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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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



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   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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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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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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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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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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