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Replace extended partial response with intermediate response draft.
2001-06-08 09:43:03 +08:00
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>.
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.
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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the copyright notice or references to the Internet Society or other
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LDAPv3 Intermediate Response March 30, 2001
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Harrison & Zeilenga Expires September 30, 2001 [Page 7]
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