Network Working Group                                           R. Faith
Request for Comments: 2229                U. North Carolina, Chapel Hill
Category: Informational                                        B. Martin
                                                    Miranda Productions
                                                           October 1997

                     A Dictionary Server Protocol


Status of this Memo

  This memo provides information for the Internet community.  It does
  not specify an Internet standard of any kind.  Distribution of this
  memo is unlimited.

Copyright Notice

  Copyright (C) The Internet Society (1997).  All Rights Reserved.

Abstract

  The Dictionary Server Protocol (DICT) is a TCP transaction based
  query/response protocol that allows a client to access dictionary
  definitions from a set of natural language dictionary databases.

Table of Contents

  1.      Introduction .........................................    2
  1.1.    Requirements .........................................    3
  2.      Protocol Overview ....................................    3
  2.1.    Link Level ...........................................    3
  2.2.    Lexical Tokens .......................................    3
  2.3.    Commands .............................................    4
  2.4.    Responses ............................................    5
  2.4.1.  Status Responses .....................................    5
  2.4.2.  General Status Responses .............................    6
  2.4.3.  Text Responses .......................................    6
  3.      Command and Response Details .........................    7
  3.1.    Initial Connection ...................................    7
  3.2.    The DEFINE Command ...................................    9
  3.3.    The MATCH Command ....................................   10
  3.4.    A Note on Virtual Databases ..........................   12
  3.5.    The SHOW Command .....................................   13
  3.5.1.  SHOW DB ..............................................   13
  3.5.2.  SHOW STRAT ...........................................   13
  3.5.3.  SHOW INFO ............................................   14
  3.5.4.  SHOW SERVER ..........................................   14
  3.6.    The CLIENT Command ...................................   15



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  3.7.    The STATUS Command ...................................   15
  3.8.    The HELP Command .....................................   15
  3.9.    The QUIT Command .....................................   16
  3.10.   The OPTION Command ...................................   16
  3.10.1. OPTION MIME ..........................................   16
  3.11.   The AUTH Command .....................................   18
  3.12.   The SASLAUTH Command .................................   18
  4.      Command Pipelining ...................................   20
  5.      URL Specification ....................................   20
  6.      Extensions ...........................................   22
  6.1.    Experimental Command Syntax ..........................   22
  6.2.    Experimental Commands and Pipelining .................   22
  7.      Summary of Response Codes ............................   23
  8.      Sample Conversations .................................   23
  8.1.    Sample 1 - HELP, DEFINE, and QUIT commands ...........   24
  8.2.    Sample 2 - SHOW commands, MATCH command ..............   25
  8.3.    Sample 3 - Server downtime ...........................   26
  8.4.    Sample 4 - Authentication ............................   26
  9.      Security Considerations ..............................   26
  10.     References ...........................................   27
  11.     Acknowledgements .....................................   29
  12.     Authors' Addresses ...................................   29
  13.     Full Copyright Statement .............................   30

1.  Introduction

  For many years, the Internet community has relied on the "webster"
  protocol for access to natural language definitions.  The webster
  protocol supports access to a single dictionary and (optionally) to a
  single thesaurus.  In recent years, the number of publicly available
  webster servers on the Internet has dramatically decreased.

  Fortunately, several freely-distributable dictionaries and lexicons
  have recently become available on the Internet.  However, these
  freely-distributable databases are not accessible via a uniform
  interface, and are not accessible from a single site.  They are often
  small and incomplete individually, but would collectively provide an
  interesting and useful database of English words.  Examples include
  the Jargon file [JARGON], the WordNet database [WORDNET], MICRA's
  version of the 1913 Webster's Revised Unabridged Dictionary
  [WEB1913], and the Free Online Dictionary of Computing [FOLDOC].
  Translating and non-English dictionaries are also becoming available
  (for example, the FOLDOC dictionary is being translated into
  Spanish).







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  The webster protocol is not suitable for providing access to a large
  number of separate dictionary databases, and extensions to the
  current webster protocol were not felt to be a clean solution to the
  dictionary database problem.

  The DICT protocol is designed to provide access to multiple
  databases.  Word definitions can be requested, the word index can be
  searched (using an easily extended set of algorithms), information
  about the server can be provided (e.g., which index search strategies
  are supported, or which databases are available), and information
  about a database can be provided (e.g., copyright, citation, or
  distribution information).  Further, the DICT protocol has hooks that
  can be used to restrict access to some or all of the databases.

1.1.  Requirements

  In this document, we adopt the convention discussed in Section 1.3.2
  of [RFC1122] of using the capitalized words MUST, REQUIRED, SHOULD,
  RECOMMENDED, MAY, and OPTIONAL to define the significance of each
  particular requirement specified in this document.

  In brief: "MUST" (or "REQUIRED") means that the item is an absolute
  requirement of the specification; "SHOULD" (or "RECOMMENDED") means
  there may exist valid reasons for ignoring this item, but the full
  implications should be understood before doing so; and "MAY" (or
  "OPTIONAL") means that his item is optional, and may be omitted
  without careful consideration.

2.  Protocol Overview

2.1.  Link Level

  The DICT protocol assumes a reliable data stream such as provided by
  TCP.  When TCP is used, a DICT server listens on port 2628.

  This server is only an interface between programs and the dictionary
  databases.  It does not perform any user interaction or
  presentation-level functions.

