Directory Assistance service

Network Working Group                                            M. Rose
Request for Comments: 1202       Performance Systems International, Inc.
                                                           February 1991


                      Directory Assistance Service

Status of this Memo

   This document defines a mechanism by which a user-interface may
   access a textual DAP-like interface over a TCP/IP connection.  This
   is a local mechanism.  This memo provides information for the
   Internet community.  It does not specify any standard.  Distribution
   of this memo is unlimited.

Table of Contents

   1. Introduction ..........................................   1
   1.1 An Aside ............................................    3
   2. Protocol ..............................................   3
   2.1 Control Connection ..................................    4
   2.1.1 Initialization ....................................    4
   2.1.2 Transactions ......................................    4
   2.1.2.1 INTR command ....................................    4
   2.1.2.2 STAT command ....................................    5
   2.1.2.3 QUIT command ....................................    5
   2.2 Data Connection .....................................    5
   2.2.1 Transactions ......................................    5
   2.2.2 Responses .........................................    6
   2.2.2.1 Numeric Responses ...............................    6
   2.2.2.2 'm' Response ....................................    6
   2.2.2.3 'y' Response ....................................    6
   2.2.2.4 'p' Response ....................................    7
   2.2.2.5 'e' Response ....................................    7
   2.2.2.6 'l' Response ....................................    7
   2.2.2.7 'd' Response ....................................    8
   2.2.2.8 'P' Response ....................................    8
   3. Example Interaction ...................................   9
   4. References ............................................  10
   5. Security Considerations...............................   11
   6. Author's Address......................................   11

1.  Introduction

   The OSI Directory [1] provides a powerful infrastructure for the
   retrieval of information objects.  This infrastructure can be used to
   support, e.g., white pages applications, application entity lookup,
   and so on.

   The Directory service is provided to applications through the
   Directory Access Protocol (DAP), which binds a Directory User Agent
   (DUA) to a Directory System Agent (DSA).

                                        | Directory Service
                                        |    provided via DAP
                                        |
               +-----------+            |            +-----------+
               |           |            |            |           |
               |    DUA    | <----------+----------> |    DSA    |
               |           |            |            |           |
               +-----------+            |            +-----------+
                                        |
                         Directory User |

   The DAP is an OSI application layer protocol which uses the rich OSI
   upper-layer infrastructure.  Unfortunately, the coding investment to
   implement the DAP is significant.  As such, it is difficult to host
   applications using the Directory on smaller workstations and personal
   computers.

   This memo details a local mechanism which has been successfully used
   to separate the functionality of the DAP from the complexity of
   implementing the DAP.  That is, a split-DUA model is used: the DAP is
   implemented on an entity (the "Directory Assistant"), which resides
   on a capable workstation or mainframe and exports a simpler
   interface, the "Directory Assistance" (DA) protocol, to other end-
   systems where the user-interface resides, termed the DA-client.

   Since this mechanism provides assistance to applications wishing to
   access the Directory, it is termed the "Directory Assistance" (DA)
   service:

                                        | Directory Service
                 split-DUA              |    provided via DAP
                                        |
               +-----------+            |            +-----------+
               |           |            |            |           |
               | Directory | <----------+----------> |    DSA    |
               | Assistant |            |            |           |
               |           |            |            +-----------+
               +-----------+            |
                    /|\                 |
                     |                  |
                     | DA-service       |
                     |   provide via    |
                     |   DA-protocol    |
                     |                  |
               ------+------            |
                     |                  |
                     |                  |
                     |                  |
                     |                  |
                     |                  |
                    \|/                 |
               +-----------+            |
               |           |            |
               | DA-client |            |
               |           |            |
               +-----------+            |
                                        |
                         Directory User |


1.1.  An Aside

   This memo documents an already existing protocol, which was
   originally used to provide a split-DUA model within the same host.
   In the absence of detailed historical and implementational
   understanding, some of the mechanisms described may not appear
   intuitive.

2.  Protocol

   The DA service operates using two TCP connections: a control
   connection, and a data connection.  The control connection defines
   the lifetime of an instance of the DA service; throughout this
   lifetime, several data connections may be established.  However, at
   any given instant, between zero and one data connections will be in
   progress.

   The DA service is provided by the "Directory Assistant", which
   consists of two entities: a DA-server, which manages the control
   connection; and, a DAP-listener, which responds to commands on the
   data connection.  The DA-server oversees the behavior of the DAP-
   listener.

2.1.  Control Connection

   Data sent over the control connection consists of a series of
   transactions.  NVT-ASCII is used to express these transactions.  Each
   transaction consists of the client sending a directive--a line of
   text terminated by CR-LF; the DA-server returns a response--a line of
   text terminated by CR-LF.  All responses from a DA-server start with
   either "+OK" or "-ERR" depending on whether the transaction was
   successful.

