Lightweight Directory Access Protocol (LDAP) Cancel Operation
An LDAP extended operation that cancels a running request and tells the client how the cancel turned out.
Zeilenga, K., "Lightweight Directory Access Protocol (LDAP) Cancel Operation", RFC 3909, DOI 10.17487/RFC3909, October 2004, <https://www.rfc-editor.org/info/rfc3909>.
@misc{rfc3909,
series = {Request for Comments},
number = 3909,
howpublished = {RFC 3909},
publisher = {RFC Editor},
doi = {10.17487/RFC3909},
url = {https://www.rfc-editor.org/info/rfc3909},
author = {K. Zeilenga},
title = {{Lightweight Directory Access Protocol (LDAP) Cancel Operation}},
pagetotal = 7,
year = 2004,
month = oct,
} RFC text
Contents
Network Working Group K. Zeilenga
Request for Comments: 3909 OpenLDAP Foundation
Category: Standards Track October 2004
Lightweight Directory Access Protocol (LDAP)
Cancel Operation
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
This specification describes a Lightweight Directory Access Protocol
(LDAP) extended operation to cancel (or abandon) an outstanding
operation. Unlike the LDAP Abandon operation, but like the X.511
Directory Access Protocol (DAP) Abandon operation, this operation has
a response which provides an indication of its outcome.
1. Background and Intent of Use
The Lightweight Directory Access Protocol (LDAP) [RFC3377] provides
an Abandon operation [RFC2251] which clients may use to cancel other
operations. The Abandon operation does not have a response and
requires no response from the abandoned operation. These semantics
provide the client with no clear indication of the outcome of the
Abandon operation.
The X.511 Directory Access Protocol (DAP) [X.511] provides an Abandon
operation which has a response and also requires the abandoned
operation to return a response indicating it was canceled. The LDAP
Cancel operation is modeled after the DAP Abandon operation.
The LDAP Cancel operation SHOULD be used instead of the LDAP Abandon
operation when the client needs an indication of the outcome. This
operation may be used to cancel both interrogation and update
operations.
Protocol elements are described using ASN.1 [X.680] with implicit
tags. The term "BER-encoded" means the element is to be encoded
using the Basic Encoding Rules [X.690] under the restrictions
detailed in Section 5.1 of [RFC2251].
DSA stands for Directory System Agent (or server).
DSE stands for DSA-specific Entry.
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 BCP 14 [RFC2119].
2. Cancel Operation
The Cancel operation is defined as an LDAP Extended Operation
[RFC2251, Section 4.12] identified by the object identifier
1.3.6.1.1.8. This section details the syntax of the Cancel request
and response messages and defines additional LDAP resultCodes.
2.1. Cancel Request
The Cancel request is an ExtendedRequest with the requestName field
containing 1.3.6.1.1.8 and a requestValue field which contains a
BER-encoded cancelRequestValue value.
cancelRequestValue ::= SEQUENCE {
cancelID MessageID
-- MessageID is as defined in [RFC2251]
}
The cancelID field contains the message ID associated with the
operation to be canceled.
2.2. Cancel Response
A Cancel response is an ExtendedResponse where the responseName and
response fields are absent.
2.3. Additional Result Codes
Implementations of this specification SHALL recognize the following
additional resultCode values:
canceled (118)
noSuchOperation (119)
tooLate (120)
cannotCancel (121)
3. Operational Semantics
The function of the Cancel Operation is to request that the server
cancel an outstanding operation issued within the same session.
The client requests the cancelation of an outstanding operation by
issuing a Cancel Response with a cancelID set to the message ID of
the outstanding operation. The Cancel Request itself has a distinct
message ID. Clients SHOULD NOT request the cancelation of an
operation multiple times.
If the server is willing and able to cancel the outstanding operation
identified by the cancelId, the server SHALL return a Cancel Response
with a success resultCode, and the canceled operation SHALL fail with
canceled resultCode. Otherwise the Cancel Response SHALL have a
non-success resultCode and SHALL NOT have an impact upon the
outstanding operation (if it exists).
The protocolError resultCode is returned if the server is unable to
parse the requestValue or the requestValue is absent,
The noSuchOperation resultCode is returned if the server has no
knowledge of the operation requested for cancelation.
