the purpose of building instant messaging and presence applications that meet the requirements of RFC 2779. Saint-Andre (ed.) Expires July 6, 2004 [Page 1] Internet-Draft XMPP Core January 2004 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Generalized Architecture . . . . . . . . . . . . . . . . . . . 4 3. Addressing Scheme . . . . . . . . . . . . . . . . . . . . . . 6 4. XML Streams . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Use of TLS . . . . . . . . . . . . . . . . . . . . . . . . . . 19 6. Use of SASL . . . . . . . . . . . . . . . . . . . . . . . . . 26 7. Resource Binding . . . . . . . . . . . . . . . . . . . . . . . 36 8. Server Dialback . . . . . . . . . . . . . . . . . . . . . . . 39 9. XML Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 46 10. Server Rules for Handling XML Stanzas . . . . . . . . . . . . 55 11. XML Usage within XMPP . . . . . . . . . . . . . . . . . . . . 57 12. Core Compliance Requirements . . . . . . . . . . . . . . . . . 60 13. Internationalization Considerations . . . . . . . . . . . . . 61 14. Security Considerations . . . . . . . . . . . . . . . . . . . 61 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 66 Normative References . . . . . . . . . . . . . . . . . . . . . 69 Informative References . . . . . . . . . . . . . . . . . . . . 71 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 72 A. Nodeprep . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 B. Resourceprep . . . . . . . . . . . . . . . . . . . . . . . . . 74 C. XML Schemas . . . . . . . . . . . . . . . . . . . . . . . . . 76 D. Differences Between Core Jabber Protocol and XMPP . . . . . . 83 E. Revision History . . . . . . . . . . . . . . . . . . . . . . . 85 Intellectual Property and Copyright Statements . . . . . . . . 94 Saint-Andre (ed.) Expires July 6, 2004 [Page 2] Internet-Draft XMPP Core January 2004 1. Introduction 1.1 Overview The Extensible Messaging and Presence Protocol (XMPP) is an open XML [XML] protocol for near-real-time messaging, presence, and request-response services. The basic syntax and semantics were developed originally within the Jabber open-source community, mainly in 1999. In 2002, the XMPP WG was chartered with developing an adaptation of the Jabber protocol that would be suitable as an IETF instant messaging (IM) and presence technology. As a result of work by the XMPP WG, the current memo defines the core features of XMPP; Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence [XMPP-IM] defines the extensions required to provide the instant messaging and presence functionality defined in RFC 2779 [IMP-REQS]. 1.2 Terminology The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [TERMS]. 1.3 Contributors Most of the core aspects of the Extensible Messaging and Presence Protocol were developed originally within the Jabber open-source community in 1999. This community was founded by Jeremie Miller, who released source code for the initial version of the jabberd server in January 1999. Major early contributors to the base protocol also included Ryan Eatmon, Peter Millard, Thomas Muldowney, and Dave Smith. Work by the XMPP Working Group has concentrated especially on security and internationalization; in these areas, protocols for the use of TLS and SASL were originally contributed by Rob Norris, and stringprep profiles were originally contributed by Joe Hildebrand. The error code syntax was suggested by Lisa Dusseault. 1.4 Acknowledgements Thanks are due to a number of individuals in addition to the contributors listed. Although it is difficult to provide a complete list, the following individuals were particularly helpful in defining the protocols or in commenting on the specifications in this memo: Thomas Charron, Richard Dobson, Sam Hartman, Schuyler Heath, Jonathan Hogg, Craig Kaes, Jacek Konieczny, Alexey Melnikov, Keith Minkler, Julian Missig, Pete Resnick, Marshall Rose, Alexey Shchepin, Jean-Louis Seguineau, Iain Shigeoka, and David Waite. Thanks also to Saint-Andre (ed.) Expires July 6, 2004 [Page 3] Internet-Draft XMPP Core January 2004 members of the XMPP Working Group and the IETF community for comments and feedback provided throughout the life of this memo. 2. Generalized Architecture 2.1 Overview Although XMPP is not wedded to any specific network architecture, to date it usually has been implemented via a typical client-server architecture, wherein a client utilizing XMPP accesses a server over a TCP [TCP] socket. The following diagram provides a high-level overview of this architecture (where "-" represents communications that use XMPP and "=" represents communications that use any other protocol). C1 - S1 - S2 - C3 / \ C2 - G1 = FN1 = FC1 The symbols are as follows: o C1, C2, C3 -- XMPP clients o S1, S2 -- XMPP servers o G1 -- A gateway that translates between XMPP and the protocol(s) used on a foreign (non-XMPP) messaging network o FN1 -- A foreign messaging network o FC1 -- A client on a foreign messaging network 2.2 Server A server acts as an intelligent abstraction layer for XMPP communications. Its primary responsibilities are: o to manage connections from or sessions for other entities, in the form of XML streams (Section 4) to and from authorized clients, servers, and other entities o to route appropriately-addressed XML stanzas (Section 9) among such entities over XML streams Most XMPP-compliant servers also assume responsibility for the storage of data that is used by clients (e.g., contact lists for Saint-Andre (ed.) Expires July 6, 2004 [Page 4] Internet-Draft XMPP Core January 2004 users of XMPP-based instant messaging and presence applications); in this case, the XML data is processed directly by the server itself on behalf of the client and is not routed to another entity. 2.3 Client Most clients connect directly to a server over a [TCP] socket and use XMPP to take full advantage of the functionality provided by a server and any associated services. Although there is no necessary coupling of an XML stream to a TCP socket (e.g., a client could connect via HTTP [HTTP] polling or some other mechanism), this specification defines a binding of XMPP to TCP only. Multiple resources (e.g., devices or locations) MAY connect simultaneously to a server on behalf of each authorized client, with each resource differentiated by the resource identifier of an XMPP address (e.g., vs. ) as defined under Addressing Scheme (Section 3). The RECOMMENDED port for connections between a client and a server is 5222, as registered with the IANA (see Port Numbers (Section 15.9)). 2.4 Gateway A gateway is a special-purpose server-side service whose primary function is to translate XMPP into the protocol used by a foreign (non-XMPP) messaging system, as well as to translate the return data back into XMPP. Examples are gateways to Internet Relay Chat (IRC), Short Message Service (SMS), SIMPLE, SMTP, and legacy instant messaging networks such as AIM, ICQ, MSN Messenger, and Yahoo! Instant Messenger. Communications between gateways and servers, and between gateways and the foreign messaging system, are not defined in this document. 2.5 Network Because each server is identified by a network address and because server-to-server communications are a straightforward extension of the client-to-server protocol, in practice the system consists of a network of servers that inter-communicate. Thus user-a@domain1 is able to exchange messages, presence, and other information with user-b@domain2. This pattern is familiar from messaging protocols (such as SMTP) that make use of network addressing standards. Communications between any two servers are OPTIONAL. If enabled, such communications SHOULD occur over XML streams that are bound to [TCP] sockets. The RECOMMENDED port for connections between servers is 5269, as registered with the IANA (see Port Numbers (Section 15.9)). Saint-Andre (ed.) Expires July 6, 2004 [Page 5] Internet-Draft XMPP Core January 2004 3. Addressing Scheme 3.1 Overview An entity is anything that can be considered a network endpoint (i.e., an ID on the network) and that can communicate using XMPP. All such entities are uniquely addressable in a form that is consistent with RFC 2396 [URI]. For historical reasons, the address of an XMPP entity is called a Jabber Identifier or JID. A valid JID contains a set of ordered elements formed of a domain identifier, node identifier, and resource identifier. The syntax for a JID is defined below using Augmented Backus-Naur Form as defined in [ABNF]. The IPv4address and IPv6address rules are defined in Appendix B of [IPv6]; the allowable character sequences that conform to the node rule are defined by the Nodeprep (Appendix A) profile of [STRINGPREP] as documented in this memo; the allowable character sequences that conform to the resource rule are defined by the Resourceprep (Appendix B) profile of [STRINGPREP] as documented in this memo; and the sub-domain rule makes reference to the concept of a domain label as described in [IDNA]. jid = [ node "@" ] domain [ "/" resource ] domain = fqdn / address-literal fqdn = (sub-domain 1*("." sub-domain)) sub-domain = ([IDNA] conformant domain label) address-literal = IPv4address / IPv6address All JIDs are based on the foregoing structure. The most common use of this structure is to identify an instant messaging user, the server to which the user connects, and the user's connected resource (e.g., a specific client) in the form of . However, node types other than clients are possible; for example, a specific chat room offered by a multi-user chat service could be addressed as (where "room" is the name of the chat room and "service" is the hostname of the multi-user chat service) and a specific occupant of such a room could be addressed as (where "nick" is the occupant's room nickname). Many other JID types are possible (e.g., could be a server-side script or service). Each allowable portion of a JID (node identifier, domain identifier, and resource identifier) MUST NOT be more than 1023 bytes in length, resulting in a maximum total size (including the '@' and '/' separators) of 3071 bytes. 3.2 Domain Identifier Saint-Andre (ed.) Expires July 6, 2004 [Page 6] Internet-Draft XMPP Core January 2004 The domain identifier is the primary identifier and is the only REQUIRED element of a JID (a mere domain identifier is a valid JID). It usually represents the network gateway or "primary" server to which other entities connect for XML routing and data management capabilities. However, the entity referenced by a domain identifier is not always a server, and may be a service that is addressed as a subdomain of a server and that provides functionality above and beyond the capabilities of a server (e.g., a multi-user chat service, a user directory, or a gateway to a foreign messaging system). The domain identifier for every server or service that will communicate over a network MAY be an IP address but SHOULD be a fully qualified domain name (see [DNS]). A domain identifier MUST be an "internationalized domain name" as defined in [IDNA], to which the Nameprep [NAMEPREP] profile of stringprep [STRINGPREP] can be applied without failing. Before comparing two domain identifiers, a server MUST (and a client SHOULD) first apply the Nameprep profile to the labels (as defined in [IDNA]) that make up each identifier. 3.3 Node Identifier The node identifier is an optional secondary identifier placed before the domain identifier and separated from the latter by the '@' character. It usually represents the entity requesting and using network access provided by the server or gateway (i.e., a client), although it can also represent other kinds of entities (e.g., a chat room associated with a multi-user chat service). The entity represented by a node identifier is addressed within the context of a specific domain; within instant messaging and presence applications of XMPP this address is called a "bare JID" and is of the form . A node identifier MUST be formatted such that the Nodeprep (Appendix A) profile of [STRINGPREP] can be applied to it without failing. Before comparing two node identifiers, a server MUST (and a client SHOULD) first apply the Nodeprep profile to each identifier. 3.4 Resource Identifier The resource identifier is an optional tertiary identifier placed after the domain identifier and separated from the latter by the '/' character. A resource identifier may modify either a or mere address. It usually represents a specific session, connection (e.g., a device or location), or object (e.g., a participant in a multi-user chat room) belonging to the entity associated with a node identifier. A resource identifier is opaque to both servers and other clients, and is typically defined by a client implementation when it provides the information necessary to Saint-Andre (ed.) Expires July 6, 2004 [Page 7] Internet-Draft XMPP Core January 2004 complete Resource Binding (Section 7) (although it may be generated by a server on behalf of a client), after which it is referred to as a "connected resource". An entity MAY maintain multiple connected resources simultaneously, with each connected resource differentiated by a distinct resource identifier. A resource identifier MUST be formatted such that the Resourceprep (Appendix B) profile of [STRINGPREP] can be applied to it without failing. Before comparing two resource identifiers, a server MUST (and a client SHOULD) first apply the Resourceprep profile to each identifier. 3.5 Determination of Addresses After SASL negotiation (Section 6) and, if appropriate, Resource Binding (Section 7), the receiving entity for a stream MUST determine the initiating entity's JID. For server-to-server communications, the initiating entity's JID SHOULD be the authorization identity, derived from the authentication identity as defined by the Simple Authentication and Security Layer (SASL) specification [SASL] if no authorization identity was specified during SASL negotiation (Section 6). For client-to-server communications, the "bare JID" () SHOULD be the authorization identity, derived from the authentication identity as defined in [SASL] if no authorization identity was specified during SASL negotiation (Section 6); the resource identifier portion of the "full JID" () SHOULD be the resource identifier negotiated by the client and server during Resource Binding (Section 7). The receiving entity MUST ensure that the resulting JID (including node identifier, domain identifier, resource identifier, and separator characters) conforms to the rules and formats defined earlier in this section; to meet this restriction, the receiving entity may need to replace the JID sent by the initiating entity with the canonicalized JID as determined by the receiving entity. 4. XML Streams 4.1 Overview Two fundamental concepts make possible the rapid, asynchronous exchange of relatively small payloads of structured information between presence-aware entities: XML streams and XML stanzas. These terms are defined as follows: Saint-Andre (ed.) Expires July 6, 2004 [Page 8] Internet-Draft XMPP Core January 2004 Definition of XML Stream: An XML stream is a container for the exchange of XML elements between any two entities over a network. An XML stream is negotiated from an initiating entity (usually a client or server) to a receiving entity (usually a server), normally over a [TCP] socket, and corresponds to the initiating entity's "session" with the receiving entity. The start of the XML stream is denoted unambiguously by an opening XML tag (with appropriate attributes and namespace declarations), while the end of the XML stream is denoted unambiguously by a closing XML tag. An XML stream is unidirectional; in order to enable bidirectional information exchange, the initiating entity and receiving entity MUST negotiate one stream in each direction (the "initial stream" and the "response stream"), normally over the same TCP connection. Definition of XML Stanza: An XML stanza is a discrete semantic unit of structured information that is sent from one entity to another over an XML stream. An XML stanza exists at the direct child level of the root element and is said to be well-balanced if it matches production [43] content of [XML]. The start of any XML stanza is denoted unambiguously by the element start tag at depth=1 of the XML stream (e.g., ), and the end of any XML stanza is denoted unambiguously by the corresponding close tag at depth=1 (e.g., ). An XML stanza MAY contain child elements (with accompanying attributes, elements, and CDATA) as necessary in order to convey the desired information. The only defined XML stanzas are , , and as defined under XML Stanzas (Section 9); an XML element sent for the purpose of Transport Layer Security (TLS) negotiation (Section 5), Simple Authentication and Security Layer (SASL) negotiation (Section 6), or server dialback (Section 8) is not considered to be an XML stanza. Consider the example of a client's session with a server. In order to connect to a server, a client MUST initiate an XML stream by sending an opening tag to the server, optionally preceded by a text declaration specifying the XML version and the character encoding supported (see Inclusion of Text Declaration (Section 11.4); see also Character Encoding (Section 11.5)). Subject to local policies and service provisioning, the server SHOULD then reply with a second XML stream back to the client, again optionally preceded by a text declaration. Once the client has completed SASL negotiation (Section 6), the client MAY send an unbounded number of XML stanzas over the stream to any recipient on the network. When the client desires to close the stream, it simply sends a closing tag to the server (alternatively, the stream may be closed by the server), after which both the client and server SHOULD close the underlying TCP connection as well. Saint-Andre (ed.) Expires July 6, 2004 [Page 9] Internet-Draft XMPP Core January 2004 Those who are accustomed to thinking of XML in a document-centric manner may wish to view a client's session with a server as consisting of two open-ended XML documents: one from the client to the server and one from the server to the client. From this perspective, the root element can be considered the document entity for each "document", and the two "documents" are built up through the accumulation of XML stanzas sent over the two XML streams. However, this perspective is a convenience only, and XMPP does not deal in documents but in XML streams and XML stanzas. In essence, then, an XML stream acts as an envelope for all the XML stanzas sent during a session. We can represent this in a simplistic fashion as follows: |--------------------| | | |--------------------| | | | | | | |--------------------| | | | | | | |--------------------| | | | | | | |--------------------| | ... | |--------------------| | | |--------------------| 4.2 Stream Attributes The attributes of the stream element are as follows: o to -- The 'to' attribute SHOULD be used only in the XML stream header from the initiating entity to the receiving entity, and MUST be set to a hostname serviced by the receiving entity. There SHOULD be no 'to' attribute set in the XML stream header by which the receiving entity replies to the initiating entity; however, if a 'to' attribute is included, it SHOULD be silently ignored by the initiating entity. o from -- The 'from' attribute SHOULD be used only in the XML stream Saint-Andre (ed.) Expires July 6, 2004 [Page 10] Internet-Draft XMPP Core January 2004 header from the receiving entity to the initiating entity, and MUST be set to a hostname serviced by the receiving entity that is granting access to the initiating entity. There SHOULD be no 'from' attribute on the XML stream header sent from the initiating entity to the receiving entity; however, if a 'from' attribute is included, it SHOULD be silently ignored by the receiving entity. o id -- The 'id' attribute SHOULD be used only in the XML stream header from the receiving entity to the initiating entity. This attribute is a unique identifier created by the receiving entity to function as a session key for the initiating entity's streams with the receiving entity, and MUST be unique within the receiving application (normally a server). Note well that the stream ID may be security-critical and therefore MUST be both unpredictable and non-repeating. There SHOULD be no 'id' attribute on the XML stream header sent from the initiating entity to the receiving entity; however, if an 'id' attribute is included, it SHOULD be silently ignored by the receiving entity. o xml:lang -- An 'xml:lang' attribute (as defined in Section 2.12 of [XML]) SHOULD be included by the initiating entity on the header for the initial stream to specify the default language of any human-readable XML character data it sends over that stream. If the attribute is included, the receiving entity SHOULD remember that value as the default for both the initial stream and the response stream; if the attribute is not included, the receiving entity SHOULD use a configurable default value for both streams, which it MUST communicate in the header for the response stream. For all stanzas sent over the initial stream, if the initiating entity does not include an 'xml:lang' attribute, the receiving entity SHOULD apply the default value; if the initiating entity does include an 'xml:lang' attribute, the receiving entity MUST NOT modify or delete it (see also xml:lang (Section 9.1.5)). The value of the 'xml:lang' attribute MUST be an NMTOKEN (as defined in Section 2.3 of [XML]) and MUST conform to the format defined in RFC 3066 [LANGTAGS]. o version -- The presence of the version attribute set to a value of "1.0" signals support for the stream-related protocols (including stream features) defined in this specification. Detailed rules regarding generation and handling of this attribute are defined below. We can summarize as follows: | initiating to receiving | receiving to initiating ---------+---------------------------+----------------------- to | hostname of receiver | silently ignored Saint-Andre (ed.) Expires July 6, 2004 [Page 11] Internet-Draft XMPP Core January 2004 from | silently ignored | hostname of receiver id | silently ignored | session key xml:lang | default language | default language version | signals XMPP 1.0 support | signals XMPP 1.0 support 4.2.1 Version Support The version of XMPP specified herein is "1.0"; in particular, this encapsulates the stream-related protocols (Use of TLS (Section 5), Use of SASL (Section 6), and Stream Errors (Section 4.6)) as well as the semantics of the three defined XML stanza types (, , and ). The major version number should be incremented only if the stream and stanza formats or required actions have changed so dramatically that an older version entity would not be able to interoperate with a newer version entity if it simply ignored the elements and attributes it did not understand and took the actions specified in the older specification. The minor version number indicates new capabilities, and MUST be ignored by an entity with a smaller minor version number, but used for informational purposes by the node with the larger minor version number. For example, a minor version number might indicate the ability to process a newly defined value of the 'type' attribute for message, presence, or IQ stanzas; the node with the larger minor version number would simply note that its correspondent would not be able to understand that value of the 'type' attribute and therefore would not send it. The following rules apply to the generation and handling by implementations of the 'version' attribute within stream headers: 1. The initiating entity MUST set the value of the 'version' attribute on the initial stream header to the highest version number it supports (e.g., if the highest version number it supports is that defined in this specification, it MUST set the value to "1.0"). 2. The receiving entity MUST set the value of the 'version' attribute on the response stream header to either the value supplied by the initiating entity or highest version number supported by the receiving entity, whichever is lower. The receiving entity MUST perform a numeric comparison, not a string match. 3. If the version number included in the response stream header is at least one major version lower than the version number included in the initial stream header and newer version entities cannot interoperate with older version entities as described above, the initiating entity SHOULD generate an Saint-Andre (ed.) Expires July 6, 2004 [Page 12] Internet-Draft XMPP Core January 2004 stream error and terminate the XML stream and underlying TCP connection. 4. If either entity receives a stream header with no 'version' attribute, the entity MUST consider the version supported by the other entity to be "0.0" and SHOULD NOT include a 'version' attribute in the stream header it sends in reply. 4.3 Namespace Declarations The stream element MUST possess both a streams namespace declaration and a default namespace declaration (as "namespace declaration" is defined in the XML namespaces specification [XML-NAMES]). For detailed information regarding the streams namespace and default namespace, see Namespace Names and Prefixes (Section 11.2). 4.4 Stream Features If the initiating entity includes the 'version' attribute set to a value of "1.0" in the initial stream header, the receiving entity MUST send a child element (prefixed by the streams namespace prefix) to the initiating entity in order to announce any stream-level features that can be negotiated (or capabilities that otherwise need to be advertised). Currently this is used only to advertise Use of TLS (Section 5), Use of SASL (Section 6), and Resource Binding (Section 7) as defined herein, and for Session Establishment as defined in [XMPP-IM]; however, the stream features functionality could be used to advertise other negotiable features in the future. If an entity does not understand or support some features, it SHOULD silently ignore them. 4.5 Stream Security When negotiating XML streams in XMPP 1.0, TLS SHOULD be used as defined under Use of TLS (Section 5) and SASL MUST be used as defined under Use of SASL (Section 6). If the initiating entity attempts to send an XML Stanza (Section 9) before the stream has been authenticated, the receiving entity SHOULD return a stream error to the initiating entity and then terminate both the XML stream and the underlying TCP connection. 4.6 Stream Errors The root stream element MAY contain an child element that is prefixed by the streams namespace prefix. The error child MUST be sent by a compliant entity (usually a server rather than a client) if it perceives that a stream-level error has occurred. Saint-Andre (ed.) Expires July 6, 2004 [Page 13] Internet-Draft XMPP Core January 2004 4.6.1 Rules The following rules apply to stream-level errors: o It is assumed that all stream-level errors are unrecoverable; therefore, if an error occurs at the level of the stream, the entity that detects the error MUST send a stream error to the other entity, send a closing tag, and terminate the underlying TCP connection. o If the error occurs while the stream is being set up, the receiving entity MUST still send the opening tag, include the element as a child of the stream element, send the closing tag, and terminate the underlying TCP connection. In this case, if the initiating entity provides an unknown host in the 'to' attribute (or provides no 'to' attribute at all), the server SHOULD provide the server's authoritative hostname in the 'from' attribute of the stream header sent before termination. 4.6.2 Syntax The syntax for stream errors is as follows: OPTIONAL descriptive text [OPTIONAL application-specific condition element] The element: o MUST contain a child element corresponding to one of the defined stanza error conditions defined below; this element MUST be qualified by the 'urn:ietf:params:xml:ns:xmpp-streams' namespace o MAY contain a child containing CDATA that describes the error in more detail; this element MUST be qualified by the 'urn:ietf:params:xml:ns:xmpp-streams' namespace and SHOULD possess an 'xml:lang' attribute o MAY contain a child element for an application-specific error condition; this element MUST be qualified by an application-defined namespace, and its structure is defined by that namespace Saint-Andre (ed.) Expires July 6, 2004 [Page 14] Internet-Draft XMPP Core January 2004 The element is OPTIONAL. If included, it SHOULD be used only to provide descriptive or diagnostic information that supplements the meaning of a defined condition or application-specific condition. It SHOULD NOT be interpreted programmatically by an application. It SHOULD NOT be used as the error message presented to a user, but MAY be shown in addition to the error message associated with the included condition element (or elements). 4.6.3 Defined Conditions The following stream-level error conditions are defined: o -- the entity has sent XML that cannot be processed; this error MAY be used rather than more specific XML-related errors such as , , , , and , although the more specific errors are preferred. o -- the entity has sent a namespace prefix that is unsupported, or has sent no namespace prefix on an element that requires such a prefix (see XML Namespace Names and Prefixes (Section 11.2)). o -- the server is closing the active stream for this entity because a new stream has been initiated that conflicts with the existing stream. o -- the entity has not generated any traffic over the stream for some period of time (configurable according to a local service policy). o -- the value of the 'to' attribute provided by the initiating entity in the stream header corresponds to a hostname that is no longer hosted by the server. o -- the value of the 'to' attribute provided by the initiating entity in the stream header does not correspond to a hostname that is hosted by the server. o -- a stanza sent between two servers lacks a 'to' or 'from' attribute (or the attribute has no value). o -- the server has experienced a misconfiguration or an otherwise-undefined internal error that prevents it from servicing the stream. o -- the JID or hostname provided in a 'from' Saint-Andre (ed.) Expires July 6, 2004 [Page 15] Internet-Draft XMPP Core January 2004 address does not match an authorized JID or validated domain negotiated between servers via SASL or dialback, or between a client and a server via authentication and resource binding. o -- the stream ID or dialback ID is invalid or does not match an ID previously provided. o -- the streams namespace name is something other than "http://etherx.jabber.org/streams" or the dialback namespace name is something other than "jabber:server:dialback" (see XML Namespace Names and Prefixes (Section 11.2)). o -- the entity has sent invalid XML over the stream to a server that performs validation (see Validation (Section 11.3)). o -- the entity has attempted to send data before the stream has been authenticated, or otherwise is not authorized to perform an action related to stream negotiation; the receiving entity MUST NOT process the offending stanza before sending the stream error. o -- the entity has violated some local service policy; the server MAY choose to specify the policy in the element. o -- the server is unable to properly connect to a remote entity that is required for authentication or authorization. o -- the server lacks the system resources necessary to service the stream. o -- the entity has attempted to send restricted XML features such as a comment, processing instruction, DTD, entity reference, or unescaped character (see Restrictions (Section 11.1)). o -- the server will not provide service to the initiating entity but is redirecting traffic to another host; the server SHOULD specify the alternate hostname or IP address (which MUST be a valid domain identifier) in the CDATA of the element. o -- the server is being shut down and all active streams are being closed. o -- the error condition is not one of those Saint-Andre (ed.) Expires July 6, 2004 [Page 16] Internet-Draft XMPP Core January 2004 defined by the other conditions in this list; this error condition SHOULD be used only in conjunction with an application-specific condition. o -- the initiating entity has encoded the stream in an encoding that is not supported by the server (see Character Encoding (Section 11.5)). o -- the initiating entity has sent a first-level child of the stream that is not supported by the server. o -- the value of the 'version' attribute provided by the initiating entity in the stream header specifies a version of XMPP that is not supported by the server; the server MAY specify the version(s) it supports in the element. o -- the initiating entity has sent XML that is not well-formed as defined by [XML]. 4.6.4 Application-Specific Conditions As noted, an application MAY provide application-specific stream error information by including a properly-namespaced child in the error element. The application-specific element SHOULD supplement or further qualify a defined element. Thus the element will contain two or three child elements: Some special application diagnostic information! 4.7 Simplified Stream Examples This section contains two simplified examples of a stream-based "session" of a client on a server (where the "C" lines are sent from the client to the server, and the "S" lines are sent from the server to the client); these examples are included for the purpose of illustrating the concepts introduced thus far. Saint-Andre (ed.) Expires July 6, 2004 [Page 17] Internet-Draft XMPP Core January 2004 A basic "session": C: S: ... encryption, authentication, and resource binding ... C: C: Art thou not Romeo, and a Montague? C: S: S: Neither, fair saint, if either thee dislike. S: C: S: A "session" gone bad: C: S: ... encryption, authentication, and resource binding ... C: Bad XML, no closing body tag! Saint-Andre (ed.) Expires July 6, 2004 [Page 18] Internet-Draft XMPP Core January 2004 S: S: 5. Use of TLS 5.1 Overview XMPP includes a method for securing the stream from tampering and eavesdropping. This channel encryption method makes use of the Transport Layer Security (TLS) protocol [TLS], along with a "STARTTLS" extension that is modelled after similar extensions for the IMAP [IMAP], POP3 [POP3], and ACAP [ACAP] protocols as described in RFC 2595 [USINGTLS]. The namespace name for the STARTTLS extension is 'urn:ietf:params:xml:ns:xmpp-tls'. An administrator of a given domain MAY require the use of TLS for client-to-server communications, server-to-server communications, or both. Clients SHOULD use TLS to secure the streams prior to attempting to complete SASL negotiation (Section 6), and servers SHOULD use TLS between two domains for the purpose of securing server-to-server communications. The following rules apply: 1. An initiating entity that complies with this specification MUST include the 'version' attribute set to a value of "1.0" in the initial stream header. 2. If the TLS negotiation occurs between two servers, communications MUST NOT proceed until the Domain Name System (DNS) hostnames asserted by the servers have been resolved (see Server-to-Server Communications (Section 14.4)). 