2.1.1.  Initialization

   A DA-server listens on TCP port 411 for incoming connections.  Upon
   establishing a control connection, the DA-server returns a response
   indicating whether the service has been started.  If successful, the
   response contains an IP-address and a TCP port, expressed in NVT-
   ASCII, and separated by one or more instances of the space character.
   This information corresponds to the TCP-endpoint that the DAP-
   listener will use for the data connection.

   Note that the DA-server and DAP-listener need not reside at the same
   IP-address.  In the future, DA-servers may employ a internal protocol
   for load-balancing purposes.

   If the DA service can not be started, an error response is returned
   and the control connection is closed.


2.1.2.  Transactions

   All transactions with the DA-server consist of a command followed by
   zero or more arguments, separated by the space character.

2.1.2.1.  INTR command

   The INTR command takes no arguments.

   The INTR command is used to interrupt any DAP transaction
   currently in progress.

   The INTR command always returns success.

2.1.2.2.  STAT command

   The STAT command takes no arguments.

   The STAT command is used to verify that the DAP-listener is
   available.

   The STAT command returns success only if the DAP-listener is
   still active.

2.1.2.3.  QUIT command

   The QUIT command takes no arguments.

   The QUIT command is used to terminate the DA service.

   The QUIT command always returns success.

2.2.  Data Connection

   Data sent over a data connection consists of a single DAP-
   transaction.  NVT-ASCII is used to express these transactions.  Each
   transaction consists of the client sending a command--a line of text
   terminated by the LF-character; the DAP-listener returns zero or more
   responses, each with a specific termination sequence.  All responses
   from a DAP-listener start with a single identifying character.  If
   the character is a digit (0-9), then the termination sequence
   consists of a closing the data connection; otherwise, if the
   character is a lower-case letter (a-z), then the response is
   interactive and is terminated by the LF-character.

2.2.1.  Transactions

   All transactions with the DAP-listener consist of a command followed
   by zero or more arguments, separated by the space character.
   Double-quotes may be used to prevent separation of tokens.

   The command set is taken from the DISH program:

               add         add a new entry
               bind        connect to the Directory
               compare     compare entry's attribute
               delete      delete an entry
               fred        back-end to FrED
               list        list children
               modify      modify an existing entry
               modifyrdn   modify an entry's name
               moveto      move to a position
               search      search for an object
               showentry   show an entry
               showname    show an entry's name
               squid       status of dish
               unbind      disconnect from the Directory

   See [2] for a complete list of commands and arguments.

   Note that commands and arguments are in lower-case, and may
   abbreviated to any unique prefix.

2.2.2.  Responses

   There are two kinds of responses: numeric-responses, which consist of
   arbitrary text; and, letter-responses, which consist of brief text,
   and expect further interaction from the client.

2.2.2.1.  Numeric Responses

   If the response is '1', then the DAP-transaction terminated normally;
   if the response is '2', then the DAP-transaction failed; if the
   response is '3', then the DAP-transaction was a search returning more
   than one result and one of the -hitone or -list option was selected
   for the search; if the response is '4', then the DAP-transaction
   terminated normally and the remainder of this line consists of the
   name of an entry (see the 'd' Response below); if the response is
   '5', then all children of an entry were found by the DAP-transaction.
   Once the response is completely sent, the DAP-listener closes the
   data connection.

   Note that although numeric responses utilize ASCII, they are not
   NVT-ASCII; in particular, the LF-character is used to indicate end-
   of-line, rather than the CR-LF line termination sequence of NVT-
   ASCII.

2.2.2.2.  'm' Response

   The 'm' response contains a one-line message which should be
   presented to the user.

   At this point, the client returns a response consisting of 'm'
   followed by the LF-character.  The client should then continue
   reading from the existing data connection.

2.2.2.3.  'y' Response

   The 'y' response contains a yes/no question which should be presented
   to the user.  After querying the user, the response (either 'y' or
   'n'), followed by the LF-character, should be sent to the DAP-
   listener.  The client should then continue reading from the existing
   data connection.

2.2.2.4.  'p' Response

   The 'p' response contains a password-prompt which should be presented
   to the user.  After querying the user, the client returns a response
   consisting of 'p' followed by the password supplied by the user
   followed by the LF-character.  The client should then continue
   reading from the existing data connection.

2.2.2.5.  'e' Response

   The 'e' response is used to ask the user to edit some text.
   Following the 'e' character is a decimal number in ASCII followed by
   the LF-character, indicating the number of octets that should be
   presented to the user for editing (these octets may include LF-
   characters).

   At this point, the client returns a response consisting of a single
   character followed by a LF-character.  If the character is 'e', the
   edit is aborted (e.g., the text is too large), and the client should
   then continue reading from the existing data connection.

   Otherwise, the DAP-listener sends the indicated number of octets
   corresponding to the buffer that the user is to edit.  After the user
   edits the buffer, one of two responses should be sent.

   If the user aborted the edit, the response sent to the DAP-listener
   is a single character 'e', followed by the LF-character.

   Otherwise, the response consists of any single character other than
   indicating the number of octets immediately following that resulted
   from the user-edit.

   Regardless of the outcome, the client should then continue reading
   from the existing data connection.

