cpython/Doc/library/asyncio-stream.rst

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.. currentmodule:: asyncio
.. _asyncio-streams:
++++++++++++++++++++++++
Streams (high-level API)
++++++++++++++++++++++++
Stream functions
================
.. function:: open_connection(host=None, port=None, \*, loop=None, limit=None, **kwds)
A wrapper for :meth:`~BaseEventLoop.create_connection()` returning a (reader,
writer) pair.
The reader returned is a :class:`StreamReader` instance; the writer is
a :class:`StreamWriter` instance.
The arguments are all the usual arguments to
:meth:`BaseEventLoop.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
:class:`StreamReader`).
(If you want to customize the :class:`StreamReader` and/or
:class:`StreamReaderProtocol` classes, just copy the code -- there's really
nothing special here except some convenience.)
This function is a :ref:`coroutine <coroutine>`.
.. function:: start_server(client_connected_cb, host=None, port=None, \*, loop=None, limit=None, **kwds)
Start a socket server, with a callback for each client connected. The return
value is the same as :meth:`~BaseEventLoop.create_server()`.
The *client_connected_cb* parameter is called with two parameters:
*client_reader*, *client_writer*. *client_reader* is a
:class:`StreamReader` object, while *client_writer* is a
:class:`StreamWriter` object. The *client_connected_cb* parameter can
either be a plain callback function or a :ref:`coroutine function
<coroutine>`; if it is a coroutine function, it will be automatically
converted into a :class:`Task`.
The rest of the arguments are all the usual arguments to
:meth:`~BaseEventLoop.create_server()` 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
:class:`StreamReader`).
This function is a :ref:`coroutine <coroutine>`.
.. function:: open_unix_connection(path=None, \*, loop=None, limit=None, **kwds)
A wrapper for :meth:`~BaseEventLoop.create_unix_connection()` returning
a (reader, writer) pair.
See :func:`open_connection` for information about return value and other
details.
This function is a :ref:`coroutine <coroutine>`.
Availability: UNIX.
.. function:: start_unix_server(client_connected_cb, path=None, \*, loop=None, limit=None, **kwds)
Start a UNIX Domain Socket server, with a callback for each client connected.
See :func:`start_server` for information about return value and other
details.
This function is a :ref:`coroutine <coroutine>`.
Availability: UNIX.
StreamReader
============
.. class:: StreamReader(limit=None, loop=None)
.. method:: exception()
Get the exception.
.. method:: feed_eof()
Acknowledge the EOF.
.. method:: feed_data(data)
Feed *data* bytes in the internal buffer. Any operations waiting
for the data will be resumed.
.. method:: set_exception(exc)
Set the exception.
.. method:: set_transport(transport)
Set the transport.
.. method:: read(n=-1)
Read up to *n* bytes. If *n* is not provided, or set to ``-1``,
read until EOF and return all read bytes.
If the EOF was received and the internal buffer is empty,
return an empty ``bytes`` object.
This method is a :ref:`coroutine <coroutine>`.
.. method:: readline()
Read one line, where "line" is a sequence of bytes ending with ``\n``.
If EOF is received, and ``\n`` was not found, the method will
return the partial read bytes.
If the EOF was received and the internal buffer is empty,
return an empty ``bytes`` object.
This method is a :ref:`coroutine <coroutine>`.
.. method:: readexactly(n)
Read exactly *n* bytes. Raise an :exc:`IncompleteReadError` if the end of
the stream is reached before *n* can be read, the
:attr:`IncompleteReadError.partial` attribute of the exception contains
the partial read bytes.
This method is a :ref:`coroutine <coroutine>`.
.. method:: at_eof()
Return ``True`` if the buffer is empty and :meth:`feed_eof` was called.
StreamWriter
============
.. class:: StreamWriter(transport, protocol, reader, loop)
Wraps a Transport.
This exposes :meth:`write`, :meth:`writelines`, :meth:`can_write_eof()`,
:meth:`write_eof`, :meth:`get_extra_info` and :meth:`close`. It adds
:meth:`drain` which returns an optional :class:`Future` on which you can
wait for flow control. It also adds a transport attribute which references
the :class:`Transport` directly.
.. attribute:: transport
Transport.
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.. method:: can_write_eof()
Return :const:`True` if the transport supports :meth:`write_eof`,
:const:`False` if not. See :meth:`WriteTransport.can_write_eof`.
.. method:: close()
Close the transport: see :meth:`BaseTransport.close`.
.. method:: drain()
Let the write buffer of the underlying transport a chance to be flushed.
The intended use is to write::
w.write(data)
yield from w.drain()
When the size of the transport buffer reaches the high-water limit (the
protocol is paused), block until the size of the buffer is drained down
to the low-water limit and the protocol is resumed. When there is nothing
to wait for, the yield-from continues immediately.
Yielding from :meth:`drain` gives the opportunity for the loop to
schedule the write operation and flush the buffer. It should especially
be used when a possibly large amount of data is written to the transport,
and the coroutine does not yield-from between calls to :meth:`write`.
This method is a :ref:`coroutine <coroutine>`.
.. method:: get_extra_info(name, default=None)
Return optional transport information: see
:meth:`BaseTransport.get_extra_info`.
.. method:: write(data)
Write some *data* bytes to the transport: see
:meth:`WriteTransport.write`.
.. method:: writelines(data)
Write a list (or any iterable) of data bytes to the transport:
see :meth:`WriteTransport.writelines`.