3. When a receiving entity that complies with this specification receives an initial stream header that includes the 'version' attribute set to a value of "1.0", after sending a stream header in reply (including the version flag) it MUST include a element (qualified by the 'urn:ietf:params:xml:ns:xmpp-tls' namespace) along with the list of other stream features it supports. 4. If the initiating entity chooses to use TLS, TLS negotiation MUST be completed before proceeding to SASL negotiation; this order of negotiation is required in order to help safeguard Saint-Andre (ed.) Expires July 6, 2004 [Page 19] Internet-Draft XMPP Core January 2004 authentication information sent during SASL negotiation, as well as to make it possible to base the use of the SASL EXTERNAL mechanism on a certificate provided during prior TLS negotiation. 5. During TLS negotiation, an entity MUST NOT send any white space characters (matching production [3] content of [XML]) within the root stream element as separators between elements (any white space characters shown in the TLS examples below are included for the sake of readability only); this prohibition helps to ensure proper security layer byte precision. 6. The receiving entity MUST consider the TLS negotiation to have begun immediately after sending the closing ">" character of the element. The initiating entity MUST consider the TLS negotiation to have begun immediately after receiving the closing ">" character of the element from the receiving entity. 7. The initiating entity MUST validate the certificate presented by the receiving entity; see Certificate Validation (Section 14.2) regarding certificate validation procedures. 8. Certificates MUST be checked against the hostname as provided by the initiating entity (e.g., a user), not the hostname as resolved via the Domain Name System; e.g., if the user or certificate specifies a hostname of "example.com" but a DNS SRV [SRV] lookup returned "im.example.com", the certificate MUST be checked as "example.com". If a JID is represented in a certificate, it SHOULD be encoded using the otherName choice of the subjectAltName type along with a type-id of "xmpp" (as these terms are profiled in [X509]). 9. Certificates MUST be checked against the hostname as provided by the initiating entity (e.g., a user), not the hostname as resolved via the Domain Name System; e.g., if the user or certificate specifies a hostname of "example.com" but a DNS SRV [SRV] lookup returned "im.example.com", the certificate MUST be checked as "example.com". If a JID is represented in a certificate, it SHOULD be encoded using the otherName choice of the subjectAltName type along with a type-id of "xmpp" (as these terms are profiled in [X509]). 10. If the TLS negotiation is successful, the receiving entity MUST discard any knowledge obtained in an insecure manner from the initiating entity before TLS takes effect. 11. If the TLS negotiation is successful, the initiating entity MUST Saint-Andre (ed.) Expires July 6, 2004 [Page 20] Internet-Draft XMPP Core January 2004 discard any knowledge obtained in an insecure manner from the receiving entity before TLS takes effect. 12. If the TLS negotiation is successful, the receiving entity MUST NOT offer the STARTTLS extension to the initiating entity along with the other stream features that are offered when the stream is restarted. 13. If the TLS negotiation is successful, the initiating entity MUST continue with SASL negotiation. 14. If the TLS negotiation results in failure, the receiving entity MUST terminate both the XML stream and the underlying TCP connection. 15. See Mandatory-to-Implement Technologies (Section 14.7) regarding mechanisms that MUST be supported. 5.2 Narrative When an initiating entity secures a stream with a receiving entity, the steps involved are as follows: 1. The initiating entity opens a TCP connection and initiates the stream by sending the opening XML stream header to the receiving entity, including the 'version' attribute set to a value of "1.0". 2. The receiving entity responds by opening a TCP connection and sending an XML stream header to the initiating entity, including the 'version' attribute set to a value of "1.0". 3. The receiving entity offers the STARTTLS extension to the initiating entity by including it with the list of other supported stream features (if TLS is required for interaction with the receiving entity, it SHOULD signal that fact by including a element as a child of the element). 4. The initiating entity issues the STARTTLS command (i.e., a element qualified by the 'urn:ietf:params:xml:ns:xmpp-tls' namespace) to instruct the receiving entity that it wishes to begin a TLS negotiation to secure the stream. 5. The receiving entity MUST reply with either a element or a element qualified by the Saint-Andre (ed.) Expires July 6, 2004 [Page 21] Internet-Draft XMPP Core January 2004 'urn:ietf:params:xml:ns:xmpp-tls' namespace. If the failure case occurs, the receiving entity MUST terminate both the XML stream and the underlying TCP connection. If the proceed case occurs, the entities MUST attempt to complete the TLS negotiation over the TCP connection and MUST NOT send any further XML data until the TLS negotiation is complete. 6. The initiating entity and receiving entity attempt to complete a TLS negotiation in accordance with [TLS]. 7. If the TLS negotiation is unsuccessful, the receiving entity MUST terminate the TCP connection (it is not necessary to send a closing tag first, since the receiving entity and initiating entity MUST consider the original stream to be closed upon sending or receiving the element). If the TLS negotiation is successful, the initiating entity MUST initiate a new stream by sending an opening XML stream header to the receiving entity. 8. Upon receiving the new stream header from the initiating entity, the receiving entity MUST respond by sending a new XML stream header to the initiating entity along with the available features (but NOT including the STARTTLS feature). 5.3 Client-to-Server Example The following example shows the data flow for a client securing a stream using STARTTLS (note: the alternate steps shown below are provided to illustrate the protocol for failure cases; they are not exhaustive and would not necessarily be triggered by the data sent in the example). Step 1: Client initiates stream to server: Step 2: Server responds by sending a stream tag to client: Step 3: Server sends the STARTTLS extension to client along with authentication mechanisms and any other stream features: DIGEST-MD5 PLAIN Step 4: Client sends the STARTTLS command to server: Step 5: Server informs client to proceed: Step 5 (alt): Server informs client that TLS negotiation has failed and closes both stream and TCP connection: Step 6: Client and server attempt to complete TLS negotiation over the existing TCP connection. Step 7: If TLS negotiation is successful, client initiates a new stream to server: Step 7 (alt): If TLS negotiation is unsuccessful, Server2 closes TCP connection. Step 8: Server responds by sending a stream header to client along with any available stream features: DIGEST-MD5 PLAIN EXTERNAL Step 9: Client continues with SASL negotiation (Section 6). 5.4 Server-to-Server Example The following example shows the data flow for two servers securing a stream using STARTTLS (note: the alternate steps shown below are provided to illustrate the protocol for failure cases; they are not exhaustive and would not necessarily be triggered by the data sent in the example). Step 1: Server1 initiates stream to Server2: Step 2: Server2 responds by sending a stream tag to Server1: Step 3: Server2 sends the STARTTLS extension to Server1 along with authentication mechanisms and any other stream features: Saint-Andre (ed.) Expires July 6, 2004 [Page 24] Internet-Draft XMPP Core January 2004 DIGEST-MD5 KERBEROS_V4 Step 4: Server1 sends the STARTTLS command to Server2: Step 5: Server2 informs Server1 to proceed: Step 5 (alt): Server2 informs Server1 that TLS negotiation has failed and closes stream: Step 6: Server1 and Server2 attempt to complete TLS negotiation via TCP. Step 7: If TLS negotiation is successful, Server1 initiates a new stream to Server2: Step 7 (alt): If TLS negotiation is unsuccessful, server closes TCP connection. Step 8: Server2 responds by sending a stream header to Server1 along with any available stream features: DIGEST-MD5 KERBEROS_V4 EXTERNAL Saint-Andre (ed.) Expires July 6, 2004 [Page 25] Internet-Draft XMPP Core January 2004 Step 9: Server1 continues with SASL negotiation (Section 6). 6. Use of SASL 6.1 Overview XMPP includes a method for authenticating a stream by means of an XMPP-specific profile of the Simple Authentication and Security Layer (SASL) protocol [SASL]. SASL provides a generalized method for adding authentication support to connection-based protocols, and XMPP uses a generic XML namespace profile for SASL that conforms to the profiling requirements of [SASL]. The following rules apply: 1. If the SASL negotiation occurs between two servers, communications MUST NOT proceed until the Domain Name System (DNS) hostnames asserted by the servers have been resolved (see Server-to-Server Communications (Section 14.4)). 2. If the initiating entity is capable of SASL negotiation, it MUST include the 'version' attribute set to a value of "1.0" in the initial stream header. 3. If the receiving entity is capable of SASL negotiation, it MUST send one or more authentication mechanisms within a element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace in reply to the opening stream tag received from the initiating entity (if the opening stream tag included the 'version' attribute set to a value of "1.0"). 4. During SASL negotiation, an entity MUST NOT send any white space characters (matching production [3] content of [XML]) within the root stream element as separators between elements (any white space characters shown in the SASL examples below are included for the sake of readability only); this prohibition helps to ensure proper security layer byte precision. 5. Any character data contained within the XML elements used during SASL negotiation MUST be encoded using base64, where the encoding adheres to the definition in Section 3 of RFC 3548 [BASE64]. 6. If provision of a "simple username" is supported by the selected SASL mechanism (e.g., this is supported by the DIGEST-MD5 and Saint-Andre (ed.) Expires July 6, 2004 [Page 26] Internet-Draft XMPP Core January 2004 CRAM-MD5 mechanisms but not by the EXTERNAL and GSSAPI mechanisms), during authentication the initiating entity SHOULD provide its sending domain (in the case of server-to-server communications) or registered account name (in the case of client-to-server communications) as the simple username. 7. If the initiating entity wishes to act on behalf of another entity and the selected SASL mechanism supports transmission of an authorization identity, the initiating entity MUST provide an authorization identity during SASL negotiation. If the initiating entity does not wish to act on behalf of another entity, it MUST NOT provide an authorization identity. As specified in [SASL], the initiating entity MUST NOT provide an authorization identity unless the authorization identity is different from the default authorization identity derived from the authentication identity as described in [SASL]. If provided, the value of the authorization identity MUST be of the form (i.e., a domain identifier only) for servers and of the form (i.e., node identifier and domain identifier) for clients. 8. Upon successful SASL negotiation that involves negotiation of a security layer, the receiving entity MUST discard any knowledge obtained from the initiating entity which was not obtained from the SASL negotiation itself. 9. Upon successful SASL negotiation that involves negotiation of a security layer, the initiating entity MUST discard any knowledge obtained from the receiving entity which was not obtained from the SASL negotiation itself. 10. See Mandatory-to-Implement Technologies (Section 14.7) regarding mechanisms that MUST be supported. 6.2 Narrative When an initiating entity authenticates with a receiving entity, the steps involved are as follows: 1. The initiating entity requests SASL authentication by including the 'version' attribute in the opening XML stream header sent to the receiving entity, with the value set to "1.0". 2. After sending an XML stream header in reply, the receiving entity sends a list of available SASL authentication mechanisms; each of these is a element included as a child within a container element qualified by the Saint-Andre (ed.) Expires July 6, 2004 [Page 27] Internet-Draft XMPP Core January 2004 'urn:ietf:params:xml:ns:xmpp-sasl' namespace, which in turn is a child of a element in the streams namespace. If Use of TLS (Section 5) needs to be established before a particular authentication mechanism may be used, the receiving entity MUST NOT provide that mechanism in the list of available SASL authentication mechanisms prior to TLS negotiation. If the initiating entity presents a valid certificate during prior TLS negotiation, the receiving entity SHOULD offer the SASL EXTERNAL mechanism to the initiating entity during SASL negotiation (refer to [SASL]), although the EXTERNAL mechanism MAY be offered under other circumstances as well. 3. The initiating entity selects a mechanism by sending an element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace to the receiving entity and including an appropriate value for the 'mechanism' attribute; this element MAY contain character data (in SASL terminology, the "initial response") if the mechanism supports or requires it. If the initiating entity selects the EXTERNAL mechanism for authentication and presented a certificate during prior TLS negotiation, the authentication credentials SHOULD be taken from that certificate. 4. If necessary, the receiving entity challenges the initiating entity by sending a element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace to the initiating entity; this element MAY contain character data (which MUST be computed in accordance with the definition of the SASL mechanism chosen by the initiating entity). 5. The initiating entity responds to the challenge by sending a element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace to the receiving entity; this element MAY contain character data (which MUST be computed in accordance with the definition of the SASL mechanism chosen by the initiating entity). 6. If necessary, the receiving entity sends more challenges and the initiating entity sends more responses. This series of challenge/response pairs continues until one of three things happens: 1. The initiating entity aborts the handshake by sending an element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace to the receiving entity. Upon receiving an element, the receiving entity SHOULD allow a configurable but reasonable number of retries (at least 2), after which it MUST terminate the TCP connection; this allows the initiating entity Saint-Andre (ed.) Expires July 6, 2004 [Page 28] Internet-Draft XMPP Core January 2004 (e.g., an end-user client) to tolerate incorrectly-provided credentials (e.g., a mistyped password) without being forced to reconnect. 2. The receiving entity reports failure of the handshake by sending a element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace to the initiating entity (the particular cause of failure SHOULD be communicated in an appropriate child element of the element as defined under SASL Errors (Section 6.4)). If the failure case occurs, the receiving entity SHOULD allow a configurable but reasonable number of retries (at least 2), after which it MUST terminate the TCP connection; this allows the initiating entity (e.g., an end-user client) to tolerate incorrectly-provided credentials (e.g., a mistyped password) without being forced to reconnect. 3. The receiving entity reports success of the handshake by sending a element qualified by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace to the initiating entity; this element MAY contain character data (in SASL terminology, "additional data with success") if required by the chosen SASL mechanism. Upon receiving the element, the initiating entity MUST initiate a new stream by sending an opening XML stream header to the receiving entity (it is not necessary to send a closing tag first, since the receiving entity and initiating entity MUST consider the original stream to be closed upon sending or receiving the element). Upon receiving the new stream header from the initiating entity, the receiving entity MUST respond by sending a new XML stream header to the initiating entity, along with any available features (but NOT including the STARTTLS feature) or an empty element (to signify that no additional features are available); any such additional features not defined herein MUST be defined by the relevant extension to XMPP. 6.3 SASL Definition The profiling requirements of [SASL] require that the following information be supplied by a protocol definition: service name: "xmpp" initiation sequence: After the initiating entity provides an opening XML stream header and the receiving entity replies in kind, the receiving entity provides a list of acceptable authentication methods. The initiating entity chooses one method from the list and sends it to the receiving entity as the value of the Saint-Andre (ed.) Expires July 6, 2004 [Page 29] Internet-Draft XMPP Core January 2004 'mechanism' attribute possessed by an element, optionally including an initial response to avoid a round trip. exchange sequence: Challenges and responses are carried through the exchange of elements from receiving entity to initiating entity and elements from initiating entity to receiving entity. The receiving entity reports failure by sending a element and success by sending a element; the initiating entity aborts the exchange by sending an element. Upon successful negotiation, both sides consider the original XML stream to be closed and new stream headers are sent by both entities. security layer negotiation: The security layer takes effect immediately after sending the closing ">" character of the element for the receiving entity, and immediately after receiving the closing ">" character of the element for the initiating entity. The order of layers is first [TCP], then [TLS], then [SASL], then XMPP. use of the authorization identity: The authorization identity may be used by xmpp to denote the of a client or the sending of a server. 6.4 SASL Errors The following SASL-related error conditions are defined: o -- The receiving entity acknowledges an element sent by the initiating entity; sent in reply to the element. o -- The data provided by the initiating entity could not be processed because the [BASE64] encoding is incorrect (e.g., because the encoding does not adhere to the the definition in Section 3 of [BASE64]); sent in reply to a element or an element with initial challenge data. o -- The authzid provided by the initiating entity is invalid, either because it is incorrectly formatted or because the initiating entity does not have permissions to authorize that ID; sent in reply to a element or an element with initial challenge data. o -- The initiating entity did not provide a mechanism or requested a mechanism that is not supported by the Saint-Andre (ed.) Expires July 6, 2004 [Page 30] Internet-Draft XMPP Core January 2004 receiving entity; sent in reply to an element. o -- The mechanism requested by the initiating entity is weaker than server policy permits for that initiating entity; sent in reply to a element or an element with initial challenge data. o -- The authentication failed because the initiating entity did not provide valid credentials (this includes but is not limited to the case of an unknown username); sent in reply to a element or an element with initial challenge data. o -- The authentication failed because of a temporary error condition within the receiving entity; sent in reply to an element or element. 6.5 Client-to-Server Example The following example shows the data flow for a client authenticating with a server using SASL, normally after successful TLS negotiation (note: the alternate steps shown below are provided to illustrate the protocol for failure cases; they are not exhaustive and would not necessarily be triggered by the data sent in the example). Step 1: Client initiates stream to server: Step 2: Server responds with a stream tag sent to client: Step 3: Server informs client of available authentication mechanisms: DIGEST-MD5 Saint-Andre (ed.) Expires July 6, 2004 [Page 31] Internet-Draft XMPP Core January 2004 PLAIN Step 4: Client selects an authentication mechanism: Step 5: Server sends a [BASE64] encoded challenge to client: cmVhbG09InNvbWVyZWFsbSIsbm9uY2U9Ik9BNk1HOXRFUUdtMmhoIixxb3A9ImF1dGgi LGNoYXJzZXQ9dXRmLTgsYWxnb3JpdGhtPW1kNS1zZXNzCg== The decoded challenge is: realm="somerealm",nonce="OA6MG9tEQGm2hh",\ qop="auth",charset=utf-8,algorithm=md5-sess Step 5 (alt): Server returns error to client: Step 6: Client sends a [BASE64] encoded response to the challenge: dXNlcm5hbWU9InNvbWVub2RlIixyZWFsbT0ic29tZXJlYWxtIixub25jZT0i T0E2TUc5dEVRR20yaGgiLGNub25jZT0iT0E2TUhYaDZWcVRyUmsiLG5jPTAw MDAwMDAxLHFvcD1hdXRoLGRpZ2VzdC11cmk9InhtcHAvZXhhbXBsZS5jb20i LHJlc3BvbnNlPWQzODhkYWQ5MGQ0YmJkNzYwYTE1MjMyMWYyMTQzYWY3LGNo YXJzZXQ9dXRmLTgK The decoded response is: username="somenode",realm="somerealm",\ nonce="OA6MG9tEQGm2hh",cnonce="OA6MHXh6VqTrRk",\ nc=00000001,qop=auth,digest-uri="xmpp/example.com",\ response=d388dad90d4bbd760a152321f2143af7,charset=utf-8 Step 7: Server sends another [BASE64] encoded challenge to client: Saint-Andre (ed.) Expires July 6, 2004 [Page 32] Internet-Draft XMPP Core January 2004 cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZAo= The decoded challenge is: rspauth=ea40f60335c427b5527b84dbabcdfffd Step 7 (alt): Server returns error to client: Step 8: Client responds to the challenge: Step 9: Server informs client of successful authentication: Step 9 (alt): Server informs client of failed authentication: Step 10: Client initiates a new stream to server: Step 11: Server responds by sending a stream header to client along with any additional features (or an empty features element): Saint-Andre (ed.) Expires July 6, 2004 [Page 33] Internet-Draft XMPP Core January 2004 6.6 Server-to-Server Example The following example shows the data flow for a server authenticating with another server using SASL, normally after successful TLS negotiation (note: the alternate steps shown below are provided to illustrate the protocol for failure cases; they are not exhaustive and would not necessarily be triggered by the data sent in the example). Step 1: Server1 initiates stream to Server2: Step 2: Server2 responds with a stream tag sent to Server1: Step 3: Server2 informs Server1 of available authentication mechanisms: DIGEST-MD5 KERBEROS_V4 Step 4: Server1 selects an authentication mechanism: Step 5: Server2 sends a [BASE64] encoded challenge to Server1: Saint-Andre (ed.) Expires July 6, 2004 [Page 34] Internet-Draft XMPP Core January 2004 dXNlcm5hbWU9ImV4YW1wbGUuY29tIixyZWFsbT0ic29tZXJlYWxtIixub25j ZT0iT0E2TUc5dEVRR20yaGgiLHFvcD0iYXV0aCIsY2hhcnNldD11dGYtOCxh bGdvcml0aG09bWQ1LXNlc3MK The decoded challenge is: username="example.com",realm="somerealm",\ nonce="OA6MG9tEQGm2hh",qop="auth",\ charset=utf-8,algorithm=md5-sess Step 5 (alt): Server2 returns error to Server1: Step 6: Server1 sends a [BASE64] encoded response to the challenge: dXNlcm5hbWU9ImV4YW1wbGUuY29tIixyZWFsbT0ic29tZXJlYWxtIixub25j ZT0iT0E2TUc5dEVRR20yaGgiLGNub25jZT0iT0E2TUhYaDZWcVRyUmsiLG5j PTAwMDAwMDAxLHFvcD1hdXRoLGRpZ2VzdC11cmk9InhtcHAvZXhhbXBsZS5j b20iLHJlc3BvbnNlPWQzODhkYWQ5MGQ0YmJkNzYwYTE1MjMyMWYyMTQzYWY3 LGNoYXJzZXQ9dXRmLTgK The decoded response is: username="example.com",realm="somerealm",\ nonce="OA6MG9tEQGm2hh",cnonce="OA6MHXh6VqTrRk",\ nc=00000001,qop=auth,digest-uri="xmpp/example.com",\ response=d388dad90d4bbd760a152321f2143af7,charset=utf-8 Step 7: Server2 sends another [BASE64] encoded challenge to Server1: cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZAo= The decoded challenge is: rspauth=ea40f60335c427b5527b84dbabcdfffd Step 7 (alt): Server2 returns error to Server1: Saint-Andre (ed.) Expires July 6, 2004 [Page 35] Internet-Draft XMPP Core January 2004 Step 8: Server1 responds to the challenge: Step 8 (alt): Server1 aborts negotiation: Step 9: Server2 informs Server1 of successful authentication: Step 9 (alt): Server2 informs Server1 of failed authentication: Step 10: Server1 initiates a new stream to Server2: Step 11: Server2 responds by sending a stream header to Server1 along with any additional features (or an empty features element): 7. Resource Binding After SASL negotiation (Section 6) with the receiving entity, the initiating entity MAY want or need to bind a specific resource to that stream. In general this applies only to clients: in order to Saint-Andre (ed.) Expires July 6, 2004 [Page 36] Internet-Draft XMPP Core January 2004 conform to the addressing format (Section 3) and stanza delivery rules (Section 10) specified herein, there MUST be a resource identifier associated with the of the client (which is either generated by the server or provided by the client application); this ensures that the address for use over that stream is a "full JID" of the form . Upon receiving a success indication within the SASL negotiation, the client MUST send a new stream header to the server, to which the server MUST respond with a stream header as well as a list of available stream features. Specifically, if the server requires the client to bind a resource to the stream after successful SASL negotiation, it MUST include an empty element qualified by the 'urn:ietf:params:xml:ns:xmpp-bind' namespace in the stream features list it presents to the client upon sending the header for the response stream sent after successful SASL negotiation (but not before): Server advertises resource binding feature to client: Upon being so informed that resource binding is required, the client MUST bind a resource to the stream by sending to the server an IQ stanza of type "set" (see IQ Semantics (Section 9.2.3)) containing data qualified by the 'urn:ietf:params:xml:ns:xmpp-bind' namespace. If the client wishes to allow the server to generate the resource identifier on its behalf, it sends an IQ stanza of type "set" that contains an empty element: Client asks server to bind a resource: A server that supports resource binding MUST be able to generate a resource identifier on behalf of a client. A resource identifier generated by the server MUST be unique for that . Saint-Andre (ed.) Expires July 6, 2004 [Page 37] Internet-Draft XMPP Core January 2004 If the client wishes to specify the resource identifier, it sends an IQ stanza of type "set" that contains the desired resource identifier as the CDATA of a element that is a child of the element: Client binds a resource: someresource Once the server has generated a resource identifier for the client or accepted the resource identifier provided by the client, it MUST return an IQ stanza of type "result" to the client, which MUST include a child element that specifies the full JID for the connected resource as determined by the server: Server informs client of successful resource binding: somenode@example.com/someresource A server is NOT REQUIRED to accept the resource identifier provided by the client, and MAY override it with a resource identifier that the server generates; in this case, the server SHOULD NOT return a stanza error (e.g., ) to the client but instead SHOULD communicate the generated resource identifier to the client in the IQ result as shown above. When a client supplies a resource identifier, the following stanza error conditions are possible (see Stanza Errors (Section 9.3)): o The provided resource identifier cannot be processed by the server in accordance with Resourceprep (Appendix B). o The client is not allowed to bind a resource to the stream (e.g., because the client has reached a limit on the number of connected resources allowed). o The provided resource identifier is already in use but the server does not allow binding of multiple connected resources with the same identifier. Saint-Andre (ed.) Expires July 6, 2004 [Page 38] Internet-Draft XMPP Core January 2004 The protocol for these error conditions is shown below. Resource identifier cannot be processed: someresource Client is not allowed to bind a resource: someresource Resource identifier is in use: someresource 8. Server Dialback 8.1 Overview The Jabber protocols from which XMPP was adapted include a "server dialback" method for protecting against domain spoofing, thus making it more difficult to spoof XML stanzas (see Server-to-Server Communications (Section 14.4) regarding this method's security characteristics). Server dialback also makes it easier to deploy systems in which outbound messages and inbound messages are handled by different machines for the same domain. Server dialback is not a security mechanism, and domains requiring robust security SHOULD use Saint-Andre (ed.) Expires July 6, 2004 [Page 39] Internet-Draft XMPP Core January 2004 TLS and SASL; see Server-to-Server Communications (Section 14.4) for details. The server dialback method is made possible by the existence of the Domain Name System (DNS), since one server can (normally) discover the authoritative server for a given domain. Because dialback depends on DNS, inter-domain communications MUST NOT proceed until the Domain Name System (DNS) hostnames asserted by the servers have been resolved (see Server-to-Server Communications (Section 14.4)). The method for generating and verifying the keys used in server dialback MUST take into account the hostnames being used, the stream ID generated by the receiving server, and a secret known by the authoritative server's network. The stream ID is security-critical in server dialback and therefore MUST be both unpredictable and non-repeating. Any error that occurs during dialback negotiation MUST be considered a stream error, resulting in termination of the stream and of the underlying TCP connection. The possible error conditions are specified in the protocol description below. The following terminology applies: o Originating Server -- the server that is attempting to establish a connection between two domains. o Receiving Server -- the server that is trying to authenticate that Originating Server represents the domain which it claims to be. o Authoritative Server -- the server that answers to the DNS hostname asserted by Originating Server; for basic environments this will be Originating Server, but it could be a separate machine in Originating Server's network. 8.2 Order of Events The following is a brief summary of the order of events in dialback: 1. Originating Server establishes a connection to Receiving Server. 2. Originating Server sends a 'key' value over the connection to Receiving Server. 3. Receiving Server establishes a connection to Authoritative Server. Saint-Andre (ed.) Expires July 6, 2004 [Page 40] Internet-Draft XMPP Core January 2004 4. Receiving Server sends the same 'key' value to Authoritative Server. 5. Authoritative Server replies that key is valid or invalid. 6. Receiving Server informs Originating Server whether it is authenticated or not. We can represent this flow of events graphically as follows: Originating Receiving Server Server ----------- --------- | | | establish connection | | ----------------------> | | | | send stream header | | ----------------------> | | | | send stream header | | <---------------------- | | | Authoritative | send dialback key | Server | ----------------------> | ------------- | | | | establish connection | | ----------------------> | | | | send stream header | | ----------------------> | | | | send stream header | | <---------------------- | | | | send verify request | | ----------------------> | | | | send verify response | | <---------------------- | | | report dialback result | | <---------------------- | | | Saint-Andre (ed.) Expires July 6, 2004 [Page 41] Internet-Draft XMPP Core January 2004 8.3 Protocol The detailed protocol interaction between the servers is as follows: 1. Originating Server establishes TCP connection to Receiving Server. 2. Originating Server sends a stream header to Receiving Server: Note: The 'to' and 'from' attributes are NOT REQUIRED on the root stream element. The inclusion of the xmlns:db namespace declaration with the name shown indicates to Receiving Server that Originating Server supports dialback. If the namespace name is incorrect, then Receiving Server MUST generate an stream error condition and terminate both the XML stream and the underlying TCP connection. 3. Receiving Server SHOULD send a stream header back to Originating Server, including a unique ID for this interaction: Note: The 'to' and 'from' attributes are NOT REQUIRED on the root stream element. If the namespace name is incorrect, then Originating Server MUST generate an stream error condition and terminate both the XML stream and the underlying TCP connection. Note well that Receiving Server is NOT REQUIRED to reply and MAY silently terminate the XML stream and underlying TCP connection depending on security policies in place; however, if Receiving Server desires to proceed, it MUST sent a stream header back to Originating Server. 4. Originating Server sends a dialback key to Receiving Server: 98AF014EDC0... Saint-Andre (ed.) Expires July 6, 2004 [Page 42] Internet-Draft XMPP Core January 2004 Note: This key is not examined by Receiving Server, since Receiving Server does not keep information about Originating Server between sessions. The key generated by Originating Server MUST be based in part on the value of the ID provided by Receiving Server in the previous step, and in part on a secret shared by Originating Server and Authoritative Server. If the value of the 'to' address does not match a hostname recognized by Receiving Server, then Receiving Server MUST generate a stream error condition and terminate both the XML stream and the underlying TCP connection. If the value of the 'from' address matches a domain with which Receiving Server already has an established connection, then Receiving Server MUST maintain the existing connection until it validates whether the new connection is legitimate; additionally, Receiving Server MAY choose to generate a stream error condition for the new connection and then terminate both the XML stream and the underlying TCP connection related to the new request. 5. Receiving Server establishes a TCP connection back to the domain name asserted by Originating Server, as a result of which it connects to Authoritative Server. (Note: As an optimization, an implementation MAY reuse an existing trusted connection here rather than opening a new TCP connection.) 6. Receiving Server sends Authoritative Server a stream header: Note: The 'to' and 'from' attributes are NOT REQUIRED on the root stream element. If the namespace name is incorrect, then Authoritative Server MUST generate an stream error condition and terminate both the XML stream and the underlying TCP connection. 