CDDB Server Protocol
--------------------

By Steve Scherf and Ti Kan
(Protocol level 5 & 6 specification by freedb developer team)


Applies to cddbd 1.5.2
$Id: CDDBPROTO,v 1.10.2.2 2006/04/14 14:45:06 joerg78 Exp $


Notation:
-> : client to server
<- : server to client

terminating marker: `.' character in the beginning of a line


Server response code (three digit code):

First digit:
1xx	Informative message
2xx	Command OK
3xx	Command OK so far, continue
4xx	Command OK, but cannot be performed for some specified reasons
5xx	Command unimplemented, incorrect, or program error
 
Second digit:
x0x	Ready for further commands
x1x	More server-to-client output follows (until terminating marker)
x2x	More client-to-server input follows (until terminating marker)
x3x	Connection will close

Third digit:
xx[0-9]	Command-specific code

Note: "*" means, that the command is only for administrative use and requires
special access permissions, that normal users don't have.


CDDB Protocol Level 1:
----------------------

Server sign-on banner:
----------------------
<- code hostname CDDBP server version ready at date

    code:
	200	OK, read/write allowed
	201	OK, read only
	432	No connections allowed: permission denied
	433	No connections allowed: X users allowed, Y currently active
	434	No connections allowed: system load too high
    hostname:
	Server host name.  Example: xyz.fubar.com
    version:
	Version number of server software.  Example: v1.0PL0
    date:
	Current date and time.  Example: Wed Mar 13 00:41:34 1996


Initial client-server handshake:
--------------------------------
Note: This handshake must occur before other cddb commands
      are accepted by the server.

Client command:
-> cddb hello username hostname clientname version

    username:
	Login name of user.  Example: johndoe
    hostname:
	Host name of client.  Example: abc.fubar.com
    clientname:
	The name of the connecting client.  Example: xmcd, cda, EasyCD,
	et cetera. Do not use the name of another client which already
	exists.
    version:
	Version number of client software.  Example: v1.0PL0

Server response:
<- code hello and welcome username@hostname running clientname version

    code:
	200	Handshake successful
	431	Handshake not successful, closing connection
	402	Already shook hands


List the genre categories:
--------------------------
Client command:
-> cddb lscat

Server response:
<- code Okay category list follows (until terminating marker)
<- category
<- category
<- (more categories...)
<- .

    code:
	210	Okay category list follows 
    category:
	CD category.  Example: rock


Query database for matching entries:
------------------------------------
Client command:
-> cddb query discid ntrks off1 off2 ... nsecs

    discid:
	CD disc ID number.  Example: f50a3b13
    ntrks:
	Total number of tracks on CD.
    off1, off2, ...:
	Frame offset of the starting location of each track.
    nsecs:
	Total playing length of CD in seconds.

Server response:
<- code categ discid dtitle
	or
<- code close matches found
<- categ discid dtitle
<- categ discid dtitle
<- (more matches...)
<- .

    code:
	200	Found exact match
	211	Found inexact matches, list follows (until terminating marker)
	202	No match found
	403	Database entry is corrupt
	409	No handshake
    categ:
	CD category.  Example: rock
    discid:
	CD disc ID number of the found entry.  Example: f50a3b13
    dtitle:
	The Disc Artist and Disc Title (The DTITLE line).  For example:
	Pink Floyd / The Dark Side of the Moon


Read entry from database:
-------------------------
Client command:
-> cddb read categ discid

    categ:
	CD category.  Example: rock
    discid:
	CD disc ID number.  Example: f50a3b13

Server response:
<- code categ discid
<- # xmcd 2.0 CD database file
<- # ...
<- (CDDB data...)
<- .
	or
<- code categ discid No such CD entry in database.

    code:
	210	OK, CDDB database entry follows (until terminating marker)
	401	Specified CDDB entry not found.
	402	Server error.
	403	Database entry is corrupt.
	409	No handshake.
    categ:
	CD category.  Example: rock
    discid:
	CD disc ID number.  Example: f50a3b13


* Delete entry from database:
-----------------------------
Client command:
-> cddb unlink categ discid

    categ:
	CD category.  Example: rock
    discid:
	CD disc ID number.  Example: f50a3b13

Server response:
<- code and message

    code and message:
	200 OK, file has been deleted.
	401 Permission denied.
	402 File access failed.
	501 Invalid category: categ.
    categ:
	CD category.  Example: rock


* Write entry to database:
--------------------------
Client command:
-> cddb write categ discid

    categ:
	CD category.  Example: rock
    discid:
	CD disc ID number.  Example: f50a3b13

Server response:
<- code and message

    code and message:
	320	OK, input CDDB data (until terminating marker)
	401	Permission denied.
	402	Server file system full/file access failed.
	409	No handshake.