.. method:: write_eof()
Close the write end of the transport after flushing buffered data:
see :meth:`WriteTransport.write_eof`.
StreamReaderProtocol
====================
.. class:: StreamReaderProtocol(stream_reader, client_connected_cb=None, loop=None)
Trivial helper class to adapt between :class:`Protocol` and
:class:`StreamReader`. Sublclass of :class:`Protocol`.
*stream_reader* is a :class:`StreamReader` instance, *client_connected_cb*
is an optional function called with (stream_reader, stream_writer) when a
connection is made, *loop* is the event loop instance to use.
(This is a helper class instead of making :class:`StreamReader` itself a
:class:`Protocol` subclass, because the :class:`StreamReader` has other
potential uses, and to prevent the user of the :class:`StreamReader` to
accidentally call inappropriate methods of the protocol.)
IncompleteReadError
===================
.. exception:: IncompleteReadError
Incomplete read error, subclass of :exc:`EOFError`.
.. attribute:: expected
Total number of expected bytes (:class:`int`).
.. attribute:: partial
Read bytes string before the end of stream was reached (:class:`bytes`).
Stream examples
===============
.. _asyncio-tcp-echo-client-streams:
TCP echo client using streams
-----------------------------
TCP echo client using the :func:`asyncio.open_connection` function::
import asyncio
@asyncio.coroutine
def tcp_echo_client(message, loop):
reader, writer = yield from asyncio.open_connection('127.0.0.1', 8888,
loop=loop)
print('Send: %r' % message)
writer.write(message.encode())
data = yield from reader.read(100)
print('Received: %r' % data.decode())
print('Close the socket')
writer.close()
message = 'Hello World!'
loop = asyncio.get_event_loop()
loop.run_until_complete(tcp_echo_client(message, loop))
loop.close()
.. seealso::
The :ref:`TCP echo client protocol <asyncio-tcp-echo-client-protocol>`
example uses the :meth:`BaseEventLoop.create_connection` method.
.. _asyncio-tcp-echo-server-streams:
TCP echo server using streams
-----------------------------
TCP echo server using the :func:`asyncio.start_server` function::
import asyncio
@asyncio.coroutine
def handle_echo(reader, writer):
data = yield from reader.read(100)
message = data.decode()
addr = writer.get_extra_info('peername')
print("Received %r from %r" % (message, addr))
print("Send: %r" % message)
writer.write(data)
yield from writer.drain()
print("Close the client socket")
writer.close()
loop = asyncio.get_event_loop()
coro = asyncio.start_server(handle_echo, '127.0.0.1', 8888, loop=loop)
server = loop.run_until_complete(coro)
# Serve requests until CTRL+c is pressed
print('Serving on {}'.format(server.sockets[0].getsockname()))
try:
loop.run_forever()
except KeyboardInterrupt:
pass
# Close the server
server.close()
loop.run_until_complete(server.wait_closed())
loop.close()
.. seealso::
The :ref:`TCP echo server protocol <asyncio-tcp-echo-server-protocol>`
example uses the :meth:`BaseEventLoop.create_server` method.
Get HTTP headers
----------------
Simple example querying HTTP headers of the URL passed on the command line::
import asyncio
import urllib.parse
import sys
@asyncio.coroutine
def print_http_headers(url):
url = urllib.parse.urlsplit(url)
if url.scheme == 'https':
connect = asyncio.open_connection(url.hostname, 443, ssl=True)
else:
connect = asyncio.open_connection(url.hostname, 80)
reader, writer = yield from connect
query = ('HEAD {path} HTTP/1.0\r\n'
'Host: {hostname}\r\n'
'\r\n').format(path=url.path or '/', hostname=url.hostname)
writer.write(query.encode('latin-1'))
while True:
line = yield from reader.readline()
if not line:
break
line = line.decode('latin1').rstrip()
if line:
print('HTTP header> %s' % line)
# Ignore the body, close the socket
writer.close()
url = sys.argv[1]
loop = asyncio.get_event_loop()
task = asyncio.async(print_http_headers(url))
loop.run_until_complete(task)
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loop.close()
Usage::
python example.py http://example.com/path/page.html
or with HTTPS::
python example.py https://example.com/path/page.html
.. _asyncio-register-socket-streams:
Register an open socket to wait for data using streams
------------------------------------------------------
Coroutine waiting until a socket receives data using the
:func:`open_connection` function::
import asyncio
try:
from socket import socketpair
except ImportError:
from asyncio.windows_utils import socketpair
@asyncio.coroutine
def wait_for_data(loop):
# Create a pair of connected sockets
rsock, wsock = socketpair()
# Register the open socket to wait for data
reader, writer = yield from asyncio.open_connection(sock=rsock, loop=loop)
# Simulate the reception of data from the network
loop.call_soon(wsock.send, 'abc'.encode())
# Wait for data
data = yield from reader.read(100)
# Got data, we are done: close the socket
print("Received:", data.decode())
writer.close()
# Close the second socket
wsock.close()
loop = asyncio.get_event_loop()
loop.run_until_complete(wait_for_data(loop))
loop.close()
.. seealso::
The :ref:`register an open socket to wait for data using a protocol
<asyncio-register-socket>` example uses a low-level protocol created by the
:meth:`BaseEventLoop.create_connection` method.
The :ref:`watch a file descriptor for read events
<asyncio-watch-read-event>` example uses the low-level
:meth:`BaseEventLoop.add_reader` method to register the file descriptor of a
socket.