@c This file is part of the GNU Dico manual.
@c Copyright (C) 2008--2021 Sergey Poznyakoff
@c This file is distributed under GFDL 1.1 or any later version
@c published by the Free Software Foundation.
  This appendix describes commands understood by Dico dictionary
server.  The examples provided follow the convention used in @acronym{RFC}
documents: a text sent by the server is prefixed with @samp{S}, whereas
a text sent by the client is prefixed with @samp{C}.
  
@menu
* Initial Reply::
* Standard Commands::
* Extended Commands::
@end menu

@node Initial Reply
@section Initial Reply
  When a connection is established, the server sends an @dfn{initial reply}
to the client.  This reply has the following format:

@smallexample
220 @var{hostname} @var{text} <@var{capabilities}> @var{msg-id}
@end smallexample

@noindent
Its parts and their meaning are described in the following table:

@table @var
@item hostname
The name of the host.  It is determined automatically, unless set
using @code{hostname} configuration file statement (@pxref{hostname
directive}).

@item text
Arbitrary text, as set via @code{initial-banner-text} configuration
statement (@pxref{General Settings, initial-banner-text}).

@item capabilities
A comma-separated list of server capabilities.  It is configured using
@code{capability} statement (@pxref{Capabilities}).

@item msg-id
A unique identifier similar to the format specified in
@uref{ftp://ftp.rfc-editor.org/in-notes/rfc822, RFC822}, except that
spaces and quoted pairs are not allowed within it.

This identifier will be used by the client when formulating the
authentication string used in the @code{AUTH} command (@pxref{AUTH}).
@end table

An example of initial reply follows:

@smallexample
220 Trurl.gnu.org.ua <auth.mime> <520.1212912026@@Trurl.gnu.org.ua>
@end smallexample

@node Standard Commands
@section Standard Commands
  The following are standard commands, defined in RFC2229.

@menu
* DEFINE::
* MATCH::
* SHOW::
* OPTION::
* AUTH::
* CLIENT::
* STATUS::
* HELP::
* QUIT::
@end menu

@node DEFINE
@subsection The DEFINE Command

The @code{DEFINE} command searches for definitions of a word.

@deffn Command DEFINE db word
Look up the word @var{word} in database @var{db}.  If @var{db} is
@samp{!}, then all the databases will be searched until the word is
found, and all matches in that database will be returned.  Similarly,
if @var{db} is @samp{*}, then all the databases will be searched and
all matches in all databases will be returned.  In these two cases,
the databases are searched in the same order as that returned by
@code{SHOW DB} command (@pxref{SHOW, SHOW DB}).

If the word was not found, response code 552 is returned.

If the word is found, a response code 150 is sent, followed by the
number of definitions found.  Then, for each definition a response
code 151 is returned, followed by the textual body of the definition.
In a 151 response, the first three space-delimited parameters give the
word looked for, the name and a short description of the database.
The latter two are the same as shown in the output from @code{SHOW DB}
command.

The textual body of each definition is terminated with a dot
(@samp{.}) on a line alone.  If any line in the definition begins with
a dot, it is duplicated to avoid confusion with body terminator.

After all of the definitions have been sent, a status code 250 is
sent.  If @code{timing} is set to @samp{true} in the configuration
file, this latter response also carries timing information.
@xref{Tuning}, for more information about timing output.

Possible responses from @code{DEFINE} command are:

@table @asis
@item 550 Invalid database, use SHOW DB for a list
@item 552 No match
@item 150 @var{n} definitions found: list follows
@item 151 @var{word} @var{database} @var{name}
@item 250 ok (optional timing information here)
@end table

Example transaction:

@smallexample
C: DEFINE eng-swa man
S: 150 1 definitions found: list follows
S: 151 "man" eng-swa "English-Swahili xFried/FreeDict Dictionary"
S: man  <n.>
S: 
S:    mwanamume
S:
S: .
S: 250 Command complete [d/m/c = 1/0/12 0.000r 0.000u 0.000s]
@end smallexample
@end deffn

@node MATCH
@subsection The MATCH Command

The @code{MATCH} command searches for word in the database index.
The searching algorithm is determined by @dfn{strategy}.  @xref{Strategies},
for a list of strategies offered by GNU Dico.

@deffn Command MATCH database strategy word
Match @var{word} in @var{database} using @var{strategy}.  As with
@code{DEFINE}, the @var{database} can be @samp{!} or @samp{*}
(@xref{DEFINE}, for a detailed description of these wildcards).

