Using the client library¶
Introduction¶
The client library can be used as follows:
client = musicpd.MPDClient() # create client object
client.connect() # use MPD_HOST/MPD_PORT if set else
# test ${XDG_RUNTIME_DIR}/mpd/socket for existence
# fallback to localhost:6600
# connect support host/port argument as well
print(client.mpd_version) # print the MPD protocol version
client.setvol('42') # sets the volume
client.disconnect() # disconnect from the server
The MPD command protocol exchanges line-based text records. The client emits a command with optional arguments. In the example above the client sends a setvol command with the string argument 42.
MPD commands are exposed as musicpd.MPDClient
methods. Methods
arguments are python strings. Some commands are composed of more than one word
(ie “tagtypes [disable|enable|all]”), for these use a snake case style to
access the method. Then “tagtypes enable” command is called with
“tagtypes_enable”.
Remember MPD protocol is text based, then all MPD command arguments are UTF-8 strings. In the example above, an integer can be used as argument for the setvol command, but it is then evaluated as a string when the command is written to the socket. To avoid confusion use regular string instead of relying on object string representation.
musicpd.MPDClient
methods returns different kinds of objects
depending on the command. Could be None
, a single object as a
str
or a dict
, a list of dict
.
Then musicpd.MPDClient
methods signatures are not hard coded
within this module since the protocol is handled on the server side. Please
refer to the protocol and MPD commands in MPD protocol documentation to
learn how to call commands and what kind of arguments they expect.
Some examples are provided for the most common cases, see Examples.
For a list of currently supported commands in this python module see Available commands.
Environment variables¶
musicpd.MPDClient
honors the following environment variables:
- MPD_HOST¶
MPD host (FQDN, IP, socket path or abstract socket) and password.
To define a password setMPD_HOST
to “password@host” (password only “password@”)For abstract socket use “@” as prefix : “@socket” and then with a password “pass@@socket”Regular unix socket are set with an absolute path: “/run/mpd/socket”
- MPD_PORT¶
MPD port, relevant for TCP socket only
- MPD_TIMEOUT¶
socket timeout when connecting to MPD and waiting for MPD’s response (in seconds)
- XDG_RUNTIME_DIR¶
path to look for potential socket
Default settings¶
- Default host:
use
MPD_HOST
environment variable if set, extract password if present,else use
XDG_RUNTIME_DIR
to looks for an existing file in${XDG_RUNTIME_DIR}/mpd/socket
,XDG_RUNTIME_DIR
defaults to/run
if not set.else set host to
localhost
- Default port:
use
MPD_PORT
environment variable if setelse use
6600
- Default timeout:
use
MPD_TIMEOUT
if setelse use
musicpd.CONNECTION_TIMEOUT
Context manager¶
Calling MPDClient in a context manager musicpd.MPDClient.connect
is
transparently called with default setting (use
environment variables to override defaults).
Leaving the context manager musicpd.MPDClient.disconnect
is called.
import os
os.environ['MPD_HOST'] = 'mpdhost'
with MPDClient() as c:
c.status()
c.next()
Command lists¶
Command lists are also supported using command_list_ok_begin() and command_list_end() :
client.command_list_ok_begin() # start a command list
client.update() # insert the update command into the list
client.status() # insert the status command into the list
results = client.command_list_end() # results will be a list with the results
Ranges¶
Some commands (e.g. delete) allow specifying a range in the form “START:END” (cf. MPD protocol documentation for more details).
Possible ranges are: “START:END”, “START:” and “:” :
Instead of giving the plain string as “START:END”, you can provide a tuple
as (START,END). The module is then ensuring the format is correct and raises an musicpd.CommandError
exception otherwise. Empty start or end can be specified as en empty string ''
or None
.
# An intelligent clear
# clears played track in the queue, currentsong included
pos = client.currentsong().get('pos', 0)
# the range object accepts str, no need to convert to int
client.delete((0, pos))
# missing end interpreted as highest value possible, pay attention still need a tuple.
client.delete((pos,)) # purge queue from current to the end
A notable case is the rangeid command allowing an empty range specified
as a single colon as argument (i.e. sending just ":"
):
# sending "rangeid :" to clear the range, play everything
client.rangeid(()) # send an empty tuple
Empty start in range (i.e. “:END”) are not possible and will raise a CommandError.
Note
Remember the use of a tuple is optional. Range can still be specified as a plain string "START:END"
.