Client data:
-> # xmcd 2.0 CD database file
-> # ...
-> (CDDB data)
-> .

Server response:
<- code message

    code:
	200	CDDB entry accepted
	501	Entry rejected: reason for rejection.
    message:
	Message string to indicate write status:
	CDDB entry accepted, or CDDB entry rejected.


Discid calculation:
------------------
Client command:
-> discid ntrks off_1 off_2 ... off_n nsecs
	
	ntrks:  
		total number of tracks on CD.
        off_X:  
		frame offset of track X.
        nsecs:  
		total playing length of the CD in seconds.

Server response:
<- code Disc ID is discid

	code:
		200 Calculated disc ID properly
		500 Command Syntax error
	discid:
		CD disc ID number calculated from the given arguments.


* Get a server system file:
---------------------------
Client command:
-> get file

    file:
	filename of the file to get
	
Server response:

<- code message

	or

<- code OK, (filename) follows (until terminating `.')
<- (file content)
<- .

    code and message:
	210 OK, %s follows (until terminating `.')
	401 Permission denied.
	402 File access failed.
	402 File not found.
	

Help information:
-----------------
Client command:
-> help
	or
-> help cmd

    cmd:
	CDDB command.  Example: quit

	or

-> help cmd subcmd

    cmd:
	CDDB command.  Example: cddb
    subcmd:
	CDDB command argument.  Example: query

Server response:
<- code Help information follows
<- (help data ...)
<- .
	or
<- code no help information available

    code:
	210	OK, help information follows (until terminating marker)
	401	No help information available


* Log statistics:
-----------------
Client command:
-> log [[-l lines] [start date [end date]] | [day [days]] | [get]]

    lines:
	The maximum number of lines to print for each data list in the
	log statistics.
    start date:
	The date after which statistics should be calculated. Date is
	of the format: hh[mm[ss[MM[DD[[CC]YY]]]]]

	E.g.:	201200053196 for 8:12 PM on May 31, 1996.
		20120005312096 for 8:12 PM on May 31, 2096.
		080530 for today at at 8:15 and 30 seconds.

	If the century ("CC") is omitted, a reasonable guess is made. If
	this argument is omitted, all messages are considered.
    end date:
	The date after which statistics should not be calculated. If
	omitted, the end date is assumed to be the current date.
    day:
	The string "day". This solitary argument will cause a log search
	of messages generated within the last day.
    days:
	A positive numerical argument which modifies the number of days'
        messages to searh. If this argument is left out, the default is 1.
    get:
	The string "get". This solitary argument will cause the server
	to send the contents of the log file.

Server response:
<- code Log summary follows
<- (log stats)
<- .
	or
<- code Log follows
<- (log stats)
<- .

    code:
	210	OK, log summary follows (until terminating marker)
	211	OK, log follows (until terminating marker)
	401	Permission denied
	402	No log information available
	501	Invalid start/end date


Message of the day:
------------------
Client command:
-> motd

Server response:
<- code Last modified: date MOTD follows (until terminating marker)
<- (message text)
<- .

    code:
	210	Last modified: 05/31/96 06:31:14 MOTD follows (until terminating marker)
	401	No message of the day available
    date:
	The date the text of the message of the day was modified. The date
	appears in the following format:

		05/31/96 06:31:14

	This value may be used by client software as a message timestamp
	for purposes of determining if it has already been displayed. This
	format was chosen because it is more easily parsed than the standard
	ctime() format.


Server protocol level:
----------------------
Client command:
-> proto [level]

    level:
	The (numerical) protocol level to set the server to.

Server response:
<- code CDDB protocol level: current cur_level, supported supported_level
	or
<- code OK, protocol version now: cur_level

    code:
	200	CDDB protocol level: current cur_level, supported supp_level
	201	OK, protocol version now: cur_level
	501	Illegal protocol level.
	502	Protocol level already cur_level.
    cur_level:
	The current protocol level at which the server is running.
    supported_level:
	The maximum supported protocol level.