7. Authoritative Server sends Receiving Server a stream header: Note: If the namespace name is incorrect, then Receiving Server MUST generate an stream error condition and Saint-Andre (ed.) Expires July 6, 2004 [Page 43] Internet-Draft XMPP Core January 2004 terminate both the XML stream and the underlying TCP connection between it and Authoritative Server. If a stream error occurs between Receiving Server and Authoritative Server, then Receiving Server MUST generate a stream error condition and terminate both the XML stream and the underlying TCP connection between it and Originating Server. 8. Receiving Server sends Authoritative Server a stanza requesting that Authoritative Server verify a key: 98AF014EDC0... Note: Passed here are the hostnames, the original identifier from Receiving Server's stream header to Originating Server in Step 3, and the key that Originating Server sent to Receiving Server in Step 4. Based on this information as well as shared secret information within the Authoritative Server's network, the key is verified. Any verifiable method MAY be used to generate the key. If the value of the 'to' address does not match a hostname recognized by Authoritative Server, then Authoritative Server MUST generate a stream error condition and terminate both the XML stream and the underlying TCP connection. If the value of the 'from' address does not match the hostname represented by Receiving Server when opening the TCP connection (or any validated domain), then Authoritative Server MUST generate an stream error condition and terminate both the XML stream and the underlying TCP connection. 9. Authoritative Server sends a stanza back to Receiving Server verifying whether the key was valid or invalid: or Note: If the ID does not match that provided by Receiving Server in Step 3, then Receiving Server MUST generate an stream error condition and terminate both the XML stream and the underlying TCP connection. If the value of the 'to' address does not match a hostname recognized by Receiving Server, then Receiving Server MUST generate a stream error condition and terminate both the XML stream and the underlying TCP connection. If the value of the 'from' address does not match the hostname represented by Originating Server when opening the TCP connection (or any validated domain), then Receiving Server MUST generate an stream error condition and terminate both the XML stream and the underlying TCP connection. After returning the verification to Receiving Server, Authoritative Server SHOULD terminate the stream between them. 10. Receiving Server informs Originating Server of the result: Note: At this point the connection has either been validated via a type='valid', or reported as invalid. If the connection is invalid, then Receiving Server MUST terminate both the XML stream and the underlying TCP connection. If the connection is validated, data can be sent by Originating Server and read by Receiving Server; before that, all data stanzas sent to Receiving Server SHOULD be silently dropped. Even if dialback negotiation is successful, a server MUST verify that all XML stanzas received from the other server include a 'from' attribute and a 'to' attribute; if a stanza does not meet this restriction, the server that receives the stanza MUST generate an stream error condition and terminate both the XML stream and the underlying TCP connection. Furthermore, a server MUST verify that the 'from' attribute of stanzas received from the other server includes a validated domain for the stream; if a stanza does not meet this restriction, the server that receives the stanza MUST generate an stream error condition and terminate both the XML stream and the underlying TCP connection. Both of these checks help to prevent spoofing related to particular stanzas. Saint-Andre (ed.) Expires July 6, 2004 [Page 45] Internet-Draft XMPP Core January 2004 9. XML Stanzas After TLS negotiation (Section 5) if desired, SASL negotiation (Section 6), and Resource Binding (Section 7) if necessary, XML stanzas can be sent over the streams. Three kinds of XML stanza are defined for the 'jabber:client' and 'jabber:server' namespaces: , , and . In addition, there are five common attributes for these kinds of stanza. These common attributes, as well as the basic semantics of the three stanza kinds, are defined herein; more detailed information regarding the syntax of XML stanzas in relation to instant messaging and presence applications is provided in [XMPP-IM]. 9.1 Common Attributes The following five attributes are common to message, presence, and IQ stanzas: 9.1.1 to The 'to' attribute specifies the JID of the intended recipient for the stanza. In the 'jabber:client' namespace, a stanza SHOULD possess a 'to' attribute, although a stanza sent from a client to a server for handling by that server (e.g., presence sent to the server for broadcasting to other entities) SHOULD NOT possess a 'to' attribute. In the 'jabber:server' namespace, a stanza MUST possess a 'to' attribute; if a server receives a stanza that does not meet this restriction, it MUST generate an stream error condition and terminate both the XML stream and the underlying TCP connection with the offending server. If the value of the 'to' attribute is invalid or cannot be contacted, the entity discovering that fact (usually the sender's or recipient's server) MUST return an appropriate error to the sender, setting the 'from' attribute of the error stanza to the value provided in the 'to' attribute of the offending stanza. 9.1.2 from The 'from' attribute specifies the JID of the sender. When a server receives an XML stanza within the context of an authenticated stream qualified by the 'jabber:client' namespace, it MUST do one of the following: Saint-Andre (ed.) Expires July 6, 2004 [Page 46] Internet-Draft XMPP Core January 2004 1. validate that the value of the 'from' attribute provided by the client is that of a connected resource for the associated entity 2. add a 'from' address to the stanza whose value is the full JID () determined by the server for the connected resource that generated the stanza (see Determination of Addresses (Section 3.5)) If a client attempts to send an XML stanza for which the value of the 'from' attribute does not match one of the connected resources for that entity, the server SHOULD return an stream error to the client. If a client attempts to send an XML stanza over a stream that is not yet authenticated, the server SHOULD return a stream error to the client. If generated, both of these conditions MUST result in closing of the stream and termination of the underlying TCP connection; this helps to prevent a denial of service attack launched from a rogue client. When a server generates a stanza from the server itself for delivery to a connected client (e.g., in the context of data storage services provided by the server on behalf of the client), the stanza MUST either (1) not include a 'from' attribute or (2) include a 'from' attribute whose value is the account's bare JID () or client's full JID (). A server MUST NOT send to the client a stanza without a 'from' attribute if the stanza was not generated by the server itself. When a client receives a stanza that does not include a 'from' attribute, it MUST assume that the stanza is from the server to which the client is connected. In the 'jabber:server' namespace, a stanza MUST possess a 'from' attribute; if a server receives a stanza that does not meet this restriction, it MUST generate an stream error condition. Furthermore, the domain identifier portion of the JID contained in the 'from' attribute MUST match the hostname (or any validated domain) of the sending server as communicated in the SASL negotiation or dialback negotiation; if a server receives a stanza that does not meet this restriction, it MUST generate an stream error condition. Both of these conditions MUST result in closing of the stream and termination of the underlying TCP connection; this helps to prevent a denial of service attack launched from a rogue server. 9.1.3 id The optional 'id' attribute MAY be used by a sending entity for internal tracking of stanzas that it sends and receives (especially for tracking the request-response interaction inherent in the semantics of IQ stanzas). The value of the 'id' attribute is NOT Saint-Andre (ed.) Expires July 6, 2004 [Page 47] Internet-Draft XMPP Core January 2004 REQUIRED to be unique either globally, within a domain, or within a stream. The semantics of IQ stanzas impose additional restrictions; see IQ Semantics (Section 9.2.3). 9.1.4 type The 'type' attribute specifies detailed information about the purpose or context of the message, presence, or IQ stanza. The particular allowable values for the 'type' attribute vary depending on whether the stanza is a message, presence, or IQ; the values for message and presence stanzas are specific to instant messaging and presence applications and therefore are defined in [XMPP-IM], whereas the values for IQ stanzas specify the role of an IQ stanza in a structured request-response "conversation" and thus are defined under IQ Semantics (Section 9.2.3) below. The only 'type' value common to all three stanzas is "error", for which see Stanza Errors (Section 9.3). 9.1.5 xml:lang A stanza SHOULD possess an 'xml:lang' attribute (as defined in Section 2.12 of [XML]) if the stanza contains XML character data that is intended to be presented to a human user (as explained in RFC 2277 [CHARSET], "internationalization is for humans"). The value of the 'xml:lang' attribute specifies the default language of any such human-readable XML character data, which MAY be overridden by the 'xml:lang' attribute of a specific child element. If a stanza does not possess an 'xml:lang' attribute, an implementation MUST assume that the default language is that specified for the stream as defined under Stream Attributes (Section 4.2) above. The value of the 'xml:lang' attribute MUST be an NMTOKEN and MUST conform to the format defined in RFC 3066 [LANGTAGS]. 9.2 Basic Semantics 9.2.1 Message Semantics The stanza kind can be seen as a "push" mechanism whereby one entity pushes information to another entity, similar to the communications that occur in a system such as email. All message stanzas SHOULD possess a 'to' attribute that specifies the intended recipient of the message; upon receiving such a stanza, a server SHOULD route or deliver it to the intended recipient (see Server Rules for Handling XML Stanzas (Section 10) for general routing and delivery rules related to XML stanzas). 9.2.2 Presence Semantics Saint-Andre (ed.) Expires July 6, 2004 [Page 48] Internet-Draft XMPP Core January 2004 The element can be seen as a basic broadcast or "publish-subscribe" mechanism, whereby multiple entities receive information (in this case, presence information) about an entity to which they have subscribed. In general, a publishing entity SHOULD send a presence stanza with no 'to' attribute, in which case the server to which the entity is connected SHOULD broadcast or multiplex that stanza to all subscribing entities. However, a publishing entity MAY also send a presence stanza with a 'to' attribute, in which case the server SHOULD route or deliver that stanza to the intended recipient. See Server Rules for Handling XML Stanzas (Section 10) for general routing and delivery rules related to XML stanzas, and [XMPP-IM] for presence-specific rules in the context of an instant messaging and presence application. 9.2.3 IQ Semantics Info/Query, or IQ, is a request-response mechanism, similar in some ways to [HTTP]. The semantics of IQ enable an entity to make a request of, and receive a response from, another entity. The data content of the request and response is defined by the namespace declaration of a direct child element of the IQ element, and the interaction is tracked by the requesting entity through use of the 'id' attribute. Thus IQ interactions follow a common pattern of structured data exchange such as get/result or set/result (although an error may be returned in reply to a request if appropriate): Requesting Responding Entity Entity ---------- ---------- | | | | | ------------------------> | | | | | | <------------------------ | | | | | | ------------------------> | | | | | | <------------------------ | | | In order to enforce these semantics, the following rules apply: 1. The 'id' attribute is REQUIRED for IQ stanzas. 2. The 'type' attribute is REQUIRED for IQ stanzas. The value MUST Saint-Andre (ed.) Expires July 6, 2004 [Page 49] Internet-Draft XMPP Core January 2004 be one of the following: 3. * get -- The stanza is a request for information or requirements. * set -- The stanza provides required data, sets new values, or replaces existing values. * result -- The stanza is a response to a successful get or set request. * error -- An error has occurred regarding processing or delivery of a previously-sent get or set (see Stanza Errors (Section 9.3)). 4. An entity that receives an IQ request of type "get" or "set" MUST reply with an IQ response of type "result" or "error" (which response MUST preserve the 'id' attribute of the request). 5. An entity that receives a stanza of type "result" or "error" MUST NOT respond to the stanza by sending a further IQ response of type "result" or "error"; however, as shown above, the requesting entity MAY send another request (e.g., an IQ of type "set" in order to provide required information discovered through a get/ result pair). 6. An IQ stanza of type "get" or "set" MUST contain one and only one child element (properly-namespaced as defined in [XMPP-IM]) that specifies the semantics of the particular request or response. 7. An IQ stanza of type "result" MUST include zero or one child elements. 8. An IQ stanza of type "error" SHOULD include the child element contained in the associated "get" or "set" and MUST include an child; for details, see Stanza Errors (Section 9.3). 9.3 Stanza Errors Stanza-related errors are handled in a manner similar to stream errors (Section 4.6). However, unlike stream errors, stanza errors are recoverable; therefore error stanzas include hints regarding actions that the original sender can take in order to remedy the error. Saint-Andre (ed.) Expires July 6, 2004 [Page 50] Internet-Draft XMPP Core January 2004 9.3.1 Rules The following rules apply to stanza-related errors: o The receiving or processing entity that detects an error condition in relation to a stanza MUST return to the sending entity a stanza of the same kind (message, presence, or IQ) whose 'type' attribute is set to a value of "error" (such a stanza is called an "error stanza" herein). o The entity that generates an error stanza SHOULD (but is NOT REQUIRED to) include the original XML sent so that the sender can inspect and if necessary correct the XML before attempting to resend. o An error stanza MUST contain an child element. o An child MUST NOT be included if the 'type' attribute has a value other than "error" (or if there is no 'type' attribute). o An entity that receives an error stanza MUST NOT respond to the stanza with a further error stanza; this helps to prevent looping. 9.3.2 Syntax The syntax for stanza-related errors is as follows: [RECOMMENDED to include sender XML here] OPTIONAL descriptive text [OPTIONAL application-specific condition element] The stanza-name is one of message, presence, or iq. The value of the element's 'type' attribute MUST be one of the following: o cancel -- do not retry (the error is unrecoverable) o continue -- proceed (the condition was only a warning) Saint-Andre (ed.) Expires July 6, 2004 [Page 51] Internet-Draft XMPP Core January 2004 o modify -- retry after changing the data sent o auth -- retry after providing credentials o wait -- retry after waiting (the error is temporary) The element: o MUST contain a child element corresponding to one of the defined stanza error conditions specified below; this element MUST be qualified by the 'urn:ietf:params:xml:ns:xmpp-stanzas' namespace. o MAY contain a child containing CDATA that describes the error in more detail; this element MUST be qualified by the 'urn:ietf:params:xml:ns:xmpp-stanzas' namespace and SHOULD possess an 'xml:lang' attribute. o MAY contain a child element for an application-specific error condition; this element MUST be qualified by an application-defined namespace, and its structure is defined by that namespace. The element is OPTIONAL. If included, it SHOULD be used only to provide descriptive or diagnostic information that supplements the meaning of a defined condition or application-specific condition. It SHOULD NOT be interpreted programmatically by an application. It SHOULD NOT be used as the error message presented to a user, but MAY be shown in addition to the error message associated with the included condition element (or elements). Finally, to maintain backward compatibility, the schema (specified in [XMPP-IM]) allows the optional inclusion of a 'code' attribute on the element. 9.3.3 Defined Conditions The following stanza-related error conditions are defined for use in stanza errors. o -- the sender has sent XML that is malformed or that cannot be processed (e.g., an IQ stanza that includes an unrecognized value of the 'type' attribute); the associated error type SHOULD be "modify". o -- access cannot be granted because an existing resource or session exists with the same name or address; the associated error type SHOULD be "cancel". Saint-Andre (ed.) Expires July 6, 2004 [Page 52] Internet-Draft XMPP Core January 2004 o -- the feature requested is not implemented by the recipient or server and therefore cannot be processed; the associated error type SHOULD be "cancel". o -- the requesting entity does not possess the required permissions to perform the action; the associated error type SHOULD be "auth". o -- the recipient or server can no longer be contacted at this address (the error stanza MAY contain a new address in the CDATA of the element); the associated error type SHOULD be "modify". o -- the server could not process the stanza because of a misconfiguration or an otherwise-undefined internal server error; the associated error type SHOULD be "wait". o -- the addressed JID or item requested cannot be found; the associated error type SHOULD be "cancel". o -- the value of the 'to' attribute in the sender's stanza does not adhere to the syntax defined in Addressing Scheme (Section 3); the associated error type SHOULD be "modify". o -- the recipient or server understands the request but is refusing to process it because it does not meet criteria defined by the recipient or server (e.g., a local policy regarding acceptable words in messages); the associated error type SHOULD be "modify". o -- the recipient or server does not allow any entity to perform the action; the associated error type SHOULD be "cancel". o -- the sender must provide proper credentials before being allowed to perform the action, or has provided improper credentials; the associated error type SHOULD be "auth". o -- the requesting entity is not authorized to access the requested service because payment is required; the associated error type SHOULD be "auth". o -- the intended recipient is temporarily unavailable; the associated error type SHOULD be "wait" (note: an application MUST NOT return this error if doing so would provide information about the intended recipient's network availability to an entity that is not authorized to know such information). Saint-Andre (ed.) Expires July 6, 2004 [Page 53] Internet-Draft XMPP Core January 2004 o -- the recipient or server is redirecting requests for this information to another entity, usually temporarily (the error stanza SHOULD contain the alternate address, which MUST be a valid JID, in the CDATA of the element); the associated error type SHOULD be "modify". o -- the requesting entity is not authorized to access the requested service because registration is required; the associated error type SHOULD be "auth". o -- a remote server or service specified as part or all of the JID of the intended recipient does not exist; the associated error type SHOULD be "cancel". o -- a remote server or service specified as part or all of the JID of the intended recipient could not be contacted within a reasonable amount of time; the associated error type SHOULD be "wait". o -- the server or recipient lacks the system resources necessary to service the request; the associated error type SHOULD be "wait". o -- the server or recipient does not currently provide the requested service; the associated error type SHOULD be "cancel". o -- the requesting entity is not authorized to access the requested service because a subscription is required; the associated error type SHOULD be "auth". o -- the error condition is not one of those defined by the other conditions in this list; any error type may be associated with this condition, and it SHOULD be used only in conjunction with an application-specific condition. o -- the recipient or server understood the request but was not expecting it at this time (e.g., the request was out of order); the associated error type SHOULD be "wait". 9.3.4 Application-Specific Conditions As noted, an application MAY provide application-specific stanza error information by including a properly-namespaced child in the error element. The application-specific element SHOULD supplement or further qualify a defined element. Thus the element will contain two or three child elements: Saint-Andre (ed.) Expires July 6, 2004 [Page 54] Internet-Draft XMPP Core January 2004 Some special application diagnostic information... 10. Server Rules for Handling XML Stanzas Compliant server implementations MUST ensure in-order processing of XML stanzas between any two entities. Beyond the requirement for in-order processing, each server implementation will contain its own "delivery tree" for handling stanzas it receives. Such a tree determines whether a stanza needs to be routed to another domain, processed internally, or delivered to a resource associated with a connected node. The following rules apply: 10.1 No 'to' Address If the stanza possesses no 'to' attribute, the server SHOULD process it on behalf of the entity that sent it. Because all stanzas received from other servers MUST possess a 'to' attribute, this rule applies only to stanzas received from a registered entity (such as a client) that is connected to the server. If the server receives a presence stanza with no 'to' attribute, the server SHOULD broadcast it to the entities that are subscribed to the sending entity's presence, if applicable (the semantics of presence broadcast for instant messaging and presence applications are defined in [XMPP-IM]). If the server receives an IQ stanza of type "get" or "set" with no 'to' attribute and it understands the namespace that qualifies the content of the stanza, it MUST either process the stanza on behalf of sending entity (where the meaning of "process" is Saint-Andre (ed.) Expires July 6, 2004 [Page 55] Internet-Draft XMPP Core January 2004 determined by the semantics of the qualifying namespace) or return an error to the sending entity. 10.2 Foreign Domain If the hostname of the domain identifier portion of the JID contained in the 'to' attribute does not match one of the configured hostnames of the server itself or a subdomain thereof, the server SHOULD route the stanza to the foreign domain (subject to local service provisioning and security policies regarding inter-domain communication). There are two possible cases: A server-to-server stream already exists between the two domains: The sender's server routes the stanza to the authoritative server for the foreign domain over the existing stream There exists no server-to-server stream between the two domains: The sender's server (1) resolves the hostname of the foreign domain (as defined under Server-to-Server Communications (Section 14.4)), (2) negotiates a server-to-server stream between the two domains (as defined under Use of TLS (Section 5) and Use of SASL (Section 6)), and (3) routes the stanza to the authoritative server for the foreign domain over the newly-established stream If routing to the recipient's server is unsuccessful, the sender's server MUST return an error to the sender; if the recipient's server can be contacted but delivery by the recipient's server to the recipient is unsuccessful, the recipient's server MUST return an error to the sender by way of the sender's server. 10.3 Subdomain If the hostname of the domain identifier portion of the JID contained in the 'to' attribute matches a subdomain of one of the configured hostnames of the server itself, the server MUST either process the stanza itself or route the stanza to a specialized service that is responsible for that subdomain (if the subdomain is configured), or return an error to the sender (if the subdomain is not configured). 10.4 Mere Domain or Specific Resource If the hostname of the domain identifier portion of the JID contained in the 'to' attribute matches a configured hostname of the server itself and the JID contained in the 'to' attribute is of the form or , the server (or a defined resource thereof) MUST either process the stanza as appropriate for the stanza kind or return an error stanza to the sender. Saint-Andre (ed.) Expires July 6, 2004 [Page 56] Internet-Draft XMPP Core January 2004 10.5 Node in Same Domain If the hostname of the domain identifier portion of the JID contained in the 'to' attribute matches a configured hostname of the server itself and the JID contained in the 'to' attribute is of the form or , the server SHOULD deliver the stanza to the intended recipient of the stanza as represented by the JID contained in the 'to' attribute. The following rules apply: 1. If the JID contains a resource identifier (i.e., is of the form ) and there exists a connected resource that matches the full JID, the recipient's server SHOULD deliver the stanza to the stream or session that exactly matches the resource identifier. 2. If the JID contains a resource identifier and there exists no connected resource that matches the full JID, the recipient's server SHOULD return a stanza error to the sender. 3. If the JID is of the form and there exists at least one connected resource for the node, the recipient's server MUST deliver the stanza to at least one of the connected resources, according to application-specific rules (a set of delivery rules for instant messaging and presence applications is defined in [XMPP-IM]). 11. XML Usage within XMPP 11.1 Restrictions XMPP is a simplified and specialized protocol for streaming XML elements in order to exchange structured information in close to real time. Because XMPP does not require the parsing of arbitrary and complete XML documents, there is no requirement that XMPP needs to support the full feature set of [XML]. In particular, the following restrictions apply. With regard to XML generation, an XMPP implementation MUST NOT inject into an XML stream any of the following: o comments (as defined in Section 2.5 of [XML]) o processing instructions (Section 2.6 therein) o internal or external DTD subsets (Section 2.8 therein) Saint-Andre (ed.) Expires July 6, 2004 [Page 57] Internet-Draft XMPP Core January 2004 o internal or external entity references (Section 4.2 therein) with the exception of predefined entities (Section 4.6 therein) o character data or attribute values containing unescaped characters that map to the predefined entities (Section 4.6 therein); such characters MUST be escaped With regard to XML processing, if an XMPP implementation receives such restricted XML data, it MUST ignore the data. 11.2 XML Namespace Names and Prefixes XML Namespaces [XML-NAMES] are used within all XMPP-compliant XML to create strict boundaries of data ownership. The basic function of namespaces is to separate different vocabularies of XML elements that are structurally mixed together. Ensuring that XMPP-compliant XML is namespace-aware enables any allowable XML to be structurally mixed with any data element within XMPP. Rules for XML namespace names and prefixes are defined in the following subsections. 11.2.1 Streams Namespace A streams namespace declaration is REQUIRED in all XML stream headers. The name of the streams namespace MUST be 'http:// etherx.jabber.org/streams'. The element names of the element and its and children MUST be qualified by the streams namespace prefix in all instances. An implementation SHOULD generate only the 'stream:' prefix for these elements, and for historical reasons MAY accept only the 'stream:' prefix. 11.2.2 Default Namespace A default namespace declaration is REQUIRED and is used in all XML streams in order to define the allowable first-level children of the root stream element. This namespace declaration MUST be the same for the initial stream and the response stream so that both streams are qualified consistently. The default namespace declaration applies to the stream and all stanzas sent within a stream (unless explicitly qualified by another namespace, or by the prefix of the streams namespace or the dialback namespace). A server implementation MUST support the following two default namespaces (for historical reasons, some implementations MAY support only these two default namespaces): o jabber:client -- this default namespace is declared when the stream is used for communications between a client and a server Saint-Andre (ed.) Expires July 6, 2004 [Page 58] Internet-Draft XMPP Core January 2004 o jabber:server -- this default namespace is declared when the stream is used for communications between two servers A client implementation MUST support the 'jabber:client' default namespace, and for historical reasons MAY support only that default namespace. An implementation MUST NOT generate namespace prefixes for elements in the default namespace if the default namespace is 'jabber:client' or 'jabber:server'. An implementation SHOULD NOT generate namespace prefixes for elements qualified by content (as opposed to stream) namespaces other than 'jabber:client' and 'jabber:server'. Note: The 'jabber:client' and 'jabber:server' namespaces are nearly identical but are used in different contexts (client-to-server communications for 'jabber:client' and server-to-server communications for 'jabber:server'). The only difference between the two is that the 'to' and 'from' attributes are OPTIONAL on stanzas sent within 'jabber:client', whereas they are REQUIRED on stanzas sent within 'jabber:server'. If a compliant implementation accepts a stream that is qualified by the 'jabber:client' or 'jabber:server' namespace, it MUST support the common attributes (Section 9.1) and basic semantics (Section 9.2) of all three core stanza kinds (message, presence, and IQ). 11.2.3 Dialback Namespace A dialback namespace declaration is REQUIRED for all elements used in server dialback (Section 8). The name of the dialback namespace MUST be 'jabber:server:dialback'. All elements qualified by this namespace MUST be prefixed. An implementation SHOULD generate only the 'db:' prefix for such elements and MAY accept only the 'db:' prefix. 11.3 Validation Except as noted with regard to 'to' and 'from' addresses for stanzas within the 'jabber:server' namespace, a server is not responsible for validating the XML elements forwarded to a client or another server; an implementation MAY choose to provide only validated data elements but is NOT REQUIRED to do so (although an implementation MUST NOT accept XML that is not well-formed). Clients SHOULD NOT rely on the ability to send data which does not conform to the schemas, and SHOULD ignore any non-conformant elements or attributes on the incoming XML stream. Validation of XML streams and stanzas is NOT REQUIRED or recommended, and schemas are included herein for descriptive purposes only. Saint-Andre (ed.) Expires July 6, 2004 [Page 59] Internet-Draft XMPP Core January 2004 11.4 Inclusion of Text Declaration Implementations SHOULD send a text declaration before sending a stream header. Applications MUST follow the rules in [XML] regarding the circumstances under which a text declaration is included. 11.5 Character Encoding Implementations MUST support the UTF-8 (RFC 3269 [UTF-8]) transformation of Universal Character Set (ISO/IEC 10646-1 [UCS2]) characters, as required by RFC 2277 [CHARSET]. Implementations MUST NOT attempt to use any other encoding. 12. Core Compliance Requirements This section summarizes the specific aspects of the Extensible Messaging and Presence Protocol that MUST be supported by servers and clients in order to be considered compliant implementations, as well as additional protocol aspects that SHOULD be supported. For compliance purposes, we draw a distinction between core protocols (which MUST be supported by any server or client, regardless of the specific application) and instant messaging protocols (which MUST be supported only by instant messaging and presence applications built on top of the core protocols). Compliance requirements that apply to all servers and clients are specified in this section; compliance requirements for instant messaging servers and clients are specified in the corresponding section of [XMPP-IM]. 12.1 Servers In addition to all defined requirements with regard to security, XML usage, and internationalization, a server MUST support the following core protocols in order to be considered compliant: o Application of the [NAMEPREP], Nodeprep (Appendix A), and Resourceprep (Appendix B) profiles of [STRINGPREP] to addresses (including ensuring that domain identifiers are internationalized domain names as defined in [IDNA]) o XML streams (Section 4), including Use of TLS (Section 5), Use of SASL (Section 6), and Resource Binding (Section 7) o The basic semantics of the three defined stanza kinds (i.e., , , and ) as specified in stanza semantics (Section 9.2) o Generation (and, where appropriate, handling) of error syntax and semantics related to streams, TLS, SASL, and XML stanzas Saint-Andre (ed.) Expires July 6, 2004 [Page 60] Internet-Draft XMPP Core January 2004 In addition, a server SHOULD support the following core protocol: o Server dialback (Section 8) 12.2 Clients A client MUST support the following core protocols in order to be considered compliant: o XML streams (Section 4), including Use of TLS (Section 5), Use of SASL (Section 6), and Resource Binding (Section 7) o The basic semantics of the three defined stanza kinds (i.e., , , and ) as specified in stanza semantics (Section 9.2) o Handling (and, where appropriate, generation) of error syntax and semantics related to streams, TLS, SASL, and XML stanzas In addition, a client SHOULD support the following core protocols: o Generation of addresses to which the [NAMEPREP], Nodeprep (Appendix A), and Resourceprep (Appendix B) profiles of [STRINGPREP] can be applied without failing 13. Internationalization Considerations XML streams MUST be encoded in UTF-8 as specified under Character Encoding (Section 11.5). As specified under Stream Attributes (Section 4.2), an XML stream SHOULD include an 'xml:lang' attribute that is treated as the default language for any XML character data sent over the stream that is intended to be presented to a human user. As specified under xml:lang (Section 9.1.5), an XML stanza SHOULD include an 'xml:lang' attribute if the stanza contains XML character data that is intended to be presented to a human user. A server SHOULD apply the default 'xml:lang' attribute to stanzas it routes or delivers on behalf of connected entities, and MUST NOT modify or delete 'xml:lang' attributes from stanzas it receives from other entities. 