The @var{strategy} is either the name of a strategy to use, or
a dot (@samp{.}), meaning to use default strategy.  The default
strategy is set using @code{default-strategy} configuration file
statement (@pxref{General Settings, default-strategy}.  Its default
value is @samp{lev}, which means @samp{use Levenshtein algorithm}
(@pxref{Strategies}).

If no matches are found in any of the searched databases, then response
code 552 will be returned.     Otherwise, response code 152 will be
returned followed by a list of matched words, one per line, in the form:

@smallexample
@var{database} @var{word}
@end smallexample

Thus, prepending a @samp{DEFINE } to each such response, one obtains a
valid @code{DEFINE} command.

The textual body of the match list is terminated with a line
containing only a dot character.

Following the list, response code 250 is sent, which includes
timing information, if @code{timing} directive is set in the
configuration file (@pxref{Tuning}).

Possible responses:

@table @asis
@item 550 Invalid database, use SHOW DB for a list
@item 551 Invalid strategy, use SHOW STRAT for a list
@item 552 No match
@item 152 @var{n} matches found: list follows
@item 250 ok (optional timing information here)
@end table

Examples:

@smallexample
C: MATCH * . "weather"
S: 152 12 matches found: list follows
C: eng-afr "feather"
C: eng-afr "leather"
C: eng-afr "weather"
C: eng-deu "feather"
C: eng-deu "heather"
C: eng-deu "leather"
C: eng-deu "weather"
C: eng-deu "wether"
C: eng-deu "wheather"
C: devils "WEATHER"
S: .
S: 250 Command complete [d/m/c = 0/12/100677 0.489r 0.479u 0.007s]
@end smallexample
@end deffn

@node SHOW
@subsection The SHOW Command
  The @code{SHOW} command outputs various information about the server
and databases.

@deffn Command {SHOW DB}
@deffnx Command {SHOW DATABASES}
Display the list of currently accessible databases, one per line, in
the form:

@smallexample
@var{database} @var{description}
@end smallexample

The list is terminated with is a dot (@samp{.}) on a line alone.

Possible responses:

@table @asis
@item 110 @var{n} databases present
@item 554 No databases present
@end table
@end deffn

@deffn Command {SHOW STRAT}
@deffnx Command {SHOW STRATEGIES}
Display the list of currently supported search strategies, one per
line, in the form:

@smallexample
@var{strategy} @var{description}
@end smallexample

The list is terminated with is a dot (@samp{.}) on a line alone.

Possible responses:

@table @asis
@item 111 @var{n} strategies available
@item 555 No strategies available
@end table
@end deffn

@deffn Command {SHOW INFO} database
Displays the information about the specified database.  The
information is a free-form text and is suitable for display to the user
in the same manner as a definition.  The textual body of the response
is terminated with is a dot (@samp{.}) on a line alone.

Possible responses:
@table @asis
@item 550 Invalid database, use SHOW DB for a list
@item 112 database information follows
@end table

The textual body is retrieved from the @code{info} statement in the
configuration file (@pxref{Databases, info}), or, if it is not
specified, from the database itself, using @code{dico_db_info}
callback function (@pxref{dico_db_info}).  If neither source
returns anything, the string @samp{No information available.} is returned.
@end deffn

@deffn Command {SHOW SERVER}
Return a server-specific information.

Response:
@table @asis
@item 114 server information follows
@end table

The information follows, terminated with a dot on a line alone.

The textual body returned by the @code{SHOW SERVER} command consists
of two parts.  It begins with a line containing host name of the
server and, optionally an additional information about the daemon and
the system it runs on.  The exact look and amount of information in
this line is controlled by @code{show-sys-info} configuration
statement (@pxref{Security Settings, show-sys-info}).  This line is
followed by the text supplied with @code{server-info} configuration
statement (@pxref{General Settings, server-info}).
@end deffn

@node OPTION
@subsection The OPTION Command
  The @code{OPTION} command allows to request optional features
on the remote server.  Currently the only implemented subcommand is:

@deffn Command {OPTION MIME}
Requests that all text responses be prefaced by a @acronym{MIME} header
(@uref{ftp://ftp.rfc-editor.org/in-notes/rfc2045.txt, RFC2045})
followed by a single blank line.