* Put a server system file:
---------------------------
Client command:
-> put file

    file:
	sites or motd

Server response: 
<- code message

    code and message:
	320 OK, input file data (terminate with `.')
	401 Permission denied.
	402 File access failed.
	402 Not a regular file.

Client data:
-> (file data of the file, that shall be written)
-> .

Server response

<- code message

    code and message:
	200 Put successful.
	402 File access failed.
	501 Input too long.


Close connection to server:
---------------------------
Client command:
-> quit

Server response:
<- code hostname message

    code and message:
	230 Closing connection.  Goodbye.
	530 error, closing connection.
    hostname:
	Server host name.  Example: xyz.fubar.com


Server sites:
--------------
Client command:
-> sites

Server response:
<- code OK, site information follows (until terminating `.')
<- (data)
<- .

    code:
	210	Ok, site information follows
	401	No site information available.

    The data format is as follows:
	site port latitude longitude description

    The fields are as follows:
	site:
	    The Internet address of the remote site.
	port:
	    The port at which the server resides on that site.
	latitude:
	    The latitude of the server site. The format is as follows:
		CDDD.MM
	    Where "C" is the compass direction (N, S), "DDD" is the
	    degrees, and "MM" is the minutes.
	longitude:
	    The longitude of the server site. Format is as above, except
	    the compass direction must be one of (E, W).
	description:
	    A short description of the geographical location of the site.

    Example:
	us.freedb.org 8880 N037.21 W121.55 San Jose, CA USA


Server status:
--------------
Client command:
-> stat

Server response:
<- code OK, status information follows (until terminating `.')
<- (data)
<- .

    code:
	210	Ok, status information follows

    The possible data is as follows:
	current proto: <current_level>
	    An integer representing the server's current operating protocol
	    level.
	max proto:     <max_level>
	    The maximum supported protocol level.
	gets:          <yes | no>
	    Whether or not the client is allowed to get log information,
	    according to the string "yes" or "no".
	updates:       <yes | no>
	    Whether or not the client is allowed to initiate a database
	    update, according to the string "yes" or "no".
	posting:       <yes | no>
	    Whether or not the client is allowed to post new entries,
	    according to the string "yes" or "no".
	quotes:        <yes | no>
	    Whether or not quoted arguments are enabled, according to
	    the string "yes" or "no".
	current users: <num_users>
	    The number of users currently connected to the server.
	max users:     <num_max_users>
	    The number of users that can concurrently connect to the server.
	strip ext:	<yes | no>
	    Whether or not extended data is stripped by the server before
	    presented to the user.
	Database entries: <num_db_entries>
	    The total number of entries in the database.
	Database entries by category:
	    This field is followed by a list of catgories and the number
	    of entries in that category. Each entry is of the following
	    format:

		<white space>catgory: <num_db_entries>

	    The list of entries is terminated by the first line that does
	    not begin with white space.

	* Pending file transmissions:
	    This field is followed by a list of sites that are fed new
	    database entries at periodic intervals, and the number of
	    entries that have yet to be transmitted to that site.
	    Each entry is of the following format:

		<white space>site: <num_db_entries>

	    The list of entries is terminated by the first line that does
	    not begin with white space.

	This list may grow as needed, so clients must expect possible
	unrecognizable data. Also, additional fields may be added to
	the currently existing lines, although no existing fields will
	be removed or change position.
	

* Database update:
----------------
Client command:
-> update

Server response:
<- code Updating the database.
	or
<- code Permission denied.
	or
<- code Unable to update the database.

    code:
	200 Updating the database.
	401 Permission denied.
	402 Unable to update the database.


* Perform user validation:
--------------------------
Client command:
-> validate

Server response:
<- 503 Validation not required.

or

<- 320 OK, input validation string, salt=saltvalue (terminate with newline)

Client data:
-> validation string

Server response:

-> code message

    code and message:
	200 Validation successful.
	501 Incorrect validation string length.
	502 Invalid validation string.


Server version:
---------------
Client command:
-> ver

Server response:
<- code servername version copyright
	or
<- code Version information follows

    code:
	200	Version information.
	211	OK, version information follows (until terminating marker)
    version:
	Server version.  Example: v1.5PL0
    copyright:
	Copyright string.  Example: Copyright (c) 1996-2001 Steve Scherf et al.


