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CDDB.pm - a high-level interface to cddb protocol servers

• NAME
• SYNOPSIS
• DESCRIPTION
• PUBLIC METHODS
• PRIVATE METHODS
• EXAMPLES
• BUGS
• CONTACT AND COPYRIGHT

NAME

CDDB.pm - a high-level interface to cddb protocol servers (freedb and CDDB)

SYNOPSIS

  use CDDB;

  ### Connect to the cddbp server.
  my $cddbp = new CDDB( Host  => 'freedb.freedb.org', # default
                        Port  => 8880,                # default
                        Login => $login_id,           # defaults to %ENV's
                      ) or die $!;

  ### Retrieve known genres.
  my @genres = $cddbp->get_genres();

  ### Calculate cddbp ID based on MSF info.
  my @toc = ( '1    0  2 37',           # track, CD-i MSF (space-delimited)
              '999  1 38 17',           # lead-out track MSF
              '1000 0  0 Error!',       # error track (don't include if ok)
            );
  my ($cddbp_id,      # used for further cddbp queries
      $track_numbers, # padded with 0's (for convenience)
      $track_lengths, # length of each track, in MM:SS format
      $track_offsets, # absolute offsets (used for further cddbp queries)
      $total_seconds  # total play time, in seconds (for cddbp queries)
     ) = $cddbp->calculate_id(@toc);

  ### Query discs based on cddbp ID and other information.
  my @discs = $cddbp->get_discs($cddbp_id, $track_offsets, $total_seconds);
  foreach my $disc (@discs) {
    my ($genre, $cddbp_id, $title) = @$disc;
  }

  ### Query disc details (usually done with get_discs() information).
  my $disc_info     = $cddbp->get_disc_details($genre, $cddbp_id);
  my $disc_time     = $disc_info->{'disc length'};
  my $disc_id       = $disc_info->{discid};
  my $disc_title    = $disc_info->{dtitle};
  my @track_offsets = @{$disc_info->{offsets}};
  my @track_seconds = @{$disc_info->{seconds}};
  my @track_titles  = @{$disc_info->{ttitles}};
  # other information may be returned... explore!

  ### Submit a disc via e-mail. (Requires MailTools)

  die "can't submit a disc (no mail modules; see README)"
    unless $cddbp->can_submit_disc();

  # These are useful for prompting the user to fix defaults:
  print "I will send mail through: ", $cddbp->get_mail_host(), "\n";
  print "I assume your e-mail address is: ", $cddbp->get_mail_address(), "\n";

  # Actually submit a disc record.
  $cddbp->submit_disc
    ( Genre       => 'classical',
      Id          => 'b811a20c',
      Artist      => 'Various',
      DiscTitle   => 'Cartoon Classics',
      Offsets     => $disc_info->{offsets},   # array reference
      TrackTitles => $disc_info->{ttitles},   # array reference
      From        => 'login@host.domain.etc', # will try to determine
    );

DESCRIPTION

CDDB protocol (cddbp) servers provide compact disc information for programs that need it. This allows such programs to display disc and track titles automatically, and it provides extended information like liner notes and lyrics.

This module provides a high-level Perl interface to cddbp servers. With it, a Perl program can identify and possibly gather details about a CD based on its ``table of contents'' (the disc's track times and offsets).

Disc details have been useful for generating CD catalogs, naming mp3 files, printing CD liners, or even just playing discs in an automated jukebox.

PUBLIC METHODS

new PARAMETERS

Creates a high-level interface to a cddbp server, returning a handle to it. The handle is not a filehandle. It is an object. The new() constructor provides defaults for just about everything, but everything is overrideable if the defaults aren't appropriate.

The interface will not actually connect to a cddbp server until it's used, and a single cddbp interface may actually make several connections (to possibly several servers) over the course of its use.

The new() constructor accepts several parameters, all of which have reasonable defaults.

Host and Port describe the cddbp server to connect to. These default to 'freedb.freedb.org' and 8880, which is a multiplexor for all the other freedb servers.

Protocol_Version sets the cddbp version to use. CDDB.pm will not connect to servers that don't support the version specified here. The requested protocol version defaults to 1 if omitted.