2.2.  Lexical Tokens

  Commands and replies are composed of characters from the UCS
  character set [ISO10646] using the UTF-8 [RFC2044] encoding.  More
  specifically, using the grammar conventions from [RFC822]:







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                                              ; (  Octal, Decimal.)
  CHAR        =  <any UTF-8 character (1 to 6 octets)>
  CTL         =  <any ASCII control           ; (  0- 37,  0.- 31.)
                  character and DEL>          ; (    177,     127.)
  CR          =  <ASCII CR, carriage return>  ; (     15,      13.)
  LF          =  <ASCII LF, linefeed>         ; (     12,      10.)
  SPACE       =  <ASCII SP, space>            ; (     40,      32.)
  HTAB        =  <ASCII HT, horizontal-tab>   ; (     11,       9.)
  <">         =  <ASCII quote mark>           ; (     42,      34.)
  <'>         =  <ASCII single quote mark>    ; (     47,      39.)
  CRLF        =  CR LF
  WS          =  1*(SPACE / HTAB)

  dqstring    =  <"> *(dqtext/quoted-pair) <">
  dqtext      =  <any CHAR except <">, "\", and CTLs>
  sqstring    =  <'> *(dqtext/quoted-pair) <'>
  sqtext      =  <any CHAR except <'>, "\", and CTLs>
  quoted-pair =  "\" CHAR

  atom        =  1*<any CHAR except SPACE, CTLs, <'>, <">, and "\">
  string      =  *<dqstring / sqstring / quoted-pair>
  word        =  *<atom / string>
  description =  *<word / WS>
  text        =  *<word / WS>

2.3.  Commands

  Commands consist of a command word followed by zero or more
  parameters.  Commands with parameters must separate the parameters
  from each other and from the command by one or more space or tab
  characters.  Command lines must be complete with all required
  parameters, and may not contain more than one command.

  Each command line must be terminated by a CRLF.

  The grammar for commands is:

            command     = cmd-word *<WS cmd-param>
            cmd-word    = atom
            cmd-param   = database / strategy / word
            database    = atom
            strategy    = atom

  Commands are not case sensitive.







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  Command lines MUST NOT exceed 1024 characters in length, counting all
  characters including spaces, separators, punctuation, and the
  trailing CRLF.  There is no provision for the continuation of command
  lines.  Since UTF-8 may encode a character using up to 6 octets, the
  command line buffer MUST be able to accept up to 6144 octets.

2.4.  Responses

  Responses are of two kinds, status and textual.

2.4.1.  Status Responses

  Status responses indicate the server's response to the last command
  received from the client.

  Status response lines begin with a 3 digit numeric code which is
  sufficient to distinguish all responses.  Some of these may herald
  the subsequent transmission of text.

  The first digit of the response broadly indicates the success,
  failure, or progress of the previous command (based generally on
  [RFC640,RFC821]):

      1yz - Positive Preliminary reply
      2yz - Positive Completion reply
      3yz - Positive Intermediate reply
      4yz - Transient Negative Completion reply
      5yz - Permanent Negative Completion reply

  The next digit in the code indicates the response category:

      x0z - Syntax
      x1z - Information (e.g., help)
      x2z - Connections
      x3z - Authentication
      x4z - Unspecified as yet
      x5z - DICT System (These replies indicate the status of the
            receiver DICT system vis-a-vis the requested transfer
            or other DICT system action.)
      x8z - Nonstandard (private implementation) extensions

  The exact response codes that should be expected from each command
  are detailed in the description of that command.

  Certain status responses contain parameters such as numbers and
  strings.  The number and type of such parameters is fixed for each
  response code to simplify interpretation of the response.  Other
  status responses do not require specific text identifiers.  Parameter



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  requirements are detailed in the description of relevant commands.
  Except for specifically detailed parameters, the text following
  response codes is server-dependent.

  Parameters are separated from the numeric response code and from each
  other by a single space.  All numeric parameters are decimal, and may
  have leading zeros.  All string parameters MUST conform to the "atom"
  or "dqstring" grammar productions.

  If no parameters are present, and the server implementation provides
  no implementation-specific text, then there MAY or MAY NOT be a space
  after the response code.

  Response codes not specified in this standard may be used for any
  installation-specific additional commands also not specified.

  These should be chosen to fit the pattern of x8z specified above.
  The use of unspecified response codes for standard commands is
  prohibited.

2.4.2.  General Status Responses

  In response to every command, the following general status responses
  are possible:

            500 Syntax error, command not recognized
            501 Syntax error, illegal parameters
            502 Command not implemented
            503 Command parameter not implemented
            420 Server temporarily unavailable
            421 Server shutting down at operator request

2.4.3.  Text Responses

  Before text is sent a numeric status response line, using a 1yz code,
  will be sent indicating text will follow. Text is sent as a series of
  successive lines of textual matter, each terminated with a CRLF.  A
  single line containing only a period (decimal code 46, ".") is sent
  to indicate the end of the text (i.e., the server will send a CRLF at
  the end of the last line of text, a period, and another CRLF).

  If a line of original text contained a period as the first character
  of the line, that first period is doubled by the DICT server.
  Therefore, the client must examine the first character of each line
  received.  Those that begin with two periods must have those two
  periods collapsed into one period.  Those that contain only a single
  period followed by a CRLF indicate the end of the text response.




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  If the OPTION MIME command has been given, all textual responses will
  be prefaced by a MIME header [RFC2045] followed by a single blank
  line (CRLF).  See section 3.10.1 for more details on OPTION MIME.

  Following a text response, a 2yz response code will be sent.

  Text lines MUST NOT exceed 1024 characters in length, counting all
  characters including spaces, separators, punctuation, the extra
  initial period (if needed), and the trailing CRLF.  Since UTF-8 may
  encode a character using up to 6 octets, the text line input buffer
  MUST be able to accept up to 6144 octets.

  By default, the text of the definitions MUST be composed of
  characters from the UCS character set [ISO10644] using the UTF-8
  [RFC2044] encoding.  The UTF-8 encoding has the advantage of
  preserving the full range of 7-bit US ASCII [USASCII] values.
  Clients and servers MUST support UTF-8, even if only in some minimal
  fashion.