* Server users:
---------------
Client command:
-> whom

Server response:
<- code message

    code and message:
	210	OK, user list follows (until terminating marker)
	401	No user information available.


General errors:
---------------

Server response:
<- code error
    code:
	402	Server error.
	408	CGI environment error.
	500	Command syntax error, command unknown, command unimplemented.
	530	Server error, server timeout.


Reserved errors:
----------------

The following error codes are reserved, and will never be returned as a
response to a CDDB protocol command. They are intended to be used internally
by clients that have a need for generating pseudo-responses.

	600-699


CDDB Protocol Level 2:
----------------------

In all respects, protocol level 2 is the same as level 1, with the exceptions
listed below.

Arguments to commands may be surrounded by double quotes. All characters
within the quotes, including white space, are included in the argument. All
white space is replaced by the `_' (2Dh) character by the server. White space
is defined as ` ' (20h) and `^I' (control-I, or 09h).

Arguments containing quotes that should not be interpreted with the special
meaning described above should be escaped with a preceding backslash character,
or '\' (5Ch). If an actual backslash appears in an argument, it should be
escaped with a preceding backslash. In both cases, the preceding backslash
will be removed from the input before being interpreted.


CDDB Protocol Level 3:
----------------------

Protocol level 3 is the same as level 2, with the exception listed below.

The output of the "sites" command has changed to meet the folowing description:

    The data format is as follows:
	site protocol port address latitude longitude description

    The fields are as follows:
	site:
	    The Internet address of the remote site.
	protocol:
	    The transfer protocol used to access the site.
	port:
	    The port at which the server resides on that site.
	address:
	    Any additional addressing information needed to access the
	    server. For example, for HTTP protocol servers, this would be
	    the path to the CDDB server CGI script. This field will be
	    "-" if no additional addressing information is needed.
	latitude:
	    The latitude of the server site. The format is as follows:
		CDDD.MM
	    Where "C" is the compass direction (N, S), "DDD" is the
	    degrees, and "MM" is the minutes.
	longitude:
	    The longitude of the server site. Format is as above, except
	    the compass direction must be one of (E, W).
	description:
	    A short description of the geographical location of the site.

    Example:
	us.freedb.org cddbp 8880 - N037.21 W121.55 San Jose, CA USA
	us.freedb.org http 80 /~cddb/cddb.cgi N037.21 W121.55 San Jose, CA USA

Note that a site may appear once for each type of protocol it supports for
accessing the server.


CDDB Protocol Level 4:
----------------------

Protocol level 4 is the same as level 3, with the exception listed below.

The output of the "cddb query" command may result in multiple exact matches.
A new response code, 210, has been added to indicate that more than one
exact match has been found.

Server response:
----------------
<- code exact matches found
<- categ discid dtitle
<- categ discid dtitle
<- (more matches...)
<- .

    code:
        210 Found exact matches, list follows (until terminating marker)


CDDB Protocol Level 5:
----------------------

Protocol level 5 is the same as level 4, with the following exception:

The database entries returned when issuing the "cddb read" command now also 
contain DYEAR and DGENRE fields (between the DTITLE and the TTITLE's).
For more info on the new database entry fields take a look at the
database format specification


CDDB Protocol Level 6:
----------------------

Protocol level 6 is the same as level 5 except that the character set
is now UTF-8 instead of ISO-8859-1. Note that UTF-8 is an extension of
US-ASCII, just like ISO-8859-1 is an extension of US-ASCII, so there
is no difference between levels 5 and 6 as far as 7-bit ASCII data is
concerned.

Clients can convert data between UTF-8 and the user's preferred
character set using the iconv program and library function which are
provided by glibc-2.2 or by the portable library libiconv. (They are
also provided by the C library on some non-glibc systems, but often in
a buggy or incompatible form.) For example, to convert data to UTF-8
from the character set of the current locale in a shell script use
"iconv -t utf-8 < in > out".