Login is the login ID you want to advertise to the cddbp server. It defaults to the login ID your computer assigns you, if that can be determined. The default login ID is determined by the presence of a LOGNAME or USER environment variable, or by the getpwuid() function. On Windows systems, it defaults to ``win32usr'' if no default method can be found and no Login parameter is set.

Submit_Address is the e-mail address where new disc submissions go. This defaults to 'freedb-submit@freedb.org'.

Client_Name and Client_Version describe the client software used to connect to the cddbp server. They default to 'CDDB.pm' and CDDB.pm's version number. If developers change this, please consult freedb's web site for a list of client names already in use.

Debug enables verbose operational information on STDERR when set to true. It's normally not needed, but it can help explain why a program is failing. If someone finds a reproduceable bug, the Debug output and a test program would be a big help towards having it fixed.

get_genres

Takes no parameters. Returns a list of genres known by the cddbp server, or undef if there is a problem retrieving them.

calculate_id TOC

The cddb protocol defines an ID as a hash of track lengths and the number of tracks, with an added checksum. The most basic information required to calculate this is the CD table of contents (the CD-i track offsets, in ``MSF'' [Minutes, Seconds, Frames] format).

Note however that there is no standard way to acquire this information from a CD-ROM device. Therefore this module does not try to read the TOC itself. Instead, developers must combine CDDB.pm with a CD library which works with their system. The AudioCD suite of modules is recommended: it has system specific code for MacOS, Linux and FreeBSD. CDDB.pm's author has used external programs like dagrab to fetch the offsets. Actual CDs aren't always necessary: the author has heard of people generating TOC information from mp3 file lengths.

That said, see parse_cdinfo() for a routine to parse ``cdinfo'' output into a table of contents list suitable for calculate_id().

calculate_id() accepts TOC information as a list of strings. Each string contains four fields, separated by whitespace:

offset 0: the track number

Track numbers start with 1 and run sequentially through the number of tracks on a disc. Note: data tracks count on hybrid audio/data CDs.

CDDB.pm understands two special track numbers. Track 999 holds the lead-out information, which is required by the cddb protocol. Track 1000 holds information about errors which have occurred while physically reading the disc.

offset 1: the track start time, minutes field

Tracks are often addressed on audio CDs using ``MSF'' offsets. This stands for Minutes, Seconds, and Frames (fractions of a second). The combination pinpoints the exact disc frame where a song starts.

Field 1 contains the M part of MSF. It is ignored for error tracks, but it still must contain a number. Zero is suggested.

offset 2: the track start time, seconds field

This field contains the S part of MSF. It is ignored for error tracks, but it still must contain a number. Zero is suggested.

offset 3: the track start time, frames field

This field contains the F part of MSF. For error tracks, it contains a description of the error.

Example track file. Note: the comments should not appear in the file.

     1   0  2 37  # track 1 starts at 00:02 and 37 frames
     2   1 38 17  # track 2 starts at 01:38 and 17 frames
     3  11 57 30  # track 3 starts at 11:57 and 30 frames
     ...
   999  75 16  5  # leadout starts at 75:16 and  5 frames

Track 1000 should not be present if everything is okay:

  1000   0  0  Error reading TOC: no disc in drive

In scalar context, calculate_id() returns just the cddbp ID. In a list context, it returns an array containing the following values:

  ($cddbp_id, $track_numbers, $track_lengths, $track_offsets, $total_seconds)
    = $cddbp->calculate_id(@toc);

  print( "cddbp ID      = $cddbp_id\n",        # b811a20c
         "track numbers = @$track_numbers\n",  # 001 002 003 ...
         "track lengths = @$track_lengths\n",  # 01:36 10:19 04:29 ...
         "track offsets = @$track_offsets\n",  # 187 7367 53805 ...
         "total seconds = $total_seconds\n",   # 4514
       );

CDDBP_ID

The 0th returned value is the hashed cddbp ID, required for any queries or submissions involving this disc.

TRACK_NUMBERS

The 1st returned value is a reference to a list of track numbers, one for each track (excluding the lead-out), padded to three characters with leading zeroes. These values are provided for convenience, but they are not required by cddbp servers.

TRACK_LENGTHS

The 2nd returned value is a reference to a list of track lengths, one for each track (excluding the lead-out), in HH:MM format. These values are returned as a convenience. They are not required by cddbp servers.

