NAME

Net::Async::MPD - A non-blocking interface to MPD

SYNOPSIS

  use Net::Async::MPD;

  my $mpd = Net::Async::MPD->new(
    host => 'localhost',
    auto_connect => 1,
  );

  my @subsystems = qw( player mixer database );

  # Register a listener
  foreach my $subsystem (@subsystems) {
    $mpd->on( $subsystem => sub {
      my ($self) = @_;
      print "$subsystem has changed\n";

      # Stop listening if mixer changes
      $mpd->noidle if $subsystem eq 'mixer';
    });
  }

  # Send a command
  my $stats = $mpd->send( 'stats' );

  # Or in blocking mode
  my $status = $mpd->send( 'status' )->get;

  # Which is the same as
  $status = $mpd->get( 'status' );

  print 'Server is in ', $status->{state}, " state\n";
  print 'Server has ', $stats->get->{albums}, " albums in the database\n";

  # Put the client in looping idle mode
  my $idle = $mpd->idle( @subsystems );

  # Set the emitter in motion, until the next call to noidle
  $idle->get;

DESCRIPTION

Net::Async::MPD provides a non-blocking interface to an MPD server.

Command Lists

MPD supports sending command lists to make it easier to perform a series of steps as a single one. No command is executed until all commands in the list have been sent, and then the server returns the result for all of them together. See the MPD documentation for more information.

Net::Async::MPD fully supports sending command lists, and makes it easy to structure the results received from MPD, or not to if the user so desires. See the "send" method for more information.

Error Handling

Most operations in this module return Future objects, and to keep things consistent, any errors that are encountered during processing will result in those futures being failed or canceled as appropriate.

This module also makes use of the events in Role::EventEmitter, which provides it's own method for error handling: the error event. Normally, if a class does that role, it is expected that users will register some listener to the error event to handle failures. However, since errors are alredy being handled by the Futures (one woudl hope), this distribution registers a dummy listener to the error event, and turns into one that is mostly useful for debugging and monitoring.

Of course, the author cannot really stop overly zealous users from unsubscribing the error dummy listener, but they do so at their own risk.

Server Responses

MPD normally returns results as a flat list of response lines. Net::Async::MPD tries to make it easier to provide some structure to these responses by providing pre-set parser subroutines for each command. Although the default parser will be fine in most cases, it is possible to override this with a custom parser, or to disable the parsing entirely to get the raw lines from the server. For information on how to override the parser, see the documentation for the "send" method.

By default, the results of each command are parsed independently, and passed to the Future returned by the corresponding call to "send". This is true regardless of whether those commands were sent as part of a list or not.

This means that, by default, the Future that represents a given call to "send" will receive the results of as many commands as were originall sent.

This might not be desireable when eg. sending multiple commands whose results should be aggregated. In those cases, it is possible to flatten the list by passing a false value to the list option to "send" or "get".

This means that when calling

    ($stats, $status) = $mpd->get(
      { list => 1 }, # This is the default
      [ 'stats', 'status' ]
    );

$stats and $status will each have a hash reference with the results of their respective commands; while when calling

    $combined_list = $mpd->get( { list => 0 }, [
      [ search => artist => '"Tom Waits"'   ],
      [ search => artist => '"David Bowie"' ],
    ]);

$combined_list will hold an array reference with the combined results of both search commands.

ATTRIBUTES

host

The host to connect to. Defaults to localhost.

port

The port to connect to. Defaults to 6600.

password

The password to use to connect to the server. Defaults to undefined, which means to use no password.

auto_connect

If set to true, the constructor will block until the connection to the MPD server has been established. Defaults to false.

METHODS

connect

Starts a connection to an MPD server, and returns a Future that will be done when the connection is complete (or failed if the connection couldn't be established). If the client is already connected, this function will return an immediately completed Future.

send
    $future = $mpd->send( 'status' );
    $future = $mpd->send( { parser => 'none' }, 'stats' );

    $future = $mpd->send( search => artist => '"Tom Waits"' );

    # Note the dumb string quoting
    $future = $mpd->send( { list => 0 }, [
      [ search => artist => '"Tom Waits"'   ],
      [ search => artist => '"David Bowie"' ],
    ]);

    $future = $mpd->send( \%options, 'stats', sub { ... } );

Asynchronously sends a command to an MPD server, and returns a Future. For information on what the value of this Future will be, please see the "Server Responses" section.

This method can be called in a number of different ways:

  • If called with a single string, then that string will be sent as the command.

  • If called with a list, the list will be joined with spaces and sent as the command.