3.  Command and Response Details

  Below, each DICT command and appropriate responses are detailed.
  Each command is shown in upper case for clarity, but the DICT server
  is case-insensitive.

  Except for the AUTH and SASLAUTH commands, every command described in
  this section MUST be implemented by all DICT servers.

3.1.  Initial Connection

  When a client initially connects to a DICT server, a code 220 is sent
  if the client's IP is allowed to connect:

            220 text capabilities msg-id

  The code 220 is a banner, usually containing host name and DICT
  server version information.

  The second-to-last sequence of characters in the banner is the
  optional capabilities string, which will allow servers to declare
  support for extensions to the DICT protocol.  The capabilities string
  is defined below:

            capabilities =  ["<" msg-atom *("." msg-atom) ">"]
            msg-atom     =  1*<any CHAR except SPACE, CTLs,
                               "<", ">", ".", and "\">





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  Individual capabilities are described by a single msg-atom.  For
  example, the string <html.gzip> might be used to describe a server
  that supports extensions which allow HTML or compressed output.
  Capability names beginning with "x" or "X" are reserved for
  experimental extensions, and SHOULD NOT be defined in any future DICT
  protocol specification.  Some of these capabilities may inform the
  client that certain functionality is available or can be requested.
  The following capabilities are currently defined:

      mime        The OPTION MIME command is supported
      auth        The AUTH command is supported
      kerberos_v4 The SASL Kerberos version 4 mechanism is supported
      gssapi      The SASL GSSAPI [RFC2078] mechanism is supported
      skey        The SASL S/Key [RFC1760] mechanism is supported
      external    The SASL external mechanism is supported

  The last sequence of characters in the banner is a msg-id, similar to
  the format specified in [RFC822].  The simplified description is
  given below:

      msg-id       =  "<" spec ">"            ; Unique message id
      spec         =  local-part "@" domain
      local-part   =  msg-atom *("." msg-atom)
      domain       =  msg-atom *("." msg-atom)

  Note that, in contrast to [RFC822], spaces and quoted pairs are not
  allowed in the msg-id.  This restriction makes the msg-id much easier
  for the client to locate and parse but does not significantly
  decrease any security benefits, since the msg-id may be arbitrarily
  long (as bounded by the response length limits set forth elsewhere in
  this document).

  Note also that the open and close brackets are part of the msg-id and
  should be included in the string that is used to compute the MD5
  checksum.

  This message id will be used by the client when formulating the
  authentication string used in the AUTH command.

  If the client's IP is not allowed to connect, then a code 530 is sent
  instead:

            530 Access denied

  Transient failure responses are also possible:

            420 Server temporarily unavailable
            421 Server shutting down at operator request



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  For example, response code 420 should be used if the server cannot
  currently fork a server process (or cannot currently obtain other
  resources required to proceed with a usable connection), but expects
  to be able to fork or obtain these resources in the near future.

  Response code 421 should be used when the server has been shut down
  at operator request, or when conditions indicate that the ability to
  service more requests in the near future will be impossible.  This
  may be used to allow a graceful operator-mediated temporary shutdown
  of a server, or to indicate that a well known server has been
  permanently removed from service (in which case, the text message
  might provide more information).

3.2.  The DEFINE Command

  DEFINE database word

3.2.1.  Description

  This command will look up the specified word in the specified
  database.  All DICT servers MUST implement this command.

  If the database name is specified with an exclamation point (decimal
  code 33, "!"), then all of the databases will be searched until a
  match is found, and all matches in that database will be displayed.
  If the database name is specified with a star (decimal code 42, "*"),
  then all of the matches in all available databases will be displayed.
  In both of these special cases, the databases will be searched in the
  same order as that printed by the "SHOW DB" command.

  If the word was not found, then status code 552 is sent.

  If the word was found, then status code 150 is sent, indicating that
  one or more definitions follow.

  For each definition, status code 151 is sent, followed by the textual
  body of the definition.  The first three space-delimited parameters
  following status code 151 give the word retrieved, the name of the
  database (which is the same as the first column of the SHOW DB
  command), and a short description for the database (which is the same
  as the second column of the SHOW DB command).  The short name is
  suitable for printing as:

            From name:

  before the definition is printed.  This provides source information
  for the user.




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  The textual body of each definition is terminated with a CRLF period
  CRLF sequence.

  After all of the definitions have been sent, status code 250 is sent.
  This command can provide optional timing information (which is server
  dependent and is not intended to be parsable by the client).  This
  additional information is useful when debugging and tuning the
  server.

3.2.2.  Responses

      550 Invalid database, use "SHOW DB" for list of databases
      552 No match
      150 n definitions retrieved - definitions follow
      151 word database name - text follows
      250 ok (optional timing information here)

  Response codes 150 and 151 require special parameters as part of
  their text.  The client can use these parameters to display
  information on the user's terminal.

  For code 150, parameters 1 indicates the number of definitions
  retrieved.

  For code 151, parameter 1 is the word retrieved, parameter 2 is the
  database name (the first name as shown by "SHOW DB") from which the
  definition has been retrieved, and parameter 3 is the the short
  database description (the second column of the "SHOW DB" command).

3.3.  The MATCH Command

  MATCH database strategy word

3.3.1.  Description

  This command searches an index for the dictionary, and reports words
  which were found using a particular strategy.  Not all strategies are
  useful for all dictionaries, and some dictionaries may support
  additional search strategies (e.g., reverse lookup).  All DICT
  servers MUST implement the MATCH command, and MUST support the
  "exact" and "prefix" strategies.  These are easy to implement and are
  generally the most useful.  Other strategies are server dependent.