2.2.2.6.  'l' Response

   The 'l' response contains an entry for a selection list to be
   presented to the user.  The form of this entry consists of two
   strings separated by the '$' character, and terminated by the LF-
   character.  The first string is a user-friendly name, suitable for
   display to the user; the second string is a fully-qualified
   Distinguished Name in textual format.

   At this point, the client returns a response consisting of 'l'
   followed by the LF-character.

   The client should continue to accumulate selection entries until an
   LF-character.

   At this point, the user should be asked to select one or more of the
   selection entries.  After this selection, the client sends back a
   response consisting of 'L' followed by one or more decimal numbers in
   ASCII followed by the LF-character.  The numbers are separated by
   spaces, and correspond to the entries selected by the user.  (The
   entry corresponding to the first 'l' response is numbered 1, etc.)

   The client should then continue reading from the existing data
   connection.

2.2.2.7.  'd' Response

   The 'd' response contains a name that the client may be interested
   in.  The form of this name consists of two strings separated by the
   '$' character, and terminated by the LF-character.  The first string
   is a user-friendly name, suitable for display to the user; the second
   string is a fully-qualified Distinguished Name in textual format.

   At this point, the client returns a response consisting of 'd'
   followed by the LF-character.  The client should then continue
   reading from the existing data connection.

2.2.2.8.  'P' Response

   The 'P' response is used to transmit a picture to the client.
   Following the 'P' character is a decimal number in ASCII followed by
   a name and then the LF-character.  The decimal number indicates the
   size of the picture.  The name contains three strings separated by
   the '$' character.  The first string is the name of the attribute
   corresponding to the picture, in textual format; the second string is
   a user-friendly name, suitable for display to the user; and, the
   third string is a fully-qualified DistingiushedName in textual
   format.

   At this point, the client returns a response consisting of a single
   character followed by a LF-character.  If the character is 'P', the
   picture will not be sent (e.g., the image is too large), and the
   client should then continue reading from the existing data
   connection.

   Otherwise, the DAP-listener sends the indicated number of octets
   corresponding to the picture.  The picture is encoded using the PBM
   format from the PBMPLUS package.

   Regardless of the outcome, the client should then continue reading
   from the existing data connection.

3.  Example Interaction

   In the text that follows, "S:" refers to the DA-server, "L:" refers
   to the DAP-listener, "C:" refers to the client talking to the DA-
   server, and, "I:" refers to the client talking to the DAP-listener.

          S: <wait for connection on TCP port 411>

          C: <open connection to DA-server>
          L: <wait for connections>
          S: +OK 192.33.4.21 32867

          I: <open connection to DAP-listener>
          I: bind -simple -user "@c=US@cn=Manager"
          L: pc=US@cn=Manager
          -- client asks user for password for "c=US@cn=Manager"
          I: psecret
          L: <closes connection, signaling success but no response>

          -- since response was null, client verifies that DAP-listener
          -- is still operating...
          C: STAT
          S: +OK

          I: <open connection to DAP-listener>
          I: fred -expand "@"
          L: 5
             North America$l=North America
             US$c=US
             ...
          L: <closes connection>

          I: <open connection to DAP-listener>
          I: fred -ufn rose,psi,us
          L: 1
             <followed by much data>
          L: <closes connection>

          I: <open connection to DAP-listener>
          I: fred -ufn -list,rose,ps,us
          L: lHewlett-Packard, US$c=US@o=Hewlett-Packard
          I: l
          L: lPerformance Systems International, US$c=US@o=Performance...

          I: l
          L: lRutgers University, US$c=US@o=Rutgers University
          I: l
          L: Lps
          -- client presents selection list to user asking to select
          -- matches for 'ps', user selects the 2nd
          I: L 2
          L: dManager, US$c=US@cn=Manager
          I: d
          L: 4Marshall Rose, ...$c=US@o=Performance...
             <followed by much data>
          L: <closes connection>

          I: <open connection to DAP-listener>
          I: fred -ufn -list,schoffstall,ps,us
          L: 33 matches found.
          Martin Schoffstall, ...$c=US@o=Performance...
          Marvin Schoffstall, ...$c=US@o=Performance...
          Steve Schoffstall, ...$c=US@o=Performance...
          L: <closes connection>

          C: QUIT
          L: <stop listening for connections>
          S: +OK
          C: <close connection>

          S: <wait for next connection>

4.  References

   [1] Information Processing - Open Systems Interconnection - The
       Directory, International Organization for Standardization.
       International Standard 9594, (1988).

   [2] Kille, S., Robbins, C., Roe, M., and A. Turland, "The ISO
       Development Environment: User's Manual", Volume 5: QUIPU,
       Performance Systems International, January 1990.

5.  Security Considerations

   Security considerations are not discussed in this memo.

6.  Author's Address

   Marshall T. Rose
   PSI, Inc.
   PSI California Office
   P.O. Box 391776
   Mountain View, CA 94039

   Phone: (415) 961-3380

   EMail: mrose@psi.com