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+Network Working Group C. Weider
+Request for Comments: 2696 A. Herron
+Category: Informational A. Anantha
+ Microsoft
+ T. Howes
+ Netscape
+ September 1999
+
+
+ LDAP Control Extension for Simple Paged Results Manipulation
+
+Status of this Memo
+
+ This memo provides information for the Internet community. It does
+ not specify an Internet standard of any kind. Distribution of this
+ memo is unlimited.
+
+Copyright Notice
+
+ Copyright (C) The Internet Society (1999). All Rights Reserved.
+
+1. Abstract
+
+ This document describes an LDAPv3 control extension for simple paging
+ of search results. This control extension allows a client to control
+ the rate at which an LDAP server returns the results of an LDAP
+ search operation. This control may be useful when the LDAP client has
+ limited resources and may not be able to process the entire result
+ set from a given LDAP query, or when the LDAP client is connected
+ over a low-bandwidth connection. Other operations on the result set
+ are not defined in this extension. This extension is not designed to
+ provide more sophisticated result set management.
+
+ The key words "MUST", "SHOULD", and "MAY" used in this document are
+ to be interpreted as described in [bradner97].
+
+2. The Control
+
+ This control is included in the searchRequest and searchResultDone
+ messages as part of the controls field of the LDAPMessage, as defined
+ in Section 4.1.12 of [LDAPv3]. The structure of this control is as
+ follows:
+
+
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+
+
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+Weider, et al. Informational [Page 1]
+
+RFC 2696 LDAP Control Ext. for Simple Paged Results September 1999
+
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+pagedResultsControl ::= SEQUENCE {
+ controlType 1.2.840.113556.1.4.319,
+ criticality BOOLEAN DEFAULT FALSE,
+ controlValue searchControlValue
+}
+
+The searchControlValue is an OCTET STRING wrapping the BER-encoded
+version of the following SEQUENCE:
+
+realSearchControlValue ::= SEQUENCE {
+ size INTEGER (0..maxInt),
+ -- requested page size from client
+ -- result set size estimate from server
+ cookie OCTET STRING
+}
+
+3. Client-Server Interaction
+
+ An LDAP client application that needs to control the rate at which
+ results are returned MAY specify on the searchRequest a
+ pagedResultsControl with size set to the desired page size and cookie
+ set to the zero-length string. The page size specified MAY be greater
+ than zero and less than the sizeLimit value specified in the
+ searchRequest.
+
+ If the page size is greater than or equal to the sizeLimit value, the
+ server should ignore the control as the request can be satisfied in a
+ single page. If the server does not support this control, the server
+ MUST return an error of unsupportedCriticalExtension if the client
+ requested it as critical, otherwise the server SHOULD ignore the
+ control. The remainder of this section assumes the server does not
+ ignore the client's pagedResultsControl.
+
+ Each time the server returns a set of results to the client when
+ processing a search request containing the pagedResultsControl, the
+ server includes the pagedResultsControl control in the
+ searchResultDone message. In the control returned to the client, the
+ size MAY be set to the server's estimate of the total number of
+ entries in the entire result set. Servers that cannot provide such an
+ estimate MAY set this size to zero (0). The cookie MUST be set to an
+ empty value if there are no more entries to return (i.e., the page of
+ search results returned was the last), or, if there are more entries
+ to return, to an octet string of the server's choosing,used to resume
+ the search.
+
+ The client MUST consider the cookie to be an opaque structure and
+ make no assumptions about its internal organization or value. When
+ the client wants to retrieve more entries for the result set, it MUST
+
+
+
+Weider, et al. Informational [Page 2]
+
+RFC 2696 LDAP Control Ext. for Simple Paged Results September 1999
+
+
+ send to the server a searchRequest with all values identical to the
+ initial request with the exception of the messageID, the cookie, and
+ optionally a modified pageSize. The cookie MUST be the octet string
+ on the last searchResultDone response returned by the server.
+ Returning cookies from previous searchResultDone responses besides
+ the last one is undefined, as the server implementation may restrict
+ cookies from being reused.
+
+ The server will then return the next set of results from the whole
+ result set. This interaction will continue until the client has
+ retrieved all the results, in which case the cookie in the
+ searchResultDone field will be empty, or until the client abandons
+ the search sequence as described below. Once the paged search
+ sequence has been completed, the cookie is no longer valid and MUST
+ NOT be used.
+
+ A sequence of paged search requests is abandoned by the client
+ sending a search request containing a pagedResultsControl with the
+ size set to zero (0) and the cookie set to the last cookie returned
+ by the server. A client MAY use the LDAP Abandon operation to
+ abandon one paged search request in progress, but this is discouraged
+ as it MAY invalidate the client's cookie.
+
+ If, for any reason, the server cannot resume a paged search operation
+ for a client, then it SHOULD return the appropriate error in a
+ searchResultDone entry. If this occurs, both client and server should
+ assume the paged result set is closed and no longer resumable.