  The "exact" strategy matches a word exactly, although different
  servers may treat non-alphanumeric data differently.  We have found
  that a case-insensitive comparison which ignores non-alphanumeric





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  characters and which folds whitespace is useful for English-language
  dictionaries.  Other comparisons may be more appropriate for other
  languages or when using extended character sets.

  The "prefix" strategy is similar to "exact", except that it only
  compares the first part of the word.

  Different servers may implement these algorithms differently.  The
  requirement is that strategies with the names "exact" and "prefix"
  exist so that a simple client can use them.

  Other strategies that might be considered by a server implementor are
  matches based on substring, suffix, regular expressions, soundex
  [KNUTH73], and Levenshtein [PZ85] algorithms.  These last two are
  especially useful for correcting spelling errors.  Other useful
  strategies perform some sort of "reverse" lookup (i.e., by searching
  definitions to find the word that the query suggests).

  If the database name is specified with an exclamation point (decimal
  code 33, "!"), then all of the databases will be searched until a
  match is found, and all matches in that database will be displayed.
  If the database name is specified with a star (decimal code 42, "*"),
  then all of the matches in all available databases will be displayed.
  In both of these special cases, the databases will be searched in the
  same order as that printed by the "SHOW DB" command.

  If the strategy is specified using a period (decimal code 46, "."),
  then the word will be matched using a server-dependent default
  strategy, which should be the best strategy available for interactive
  spell checking.  This is usually a derivative of the Levenshtein
  algorithm [PZ85].

  If no matches are found in any of the searched databases, then status
  code 552 will be returned.

  Otherwise, status code 152 will be returned followed by a list of
  matched words, one per line, in the form:

            database word

  This makes the responses directly useful in a DEFINE command.

  The textual body of the match list is terminated with a CRLF period
  CRLF sequence.

  Following the list, status code 250 is sent, which may include
  server-specific timing and statistical information, as discussed in
  the section on the DEFINE command.



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3.3.2.  Responses

       550 Invalid database, use "SHOW DB" for list of databases
       551 Invalid strategy, use "SHOW STRAT" for a list of strategies
       552 No match
       152 n matches found - text follows
       250 ok (optional timing information here)

  Response code 152 requires a special parameter as part of its text.
  Parameter 1 must be the number of matches retrieved.

3.4.  A Note on Virtual Databases

  The ability to search all of the provided databases using a single
  command is given using the special "*" and "!" databases.

  However, sometimes, a client may want to search over some but not all
  of the databases that a particular server provides.  One alternative
  is for the client to use the SHOW DB command to obtain a list of
  databases and descriptions, and then (perhaps with the help of a
  human), select a subset of these databases for an interactive search.
  Once this selection has been done once, the results can be saved, for
  example, in a client configuration file.

  Another alternative is for the server to provide "virtual" databases
  which merge several of the regular databases into one.  For example,
  a virtual database may be provided which includes all of the
  translating dictionaries, but which does not include regular
  dictionaries or thesauri.  The special "*" and "!" databases can be
  considered as names of virtual databases which provide access to all
  of the databases.  If a server implements virtual databases, then the
  special "*" and "!" databases should probably exclude other virtual
  databases (since they merely provide information duplicated in other
  databases).  If virtual databases are supported, they should be
  listed as a regular database with the SHOW DB command (although,
  since "*" and "!" are required, they need not be listed).

  Virtual databases are an implementation-specific detail which has
  absolutely no impact on the DICT protocol.  The DICT protocol views
  virtual and non-virtual databases the same way.

  We mention virtual databases here, however, because they solve a
  problem of database selection which could also have been solved by
  changes in the protocol.  For example, each dictionary could be
  assigned attributes, and the protocol could be extended to specify
  searches over databases with certain attributes.  However, this
  needlessly complicates the parsing and analysis that must be
  performed by the implementation.  Further, unless the classification



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  system is extremely general, there is a risk that it would restrict
  the types of databases that can be used with the DICT protocol
  (although the protocol has been designed with human-language
  databases in mind, it is applicable to any read-only database
  application, especially those with a single semi-unique alphanumeric
  key and textual data).

3.5.  The SHOW Command

3.5.1.  SHOW DB

  SHOW DB
  SHOW DATABASES

3.5.1.1.  Description

  Displays the list of currently accessible databases, one per line, in
  the form:

            database description

  The textual body of the database list is terminated with a CRLF
  period CRLF sequence.  All DICT servers MUST implement this command.

  Note that some databases may be restricted due to client domain or
  lack of user authentication (see the AUTH and SASLAUTH commands in
  sections 3.11 and 3.12).  Information about these databases is not
  available until authentication is performed.  Until that time, the
  client will interact with the server as if the additional databases
  did not exist.

3.5.1.2.  Responses

            110 n databases present - text follows
            554 No databases present

       Response code 110 requires a special parameter.  Parameter 1
       must be the number of databases available to the user.

3.5.2.  SHOW STRAT

  SHOW STRAT
  SHOW STRATEGIES








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3.5.2.1.  Description

  Displays the list of currently supported search strategies, one per
  line, in the form:

            strategy description

  The textual body of the strategy list is terminated with a CRLF
  period CRLF sequence.  All DICT servers MUST implement this command.

3.5.2.2.  Responses

            111 n strategies available - text follows
            555 No strategies available

  Response code 111 requires a special parameter.  Parameter 1 must be
  the number of strategies available.

3.5.3.  SHOW INFO

  SHOW INFO database

3.5.3.1.  Description

  Displays the source, copyright, and licensing information about the
  specified database.  The information is free-form text and is
  suitable for display to the user in the same manner as a definition.
  The textual body of the information is terminated with a CRLF period
  CRLF sequence.  All DICT servers MUST implement this command.

3.5.3.2.  Responses

            550 Invalid database, use "SHOW DB" for list of databases
            112 database information follows

  These response codes require no special parameters.

