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+Network Working Group T. Howes
+Request for Comments: 2891 Loudcloud
+Category: Standards Track M. Wahl
+ Sun Microsystems
+ A. Anantha
+ Microsoft
+ August 2000
+
+
+ LDAP Control Extension for Server Side Sorting of Search Results
+
+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 (2000). All Rights Reserved.
+
+Abstract
+
+ This document describes two LDAPv3 control extensions for server side
+ sorting of search results. These controls allows a client to specify
+ the attribute types and matching rules a server should use when
+ returning the results to an LDAP search request. The controls may be
+ useful when the LDAP client has limited functionality or for some
+ other reason cannot sort the results but still needs them sorted.
+ Other permissible controls on search operations are not defined in
+ this extension.
+
+ The sort controls allow a server to return a result code for the
+ sorting of the results that is independent of the result code
+ returned for the search operation.
+
+ The key words "MUST", "SHOULD", and "MAY" used in this document are
+ to be interpreted as described in [bradner97].
+
+
+
+
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+
+
+Howes, et al. Standards Track [Page 1]
+\f
+RFC 2891 LDAP Control Extension for Server Side Sorting August 2000
+
+
+1. The Controls
+
+1.1 Request Control
+
+ This control is included in the searchRequest message as part of the
+ controls field of the LDAPMessage, as defined in Section 4.1.12 of
+ [LDAPv3].
+
+ The controlType is set to "1.2.840.113556.1.4.473". The criticality
+ MAY be either TRUE or FALSE (where absent is also equivalent to
+ FALSE) at the client's option. The controlValue is an OCTET STRING,
+ whose value is the BER encoding of a value of the following SEQUENCE:
+
+ SortKeyList ::= SEQUENCE OF SEQUENCE {
+ attributeType AttributeDescription,
+ orderingRule [0] MatchingRuleId OPTIONAL,
+ reverseOrder [1] BOOLEAN DEFAULT FALSE }
+
+ The SortKeyList sequence is in order of highest to lowest sort key
+ precedence.
+
+ The MatchingRuleId, as defined in section 4.1.9 of [LDAPv3], SHOULD
+ be one that is valid for the attribute type it applies to. If it is
+ not, the server will return inappropriateMatching.
+
+ Each attributeType should only occur in the SortKeyList once. If an
+ attributeType is included in the sort key list multiple times, the
+ server should return an error in the sortResult of
+ unwillingToPerform.
+
+ If the orderingRule is omitted, the ordering MatchingRule defined for
+ use with this attribute MUST be used.
+
+ Any conformant implementation of this control MUST allow a sort key
+ list with at least one key.
+
+1.2 Response Control
+
+ This control is included in the searchResultDone message as part of
+ the controls field of the LDAPMessage, as defined in Section 4.1.12
+ of [LDAPv3].
+
+ The controlType is set to "1.2.840.113556.1.4.474". The criticality
+ is FALSE (MAY be absent). The controlValue is an OCTET STRING, whose
+ value is the BER encoding of a value of the following SEQUENCE:
+
+
+
+
+
+
+Howes, et al. Standards Track [Page 2]
+\f
+RFC 2891 LDAP Control Extension for Server Side Sorting August 2000
+
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+ SortResult ::= SEQUENCE {
+ sortResult ENUMERATED {
+ success (0), -- results are sorted
+ operationsError (1), -- server internal failure
+ timeLimitExceeded (3), -- timelimit reached before
+ -- sorting was completed
+ strongAuthRequired (8), -- refused to return sorted
+ -- results via insecure
+ -- protocol
+ adminLimitExceeded (11), -- too many matching entries
+ -- for the server to sort
+ noSuchAttribute (16), -- unrecognized attribute
+ -- type in sort key
+ inappropriateMatching (18), -- unrecognized or
+ -- inappropriate matching
+ -- rule in sort key
+ insufficientAccessRights (50), -- refused to return sorted
+ -- results to this client
+ busy (51), -- too busy to process
+ unwillingToPerform (53), -- unable to sort
+ other (80)
+ },
+ attributeType [0] AttributeDescription OPTIONAL }
+
+2. Client-Server Interaction
+
+ The sortKeyRequestControl specifies one or more attribute types and
+ matching rules for the results returned by a search request. The
+ server SHOULD return all results for the search request in the order
+ specified by the sort keys. If the reverseOrder field is set to TRUE,
+ then the entries will be presented in reverse sorted order for the
+ specified key.
