INTERNET-DRAFT R. Harrison draft-rharrison-ldap-intermediate-resp-01.txt Novell, Inc. Updates: 2251 K. Zeilenga Intended Category: Standards Track OpenLDAP Foundation March 28, 2003 The Lightweight Directory Access Protocol (LDAP) Intermediate Response Message Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. This document is intended to be, after appropriate review and revision, submitted to the RFC Editor as a Standard Track document. Distribution of this memo is unlimited. Technical discussion of this document will take place on the IETF LDAP Extensions Working Group (ldapext) mailing list . Please send editorial comments directly to the document editor 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. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract The Lightweight Directory Access Protocol (LDAP) version 3 is a client-request/server-response based protocol. With the exception of the search operation, the entire response to an operation request is returned in a single LDAP message. While this single- request/single-response paradigm is sufficient for many operations (including all but one of those currently defined by LDAP), both intuition and practical experience validate the notion that it is insufficient for some operations. When multiple messages are sent Harrison & Zeilenga Expires September 28, 2003 [Page 1] Internet-Draft LDAP Intermediate Response 28 March 2003 in response to a single request, all but the last of these response messages are referred to as "intermediate responses". This document defines and describes the IntermediateResponse message, a general mechanism for defining single-request/multiple- response operations in LDAP. The IntermediateResponse message is defined in a way that maintains the protocol behavior of existing LDAP operations. This message is intended to be used in conjunction with the LDAP ExtendedRequest and ExtendedResponse to define new single-request/multiple-response operations or in conjunction with a control when extending existing LDAP operations in a way that requires them to return intermediate response information. 1. Introduction The Lightweight Directory Access Protocol (LDAP), version 3 [RFC3377] is an extensible protocol. Extended operations ([RFC2251] Section 4.12) are defined to allow operations to be added to LDAP without requiring a new revision of the protocol. Similarly, controls ([RFC2251] section 4.1.12) are defined to extend or modify the behavior of existing LDAP operations. LDAP is a client-request/server-response based protocol. With the exception of the search operation, the entire response to an operation request is returned in a single protocol data unit (i.e. LDAP message). While this single-request/single-response paradigm is sufficient for many operations (including all but one of those currently defined by [RFC3377]), both intuition and practical experience validate the notion that it is insufficient for some operations. For example, the LDAP delete operation could be extended via a subtree control to mean that an entire subtree is to be deleted. A subtree delete operation needs to return continuation references based upon subordinate knowledge information contained in the server so that the client can complete the operation. Returning references as they are found instead of with the final result allows the client to progress the operation more efficiently because it does not have to wait for the final result to get this continuation reference information. Similarly, an engineer might choose to design the subtree delete operation as an extended operation of its own rather than using a subtree control in conjunction with the delete operation. Once again, the same continuation reference information is needed by the client to complete the operation, and sending the continuation references as they are found would allow the client progress the operation more efficiently. Operations that complete in stages or that progress through various states as they complete might want to send intermediate responses to the client, thereby informing it of the status of the operation. For example, an LDAP implementation might define an extended Harrison & Zeilenga Expires September 28, 2003 [Page 2] Internet-Draft LDAP Intermediate Response 28 March 2003 operation to create a new replica of an administrative area on a server, and the operation completes in three stages: (1) begin creation of replica, (2) send replica data to server, (3) replica creation complete. Intermediate messages might be sent from the server to the client at the beginning of each stage with the final response for the extended operation being sent after stage (3) is complete. As LDAP [RFC3377] is currently defined, there is no general LDAP message type that can be used to return intermediate results. A single, reusable LDAP message for carrying intermediate response information is desired to avoid repeated modification of the protocol. Although the ExtendedResponse message is defined in LDAP, it is defined to be the one and only response message to an ExtendedRequest message ([RFC2251] Section 4.12), for unsolicited responses (LDAP Section 4.4), and to return intermediate responses for the search operation ([RFC3377] Section 4.5.2, also see Section 5 below). The adaptation of ExtendedResponse