TRACK_OFFSETS

The 3rd returned value is a reference to a list of absolute track offsets, in frames. They are calculated from the MSF values, and they are required by get_discs() and submit_disc().

TOTAL_SECONDS

The 4th and final value is the total playing time for the CD, in seconds. The get_discs() function needs it.

get_discs CDDBP_ID, TRACK_OFFSETS, TOTAL_SECONDS

get_discs() asks the cddbp server for a summary of all the CDs matching a given cddbp ID, track offsets, and total playing time. These values can be retrieved from calculade_id().

  my @id_info       = $cddbp->calculate_id(@toc);
  my $cddbp_id      = $id_info->[0];
  my $track_offsets = $id_info->[3];
  my $total_seconds = $id_info->[4];

get_discs() returns an array of matching discs, each of which is represented by an array reference. It returns an empty array if the query succeeded but did not match, and it returns undef on error.

  my @discs = $cddbp->get_discs( $cddbp_id, $track_offsets, $total_seconds );
  foreach my $disc (@discs) {
    my ($disc_genre, $disc_id, $disc_title) = @$disc;
    print( "disc id    = $disc_id\n",
           "disc genre = $disc_genre\n",
           "disc title = $disc_title\n",
         );
  }

DISC_GENRE is the genre this disc falls into, as determined by whoever submitted or last edited the disc. The genre is required when requesting a disc's details. See get_genres() for how to retrieve a list of cddbp genres.

CDDBP_ID is the cddbp ID of this disc. Cddbp servers perform fuzzy matches, returning near misses as well as direct hits on a cddbp ID, so knowing the exact ID for a disc is important when submitting changes or requesting a particular near-miss' details.

DISC_TITLE is the disc's title, which may help a human to pick the correct disc out of several close mathches.

get_discs_by_toc TOC

This function acts as a macro, combining calculate_id() and get_discs() calls into one function. It takes the same parameters as calculate_id(), and it returns the same information as get_discs().

get_discs_by_query QUERY_STRING

Fetch discs by a pre-built cddbp query string. Some disc querying programs report this string, and get_discs_by_query() is a convenient way to use that.

Cddb protocol query strings look like:

  cddb query $cddbp_id $track_count @offsets $total_seconds

get_disc_details DISC_GENRE, CDDBP_ID

This function fetches a disc's detailed information from a cddbp server. It takes two parameters: the DISC_GENRE and the CDDP_ID. These parameters usually come from a call to get_discs().

The disc's details are returned in a reference to a fairly complex hash. It includes information normally stored in comments. The most common entries in this hash include:

  $disc_details = get_disc_details( $disc_genre, $cddbp_id );

$disc_details->{``disc length''}

The disc length is commonly stored in the form ``### seconds'', where ### is the disc's total playing time in seconds. It may hold other time formats.

$disc_details->{discid}

This is a rehash (get it?) of the cddbp ID. It should match the CDDBP_ID given to get_disc_details().

$disc_details->{dtitle}

This is the disc's title. I do not know whether it will match the one returned by get_discs().

$disc_details->{offsets}

This is a reference to a list of absolute disc track offsets, similar to the TRACK_OFFSETS returned by calculate_id().

$disc_details->{seconds}

This is a reference to a list of track length, in seconds.

$disc_details->{ttitles}

This is a reference to a list of track titles. These are the droids you are looking for.

$disc_details->{``processed by''}

This is a comment field identifying the name and version of the cddbp server which accepted and entered the disc record into the database.

$disc_details->{revision}

This is the disc record's version number, used as a sanity check (semaphore?) to prevent simultaneous revisions. Revisions start at 0 for new submissions and are incremented for every correction. It is the responsibility of the submitter (be it a person or a program using CDDB.pm) to provide a correct revision number.

$disc_details->{``submitted via''}

This is the name and version of the software that submitted this cddbp record. The main intention is to identify records that are submitted by broken software so they can be purged or corrected.

