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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 Sermersheim Internet-Draft - Expires Mar 2003 Page 1  LDAP Control for a Duplicate Entry Representation of Search Results 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 Sermersheim Internet-Draft - Expires Mar 2003 Page 2  LDAP Control for a Duplicate Entry Representation of Search Results 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 Sermersheim Internet-Draft - Expires Mar 2003 Page 3  LDAP Control for a Duplicate Entry Representation of Search Results 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 Sermersheim Internet-Draft - Expires Mar 2003 Page 4  LDAP Control for a Duplicate Entry Representation of Search Results 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 Sermersheim Internet-Draft - Expires Mar 2003 Page 5  LDAP Control for a Duplicate Entry Representation of Search Results 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 Sermersheim Internet-Draft - Expires Mar 2003 Page 6  LDAP Control for a Duplicate Entry Representation of Search Results 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 Sermersheim Internet-Draft - Expires Mar 2003 Page 7  LDAP Control for a Duplicate Entry Representation of Search Results 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 Sermersheim Internet-Draft - Expires Mar 2003 Page 8  LDAP Control for a Duplicate Entry Representation of Search Results [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 Sermersheim Internet-Draft - Expires Mar 2003 Page 9