

LDAPEXT Working Group                                    J. Sermersheim
Internet Draft                                              Novell, Inc
Document: draft-ietf-ldapext-ldapv3-dupent-06.txt          October 2000
Intended Category: Standard Track


  LDAP Control for a Duplicate Entry Representation 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 [1].

   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.

2. Abstract

   This document describes a Duplicate Entry Representation control
   extension for the LDAP Search operation. By using the control with
   an LDAP search, a client requests that the server return separate
   entries for each value held in the specified attributes. For
   instance, if a specified attribute of an entry holds multiple
   values, the search operation will return multiple instances of that
   entry, each instance holding a separate single value in that
   attribute.

3. Overview

   The Server-Side Sorting control [RFC2891] allows the server to order
   search result entries based on attribute values (sort keys).  It
   does not allow one to specify behavior when an attribute contains
   multiple values.  The default behavior, as outlined in 7.9 of
   [X.511], is to use the smallest value as the sort key.

   An application may need to produce an ordered list of entries,
   sorted by a multi-valued attribute, where each attribute value is
   represented in the list.  In order to do this, a separate control is
   needed which causes the set of entries to be expanded sufficiently
   to represent each attribute value prior to sorting.


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   This document describes controls, which allow duplicate entries in
   the result set of search, where each entry represents a distinct
   value of a given multiple valued attribute.

   An example of this would be a sorted list of all telephone numbers
   in an organization.  Because any entry may have multiple telephone
   numbers, and the list is to be sorted by telephone number, the list
   must be able to contain duplicate entries, each with its own unique
   telephone number.

   Another example would be an application that needs to display an
   ordered list of all members of a group.  It would use this control
   to create a result set of duplicate groupOfNames entries, each with
   a single, unique value in its member attribute.

   The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
   used in this document carry the meanings described in [RFC2119].

4. The Controls

   Support for the controls is advertised by the presence of their OID
   in the supportedControl attribute of a server's root DSE.  The OID
   for the request control is "2.16.840.1.113719.1.27.101.1" and the
   OIDs for the response controls are "2.16.840.1.113719.1.27.101.2"
   and "2.16.840.1.113719.1.27.101.3".

4.1 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
   [RFC2251].

   The controlType is set to "2.16.840.1.113719.1.27.101.1". The
   criticality MAY be set to either TRUE or FALSE.  The controlValue is
   an OCTET STRING, whose value is the BER encoding of the following
   type:

   DuplicateEntryRequest ::= SEQUENCE {
        AttributeDescriptionList, -- from [RFC2251]
        PartialApplicationAllowed BOOLEAN DEFAULT TRUE }


4.1.1 AttributeDescriptionList Semantics

   The AttributeDescriptionList data type is described in 4.1.5 of
   [RFC2251] and describes a list of zero or more AttributeDescription
   types as also described in 4.1.5 of [RFC2251]. Both definitions are
   repeated here for convenience:

        AttributeDescriptionList ::= SEQUENCE OF
                AttributeDescription

        AttributeDescription ::= LDAPString

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   A value of AttributeDescription is based on the following BNF:

        attributeDescription = AttributeType [ ";" <options> ]

   While processing a search request, a server implementation examines
   this list.  If a specified attribute or attribute subtype exists in
   an entry to be returned by search, and that attribute holds multiple
   values, the server treats the entry as if it were multiple,
   duplicate entries -- the specified attributes each holding a single,
   unique value from the original set of values of that attribute.

   Client implementations SHOULD NOT specify attribute type options
   that indicate transfer encoding (e.g. ;binary).

   When two or more attributes are specified by this control, the
   number of duplicate entries is the combination of all values in each
   attribute. Because of the potential complexity involved in servicing
   multiple attributes, server implementations MAY choose to support a
   limited number of attributes in the control.

   There is a special case where either no attributes are specified, or
   an attribute description value of "*" is specified.  In this case,
   all attributes are used.  (The "*" allows the client to request all
   user attributes in addition to specific operational attributes).

   If an attribute is unrecognized, that attribute is ignored when
   processing the control.

4.1.2 PartialApplicationAllowed Semantics

   The PartialApplicationAllowed field is used to specify whether the
   client will allow the server to apply this control to a subset of
   the search result set. If TRUE, the server is free to arbitrarily
   apply this control to no, any, or all search results. If FALSE, the
   server MUST either apply the control to all search results or fail
   to support the control at all.

   Client implementations use the DuplicateSearchResult control to
   discover which search results have been affected by this control

4.2 Response Controls

   Two response controls are defined to provide feedback while the
   search results are being processed; DuplicateSearchResult and
   DuplicateEntryResponseDone.

   The DuplicateSearchResult control is sent with all SearchResultEntry
   operations that contain search results which have been modified by
   the DuplicateEntryRequest control.




