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Topic: LDAP Server Side Sorting (SSS) Control -- RFC 2891 |
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SteveHB
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| LDAP Server Side Sorting (SSS) Control -- RFC 2891 |
http://tools.ietf.org/html/rfc2891
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.
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.
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SteveHB
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| SSS 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.
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SteveHB
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| SSS 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
}
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SteveHB
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| Client-Server Interaction |
The Server Side:
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].
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 Side:
1- 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.
2- 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.
3- 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.
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SteveHB
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| 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.
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SteveHB
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| 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 thatkey. 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).
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SteveHB
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| 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.
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SteveHB
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posted on: 01/06/2009 07:52:46 PM
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