cpython/Lib/asyncio/streams.py

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"""Stream-related things."""
__all__ = ['StreamReader', 'StreamWriter', 'StreamReaderProtocol',
'open_connection', 'start_server',
]
import collections
from . import events
from . import futures
from . import protocols
from . import tasks
_DEFAULT_LIMIT = 2**16
@tasks.coroutine
def open_connection(host=None, port=None, *,
loop=None, limit=_DEFAULT_LIMIT, **kwds):
"""A wrapper for create_connection() returning a (reader, writer) pair.
The reader returned is a StreamReader instance; the writer is a
StreamWriter.
The arguments are all the usual arguments to create_connection()
except protocol_factory; most common are positional host and port,
with various optional keyword arguments following.
Additional optional keyword arguments are loop (to set the event loop
instance to use) and limit (to set the buffer limit passed to the
StreamReader).
(If you want to customize the StreamReader and/or
StreamReaderProtocol classes, just copy the code -- there's
really nothing special here except some convenience.)
"""
if loop is None:
loop = events.get_event_loop()
reader = StreamReader(limit=limit, loop=loop)
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protocol = StreamReaderProtocol(reader, loop=loop)
transport, _ = yield from loop.create_connection(
lambda: protocol, host, port, **kwds)
writer = StreamWriter(transport, protocol, reader, loop)
return reader, writer
@tasks.coroutine
def start_server(client_connected_cb, host=None, port=None, *,
loop=None, limit=_DEFAULT_LIMIT, **kwds):
"""Start a socket server, call back for each client connected.
The first parameter, `client_connected_cb`, takes two parameters:
client_reader, client_writer. client_reader is a StreamReader
object, while client_writer is a StreamWriter object. This
parameter can either be a plain callback function or a coroutine;
if it is a coroutine, it will be automatically converted into a
Task.
The rest of the arguments are all the usual arguments to
loop.create_server() except protocol_factory; most common are
positional host and port, with various optional keyword arguments
following. The return value is the same as loop.create_server().
Additional optional keyword arguments are loop (to set the event loop
instance to use) and limit (to set the buffer limit passed to the
StreamReader).
The return value is the same as loop.create_server(), i.e. a
Server object which can be used to stop the service.
"""
if loop is None:
loop = events.get_event_loop()
def factory():
reader = StreamReader(limit=limit, loop=loop)
protocol = StreamReaderProtocol(reader, client_connected_cb,
loop=loop)
return protocol
return (yield from loop.create_server(factory, host, port, **kwds))
class StreamReaderProtocol(protocols.Protocol):
"""Trivial helper class to adapt between Protocol and StreamReader.
(This is a helper class instead of making StreamReader itself a
Protocol subclass, because the StreamReader has other potential
uses, and to prevent the user of the StreamReader to accidentally
call inappropriate methods of the protocol.)
"""
def __init__(self, stream_reader, client_connected_cb=None, loop=None):
self._stream_reader = stream_reader
self._stream_writer = None
self._drain_waiter = None
self._paused = False
self._client_connected_cb = client_connected_cb
self._loop = loop # May be None; we may never need it.
def connection_made(self, transport):
self._stream_reader.set_transport(transport)
if self._client_connected_cb is not None:
self._stream_writer = StreamWriter(transport, self,
self._stream_reader,
self._loop)
res = self._client_connected_cb(self._stream_reader,
self._stream_writer)
if tasks.iscoroutine(res):
tasks.Task(res, loop=self._loop)
def connection_lost(self, exc):
if exc is None:
self._stream_reader.feed_eof()
else:
self._stream_reader.set_exception(exc)
# Also wake up the writing side.
if self._paused:
waiter = self._drain_waiter
if waiter is not None:
self._drain_waiter = None
if not waiter.done():
if exc is None:
waiter.set_result(None)
else:
waiter.set_exception(exc)
def data_received(self, data):
self._stream_reader.feed_data(data)
def eof_received(self):
self._stream_reader.feed_eof()
def pause_writing(self):
assert not self._paused
self._paused = True
def resume_writing(self):
assert self._paused
self._paused = False
waiter = self._drain_waiter
if waiter is not None:
self._drain_waiter = None
if not waiter.done():
waiter.set_result(None)
class StreamWriter:
"""Wraps a Transport.
This exposes write(), writelines(), [can_]write_eof(),
get_extra_info() and close(). It adds drain() which returns an
optional Future on which you can wait for flow control. It also
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adds a transport property which references the Transport
directly.
"""
def __init__(self, transport, protocol, reader, loop):
self._transport = transport
self._protocol = protocol
self._reader = reader
self._loop = loop
@property
def transport(self):
return self._transport
def write(self, data):
self._transport.write(data)
def writelines(self, data):
self._transport.writelines(data)
def write_eof(self):
return self._transport.write_eof()
def can_write_eof(self):
return self._transport.can_write_eof()
def close(self):
return self._transport.close()
def get_extra_info(self, name, default=None):
return self._transport.get_extra_info(name, default)
def drain(self):
"""This method has an unusual return value.
