.. currentmodule:: asyncio .. _asyncio-streams: +++++++++++++++++++++++++++++ Streams (coroutine based API) +++++++++++++++++++++++++++++ **Source code:** :source:`Lib/asyncio/streams.py` Stream functions ================ .. note:: The top-level functions in this module are meant as convenience wrappers only; there's really nothing special there, and if they don't do exactly what you want, feel free to copy their code. .. coroutinefunction:: open_connection(host=None, port=None, \*, loop=None, limit=None, ssl=None, family=0, proto=0, flags=0, sock=None, local_addr=None, server_hostname=None, ssl_handshake_timeout=None) A wrapper for :meth:`~AbstractEventLoop.create_connection()` returning a (reader, writer) pair. The reader returned is a :class:`StreamReader` instance; the writer is a :class:`StreamWriter` instance. When specified, the *loop* argument determines which event loop to use, and the *limit* argument determines the buffer size limit used by the returned :class:`StreamReader` instance. The rest of the arguments are passed directly to :meth:`AbstractEventLoop.create_connection`. This function is a :ref:`coroutine `. .. versionadded:: 3.7 The *ssl_handshake_timeout* parameter. .. coroutinefunction:: start_server(client_connected_cb, host=None, port=None, \*, loop=None, limit=None, family=socket.AF_UNSPEC, flags=socket.AI_PASSIVE, sock=None, backlog=100, ssl=None, reuse_address=None, reuse_port=None, ssl_handshake_timeout=None, start_serving=True) Start a socket server, with a callback for each client connected. The return value is the same as :meth:`~AbstractEventLoop.create_server()`. The *client_connected_cb* callback is called whenever a new client connection is established. It receives a reader/writer pair as two arguments, the first is a :class:`StreamReader` instance, and the second is a :class:`StreamWriter` instance. *client_connected_cb* accepts a plain callable or a :ref:`coroutine function `; if it is a coroutine function, it will be automatically converted into a :class:`Task`. When specified, the *loop* argument determines which event loop to use, and the *limit* argument determines the buffer size limit used by the :class:`StreamReader` instance passed to *client_connected_cb*. The rest of the arguments are passed directly to :meth:`~AbstractEventLoop.create_server()`. This function is a :ref:`coroutine `. .. versionadded:: 3.7 The *ssl_handshake_timeout* and *start_serving* parameters. .. coroutinefunction:: open_unix_connection(path=None, \*, loop=None, limit=None, ssl=None, sock=None, server_hostname=None, ssl_handshake_timeout=None) A wrapper for :meth:`~AbstractEventLoop.create_unix_connection()` returning a (reader, writer) pair. When specified, the *loop* argument determines which event loop to use, and the *limit* argument determines the buffer size limit used by the returned :class:`StreamReader` instance. The rest of the arguments are passed directly to :meth:`~AbstractEventLoop.create_unix_connection()`. This function is a :ref:`coroutine `. Availability: UNIX. .. versionadded:: 3.7 The *ssl_handshake_timeout* parameter. .. versionchanged:: 3.7 The *path* parameter can now be a :term:`path-like object` .. coroutinefunction:: start_unix_server(client_connected_cb, path=None, \*, loop=None, limit=None, sock=None, backlog=100, ssl=None, ssl_handshake_timeout=None, start_serving=True) Start a UNIX Domain Socket server, with a callback for each client connected. The *client_connected_cb* callback is called whenever a new client connection is established. It receives a reader/writer pair as two arguments, the first is a :class:`StreamReader` instance, and the second is a :class:`StreamWriter` instance. *client_connected_cb* accepts a plain callable or a :ref:`coroutine function `; if it is a coroutine function, it will be automatically converted into a :class:`Task`. When specified, the *loop* argument determines which event loop to use, and the *limit* argument determines the buffer size limit used by the :class:`StreamReader` instance passed to *client_connected_cb*. The rest of the arguments are passed directly to :meth:`~AbstractEventLoop.create_unix_server()`. This function is a :ref:`coroutine `. Availability: UNIX. .. versionadded:: 3.7 The *ssl_handshake_timeout* and *start_serving* parameters. .. versionchanged:: 3.7 The *path* parameter can now be a :term:`path-like object`. StreamReader ============ .. class:: StreamReader(limit=None, loop=None) This class is :ref:`not thread safe `. .. 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. .. coroutinemethod:: 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 `. .. coroutinemethod:: 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 `. .. coroutinemethod:: 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 `. .. coroutinemethod:: readuntil(separator=b'\\n') Read data from the stream until ``separator`` is found. On success, the data and separator will be removed from the internal buffer (consumed). Returned data will include the separator at the end. Configured stream limit is used to check result. Limit sets the maximal length of data that can be returned, not counting the separator. If an EOF occurs and the complete separator is still not found, an :exc:`IncompleteReadError` exception will be raised, and the internal buffer will be reset. The :attr:`IncompleteReadError.partial` attribute may contain the separator partially. If the data cannot be read because of over limit, a :exc:`LimitOverrunError` exception will be raised, and the data will be left in the internal buffer, so it can be read again. .. versionadded:: 3.5.2 .. 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. This class is :ref:`not thread safe `. .. attribute:: transport Transport. .. 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:: is_closing() Return ``True`` if the writer is closing or is closed. .. versionadded:: 3.7 .. coroutinemethod:: wait_closed() Wait until the writer is closed. Should be called after :meth:`close` to wait until the underlying connection (and the associated transport/protocol pair) is closed. .. versionadded:: 3.7 .. coroutinemethod:: drain() Let the write buffer of the underlying transport a chance to be flushed. The intended use is to write:: w.write(data) await 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 `. .. 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`. Subclass 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` from accidentally calling 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`). LimitOverrunError ================= .. exception:: LimitOverrunError Reached the buffer limit while looking for a separator. .. attribute:: consumed Total number of to be consumed 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 async def tcp_echo_client(message, loop): reader, writer = await asyncio.open_connection('127.0.0.1', 8888, loop=loop) print('Send: %r' % message) writer.write(message.encode()) data = await 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 ` example uses the :meth:`AbstractEventLoop.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 async def handle_echo(reader, writer): data = await 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) await 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 ` example uses the :meth:`AbstractEventLoop.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 async 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 = await 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 = await 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.ensure_future(print_http_headers(url)) loop.run_until_complete(task) 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 from socket import socketpair async def wait_for_data(loop): # Create a pair of connected sockets rsock, wsock = socketpair() # Register the open socket to wait for data reader, writer = await 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 = await 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 ` example uses a low-level protocol created by the :meth:`AbstractEventLoop.create_connection` method. The :ref:`watch a file descriptor for read events ` example uses the low-level :meth:`AbstractEventLoop.add_reader` method to register the file descriptor of a socket.