as a general intermediate response mechanism would be problematic. In particular, existing APIs would likely have to be redesigned. It is believed (based upon operational experience) that the addition of a new message to carry intermediate result information is easier to implement and is less likely to cause interoperability problems with existing deployed implementations. This document defines and describes the LDAP IntermediateResponse message. This message is intended to be used in conjunction with ExtendedRequest and ExtendedResponse to define new single- request/multiple-response operations or in conjunction with a control when extending existing LDAP operations in a way that requires them to return intermediate response information. It is intended that the definitions and descriptions of extended operations and controls that make use of the IntermediateResponse message will define the circumstances when an IntermediateResponse message can be sent by a server and the associated meaning of an IntermediateResponse message sent in a particular circumstance. Similarly, it is intended that clients will explicitly solicit IntermediateResponse messages by issuing operations that specifically call for their return. The LDAP Content Sync Operation [draft-zeilenga-ldup-sync] (a work in progress) demonstrates one use of LDAP Intermediate Response messages. 2. Conventions used in this document The 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 [RFC2119]. Harrison & Zeilenga Expires September 28, 2003 [Page 3] Internet-Draft LDAP Intermediate Response 28 March 2003 The term "request control" is used to describe a control that is included in an LDAP request message sent from an LDAP client to an LDAP server. 3. The IntermediateResponse Message This document extends the protocolOp CHOICE of LDAPMessage ([RFC2251] Section 4.1.1) to include the field: intermediateResponse IntermediateResponse where IntermediateResponse is defined as: IntermediateResponse ::= [APPLICATION 25] SEQUENCE { responseName [0] LDAPOID OPTIONAL, responseValue [1] OCTET STRING OPTIONAL } IntermediateResponse messages SHALL NOT be returned to the client unless the client issues a request that specifically solicits their return. This document defines two forms of solicitation: extended operation and request control. Although the responseName and responseValue are optional in some circumstances, generally speaking IntermediateResponse messages have a predefined responseName and a responseValue. The value of the responseName (if present), the syntax of the responseValue (if present) and the semantics associated with a particular IntermediateResponse message MUST be specified in documents describing the extended operation or request control that uses them. Sections 3.1 and 3.2 describe additional requirements on the inclusion of responseName and responseValue in IntermediateResponse messages. 3.1. Usage with LDAP ExtendedRequest and ExtendedResponse A single-request/multiple-response operation may be defined using a single ExtendedRequest message to solicit zero or more IntermediateResponse messages of one or more kinds followed by an ExtendedResponse message. An extended operation that defines the return of multiple kinds of IntermediateResponse messages MUST provide and document a mechanism for the client to distinguish the kind of IntermediateResponse message being sent. This SHALL be accomplished by using different responseName values for each type of IntermediateResponse message associated with the extended operation or by including identifying information in the responseValue of each type of IntermediateResponse message associated with the extended operation. 3.2. Usage with LDAP Request Controls Any LDAP operation may be extended by the addition of one or more controls ([RFC2251] Section 4.1.12). A control's semantics may Harrison & Zeilenga Expires September 28, 2003 [Page 4] Internet-Draft LDAP Intermediate Response 28 March 2003 include the return of zero or more IntermediateResponse messages prior to returning the final result code for the operation. One or more kinds of IntermediateResponse messages may be sent in response to a request control. All IntermediateResponse messages associated with request controls SHALL include a responseName. This requirement ensures that the client can correctly identify the source of IntermediateResponse messages when (a) two or more controls using IntermediateResponse messages are included in a request for any LDAP operation or (b) one or more controls using IntermediateResponse messages are included in a request with an LDAP extended operation that uses IntermediateResponse messages. A request control that defines the return of multiple kinds of IntermediateResponse messages MUST provide and document a mechanism for the client to distinguish the kind of IntermediateResponse message being sent. This SHALL be accomplished by using different responseName values for each type of IntermediateResponse message associated with the request control or by including identifying information in the responseValue of each type of IntermediateResponse message associated with the request control. 