Iterators¶
Commands may also return iterators instead of lists if iterate is set to True:
client.iterate = True
for song in client.playlistinfo():
print song['file']
Idle prefixed commands¶
Each command have a send_<CMD> and a fetch_<CMD> variant, which allows to send a MPD command and then fetch the result later (non-blocking call). This is useful for the idle command:
>>> client.send_idle()
# do something else or use function like select()
# http://docs.python.org/howto/sockets.html#non-blocking-sockets
# ex. select([client], [], [])
>>> events = client.fetch_idle()
# more complex use for example, with glib/gobject:
>>> def callback(source, condition):
>>> changes = client.fetch_idle()
>>> print changes
>>> return False # removes the IO watcher
>>> client.send_idle()
>>> gobject.io_add_watch(client, gobject.IO_IN, callback)
>>> gobject.MainLoop().run()
See also use of socket timeout with idle command.
Fetching binary content (cover art)¶
Fetching album covers is possible with albumart, here is an example:
>>> cli = musicpd.MPDClient()
>>> cli.connect()
>>> track = "Steve Reich/1978-Music for 18 Musicians"
>>> aart = cli.albumart(track, 0)
>>> received = int(aart.get('binary'))
>>> size = int(aart.get('size'))
>>> with open('/tmp/cover', 'wb') as cover:
>>> # aart = {'size': 42, 'binary': 2051, data: bytes(...)}
>>> cover.write(aart.get('data'))
>>> while received < size:
>>> aart = cli.albumart(track, received)
>>> cover.write(aart.get('data'))
>>> received += int(aart.get('binary'))
>>> if received != size:
>>> print('something went wrong', file=sys.stderr)
>>> cli.disconnect()
A musicpd.CommandError
is raised if the album does not expose a cover.
You can also use readpicture command to fetch embedded picture:
>>> cli = musicpd.MPDClient()
>>> cli.connect()
>>> track = 'muse/Amon Tobin/2011-ISAM/01-Amon Tobin - Journeyman.mp3'
>>> rpict = cli.readpicture(track, 0)
>>> if not rpict:
>>> print('No embedded picture found', file=sys.stderr)
>>> sys.exit(1)
>>> size = int(rpict['size'])
>>> done = int(rpict['binary'])
>>> with open('/tmp/cover', 'wb') as cover:
>>> cover.write(rpict['data'])
>>> while size > done:
>>> rpict = cli.readpicture(track, done)
>>> done += int(rpict['binary'])
>>> print(f'writing {rpict["binary"]}, done {100*done/size:03.0f}%')
>>> cover.write(rpict['data'])
>>> cli.disconnect()
Refer to MPD protocol documentation for the meaning of binary, size and data.
Socket timeout¶
Note
When the timeout is reached it raises a socket.timeout
exception. An OSError
subclass.
A timeout is used for the initial MPD connection (connect
command), then
the socket is put in blocking mode with no timeout. Its value is set in
musicpd.CONNECTION_TIMEOUT
at module level and
musicpd.MPDClient.mpd_timeout
in MPDClient instances . However it
is possible to set socket timeout for all command setting
musicpd.MPDClient.socket_timeout
attribute to a value in second.
Having socket_timeout
enabled can help to detect “half-open connection”.
For instance loosing connectivity without the server explicitly closing the
connection (switching network interface ethernet/wifi, router down, etc…).
Nota bene: with socket_timeout
enabled each command sent to MPD might
timeout. A couple of seconds should be enough for commands to complete except
for the special case of idle
command which by definition “ waits until
there is a noteworthy change in one or more of MPD’s subsystems.” (cf. MPD
protocol documentation).
Here is a solution to use idle
command with socket_timeout
:
import musicpd
import select
import socket
cli = musicpd.MPDClient()
try:
cli.socket_timeout = 10 # seconds
select_timeout = 5 # second
cli.connect()
while True:
cli.send_idle() # use send_ API to avoid blocking on read
_read, _, _ = select.select([cli], [], [], select_timeout)
if _read: # tries to read response
ret = cli.fetch_idle()
print(', '.join(ret)) # Do something
else: # cancels idle
cli.noidle()
except socket.timeout as err:
print(f'{err} (timeout {cli.socket_timeout})')
except (OSError, musicpd.MPDError) as err:
print(f'{err!r}')
if cli._sock is not None:
cli.disconnect()
except KeyboardInterrupt:
pass
Some explanations:
First launch a non blocking
idle
command. This call do not wait for a response to avoid socket timeout waiting for an MPD event.
select
waits for something to read on the socket (the idle response in this case), returns afterselect_timeout
seconds anyway.In case there is something to read read it using
fetch_idle
Nothing to read, cancel idle with
noidle
All three commands in the while loop (send_idle, fetch_idle, noidle) are not triggering a socket timeout unless the connection is actually lost (actually it could also be that MPD took too much time to answer, but MPD taking more than a couple of seconds for these commands should never occur).
Exceptions¶
The connect
method raises
ConnectionError
only (an MPDError
exception) but then, calling other MPD commands, the module can raise
MPDError
or an OSError
depending on the error and
where it occurs.
Then using musicpd module both musicpd.MPDError
and OSError
exceptions families are expected, see examples for a
way to deal with this.