For more information about Unicode and UTF-8 see:

    ftp://ftp.ilog.fr/pub/Users/haible/utf8/Unicode-HOWTO.html
    http://www.cl.cam.ac.uk/~mgk25/unicode.html


Addendum A: Proper use of CDDBP:
--------------------------------

There are a few guidelines that must be followed in order to make proper use
of CDDBP:

- When handshaking with the server via the "cddb hello" command, the client
  must specify its own name and version, not that of some other client (such
  as xmcd).

- Before performing a "cddb read", the client program MUST perform a
  "cddb query". Failure to do so may result in the client program receiving
  incorrect data from the server. Also, without performing a query, the
  client program will not benefit from close matches in the event of the
  lack of an exact match in the database.


Addendum B: CDDBP under HTTP:
-----------------------------

Accessing a server as a CGI script is done in much the same way as through
direct interaction. The command set is identical, though the method of
communication is through CDDBP commands encapsulated in the HTTP protocol.
The only limitation is that a single command may be executed per connection,
since HTTP is not truly interactive. For the server to be accessed in this
way, it must reside on the target host at a known URL which is accessible by
the host HTTP server. The client program must connect to the HTTP server on
the target host and issue an HTTP command with the appropriate CDDBP command
encapsulated within.

Commands may be submitted to servers in CGI mode using either the "GET" or
"POST" HTTP commands. Both methods are supported, and there is no real
difference between how both are to be used other than the syntactical
difference between the two methods. The "POST" method may provide the ability
to issue longer commands, though, depending on the architecture of the system
on which the server resides.

The server command must be sent as part of the "Request-URL" in the case
of the "GET" method, and as the "Entity-Body" in the case of the "POST"
method. In both cases, the command must be of the following form:

cmd=server+command&hello=joe+my.host.com+clientname+version&proto=6

Where the text following the "cmd=" represents the CDDBP command to be
executed, the text following the "hello=" represents the arguments to
the "cddb hello" command that is implied by this operation, and the
text following the "proto=" represents the argument to the "proto" command
that is implied by this operation.

The "+" characters in the input represent spaces, and will be translated
by the server before performing the request. Special characters may be
represented by the sequence "%XX" where "XX" is a two-digit hex number
corresponding to the ASCII (ISO-8859-1) sequence of that character. The
"&" characters denote separations between the command, hello and proto
arguments. Newlines and carriage returns must not appear anywhere in the
string except at the end.

All CDDBP commands are supported under HTTP, except for "cddb hello",
"cddb write", "proto", "put", "validate" and "quit".

For example, should user "joe" on system "my.host.com" be running xmcd 2.1,
a read request for his currenly playing CD might look like this:

cmd=cddb+read+rock+12345678&hello=joe+my.host.com+xmcd+2.1&proto=3

The server will perform the implied "proto" and "cddb hello" commands,
and then perform the requested "cddb read" command.

Server response to the command is encapsulated in the HTTP server response,
and appears in the "Entity-Body" exactly as it would appear using the CDDBP
protocol. Note that the HTTP response "Entity-Header" is not guaranteed to
contain a "Content-Length" field, so clients should be prepared to accept
variable length input. This is no different from operation under CDDBP. The
header will always contain a Mime "Content-Type" field which describes the
body of data as "text/plain".

For more detailed information on HTTP and Mime, see RFC 1945 and RFC 1521.


Addendum C: CDDBP under SMTP:
-----------------------------

The use of e-mail mode (SMTP) commands is simple. A special subject line
lets the server know that the e-mail contains a command, and somewhere in the
body there should be a HTTP-style server command; the server will execute
only one such commands per e-mail.

The subject for e-mail commands should look like this:

Subject: cddb #command arbitrary_string

The "arbitrary_string" should be some randomly-chosen string. The server
will include this string in the subject of the response. The rest of the
subject should appear literally as it does here.

Somewhere in the body of the e-mail should be exactly one server command. For
example:

cmd=motd&hello=joe+my.host.com+xmcd_via_email+v1.0&proto=6

As you might have noticed, this command is exactly the same as a HTTP-mode
CDDBP command. The command response will be mailed to the sender. Upon
successful completion of an e-mail command request (even if the command
itself was not successful), the reply will contain a subject which looks
like this:

Subject cddb #response ok arbitrary_string

Should the server be unable to process the e-mail command for some reason, the
subject will look like this:

Subject cddb #response failed arbitrary_string

In both cases, the "arbitrary_string" is the same as the one specified in the
initial command e-mail.