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Network Working Group T. Howes, Netscape
INTERNET DRAFT M. Wahl, Critical Angle Inc
Intended Category: Standards Track A. Anantha, Microsoft
Expires: December 5, 2000 June 5, 2000
LDAP Control Extension for Server Side Sorting of Search Results
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026. 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.
This draft document will be submitted to the RFC Editor as a Standards
Track document. Distribution of this memo is unlimited. Technical
discussion of this document will take place on the IETF LDAP Extension
Working Group mailing list <ietf-ldapext@netscape.com>. Please send
editorial comments directly to the authors.
2. 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].
3. The Controls
3.1 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 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.
3.2 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:
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 }
4. 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
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[LDAPv3].
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.
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.
4.1 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.
4.2 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).
5. 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.
6. 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.
7. References
[LDAPv3]
Wahl, M, S. Kille and T. Howes, "Lightweight Directory Access
Protocol (v3)", RFC 2251, December, 1997.
[Bradner97]
Bradner, Scott, "Key Words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March, 1997.
[LdapPaged]
C. Weider, A. Herron, A. Anantha and T. Howes, "LDAP Control
Extension for Simple Paged Results Manipulation", RFC 2696,
September 1999.
8. Author's Address
Anoop Anantha
Microsoft Corp.
1 Microsoft Way
Redmond, WA 98052
USA
anoopa@microsoft.com
+1 425 882-8080
Tim Howes
Loudcloud, Inc.
615 Tasman Dr.
Sunnyvale, CA 94089
USA
howes@loudcloud.com
Mark Wahl
Sun Microsystems, Inc.
8911 Capital of Texas Hwy Suite 4140
Austin, TX 78759
USA
M.Wahl@innosoft.com