+
+ There are six possible scenarios that may occur as a result of the
+ sort control being included on the search request:
+
+ 1 - If the server does not support this sorting control and the
+ client specified TRUE for the control's criticality field, then
+ the server MUST return unavailableCriticalExtension as a return
+ code in the searchResultDone message and not send back any other
+ results. This behavior is specified in section 4.1.12 of
+ [LDAPv3].
+
+ 2 - If the server does not support this sorting control and the
+ client specified FALSE for the control's criticality field, then
+ the server MUST ignore the sort control and process the search
+ request as if it were not present. This behavior is specified in
+ section 4.1.12 of [LDAPv3].
+
+
+
+Howes, et al. Standards Track [Page 3]
+\f
+RFC 2891 LDAP Control Extension for Server Side Sorting August 2000
+
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+ 3 - If the server supports this sorting control but for some reason
+ cannot sort the search results using the specified sort keys and
+ the client specified TRUE for the control's criticality field,
+ then the server SHOULD do the following: return
+ unavailableCriticalExtension as a return code in the
+ searchResultDone message; include the sortKeyResponseControl in
+ the searchResultDone message, and not send back any search result
+ entries.
+
+ 4 - If the server supports this sorting control but for some reason
+ cannot sort the search results using the specified sort keys and
+ the client specified FALSE for the control's criticality field,
+ then the server should return all search results unsorted and
+ include the sortKeyResponseControl in the searchResultDone
+ message.
+
+ 5 - If the server supports this sorting control and can sort the
+ search results using the specified sort keys, then it should
+ include the sortKeyResponseControl in the searchResultDone
+ message with a sortResult of success.
+
+ 6 - If the search request failed for any reason and/or there are no
+ searchResultEntry messages returned for the search response, then
+ the server SHOULD omit the sortKeyResponseControl from the
+ searchResultDone message.
+
+ The client application is assured that the results are sorted in the
+ specified key order if and only if the result code in the
+ sortKeyResponseControl is success. If the server omits the
+ sortKeyResponseControl from the searchResultDone message, the client
+ SHOULD assume that the sort control was ignored by the server.
+
+ The sortKeyResponseControl, if included by the server in the
+ searchResultDone message, should have the sortResult set to either
+ success if the results were sorted in accordance with the keys
+ specified in the sortKeyRequestControl or set to the appropriate
+ error code as to why it could not sort the data (such as
+ noSuchAttribute or inappropriateMatching). Optionally, the server MAY
+ set the attributeType to the first attribute type specified in the
+ SortKeyList that was in error. The client SHOULD ignore the
+ attributeType field if the sortResult is success.
+
+ The server may not be able to sort the results using the specified
+ sort keys because it may not recognize one of the attribute types,
+ the matching rule associated with an attribute type is not
+ applicable, or none of the attributes in the search response are of
+ these types. Servers may also restrict the number of keys allowed in
+ the control, such as only supporting a single key.
+
+
+
+Howes, et al. Standards Track [Page 4]
+\f
+RFC 2891 LDAP Control Extension for Server Side Sorting August 2000
+
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+ Servers that chain requests to other LDAP servers should ensure that
+ the server satisfying the client's request sort the entire result set
+ prior to sending back the results.
+
+2.1 Behavior in a chained environment
+
+ If a server receives a sort request, the client expects to receive a
+ set of sorted results. If a client submits a sort request to a server
+ which chains the request and gets entries from multiple servers, and
+ the client has set the criticality of the sort extension to TRUE, the
+ server MUST merge sort the results before returning them to the
+ client or MUST return unwillingToPerform.