14. Security Considerations 14.1 High Security For the purposes of XMPP communications (client-to-server and server-to-server), the term "high security" refers to the use of Saint-Andre (ed.) Expires July 6, 2004 [Page 61] Internet-Draft XMPP Core January 2004 security technologies that provide both mutual authentication and integrity-checking; in particular, when using certificate-based authentication to provide high security, a chain-of-trust SHOULD be established out-of-band, although a shared certificate authority signing certificates could allow a previously unknown certificate to establish trust in-band. See Section 14.2 below regarding certificate validation procedures. Implementations MUST support high security. Service provisioning SHOULD use high security, subject to local security policies. 14.2 Certificate Validation When an XMPP peer communicates with another peer securely, it MUST validate the peer's certificate. There are three possible cases: Case #1: The peer contains an End Entity certificate which appears to be certified by a chain of certificates terminating in a trust anchor (as described in Section 6.1 of [X509]). Case #2: The peer certificate is certified by a Certificate Authority not known to the validating peer. Case #3: The peer certificate is self-signed. In Case #1, the validating peer MUST do one of two things: 1. Verify the peer certificate according to the rules of [X509]. The certificate SHOULD then be checked against the expected identity of the peer following the rules described in [HTTP-TLS], except that a subjectAltName extension of type "xmpp" MUST be used as the identity if present. If one of these checks fails, user-oriented clients MUST either notify the user (clients MAY give the user the opportunity to continue with the connection in any case) or terminate the connection with a bad certificate error. Automated clients SHOULD terminate the connection (with a bad certificate error) and log the error to an appropriate audit log. Automated clients MAY provide a configuration setting that disables this check, but MUST provide a setting which enables it. 2. The peer SHOULD show the certificate to a user for approval, including the entire certificate chain. The peer MUST Cache the certificate (or some non-forgeable representation such as a hash). In future connections, the peer MUST verify that the same certificate was presented and MUST notify the user if it has changed. In Case #2 and Case #3, implementations SHOULD act as in (2) above. Saint-Andre (ed.) Expires July 6, 2004 [Page 62] Internet-Draft XMPP Core January 2004 14.3 Client-to-Server Communications A compliant implementation MUST support both TLS and SASL for connections to a server. The TLS protocol for encrypting XML streams (defined under Use of TLS (Section 5)) provides a reliable mechanism for helping to ensure the confidentiality and data integrity of data exchanged between two entities. The SASL protocol for authenticating XML streams (defined under Use of SASL (Section 6)) provides a reliable mechanism for validating that a client connecting to a server is who it claims to be. Client-to-server communications MUST NOT proceed until the DNS hostname asserted by the server has been resolved. Such resolutions SHOULD first attempt to resolve the hostname using an [SRV] Service of "xmpp-client" and Proto of "tcp", resulting in resource records such as "_xmpp-client._tcp.example.com." (the use of the string "xmpp-client" for the service identifier is consistent with the IANA registration). If the SRV lookup fails, the fallback is a normal IPv4/IPv6 address record resolution to determine the IP address, using the "xmpp-client" port of 5222 registered with the IANA. The IP address and method of access of clients MUST NOT be made public by a server, nor are any connections other than the original server connection required. This helps to protect the client's server from direct attack or identification by third parties. 14.4 Server-to-Server Communications A compliant implementation MUST support both TLS and SASL for inter-domain communications. For historical reasons, a compliant implementation SHOULD also support Server Dialback (Section 8). Because service provisioning is a matter of policy, it is OPTIONAL for any given domain to communicate with other domains, and server-to-server communications MAY be disabled by the administrator of any given deployment. If a particular domain enables inter-domain communications, it SHOULD enable high security. Administrators may want to require use of SASL for server-to-server communications in order to ensure both authentication and confidentiality (e.g., on an organization's private network). Compliant implementations SHOULD support SASL for this purpose. Inter-domain connections MUST NOT proceed until the DNS hostnames asserted by the servers have been resolved. Such resolutions MUST Saint-Andre (ed.) Expires July 6, 2004 [Page 63] Internet-Draft XMPP Core January 2004 first attempt to resolve the hostname using an [SRV] Service of "xmpp-server" and Proto of "tcp", resulting in resource records such as "_xmpp-server._tcp.example.com." (the use of the string "xmpp-server" for the service identifier is consistent with the IANA registration; note well that the "xmpp-server" service identifier supersedes the earlier use of a "jabber" service identifier, since the earlier usage did not conform to [SRV]; implementations desiring to be backward compatible should continue to look for or answer to the "jabber" service identifier as well). If the SRV lookup fails, the fallback is a normal IPv4/IPv6 address record resolution to determine the IP address, using the "xmpp-server" port of 5269 registered with the IANA. Server dialback helps protect against domain spoofing, thus making it more difficult to spoof XML stanzas. It is not a mechanism for authenticating, securing, or encrypting streams between servers as is done via SASL and TLS. Furthermore, it is susceptible to DNS poisoning attacks unless DNSSec [DNSSEC] is used, and even if the DNS information is accurate, dialback cannot protect from attacks where the attacker is capable of hijacking the IP address of the remote domain. Domains requiring robust security SHOULD use TLS and SASL. If SASL is used for server-to-server authentication, dialback SHOULD NOT be used since it is unnecessary. 14.5 Order of Layers The order of layers in which protocols MUST be stacked is as follows: 1. TCP 2. TLS 3. SASL 4. XMPP The rationale for this order is that [TCP] is the base connection layer used by all of the protocols stacked on top of TCP, [TLS] is often provided at the operating system layer, [SASL] is often provided at the application layer, and XMPP is the application itself. 14.6 Lack of SASL Channel Binding to TLS The SASL framework does not provide a mechanism to bind SASL authentication to a security layer providing confidentiality and integrity protection that was negotiated at a lower layer. This lack of a "channel binding" prevents SASL from being able to verify that Saint-Andre (ed.) Expires July 6, 2004 [Page 64] Internet-Draft XMPP Core January 2004 the source and destination end points to which the lower layer's security is bound are equivalent to the end points that SASL is authenticating. If the end points are not identical, the lower layer's security cannot be trusted to protect data transmitted between the SASL authenticated entities. In such a situation, a SASL security layer should be negotiated which effectively ignores the presence of the lower layer security. 14.7 Mandatory-to-Implement Technologies At a minimum, all implementations MUST support the following mechanisms: for authentication: the SASL [DIGEST-MD5] mechanism for confidentiality: TLS (using the TLS_RSA_WITH_3DES_EDE_CBC_SHA cipher) for both: TLS plus SASL EXTERNAL(using the TLS_RSA_WITH_3DES_EDE_CBC_SHA cipher supporting client-side certificates) 14.8 Firewalls Communications using XMPP normally occur over [TCP] sockets on port 5222 (client-to-server) or port 5269 (server-to-server), as registered with the IANA (see IANA Considerations (Section 15)). Use of these well-known ports allows administrators to easily enable or disable XMPP activity through existing and commonly-deployed firewalls. 14.9 Use of base64 in SASL Both the client and the server MUST verify any [BASE64] data received during SASL negotiation. An implementation MUST reject (not ignore) any characters that are not explicitly allowed by the base64 alphabet; this helps to guard against creation of a covert channel that could be used to "leak" information. An implementation MUST NOT break on invalid input and MUST reject any sequence of base64 characters containing the pad ('=') character if that character is included as something other than the last character of the data (e.g. "=AAA" or "BBBB=CCC"); this helps to guard against buffer overflow attacks and other attacks on the implementation. Base encoding visually hides otherwise easily recognized information, such as passwords, but does not provide any computational confidentiality. Base 64 encoding MUST follow the definition in Section 3 of RFC 3548 [BASE64]. Saint-Andre (ed.) Expires July 6, 2004 [Page 65] Internet-Draft XMPP Core January 2004 14.10 Stringprep Profiles XMPP makes use of the [NAMEPREP] profile of [STRINGPREP] for processing of domain identifiers; for security considerations related to Nameprep, refer to the appropriate section of [NAMEPREP]. In addition, XMPP defines two profiles of [STRINGPREP]: Nodeprep (Appendix A) for node identifiers and Resourceprep (Appendix B) for resource identifiers. The Unicode and ISO/IEC 10646 repertoires have many characters that look similar. In many cases, users of security protocols might do visual matching, such as when comparing the names of trusted third parties. Because it is impossible to map similar-looking characters without a great deal of context such as knowing the fonts used, stringprep does nothing to map similar-looking characters together nor to prohibit some characters because they look like others. A node identifier can be employed as one part of an entity's address in XMPP. One common usage is as the username of an instant messaging user; another is as the name of a multi-user chat room; and many other kinds of entities could use node identifiers as part of their addresses. The security of such services could be compromised based on different interpretations of the internationalized node identifier; for example, a user entering a single internationalized node identifier could access another user's account information, or a user could gain access to an otherwise restricted chat room or service. A resource identifier can be employed as one part of an entity's address in XMPP. One common usage is as the name for an instant messaging user's connected resource (active session); another is as the nickname of a user in a multi-user chat room; and many other kinds of entities could use resource identifiers as part of their addresses. The security of such services could be compromised based on different interpretations of the internationalized resource identifier; for example, a user could attempt to initiate multiple sessions with the same name, or a user could send a message to someone other than the intended recipient in a multi-user chat room. 15. IANA Considerations 15.1 XML Namespace Name for TLS Data A URN sub-namespace for TLS-related data in the Extensible Messaging and Presence Protocol (XMPP) is defined as follows. (This namespace name adheres to the format defined in The IETF XML Registry [XML-REG].) Saint-Andre (ed.) Expires July 6, 2004 [Page 66] Internet-Draft XMPP Core January 2004 URI: urn:ietf:params:xml:ns:xmpp-tls Specification: XXXX Description: This is the XML namespace name for TLS-related data in the Extensible Messaging and Presence Protocol (XMPP) as defined by XXXX. Registrant Contact: IETF, XMPP Working Group, 15.2 XML Namespace Name for SASL Data A URN sub-namespace for SASL-related data in the Extensible Messaging and Presence Protocol (XMPP) is defined as follows. (This namespace name adheres to the format defined in [XML-REG].) URI: urn:ietf:params:xml:ns:xmpp-sasl Specification: XXXX Description: This is the XML namespace name for SASL-related data in the Extensible Messaging and Presence Protocol (XMPP) as defined by XXXX. Registrant Contact: IETF, XMPP Working Group, 15.3 XML Namespace Name for Stream Errors A URN sub-namespace for stream-related error data in the Extensible Messaging and Presence Protocol (XMPP) is defined as follows. (This namespace name adheres to the format defined in [XML-REG].) URI: urn:ietf:params:xml:ns:xmpp-streams Specification: XXXX Description: This is the XML namespace name for stream-related error data in the Extensible Messaging and Presence Protocol (XMPP) as defined by XXXX. Registrant Contact: IETF, XMPP Working Group, 15.4 XML Namespace Name for Resource Binding A URN sub-namespace for resource binding in the Extensible Messaging Saint-Andre (ed.) Expires July 6, 2004 [Page 67] Internet-Draft XMPP Core January 2004 and Presence Protocol (XMPP) is defined as follows. (This namespace name adheres to the format defined in [XML-REG].) URI: urn:ietf:params:xml:ns:xmpp-bind Specification: XXXX Description: This is the XML namespace name for resource binding in the Extensible Messaging and Presence Protocol (XMPP) as defined by XXXX. Registrant Contact: IETF, XMPP Working Group, 15.5 XML Namespace Name for Stanza Errors A URN sub-namespace for stanza-related error data in the Extensible Messaging and Presence Protocol (XMPP) is defined as follows. (This namespace name adheres to the format defined in [XML-REG].) URI: urn:ietf:params:xml:ns:xmpp-stanzas Specification: XXXX Description: This is the XML namespace name for stanza-related error data in the Extensible Messaging and Presence Protocol (XMPP) as defined by XXXX. Registrant Contact: IETF, XMPP Working Group, 15.6 Nodeprep Profile of Stringprep The Nodeprep profile of stringprep is defined under Nodeprep (Appendix A). The IANA registers Nodeprep in the stringprep profile registry. Name of this profile: Nodeprep RFC in which the profile is defined: XXXX Indicator whether or not this is the newest version of the profile: Saint-Andre (ed.) Expires July 6, 2004 [Page 68] Internet-Draft XMPP Core January 2004 This is the first version of Nodeprep 15.7 Resourceprep Profile of Stringprep The Resourceprep profile of stringprep is defined under Resourceprep (Appendix B). The IANA registers Resourceprep in the stringprep profile registry. Name of this profile: Resourceprep RFC in which the profile is defined: XXXX Indicator whether or not this is the newest version of the profile: This is the first version of Resourceprep 15.8 GSSAPI Service Name The IANA registers "xmpp" as a GSSAPI [GSS-API] service name, as defined under SASL Definition (Section 6.3). 15.9 Port Numbers The IANA currently registers "jabber-client" and "jabber-server" as keywords for [TCP] ports 5222 and 5269 respectively. The IANA shall change these registrations to "xmpp-client" and "xmpp-server" respectively. These ports SHOULD be used for client-to-server and server-to-server communications respectively, but their use is NOT REQUIRED. Normative References [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [BASE64] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 3548, July 2003. [CHARSET] Alvestrand, H., "IETF Policy on Character Sets and Languages", BCP 18, RFC 2277, January 1998. Saint-Andre (ed.) Expires July 6, 2004 [Page 69] Internet-Draft XMPP Core January 2004 [DIGEST-MD5] Leach, P. and C. Newman, "Using Digest Authentication as a SASL Mechanism", RFC 2831, May 2000. [DNS] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. [GSS-API] Linn, J., "Generic Security Service Application Program Interface, Version 2", RFC 2078, January 1997. [HTTP-TLS] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [IMP-REQS] Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging / Presence Protocol Requirements", RFC 2779, February 2000. [IPv6] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 2373, July 1998. [LANGTAGS] Alvestrand, H., "Tags for the Identification of Languages", BCP 47, RFC 3066, January 2001. [IDNA] Faltstrom, P., Hoffman, P. and A. Costello, "Internationalizing Domain Names in Applications (IDNA)", RFC 3490, March 2003. [NAMEPREP] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep Profile for Internationalized Domain Names (IDN)", RFC 3491, March 2003. [SASL] Myers, J., "Simple Authentication and Security Layer (SASL)", RFC 2222, October 1997. [SRV] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, February 2000. [STRINGPREP] Hoffman, P. and M. Blanchet, "Preparation of Internationalized Strings ("STRINGPREP")", RFC 3454, December 2002. [TCP] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. Saint-Andre (ed.) Expires July 6, 2004 [Page 70] Internet-Draft XMPP Core January 2004 [TERMS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [TLS] Dierks, T., Allen, C., Treese, W., Karlton, P., Freier, A. and P. Kocher, "The TLS Protocol Version 1.0", RFC 2246, January 1999. [UCS2] International Organization for Standardization, "Information Technology - Universal Multiple-octet coded Character Set (UCS) - Amendment 2: UCS Transformation Format 8 (UTF-8)", ISO Standard 10646-1 Addendum 2, October 1996. [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [X509] Housley, R., Polk, W., Ford, W. and D. Solo, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3280, April 2002. [XML] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler, "Extensible Markup Language (XML) 1.0 (2nd ed)", W3C REC-xml, October 2000, . [XML-NAMES] Bray, T., Hollander, D. and A. Layman, "Namespaces in XML", W3C REC-xml-names, January 1999, . Informative References [ACAP] Newman, C. and J. Myers, "ACAP -- Application Configuration Access Protocol", RFC 2244, November 1997. [DNSSEC] Eastlake, D., "Domain Name System Security Extensions", RFC 2535, March 1999. [HTTP] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. [IMAP] Crispin, M., "Internet Message Access Protocol - Version 4rev1", RFC 2060, December 1996. [JSF] Jabber Software Foundation, "Jabber Software Foundation", . Saint-Andre (ed.) Expires July 6, 2004 [Page 71] Internet-Draft XMPP Core January 2004 [POP3] Myers, J. and M. Rose, "Post Office Protocol - Version 3", STD 53, RFC 1939, May 1996. [URI] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998. [USINGTLS] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC 2595, June 1999. [XML-REG] Mealling, M., "The IETF XML Registry", draft-mealling-iana-xmlns-registry-05 (work in progress), June 2003. [XMPP-IM] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence", draft-ietf-xmpp-im-19 (work in progress), November 2003. Author's Address Peter Saint-Andre Jabber Software Foundation EMail: stpeter@jabber.org Appendix A. Nodeprep A.1 Introduction This appendix defines the "Nodeprep" profile of [STRINGPREP]. As such, it specifies processing rules that will enable users to enter internationalized node identifiers in the Extensible Messaging and Presence Protocol (XMPP) and have the highest chance of getting the content of the strings correct. (An XMPP node identifier is the optional portion of an XMPP address that precedes a domain identifier and the '@' separator; it is often but not exclusively associated with an instant messaging username.) These processing rules are intended only for XMPP node identifiers and are not intended for arbitrary text or any other aspect of an XMPP address. This profile defines the following, as required by [STRINGPREP]: o The intended applicability of the profile: internationalized node identifiers within XMPP o The character repertoire that is the input and output to Saint-Andre (ed.) Expires July 6, 2004 [Page 72] Internet-Draft XMPP Core January 2004 stringprep: Unicode 3.2, specified in Section 2 of this Appendix o The mappings used: specified in Section 3 o The Unicode normalization used: specified in Section 4 o The characters that are prohibited as output: specified in Section 5 o Bidirectional character handling: specified in Section 6 A.2 Character Repertoire This profile uses Unicode 3.2 with the list of unassigned code points being Table A.1, both defined in Appendix A of [STRINGPREP]. A.3 Mapping This profile specifies mapping using the following tables from [STRINGPREP]: Table B.1 Table B.2 A.4 Normalization This profile specifies using Unicode normalization form KC, as described in [STRINGPREP]. A.5 Prohibited Output This profile specifies prohibiting use of the following tables from [STRINGPREP]. Table C.1.1 Table C.1.2 Table C.2.1 Table C.2.2 Table C.3 Saint-Andre (ed.) Expires July 6, 2004 [Page 73] Internet-Draft XMPP Core January 2004 Table C.4 Table C.5 Table C.6 Table C.7 Table C.8 Table C.9 In addition, the following Unicode characters are also prohibited: #x22 (") #x26 (&) #x27 (') #x2F (/) #x3A (:) #x3C (<) #x3E (>) #x40 (@) A.6 Bidirectional Characters This profile specifies checking bidirectional strings as described in Section 6 of [STRINGPREP]. Appendix B. Resourceprep B.1 Introduction This appendix defines the "Resourceprep" profile of [STRINGPREP]. As such, it specifies processing rules that will enable users to enter internationalized resource identifiers in the Extensible Messaging and Presence Protocol (XMPP) and have the highest chance of getting the content of the strings correct. (An XMPP resource identifier is the optional portion of an XMPP address that follows a domain identifier and the '/' separator; it is often but not exclusively associated with an instant messaging session name.) These processing Saint-Andre (ed.) Expires July 6, 2004 [Page 74] Internet-Draft XMPP Core January 2004 rules are intended only for XMPP resource identifiers and are not intended for arbitrary text or any other aspect of an XMPP address. This profile defines the following, as required by [STRINGPREP]: o The intended applicability of the profile: internationalized resource identifiers within XMPP o The character repertoire that is the input and output to stringprep: Unicode 3.2, specified in Section 2 of this Appendix o The mappings used: specified in Section 3 o The Unicode normalization used: specified in Section 4 o The characters that are prohibited as output: specified in Section 5 o Bidirectional character handling: specified in Section 6 B.2 Character Repertoire This profile uses Unicode 3.2 with the list of unassigned code points being Table A.1, both defined in Appendix A of [STRINGPREP]. B.3 Mapping This profile specifies mapping using the following tables from [STRINGPREP]: Table B.1 B.4 Normalization This profile specifies using Unicode normalization form KC, as described in [STRINGPREP]. B.5 Prohibited Output This profile specifies prohibiting use of the following tables from [STRINGPREP]. Table C.1.2 Saint-Andre (ed.) Expires July 6, 2004 [Page 75] Internet-Draft XMPP Core January 2004 Table C.2.1 Table C.2.2 Table C.3 Table C.4 Table C.5 Table C.6 Table C.7 Table C.8 Table C.9 B.6 Bidirectional Characters This profile specifies checking bidirectional strings as described in Section 6 of [STRINGPREP]. Appendix C. XML Schemas The following XML schemas are descriptive, not normative. For schemas defining the 'jabber:client' and 'jabber:server' namespaces, refer to [XMPP-IM]. C.1 Streams namespace Saint-Andre (ed.) Expires July 6, 2004 [Page 76] Internet-Draft XMPP Core January 2004 C.2 Stream error namespace Saint-Andre (ed.) Expires July 6, 2004 [Page 77] Internet-Draft XMPP Core January 2004 Saint-Andre (ed.) Expires July 6, 2004 [Page 78] Internet-Draft XMPP Core January 2004 C.3 TLS namespace C.4 SASL namespace Saint-Andre (ed.) Expires July 6, 2004 [Page 79] Internet-Draft XMPP Core January 2004 Saint-Andre (ed.) Expires July 6, 2004 [Page 80] Internet-Draft XMPP Core January 2004 C.5 Resource binding namespace C.6 Dialback namespace Saint-Andre (ed.) Expires July 6, 2004 [Page 81] Internet-Draft XMPP Core January 2004 C.7 Stanza error namespace Saint-Andre (ed.) Expires July 6, 2004 [Page 82] Internet-Draft XMPP Core January 2004 Appendix D. Differences Between Core Jabber Protocol and XMPP This section is non-normative. XMPP has been adapted from the protocols originally developed in the Jabber open-source community, which can be thought of as "XMPP 0.9". Because there exists a large installed base of Jabber implementations and deployments, it may be helpful to specify the key differences between Jabber and XMPP in order to expedite and encourage upgrades of those implementations and deployments to XMPP. This section summarizes the core differences, while the corresponding section of Saint-Andre (ed.) Expires July 6, 2004 [Page 83] Internet-Draft XMPP Core January 2004 [XMPP-IM] summarizes the differences that relate specifically to instant messaging and presence applications. D.1 Channel Encryption It is common practice in the Jabber community to use SSL for channel encryption on ports other than 5222 and 5269 (the convention is to use ports 5223 and 5270). XMPP uses TLS over the IANA-registered ports for channel encryption, as defined under Use of TLS (Section 5) herein. D.2 Authentication The client-server authentication protocol developed in the Jabber community uses a basic IQ interaction qualified by the 'jabber:iq:auth' namespace (documentation of this protocol is contained in "JEP-0078: Non-SASL Authentication", published by the Jabber Software Foundation [JSF]). XMPP uses SASL for authentication, as defined under Use of SASL (Section 6) herein. The Jabber community does not currently possess an authentication protocol for server-to-server communications, only the Server Dialback (Section 8) protocol to prevent server spoofing. XMPP augments Server Dialback with a true server-to-server authentication protocol, as defined under Use of SASL (Section 6) herein. D.3 Resource Binding Resource binding in the Jabber community is handled via the 'jabber:iq:auth' namespace that is also used for client authentication with a server. XMPP defines a dedicated namespace for resource binding as well as the ability for a server to generate a resource identifier on behalf of a client, as defined under Resource Binding (Section 7). D.4 JID Processing JID processing was somewhat loosely defined by the Jabber community (documentation of forbidden characters and case handling is contained in "JEP-0029: Definition of Jabber Identifiers", published by the Jabber Software Foundation [JSF]). XMPP specifies the use of [NAMEPREP] for domain identifiers and supplements Nameprep with two additional [STRINGPREP] profiles for JID processing: Nodeprep (Appendix A) for node identifiers and Resourceprep (Appendix B) for resource identifiers . D.5 Error Handling Saint-Andre (ed.) Expires July 6, 2004 [Page 84] Internet-Draft XMPP Core January 2004 Stream-related errors are handled in the Jabber community via simple CDATA text in a element. In XMPP, stream-related errors are handled via an extensible mechanism defined under Stream Errors (Section 4.6) herein. Stanza-related errors are handled in the Jabber community via HTTP-style error codes. In XMPP, stanza-related errors are handled via an extensible mechanism defined under Stanza Errors (Section 9.3) herein. (Documentation of a mapping between Jabber and XMPP error handling mechanisms is contained in "JEP-0086: Legacy Errors", published by the Jabber Software Foundation [JSF].) D.6 Internationalization Although use of UTF-8 has always been standard practice within the Jabber community, the community did not define mechanisms for specifying the language of human-readable text provided in CDATA sections. XMPP specifies the use of the 'xml:lang' attribute in such contexts, as defined under Stream Attributes (Section 4.2) and xml:lang (Section 9.1.5) herein. D.7 Stream Version Attribute The Jabber community does not include a 'version' attribute in stream headers. XMPP specifies inclusion of that attribute, with a value of '1.0', as a way to signal support for the stream features (authentication, encryption, etc.) defined under Version Support (Section 4.2.1) herein. Appendix E. Revision History Note to RFC Editor: please remove this entire appendix, and the corresponding entries in the table of contents, prior to publication. E.1 Changes from draft-ietf-xmpp-core-20 o Completed changes necessary to address IESG feedback. E.2 Changes from draft-ietf-xmpp-core-19 o Fixed several typographical errors. o Restricted values of 'type' attribute for IQ stanzas to those defined in the schema (i.e., changed SHOULD to MUST) to ensure consistency with text in XMPP IM. o Added reference to RFC 3548. Saint-Andre (ed.) Expires July 6, 2004 [Page 85] Internet-Draft XMPP Core January 2004 o Added the stanza error. o Replaced RFC 2222 reference with reference to draft-ietf-sasl-rfc2222bis. o Further clarified role and usage of user names in SASL mechanisms. o Added mention of 'code' attribute on error element. o Clarified several sentences in the dialback narrative. o Clarified use of stringprep profiles and added reference to RFC 3490. o Added security consideration regarding lack of SASL channel binding to TLS per discussion at IETF 58 meeting. o Adjusted formatting to conform to RFC Editor requirements. E.3 Changes from draft-ietf-xmpp-core-18 o Added the 'xml:lang' attribute to the root element per previous consensus and list discussion. o Changed "jabber-server" and "jabber-client" service names to "xmpp-server" and "xmpp-client". o Added the , , and stanza errors. o Changed dataype of stream error and of and stanza errors to xs:string so that these elements may contain programmatic information. o Removed and SASL errors. o Removed references to RFC 952 and RFC 1123 (domain name format is handled by reference to Nameprep). o Changed address record resolution text so that it is not specific to IPv4. o Clarified text in appendices regarding scope of Nodeprep and Resourceprep. o Removed requirement that receiving entity terminate the TCP connection upon receiving an element from or sending a Saint-Andre (ed.) Expires July 6, 2004 [Page 86] Internet-Draft XMPP Core January 2004 element to the initiating entity during SASL negotiation. o Removed recommendation that TLS and SASL security layer should not both be used simultaneously. o Added subsection to Security Considerations regarding use of base64 in SASL. o Specified rules regarding inclusion of username in SASL negotiation. o Adjusted content related to SASL authorization identities, since the previous text did not track SASL. o Added section on resource binding to compensate for changes to SASL authorization identity text. o Specified ABNF for JIDs. o Checked all references. o Completed a thorough proofreading and consistency check of the entire text. E.4 Changes from draft-ietf-xmpp-core-17 o Specified that UTF-8 is the only allowable encoding. o Added stream errors for , , and , as well as a error for generic XML error conditions. o Folded Nodeprep and Resourceprep profiles into this document. o Moved most delivery handling rules from XMPP IM to XMPP Core. o Moved detailed stanza syntax descriptions from XMPP Core to XMPP IM. o Moved stanza schemas from XMPP Core to XMPP IM. E.5 Changes from draft-ietf-xmpp-core-16 o Added and stream errors. Saint-Andre (ed.) Expires July 6, 2004 [Page 87] Internet-Draft XMPP Core January 2004 o Changed the datatype for the and stream errors from 'xs:string' to 'empty'. o Further clarified server handling of the basic stanza kinds. o Further clarified character encoding rules per list discussion. o Specified meaning of version='1.0' flag in stream headers. o Added stream closure to SASL failure cases in order to mirror handling of TLS failures. o Added section on compliance requirements for server and client implementations. o Added non-normative section on differences between Jabber usage and XMPP specifications. E.6 Changes from draft-ietf-xmpp-core-15 o Added and stream errors. o Added SASL error and clarified error. o Made 'id' required for IQ stanzas. E.7 Changes from draft-ietf-xmpp-core-14 o Added SRV lookup for client-to-server communications. o Changed server SRV record to conform to RFC 2782; specifically, the service identifier was changed from 'jabber' to 'jabber-server'. E.8 Changes from draft-ietf-xmpp-core-13 o Clarified stream restart after successful TLS and SASL negotiation. o Clarified requirement for resolution of DNS hostnames. o Clarified text regarding namespaces. o Clarified examples regarding empty element. Saint-Andre (ed.) Expires July 6, 2004 [Page 88] Internet-Draft XMPP Core January 2004 o Added several more SASL error conditions. o Changed stream error to and added to schema. o Made small editorial changes and fixed several schema errors. E.9 Changes from draft-ietf-xmpp-core-12 o Moved server dialback to a separate section; clarified its security characteristics and its role in the protocol. o Adjusted error handling syntax and semantics per list discussion. o Further clarified length of node identifiers and total length of JIDs. o Documented message type='normal'. o Corrected several small errors in the TLS and SASL sections. o Corrected several errors in the schemas. E.10 Changes from draft-ietf-xmpp-core-11 o Corrected several small errors in the TLS and SASL sections. o Made small editorial changes and fixed several schema errors. E.11 Changes from draft-ietf-xmpp-core-10 o Adjusted TLS content regarding certificate validation process. o Specified that stanza error extensions for specific applications are to be properly namespaced children of the relevant descriptive element. o Clarified rules for inclusion of the 'id' attribute. o Specified that the 'xml:lang' attribute SHOULD be included (per list discussion). o Made small editorial changes and fixed several schema errors. Saint-Andre (ed.) Expires July 6, 2004 [Page 89] Internet-Draft XMPP Core January 2004 E.12 Changes from draft-ietf-xmpp-core-09 o Fixed several dialback error conditions. o Cleaned up rules regarding TLS and certificate processing based on off-list feedback. o Changed and elements to . o Added or modified several stream and stanza error conditions. o Specified only one child allowed for IQ, or two if type="error". o Fixed several errors in the schemas. E.13 Changes from draft-ietf-xmpp-core-08 o Incorporated list discussion regarding addressing, SASL, TLS, TCP, dialback, namespaces, extensibility, and the meaning of 'ignore' for routers and recipients. o Specified dialback error conditions. o Made small editorial changes to address RFC Editor requirements. E.14 Changes from draft-ietf-xmpp-core-07 o Made several small editorial changes. E.15 Changes from draft-ietf-xmpp-core-06 o Added text regarding certificate validation in TLS negotiation per list discussion. o Clarified nature of XML restrictions per discussion with W3C, and moved XML Restrictions subsection under "XML Usage within XMPP". o Further clarified that XML streams are unidirectional. o Changed stream error and stanza error namespace names to conform to the format defined in The IETF XML Registry. o Removed note to RFC Editor regarding provisional namespace names. Saint-Andre (ed.) Expires July 6, 2004 [Page 90] Internet-Draft XMPP Core January 2004 E.16 Changes from draft-ietf-xmpp-core-05 o Added as a stream error condition. o Adjusted security considerations per discussion at IETF 56 and on list. E.17 Changes from draft-ietf-xmpp-core-04 o Added server-to-server examples for TLS and SASL. o Changed error syntax, rules, and examples based on list discussion. o Added schemas for the TLS, stream error, and stanza error namespaces. o Added note to RFC Editor regarding provisional namespace names. o Made numerous small editorial changes and clarified text throughout. E.18 Changes from draft-ietf-xmpp-core-03 o Clarified rules and procedures for TLS and SASL. o Amplified stream error code syntax per list discussion. o Made numerous small editorial changes. E.19 Changes from draft-ietf-xmpp-core-02 o Added dialback schema. o Removed all DTDs since schemas provide more complete definitions. o Added stream error codes. o Clarified error code "philosophy". E.20 Changes from draft-ietf-xmpp-core-01 o Updated the addressing restrictions per list discussion and added references to the new Nodeprep and Resourceprep profiles. Saint-Andre (ed.) Expires July 6, 2004 [Page 91] Internet-Draft XMPP Core January 2004 o Corrected error in Use of SASL regarding 'version' attribute. o Made numerous small editorial changes. E.21 Changes from draft-ietf-xmpp-core-00 o Added information about TLS from list discussion. o Clarified meaning of "ignore" based on list discussion. o Clarified information about Universal Character Set data and character encodings. o Provided base64-decoded information for examples. o Fixed several errors in the schemas. o Made numerous small editorial fixes. E.22 Changes from draft-miller-xmpp-core-02 o Brought Use of SASL section into line with discussion on list and at IETF 55 meeting. o Added information about the optional 'xml:lang' attribute per discussion on list and at IETF 55 meeting. o Specified that validation is neither required nor recommended, and that the formal definitions (DTDs and schemas) are included for descriptive purposes only. o Specified that the response to an IQ stanza of type "get" or "set" must be an IQ stanza of type "result" or "error". o Specified that compliant server implementations must process stanzas in order. o Specified that for historical reasons some server implementations may accept 'stream:' as the only valid namespace prefix on the root stream element. o Clarified the difference between 'jabber:client' and 'jabber:server' namespaces, namely, that 'to' and 'from' attributes are required on all stanzas in the latter but not the former. Saint-Andre (ed.) Expires July 6, 2004 [Page 92] Internet-Draft XMPP Core January 2004 o Fixed typo in Step 9 of the dialback protocol (changed db:result to db:verify). o Removed references to TLS pending list discussion. o Removed the non-normative appendix on OpenPGP usage pending its inclusion in a separate I-D. o Simplified the architecture diagram, removed most references to services, and removed references to the 'jabber:component:*' namespaces. o Noted that XMPP activity respects firewall administration policies. o Further specified the scope and uniqueness of the 'id' attribute in all stanza kinds and the element in message stanzas. o Nomenclature changes: (1) from "chunks" to "stanzas"; (2) from "host" to "server" and from "node" to "client" (except with regard to definition of the addressing scheme). Saint-Andre (ed.) Expires July 6, 2004 [Page 93] Internet-Draft XMPP Core January 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. Full Copyright Statement Copyright (C) The Internet Society (2004). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assignees. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION Saint-Andre (ed.) Expires July 6, 2004 [Page 94] Internet-Draft XMPP Core January 2004 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Saint-Andre (ed.) Expires July 6, 2004 [Page 95] XMPP Working Group P. Saint-Andre (ed.) Internet-Draft Jabber Software Foundation Expires: July 6, 2004 January 6, 2004 Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence draft-ietf-xmpp-im-20 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on July 6, 2004. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This memo describes extensions to and applications of the core features of the Extensible Messaging and Presence Protocol (XMPP) that provide the basic instant messaging (IM) and presence functionality defined in RFC 2779. Saint-Andre (ed.) Expires July 6, 2004 [Page 1] Internet-Draft XMPP IM January 2004 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Syntax of XML Stanzas . . . . . . . . . . . . . . . . . . . 4 3. Session Establishment . . . . . . . . . . . . . . . . . . . 11 4. Exchanging Messages . . . . . . . . . . . . . . . . . . . . 14 5. Exchanging Presence Information . . . . . . . . . . . . . . 16 6. Managing Subscriptions . . . . . . . . . . . . . . . . . . . 25 7. Roster Management . . . . . . . . . . . . . . . . . . . . . 26 8. Integration of Roster Items and Presence Subscriptions . . . 31 9. Subscription States . . . . . . . . . . . . . . . . . . . . 54 10. Blocking Communication . . . . . . . . . . . . . . . . . . . 59 11. Server Rules for Handling XML Stanzas . . . . . . . . . . . 79 12. IM and Presence Compliance Requirements . . . . . . . . . . 81 13. Internationalization Considerations . . . . . . . . . . . . 82 14. Security Considerations . . . . . . . . . . . . . . . . . . 82 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . 83 Normative References . . . . . . . . . . . . . . . . . . . . 84 Informative References . . . . . . . . . . . . . . . . . . . 85 Author's Address . . . . . . . . . . . . . . . . . . . . . . 85 A. vCards . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 B. XML Schemas . . . . . . . . . . . . . . . . . . . . . . . . 86 C. Differences Between Jabber IM/Presence and XMPP . . . . . . 98 D. Revision History . . . . . . . . . . . . . . . . . . . . . . 99 Intellectual Property and Copyright Statements . . . . . . . 106 Saint-Andre (ed.) Expires July 6, 2004 [Page 2] Internet-Draft XMPP IM January 2004 1. Introduction 1.1 Overview The Extensible Messaging and Presence Protocol (XMPP) is a protocol for streaming XML [XML] elements in order to exchange messages and presence information in close to real time. The core features of XMPP are defined in Extensible Messaging and Presence Protocol (XMPP): Core [XMPP-CORE]. These features -- mainly XML streams, use of TLS and SASL, and the , , and children of the stream root -- provide the building blocks for many types of near-real-time applications, which may be layered on top of the core by sending application-specific data qualified by particular XML namespaces [XML-NAMES]. This memo describes extensions to and applications of the core features of XMPP that provide the basic functionality expected of an instant messaging (IM) and presence application as defined in RFC 2779 [IMP-REQS]. 1.2 Requirements For the purposes of this memo, the requirements of a basic instant messaging and presence application are defined by [IMP-REQS], which at a high level stipulates that a user must be able to complete the following use cases: o Exchange messages with other users o Exchange presence information with other users o Manage subscriptions to and from other users o Manage items in a contact list (in XMPP this is called a "roster") o Block communications to or from specific other users Detailed definitions of these functionality areas are contained in [IMP-REQS], and the interested reader is directed to that document regarding the requirements addressed herein. [IMP-REQS] also stipulates that presence services must be separable from instant messaging services; i.e., it must be possible to use the protocol to provide a presence service, an instant messaging service, or both. Although the text of this memo assumes that implementations and deployments will want to offer a unified instant messaging and presence service, there is no requirement that a service must offer both a presence service and an instant messaging service, and the protocol makes it possible to offer separate and distinct services for presence and for instant messaging. Saint-Andre (ed.) Expires July 6, 2004 [Page 3] Internet-Draft XMPP IM January 2004 Note: While XMPP-based instant messaging and presence meets the requirements of [IMP-REQS], it was not designed explicitly with that specification in mind, since the base protocol evolved through an open development process within the Jabber open-source community before RFC 2779 was written. Note also that although protocols addressing many other functionality areas have been defined in the Jabber community, such protocols are not included in this memo because they are not required by [IMP-REQS]. 1.3 Terminology This memo inherits the terminology defined in [XMPP-CORE]. The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [TERMS]. 1.4 Contributors Most of the core aspects of the Extensible Messaging and Presence Protocol were developed originally within the Jabber open-source community in 1999. This community was founded by Jeremie Miller, who released source code for the initial version of the jabberd server in January 1999. Major early contributors to the base protocol also included Ryan Eatmon, Peter Millard, Thomas Muldowney, and Dave Smith. Work specific to instant messaging and presence by the XMPP Working Group has concentrated especially on IM session establishment and communication blocking (privacy rules); the session establishment protocol was mainly developed by Rob Norris and Joe Hildebrand, and the privacy rules protocol was originally contributed by Peter Millard. 1.5 Acknowledgements Thanks are due to a number of individuals in addition to the contributors listed. Although it is difficult to provide a complete list, the following individuals were particularly helpful in defining the protocols or in commenting on the specifications in this memo: Thomas Charron, Richard Dobson, Schuyler Heath, Jonathan Hogg, Craig Kaes, Jacek Konieczny, Alexey Melnikov, Keith Minkler, Julian Missig, Pete Resnick, Marshall Rose, Alexey Shchepin, Jean-Louis Seguineau, Iain Shigeoka, and David Waite. Thanks also to members of the XMPP Working Group and the IETF community for comments and feedback provided throughout the life of this memo. 2. Syntax of XML Stanzas Saint-Andre (ed.) Expires July 6, 2004 [Page 4] Internet-Draft XMPP IM January 2004 The basic semantics and common attributes of XML stanzas qualified by the 'jabber:client' and 'jabber:server' namespaces are defined in [XMPP-CORE]. However, these namespaces also define various child elements, as well as values for the common 'type' attribute, that are specific to instant messaging and presence applications. Thus, before addressing particular "use cases" for such applications, we here further describe the syntax of XML stanzas, thereby supplementing the discussion in [XMPP-CORE]. 2.1 Message Syntax Message stanzas in the 'jabber:client' or 'jabber:server' namespace are used to "push" information to another entity. Common uses in instant messaging applications include single messages, messages sent in the context of a chat conversation, messages sent in the context of a multi-user chat room, headlines, and errors. 2.1.1 Types of Message The 'type' attribute of a message stanza is RECOMMENDED; if included, it specifies the conversational context of the message, thus providing a hint regarding presentation (e.g., in a GUI). If included, the 'type' attribute MUST have one of the following values: o chat -- The message is sent in the context of a one-to-one chat conversation. A compliant client SHOULD present the message an interface enabling one-to-one chat between the two parties, including an appropriate conversation history. o error -- An error has occurred related to a previous message sent by the sender (for details regarding stanza error syntax, refer to [XMPP-CORE]). A compliant client SHOULD present an appropriate interface informing the sender of the nature of the error. o groupchat -- The message is sent in the context of a multi-user chat environment. A compliant client SHOULD present the message an interface enabling many-to-many chat between the parties, including a roster of parties in the chatroom and an appropriate conversation history. Full definition of XMPP-based groupchat protocols is out of scope for this memo. o headline -- The message is probably generated by an automated service that delivers or broadcasts content (news, sports, market information, RSS feeds, etc.). No reply to the message is expected, and a compliant client SHOULD present the message an interface that appropriately differentiates the message from standalone messages, chat sessions, or groupchat sessions (e.g., by not providing the recipient with the ability to reply). Saint-Andre (ed.) Expires July 6, 2004 [Page 5] Internet-Draft XMPP IM January 2004 o normal -- The message is a single message that is sent outside the context of a one-to-one conversation or groupchat, and to which it is expected that the recipient will reply. A compliant client SHOULD present the message in an interface enabling the recipient to reply. An IM application SHOULD support all of the foregoing message types; if an application receives a message with no 'type' attribute or the application does not understand the value of the 'type' attribute provided, it MUST consider the message to be of type "normal" (i.e., "normal" is the default). The "error" type MUST be generated only in response to an error related to a message received from another entity. Although the 'type' attribute is NOT REQUIRED, it is considered polite to mirror the type in any replies to a message; furthermore, some specialized applications (e.g., a multi-user chat service) MAY at their discretion enforce the use of a particular message type (e.g., type='groupchat'). 2.1.2 Child Elements As described under extended namespaces (Section 2.4), a message stanza MAY contain any properly-namespaced child element. In accordance with the default namespace declaration, by default a message stanza is in the 'jabber:client' or 'jabber:server' namespace, which defines certain allowable children of message stanzas. If the message stanza is of type "error", it MUST include an child; for details, see [XMPP-CORE]. Otherwise, the message stanza MAY contain any of the following child elements without an explicit namespace declaration: 1. 2. 3. 2.1.2.1 Subject The element contains XML character data that specifies the topic of the message. The element MUST NOT possess any attributes, with the exception of the 'xml:lang' attribute. Multiple instances of the element MAY be included for the purpose of providing alternate versions of the same subject, but only if each instance possesses an 'xml:lang' attribute with a distinct language Saint-Andre (ed.) Expires July 6, 2004 [Page 6] Internet-Draft XMPP IM January 2004 value. The element MUST NOT contain mixed content (as defined in Section 3.2.2 of [XML]). 2.1.2.2 Body The element contains XML character data that specifies the textual contents of the message; this child element is normally included but NOT REQUIRED. The element MUST NOT possess any attributes, with the exception of the 'xml:lang' attribute. Multiple instances of the element MAY be included but only if each instance possesses an 'xml:lang' attribute with a distinct language value. The element MUST NOT contain mixed content (as defined in Section 3.2.2 of [XML]). 2.1.2.3 Thread The element contains XML character data that specifies an identifier that is used for tracking a conversation thread (sometimes referred to as an "instant messaging session") between two entities. The value of the element is generated by the sender and that SHOULD be copied back in any replies. If used, it MUST be unique to that conversation thread within the stream and MUST be consistent throughout that conversation (a client that receives a message from the same full JID but with a different thread ID MUST assume that the message in question exists outside the context of the existing conversation thread). The use of the element is OPTIONAL and is not used to identify individual messages, only conversations. A message stanza MUST NOT contain more than one element. The element MUST NOT possess any attributes. The value of the element MUST be treated as opaque by entities; no semantic meaning may be derived from it, and only exact comparisons may be made against it. The element MUST NOT contain mixed content (as defined in Section 3.2.2 of [XML]). 2.2 Presence Syntax Presence stanzas are used in the 'jabber:client' or 'jabber:server' namespace to express an entity's current availability status (offline or online, along with various sub-states of the latter and optional user-defined descriptive text), and to communicate that status to other entities. Presence stanzas are also used to negotiate and manage subscriptions to the presence of other entities. 2.2.1 Types of Presence The 'type' attribute of a presence stanza is OPTIONAL. A presence stanza that does not possess a 'type' attribute is used to signal to Saint-Andre (ed.) Expires July 6, 2004 [Page 7] Internet-Draft XMPP IM January 2004 the server that the sender is online and available for communication. If included, the 'type' attribute specifies a lack of availability, a request to manage a subscription to another entity's presence, a request for another entity's current presence, or an error related to a previously-sent presence stanza. If included, the 'type' attribute MUST have one of the following values: o unavailable -- Signals that the entity is no longer available for communication. o subscribe -- The sender wishes to subscribe to the recipient's presence. o subscribed -- The sender has allowed the recipient to receive their presence. o unsubscribe -- A notification that an entity is unsubscribing from another entity's presence. o unsubscribed -- The subscription request has been denied or a previously-granted subscription has been cancelled. o probe -- A request for an entity's current presence; SHOULD be generated only by a server and SHOULD NOT be generated by a client. o error -- An error has occurred regarding processing or delivery of a previously-sent presence stanza. For detailed information regarding presence semantics and the subscription model used in the context of XMPP-based instant messaging and presence applications, refer to Exchanging Presence Information (Section 5) and Managing Subscriptions (Section 6). 2.2.2 Child Elements As described under extended namespaces (Section 2.4), a presence stanza MAY contain any properly-namespaced child element. In accordance with the default namespace declaration, by default a presence stanza is in the 'jabber:client' or 'jabber:server' namespace, which defines certain allowable children of presence stanzas. If the presence stanza is of type "error", it MUST include an child; for details, see [XMPP-CORE]. If the presence stanza possesses no 'type' attribute, it MAY contain any of the following child elements (note that the child MAY be sent in a presence stanza of type "unavailable" or, for historical reasons, "subscribe"): Saint-Andre (ed.) Expires July 6, 2004 [Page 8] Internet-Draft XMPP IM January 2004 1. 2. 3. 2.2.2.1 Show The OPTIONAL element contains XML character data that specifies the particular availability status of an entity or specific resource. A presence stanza MUST NOT contain more than one element. The element MUST NOT possess any attributes. The XML character data contained in the element is not intended to be human-readable. If provided, the CDATA value MUST be one of the following (additional availability types could be defined through a properly-namespaced child element of the presence stanza): o away -- The entity or resource is temporarily away. o chat -- The entity or resource is actively interested in chatting. o xa -- The entity or resource is away for an extended period (xa = "eXtended Away"). o dnd -- The entity or resource is busy (dnd = "Do Not Disturb"). If no element is provided, the entity is assumed to be online and available. 2.2.2.2 Status The OPTIONAL element contains a natural-language description of availability status. It is normally used in conjunction with the show element to provide a detailed description of an availability state (e.g., "In a meeting"). The element MUST NOT possess any attributes, with the exception of the 'xml:lang' attribute. Multiple instances of the element MAY be included but only if each instance possesses an 'xml:lang' attribute with a distinct language value. 2.2.2.3 Priority The OPTIONAL element contains XML character data that specifies the priority level of the resource. The value may be any integer between -128 and +127. A presence stanza MUST NOT contain more than one element. The element MUST NOT possess any attributes. If no priority is provided, a server SHOULD Saint-Andre (ed.) Expires July 6, 2004 [Page 9] Internet-Draft XMPP IM January 2004 consider the priority to be zero. For information regarding the semantics of priority values in stanza routing within instant messaging and presence applications, refer to Server Rules for Handling XML Stanzas (Section 11). 2.3 IQ Syntax IQ stanzas provide a structured request-response mechanism. The basic semantics of that mechanism are defined in [XMPP-CORE], whereas the specific semantics required to complete particular use cases are defined in all cases by an extended namespace (Section 2.4) (note that the 'jabber:client' and 'jabber:server' namespaces do not define any children of IQ stanzas). This memo defines two such extended namespaces, one for Roster Management (Section 7) and the other for Blocking Communication (Section 10); however, an IQ stanza MAY contain structured information qualified by any extended namespace. 2.4 Extended Namespaces While the three XML stanza kinds defined in the "jabber:client" or "jabber:server" namespace (along with their attributes and child elements) provide a basic level of functionality for messaging and presence, XMPP uses XML namespaces to extend the stanzas for the purpose of providing additional functionality. Thus a message or presence MAY contain one or more optional child elements containing content that extends the meaning of the message (e.g., an XHTML-formatted version of the message body), and an IQ stanza MAY contain one such child element. This child element MAY have any name and MUST possess an 'xmlns' namespace declaration (other than "jabber:client", "jabber:server", or "http://etherx.jabber.org/ streams") that defines all data contained within the child element. Support for any given extended namespace is OPTIONAL on the part of any implementation (aside from the extended namespaces defined herein). If an entity does not understand such a namespace, the entity's expected behavior depends on whether the entity is (1) the recipient or (2) an entity that is routing the stanza to the recipient: Recipient: If a recipient receives a stanza that contains a child element it does not understand, it SHOULD ignore that specific XML data, i.e., it SHOULD not process it or present it to a user or associated application (if any). In particular: * If an entity receives a message or presence stanza that contains XML data qualified by a namespace it does not understand, the portion of the stanza that is in the unknown namespace SHOULD be ignored. Saint-Andre (ed.) Expires July 6, 2004 [Page 10] Internet-Draft XMPP IM January 2004 * If an entity receives a message stanza whose only child element is qualified by a namespace it does not understand, it MUST ignore the entire stanza. * If an entity receives an IQ stanza of type "get" or "set" containing a child element qualified by a namespace it does not understand, the entity SHOULD return an IQ stanza of type "error" with an error condition of . Router: If a routing entity (usually a server) handles a stanza that contains a child element it does not understand, it SHOULD ignore the associated XML data by passing it on untouched to the recipient. 3. Session Establishment Most instant messaging and presence applications based on XMPP are implemented via a client-server architecture that requires a client to establish a session on a server in order to engage in the expected instant messaging and presence activities. However, there are several pre-conditions that MUST be met before a client can establish an instant messaging and presence session. These are: 1. Stream Authentication -- a client MUST complete stream authentication as documented in [XMPP-CORE] before attempting to establish a session or send any XML stanzas. 2. Resource Binding -- after completing stream authentication, a client MUST bind a resource to the stream so that the client's address is of the form , after which the entity is said to be a "connected resource" in the terminology of [XMPP-CORE]. If a server supports sessions, it MUST include a element qualified by the 'urn:ietf:params:xml:ns:xmpp-session' namespace in the stream features it advertises to a client after the completion of stream authentication as defined in [XMPP-CORE]: Server advertises session establishment feature to client: Saint-Andre (ed.) Expires July 6, 2004 [Page 11] Internet-Draft XMPP IM January 2004 Upon being so informed that session establishment is required (and after completing resource binding), the client MUST establish a session if it desires to engage in instant messaging and presence functionality; it completes this step by sending to the server an IQ stanza of type "set" containing an empty child element qualified by the 'urn:ietf:params:xml:ns:xmpp-session' namespace: Step 1: Client requests session with server: Step 2: Server informs client that session has been created: Upon establishing a session, a connected resource (in the terminology of [XMPP-CORE]) is said to be an "active resource". Several error conditions are possible. For example, the server may encounter an internal condition that prevents it from creating the session, the username or authorization identity may lack permissions to create a session, or there may already be an active resource associated with a resource identifier of the same name. If the server encounters an internal condition that prevents it from creating the session, it MUST return an error. Step 2 (alt): Server responds with error (internal server error): Saint-Andre (ed.) Expires July 6, 2004 [Page 12] Internet-Draft XMPP IM January 2004 If the username or resource is not allowed to create a session, the server MUST return an error (e.g., forbidden). Step 2 (alt): Server responds with error (username or resource not allowed to create session): If there is already an active resource of the same name, the server MUST either (1) terminate the active resource and allow the newly-requested session, or (2) disallow the newly-requested session and maintain the active resource. Which of these the server does is up to the implementation, although it is RECOMMENDED to implement case #1. In case #1, the server SHOULD send a stream error to the active resource, terminate the XML stream and underlying TCP connection for the active resource, and return a IQ stanza of type "result" (indicating success) to the newly-requested session. In case #2, the server SHOULD send a stanza error to the newly-requested session but maintain the XML stream for that connection so that the newly-requested session has an opportunity to negotiate a non-conflicting resource identifier before sending another request for session establishment. Step 2 (alt): Server informs active resource of resource conflict (case #1): Step 2 (alt): Server informs newly-requested session of resource conflict (case #2): After establishing a session, a client SHOULD send initial presence Saint-Andre (ed.) Expires July 6, 2004 [Page 13] Internet-Draft XMPP IM January 2004 and request its roster as described below, although these actions are NOT REQUIRED. Note: Before allowing the creation of instant messaging and presence sessions, a server MAY require prior account provisioning. Possible methods for account provisioning include account creation by a server administrator as well as in-band account registration using the 'jabber:iq:register' namespace; the latter method is documented by the Jabber Software Foundation [JSF] at but is out of scope for this memo. 4. Exchanging Messages Exchanging messages is a basic use of XMPP and is brought about when a user generates a message stanza that is addressed to another entity. As defined under Server Rules for Handling XML Stanzas (Section 11), the sender's server is responsible for delivering the message to the intended recipient (if the recipient is on the same server) or for routing the message to the recipient's server (if the recipient is on a different server). For information regarding the syntax of message stanzas as well as their defined attributes and child elements, refer to Message Syntax (Section 2.1). 4.1 Specifying an Intended Recipient An instant messaging client SHOULD specify an intended recipient for a message by providing the JID of an entity other than the sender in the 'to' attribute of the stanza. If the message is being sent in reply to a message previously received from an address of the form (e.g., within the context of a chat session), the value of the 'to' address SHOULD be the full JID (of the form ) rather than merely of the form unless the sender has knowledge (via presence) that the intended recipient's resource is no longer available. If the message is being sent outside the context of any existing chat session or received message, the value of the 'to' address SHOULD be of the form rather than of the form . 4.2 Specifying a Message Type As noted, it is RECOMMENDED for a message stanza to possess a 'type' attribute whose value captures the conversational context (if any) of the message (see Type (Section 2.1.1)). The following example shows a valid value of the 'type' attribute: Saint-Andre (ed.) Expires July 6, 2004 [Page 14] Internet-Draft XMPP IM January 2004 Example: A message of a defined type: Wherefore art thou, Romeo? 4.3 Specifying a Message Body A message stanza MAY (and often will) contain a child element whose XML character data specifies the primary meaning of the message (see Body (Section 2.1.2.2)). Example: A message with a body: Wherefore art thou, Romeo? PročeŽ jsi ty, Romeo? 4.4 Specifying a Message Subject A message stanza MAY contain one or more child elements specifying the topic of the message (see Subject (Section 2.1.2.1)). Example: A message with a subject: I implore you! Úpěnlivě prosim! Wherefore art thou, Romeo? PročeŽ jsi ty, Romeo? Saint-Andre (ed.) Expires July 6, 2004 [Page 15] Internet-Draft XMPP IM January 2004 4.5 Specifying a Conversation Thread A message stanza MAY contain a child element specifying the conversation thread in which the message is situated, for the purpose of tracking the conversation (see Thread (Section 2.1.2.3)). Example: A threaded conversation: Art thou not Romeo, and a Montague? e0ffe42b28561960c6b12b944a092794b9683a38 Neither, fair saint, if either thee dislike. e0ffe42b28561960c6b12b944a092794b9683a38 How cam'st thou hither, tell me, and wherefore? e0ffe42b28561960c6b12b944a092794b9683a38 5. Exchanging Presence Information Exchanging presence information is made relatively straightforward within XMPP by using presence stanzas. However, we see here a contrast to the handling of messages: although a client MAY send directed presence information to another entity, normally presence information is sent from a client to its server (with no 'to' address) and then broadcasted by the server to any entities that are subscribed to the presence of the sending entity (in the terminology of RFC 2778 [IMP-MODEL], we can say that the only watchers in XMPP are subscribers). (Note: While presence information MAY be provided on a user's behalf by an automated service, normally it is provided by the user's client.) For information regarding the syntax of presence stanzas as well as Saint-Andre (ed.) Expires July 6, 2004 [Page 16] Internet-Draft XMPP IM January 2004 their defined attributes and child elements, refer to [XMPP-CORE]. 5.1 Client and Server Presence Responsibilities After establishing a session, a client SHOULD (but is NOT REQUIRED to) send initial presence to the server in order to signal its availability for communications. As defined herein, the initial presence stanza (1) MUST possess no 'to' address (signalling that it is meant to be handled by the server on behalf of the client) and (2) MUST possess no 'type' attribute (signalling the user's availability). After sending initial presence, an active resource is said to be an "available resource". Upon receiving initial presence from a client, the user's server MUST do the following if there is not already one or more available resources for the user (if there is already one or more available resources for the user, the server obviously does not need to send the presence probes, since it already possesses the requisite information): 1. Send presence probes (i.e., presence stanzas whose 'type' attribute is set to a value of "probe") from the full JID (e.g., ) of the user to the bare JID (e.g., ) of any contacts to which the user is subscribed in order to determine if they are available; such contacts are those which are present in the user's roster with the 'subscription' attribute set to a value of "to" or "both". 2. Broadcast initial presence from the full JID (e.g., ) of the user to the bare JID (e.g., ) of any contacts that are subscribed to the user's presence; such contacts are those which are present in the user's roster with the 'subscription' attribute set to a value of "from" or "both". In addition, the user's server MUST broadcast initial presence from the user's new available resource to any of the user's existing available resources (if any). Upon receiving a presence probe from the user, the contact's server SHOULD reply as follows: 1. If the user is not in the contact's roster with a subscription state of "From", "From + Pending Out", or "Both" (as defined under Subscription States (Section 9)), the contact's server MUST return a presence stanza of type "error" in response to the presence probe (however, if a server receives a presence probe from a subdomain of the server's hostname or another such trusted Saint-Andre (ed.) Expires July 6, 2004 [Page 17] Internet-Draft XMPP IM January 2004 service, it MAY provide presence information about the user to that entity). Specifically: * if the user is in the contact's roster with a subscription state of "None", "None + Pending Out", or "To", the contact's server MUST return a stanza error in response to the presence probe. * if the user is in the contact's roster with a subscription state of "None + Pending In", "None + Pending Out/In", or "To + Pending In", the contact's server MUST return a stanza error in response to the presence probe. 