3.5.4.  SHOW SERVER

  SHOW SERVER

3.5.4.1.  Description

  Displays local server information written by the local administrator.
  This could include information about local databases or strategies,
  or administrative information such as who to contact for access to
  databases requiring authentication.  All DICT servers MUST implement
  this command.



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3.5.4.2.  Responses

            114 server information follows

  This response code requires no special parameters.

3.6.  The CLIENT Command

  CLIENT text

3.6.1.  Description

  This command allows the client to provide information about itself
  for possible logging and statistical purposes.  All clients SHOULD
  send this command after connecting to the server.  All DICT servers
  MUST implement this command (note, though, that the server doesn't
  have to do anything with the information provided by the client).

3.6.2.  Responses

            250 ok (optional timing information here)

  This response code requires no special parameters.

3.7.  The STATUS Command

  STATUS

3.7.1.  Description

  Display some server-specific timing or debugging information.  This
  information may be useful in debugging or tuning a DICT server.  All
  DICT servers MUST implement this command (note, though, that the text
  part of the response is not specified and may be omitted).

3.7.2.  Responses

            210 (optional timing and statistical information here)

  This response code requires no special parameters.

3.8.  The HELP Command

  HELP







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3.8.1.  Description

  Provides a short summary of commands that are understood by this
  implementation of the DICT server.  The help text will be presented
  as a textual response, terminated by a single period on a line by
  itself.  All DICT servers MUST implement this command.

3.8.2.  Responses

            113 help text follows

  This response code requires no special parameters.

3.9.  The QUIT Command

  QUIT

3.9.1.  Description

  This command is used by the client to cleanly exit the server.  All
  DICT servers MUST implement this command.

3.9.2.  Responses

            221 Closing Connection

  This response code requires no special parameters.

3.10.  The OPTION Command

3.10.1.  OPTION MIME

  OPTION MIME

3.10.1.1.  Description

  Requests that all text responses be prefaced by a MIME header
  [RFC2045] followed by a single blank line (CRLF).

  If a client requests this option, then the client MUST be able to
  parse Content-Type and Content-transfer-encoding headers, and MUST be
  able to ignore textual responses which have an unsupported content or
  encoding.  A client MUST support the UTF-8 encoding [RFC2044], which
  minimally means that the client MUST recognize UTF-8 multi-octet
  encodings and convert these into some symbol that can be printed by
  the client.





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  If a client requests this option, then the server will provide a MIME
  header.  If the header is empty, the text response will start with a
  single blank line (CRLF), in which case a client MUST interpret this
  as a default header.  The default header for SASL authentication is:

            Content-type: application/octet-stream
            Content-transfer-encoding: base64

  The default header for all other textual responses is:

            Content-type: text/plain; charset=utf-8
            Content-transfer-encoding: 8bit

  If OPTION MIME is not specified by the client, then the server may
  restrict the information content provided to the client.  For
  example, a definition may be accompanied by an image and an audio
  clip, but the server cannot transmit this information unless the
  client is able to parse MIME format headers.

  Note that, because of the line length restrictions and end-of-
  response semantics, the "binary" content-transfer-encoding MUST NOT
  be used.  In the future, extensions to the protocol may be provided
  which allow a client to request binary encodings, but the default
  SHOULD always be that the client can look for a "CRLF . CRLF"
  sequence to locate the end of the current text response.  This allows
  clients to easily skip over text responses which have unsupported
  types or encodings.

  In the future, after significant experience with large databases in
  various languages has been gained, and after evaluating the need for
  specifying character sets and other encodings (e.g., compressed or
  BASE64 encoding), standard extensions to this protocol should be
  proposed which allow the client to request certain content types or
  encodings.  Care should be taken that these extensions do not require
  a handshake which defeats pipelining.  In the mean time, private
  extensions should be used to explore the parameter space to determine
  how best to implement these extensions.

  OPTION MIME is a REQUIRED server capability, all DICT servers MUST
  implement this command.

3.10.1.2.  Responses

            250 ok (optional timing information here)

  Note that some older server implementations, completed before this
  document was finalized, will return a status code 500 if this command
  is not implemented.  Clients SHOULD be able to accept this behavior,



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  making default assumptions.  Clients may also examine the
  capabilities string in the status code 220 header to determine if a
  server supports this capability.

3.11.  The AUTH Command

  AUTH username authentication-string

3.11.1.  Description

  The client can authenticate itself to the server using a username and
  password.  The authentication-string will be computed as in the APOP
  protocol discussed in [RFC1939].  Briefly, the authentication-string
  is the MD5 checksum of the concatenation of the msg-id (obtained from
  the initial banner) and the "shared secret" that is stored in the
  server and client configuration files.  Since the user does not have
  to type this shared secret when accessing the server, the shared
  secret can be an arbitrarily long passphrase.  Because of the
  computational ease of computing the MD5 checksum, the shared secret
  should be significantly longer than a usual password.

  Authentication may make more dictionary databases available for the
  current session.  For example, there may be some publicly
  distributable databases available to all users, and other private
  databases available only to authenticated users.  Or, a server may
  require authentication from all users to minimize resource
  utilization on the server machine.

  Authentication is an optional server capability.  The AUTH command
  MAY be implemented by a DICT server.

3.11.2.  Responses

            230 Authentication successful
            531 Access denied, use "SHOW INFO" for server information

  These response codes require no special parameters.

3.12.  The SASLAUTH Command

  SASLAUTH mechanism initial-response
  SASLRESP response

3.12.1.  Description

  The Simple Authentication and Security Layer (SASL) is currently
  being developed [RFC2222].  The DICT protocol reserves the SASLAUTH
  and SASLRESP commands for this method of authentication.  The results



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  of successful authentication with SALSAUTH will be the same as the
  results of successful AUTH authentication: more dictionary databases
  may become available for the current session.