4. Advertising Support for IntermediateResponse Messages Because IntermediateResponse messages are associated with extended operations or controls and LDAP provides a means for advertising the extended operations and controls supported by a server (using the supportedExtensions and supportedControls attributes of the root DSE attributes), no separate means for advertising support for IntermediateResponse messages is needed (or provided). 5. Use of IntermediateResponse and ExtendedResponse with Search It is noted that ExtendedResponse messages may be sent in response to LDAP search operations with controls ([RFC2251] Section 4.5.1). This use of ExtendedResponse messages SHOULD be viewed as deprecated in favor of use of the IntermediateResponse messages. 6. Security Considerations This document describes an enhancement to LDAP. All security considerations of [RFC3377] apply to this document, however it does not introduce any new security considerations to LDAP. Security considerations specific to each extension using this protocol mechanism shall be discussed in the technical specification detailing the extension. 7. IANA Considerations Harrison & Zeilenga Expires September 28, 2003 [Page 5] Internet-Draft LDAP Intermediate Response 28 March 2003 Registration of the following value is requested [RFC3383]. 7.1. LDAP Message Type It is requested that IANA register upon Standards Action an LDAP Message Type to identify the LDAP IntermediateResponse message as defined in section 3 of this document. The following registration template is suggested: Subject: Request for LDAP Message Type Registration Person & email address to contact for further information: Roger Harrison Specification: RFCXXXX Author/Change Controller: IESG Comments: Identifies the LDAP IntermediateResponse Message Acknowledgments The authors would like to acknowledge the members of the IETF LDAP Extensions (ldapext) working group mail list who responded to the suggestion that a multiple-response paradigm might be useful for LDAP extended requests. Special thanks go to two individuals: David Wilbur who first introduced the idea on the working group list, and Thomas Salter, who succinctly summarized the group's discussion. Normative References [RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2251] Wahl, M., Howes, T., and S. Kille, "Lightweight Directory Access Protocol (v3)", RFC 2251, December 1997. [RFC3377] Hodges, J. and R. Morgan, "Lightweight Directory Access Protocol (v3): Technical Specification", RFC 3377, September 2002. [RFC3383] Zeilenga, K., "Internet Assigned Numbers Authority (IANA) Considerations for the Lightweight Directory Access Protocol (LDAP)", RFC 3383, September 2002. Informative References [draft-zeilenga-ldup-sync] Harrison & Zeilenga Expires September 28, 2003 [Page 6] Internet-Draft LDAP Intermediate Response 28 March 2003 Zeilenga, K., "LDAP Content Synchronization Operation", Work in Progress. Authors' Addresses Roger Harrison Novell, Inc. 1800 S. Novell Place Provo, UT 84606 +1 801 861 2642 roger_harrison@novell.com Kurt D. Zeilenga OpenLDAP Foundation Kurt@OpenLDAP.org Full Copyright Statement "Copyright (C) The Internet Society (date). 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 assigns. 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 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Appendix A - Document Revision History Editors' Note: this appendix should be removed prior to publication as an RFC. It is provided as an aid to reviewers of this "work in progress." A.1. draft-rharrison-ldap-extPartResp-00.txt Initial revision of draft. Harrison & Zeilenga Expires September 28, 2003 [Page 7] Internet-Draft LDAP Intermediate Response 28 March 2003 A.2. draft-rharrison-ldap-extPartResp-01.txt Changed responseName to be optional to align with [RFC3377] definition of ExtendedResponse. A.3. draft-rharrison-ldap-extPartResp-02.txt Minor terminology corrections. Clarified use of ExtendedPartialResponse with LDAP extended operations and other LDAP operations with controls. A.4. draft-rharrison-ldap-intermediateResp-00.txt - Changed name of ExtendedPartialResponse to IntermediateResponse. - Retitled "Motivation" section to "Background and Intended Usage" and expanded its contents. - Added detail surrounding the use of the IntermediateResponse with extended operations and request controls. - Generalized the way that Intermediate response fits into the ASN.1 definition of LDAP. - Added information on advertising IntermediateResponse. - Added information on the use of IntermediateResponse with the search operation. A.5. draft-rharrison-ldap-intermediateResp-01.txt This draft was oriented primarily to preparing the draft for publication in accordance with established RFC formatting guidelines. No substantial change in overall content was made. Changes included the following: - Retitled document - Rewrote abstract - Retitled "Background and Intended Usage" section to "Introduction" and expanded its contents. - Retitled Section 3 from "The Intermediate Response PDU" to "The Intermediate Response Message". - Renamed references to [RFCnnnn] format - Added IANA Considerations section - Retitled "References" section to "Normative References" - Other small edits to bring draft in line with RFC formatting Harrison & Zeilenga Expires September 28, 2003 [Page 8] Internet-Draft LDAP Intermediate Response 28 March 2003 guidelines. Harrison & Zeilenga Expires September 28, 2003 [Page 9]