2. Else, if the contact is blocking presence notifications to the user's bare JID or full JID (using either a default list or active list as defined under Blocking Outbound Presence Notifications (Section 10.11)), the server MUST NOT reply to the presence probe. 3. Else, if the contact has no available resources, the server MUST either (1) reply to the presence probe by sending to the user the full XML of the last presence stanza of type "unavailable" received by the server from the contact, or (2) not reply at all. 4. Else, if the contact has at least one available resource, the server MUST reply to the presence probe by sending to the user the full XML of the last presence stanza received by the server from each of the contact's available resources (again, subject to privacy rules for each session). Upon receiving initial presence from the user, the contact's server MUST deliver the user's presence stanza to the full JIDs () associated with all of the contact's available resources, but only if the user is in the contact's roster with a subscription state of "to" or "both" and the contact has not blocked inbound presence notifications from the user's bare or full JID (as defined under Blocking Inbound Presence Notifications (Section 10.10)). If the user's server receives a presence stanza of type "error" in response to the initial presence that it sent to a contact on behalf of the user, it SHOULD NOT send further presence updates to that contact (until and unless it receives a presence stanza from the contact). After sending initial presence, the user MAY update its presence information for broadcasting at any time during its session by Saint-Andre (ed.) Expires July 6, 2004 [Page 18] Internet-Draft XMPP IM January 2004 sending a presence stanza with no 'to' address and either no 'type' attribute or a 'type' attribute with a value of "unavailable". (Note: A user's client SHOULD NOT send a presence update to broadcast information that changes independently of the user's presence and availability.) If the presence stanza lacks a 'type' attribute (i.e., expresses availability), the user's server MUST broadcast the full XML of that presence stanza to all contacts (1) that are in the user's roster with a subscription type of "from" or "both", (2) to whom the user has not blocked outbound presence, and (3) from whom the server has not received a presence error during the user's session (as well as to any of the user's other available resources). If the presence stanza has a 'type' attribute set to a value of "unavailable", the user's server MUST broadcast the full XML of that presence stanza to all entities that fit the above description, as well as to any entities to which the user has sent directed available presence during the user's session (if the user has not yet sent directed unavailable presence to that entity). A user MAY send directed presence to another entity (i.e., a presence stanza with a 'to' attribute whose value is the JID of the other entity and with either no 'type' attribute or a 'type' attribute whose value is "unavailable"). There are three possible cases: 1. If the user sends directed presence to a contact that is in the user's roster with a subscription type of "from" or "both" after having sent initial presence and before sending unavailable presence broadcast, the user's server MUST route or deliver the full XML of that presence stanza (subject to privacy rules) but SHOULD NOT otherwise modify the contact's status regarding presence broadcast (i.e., it SHOULD include the contact's JID in any subsequent presence broadcasts initiated by the user). 2. If the user sends directed presence to an entity that is not in the user's roster with a subscription type of "from" or "both" after having sent initial presence and before sending unavailable presence broadcast, the user's server MUST route or deliver the full XML of that presence stanza to the entity but MUST NOT modify the contact's status regarding available presence broadcast (i.e., it MUST NOT include the entity's JID in any subsequent broadcasts of available presence initiated by the user); however, if the available resource from which the user sent the directed presence become unavailable, the user's server MUST broadcast that unavailable presence to the entity (if the user has not yet sent directed unavailable presence to that entity). 3. If the user sends directed presence without first sending initial presence or after having sent unavailable presence broadcast Saint-Andre (ed.) Expires July 6, 2004 [Page 19] Internet-Draft XMPP IM January 2004 (i.e., the resource is active but not available), the user's server MUST treat the entities to which the user sends directed presence in the same way that it treats the entities listed in case 2 above. Before ending its session with a server, a client SHOULD gracefully become unavailable by sending a final presence stanza that possesses no 'to' attribute and that possesses a 'type' attribute whose value is "unavailable" (optionally, the final presence stanza MAY contain one or more elements specifying the reason why the user is no longer available). However, the user's server MUST NOT depend on receiving final presence from an available resource, since the resource may become unavailable unexpectedly. If the user's server detects that one of the user's resources has become unavailable for any reason (either gracefully or ungracefully), it MUST broadcast unavailable presence to all contacts (1) that are in the user's roster with a subscription type of "from" or "both", (2) to whom the user has not blocked outbound presence, and (3) from whom the server has not received a presence error during the user's session; the user's server MUST also send that unavailable presence stanza to any of the user's other available resources, as well as to any entities to which the user has sent directed presence during the user's session for that resource (if the user has not yet sent directed unavailable presence to that entity). Any presence stanza with no 'type' attribute and no 'to' attribute that is sent after sending directed unavailable presence or broadcasted unavailable presence MUST be broadcasted by the server to all subscribers. 5.2 Specifying Availability Status A client MAY provide further information about its availability status by using the element (see Show (Section 2.2.2.1)). Example: Availability status: dnd 5.3 Specifying Detailed Status Information In conjunction with the element, a client MAY provide detailed status information by using the element (see Status (Section 2.2.2.2)). Example: Detailed status information: Saint-Andre (ed.) Expires July 6, 2004 [Page 20] Internet-Draft XMPP IM January 2004 dnd Wooing Juliet Ja dvořím Juliet 5.4 Specifying Presence Priority A client MAY provide a priority for its resource by using the element (see Priority (Section 2.2.2.3)). Example: Presence priority: dnd Wooing Juliet Ja dvořím Juliet 1 5.5 Presence Examples The examples in this section illustrate the presence-related protocols described above. The user is romeo@example.net, he has an available resource whose resource identifier is "orchard", and he has the following individuals in his roster: o juliet@example.com (subscription="both" and she has two available resources, one whose resource is "chamber" and another whose resource is "balcony") o benvolio@example.org (subscription="to") o mercutio@example.org (subscription="from") Example 1: User sends initial presence: Example 2: User's server sends presence probes to contacts with subscription="to" and subscription="both" on behalf of the user's available resource: Example 3: User's server sends initial presence to contacts with subscription="from" and subscription="both" on behalf of the user's available resource: Example 4: Contacts' server replies to presence probe on behalf of all of the contact's available resources: away be right back 0 1 dnd gallivanting Example 5: Contact's server delivers user's initial presence to all of the contact's available resources or returns error to user: Saint-Andre (ed.) Expires July 6, 2004 [Page 22] Internet-Draft XMPP IM January 2004 Example 6: User sends directed presence to another user not in his roster: dnd courting Juliet 0 Example 7: User sends updated available presence information for broadcasting: away I shall return! 1 Example 8: Updated presence information is delivered only to one contact (not those from whom an error was received or to whom the user sent directed presence): away I shall return! Saint-Andre (ed.) Expires July 6, 2004 [Page 23] Internet-Draft XMPP IM January 2004 1 away I shall return! 1 Example 9: One of the contact's resources sends final presence: Example 10: Contact's server sends unavailable presence information to user: Example 11: User sends final presence: gone home Example 12: Unavailable presence information is delivered to contact's one remaining resource as well as to the person to whom the user sent directed presence: gone home gone home Saint-Andre (ed.) Expires July 6, 2004 [Page 24] Internet-Draft XMPP IM January 2004 6. Managing Subscriptions In order to protect the privacy of instant messaging users and any other entities, presence and availability information is disclosed only to other entities that the user has approved. When a user has agreed that another entity may view its presence, the entity is said to have a subscription to the user's presence information. A subscription lasts across sessions; indeed, it lasts until the subscriber unsubscribes or the subscribee cancels the previously-granted subscription. Subscriptions are managed within XMPP by sending presence stanzas containing specially-defined attributes. Note: There are important interactions between subscriptions and rosters; these are defined under Integration of Roster Items and Presence Subscriptions (Section 8), and the reader must refer to that section for a complete understanding of presence subscriptions. 6.1 Requesting a Subscription A request to subscribe to another entity's presence is made by sending a presence stanza of type "subscribe". Example: Sending a subscription request: If the subscription request is being sent to an instant messaging contact, the JID supplied in the 'to' attribute SHOULD be of the form rather than , since the desired result is normally for the user to receive presence from all of the contact's resources, not merely the particular resource specified in the 'to' attribute. A user's server MUST NOT automatically approve subscription requests on the user's behalf. All subscription requests MUST be directed to the user's client, specifically to one or more available resources associated with the user. If there is no available resource associated with the user when the subscription request is received by the user's server, the user's server MUST keep a record of the subscription request and deliver the request when the user next creates an available resource, until the user either approves or denies the request. If there is more than one available resource associated with the user when the subscription request is received by the user's server, the user's server MUST broadcast that subscription request to all available resources in accordance with Server Rules for Handling XML Stanzas (Section 11). (Note: If an active resource has not provided initial presence, the server MUST NOT consider it to Saint-Andre (ed.) Expires July 6, 2004 [Page 25] Internet-Draft XMPP IM January 2004 be available and therefore MUST NOT send subscription requests to it.) However, f the user receives a presence stanza of type "subscribe" from a contact to whom the user has already granted permission to see the user's presence (e.g., in cases when the contact is seeking to resynchronize subscription states), the user's server SHOULD auto-reply on behalf of the user. 6.2 Handling a Subscription Request When a client receives a subscription request from another entity, it MUST either approve the request by sending a presence stanza of type "subscribed" or refuse the request by sending a presence stanza of type "unsubscribed". Example: Approving a subscription request: Example: Refusing a presence subscription request: 6.3 Cancelling a Subscription from Another Entity If a user would like to cancel a previously-granted subscription request, it sends a presence stanza of type "unsubscribed". Example: Cancelling a previously granted subscription request: 6.4 Unsubscribing from Another Entity's Presence If a user would like to unsubscribe from the presence of another entity, it sends a presence stanza of type "unsubscribe". Example: Unsubscribing from an entity's presence: 7. Roster Management In XMPP, one's contact list is called a roster, which consists of any number of specific roster items, each roster item being identified by a unique JID (usually of the form ). A user's Saint-Andre (ed.) Expires July 6, 2004 [Page 26] Internet-Draft XMPP IM January 2004 roster is stored by the user's server on the user's behalf so that the user may access roster information from any resource. Note: There are important interactions between rosters and subscriptions; these are defined under Integration of Roster Items and Presence Subscriptions (Section 8), and the reader must refer to that section for a complete understanding of roster management. 7.1 Syntax and Semantics Rosters are managed using IQ stanzas, specifically by means of a child element qualified by the 'jabber:iq:roster' namespace. The element MAY contain one or more children, each describing a unique roster item or "contact". The "key" or unique identifier for each roster item is a JID, encapsulated in the required 'jid' attribute of the element. The value of the 'jid' attribute SHOULD be of the form , especially if the item is associated with another (human) instant messaging user. The state of the presence subscription in relation to a roster item is captured in the 'subscription' attribute of the element. Allowable values for this attribute are: o "none" -- the user does not have a subscription to the contact, and the contact does not have a subscription to the user o "to" -- the user has a subscription to the contact, but the contact does not have a subscription to the user o "from" -- the contact has a subscription to the user, but the user does not have a subscription to the contact o "both" -- both the user and the contact have subscriptions to each other Each element MAY contain a 'name' attribute, which sets the "nickname" to be associated with the JID, as determined by the user (not the contact). The value of the 'name' attribute is opaque. Each element MAY contain one or more child elements, for use in collecting roster items into various categories. The CDATA text of the element is opaque. 7.2 Business Rules A server MUST ignore any 'to' address on a roster "set", and MUST Saint-Andre (ed.) Expires July 6, 2004 [Page 27] Internet-Draft XMPP IM January 2004 treat any roster "set" as applying to the sender. For added safety, a client SHOULD check the "from" address of a roster "push" to ensure that it is from a trusted source; specifically, the stanza MUST either have no 'from' attribute (i.e., implicitly from the server) or have a 'from' attribute whose value matches the user's bare JID (of the form ) or full JID (of the form ); otherwise, the client SHOULD ignore the roster "push". 7.3 Retrieving One's Roster on Login Upon connecting to the server, a client SHOULD request the roster (however, because receiving the roster may not be desirable for all resources, e.g., a connection with limited bandwidth, the client's request for the roster is NOT REQUIRED). If an available resource does not request the roster during a session, the server MUST NOT send it presence subscriptions and associated roster updates. Example: Client requests current roster from server: Example: Client receives roster from the server: Friends Friends Friends Saint-Andre (ed.) Expires July 6, 2004 [Page 28] Internet-Draft XMPP IM January 2004 7.4 Adding a Roster Item At any time, a user MAY add an item to his or her roster. Example: Client adds a new item: Servants The server MUST update the roster information in persistent storage, and also push the change out to all of the user's available resources that have requested the roster. This "roster push" consists of an IQ set from the server to the client and enables all available resources to remain in sync with the server-based roster information. Example: Server (1) pushes the updated roster information to all available resources that have requested the roster and (2) replies with an IQ result to the sending resource: Servants Servants Saint-Andre (ed.) Expires July 6, 2004 [Page 29] Internet-Draft XMPP IM January 2004 Example: Connected resources reply with an IQ result to the server: 7.5 Updating a Roster Item Updating an existing roster item (e.g., changing the group) is done in the same way as adding a new roster item, i.e., by sending the roster item in an IQ set to the server. Example: User updates roster item (added group): Friends Lovers As with adding a roster item, when updating a roster item the server MUST update the roster information in persistent storage, and also initiate a roster push to all of the user's available resources that have requested the roster. 7.6 Deleting a Roster Item At any time, a user MAY delete an item from its roster by doing an IQ set and making sure that the value of the 'subscription' attribute is "remove" (a compliant server MUST ignore any other values of the 'subscription' attribute when received from a client). Example: Client removes an item: Saint-Andre (ed.) Expires July 6, 2004 [Page 30] Internet-Draft XMPP IM January 2004 As with adding a roster item, when deleting a roster item the server MUST update the roster information in persistent storage, initiate a roster push to all of the user's available resources that have requested the roster (with the 'subscription' attribute set to a value of "remove"), and send an IQ result to the initiating resource. For further information about the implications of this command, see Removing a Roster Item and Cancelling All Subscriptions (Section 8.6). 8. Integration of Roster Items and Presence Subscriptions 8.1 Overview Some level of integration between roster items and presence subscriptions is normally expected by an instant messaging user regarding the user's subscriptions to and from other contacts. This section describes the level of integration that MUST be supported within XMPP instant messaging applications. There are four primary subscription states: o None -- Neither the user nor the contact is subscribed to the other's presence o To -- The user is subscribed to the contact's presence but there is no subscription from the contact to the user o From -- There is a subscription from the contact to the user, but the user has not subscribed to the contact's presence o Both -- Both the user and the contact are subscribed to each other's presence (i.e., the union of 'from' and 'to') Each of these states is reflected in the roster of both the user and the contact, thus resulting in durable subscription states. Narrative explanations of how these subscription states interact with roster items in order to complete certain defined use cases are provided in the following sub-sections. Full details regarding server and client handling of all subscription states (including pending states between the primary states listed above) is provided in Subscription States (Section 9). If an active resource does not both send initial presence and request the roster, the server MUST NOT send it presence subscription requests or roster pushes. The 'from' and 'to' addresses are OPTIONAL in roster pushes; if Saint-Andre (ed.) Expires July 6, 2004 [Page 31] Internet-Draft XMPP IM January 2004 included, their values SHOULD be the full JID of the resource for that session. A client MUST acknowledge each roster push with an IQ stanza of type "result" (for the sake of brevity, these stanzas are not shown in the following examples but are required by [XMPP-CORE]). 8.2 User Subscribes to Contact The process by which a user subscribes to a contact, including the interaction between roster items and subscription states, is defined below. 1. In preparation for being able to render the contact in the user's client interface and for the server to keep track of the subscription, the user's client SHOULD perform a "roster set" for the new roster item. This request consists of an IQ stanza of type='set' containing a element in the 'jabber:iq:roster' namespace, which in turn contains an element that defines the new roster item; the element MUST possess a 'jid' attribute, MAY possess a 'name' attribute, MUST NOT possess a 'subscription' attribute, and MAY contain one or more child elements: MyBuddies 2. As a result, the user's server (1) MUST initiate a roster push for the new roster item to all available resources associated with this user that have requested the roster, setting the 'subscription' attribute to a value of "none"; and (2) MUST reply with an IQ result related to the roster set: MyBuddies Saint-Andre (ed.) Expires July 6, 2004 [Page 32] Internet-Draft XMPP IM January 2004 3. If the user wants to request a subscription to the contact's presence, the user's client MUST send a presence stanza of type='subscribe' to the contact: 4. As a result, the user's server MUST initiate a second roster push to all of the user's available resources that have requested the roster, setting the contact to the pending sub-state of the 'none' subscription state; this pending sub-state is denoted by the inclusion of the ask='subscribe' attribute in the roster item: MyBuddies Note: If the user did not create a roster item before sending the subscription request, the server MUST now create one on behalf of the user with the 'subscription' attribute set to a value of "none", then send a roster push to all of the user's available resources that have requested the roster, absent the 'name' attribute and the child. 5. The user's server MUST also stamp the presence stanza of type "subscribe" with the user's bare JID (i.e., ) as the 'from' address. If the contact is served by a different host than the user, the user's server MUST route the presence stanza to the contact's server for delivery to the contact (this case is assumed throughout; however, if the contact is served by the same host, then the server can simply deliver the presence stanza directly): Saint-Andre (ed.) Expires July 6, 2004 [Page 33] Internet-Draft XMPP IM January 2004 Note: If the user's server receives a presence stanza of type "error" from the contact's server in response to the outgoing presence stanza of type "subscribe", it MUST revert the subscription state from the new state ("None + Pending Out") to the previous state ("None"), and MUST deliver the error stanza to the user. 6. Upon receiving the presence stanza of type "subscribe" addressed to the contact, the contact's server MUST determine if there is at least one available resource from which the contact has requested the roster. If so, it MUST deliver the subscription request to the contact (if not, the contact's server MUST store the subscription request offline for delivery when this condition is next met; normally this is done by adding a roster item for the contact to the user's roster, with a state of "None + Pending In" as defined under Subscription States (Section 9), however a server SHOULD NOT push or deliver roster items in that state to the user). No matter when the subscription request is delivered, the contact must decide whether or not to approve it (subject to configured preferences, the contact's client MAY approve or refuse the subscription request without presenting it to the contact). Here we assume the "happy path" that the contact approves the subscription request (the alternate flow of declining the subscription request is defined in Section 8.2.1). In this case, the contact's client (1) SHOULD perform a roster set specifying the desired nickname and group for the user (if any); and (2) MUST send a presence stanza of type "subscribed" to the user in order to approve the subscription request. SomeGroup 7. As a result, the contact's server (1) MUST initiate a roster push to all available resources associated with the contact that have requested the roster, containing a roster item for the user with the subscription state set to 'from' (the server MUST send this even if the contact did not perform a roster set); (2) MUST return an IQ result related to the roster set; (3) MUST route the presence stanza of type "subscribed" to the user; and (4) MUST Saint-Andre (ed.) Expires July 6, 2004 [Page 34] Internet-Draft XMPP IM January 2004 send available presence from all of the contact's available resources to the user: SomeGroup Note: If the contact's server receives a presence stanza of type "error" from the user's server in response to the outgoing presence stanza of type "subscribed", it MUST revert the subscription state from the new state ("From") to the previous state ("None + Pending In"), and MUST deliver the error stanza to the contact. 8. Upon receiving the presence stanza of type "subscribed" addressed to the user, the user's server MUST first verify that the contact is in the user's roster with either of the following states: (a) subscription='none' and ask='subscribe' or (b) subscription='from' and ask='subscribe'. If the contact is not in the user's roster with either of those states, the user's server MUST silently ignore the presence stanza of type "subscribed" (i.e., it MUST NOT route it to the user, modify the user's roster, or generate a roster push to the user's available resources). If the contact is in the user's roster with either of those states, the user's server (1) MUST deliver the presence stanza of type "subscribed" from the contact to the user; (2) MUST initiate a roster push to all of the user's available resources that have requested the roster, containing an updated roster item for the contact with the 'subscription' attribute set to a value of "to"; and (3) MUST deliver the available presence Saint-Andre (ed.) Expires July 6, 2004 [Page 35] Internet-Draft XMPP IM January 2004 stanza received from each of the contact's available resources to each of the user's available resources: MyBuddies 9. Upon receiving the presence stanza of type "subscribed", the user SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "subscribe" to the contact or "denying" it by sending a presence stanza of type "unsubscribe" to the contact; this step does not necessarily affect the subscription state (see Subscription States (Section 9) for details), but instead lets the user's server know that it MUST no longer send notification of the subscription state change to the user (see Section 9.4). From the perspective of the user, there now exists a subscription to the contact; from the perspective of the contact, there now exists a subscription from the user. (Note: If at this point the user sends another subscription request to the contact, the user's server MUST silently ignore that request.) 8.2.1 Alternate Flow: Contact Declines Subscription Request The above activity flow represents the "happy path" related to the user's subscription request to the contact. The main alternate flow occurs if the contact refuses the user's subscription request. 1. If the contact wants to refuse the request, the contact's client MUST send a presence stanza of type "unsubscribed" to the user (instead of the presence stanza of type "subscribed" sent in Step Saint-Andre (ed.) Expires July 6, 2004 [Page 36] Internet-Draft XMPP IM January 2004 6 of Section 8.2): 2. As a result, the contact's server MUST route the presence stanza of type "unsubscribed" to the user, first stamping the 'from' address as the bare JID () of the contact: Note: if the contact's server previously added the user to the contact's roster for tracking purposes, it MUST remove the relevant item at this time. 3. Upon receiving the presence stanza of type "unsubscribed" addressed to the user, the user's server (1) MUST deliver that presence stanza to the user and (2) MUST initiate a roster push to all of the user's available resources that have requested the roster, containing an updated roster item for the contact with the 'subscription' attribute set to a value of "none" and with no 'ask' attribute: MyBuddies 4. Upon receiving the presence stanza of type "unsubscribed", the user SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "unsubscribe" to the contact or "denying" it by sending a presence stanza of type "subscribe" to the contact; this step does not necessarily affect the subscription state (see Subscription States (Section 9) for details), but instead lets Saint-Andre (ed.) Expires July 6, 2004 [Page 37] Internet-Draft XMPP IM January 2004 the user's server know that it MUST no longer send notification of the subscription state change to the user (see Section 9.4). As a result of this activity, the contact is now in the user's roster with a subscription state of "none", whereas the user is not in the contact's roster at all. 8.3 Creating a Mutual Subscription The user and contact can build on the foregoing to create a mutual subscription (i.e., a subscription of type "both"). The process is defined below. 1. If the contact wants to create a mutual subscription, the contact MUST send a subscription request to the user (subject to configured preferences, the contact's client MAY send this automatically): 2. As a result, the contact's server (1) MUST initiate a roster push to all available resources associated with the contact that have requested the roster, with the user still in the 'from' subscription state but with a pending 'to' subscription denoted by the inclusion of the ask='subscribe' attribute in the roster item; and (2) MUST route the presence stanza of type "subscribe" to the user, first stamping the 'from' address as the bare JID () of the contact: SomeGroup Note: If the contact's server receives a presence stanza of type "error" from the user's server in response to the outgoing Saint-Andre (ed.) Expires July 6, 2004 [Page 38] Internet-Draft XMPP IM January 2004 presence stanza of type "subscribe", it MUST revert the subscription state from the new state ("From + Pending Out") to the previous state ("From"), and MUST deliver the error stanza to the contact. 3. Upon receiving the presence stanza of type "subscribe" addressed to the user, the user's server must determine if there is at least one available resource for which the user has requested the roster. If so, the user's server MUST deliver the subscription request to the user (if not, it MUST store the subscription request offline for delivery when this condition is next met). No matter when the subscription request is delivered, the user must then decide whether or not to approve it (subject to configured preferences, the user's client MAY approve or refuse the subscription request without presenting it to the user). Here we assume the "happy path" that the user approves the subscription request (the alternate flow of declining the subscription request is defined in Section 8.3.1). In this case, the user's client MUST send a presence stanza of type "subscribed" to the contact in order to approve the subscription request. 4. As a result, the user's server (1) MUST initiate a roster push to all of the user's available resources that have requested the roster, containing a roster item for the contact with the 'subscription' attribute set to a value of "both"; (2) MUST route the presence stanza of type "subscribed" to the contact, first stamping the 'from' address as the bare JID () of the user; and (3) MUST send available presence from each of the user's available resources to the contact: MyBuddies Saint-Andre (ed.) Expires July 6, 2004 [Page 39] Internet-Draft XMPP IM January 2004 Note: If the user's server receives a presence stanza of type "error" from the contact's server in response to the outgoing presence stanza of type "subscribed", it MUST revert the subscription state from the new state ("Both") to the previous state ("To + Pending In"), and MUST deliver the error stanza to the user. 5. Upon receiving the presence stanza of type "subscribed" addressed to the contact, the contact's server MUST first verify that the user is in the contact's roster with either of the following states: (a) subscription='none' and ask='subscribe' or (b) subscription='from' and ask='subscribe'. If the user is not in the contact's roster with either of those states, the contact's server MUST silently ignore the presence stanza of type "subscribed" (i.e., it MUST NOT route it to the contact, modify the contact's roster, or generate a roster push to the contact's available resources). If the user is in the contact's roster with either of those states, the contact's server (1) MUST deliver the presence stanza of type "subscribed" from the user to the contact; (2) MUST initiate a roster push to all available resources associated with the contact that have requested the roster, containing an updated roster item for the user with the 'subscription' attribute set to a value of "both"; and (3) MUST deliver the available presence stanza received from each of the user's available resources to each of the contact's available resources: SomeGroup 6. Upon receiving the presence stanza of type "subscribed", the contact SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "subscribe" to the user or "denying" it by sending a presence stanza of type "unsubscribe" to the user; this step does not necessarily affect the subscription state (see Subscription States (Section 9) for details), but instead lets the contact's server know that it MUST no longer send notification of the subscription state change to the contact (see Section 9.4). The user and the contact now have a mutual subscription to each other's presence -- i.e., the subscription is of type "both". The user's server MUST now send the user's current presence information to the contact. (Note: If at this point the user sends a subscription request to the contact or the contact sends a subscription request to the user, the sending user's server MUST silently ignore that request and not route it to the intended recipient.) 8.3.1 Alternate Flow: User Declines Subscription Request The above activity flow represents the "happy path" related to the contact's subscription request to the user. The main alternate flow occurs if the user refuses the contact's subscription request. 