Provided by: libnet-async-mpd-perl_0.005-2_all 
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
<https://musicpd.org/doc/protocol/command_lists.html> 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 desirable 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 parsed 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). So
$client->send( 'current_song' );
is entirely equivalent to
$client->send( 'currentsong' );
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 subscribed as a
regular listener, and the second is called only when 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 subsystems will trigger a signal. When the client receives this signal, it will
fire an event named like 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 sticker 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
• AnyEvent::Net::MPD
A previous attempt at writing this distribution, based on AnyEvent. Although the
design is largely the same, it is not as fully featured or as well tested as this one.
• Net::MPD
A lightweight blocking MPD library. Has fewer dependencies than this one, but it does
not currently 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) 2017-2018 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.