  The initial-response is an optional parameter for the SASLAUTH
  command, encoded using BASE64 encoding [RFC2045].  Some SASL
  mechanisms may allow the use of this parameter.  If SASL
  authentication is supported by a DICT server, then this parameter
  MUST also be supported.

  A typical SASL authentication will be initiated by the client using
  the SASLAUTH command.  The server will reply with status code 130,
  followed by a challenge.  The challenge will be followed by status
  code 330, indicating that the client must now send a response to the
  server.

  Depending on the details of the SASL mechanism currently in use, the
  server will either continue the exchange using status code 130, a
  challenge, and status code 330; or the server will use status code
  230 or 531 to indicate authentication was successful or has failed.

  The challenges sent by the server are defined by the mechanisms as
  binary tokens of arbitrary length, and should be sent using a
  standard DICT textual response, as described in section 2.4.3.  If
  OPTION MIME is not set, then BASE64 encoding MUST be used.  If

  OPTION MIME is set, then BASE64 is the default encoding, as specified
  in section 3.10.1.

  The client will send all responses using the SASLRESP command and a
  BASE64-encoded parameter.  The responses sent by the client are
  defined by the mechanisms as binary tokens of arbitrary length.
  Remember that DICT command lines may only be 1024 characters in
  length, so the response provided by a DICT client is limited.

  If the mechanism specified in the SASLAUTH command is not supported,
  then status code 532 will be returned.

  Authentication is an optional server capability.  The SASLAUTH
  command MAY be implemented by a DICT server.

3.12.2.  Responses

            130 challenge follows
            330 send response
            230 Authentication successful
            531 Access denied, use "SHOW INFO" for server information
            532 Access denied, unknown mechanism



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       These response codes require no special parameters.

4.  Command Pipelining

  All DICT servers MUST be able to accept multiple commands in a single
  TCP send operation.  Using a single TCP send operation for multiple
  commands can improved DICT performance significantly, especially in
  the face of high latency network links.

  The possible implementation problems for a DICT server which would
  prevent command pipelining are similar to the problems that prevent
  pipelining in an SMTP server.  These problems are discussed in detail
  in [RFC1854], which should be consulted by all DICT server
  implementors.

  The main implication is that a DICT server implementation MUST NOT
  flush or otherwise lose the contents of the TCP input buffer under
  any circumstances whatsoever.

  A DICT client may pipeline several commands and must check the
  responses to each command individually.  If the server has shut down,
  it is possible that all of the commands will not be processed.  For
  example, a simple DICT client may pipeline a CLIENT, DEFINE, and QUIT
  command sequence as it is connecting to the server.  If the server is
  shut down, the initial response code sent by the server may be 420
  (temporarily unavailable) instead of 220 (banner).  In this case, the
  definition cannot be retrieved, and the client should report and
  error or retry the command.  If the server is working, it may be able
  to send back the banner, definition, and termination message in a
  single TCP send operation.

5.  URL Specification

  The DICT URL scheme is used to refer to definitions or word lists
  available using the DICT protocol:


  dict://<user>;<auth>@<host>:<port>/d:<word>:<database>:<n>
  dict://<user>;<auth>@<host>:<port>/m:<word>:<database>:<strat>:<n>


  The "/d" syntax specifies the DEFINE command (section 3.2), whereas
  the "/m" specifies the MATCH command (section 3.3).








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  Some or all of "<user>;<auth>@", ":<port>", "<database>", "<strat>",
  and "<n>" may be omitted.

  "<n>" will usually be omitted, but when included, it specifies the
  nth definition or match of a word.  A method for extracting exactly
  this information from the server is not available using the DICT
  protocol.  However, a client using the URL specification could obtain
  all of the definitions or matches, and then select the one that is
  specified.

  If "<user>;<auth>@" is omitted, no authentication is done.  If
  ":<port>" is omitted, the default port (2628) SHOULD be used.  If
  "<database>" is omitted, "!" SHOULD be used (see section 3.2).  If
  "<strat>" is omitted, "." SHOULD be used (see section 3.3).

  "<user>;<auth>@" specifies the username and the type of
  authentication performed.  For "<auth>", the string "AUTH" indicates
  that APOP authentication using the AUTH command will be performed,
  whereas the string "SASLAUTH=<auth_type>" indicates that the SASLAUTH
  and SASLRESP commands will be used, with "<auth_type>" indicating the
  type of SASL authentication which will be used.  If "<auth_type>" is
  a star (decimal code 42, "*"), then the client will select some type
  of authentication.

  Whenever authentication is required, the client SHOULD request
  additional information (e.g., a passphrase) from the user.  In
  contrast to [RFC1738], clear text passwords are not permitted in the
  URL.

  Trailing colons may be omitted.  For example, the following URLs
  might specify definitions or matches:

            dict://dict.org/d:shortcake:
            dict://dict.org/d:shortcake:*
            dict://dict.org/d:shortcake:wordnet:
            dict://dict.org/d:shortcake:wordnet:1
            dict://dict.org/d:abcdefgh
            dict://dict.org/d:sun
            dict://dict.org/d:sun::1

            dict://dict.org/m:sun
            dict://dict.org/m:sun::soundex
            dict://dict.org/m:sun:wordnet::1
            dict://dict.org/m:sun::soundex:1
            dict://dict.org/m:sun:::






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6.  Extensions

  This protocol was designed so that flat text databases can be used
  with a server after a minimum of analysis and formatting.  Our
  experience is that merely constructing an index for a database may be
  sufficient to make it useful with a DICT server.  The ability to
  serve preformatted text is especially important since freely-
  available databases are often distributed as flat text files without
  any semantic mark-up information (and often contain "ASCII art" which
  precludes the automation of even simple formatting).