The cannotCancel resultCode is returned if the identified operation
does not support cancelation or the cancel operation could not be
performed. The following classes of operations are not cancelable:
- operations which have no response,
- operations which create, alter, or destroy authentication and/or
authorization associations,
- operations which establish, alter, or tear-down security services,
and
- operations which abandon or cancel other operations.
Specifically, the Abandon, Bind, Start TLS [RFC2830], Unbind, and
Cancel operations are not cancelable.
The Cancel operation cannot be abandoned.
The tooLate resultCode is returned to indicate that it is too late to
cancel the outstanding operation. For example, the server may return
tooLate for a request to cancel an outstanding modify operation which
has already committed updates to the underlying data store.
Servers SHOULD indicate their support for this extended operation by
providing 1.3.6.1.1.8 as a value of the 'supportedExtension'
attribute type in their root DSE. A server MAY choose to advertise
this extension only when the client is authorized to use it.
4. Security Considerations
This operation is intended to allow a user to cancel operations they
previously issued during the current LDAP association. In certain
cases, such as when the Proxy Authorization Control is in use,
different outstanding operations may be processed under different
LDAP associations. Servers MUST NOT allow a user to cancel an
operation belonging to another user.
Some operations should not be cancelable for security reasons. This
specification disallows the cancelation of the Bind operation and
Start TLS extended operation so as to avoid adding complexity to
authentication, authorization, and security layer semantics.
Designers of future extended operations and/or controls should
disallow abandonment and cancelation when appropriate.
5. IANA Considerations
The following values [RFC3383] have been registered by the IANA.
5.1. Object Identifier
The IANA has registered upon Standards Action the LDAP Object
Identifier 1.3.6.1.1.8 to identify the LDAP Cancel Operation as
defined in this document.
Subject: Request for LDAP Object Identifier Registration
Person & email address to contact for further information:
Kurt Zeilenga <kurt@OpenLDAP.org>
Specification: RFC 3909
Author/Change Controller: IESG
Comments:
Identifies the LDAP Cancel Operation
5.2. LDAP Protocol Mechanism
The IANA has registered upon Standards Action the LDAP Protocol
Mechanism described in this document.
Subject: LDAP Protocol Mechanism Registration
Object Identifier: 1.3.6.1.1.8
Description: LDAP Cancel Operation
Person & email address to contact for further information:
Kurt Zeilenga <kurt@openldap.org>
Usage: Extended Operation
Specification: RFC 3909
Author/Change Controller: IESG
Comments: none
5.3. LDAP Result Codes
The IANA has registered upon Standards Action the LDAP Result Codes
described in this document.
Subject: LDAP Result Code Registration
Person & email address to contact for further information:
Kurt Zeilenga <kurt@OpenLDAP.org>
Result Code Name: canceled (118)
Result Code Name: noSuchOperation (119)
Result Code Name: tooLate (120)
Result Code Name: cannotCancel (121)
Specification: RFC 3909
Author/Change Controller: IESG
6. Acknowledgment
The LDAP Cancel operation is modeled after the X.511 DAP Abandon
operation.
7. References
7.1. 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.
[RFC2830] Hodges, J., Morgan, R., and M. Wahl, "Lightweight
Directory Access Protocol (v3): Extension for Transport
Layer Security", RFC 2830, May 2000.
[RFC3377] Hodges, J. and R. Morgan, "Lightweight Directory Access
Protocol (v3): Technical Specification", RFC 3377,
September 2002.
[X.680] International Telecommunication Union - Telecommunication
Standardization Sector, "Abstract Syntax Notation One
(ASN.1) - Specification of Basic Notation", X.680(1997)
(also ISO/IEC 8824-1:1998).
[X.690] International Telecommunication Union - Telecommunication
Standardization Sector, "Specification of ASN.1 encoding
rules: Basic Encoding Rules (BER), Canonical Encoding
Rules (CER), and Distinguished Encoding Rules (DER)",
X.690(1997) (also ISO/IEC 8825-1:1998).
7.2. Informative References
[RFC3383] Zeilenga, K., "Internet Assigned Numbers Authority (IANA)
Considerations for the Lightweight Directory Access
Protocol (LDAP)", BCP 64, RFC 3383, September 2002.
[X.511] International Telecommunication Union - Telecommunication
Standardization Sector, "The Directory: Abstract Service
Definition", X.511(1993).
8. Author's Address
Kurt D. Zeilenga
OpenLDAP Foundation
EMail: Kurt@OpenLDAP.org
9. Full Copyright Statement
Copyright (C) The Internet Society (2004).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and at www.rfc-editor.org, and except as set
forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
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OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
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Acknowledgement
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Internet Society.