+
+ A client may have any number of outstanding search requests pending,
+ any of which may have used the pagedResultsControl. A server
+ implementation which requires a limit on the number of outstanding
+ paged search requests from a given client MAY either return
+ unwillingToPerform when the client attempts to create a new paged
+ search request, or age out an older result set. If the server
+ implementation ages out an older paged search request, it SHOULD
+ return "unwilling to perform" if the client attempts to resume the
+ paged search that was aged out.
+
+ A client may safely assume that all entries that satisfy a given
+ search query are returned once and only once during the set of paged
+ search requests/responses necessary to enumerate the entire result
+ set, unless the result set for that query has changed since the
+ searchRequest starting the request/response sequence was processed.
+ In that case, the client may receive a given entry multiple times
+ and/or may not receive all entries matching the given search
+ criteria.
+
+
+
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+Weider, et al. Informational [Page 3]
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+RFC 2696 LDAP Control Ext. for Simple Paged Results September 1999
+
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+4. Example
+
+ The following example illustrates the client-server interaction
+ between a client doing a search requesting a page size limit of 3.
+ The entire result set returned by the server contains 5 entries.
+
+ Lines beginning with "C:" indicate requests sent from client to
+ server. Lines beginning with "S:" indicate responses sent from server
+ to client. Lines beginning with "--" are comments to help explain the
+ example.
+
+ -- Client sends a search request asking for paged results
+ -- with a page size of 3.
+ C: SearchRequest + pagedResultsControl(3,"")
+ -- Server responds with three entries plus an indication
+ -- of 5 total entries in the search result and an opaque
+ -- cooking to be used by the client when retrieving subsequent
+ -- pages.
+ S: SearchResultEntry
+ S: SearchResultEntry
+ S: SearchResultEntry
+ S: SearchResultDone + pagedResultsControl(5, "opaque")
+ -- Client sends an identical search request (except for
+ -- message id), returning the opaque cooking, asking for
+ -- the next page.
+ C: SearchRequest + PagedResultsControl(3, "opaque")
+ -- Server responds with two entries plus an indication
+ -- that there are no more entries (null cookie).
+ S: SearchResultEntry
+ S: SearchResultEntry
+ S: SearchResultDone + pagedResultsControl(5,"")
+
+5. Relationship to X.500
+
+ For LDAP servers providing a front end to X.500 (93) directories, the
+ paged results control defined in this document may be mapped directly
+ onto the X.500 (93) PagedResultsRequest defined in X.511 [x500]. The
+ size parameter may be mapped onto pageSize. The cookie parameter may
+ be mapped onto queryReference. The sortKeys and reverse fields in
+ the X.500 PagedResultsRequest are excluded.
+
+
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+Weider, et al. Informational [Page 4]
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+RFC 2696 LDAP Control Ext. for Simple Paged Results September 1999
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+6. Security Considerations
+
+ Server implementors should consider the resources used when clients
+ send searches with the simple paged control, to ensure that a
+ client's misuse of this control does not lock out other legitimate
+ operations.
+
+ Servers implementations may enforce an overriding sizelimit, to
+ prevent the retrieval of large portions of a publically-accessible
+ directory.
+
+ Clients can, using this control, determine how many entries match a
+ particular filter, before the entries are returned to the client.
+ This may require special processing in servers which perform access
+ control checks on entries to determine whether the existence of the
+ entry can be disclosed to the client.
+
+7. References
+
+ [LDAPv3] Wahl, M., Howes, T. and S. Kille, "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.
+
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+Weider, et al. Informational [Page 5]
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+RFC 2696 LDAP Control Ext. for Simple Paged Results September 1999
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+8. Authors' Addresses
+
+ Chris Weider
+ Microsoft Corp.
+ 1 Microsoft Way
+ Redmond, WA 98052
+ USA
+
+ Phone: +1 425 882-8080
+ EMail: cweider@microsoft.com
+
+
+ Andy Herron
+ Microsoft Corp.
+ 1 Microsoft Way
+ Redmond, WA 98052
+ USA
+
+ Phone: +1 425 882-8080
+ EMail: andyhe@microsoft.com
+
+
+ Anoop Anantha
+ Microsoft Corp.
+ 1 Microsoft Way
+ Redmond, WA 98052
+ USA
+
+ Phone: +1 425 882-8080
+ EMail: anoopa@microsoft.com
+
+
+ Tim Howes
+ Netscape Communications Corp.
+ 501 E. Middlefield Road
+ Mountain View, CA 94043
+ USA
+
+ Phone: +1 415 937-2600
+ EMail: howes@netscape.com
+
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+Weider, et al. Informational [Page 6]
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+RFC 2696 LDAP Control Ext. for Simple Paged Results September 1999
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+9. Full Copyright Statement
+
+ Copyright (C) The Internet Society (1999). 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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