LDAPEXT Working Group J. Sermersheim
Internet Draft Novell, Inc
Document: draft-ietf-ldapext-ldapv3-dupent-08.txt Sept 2002
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 attribute(s). 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. Introduction
This document describes controls, which allow duplicate entries to
be returned in the result set of search operation. Each duplicated
entry represents a distinct value (or combination of values) of the
set of specified multi-valued attributes.
For example, 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. The Server-Side Sorting control
[RFC2891] allows the server to order search result entries based on
attribute values (sort keys). But it does not allow one to specify
behavior when an attribute contains multiple values. The default
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behavior, as outlined in 7.9 of [X.511], is to use the smallest
order value as the sort key.
In order to produce an ordered list, where each value of a multi-
valued attribute is sorted into the list, a separate control is
needed which causes the set of entries to be expanded sufficiently
to represent each attribute value prior to sorting.
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.
4. Conventions
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
used in this document carry the meanings described in [RFC2119].
All controlValue data is represented as ASN.1 in this document, and
is to be BER encoded as stated in Section 5.1 of [RFC2251].
5. 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".
5.1 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
defined as the following DuplicateEntryRequest:
DuplicateEntryRequest ::= SEQUENCE {
AttributeDescriptionList, -- from [RFC2251]
PartialApplicationAllowed BOOLEAN DEFAULT TRUE }
5.1.1 AttributeDescriptionList Semantics
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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
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 the search operation, 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. Note that this may result in search result entries that
no longer match the search filter.
Specifying an attribute supertype has the effect of treating all
values of that attribute's subtypes as if they were values of the
specified attribute supertype. See Section 6.2 for an example of
this.
When attribute descriptions contain subtyping options, they are
treated in the same manner as is described in Section 4.1.5 of
[RFC2251]. Semantics are undefined if an attribute description
contains a non-subtyping option, and SHOULD NOT be specified by
clients.
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.
5.1.2 PartialApplicationAllowed Semantics
The PartialApplicationAllowed field is used to specify whether the
client will allow the server to apply this control to a subset of
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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.
5.2 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.
The DuplicateEntryResponseDone control is sent with the
SearchResultDone operation in order to convey completion
information.
5.2.1 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
controlValue is not included.
5.2.2 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
controlValue is defined as the following DuplicateEntryResponseDone:
DuplicateEntryResponseDone ::= SEQUENCE {
resultCode, -- From [RFC2251]
errorMessage [0] LDAPString OPTIONAL,
attribute [1] AttributeDescription OPTIONAL }
A resultCode 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
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processed. If the operation is successfull, the value will be
success (0).
The errorMessage field MAY be populated with a human-readable string
in the event of an erroneous result code.
The attribute field 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.
6. Protocol Examples
6.1 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
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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
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.
6.2 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
cn: User1
givenName: User One
mail: user1@example.net
dn: cn=User2,dc=example,dc=net
cn: User2
givenName: User Two
mail: user2@example.net
mail: usertwo@example.net
In this example, we specify mail and name in the attribute list. By
specifying name, all attribute subtypes of name will also be
considered. Following is the resulting set of entries:
dn: cn=User1,dc=example,dc=net
cn: User1
mail: user1@example.net
control: 2.16.840.1.113719.1.27.101.2
dn: cn=User1,dc=example,dc=net
givenName: User One
mail: user1@example.net
control: 2.16.840.1.113719.1.27.101.2
dn: cn=User2,dc=example,dc=net
cn: User2
mail: user2@example.net
control: 2.16.840.1.113719.1.27.101.2
dn: cn=User2,dc=example,dc=net
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cn: 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
6.3 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.
7. Relationship to other controls
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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
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.
8. 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 attributes 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.
9. 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 8 for more information on how this is detected
and handled.
10. Acknowledgments
The author gratefully thanks the input and support of participants
of the LDAP-EXT working group.
11. References
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[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.
Available as draft-ietf-ldapext-ldapv3-vlv-xx.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.
12. 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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