  However, given a database with sufficient mark-up information, it may
  be possible to generate output in a variety of different formats
  (e.g., simple HTML or more sophisticated SGML).  The specification of
  formatting is beyond the scope of this document.  The requirements
  for negotiation of format (including character set and other
  encodings) is complex and should be examined over time as more
  experience is gained.  We suggest that the use of different formats,
  as well as other server features, be explored as extensions to the
  protocol.

6.1.  Experimental Command Syntax

  Single-letter commands are reserved for debugging and testing, SHOULD
  NOT be defined in any future DICT protocol specification, and MUST
  NOT be used by any client software.

  Commands beginning with the letter "X" are reserved for experimental
  extensions, and SHOULD NOT be defined in any future DICT protocol
  specification.  Authors of client software should understand that
  these commands are not part of the DICT protocol and may not be
  available on all DICT servers.

6.2.  Experimental Commands and Pipelining

  Experimental commands should be designed so that a client can
  pipeline the experimental commands without knowing if a server
  supports the commands (e.g., instead of using feature negotiation).
  If the server does not support the commands, then a response code in
  the 5yz series (usually 500) will be given, notifying the client that
  the extension is not supported.  Of course, depending on the
  complexity of the extensions added, feature negotiation may be
  necessary.  To help minimize negotiation time, server-supported
  features may be announced in the banner (code 220) using the optional
  capabilities parameter.






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7.  Summary of Response Codes

  Below is a summary of response codes.  A star (*) in the first column
  indicates the response has defined arguments that must be provided.

     * 110 n databases present - text follows
     * 111 n strategies available - text follows
       112 database information follows
       113 help text follows
       114 server information follows
       130 challenge follows
     * 150 n definitions retrieved - definitions follow
     * 151 word database name - text follows
     * 152 n matches found - text follows
       210 (optional timing and statistical information here)
     * 220 text msg-id
       221 Closing Connection
       230 Authentication successful
       250 ok (optional timing information here)
       330 send response
       420 Server temporarily unavailable
       421 Server shutting down at operator request
       500 Syntax error, command not recognized
       501 Syntax error, illegal parameters
       502 Command not implemented
       503 Command parameter not implemented
       530 Access denied
       531 Access denied, use "SHOW INFO" for server information
       532 Access denied, unknown mechanism
       550 Invalid database, use "SHOW DB" for list of databases
       551 Invalid strategy, use "SHOW STRAT" for a list of strategies
       552 No match
       554 No databases present
       555 No strategies available

8.  Sample Conversations

  Theses are samples of the conversations that might be expected with
  a typical DICT server.  The notation "C:" indicates commands set by
  the client, and "S:" indicates responses sent by the server.  Blank
  lines are included for clarity and do not indicate actual newlines
  in the transaction.









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8.1.  Sample 1 - HELP, DEFINE, and QUIT commands

C: [ client initiates connection ]

S: 220 dict.org dictd (version 0.9) <[email protected]>


C: HELP

S: 113 Help text follows
S: DEFINE database word            look up word in database
S: MATCH database strategy word    match word in database using strategy
S: [ more server-dependent help text ]
S: .
S: 250 Command complete


C: DEFINE ! penguin

S: 150 1 definitions found: list follows
S: 151 "penguin" wn "WordNet 1.5" : definition text follows
S: penguin
S:   1. n: short-legged flightless birds of cold southern esp. Antarctic
S:      regions having webbed feet and wings modified as flippers
S: .
S: 250 Command complete


C: DEFINE * shortcake

S: 150 2 definitions found: list follows
S: 151 "shortcake" wn "WordNet 1.5" : text follows
S: shortcake
S:   1. n: very short biscuit spread with sweetened fruit and usu.
S:      whipped cream
S: .
S: 151 "Shortcake" web1913 "Webster's Dictionary (1913)" : text follows
S: Shortcake
S:    \Short"cake`\, n.
S:    An unsweetened breakfast cake shortened with butter or lard,
S:    rolled thin, and baked.
S: .
S: 250 Command complete


C: DEFINE abcdefgh

S: 552 No match



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C: quit

S: 221 Closing connection

8.2.  Sample 2 - SHOW commands, MATCH command

C: SHOW DB

S: 110 3 databases present: list follows
S: wn "WordNet 1.5"
S: foldoc "Free On-Line Dictionary of Computing"
S: jargon "Hacker Jargon File"
S: .
S: 250 Command complete


C: SHOW STRAT

S: 111 5 strategies present: list follows
S: exact "Match words exactly"
S: prefix "Match word prefixes"
S: substring "Match substrings anywhere in word"
S: regex "Match using regular expressions"
S: reverse "Match words given definition keywords"
S: .
S: 250 Command complete


C: MATCH foldoc regex "s.si"

S: 152 7 matches found: list follows
S: foldoc Fast SCSI
S: foldoc SCSI
S: foldoc SCSI-1
S: foldoc SCSI-2
S: foldoc SCSI-3
S: foldoc Ultra-SCSI
S: foldoc Wide SCSI
S: .
S: 250 Command complete


C: MATCH wn substring "abcdefgh"

S: 552 No match






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8.3.  Sample 3 - Server downtime


C: [ client initiates connection ]

S: 420 Server temporarily unavailable


C: [ client initiates connection ]

S: 421 Server shutting down at operator request


8.4.  Sample 4 - Authentication

C: [ client initiates connection ]

S: 220 dict.org dictd (version 0.9) <[email protected]>


C: SHOW DB

S: 110 1 database present: list follows
S: free "Free database"
S: .
S: 250 Command complete


C: AUTH joesmith authentication-string

S: 230 Authentication successful


C: SHOW DB

S: 110 2 databases present: list follows
S: free "Free database"
S: licensed "Local licensed database"
S: .
S: 250 Command complete




9.  Security Considerations

  This RFC raises no security issues.