The intended use is to write
w.write(data)
yield from w.drain()
When there's nothing to wait for, drain() returns (), and the
yield-from continues immediately. When the transport buffer
is full (the protocol is paused), drain() creates and returns
a Future and the yield-from will block until that Future is
completed, which will happen when the buffer is (partially)
drained and the protocol is resumed.
"""
if self._reader._exception is not None:
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raise self._reader._exception
if self._transport._conn_lost: # Uses private variable.
raise ConnectionResetError('Connection lost')
if not self._protocol._paused:
return ()
waiter = self._protocol._drain_waiter
assert waiter is None or waiter.cancelled()
waiter = futures.Future(loop=self._loop)
self._protocol._drain_waiter = waiter
return waiter
class StreamReader:
def __init__(self, limit=_DEFAULT_LIMIT, loop=None):
# The line length limit is a security feature;
# it also doubles as half the buffer limit.
self._limit = limit
if loop is None:
loop = events.get_event_loop()
self._loop = loop
# TODO: Use a bytearray for a buffer, like the transport.
self._buffer = collections.deque() # Deque of bytes objects.
self._byte_count = 0 # Bytes in buffer.
self._eof = False # Whether we're done.
self._waiter = None # A future.
self._exception = None
self._transport = None
self._paused = False
def exception(self):
return self._exception
def set_exception(self, exc):
self._exception = exc
waiter = self._waiter
if waiter is not None:
self._waiter = None
if not waiter.cancelled():
waiter.set_exception(exc)
def set_transport(self, transport):
assert self._transport is None, 'Transport already set'
self._transport = transport
def _maybe_resume_transport(self):
if self._paused and self._byte_count <= self._limit:
self._paused = False
self._transport.resume_reading()
def feed_eof(self):
self._eof = True
waiter = self._waiter
if waiter is not None:
self._waiter = None
if not waiter.cancelled():
waiter.set_result(True)
def feed_data(self, data):
if not data:
return
self._buffer.append(data)
self._byte_count += len(data)
waiter = self._waiter
if waiter is not None:
self._waiter = None
if not waiter.cancelled():
waiter.set_result(False)
if (self._transport is not None and
not self._paused and
self._byte_count > 2*self._limit):
try:
self._transport.pause_reading()
except NotImplementedError:
# The transport can't be paused.
# We'll just have to buffer all data.
# Forget the transport so we don't keep trying.
self._transport = None
else:
self._paused = True
@tasks.coroutine
def readline(self):
if self._exception is not None:
raise self._exception
parts = []
parts_size = 0
not_enough = True
while not_enough:
while self._buffer and not_enough:
data = self._buffer.popleft()
ichar = data.find(b'\n')
if ichar < 0:
parts.append(data)
parts_size += len(data)
else:
ichar += 1
head, tail = data[:ichar], data[ichar:]
if tail:
self._buffer.appendleft(tail)
not_enough = False
parts.append(head)
parts_size += len(head)
if parts_size > self._limit:
self._byte_count -= parts_size
self._maybe_resume_transport()
raise ValueError('Line is too long')
if self._eof:
break
if not_enough:
assert self._waiter is None
self._waiter = futures.Future(loop=self._loop)
try:
yield from self._waiter
finally:
self._waiter = None
line = b''.join(parts)
self._byte_count -= parts_size
self._maybe_resume_transport()
return line
@tasks.coroutine
def read(self, n=-1):
if self._exception is not None:
raise self._exception
if not n:
return b''
if n < 0:
while not self._eof:
assert not self._waiter
self._waiter = futures.Future(loop=self._loop)
try:
yield from self._waiter
finally:
self._waiter = None
else:
if not self._byte_count and not self._eof:
assert not self._waiter
self._waiter = futures.Future(loop=self._loop)
try:
yield from self._waiter
finally:
self._waiter = None
if n < 0 or self._byte_count <= n:
data = b''.join(self._buffer)
self._buffer.clear()
self._byte_count = 0
self._maybe_resume_transport()
return data
parts = []
parts_bytes = 0
while self._buffer and parts_bytes < n:
data = self._buffer.popleft()
data_bytes = len(data)
if n < parts_bytes + data_bytes:
data_bytes = n - parts_bytes
data, rest = data[:data_bytes], data[data_bytes:]
self._buffer.appendleft(rest)
parts.append(data)
parts_bytes += data_bytes
self._byte_count -= data_bytes
self._maybe_resume_transport()
return b''.join(parts)
@tasks.coroutine
def readexactly(self, n):
if self._exception is not None:
raise self._exception
# There used to be "optimized" code here. It created its own
# Future and waited until self._buffer had at least the n
# bytes, then called read(n). Unfortunately, this could pause
# the transport if the argument was larger than the pause
# limit (which is twice self._limit). So now we just read()
# into a local buffer.
blocks = []
while n > 0:
block = yield from self.read(n)
if not block:
break
blocks.append(block)
n -= len(block)
# TODO: Raise EOFError if we break before n == 0? (That would
# be a change in specification, but I've always had to add an
# explicit size check to the caller.)
return b''.join(blocks)