After this command is issued, the server begins each textual response
with a @acronym{MIME} header.  This header consists of
@samp{Content-type} and @samp{Content-transfer-encoding} headers, as
supplied by the corresponding configuration file statements for this
database (@xref{Databases, content-type}, @pxref{Databases,
content-transfer-encoding}).  Any or both of these headers may be
missing.
@end deffn

@node AUTH
@subsection The AUTH Command
  The @code{AUTH} command allows client to authenticate itself to the
server.  Depending on the server configuration, authenticated users
may get access to more databases (@pxref{Database Visibility}) or more
detailed server information (@pxref{Security Settings, show-sys-info}).

@deffn Command AUTH username auth-string
Authenticate client to the server using a username and password.
The @var{auth-string} is computed as in the @acronym{APOP} protocol
(@uref{ftp://ftp.rfc-editor.org/in-notes/rfc1929.txt, RFC1939}.
Briefly, it is the MD5 checksum of the concatenation of the @var{msg-id}
(@pxref{Initial Reply}) and the @dfn{shared secret} that is
stored both on the server and client machines.  

@xref{Authentication}, for information on how to configure server for
authenticating clients.

This command is supported only if @samp{auth} capability is requested
in the configuration (@pxref{Capabilities, auth}).
@end deffn

@node CLIENT
@subsection The CLIENT Command

@deffn Command CLIENT info
Identify client to server.  The @var{info} argument contains a string
identifying the client program (e.g. its name and version number).
This information can then be used in logging (@pxref{Access Log, %C}).
@end deffn

@node STATUS
@subsection The STATUS Command

@deffn Command STATUS
Display cumulative timing information.  This command returns a
@samp{210} status code, followed by the timing information as
described in @ref{Tuning}, e.g.

@smallexample
C: STATUS
S: 210 [d/m/c = 28/1045/119856 21.180r 10.360u 1.040s]
@end smallexample
@end deffn

@node HELP
@subsection The HELP Command

@deffn Command HELP
  The @code{HELP} command provides a short summary of commands that
are understood by the server.  The response begins with a @samp{113}
code, followed by textual body defined in @code{help-text}
configuration file statement (@pxref{General Settings, help-text}),
which is terminated by a dot on a line by itself.  A @samp{250}
response code finishes the output.  For example:

@smallexample
113 help text follows
DEFINE database word         -- look up word in database
MATCH database strategy word -- match word in database 
SHOW DB                      -- list all accessible databases
SHOW DATABASES               -- list all accessible databases
SHOW STRAT                   -- list available matching strategies
SHOW STRATEGIES              -- list available matching strategies
SHOW INFO database           -- provide database information
SHOW SERVER                  -- provide site-specific information
CLIENT info                  -- identify client to server
STATUS                       -- display timing information
HELP                         -- display this help information
QUIT                         -- terminate connection
.
250 Ok
@end smallexample
@end deffn

@node QUIT
@subsection The QUIT Command

@deffn Command QUIT
Terminate connection.

This command returns a response code 221, optionally followed by
timing information (@pxref{Tuning}).
@end deffn

@node Extended Commands
@section Extended Commands
  In addition to the standard commands, the Dico server also offers a
set of experimental or extended commands.

@deffn Command XIDLE
This command displays the current inactivity timeout setting
(@pxref{inactivity-timeout}), and resets idle timer to 0.  The
timeout value is printed as the first word after a @samp{110} reply
code, e.g.:

@smallexample
C: XIDLE
S: 110 180 second(s)
@end smallexample

The value of @samp{0} means there are no timeout.
@end deffn

@deffn Command XVERSION
This command displays the daemon implementation and version number.
It becomes available only if @samp{xversion} capability was requested
in the configuration file (@pxref{Capabilities, xversion}).

@smallexample
C: XVERSION
S: 110 dicod (dico @value{VERSION})
@end smallexample
@end deffn

@deffn Command XLEV param
If @var{param} is the word @samp{tell}, displays the current value of
Levenshtein threshold.  If @var{param} is a positive integer value,
sets the Levenshtein threshold to this value.

This command becomes available only if @samp{xlev} capability was
requested in the configuration file (@pxref{Capabilities, xlev}).

@smallexample
C: xlev tell
S: 280 1
C: xlev 3
S: 250 ok - Levenshtein threshold set to 3
C: xlev tell
S: 280 3
@end smallexample
@end deffn