$disc_details->{xmcd_record}

The xmcd_record field contains a copy of the entire unprocessed cddbp response that generated all the other fields.

can_submit_disc

Returns true or false, depending on whether CDDB.pm has enough dependent modules to submit discs. If it returns false, you are missing Mail::Internet, Mail::Header, or MIME::QuotedPrint.

get_mail_address

Returns what CDDB.pm thinks your e-mail address is, or what it was last set to. It was added to fetch the default e-mail address so users can see it and have an opportunity to correct it.

  my $mail_from = $cddb->get_mail_address();
  print "New e-mail address (or blank to keep <$mail_from>): ";
  my $new_mail_from = <STDIN>;
  $new_mail_from =~ s/^\s+//;
  $new_mail_from =~ s/\s+$//;
  $new_mail_from =~ s/\s+/ /g;
  $mail_from = $new_mail_from if length $new_mail_from;

  $cddbp->submit_disc( ...,
                       From => $mail_from,
                     );

get_mail_host

Returns what CDDB.pm thinks your SMTP host is, or what it was last set to. It was added to fetch the default e-mail transfer host so users can see it and have an opportunity to correct it.

  my $mail_host = $cddb->get_mail_host();
  print "New e-mail host (or blank to keep <$mail_host>): ";
  my $new_mail_host = <STDIN>;
  $new_mail_host =~ s/^\s+//;
  $new_mail_host =~ s/\s+$//;
  $new_mail_host =~ s/\s+/ /g;
  $mail_host = $new_mail_host if length $new_mail_host;

  $cddbp->submit_disc( ...,
                       Host => $mail_host,
                     );

parse_cdinfo CDINFO_FILE

Generates a table of contents suitable for calculate_id() based on the output of a program called ``cdinfo''. CDINFO_FILE may either be a text file, or it may be the cdinfo program itself.

  my @toc = parse_cdinfo("cdinfo.txt"); # read cdinfo.txt
  my @toc = parse_cdinfo("cdinfo|");    # run cdinfo directly

The table of contents can be passed directly to calculate_id().

submit_disc DISC_DETAILS

submit_disc() submits a disc record to a cddbp server. Currently it only uses e-mail, although it will try different ways to send that. It returns true or false depending on whether it was able to send the submission e-mail.

The rest of CDDB.pm will work without the ability to submit discs. While cddbp submissions are relatively rare, most CD collections will have one or two discs not present in the system. Please submit new discs to the system: the amazing number of existing discs got there because others submitted them before you needed them.

submit_disc() takes six required parameters and two optional ones. The parameters are named, like hash elements, and can appear in any order.

Genre => DISC_GENRE

This is the disc's genre. It must be one of the genres that the server knows. See get_genres().

Id => CDDBP_ID

This is the cddbp ID that identifies the disc. It should come from calculate_id() if this is a new submission, or from get_disc_details() if this is a revision.

Artist => DISC_ARTIST

This is the disc's artist, a freeform text field describing the party responsible for the album. It will need to be entered from the disc's notes for new submissions, or it can come from get_disc_details() on subsequent revisions.

DiscTitle => DISC_TITLE

This is the disc's title, a freeform text field describing the album. It must be entered from the disc's notes for new submissions. It can come from get_disc_details() on subsequent revisions.

Offsets => TRACK_OFFSETS

This is a reference to an array of absolute track offsets, as provided by calculate_id().

TrackTitles => TRACK_TITLES

This is a reference to an array of track titles, either entered by a human or provided by get_disc_details().

From => EMAIL_ADDRESS

This is the disc submitter's e-mail address. It's not required, and CDDB.pm will try to figure one out on its own if an address is omitted. It may be more reliable to provide your own, however.

The default return address may not be a deliverable one, especially if CDDB.pm is being used on a dial-up machine that isn't running its own MTA. If the current machine has its own MTA, problems still may occur if the machine's Internet address changes.

Host => SMTP_HOST

This is the SMTP host to contact when sending mail. It's not required, and CDDB.pm will try to figure one out on its own. It will look at the SMTPHOSTS environment variable is not defined, it will try 'mail' and 'localhost' before finally failing.

PRIVATE METHODS

Documented as being not documented.

EXAMPLES

Please see the cddb.t program in the t (tests) directory. It exercises every aspect of CDDB.pm, including submissions.

BUGS

There are no known bugs, but see the README for things that need to be done.

CONTACT AND COPYRIGHT

Copyright 1998-2002 Rocco Caputo. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

Rocco may be contacted at rcaputo@cpan.org.

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