+.. SPDX-FileCopyrightText: 2018-2021 kaliko <kaliko@azylum.org>
+.. SPDX-License-Identifier: GPL-3.0-or-later
+
Using the client library
=========================
See the `MPD protocol documentation`_ for more details.
+.. _environment_variables:
+
+Environment variables
+---------------------
+
+The client honors the following environment variables:
+
+ * ``MPD_HOST`` MPD host (:abbr:`FQDN (fully qualified domain name)`, socket path or abstract socket) and password.
+
+ | To define a password set MPD_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, ie with :abbr:`FQDN (fully qualified domain name)` defined host
+ * ``MPD_TIMEOUT`` timeout for connecting to MPD and waiting for MPD’s response in seconds
+ * ``XDG_RUNTIME_DIR`` path to look for potential socket: ``${XDG_RUNTIME_DIR}/mpd/socket``
+
+.. _default_settings:
+
+Default settings
+----------------
+
+ * If ``MPD_HOST`` is not set, then look for a socket in ``${XDG_RUNTIME_DIR}/mpd/socket``
+ * If there is no socket use ``localhost``
+ * If ``MPD_PORT`` is not set, then use ``6600``
+ * If ``MPD_TIMEOUT`` is not set, then uses :py:obj:`musicpd.CONNECTION_TIMEOUT`
+
+
+Context manager
+---------------
+
+Calling MPDClient in a context manager :py:obj:`musicpd.MPDClient.connect` is
+transparently called with :ref:`default setting<default_settings>` (use
+:ref:`environment variables<environment_variables>` to override defaults).
+Leaving the context manager :py:obj:`musicpd.MPDClient.disconnect` is called.
+
+.. code-block:: python
+
+ import os
+ os.environ['MPD_HOST'] = 'mpdhost'
+ with MPDClient() as c:
+ c.status()
+ c.next()
+
Command lists
-------------
----------------------
Each command have a *send\_<CMD>* and a *fetch\_<CMD>* variant, which allows to
-send a MPD command and then fetch the result later.
+send a MPD command and then fetch the result later (non-blocking call).
This is useful for the idle command:
.. code-block:: python
>>> gobject.io_add_watch(client, gobject.IO_IN, callback)
>>> gobject.MainLoop().run()
+See also use of :ref:`socket timeout<socket_timeout>` with idle command.
+
Fetching binary content (cover art)
-----------------------------------
Refer to `MPD protocol documentation`_ for the meaning of `binary`, `size` and `data`.
+.. _socket_timeout:
+
+Socket timeout
+--------------
+
+.. note::
+ When the timeout is reached it raises a :py:obj:`socket.timeout` exception. An :py:obj:`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
+:py:obj:`musicpd.CONNECTION_TIMEOUT` at module level and
+:py:obj:`musicpd.MPDClient.mpd_timeout` in MPDClient instances . However it
+is possible to set socket timeout for all command setting
+:py:obj:`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``:
+
+.. code-block:: python
+
+ 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 after ``select_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).
+
+
.. _MPD protocol documentation: http://www.musicpd.org/doc/protocol/
+.. vim: spell spelllang=en
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