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   The DuplicateEntryResponseDone control is sent with the
   SearchResultDone operation in order to convey completion
   information.

4.2.1 The DuplicateSearchResult control

   This control is included in the SearchResultEntry message of any
   search result that holds an entry that has been modified by the
   DuplicateEntryRequest control as part of the controls field of the
   LDAPMessage, as defined in Section 4.1.12 of [RFC2251]. This control
   is absent on search results that are unaffected by
   DuplicateEntryRequest control.

   The controlType is set to "2.16.840.1.113719.1.27.101.2". The
   criticality is ignored. The controlValue is not included.

4.2.2 The DuplicateEntryResponseDone 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 [RFC2251].

   The controlType is set to "2.16.840.1.113719.1.27.101.3". The
   criticality is ignored. The controlValue is an OCTET STRING, whose
   value is the BER encoding of the following SEQUENCE:

      DuplicateEntryResponseDone ::= SEQUENCE {
          resultCode,     -- From [RFC2251]
          errorMessage    [0] LDAPString OPTIONAL,
          attribute       [1] AttributeDescription OPTIONAL }

   A result field is provided here to allow the server to convey to the
   client that an error resulted due to the control being serviced. For
   example, a search that would ordinarily complete successfully may
   fail with a sizeLimitExceeded error due to this control being
   processed.

   Though any result code that is defined in [RFC2251] MAY be returned
   the following list assigns special meanings to certain result codes
   when returned in this control:

   - success:             The control was successful.
   - timeLimitExceeded    Time limit reached before attribute values
                          could be processed.
   - sizeLimitExceeded    Size limit reached as a result of this
                          control.
   - adminLimitExceeded   result set too large for server to handle.
   - unwillingToPerform   Server cannot process control.

   errorMessage MAY be populated with a human-readable string in the
   event of an erroneous result code.



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   attribute MAY be set to the value of the first attribute specified
   by the DuplicateEntryRequest that was in error.  The client MUST
   ignore the attribute field if the result is success.

5. Protocol Examples

5.1 Simple example

   This example will show this control being used to produce a list of
   all telephone numbers in the dc=example,dc=net container.  Let's say
   the following three entries exist in this container;

   dn: cn=User1,dc=example,dc=net
   telephoneNumber: 555-0123

   dn: cn=User2,dc=example,dc=net
   telephoneNumber: 555-8854
   telephoneNumber: 555-4588
   telephoneNumber: 555-5884

   dn: cn=User3,dc=example,dc=net
   telephoneNumber: 555-9425
   telephoneNumber: 555-7992

   First an LDAP search is specified with a baseDN of
   "dc=example,dc=net", subtree scope, filter set to
   "(telephoneNumber=*)".  A DuplicateEntryRequest control is attached
   to the search, specifying "telephoneNumber" as the attribute
   description, and the search request is sent to the server.

   The set of search results returned by the server would then consist
   of the following entries:

   dn: cn=User1,dc=example,dc=net
   telephoneNumber: 555-0123
   <no DuplicateSearchResult control sent with search result>

   dn: cn=User2,dc=example,dc=net
   telephoneNumber: 555-8854
   control: 2.16.840.1.113719.1.27.101.2

   dn: cn=User2,dc=example,dc=net
   telephoneNumber: 555-4588
   control: 2.16.840.1.113719.1.27.101.2

   dn: cn=User2,dc=example,dc=net
   telephoneNumber: 555-5884
   control: 2.16.840.1.113719.1.27.101.2

   dn: cn=User3,dc=example,dc=net
   telephoneNumber: 555-9425
   control: 2.16.840.1.113719.1.27.101.2


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   dn: cn=User3,dc=example,dc=net
   telephoneNumber: 555-7992
   control: 2.16.840.1.113719.1.27.101.2

   All but the first entry are accompanied by the DuplicateSearchResult
   control when sent from the server.

   Note that it is not necessary to use an attribute in this control
   that is specified in the search filter.  This example only does so,
   because the result was to obtain a list of telephone numbers.

5.2 Specifying multiple attributes

   A more complicated example involving multiple attributes will result
   in more entries.  If we assume these entries in the directory:

   dn: cn=User1,dc=example,dc=net
   givenName: User1
   mail: user1@example.net

   dn: cn=User2,dc=example,dc=net
   givenName: User2
   givenName: User Two
   mail: user2@example.net
   mail: usertwo@example.net

   And both "mail" and "givenName" are specified as attributes in this
   control, the resulting set of entries would be this:

   dn: cn=User1,dc=example,dc=net
   givenName: User1
   mail: user1@example.net

   dn: cn=User2,dc=example,dc=net
   givenName: User2
   mail: user2@example.net
   control: 2.16.840.1.113719.1.27.101.2

   dn: cn=User2,dc=example,dc=net
   givenName: User2
   mail: usertwo@example.net
   control: 2.16.840.1.113719.1.27.101.2

   dn: cn=User2,dc=example,dc=net
   givenName: User Two
   mail: user2@example.net
   control: 2.16.840.1.113719.1.27.101.2

   dn: cn=User2,dc=example,dc=net
   givenName: User Two
   mail: usertwo@example.net
   control: 2.16.840.1.113719.1.27.101.2