AI ELI5
On this page
§1Why Cancel Exists
LDAP (the Lightweight Directory Access Protocol) already has an Abandon operation that clients can use to stop other operations. Abandon has no response, and it does not require a response from the abandoned operation. The client therefore gets no clear indication of the outcome.
The X.511 Directory Access Protocol (DAP) has an Abandon operation that does have a response, and it requires the abandoned operation to return a response saying it was cancelled. The LDAP Cancel operation is modeled after that DAP Abandon.
The RFC says Cancel SHOULD be used instead of Abandon when the client needs an indication of the outcome. It may be used to cancel both interrogation (read) and update operations.
Telling a friend "never mind" and walking away leaves you unsure whether they heard you. Cancel is like asking them to wave back so you know.
§2The Cancel Request and Response
Cancel is an LDAP extended operation (RFC 2251, Section 4.12) identified by the object identifier 1.3.6.1.1.8. The request is an ExtendedRequest whose requestName is that OID and whose requestValue holds a BER-encoded cancelRequestValue.
That value is a SEQUENCE with a single field, cancelID, which is the message ID of the operation to cancel. The response is an ExtendedResponse in which the responseName and response fields are absent, so the outcome is carried in the result code alone.
The request is a note that says "please stop job number 7". The reply is a short note back saying yes or no.
§3How Cancel Behaves
Cancel asks the server to cancel an outstanding operation issued within the same session. The Cancel request has its own, distinct message ID, and its cancelID carries the ID of the target. Clients SHOULD NOT request the cancelation of an operation multiple times.
If the server is willing and able to cancel, it SHALL return a Cancel response with a success result code, and the cancelled operation SHALL fail with the canceled result code. Otherwise the Cancel response SHALL have a non-success result code and SHALL NOT affect the outstanding operation, if it exists.
Servers SHOULD advertise support by listing 1.3.6.1.1.8 in the supportedExtension attribute of the root DSE. A server MAY advertise it only to clients that are authorized to use it.
If the helper can stop the job, they say "done" and the job is marked as stopped. If they cannot, the job just carries on as if you never asked.
§4Result Codes and What Cannot Be Cancelled
Implementations SHALL recognize four additional result codes: canceled (118), noSuchOperation (119), tooLate (120) and cannotCancel (121).
protocolErrorcomes back if the server cannot parse the request value, or it is absent.noSuchOperationmeans the server has no knowledge of the named operation.tooLatemeans it is too late. For example, a modify that has already committed updates to the data store.cannotCancelmeans the operation does not support cancelation, or the cancel could not be performed.
Some classes of operation are not cancelable: those with no response, those that create, alter or destroy authentication or authorization associations, those that establish, alter or tear down security services, and those that abandon or cancel other operations. Specifically, Abandon, Bind, Start TLS, Unbind and Cancel cannot be cancelled. The Cancel operation also cannot be abandoned.
You cannot cancel a job that is already finished, one the helper never heard of, or special jobs like logging in. Each "no" comes with its own reason.
- 118canceled — The cancelled operation fails with this code.
- 119noSuchOperation — The server has no knowledge of the named operation.
- 120tooLate — It is too late to cancel the operation.
- 121cannotCancel — The operation is not cancelable or the cancel could not be done.
§5Security Considerations
Cancel is meant to let a user cancel operations they previously issued during the current LDAP association. When something like the Proxy Authorization Control is in use, different outstanding operations may be processed under different associations, so servers MUST NOT allow a user to cancel an operation belonging to another user.
Some operations should not be cancelable for security reasons. Bind and Start TLS are excluded to avoid adding complexity to authentication, authorization and security layer semantics. Designers of future extended operations and controls are told to disallow abandonment and cancelation when appropriate.
You can only cancel your own jobs, never someone else's. Login jobs cannot be cancelled either, to keep things safe.
§6IANA Registrations
The IANA registered three things upon Standards Action. First, the LDAP Object Identifier 1.3.6.1.1.8 for the Cancel operation. Second, an LDAP Protocol Mechanism entry for the same OID, with usage "Extended Operation". Third, the four result codes: canceled (118), noSuchOperation (119), tooLate (120) and cannotCancel (121).
The new number for Cancel and the four new answer codes were written down in an official list so nobody else reuses them.