18.5.5. Streams (high-level API)

18.5.5.1. Stream functions

Note

The top-level functions in this module are meant 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.

18.5.5.2. StreamReader

class asyncio.StreamReader(limit=None, loop=None)

This class is not thread safe.

exception()

Get the exception.

feed_eof()

Acknowledge the EOF.

feed_data(data)

Feed data bytes in the internal buffer. Any operations waiting for the data will be resumed.

set_exception(exc)

Set the exception.

set_transport(transport)

Set the transport.

at_eof()

Return True if the buffer is empty and feed_eof() was called.

18.5.5.3. StreamWriter

class asyncio.StreamWriter(transport, protocol, reader, loop)

Wraps a Transport.

This exposes write(), writelines(), can_write_eof(), 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 adds a transport attribute which references the Transport directly.

This class is not thread safe.

transport

Transport.

can_write_eof()

Return True if the transport supports write_eof(), False if not. See WriteTransport.can_write_eof().

close()

Close the transport: see BaseTransport.close().

get_extra_info(name, default=None)

Return optional transport information: see BaseTransport.get_extra_info().

write(data)

Write some data bytes to the transport: see WriteTransport.write().

writelines(data)

Write a list (or any iterable) of data bytes to the transport: see WriteTransport.writelines().

write_eof()

Close the write end of the transport after flushing buffered data: see WriteTransport.write_eof().

18.5.5.4. StreamReaderProtocol

class asyncio.StreamReaderProtocol(stream_reader, client_connected_cb=None, loop=None)

Trivial helper class to adapt between Protocol and StreamReader. Sublclass of Protocol.

stream_reader is a 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 StreamReader itself a Protocol subclass, because the StreamReader has other potential uses, and to prevent the user of the StreamReader from accidentally calling inappropriate methods of the protocol.)

18.5.5.5. IncompleteReadError

exception asyncio.IncompleteReadError
Incomplete read error, subclass of EOFError.
expected

Total number of expected bytes (int).

partial

Read bytes string before the end of stream was reached (bytes).

18.5.5.6. Stream examples

18.5.5.6.1. TCP echo client using streams

TCP echo client using the 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()

See also

The TCP echo client protocol example uses the BaseEventLoop.create_connection() method.

18.5.5.6.2. TCP echo server using streams

TCP echo server using the 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()

See also

The TCP echo server protocol example uses the BaseEventLoop.create_server() method.

18.5.5.6.3. 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.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

18.5.5.6.4. Register an open socket to wait for data using streams

Coroutine waiting until a socket receives data using the 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()

See also

The register an open socket to wait for data using a protocol example uses a low-level protocol created by the BaseEventLoop.create_connection() method.

The watch a file descriptor for read events example uses the low-level BaseEventLoop.add_reader() method to register the file descriptor of a socket.