  • If called with an array reference, then the value of each of item in that array will be processed as above (with array references instead of plain lists).

If sending multiple commands in one request, the command_list... commands can be left out and they will be automatically provided for you.

An optional subroutine reference passed as the last argument will be set as the the on_ready of the Future, which will fire when there is a response from the server.

A hash reference with additional options can be passed as the first argument. Valid keys to use are:

list

If set to false, results of command lists will be parsed as a single result. When set to true, each command in a command list is aprsed independently. See "Server Responses" for more details.

Defaults to true. This value is ignored when not sending a command list.

parser

Specify the parser to use for the entire response. Parser labels are MPD commands. If the requested parser is not found, the fallback none will be used.

Alternatively, if the value itself is a code reference, then that will be called as

    $parser->( \@response_lines, \@command_names );

Where each element in @response_lines is a reference to the list of lines received after completing the corresponding element in @command_names.

When setting list to false, @response_lines will have a single value, regardless of how many commands were sent.

For ease of use, underscores in the final command name will be removed before sending to the server (unless the command name requires them).

get

Send a command in a blocking way. Internally calls send and immediately waits for the response.

idle

Put the client in idle loop. This sends the idle command and registers an internal listener that will put the client back in idle mode after each server response.

If called with a list of subsystem names, then the client will only listen to those subsystems. Otherwise, it will listen to all of them.

If you are using this module for an event-based application (see below), this will configure the client to fire the events at the appropriate times.

Returns a Future. Waiting on this future will block until the next call to noidle (see below).

noidle

Cancel the client's idle mode. Sends an undefined value to the future created by idle and breaks the internal idle loop.

version

Returns the version number of the protocol spoken by the server, and not the version of the daemon.

As this is provided by the server, this is undef until after a connection has been established with the connect method, or by setting auto_connect to true in the constructor.

EVENTS

Net::Async::MPD does the Role::EventEmitter role, and inherits all the methods defined therein. Please refer to that module's documentation for information on how to register subscribers to the different events.

Additional methods

until

In addition to methods like on and once, provided by Role::EventEmitter,this module also exposes an until method, which registers a listener until a certain condition is true, and then deregisters it.

The method is called with two subroutine references. The first is unsubscribed as a regular listener, and the second is called only then the first one returns a true value. At that point, the entire set is unsubscribed.

Event descriptions

After calling idle, the client will be in idle mode, which means that any changes to the specified subsystemswill trigger a signal. When the client receives this signal, it will fire an event named as the subsystem that fired it.

The event will be fired with the client as the first argument, and the response from the server as the second argument. This can safely be ignored, since the server response will normally just hold the name of the subsystem that changed, which you already know.

The existing events are the following, as defined by the MPD documentation.

database

The song database has been changed after update.

udpate

A database update has started or finished. If the database was modified during the update, the database event is also emitted.

stored_playlist

A stored playlist has been modified, renamed, created or deleted.

playlist

The current playlist has been modified.

player

The player has been started stopped or seeked.

mixer

The volume has been changed.

output

An audio output has been added, removed or modified (e.g. renamed, enabled or disabled)

options

Options like repeat, random, crossfade, replay gain.

partition

A partition was added, removed or changed.

sticker

The sticket database has been modified.

subscription

A client has subscribed or unsubscribed from a channel.

message

A message was received on a channel this client is subscribed to.

Other events

close

The connection to the server has been closed. This event is not part of the MPD protocol, and is fired by Net::Async::MPD directly.

error

The error event is inherited from Role::EventEmitter. However, unlike stated in that module's documentation, and as explained in "Error Handling", users are not required to register to this event for safe execution.

SEE ALSO

  • Net::MPD

    A lightweight blocking MPD library. Has fewer dependencies than this one, but it does not curently support command lists. I took the idea of allowing for underscores in command names from this module.

  • AnyEvent::Net::MPD

    The original version of this module, which used AnyEvent. The interface on both of these modules is virtually identical.

  • Audio::MPD

    The first MPD library on CPAN. This one also blocks and is based on Moose. However, it seems to be unmaintained at the moment.

  • Dancer::Plugin::MPD

    A Dancer plugin to connect to MPD. Haven't really tried it, since I haven't used Dancer...

  • POE::Component::Client::MPD

    A POE component to connect to MPD. This uses Audio::MPD in the background.

AUTHOR

  • José Joaquín Atria <jjatria@cpan.org>

COPYRIGHT AND LICENSE

This software is copyright (c) 2017 by José Joaquín Atria.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.