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5.3 Listing the members of a groupOfNames

   This example shows how the controls can be used to turn a single
   groupOfNames entry into multiple duplicate entries.  Let's say this
   is our groupOfNames entry:

   dn: cn=Administrators,dc=example,dc=net
   cn: Administrators
   member: cn=aBaker,dc=example,dc=net
   member: cn=cDavis,dc=example,dc=net
   member: cn=bChilds,dc=example,dc=net
   member: cn=dEvans,dc=example,dc=net

   We could set our search base to "cn=Administrators,dc=example,dc=net
   ", filter to "(objectClass=*)", use an object scope (to restrict it
   to this entry) and send the duplicateEntryRequest control with
   "member" as its attribute value.  The resulting set would look like
   this:

   dn: cn=Administrators,dc=example,dc=net
   member: cn=aBaker,dc=example,dc=net
   control: 2.16.840.1.113719.1.27.101.2

   dn: cn=Administrators,dc=example,dc=net
   member: cn=cDavis,dc=example,dc=net
   control: 2.16.840.1.113719.1.27.101.2

   dn: cn=Administrators,dc=example,dc=net
   member: cn=bChilds,dc=example,dc=net
   control: 2.16.840.1.113719.1.27.101.2

   dn: cn=Administrators,dc=example,dc=net
   member: cn=dEvans,dc=example,dc=net
   control: 2.16.840.1.113719.1.27.101.2

   This list can then be sorted by member and displayed (also by
   member) in a list.

6 Relationship to other controls

   This control is intended (but not limited) to be used with the
   Server Side Sorting control [RFC2891].  By pairing this control with
   the Server Side Sorting control, One can produce a set of entries,
   sorted by attribute values, where each attribute value is
   represented in the sorted set.  Server implementations MUST ensure
   that this control is processed before sorting the result of a
   search, as this control alters the result set of search.

   This control MAY also be used with the Virtual List View [VLV]
   control (which has a dependency on the Server Side Sort control).
   The nature of the dependency between the VLV control and the Sort
   control is such that the Sorting takes place first. Because the sort
   happens first, and because this control is processed before the sort

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   control, the impact of this control on the VLV control is minimal.
   Some server implementations may need to carefully consider how to
   handle the typedown functionality of the VLV control when paired
   with this control. The details of this are heavily implementation
   dependent and are beyond the scope of this document.

7. Notes for Implementers

   Both client and server implementations MUST be aware that using this
   control could potentially result in a very large set of search
   results. Servers MAY return an adminLimitExceeded result in the
   response control due to inordinate consumption of resources. This
   may be due to some a priori knowledge such as a server restriction
   of the number of attribute in the request control that it's willing
   to service, or it may be due to the server attempting to service the
   control and running out of resources.

   Client implementations MUST be aware that when using this control,
   search entries returned will contain a subset of the values of any
   specified attribute.

   If this control is used in a chained environment, servers SHOULD NOT
   pass this control to other servers. Instead they SHOULD gather
   results and apply this control themselves.

8. Security Considerations

   This control allows finer control of the result set returned by an
   LDAP search operation and as such may be used in a denial of service
   attack. See Section 7 for more information on how this is detected
   and handled.

9. Acknowledgments

   The author gratefully thanks the input and support of participants
   of the LDAP-EXT working group.

10. References

   [RFC2251]
   Wahl, M, S. Kille and T. Howes, "Lightweight Directory Access
   Protocol (v3)", Internet RFC, December, 1997.
   Available as RFC 2251.

   [RFC2891]
   Wahl, M, A. Herron and T. Howes, "LDAP Control Extension for Server
   Side Sorting of Search Results", Internet RFC, August, 2000.
   Available as RFC 2891.

   [VLV]
   Boreham, D, Sermersheim, J, Anantha, A, Armijo, M, "LDAP Extensions
   for Scrolling View Browsing of Search Results", Internet Draft,
   April, 2000.

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   Available as draft-ietf-ldapext-ldapv3-vlv-04.txt.

   [X.511]
   ITU-T Rec. X.511, "The Directory: Abstract Service Definition",
   1993.

   [RFC2119]
   Bradner, Scott, "Key Words for use in RFCs to Indicate Requirement
   Levels", Internet Draft, March, 1997.
   Available as RFC 2119.

11. Author's Address

   Jim Sermersheim
   Novell, Inc.
   1800 South Novell Place
   Provo, Utah 84606, USA
   jimse@novell.com
   +1 801 861-3088



































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