1. If the user wants to refuse the request, the user's client MUST send a presence stanza of type "unsubscribed" to the contact (instead of the presence stanza of type "subscribed" sent in Step 3 of Section 8.3): 2. As a result, the user's server MUST route the presence stanza of type "unsubscribed" to the contact, first stamping the 'from' address as the bare JID () of the user: 3. Upon receiving the presence stanza of type "unsubscribed" addressed to the contact, the contact's server (1) MUST deliver that presence stanza to the contact; and (2) MUST initiate a Saint-Andre (ed.) Expires July 6, 2004 [Page 41] Internet-Draft XMPP IM January 2004 roster push to all available resources associated with the contact that have requested the roster, containing an updated roster item for the user with the 'subscription' attribute set to a value of "from" and with no 'ask' attribute: SomeGroup 4. Upon receiving the presence stanza of type "unsubscribed", the contact SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "unsubscribe" to the user or "denying" it by sending a presence stanza of type "subscribe" to the user; this step does not necessarily affect the subscription state (see Subscription States (Section 9) for details), but instead lets the contact's server know that it MUST no longer send notification of the subscription state change to the contact (see Section 9.4). As a result of this activity, there has been no change in the subscription state; i.e., the contact is in the user's roster with a subscription state of "to" and the user is in the contact's roster with a subscription state of "from". 8.4 Unsubscribing At any time after subscribing to a contact's presence, a user MAY unsubscribe. While the XML that the user sends to make this happen is the same in all instances, the subsequent subscription state is different depending on the subscription state obtaining when the unsubscribe "command" is sent. Both possible scenarios are defined below. 8.4.1 Case #1: Unsubscribing When Subscription is Not Mutual Saint-Andre (ed.) Expires July 6, 2004 [Page 42] Internet-Draft XMPP IM January 2004 In the first case, the user has a subscription to the contact but the contact does not have a subscription to the user (i.e., the subscription is not yet mutual). 1. If the user wants to unsubscribe from the contact's presence, the user MUST send a presence stanza of type "unsubscribe" to the contact: 2. As a result, the user's server (1) MUST send a roster push to all of the user's available resources that have requested the roster, containing an updated roster item for the contact with the 'subscription' attribute set to a value of "none"; and (2) MUST route the presence stanza of type "unsubscribe" to the contact, first stamping the 'from' address as the bare JID () of the user: MyBuddies 3. Upon receiving the presence stanza of type "unsubscribe" addressed to the contact, the contact's server (1) MUST initiate a roster push to all available resources associated with the contact that have requested the roster, containing an updated roster item for the user with the 'subscription' attribute set to a value of "none" (if the contact is offline, the contact's server MUST modify the roster item and send that modified item the next time the contact requests the roster); and (2) MUST deliver the "unsubscribe" state change notification to the contact: SomeGroup 4. Upon receiving the presence stanza of type "unsubscribe", the contact SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "unsubscribed" to the user or "denying" it by sending a presence stanza of type "subscribed" to the user; this step does not necessarily affect the subscription state (see Subscription States (Section 9) for details), but instead lets the contact's server know that it MUST no longer send notification of the subscription state change to the contact (see Section 9.4). 5. The contact's server then (1) MUST send a presence stanza of type "unsubscribed" to the user; and (2) SHOULD send unavailable presence from the contact to the user: 6. When the user's server receives a presence stanza of type "unsubscribed" and/or unavailable presence, it MUST deliver them to the user: 7. Upon receiving the presence stanza of type "unsubscribed", the user SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "unsubscribe" to the contact or "denying" it by sending a presence stanza of type "subscribe" to the contact; this step does not necessarily affect the subscription state (see Subscription States (Section 9) for details), but instead lets the user's server know that it MUST no longer send notification of the subscription state change to the user (see Section 9.4). 8.4.2 Case #2: Unsubscribing When Subscription is Mutual In the second case, the user has a subscription to the contact and the contact also has a subscription to the user (i.e., the subscription is mutual). 1. If the user wants to unsubscribe from the contact's presence, the user MUST send a presence stanza of type "unsubscribe" to the contact: 2. As a result, the user's server (1) MUST send a roster push to all of the user's available resources that have requested the roster, containing an updated roster item for the contact with the 'subscription' attribute set to a value of "from"; and (2) MUST route the presence stanza of type "unsubscribe" to the contact, first stamping the 'from' address as the bare JID () of the user: MyBuddies 3. Upon receiving the presence stanza of type "unsubscribe" addressed to the contact, the contact's server (1) MUST initiate a roster push to all available resources associated with the contact that have requested the roster, containing an updated roster item for the user with the 'subscription' attribute set to a value of "to" (if the contact is offline, the contact's server MUST modify the roster item and send that modified item the next time the contact requests the roster); and (2) MUST deliver the "unsubscribe" state change notification to the contact: SomeGroup 4. Upon receiving the presence stanza of type "unsubscribe", the contact SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "unsubscribed" to the user or "denying" it by sending a presence stanza of type "subscribed" to the user; this step does not necessarily affect the subscription state (see Subscription States (Section 9) for details), but instead lets the contact's server know that it MUST no longer send notification of the subscription state change to the contact (see Section 9.4). 5. The contact's server then (1) MUST send a presence stanza of type "unsubscribed" to the user; and (2) SHOULD send unavailable presence from the contact to the user: Saint-Andre (ed.) Expires July 6, 2004 [Page 46] Internet-Draft XMPP IM January 2004 6. When the user's server receives a presence stanza of type "unsubscribed" and/or unavailable presence, it MUST deliver them to the user: 7. Upon receiving the presence stanza of type "unsubscribed", the user SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "unsubscribe" to the contact or "denying" it by sending a presence stanza of type "subscribe" to the contact; this step does not necessarily affect the subscription state (see Subscription States (Section 9) for details), but instead lets the user's server know that it MUST no longer send notification of the subscription state change to the user (see Section 9.4). Note: Obviously this does not result in removal of the roster item from the user's roster, and the contact still has a subscription to the user's presence. In order to both completely cancel a mutual subscription and fully remove the roster item from the user's roster, the user SHOULD update the roster item with subscription='remove' as defined under Removing a Roster Item and Cancelling All Subscriptions (Section 8.6). 8.5 Cancelling a Subscription At any time after approving a subscription request from a user, a contact MAY cancel that subscription. While the XML that the contact sends to make this happen is the same in all instances, the subsequent subscription state is different depending on the subscription state obtaining when the cancellation was sent. Both possible scenarios are defined below. 8.5.1 Case #1: Cancelling When Subscription is Not Mutual Saint-Andre (ed.) Expires July 6, 2004 [Page 47] Internet-Draft XMPP IM January 2004 In the first case, the user has a subscription to the contact but the contact does not have a subscription to the user (i.e., the subscription is not yet mutual). 1. If the contact wants to cancel the user's subscription, the contact MUST send a presence stanza of type "unsubscribed" to the user: 2. As a result, the contact's server (1) MUST send a roster push to all of the contact's available resources that have requested the roster, containing an updated roster item for the user with the 'subscription' attribute set to a value of "none"; (2) MUST route the presence stanza of type "unsubscribed" to the user, first stamping the 'from' address as the bare JID () of the contact; and (3) SHOULD send unavailable presence from the contact to the user: SomeGroup 3. Upon receiving the presence stanza of type "unsubscribed" addressed to the user, the user's server (1) MUST initiate a roster push to all of the user's available resources that have requested the roster, containing an updated roster item for the contact with the 'subscription' attribute set to a value of "none" (if the user is offline, the user's server MUST modify the roster item and send that modified item the next time the user requests the roster); (2) MUST deliver the "unsubscribed" state Saint-Andre (ed.) Expires July 6, 2004 [Page 48] Internet-Draft XMPP IM January 2004 change notification to the user; and (3) MUST deliver the unavailable presence to the user: MyBuddies 4. Upon receiving the presence stanza of type "unsubscribed", the user SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "unsubscribe" to the contact or "denying" it by sending a presence stanza of type "subscribe" to the contact; this step does not necessarily affect the subscription state (see Subscription States (Section 9) for details), but instead lets the user's server know that it MUST no longer send notification of the subscription state change to the user (see Section 9.4). 8.5.2 Case #2: Cancelling When Subscription is Mutual In the second case, the user has a subscription to the contact and the contact also has a subscription to the user (i.e., the subscription is mutual). 1. If the contact wants to cancel the user's subscription, the contact MUST send a presence stanza of type "unsubscribed" to the user: Saint-Andre (ed.) Expires July 6, 2004 [Page 49] Internet-Draft XMPP IM January 2004 2. As a result, the contact's server (1) MUST send a roster push to all of the contact's available resources that have requested the roster, containing an updated roster item for the user with the 'subscription' attribute set to a value of "to"; (2) MUST route the presence stanza of type "unsubscribed" to the user, first stamping the 'from' address as the bare JID () of the contact; and (3) SHOULD send unavailable presence from the contact to the user: SomeGroup 3. Upon receiving the presence stanza of type "unsubscribed" addressed to the user, the user's server (1) MUST initiate a roster push to all of the user's available resources that have requested the roster, containing an updated roster item for the contact with the 'subscription' attribute set to a value of "from" (if the user is offline, the user's server MUST modify the roster item and send that modified item the next time the user requests the roster); and (2) MUST deliver the "unsubscribed" state change notification to the user; and (3) MUST deliver the unavailable presence to the user: MyBuddies Saint-Andre (ed.) Expires July 6, 2004 [Page 50] Internet-Draft XMPP IM January 2004 4. Upon receiving the presence stanza of type "unsubscribed", the user SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "unsubscribe" to the contact or "denying" it by sending a presence stanza of type "subscribe" to the contact; this step does not necessarily affect the subscription state (see Subscription States (Section 9) for details), but instead lets the user's server know that it MUST no longer send notification of the subscription state change to the user (see Section 9.4). Note: Obviously this does not result in removal of the roster item from the contact's roster, and the contact still has a subscription to the user's presence. In order to both completely cancel a mutual subscription and fully remove the roster item from the contact's roster, the contact should update the roster item with subscription='remove' as defined under Removing a Roster Item and Cancelling All Subscriptions (Section 8.6). 8.6 Removing a Roster Item and Cancelling All Subscriptions Because there may be many steps involved in completely removing a roster item and cancelling subscriptions in both directions, the roster management protocol includes a "shortcut" method for doing so. The process may be initiated no matter what the current subscription state is by sending a roster set containing an item for the contact with the 'subscription' attribute set to a value of "remove": Saint-Andre (ed.) Expires July 6, 2004 [Page 51] Internet-Draft XMPP IM January 2004 When the user removes a contact from his or her roster by setting the 'subscription' attribute to a value of "remove", the user's server (1) MUST automatically cancel any existing presence subscription between the user and the contact (both 'to' and 'from' as appropriate); (2) MUST remove the roster item from the user's roster and inform all of the user's available resources that have requested the roster of the roster item removal; (3) MUST inform the resource that initiated the removal of success; and (4) SHOULD send unavailable presence to the contact: Upon receiving the presence stanza of type "unsubscribe", the contact's server (1) MUST initiate a roster push to all available resources associated with the contact that have requested the roster, containing an updated roster item for the user with the 'subscription' attribute set to a value of "to" (if the contact is offline, the contact's server MUST modify the roster item and send that modified item the next time the contact requests the roster); and (2) MUST also deliver the "unsubscribe" state change notification to the contact: SomeGroup Upon receiving the presence stanza of type "unsubscribed", the contact's server (1) MUST initiate a roster push to all available resources associated with the contact that have requested the roster, containing an updated roster item for the user with the 'subscription' attribute set to a value of "none" (if the contact is offline, the contact's server MUST modify the roster item and send that modified item the next time the contact requests the roster); and (2) MUST also deliver the "unsubscribe" state change notification to the contact: SomeGroup Upon receiving the presence stanza of type "unavailable" addressed to the contact, the contact's server MUST deliver the unavailable presence to the user: Saint-Andre (ed.) Expires July 6, 2004 [Page 53] Internet-Draft XMPP IM January 2004 Note that when the user removes the contact from the user's roster, the end state of the contact's roster is that the user is still in the contact's roster with a subscription state of "none"; in order to completely remove the roster item for the user, the contact needs to also send a roster removal request. 9. Subscription States This section provides detailed information about subscription states and server handling of subscription-related presence stanzas (i.e., presence stanzas of type "subscribe", "subscribed", "unsubscribe", and "unsubscribed"). 9.1 Defined States There are nine possible subscription states, which are described here from the user's (not contact's) perspective: 1. "None" = contact and user are not subscribed to each other, and neither has requested a subscription from the other 2. "None + Pending Out" = contact and user are not subscribed to each other, and user has sent contact a subscription request but contact has not replied yet 3. "None + Pending In" = contact and user are not subscribed to each other, and contact has sent user a subscription request but user has not replied yet (note: contact's server SHOULD NOT push or deliver roster items in this state, but instead SHOULD wait until contact has approved subscription request from user) 4. "None + Pending Out/In" = contact and user are not subscribed to each other, contact has sent user a subscription request but user has not replied yet, and user has sent contact a subscription request but contact has not replied yet 5. "To" = user is subscribed to contact (one-way) 6. "To + Pending In" = user is subscribed to contact, and contact has send user a subscription request but user has not replied yet 7. "From" = contact is subscribed to user (one-way) 8. "From + Pending Out" = contact is subscribed to user, and user has sent contact a subscription request but contact has not replied yet 9. "Both" = user and contact are subscribed to each other (two-way) Saint-Andre (ed.) Expires July 6, 2004 [Page 54] Internet-Draft XMPP IM January 2004 9.2 Server Handling of Outbound Presence Subscription Stanzas Outbound presence subscription stanzas enable the user to manage his or her subscription to the contact (via the "subscribe" and "unsubscribe" types), and to manage the contact's access to the user's presence information (via the "subscribed" and "unsubscribed" types). Because it is possible for the user's server and the contact's server to lose synchronization regarding subscription states, the user's server MUST route all outbound presence stanzas of type "subscribe" or "unsubscribe" to the contact so that the user is able to resynchronize his or her subscription to the contact if needed. The user's server SHOULD NOT route a presence stanza of type "subscribed" or "unsubscribed" to the contact if the stanza does not result in a subscription state change from the user's perspective, and MUST NOT make a state change. If the stanza results in a subscription state change, the user's server MUST route the stanza to the contact and MUST make the appropriate state change. These rules are summarized in the following tables. Table 1: Recommended handling of outbound "subscribed" stanzas +----------------------------------------------------------------+ | EXISTING STATE | ROUTE? | NEW STATE | +----------------------------------------------------------------+ | "None" | no | no state change | | "None + Pending Out" | no | no state change | | "None + Pending In" | yes | "From" | | "None + Pending Out/In" | yes | "From + Pending Out" | | "To" | no | no state change | | "To + Pending In" | yes | "Both" | | "From" | no | no state change | | "From + Pending Out" | no | no state change | | "Both" | no | no state change | +----------------------------------------------------------------+ Table 2: Recommended handling of outbound "unsubscribed" stanzas +----------------------------------------------------------------+ | EXISTING STATE | ROUTE? | NEW STATE | +----------------------------------------------------------------+ | "None" | no | no state change | | "None + Pending Out" | no | no state change | | "None + Pending In" | yes | "None" | | "None + Pending Out/In" | yes | "None + Pending Out" | | "To" | no | no state change | Saint-Andre (ed.) Expires July 6, 2004 [Page 55] Internet-Draft XMPP IM January 2004 | "To + Pending In" | yes | "To" | | "From" | yes | "None" | | "From + Pending Out" | yes | "None + Pending Out" | | "Both" | yes | "To" | +----------------------------------------------------------------+ 9.3 Server Handling of Inbound Presence Subscription Stanzas Inbound presence subscription stanzas request a subscription-related action from the user (via the "subscribe" type), inform the user of subscription-related actions taken by the contact (via the "unsubscribe" type), or enable the user to manage the contact's access to the user's presence information (via the "subscribed" and "unsubscribed" types). When the user's server receives a subscription request for the user from the contact (i.e., a presence stanza of type "subscribe"), it MUST deliver that request to the user for approval if the user has not already granted the contact access to the user's presence information and if there is no pending inbound subscription request; however, the user's server SHOULD NOT deliver the new request if there is a pending inbound subscription request, since the previous subscription request will have been recorded. If the user has already granted the contact access to the user's presence information, the user's server SHOULD auto-reply to an inbound presense stanza of type "subscribe" from the contact by sending a presence stanza of type "subscribed" to the contact on behalf of the user; this rule enables the contact to resynchronize the subscription state if needed. These rules are summarized in the following table. Table 3: Recommended handling of inbound "subscribe" stanzas +------------------------------------------------------------------+ | EXISTING STATE | DELIVER? | NEW STATE | +------------------------------------------------------------------+ | "None" | yes | "None + Pending In" | | "None + Pending Out" | yes | "None + Pending Out/In" | | "None + Pending In" | no | no state change | | "None + Pending Out/In" | no | no state change | | "To" | yes | "To + Pending In" | | "To + Pending In" | no | no state change | | "From" | no * | no state change | | "From + Pending Out" | no * | no state change | | "Both" | no * | no state change | +------------------------------------------------------------------+ * Server SHOULD auto-reply with "subscribed" stanza Saint-Andre (ed.) Expires July 6, 2004 [Page 56] Internet-Draft XMPP IM January 2004 When the user's server receives a presence stanza of type "unsubscribe" for the user from the contact, if the stanza results in a subscription state change from the user's perspective then the user's server SHOULD auto-reply by sending a presence stanza of type "unsubscribed" to the contact on behalf of the user, MUST deliver the "unsubscribe" stanza to the user, and MUST change the state. If no subscription state change results, the user's server SHOULD NOT deliver the stanza and MUST NOT change the state. These rules are summarized in the following table. Table 4: Recommended handling of inbound "unsubscribe" stanzas +------------------------------------------------------------------+ | EXISTING STATE | DELIVER? | NEW STATE | +------------------------------------------------------------------+ | "None" | no | no state change | | "None + Pending Out" | no | no state change | | "None + Pending In" | yes * | "None" | | "None + Pending Out/In" | yes * | "None + Pending Out" | | "To" | no | no state change | | "To + Pending In" | yes * | "To" | | "From" | yes * | "None" | | "From + Pending Out" | yes * | "None + Pending Out | | "Both" | yes * | "To" | +------------------------------------------------------------------+ * Server SHOULD auto-reply with "unsubscribed" stanza When the user's server receives a presence stanza of type "subscribed" for the user from the contact, it MUST NOT deliver the stanza to the user and MUST NOT change the subscription state if there is no pending outbound request for access to the contact's presence information. If there is a pending outbound request for access to the contact's presence information and the inbound presence stanza of type "subscribed" results in a subscription state change, the user's server MUST deliver the stanza to the user and MUST change the subscription state. If the user already has access to the contact's presence information, the inbound presence stanza of type "subscribed" does not result in a subscription state change; therefore the user's server SHOULD NOT deliver the stanza to the user and MUST NOT change the subscription state. These rules are summarized in the following table. Table 5: Recommended handling of inbound "subscribed" stanzas +------------------------------------------------------------------+ | EXISTING STATE | DELIVER? | NEW STATE | +------------------------------------------------------------------+ Saint-Andre (ed.) Expires July 6, 2004 [Page 57] Internet-Draft XMPP IM January 2004 | "None" | no | no state change | | "None + Pending Out" | yes | "To" | | "None + Pending In" | no | no state change | | "None + Pending Out/In" | yes | "To + Pending In" | | "To" | no | no state change | | "To + Pending In" | no | no state change | | "From" | no | no state change | | "From + Pending Out" | yes | "Both" | | "Both" | no | no state change | +------------------------------------------------------------------+ When the user's server receives a presence stanza of type "unsubscribed" for the user from the contact, it MUST deliver the stanza to the user and MUST change the subscription state if there is a pending outbound request for access to the contact's presence information or if the user currently has access to the contact's presence information. Otherwise, the user's server SHOULD NOT deliver the stanza and MUST NOT change the subscription state. These rules are summarized in the following table. Table 6: Recommended handling of inbound "unsubscribed" stanzas +------------------------------------------------------------------+ | EXISTING STATE | DELIVER? | NEW STATE | +------------------------------------------------------------------+ | "None" | no | no state change | | "None + Pending Out" | yes | "None" | | "None + Pending In" | no | no state change | | "None + Pending Out/In" | yes | "None + Pending In" | | "To" | yes | "None" | | "To + Pending In" | yes | "None + Pending In" | | "From" | no | no state change | | "From + Pending Out" | yes | "From" | | "Both" | yes | "From" | +------------------------------------------------------------------+ 9.4 Server Delivery and Client Acknowledgement of Subscription State Change Notifications When a server receives an inbound presence stanza of type "subscribe", "subscribed", "unsubscribe", or "unsubscribed" that consists of a subscription state change request or notification, in addition to sending the appropriate roster push (or updated roster when the roster is next requested), it MUST deliver the request or notification to the intended recipient at least once. A server MAY require the recipient to acknowledge receipt of all state change notifications (and MUST require acknowledgement in the case of Saint-Andre (ed.) Expires July 6, 2004 [Page 58] Internet-Draft XMPP IM January 2004 subscription requests, i.e., presence stanzas of type "subscribe"). In order to require acknowledgement, a server SHOULD send the notification to the recipient each time the recipient logs in, until the recipient acknowledges receipt of the notification by "affirming" or "denying" the notification, as shown in the following table: Table 7: Acknowledgement of subscription state change notifications +--------------------------------------------------+ | STANZA TYPE | ACCEPT | DENY | +--------------------------------------------------+ | subscribe | subscribed | unsubscribed | | subscribed | subscribe | unsubscribe | | unsubscribe | unsubscribed | subscribed | | unsubscribed | unsubscribe | subscribe | +--------------------------------------------------+ Obviously, given the foregoing subscription state charts, some of the acknowledgement stanzas will be routed to the contact and result in subscription state changes, while others will not. However, any such stanzas MUST result in the server's no longer sending the subscription state notification to the user. Because a user's server MUST automatically generate outbound presence stanzas of type "unsubscribe" and "unsubscribed" upon receiving a roster set with the 'subscription' attribute set to a value of "remove" (see Removing a Roster Item and Cancelling All Subscriptions (Section 8.6)), the server MUST treat a roster remove request as equivalent to sending both of those presence stanzas for purposes of determining whether to continue sending subscription state change notifications of type "subscribe" or "subscribed" to the user. 10. Blocking Communication Most instant messaging systems have found it necessary to implement some method for users to block communications from particular other users (this is also required by sections 5.1.5, 5.1.15, 5.3.2, and 5.4.10 of [IMP-REQS]). In XMPP this is done using the 'jabber:iq:privacy' namespace by managing one's privacy lists. Server-side privacy lists enable successful completion of the following use cases: o Retrieving one's privacy lists. o Adding, removing, and editing one's privacy lists. o Setting, changing, or declining active lists. Saint-Andre (ed.) Expires July 6, 2004 [Page 59] Internet-Draft XMPP IM January 2004 o Setting, changing, or declining the default list (i.e., the list that is active by default). o Allowing or blocking messages based on JID, group, or subscription type (or globally). o Allowing or blocking inbound presence notifications based on JID, group, or subscription type (or globally). o Allowing or blocking outbound presence notifications based on JID, group, or subscription type (or globally). o Allowing or blocking IQs based on JID, group, or subscription type (or globally). o Allowing or blocking all communications based on JID, group, or subscription type (or globally). Note: presence notifications do not include presence subscriptions, only presence information that is broadcasted to entities that are subscribed to a user's presence information. Thus this includes presence stanzas with no 'type' attribute or of type='unavailable' only. 10.1 Syntax and Semantics A user MAY define one or more privacy lists, which are stored by the user's server. Each element contains one or more rules in the form of elements, and each element uses attributes to define a privacy rule type, a specific value to which the rules applies, the relevant action, and the place of the item in the processing order. The syntax is as follows: [] [] [] [] Saint-Andre (ed.) Expires July 6, 2004 [Page 60] Internet-Draft XMPP IM January 2004 If the type is "jid", then the 'value' attribute MUST contain a valid Jabber ID. JIDs are matched in the following order: , then , then , then . If the value is , then any resource for that user@domain matches. If the value is , then only that resource matches. If the value is , then any user@domain (or subdomain) matches. If the type is "group", then the 'value' attribute SHOULD contain the name of a group in the user's roster. (If a client attempts to update, create, or delete a list item with a group that is not in the user's roster, the server SHOULD return to the client an stanza error.) If the type is "subscription", then the 'value' attribute MUST be one of "both", "to", "from", or "none" as defined under Roster Syntax and Semantics (Section 7.1). If no 'type' attribute is included, the rule provides the "fall-through" case. The 'action' attribute MUST be included and its value MUST be either "accept" or "deny". The 'order' attribute MUST be included and its value MUST be a non-negative integer that is unique among all items in the list. (If a client attempts to create or update a list with non-unique order values, the server MUST return to the client a stanza error.) The element MAY contain one or more child elements that enable an entity to specify more granular control over which kinds of stanzas are to be blocked (i.e., rather than blocking all stanzas). The allowable child elements are: o -- blocks incoming message stanzas o -- blocks incoming IQ stanzas o -- blocks incoming presence notifications o -- blocks outgoing presence notifications Within the 'jabber:iq:privacy' namespace, the child of a Saint-Andre (ed.) Expires July 6, 2004 [Page 61] Internet-Draft XMPP IM January 2004 client-generated IQ stanza of type "set" MUST NOT include more than one child element (i.e., the stanza must contain only one element, one element, or one element); if a client violates this rule, the server MUST return to the client a stanza error. When a client adds or updates a privacy list, the element SHOULD contain at least one child element; when a client removes a privacy list, the element SHOULD contain no child element. When a client updates a privacy list, it must include all of the desired items (i.e., not a "delta"). 10.2 Business Rules 1. If there is an active list set for a session, it affects only the session for which it is activated, and only for the duration of the session. The server MUST apply the active list only and MUST NOT apply the default list. 2. The default list applies to the user as a whole, and is processed if there is no active list set for the target session/ resource to which a stanza is addressed, or if there are no current sessions for the user. 3. If there is no active list set for a session (or there are no current sessions for the user), and there is no default list, then all stanzas SHOULD BE accepted or appropriately processed by the server on behalf of the user. 4. Privacy lists MUST be the first rule applied by a server, superseding (1) the routing and delivery rules specified in Server Rules for Handling XML Stanzas (Section 11), and (2) the handling of subscription-related presence stanzas (and corresponding generation of roster pushes) specified in Integration of Roster Items and Presence Subscriptions (Section 8). 5. The order in which privacy list items are processed by the server is important. List items MUST be processed in ascending order determined by the integer values of the 'order' attribute for each . 6. As soon as a stanza is matched against a privacy list, the server SHOULD appropriately handle the stanza and cease processing. Saint-Andre (ed.) Expires July 6, 2004 [Page 62] Internet-Draft XMPP IM January 2004 7. If no fall-through item is provided in a list, the fall-through action is assumed to be "accept". 8. If a user updates the definition for an active list, subsequent processing based on that active list MUST use the updated definition (for all resources to which that active list currently applies). 9. If a user modifies an active list by adding, modifying, or deleting an item with the result that subsequent outbound presence notifications will be blocked to certain subscribed contacts, the server MUST also send unavailable presence from the user to the affected contacts. 10. If a user modifies an active list by adding, modifying, or deleting an item with the result that subsequent outbound presence notifications will no longer be blocked to certain subscribed contacts, the server MUST also send last available presence from the user to the affected contacts. 11. If a change to the subscription state or roster group of a roster item defined in an active or default list occurs during a user's session, subsequent processing based on that list MUST take into account the changed state or group (for all resources to which that list currently applies). 