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10.  References

  [ASCII] US-ASCII. Coded Character Set - 7-Bit American Standard
       Code for Information Interchange. Standard ANSI X3.4-1986,
       ANSI, 1986.

  [FOLDOC] Howe, Denis, ed.  The Free On-Line Dictionary of
       Computing, <URL:http://wombat.doc.ic.ac.uk/>

  [ISO10646] ISO/IEC 10646-1:1993. International Standard --
       Information technology -- Universal Multiple-Octet Coded
       Character Set (UCS) -- Part 1: Architecture and Basic
       Multilingual Plane.  UTF-8 is described in Annex R, adopted
       but not yet published.  UTF-16 is described in Annex Q,
       adopted but not yet published.

  [JARGON] The on-line hacker Jargon File, version 4.0.0, 25 JUL
       1996, <URL:http://www.ccil.org/jargon/>

  [KNUTH73] Knuth, Donald E. "The Art of Computer Programming",
       Volume 3: Sorting and Searching (Addison-Wesley Publishing
       Co., 1973, pages 391 and 392). Knuth notes that the soundex
       method was originally described by Margaret K. Odell and
       Robert C. Russell [US Patents 1261167 (1918) and 1435663
       (1922)].

  [PZ85] Pollock, Joseph J. and Zamora, Antonio, "Automatic spelling
       correction in scientific and scholarly text," CACM, 27(4):
       Apr. 1985, 358-368.

  [RFC640] Postel, J., "Revised FTP Reply Codes", RFC 640, June,
       1975.

  [RFC821] Postel, J., "Simple Mail Transfer Protocol", STD 10,
       RFC 821, August 1982.

  [RFC822] Crocker, D., "Standard for the Format of ARPA Internet
       Text Messages", STD 11, RFC 822, August 1982.

  [RFC977] Kantor, B., and P. Lapsley, "Network News Transfer
       Protocol: A Proposed Standard for the Stream-Based
       Transmission of News", RFC 977, February 1986.

  [RFC2045] Freed, N., and N. Borenstein, "Multipurpose Internet
       Mail Extensions (MIME) Part One: Format of Internet Message
       Bodies", RFC 2045, November 1996.





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  [RFC1738] Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform
       Resource Locators (URL)", RFC 1738, December 1994.

  [RFC1760] Haller, N., "The S/KEY One-Time Password System",
       RFC 1760, February 1995.

  [RFC1985] Freed, N., and A. Cargille, "SMTP Service Extension for
       Command Pipelining", RFC 1854, October 1995.

  [RFC1939] Myers, J., and M. Rose, "Post Office Protocol - Version 3",
       STD 53, RFC 1939, May 1996.

  [RFC2044] Yergeau, F., "UTF-8, a transformation format of Unicode
       and ISO 10646", RFC 2044, October 1996.

  [RFC2068] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
       and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
       RFC 2068, January 1997.

  [RFC2078] Linn, J., "Generic Security Service Application Program
       Interface, Version 2", RFC 2078, January 1997.

  [RFC2222] Myers, J., "Simple Authentication and Security Layer
       (SASL)", RFC 2222, October 1997.

  [WEB1913] Webster's Revised Unabridged Dictionary (G & C. Merriam
       Co., 1913, edited by Noah Porter).  Online version prepared by
       MICRA, Inc., Plainfield, N.J. and edited by Patrick Cassidy
       <[email protected]>.  For further information, see
  <URL:ftp://uiarchive.cso.uiuc.edu/pub/etext/gutenberg/etext96/pgw*>,
       and
  <URL:http://humanities.uchicago.edu/forms_unrest/webster.form.html>

  [WORDNET] Miller, G.A. (1990), ed. WordNet: An On-Line Lexical
       Database. International Journal of Lexicography. Volume 3,
       Number 4.  <URL:http://www.cogsci.princeton.edu/~wn/>















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11.  Acknowledgements

  Thanks to Arnt Gulbrandsen and Nicolai Langfeldt for many helpful
  discussions.  Thanks to Bennet Yee, Doug Hoffman, Kevin Martin, and
  Jay Kominek for extensive testing and feedback on the initial
  implementations of the DICT server.  Thanks to Zhong Shao for advice
  and support.

  Thanks to Brian Kanto, Phil Lapsley, and Jon Postel for writing
  exemplary RFCs which were consulted during the preparation of this
  document.

  Thanks to Harald T. Alvestrand, whose comments helped improve this
  document.

12.  Authors' Addresses


  Rickard E. Faith
  EMail: [email protected] (or [email protected])


  Bret Martin
  EMail: [email protected]

  The majority of this work was completed while Bret Martin was a
  student at Yale University.
























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13.  Full Copyright Statement

  Copyright (C) The Internet Society (1997).  All Rights Reserved.

  This document and translations of it may be copied and furnished to
  others, and derivative works that comment on or otherwise explain it
  or assist in its implmentation may be prepared, copied, published
  andand distributed, in whole or in part, without restriction of any
  kind, provided that the above copyright notice and this paragraph are
  included on all such copies and derivative works.  However, this
  document itself may not be modified in any way, such as by removing
  the copyright notice or references to the Internet Society or other
  Internet organizations, except as needed for the purpose of
  developing Internet standards in which case the procedures for
  copyrights defined in the Internet Standards process must be
  followed, or as required to translate it into languages other than
  English.

  The limited permissions granted above are perpetual and will not be
  revoked by the Internet Society or its successors or assigns.

  This document and the information contained herein is provided on an
  "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
  TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
  BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
  HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
  MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
























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