+
+2.2 Other sort issues
+
+ An entry that meets the search criteria may be missing one or more of
+ the sort keys. In that case, the entry is considered to have a value
+ of NULL for that key. This standard considers NULL to be a larger
+ value than all other valid values for that key. For example, if only
+ one key is specified, entries which meet the search criteria but do
+ not have that key collate after all the entries which do have that
+ key. If the reverseOrder flag is set, and only one key is specified,
+ entries which meet the search criteria but do not have that key
+ collate BEFORE all the entries which do have that key.
+
+ If a sort key is a multi-valued attribute, and an entry happens to
+ have multiple values for that attribute and no other controls are
+ present that affect the sorting order, then the server SHOULD use the
+ least value (according to the ORDERING rule for that attribute).
+
+3. Interaction with other search controls
+
+ When the sortKeyRequestControl control is included with the
+ pagedResultsControl control as specified in [LdapPaged], then the
+ server should send the searchResultEntry messages sorted according to
+ the sort keys applied to the entire result set. The server should not
+ simply sort each page, as this will give erroneous results to the
+ client.
+
+ The sortKeyList must be present on each searchRequest message for the
+ paged result. It also must not change between searchRequests for the
+ same result set. If the server has sorted the data, then it SHOULD
+ send back a sortKeyResponseControl control on every searchResultDone
+ message for each page. This will allow clients to quickly determine
+ if the result set is sorted, rather than waiting to receive the
+ entire result set.
+
+
+
+
+
+Howes, et al. Standards Track [Page 5]
+\f
+RFC 2891 LDAP Control Extension for Server Side Sorting August 2000
+
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+4. Security Considerations
+
+ Implementors and administrators should be aware that allowing sorting
+ of results could enable the retrieval of a large number of records
+ from a given directory service, regardless of administrative limits
+ set on the maximum number of records to return.
+
+ A client that desired to pull all records out of a directory service
+ could use a combination of sorting and updating of search filters to
+ retrieve all records in a database in small result sets, thus
+ circumventing administrative limits.
+
+ This behavior can be overcome by the judicious use of permissions on
+ the directory entries by the administrator and by intelligent
+ implementations of administrative limits on the number of records
+ retrieved by a client.
+
+5. References
+
+ [LDAPv3] Wahl, M, Kille, S. and T. Howes, "Lightweight Directory
+ Access Protocol (v3)", RFC 2251, December 1997.
+
+ [Bradner97] Bradner, S., "Key Words for use in RFCs to Indicate
+ Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+ [LdapPaged] Weider, C., Herron, A., Anantha, A. and T. Howes, "LDAP
+ Control Extension for Simple Paged Results Manipulation",
+ RFC 2696, September 1999.
+
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+Howes, et al. Standards Track [Page 6]
+\f
+RFC 2891 LDAP Control Extension for Server Side Sorting August 2000
+
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+6. Authors' Addresses
+
+ Anoop Anantha
+ Microsoft Corp.
+ 1 Microsoft Way
+ Redmond, WA 98052
+ USA
+
+ Phone: +1 425 882-8080
+ EMail: anoopa@microsoft.com
+
+
+ Tim Howes
+ Loudcloud, Inc.
+ 615 Tasman Dr.
+ Sunnyvale, CA 94089
+ USA
+
+ EMail: howes@loudcloud.com
+
+
+ Mark Wahl
+ Sun Microsystems, Inc.
+ 8911 Capital of Texas Hwy Suite 4140
+ Austin, TX 78759
+ USA
+
+ EMail: Mark.Wahl@sun.com
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+Howes, et al. Standards Track [Page 7]
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+RFC 2891 LDAP Control Extension for Server Side Sorting August 2000
+
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+7. Full Copyright Statement
+
+ Copyright (C) The Internet Society (2000). 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.
+
+Acknowledgement
+
+ Funding for the RFC Editor function is currently provided by the
+ Internet Society.
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+Howes, et al. Standards Track [Page 8]
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