10.3 Retrieving One's Privacy Lists Example: Client requests names of privacy lists from server: Example: Server sends names of privacy lists to client, preceded by active list and default list: Saint-Andre (ed.) Expires July 6, 2004 [Page 63] Internet-Draft XMPP IM January 2004 Example: Client requests a privacy list from server: Example: Server sends a privacy list to client: Example: Client requests another privacy list from server: Example: Server sends another privacy list to client: Example: Client requests yet another privacy list from server: Saint-Andre (ed.) Expires July 6, 2004 [Page 64] Internet-Draft XMPP IM January 2004 Example: Server sends yet another privacy list to client: In this example, the user has three lists: (1) 'public', which allows communications from everyone except one specific entity (this is the default list); (2) 'private', which allows communications only with contacts who have a bidirectional subscription with the user (this is the active list); and (3) 'special', which allows communications only with three specific entities. If the user attempts to retrieve a list but a list by that name does not exist, the server MUST return an stanza error to the user: Example: Client attempts to retrieve non-existent list: Saint-Andre (ed.) Expires July 6, 2004 [Page 65] Internet-Draft XMPP IM January 2004 The user is allowed to retrieve only one list at a time. If the user attempts to retrieve more than one list in the same request, the server MUST return a stanza error to the user: Example: Client attempts to retrieve more than one list: 10.4 Managing Active Lists In order to set or change the active list currently being applied by the server, the user MUST send an IQ stanza of type "set" with a element qualified by the 'jabber:iq:privacy' namespace that contains an empty child element possessing a 'name' attribute whose value is set to the desired list name. Example: Client requests change of active list: The server MUST activate and apply the requested list before sending the result back to the client. Example: Server acknowledges success of active list change: If the user attempts to set an active list but a list by that name does not exist, the server MUST return an stanza error to the user: Example: Client attempts to set a non-existent list as active: Saint-Andre (ed.) Expires July 6, 2004 [Page 66] Internet-Draft XMPP IM January 2004 In order to decline the use of any active list, the user MUST send an empty element with no name. Example: Client declines the use of active lists: 10.5 Managing the Default List In order to change its default list, the user MUST send an IQ stanza of type "set" with a element qualified by the 'jabber:iq:privacy' namespace that contains an empty child element possessing a 'name' attribute whose value is set to the desired list name. Example: Client requests change of default list: Example: Server acknowledges success of default list change: If the user attempts to set a default list but a list by that name does not exist, the server MUST return an stanza error to the user: Example: Client attempts to set a non-existent list as default: Saint-Andre (ed.) Expires July 6, 2004 [Page 67] Internet-Draft XMPP IM January 2004 In order to decline the use of a default list (i.e., to use the domain's stanza routing rules at all times), the user MUST send an empty element with no name. Example: Client declines the use of the default list: 10.6 Editing a Privacy List In order to edit a privacy list, the user MUST send an IQ stanza of type "set" with a element qualified by the 'jabber:iq:privacy' namespace that contains one child element possessing a 'name' attribute whose value is set to the list name the user would like to edit. The element MUST contain one or more elements, which specify the user's desired changes to the list by including all elements in the list (not the "delta"). Example: Client edits a privacy list: Saint-Andre (ed.) Expires July 6, 2004 [Page 68] Internet-Draft XMPP IM January 2004 Example: Server acknowledges success of list edit: Note: The value of the 'order' attribute for any given item is not fixed. Thus in the foregoing example if the user would like to add 4 items between the "tybalt@example.com" item and the "paris@example.org" item, the user's client MUST renumber the relevant items before submitting the list to the server. 10.7 Adding a New Privacy List The same protocol used to edit an existing list is used to create a new list. If the list name matches that of an existing list, the request to add a new list will overwrite the old one. 10.8 Removing a Privacy List In order to remove a privacy list, the user MUST send an IQ stanza of type "set" with a element qualified by the 'jabber:iq:privacy' namespace that contains one empty child element possessing a 'name' attribute whose value is set to the list name the user would like to remove. Example: Client removes a privacy list: Example: Server acknowledges success of list removal: If a user attempts to remove an active list or the default list, the server MUST return a stanza error to the user. The user MUST first set another list to active or default before removing it. If the user attempts to remove a list but a list by that name does not exist, the server MUST return an stanza error to the user: If the user attempts to remove more than one list in the same Saint-Andre (ed.) Expires July 6, 2004 [Page 69] Internet-Draft XMPP IM January 2004 request, the server MUST return a stanza error to the user. 10.9 Blocking Messages Server-side privacy lists enable a user to block incoming messages from other users based on the other user's JID, roster group, or subscription status (or globally). The following examples illustrate the protocol. Example: User blocks based on JID: As a result of creating and applying the foregoing list, the user will not receive messages from the user with the specified JID. Example: User blocks based on roster group: As a result of creating and applying the foregoing list, the user will not receive messages from any users in the specified roster group. Example: User blocks based on subscription type: Saint-Andre (ed.) Expires July 6, 2004 [Page 70] Internet-Draft XMPP IM January 2004 As a result of creating and applying the foregoing list, the user will not receive messages from any users with the specified subscription type. Example: User blocks globally: As a result of creating and applying the foregoing list, the user will not receive messages from any other users. 10.10 Blocking Inbound Presence Notifications Server-side privacy lists enable a user to block incoming presence notifications from other users based on the other user's JID, roster group, or subscription status (or globally). The following examples illustrate the protocol. Note: presence notifications do not include presence subscriptions, only presence information that is broadcasted to the user because the user is currently subscribed to a contact's presence information. Thus this includes presence stanzas with no 'type' attribute or of type='unavailable' only. Example: User blocks based on JID: Saint-Andre (ed.) Expires July 6, 2004 [Page 71] Internet-Draft XMPP IM January 2004 As a result of creating and applying the foregoing list, the user will not receive presence notifications from the user with the specified JID. Example: User blocks based on roster group: As a result of creating and applying the foregoing list, the user will not receive presence notifications from any users in the specified roster group. Example: User blocks based on subscription type: Saint-Andre (ed.) Expires July 6, 2004 [Page 72] Internet-Draft XMPP IM January 2004 As a result of creating and applying the foregoing list, the user will not receive presence notifications from any users with the specified subscription type. Example: User blocks globally: As a result of creating and applying the foregoing list, the user will not receive presence notifications from any other users. 10.11 Blocking Outbound Presence Notifications Server-side privacy lists enable a user to block outgoing presence notifications to other users based on the other user's JID, roster group, or subscription status (or globally). The following examples illustrate the protocol. Note: presence notifications do not include presence subscriptions, only presence information that is broadcasted to contacts because those contacts are currently subscribed to the user's presence information. Thus this includes presence stanzas with no 'type' attribute or of type='unavailable' only. Example: User blocks based on JID: Saint-Andre (ed.) Expires July 6, 2004 [Page 73] Internet-Draft XMPP IM January 2004 As a result of creating and applying the foregoing list, the user will not send presence notifications to the user with the specified JID. Example: User blocks based on roster group: As a result of creating and applying the foregoing list, the user will not send presence notifications to any users in the specified roster group. Example: User blocks based on subscription type: As a result of creating and applying the foregoing list, the user will not send presence notifications to any users with the specified subscription type. Example: User blocks globally: Saint-Andre (ed.) Expires July 6, 2004 [Page 74] Internet-Draft XMPP IM January 2004 As a result of creating and applying the foregoing list, the user will not send presence notifications to any other users. 10.12 Blocking IQs Server-side privacy lists enable a user to block incoming IQ stanzas from other users based on the other user's JID, roster group, or subscription status (or globally). The following examples illustrate the protocol. Example: User blocks based on JID: As a result of creating and applying the foregoing list, the user will not receive IQ stanzas from the user with the specified JID. Example: User blocks based on roster group: Saint-Andre (ed.) Expires July 6, 2004 [Page 75] Internet-Draft XMPP IM January 2004 As a result of creating and applying the foregoing list, the user will not receive IQ stanzas from any users in the specified roster group. Example: User blocks based on subscription type: As a result of creating and applying the foregoing list, the user will not receive IQ stanzas from any users with the specified subscription type. Example: User blocks globally: As a result of creating and applying the foregoing list, the user will not receive IQ stanzas from any other users. 10.13 Blocking All Communication Server-side privacy lists enable a user to block all stanzas from and to other users based on the other user's JID, roster group, or subscription status (or globally). Note that this includes subscription-related presence stanzas, which are excluded by Blocking Inbound Presence Notifications (Section 10.10). The following examples illustrate the protocol. Example: User blocks based on JID: Saint-Andre (ed.) Expires July 6, 2004 [Page 76] Internet-Draft XMPP IM January 2004 As a result of creating and applying the foregoing list, the user will not receive any communications from, nor send any stanzas to, the user with the specified JID. Example: User blocks based on roster group: As a result of creating and applying the foregoing list, the user will not receive any communications from, nor send any stanzas to, any users in the specified roster group. Example: User blocks based on subscription type: As a result of creating and applying the foregoing list, the user will not receive any communications from, nor send any stanzas to, any users with the specified subscription type. Saint-Andre (ed.) Expires July 6, 2004 [Page 77] Internet-Draft XMPP IM January 2004 Example: User blocks globally: As a result of creating and applying the foregoing list, the user will not receive any communications from, nor send any stanzas to, any other users. 10.14 Blocked Entity Attempts to Communicate with User If a blocked entity attempts to send message or presence stanzas to the user, the user's server SHOULD silently drop the stanza and MUST NOT return an error to the sending entity. If a blocked entity attempts to send an IQ stanza of type "get" or "set" to the user, the user's server MUST return to the sending entity a stanza error, since this is the standard error code sent from a client that does not understand the namespace of an IQ get or set. IQ stanzas of other types SHOULD be silently dropped by the server. Example: Blocked entity attempts to send IQ get: Example: Server returns error to blocked entity: Saint-Andre (ed.) Expires July 6, 2004 [Page 78] Internet-Draft XMPP IM January 2004 10.15 Higher-Level Heuristics When building a representation of a higher-level privacy heuristic, a client SHOULD use the simplest possible representation. For example, the heuristic "block all communications with any user not in my roster" could be constructed in any of the following ways: o allow communications from all JIDs in my roster (i.e., listing each JID as a separate list item), but block communications with everyone else o allow communications from any user who is in one of the groups that make up my roster (i.e., listing each group as a separate list item), but block communications from everyone else o allow communications from any user with whom I have a subscription of 'both' or 'to' or 'from' (i.e., listing each subscription value separately), but block communications from everyone else o block communications from anyone whose subscription state is 'none' The final representation is the simplest and SHOULD be used; here is the XML that would be sent in this case: 11. Server Rules for Handling XML Stanzas Basic routing and delivery rules for servers are defined in [XMPP-CORE]. This section defines additional rules for XMPP-compliant instant messaging and presence servers. If the hostname of the domain identifier portion of the JID contained in the 'to' attribute of a stanza matches the hostname of the server itself and the JID contained in the 'to' attribute is of the form or , the server MUST Saint-Andre (ed.) Expires July 6, 2004 [Page 79] Internet-Draft XMPP IM January 2004 first apply any privacy rules (Section 10) that are in force. If privacy rules allow the stanza, it SHOULD be routed or delivered to the intended recipient of the stanza as represented by the JID contained in the 'to' attribute. The following additional rules apply to instant messaging and presence applications, over and above those defined in [XMPP-CORE]: 1. If the JID is of the form and an active resource matches the full JID, the recipient's server MUST deliver the stanza to that resource. 2. If the JID is of the form and no active resource matches the full JID, the recipient's server (a) SHOULD silently ignore the stanza (i.e., neither deliver it nor return an error) if it is a presence stanza, (b) MUST return a stanza error to the sender if it is an IQ stanza, and (c) SHOULD treat the stanza as if it were addressed to if it is a message stanza. 3. If the JID is of the form and there is at least one available resource available for the user, the recipient's server MUST follow these rules: 1. For message stanzas, the server SHOULD deliver the stanza to the highest-priority available resource (if the resource did not provide a value for the element, the server SHOULD consider it to have provided a value of zero). If two available resources have the same priority, the server MAY use some other rule (e.g., most recent connect time, most recent activity time, or highest availability as determined by some hierarchy of values) to choose between them. However, the server MUST NOT deliver the stanza to an available resource with a negative priority; if the only available resource has a negative priority, the server SHOULD handle the message as if there were no available resources (defined below). In addition, the server MUST NOT rewrite the 'to' attribute (i.e., it MUST leave it as rather than change it to ). 2. For presence stanzas other than those of type "probe", the server MUST deliver the stanza to all available resources; for presence probes, the server SHOULD reply based on the rules defined in Client and Server Presence Responsibilities (Section 5.1). In addition, the server MUST NOT rewrite the 'to' attribute (i.e., it MUST leave it as rather than change it to ). 3. For IQ stanzas, the server itself MUST reply on behalf of the Saint-Andre (ed.) Expires July 6, 2004 [Page 80] Internet-Draft XMPP IM January 2004 user with either an IQ result or an IQ error, and MUST NOT deliver the IQ stanza to any of the available resources. Specifically, if the semantics of the qualifying namespace define a reply that the server can provide, the server MUST reply to the stanza on behalf of the user; if not, the server MUST reply with a stanza error. 4. If the JID is of the form and there are no available resources associated with the user, how the stanza is handled depends on the stanza type: 1. For presence stanzas of type "subscribe", the server MUST maintain a record of the stanza and deliver the request when the user next creates an available resource, until the user either approves or denies it. 2. For all other presence stanzas, the server SHOULD silently ignore the stanza by not storing it for later delivery or replying to it on behalf of the user. 3. For message stanzas, the server MAY choose to store the stanza on behalf of the user and deliver it when the user next becomes available. However, if offline message storage is not enabled, the server MUST return to the sender a stanza error. (Note: offline message storage is not defined in XMPP since it strictly is a matter of implementation and service provisioning.) 4. For IQ stanzas, the server itself MUST reply on behalf of the user with either an IQ result or an IQ error. Specifically, if the semantics of the qualifying namespace define a reply that the server can provide, the server MUST reply to the stanza on behalf of the user; if not, the server MUST reply with a stanza error. 12. IM and Presence Compliance Requirements This section summarizes the specific aspects of the Extensible Messaging and Presence Protocol that MUST be supported by instant messaging and presence servers and clients in order to be considered compliant implementations. All such applications MUST comply with the requirements specified in [XMPP-CORE]. The text in this section specifies additional compliance requirements for instant messaging and presence servers and clients; note well that the requirements described here supplement but do not supersede the core requirements. Note also that a server or client may support only presence or instant messaging, and is not required to support both if only a Saint-Andre (ed.) Expires July 6, 2004 [Page 81] Internet-Draft XMPP IM January 2004 presence service or an instant messaging service is desired. 12.1 Servers In addition to core server compliance requirements, an instant messaging and presence server MUST additionally support the following protocols: o All server-related instant messaging and presence syntax and semantics defined in this document, including presence broadcast on behalf of clients, presence subscriptions, roster storage and manipulation, privacy rules, and IM-specific routing and delivery rules 12.2 Clients In addition to core client compliance requirements, an instant messaging and presence client MUST additionally support the following protocols: o Generation and handling of the IM-specific semantics of XML stanzas as defined by the XML schemas, including the 'type' attribute of message and presence stanzas as well as their child elements o All client-related instant messaging syntax and semantics defined in this document, including presence subscriptions, roster management, and privacy rules o End-to-end object encryption as defined in XMPP e2e [XMPP-E2E] 13. Internationalization Considerations For internationalization considerations, refer to the relevant section of [XMPP-CORE]. 14. Security Considerations Core security considerations for XMPP are defined in the relevant section of [XMPP-CORE]. Additional considerations that apply only to instant messaging and presence applications of XMPP are defined in several places within this memo; specifically: Saint-Andre (ed.) Expires July 6, 2004 [Page 82] Internet-Draft XMPP IM January 2004 o When a server processes a stanza of any kind whose intended recipient is a user associated with one of the server's hostnames, the server MUST first apply any privacy rules (Section 10) that are in force (see Server Rules for Handling XML Stanzas (Section 11)). o When a server processes an inbound presence stanza of type "probe" whose intended recipient is a user associated with one of the server's hostnames, the server MUST NOT reveal the user's presence information if the sender is a user who is not authorized to receive that information as determined by presence subscriptions (see Client and Server Presence Responsibilities (Section 5.1)). o When a server processes an outbound presence stanza with no type or of type "unavailable", it MUST follow the rules defined under Client and Server Presence Responsibilities (Section 5.1) in order to ensure that such presence information is not broadcasted to entities that are not authorized to know such information. 15. IANA Considerations For a number of related IANA considerations, refer to the relevant section of [XMPP-CORE]. 15.1 XML Namespace Name for Session Data A URN sub-namespace for session-related data in the Extensible Messaging and Presence Protocol (XMPP) is defined as follows. (This namespace name adheres to the format defined in The IETF XML Registry [XML-REG].) URI: urn:ietf:params:xml:ns:xmpp-session Specification: XXXX Description: This is the XML namespace name for session-related data in the Extensible Messaging and Presence Protocol (XMPP) as defined by XXXX. Registrant Contact: IETF, XMPP Working Group, 15.2 Instant Messaging SRV Protocol Label Registration Address Resolution for Instant Messaging and Presence [IMP-SRV] defines an Instant Messaging SRV Protocol Label registry for protocols that can provide services that conform to the "_im" SRV Saint-Andre (ed.) Expires July 6, 2004 [Page 83] Internet-Draft XMPP IM January 2004 Service label. Because XMPP is one such protocol, the IANA registers the "_xmpp" protocol label in the appropriate registry, as follows: Protocol label: _xmpp Specification: XXXX Description: Instant messaging protocol label for the Extensible Messaging and Presence Protocol (XMPP) as defined by XXXX. Registrant Contact: IETF, XMPP Working Group, 15.3 Presence SRV Protocol Label Registration Address Resolution for Instant Messaging and Presence [IMP-SRV] defines a Presence SRV Protocol Label registry for protocols that can provide services that conform to the "_pres" SRV Service label. Because XMPP is one such protocol, the IANA registers the "_xmpp" protocol label in the appropriate registry, as follows: Protocol label: _xmpp Specification: XXXX Description: Presence protocol label for the Extensible Messaging and Presence Protocol (XMPP) as defined by XXXX. Registrant Contact: IETF, XMPP Working Group, Normative References [IMP-REQS] Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging / Presence Protocol Requirements", RFC 2779, February 2000. [IMP-SRV] Peterson, J., "Address Resolution for Instant Messaging and Presence", draft-ietf-impp-srv-04 (work in progress), October 2003. [TERMS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [XML] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler, "Extensible Markup Language (XML) 1.0 (2nd ed)", W3C REC-xml, October 2000, . [XML-NAMES] Saint-Andre (ed.) Expires July 6, 2004 [Page 84] Internet-Draft XMPP IM January 2004 Bray, T., Hollander, D. and A. Layman, "Namespaces in XML", W3C REC-xml-names, January 1999, . [XMPP-CORE] Saint-Andre, P., "Extensible Messaging and Presence Protocol (XMPP): Core", draft-ietf-xmpp-core-20 (work in progress), November 2003. [XMPP-E2E] Saint-Andre, P., "End-to-End Object Encryption in the Extensible Messaging and Presence Protocol (XMPP)", draft-ietf-xmpp-e2e-05 (work in progress), August 2003. Informative References [JSF] Jabber Software Foundation, "Jabber Software Foundation", . [IMP-MODEL] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and Instant Messaging", RFC 2778, February 2000. [VCARD] Dawson, F. and T. Howes, "vCard MIME Directory Profile", RFC 2426, September 1998. [XML-REG] Mealling, M., "The IETF XML Registry", draft-mealling-iana-xmlns-registry-05 (work in progress), June 2003. Author's Address Peter Saint-Andre Jabber Software Foundation EMail: stpeter@jabber.org Appendix A. vCards Sections 3.1.3 and 4.1.4 of [IMP-REQS] require that it be possible to retrieve out-of-band contact information for other users (e.g., telephone number or email address). An XML representation of the vCard specification defined in RFC 2426 [VCARD] is in common use within the Jabber community to provide such information but is out of scope for XMPP (documentation of this protocol is contained in "JEP-0054: vcard-temp", published by the Jabber Software Foundation [JSF]). Saint-Andre (ed.) Expires July 6, 2004 [Page 85] Internet-Draft XMPP IM January 2004 Appendix B. XML Schemas The following XML schemas are descriptive, not normative. For schemas defining the core features of XMPP, refer to [XMPP-CORE]. B.1 jabber:client Saint-Andre (ed.) Expires July 6, 2004 [Page 86] Internet-Draft XMPP IM January 2004 Saint-Andre (ed.) Expires July 6, 2004 [Page 87] Internet-Draft XMPP IM January 2004 Saint-Andre (ed.) Expires July 6, 2004 [Page 88] Internet-Draft XMPP IM January 2004 B.2 jabber:server Saint-Andre (ed.) Expires July 6, 2004 [Page 91] Internet-Draft XMPP IM January 2004 Saint-Andre (ed.) Expires July 6, 2004 [Page 92] Internet-Draft XMPP IM January 2004 Saint-Andre (ed.) Expires July 6, 2004 [Page 93] Internet-Draft XMPP IM January 2004 B.3 session B.4 jabber:iq:privacy Saint-Andre (ed.) Expires July 6, 2004 [Page 96] Internet-Draft XMPP IM January 2004 B.5 jabber:iq:roster Saint-Andre (ed.) Expires July 6, 2004 [Page 97] Internet-Draft XMPP IM January 2004 Appendix C. Differences Between Jabber IM/Presence and XMPP This section is non-normative. Saint-Andre (ed.) Expires July 6, 2004 [Page 98] Internet-Draft XMPP IM January 2004 XMPP has been adapted from the protocols originally developed in the Jabber open-source community, which can be thought of as "XMPP 0.9". Because there exists a large installed base of Jabber implementations and deployments, it may be helpful to specify the key differences between Jabber and XMPP in order to expedite and encourage upgrades of those implementations and deployments to XMPP. This section summarizes the differences that relate specifically to instant messaging and presence applications, while the corresponding section of [XMPP-CORE] summarizes the differences that relate to all XMPP applications. C.1 Session Establishment The client-to-server authentication protocol developed in the Jabber community assumes that every client is an IM client and therefore initiates an IM session upon successful authentication and resource binding, which are performed simultaneously (documention of this protocol is contained in "JEP-0078: Non-SASL Authentication", published by the Jabber Software Foundation [JSF]). XMPP maintains a stricter separation between core functionality and IM functionality; therefore, an IM session is not created until the client specifically requests one using the protocol defined under Session Establishment (Section 3). C.2 Privacy Rules The Jabber community began to define a protocol for communications blocking (privacy rules) in late 2001, but that effort was deprecated once the XMPP Working Group was formed. Therefore the protocol defined under Blocking Communication (Section 10) is the only such protocol defined for use in the Jabber community. Appendix D. Revision History Note to RFC Editor: please remove this entire appendix, and the corresponding entries in the table of contents, prior to publication. D.1 Changes from draft-ietf-xmpp-im-19 o Completed changes necessary to address IESG feedback. D.2 Changes from draft-ietf-xmpp-im-18 o Added presence type of "probe" to XML schema. o Added error 'code' attribute to XML schema. Saint-Andre (ed.) Expires July 6, 2004 [Page 99] Internet-Draft XMPP IM January 2004 o Added protocol label registrations for "_im" and "_pres" service labels. o Adjusted formatting to conform to RFC Editor requirements. o Clarified meaning of "connected", "active", and "available" resources. D.3 Changes from draft-ietf-xmpp-im-17 o Added missing server handling rules for cases. o Further clarified privacy rules syntax by describing child elements of . o Clarified several points related to session establishment. o Checked all references. o Completed a thorough proofreading and consistency check of the entire text. D.4 Changes from draft-ietf-xmpp-im-16 o Added sentence to make explicit that blocking all communication includes subscription-related presence stanzas. o Added clause to make explicit that privacy rules must be applied before handling of subscription-related presence stanzas and corresponding generation of roster pushes. o Added syntax and semantics section for the 'jabber:iq:roster' namespace. o Removed content about 'jabber:iq:last' namespace. o Added several internal references from the security considerations section to other sections of this document. o Moved most delivery handling rules from XMPP IM to Extensible Messaging and Presence Protocol (XMPP): Core. o Moved detailed stanza syntax descriptions from Extensible Messaging and Presence Protocol (XMPP): Core to XMPP IM. Saint-Andre (ed.) Expires July 6, 2004 [Page 100] Internet-Draft XMPP IM January 2004 o Moved stanza schemas from Extensible Messaging and Presence Protocol (XMPP): Core to XMPP IM. D.5 Changes from draft-ietf-xmpp-im-15 o Specified stream error to be sent to active resource if there is a conflict regarding session creation. o Fixed several more typographical errors in the privacy rules examples. o Corrected an error regarding server handling of IQ stanzas sent to bare JIDs. o Added section on compliance requirements for instant messaging server and client implementations. o Added non-normative section on differences between Jabber usage and XMPP specifications. D.6 Changes from draft-ietf-xmpp-im-14 o Added subscription state charts. o Fixed several typographical errors in the privacy rules examples. o Changed datatype of 'order' attribute in privacy rules from nonNegativeInteger to unsignedInt. D.7 Changes from draft-ietf-xmpp-im-13 o Made one small change to privacy list syntax rules. D.8 Changes from draft-ietf-xmpp-im-12 o Clarified meaning of the default message type as well as handling of unknown or unsupported types. o Made several small editorial changes. D.9 Changes from draft-ietf-xmpp-im-11 Saint-Andre (ed.) Expires July 6, 2004 [Page 101] Internet-Draft XMPP IM January 2004 o Further clarified subscription syntax and semantics. o Further clarified presence responsibilities for clients and servers. o Added 'xml:lang' example to presence status. o Added subsection on presence priority. o Defined server handling of unsolicited presence stanzas of type "subscribed". o Specified default resource priority if not provided. o Corrected several errors in the schemas. o Added privacy list business rule regarding roster changes. o Removed the 'jabber:iq:privacy:error' namespace (not necessary). o Documented message type='normal'. o Made numerous small editorial changes throughout. D.10 Changes from draft-ietf-xmpp-im-10 o Clarified presence responsibilities for servers and clients. o Clarified the routing and delivery rules for servers. o Made the 'xml:lang' examples more complete. o Corrected several errors in the unsubscribe workflow. o Made small editorial changes in several sections. D.11 Changes from draft-ietf-xmpp-im-09 o Clarified rules regarding allowable JID types in rosters. o Further clarified the semantics and routing implications of presence priorities. o Removed several obsolete subsections. Saint-Andre (ed.) Expires July 6, 2004 [Page 102] Internet-Draft XMPP IM January 2004 D.12 Changes from draft-ietf-xmpp-im-08 o Removed authorization content (now addressed in Extensible Messaging and Presence Protocol (XMPP): Core). o Added protocol for initiating an IM session, including schema and IANA registration template. o Corrected <*-condition/> elements to be . o Made small editorial changes to address RFC Editor requirements. D.13 Changes from draft-ietf-xmpp-im-07 o Added several error cases for resource authorization and updated relevant schema. D.14 Changes from draft-ietf-xmpp-im-06 o Specified that IQ result stanzas are required in response to roster pushes. o Changed stanza error namespace names to conform to the format defined in "The IETF XML Registry" as specified in Extensible Messaging and Presence Protocol (XMPP): Core. o Removed note to RFC Editor regarding provisional namespace names. D.15 Changes from draft-ietf-xmpp-im-05 o Removed use of ask='unsubscribe' per list discussion. o Clarified handling of resource conflict during authorization. o Added schemas for jabber:iq:auth, jabber:iq:auth:error, and jabber:iq:privacy:error. o Corrected several small protocol errors in the examples. o Clarified semantics of message types. D.16 Changes from draft-ietf-xmpp-im-04 Saint-Andre (ed.) Expires July 6, 2004 [Page 103] Internet-Draft XMPP IM January 2004 o Specified sending of unavailable presence after unsubscribe and subscription-cancellation actions. o Further specified syntax and business rules for privacy lists. o Brought error codes into line with definitions in draft-ietf-xmpp-core. o Added note to RFC Editor regarding provisional namespace names. o Removed vCard content and DTD, instead pointing to JSF documentation. D.17 Changes from draft-ietf-xmpp-im-03 o Fixed order processing on privacy rules per list discussion. o Made numerous small editorial changes. D.18 Changes from draft-ietf-xmpp-im-02 o Added a great deal more detail to the narrative regarding server-side privacy rules as well as the interaction between rosters and subscriptions. o Removed DTDs in favor of schemas (with the exception of vCard XML). o Removed non-normative documentation of authentication using jabber:iq:auth and of in-band registration using jabber:iq:register, since these are maintained by the Jabber Software Foundation and are not part of the XMPP specification. D.19 Changes from draft-ietf-xmpp-im-01 o Made numerous small editorial changes. D.20 Changes from draft-ietf-xmpp-im-00 o Moved registration and authentication via jabber:iq:auth to non-normative appendices. o Changed initial presence stanza from MUST be empty to SHOULD be empty. Saint-Andre (ed.) Expires July 6, 2004 [Page 104] Internet-Draft XMPP IM January 2004 o Specified that user or clients should not send presence stanzas of type='probe'. o Specified the algorithm for digest passwords. D.21 Changes from draft-miller-xmpp-im-02 o Added information about the 'jabber:iq:last' protocol to meet the requirement defined in section 3.2.4 of RFC 2779. o Added information about the 'jabber:iq:privacy' protocol to meet the requirement defined in section 2.3.5 of RFC 2779. o Added information about the vCard XML protocol to meet the requirement defined in sections 3.1.3 and 4.1.4 of RFC 2779. o Changed the material describing authentication (but not resource authorization) with 'jabber:iq:auth' to non-normative. o Noted that the only watchers are subscribers. o Nomenclature changes: (1) from "chunks" to "stanzas"; (2) from "host" to "server"; (3) from "node" to "client" or "user" (as appropriate). Saint-Andre (ed.) Expires July 6, 2004 [Page 105] Internet-Draft XMPP IM January 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. 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Expires July 6, 2004 [Page 106] Internet-Draft XMPP IM January 2004 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Saint-Andre (ed.) Expires July 6, 2004 [Page 107]