/usr/lib/python3/dist-packages/mpd/asyncio.py is in python3-mpd 1.0.0-1.
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Interaction happens over the mpd.asyncio.MPDClient class, whose connect and
command methods are coroutines.
Some commands (eg. listall) additionally support the asynchronous iteration
(aiter, `async for`) interface; using it allows the library user to obtain
items of result as soon as they arrive.
The .idle() method works differently here: It is an asynchronous iterator that
produces a list of changed subsystems whenever a new one is available. The
MPDClient object automatically switches in and out of idle mode depending on
which subsystems there is currently interest in.
Command lists are currently not supported.
This module requires Python 3.5.2 or later to run.
"""
import asyncio
from functools import partial
from mpd.base import HELLO_PREFIX, ERROR_PREFIX, SUCCESS
from mpd.base import MPDClientBase
from mpd.base import MPDClient as SyncMPDClient
from mpd.base import ProtocolError, ConnectionError, CommandError
from mpd.base import mpd_command_provider
class BaseCommandResult(asyncio.Future):
"""A future that carries its command/args/callback with it for the
convenience of passing it around to the command queue."""
def __init__(self, command, args, callback):
super().__init__()
self._command = command
self._args = args
self._callback = callback
class CommandResult(BaseCommandResult):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self.__spooled_lines = []
def _feed_line(self, line):
"""Put the given line into the callback machinery, and set the result on a None line."""
if line is None:
self.set_result(self._callback(self.__spooled_lines))
else:
self.__spooled_lines.append(line)
def _feed_error(self, error):
self.set_exception(error)
class CommandResultIterable(BaseCommandResult):
"""Variant of CommandResult where the underlying callback is an
asynchronous` generator, and can thus interpret lines as they come along.
The result can be used with the aiter interface (`async for`). If it is
still used as a future instead, it eventually results in a list.
Commands used with this CommandResult must use their passed lines not like
an iterable (as in the synchronous implementation), but as a asyncio.Queue.
Furthermore, they must check whether the queue elements are exceptions, and
raise them.
"""
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self.__spooled_lines = asyncio.Queue()
def _feed_line(self, line):
self.__spooled_lines.put_nowait(line)
_feed_error = _feed_line
def __await__(self):
asyncio.Task(self.__feed_future())
return super().__await__()
__iter__ = __await__ # for 'yield from' style invocation
async def __feed_future(self):
result = []
async for r in self:
result.append(r)
self.set_result(result)
def __aiter__(self):
if self.done():
raise RuntimeError("Command result is already being consumed")
return self._callback(self.__spooled_lines).__aiter__()
@mpd_command_provider
class MPDClient(MPDClientBase):
__run_task = None # doubles as indicator for being connected
#: When in idle, this is a Future on which incoming commands should set a
#: result. (This works around asyncio.Queue not having a .peek() coroutine)
__command_enqueued = None
#: Seconds after a command's completion to send idle. Setting this too high
# causes "blind spots" in the client's view of the server, setting it too
# low sends needless idle/noidle after commands in quick succession.
IMMEDIATE_COMMAND_TIMEOUT = 0.1
async def connect(self, host, port=6600, loop=None):
self.__loop = loop
if '/' in host:
r, w = await asyncio.open_unix_connection(path, loop=loop)
else:
r, w = await asyncio.open_connection(host, port, loop=loop)
self.__rfile, self.__wfile = r, w
self.__commandqueue = asyncio.Queue(loop=loop)
self.__idle_results = asyncio.Queue(loop=loop) #: a queue of CommandResult("idle") futures
self.__idle_consumers = [] #: list of (subsystem-list, callbacks) tuples
try:
helloline = await asyncio.wait_for(self.__readline(), timeout=5)
except asyncio.TimeoutError:
self.disconnect()
raise ConnectionError("No response from server while reading MPD hello")
# FIXME should be reusable w/o reaching in
SyncMPDClient._hello(self, helloline)
self.__run_task = asyncio.Task(self.__run())
self.__idle_task = asyncio.Task(self.__distribute_idle_results())
def disconnect(self):
if self.__run_task is not None: # is None eg. when connection fails in .connect()
self.__run_task.cancel()
if self.__idle_task is not None:
self.__idle_task.cancel()
self.__rfile = self.__wfile = None
self.__run_task = self.__idle_task = None
self.__commandqueue = self.__command_enqueued = None
self.__idle_results = self.__idle_consumers = None
def _get_idle_interests(self):
"""Accumulate a set of interests from the current __idle_consumers.
Returns the union of their subscribed subjects, [] if at least one of
them is the empty catch-all set, or None if there are no interests at
all."""
if not self.__idle_consumers:
return None
if any(len(s) == 0 for (s, c) in self.__idle_consumers):
return []
return set.union(*(set(s) for (s, c) in self.__idle_consumers))
def _nudge_idle(self):
"""If the main task is currently idling, make it leave idle and process
the next command (if one is present) or just restart idle"""
if self.__command_enqueued is not None and not self.__command_enqueued.done():
self.__command_enqueued.set_result(None)
async def __run(self):
result = None
try:
while True:
try:
result = await asyncio.wait_for(
self.__commandqueue.get(),
timeout=self.IMMEDIATE_COMMAND_TIMEOUT,
loop=self.__loop,
)
except asyncio.TimeoutError:
# The cancellation of the __commandqueue.get() that happens
# in this case is intended, and is just what asyncio.Queue
# suggests for "get with timeout".
subsystems = self._get_idle_interests()
if subsystems is None:
# The presumably most quiet subsystem -- in this case,
# idle is only used to keep the connection alive.
subsystems = ["database"]
result = CommandResult("idle", subsystems, self._parse_list)
self.__idle_results.put_nowait(result)
self.__command_enqueued = asyncio.Future()
self._write_command(result._command, result._args)
while True:
try:
if self.__command_enqueued is not None:
# We're in idle mode.
line_future = asyncio.shield(self.__read_output_line())
await asyncio.wait([line_future, self.__command_enqueued],
return_when=asyncio.FIRST_COMPLETED)
if self.__command_enqueued.done():
self._write_command("noidle")
self.__command_enqueued = None
l = await line_future
else:
l = await self.__read_output_line()
except CommandError as e:
result._feed_error(e)
break
result._feed_line(l)
if l is None:
break
result = None
except Exception as e:
# Prevent the destruction of the pending task in the shutdown
# function -- it's just shutting down by itself.
self.__run_task = None
self.disconnect()
if result is not None:
result._feed_error(e)
return
else:
# Typically this is a bug in mpd.asyncio.
raise
async def __distribute_idle_results(self):
# An exception flying out of here probably means a connection
# interruption during idle. This will just show like any other
# unhandled task exception and that's probably the best we can do.
while True:
result = await self.__idle_results.get()
idle_changes = list(await result)
if not idle_changes:
continue
for subsystems, callback in self.__idle_consumers:
if not subsystems or any(s in subsystems for s in idle_changes):
callback(idle_changes)
# helper methods
async def __readline(self):
"""Wrapper around .__rfile.readline that handles encoding"""
data = await self.__rfile.readline()
try:
return data.decode('utf8')
except UnicodeDecodeError:
self.disconnect()
raise ProtocolError("Invalid UTF8 received")
def __write(self, text):
"""Wrapper around .__wfile.write that handles encoding."""
self.__wfile.write(text.encode('utf8'))
# copied and subtly modifiedstuff from base
# This is just a wrapper for the below.
def _write_line(self, text):
self.__write(text + "\n")
# FIXME This code should be shareable.
_write_command = SyncMPDClient._write_command
async def __read_output_line(self):
"""Kind of like SyncMPDClient._read_line"""
line = await self.__readline()
if not line.endswith("\n"):
raise ConnectionError("Connection lost while reading line")
line = line.rstrip("\n")
if line.startswith(ERROR_PREFIX):
error = line[len(ERROR_PREFIX):].strip()
raise CommandError(error)
if line == SUCCESS:
return None
return line
# async def _parse_objects_direct(self, lines, delimiters=[]):
# obj = {}
# while True:
# line = await lines.get()
# if isinstance(line, BaseException):
# raise line
# if line is None:
# break
# key, value = self._parse_pair(line, separator=": ")
# key = key.lower()
# if obj:
# if key in delimiters:
# yield obj
# obj = {}
# elif key in obj:
# if not isinstance(obj[key], list):
# obj[key] = [obj[key], value]
# else:
# obj[key].append(value)
# continue
# obj[key] = value
# if obj:
# yield obj
def _parse_objects_direct(self, lines, delimiters=[]):
# This is a workaround implementing the above comment on Python 3.5. It
# is recommended that the commented-out code be used for reasoning, and
# that changes are applied there and only copied over to this
# implementation.
outerself = self
class WrappedLoop:
def __init__(self):
self.obj = {}
self.exhausted = False
def __aiter__(self):
return self
async def __anext__(self):
while True:
if self.exhausted:
raise StopAsyncIteration()
line = await lines.get()
if isinstance(line, BaseException):
raise line
if line is None:
self.exhausted = True
if self.obj:
return self.obj
continue
key, value = outerself._parse_pair(line, separator=": ")
key = key.lower()
if self.obj:
if key in delimiters:
oldobj = self.obj
self.obj = {key: value}
return oldobj
elif key in self.obj:
if not isinstance(self.obj[key], list):
self.obj[key] = [self.obj[key], value]
else:
self.obj[key].append(value)
continue
self.obj[key] = value
return WrappedLoop()
# command provider interface
@classmethod
def add_command(cls, name, callback):
command_class = CommandResultIterable if callback.mpd_commands_direct else CommandResult
if hasattr(cls, name):
# Idle and noidle are explicitly implemented, skipping them.
return
def f(self, *args):
result = command_class(name, args, partial(callback, self))
if self.__run_task is None:
raise ConnectionError("Can not send command to disconnected client")
self.__commandqueue.put_nowait(result)
self._nudge_idle()
return result
escaped_name = name.replace(" ", "_")
f.__name__ = escaped_name
setattr(cls, escaped_name, f)
# commands that just work differently
# async def idle(self, subsystems=()):
# interests_before = self._get_idle_interests()
# changes = asyncio.Queue()
# try:
# entry = (subsystems, changes.put_nowait)
# self.__idle_consumers.append(entry)
# if self._get_idle_interests != interests_before:
# self._nudge_idle()
# while True:
# yield await changes.get()
# finally:
# self.__idle_consumers.remove(entry)
def idle(self, subsystems=()):
# This is a desugared workaround for python 3.5.
# Please consider the above block authoritative and this a workaround,
# and only apply changes here once they're incorporated there.
def final():
self.__idle_consumers.remove(entry)
class IdleAIter:
def __aiter__(self):
return self
def __anext__(self):
return changes.get()
def __del__(self):
final()
interests_before = self._get_idle_interests()
changes = asyncio.Queue()
entry = (subsystems, changes.put_nowait)
self.__idle_consumers.append(entry)
if self._get_idle_interests != interests_before:
self._nudge_idle()
return IdleAIter()
def noidle(self):
raise AttributeError("noidle is not supported / required in mpd.asyncio")
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