openldap/doc/drafts/draft-rharrison-ldap-intermediate-resp-xx.txt

Individual Submission to ldapext Working Group        Roger G. Harrison
Internet Draft                                             Novell, Inc.
Intended Category: Standards Track
                                                       Kurt D. Zeilenga
                                                    OpenLDAP Foundation

                                                         March 30, 2001



                       LDAP Intermediate Response
             <draft-rharrison-ldap-intermediate-resp-00.txt>


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 <ietf-ldapext@netscape.com>.  Please
   send editorial comments directly to the document editor
   <roger_harrison@novell.com>.

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1. Abstract

   This document extends LDAPv3 to provide a general mechanism for
   defining single-request/multiple-response operations by defining and
   describing the IntermediateResponse message.


2. Background and Intended Usage

   The Lightweight Directory Access Protocol, version 3 [LDAPv3] is an
   extensible protocol. Extended operations ([LDAPv3] Section 4.12) are
   defined to allow operations to be added to LDAP without requiring a
   new revision of the protocol. Similarly, controls ([LDAPv3] section

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   4.1.12) are defined to extend or modify the behavior of existing
   LDAP operations.

   LDAPv3 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 (LDAP
   message).  While this single-request/single-response paradigm is
   sufficient for many operations (including almost all but one of
   those currently defined by [LDAPv3]), both intuition and practical
   experience validate the notion that it is insufficient for some
   operations.

   For example, the LDAPv3 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 apprising it of the status of the operation. For example,
   an LDAP implementation might define an extended 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 stages (1) and (2) with the final response for the
   extended operation being sent for stage (3).

   As LDAPv3 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 LDAPv3, it is defined to
   be the one and only response message to an ExtendedRequest message
   ([LDAPv3] Section 4.12, also see Section 6 below), for unsolicited
   responses (LDAPv3 Section 4.4), and to return intermediate responses
   for the search operation ([LDAPv3] Section 4.5.2). The adaptation of
   ExpendedResponse 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)

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   the addition of a new message to carry intermediate result
   information is easier to implement.

   This document defines the LDAPv3 IntermediateResponse message. This
   message is intended to be used (1) in conjunction with
   ExtendedRequest and ExtendedResponse to define new single-
   request/multiple-response operations and (2) in conjunction with a
   control when extending existing 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 a IntermediateResponse
   message can be sent by a server and the associated meaning of a
   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.


3. 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 [ReqsKeywords].

   The term "request control" is used to describe a control that is
   included in an LDAPv3 request message sent from an LDAPv3 client to
   an LDAPv3 server.


4. The IntermediateResponse PDU

   This document extends the protocolOp CHOICE of LDAPMessage ([LDAPv3]
   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

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   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 4.1 and 4.2 describe additional requirements on the
   inclusion of responseName and responseValue in IntermediateResponse
   messages.


4.1. Usage with LDAPv3 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.

4.2. Usage with LDAPv3 Request Controls

   Any LDAPv3 operation may be extended by the addition of one or more
   controls. A control's semantics may 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 LDAPv3 operation or

           (b) one or more controls using IntermediateResponse messages
               are included in a request with an LDAPv3 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.

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5. 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).

6. Use of IntermediateResponse and ExtendedResponse with Search

   It is noted that ExtendedResponse messages may be sent in response
   to LDAPv3 search operations with controls ([LDAPv3] Section 4.5.1).
   This use of ExtendedResponse messages SHOULD be viewed as deprecated
   in favor of use of the IntermediateResponse messages.


7. Security Considerations

   This document describes an enhancement to LDAPv3.  All security
   considerations of [LDAPv3] apply to this document, however it does
   not introduce any new security considerations to the LDAPv3.

8. References

    [LDAPv3]
        Wahl, M., Howes, T., and S. Kille, "Lightweight Directory
        Access Protocol (v3)", RFC 2251, December 1997.

   [ReqsKeywords]
        Scott Bradner. "Key Words for use in RFCs to Indicate
        Requirement Levels". RFC 2119.


9. 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.

10. Authors' Addresses

   Roger Harrison
   Novell, Inc.
   1800 S. Novell Place
   Provo, UT 84606
   +1 801 861 2642
   roger_harrison@novell.com


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   Kurt D. Zeilenga
   OpenLDAP Foundation
   Kurt@OpenLDAP.org

Appendix A - Document Revision History
   Editors' Note: this non-normative 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.

A.2. draft-rharrison-ldap-extPartResp-01.txt

   Changed responseName to be optional to align with [LDAPv3]
   definition of ExtendedResponse.

A.3. draft-rharrison-ldap-extPartResp-02.txt

   Minor terminology corrections. Clarified use of
   ExtendedPartialResponse with LDAPv3 extended operations and other
   LDAPv3 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 LDAPv3.

   - Added information on advertising IntermediateResponse.

   - Added information on the use of IntermediateResponse with the
     search operation.

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