18.5.5. Streams (high-level API)
18.5.5.1. Stream functions
-
coroutine
asyncio.
open_connection
(host=None, port=None, *, loop=None, limit=None, **kwds) A wrapper for
create_connection()
returning a (reader, writer) pair.The reader returned is a
StreamReader
instance; the writer is aStreamWriter
instance.The arguments are all the usual arguments to
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
StreamReader
).(If you want to customize the
StreamReader
and/orStreamReaderProtocol
classes, just copy the code – there’s really nothing special here except some convenience.)This function is a coroutine.
-
coroutine
asyncio.
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
create_server()
.The client_connected_cb parameter is called with two parameters: client_reader, client_writer. client_reader is a
StreamReader
object, while client_writer is aStreamWriter
object. The client_connected_cb parameter can either be a plain callback function or a coroutine function; if it is a coroutine function, it will be automatically converted into aTask
.The rest of the arguments are all the usual arguments to
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
StreamReader
).This function is a coroutine.
-
coroutine
asyncio.
open_unix_connection
(path=None, *, loop=None, limit=None, **kwds) A wrapper for
create_unix_connection()
returning a (reader, writer) pair.See
open_connection()
for information about return value and other details.This function is a coroutine.
Availability: UNIX.
-
coroutine
asyncio.
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
start_server()
for information about return value and other details.This function is a coroutine.
Availability: UNIX.
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.
-
coroutine
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 coroutine.
-
coroutine
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 coroutine.
-
coroutine
readexactly
(n) Read exactly n bytes. Raise an
IncompleteReadError
if the end of the stream is reached before n can be read, theIncompleteReadError.partial
attribute of the exception contains the partial read bytes.This method is a coroutine.
-
at_eof
() Return
True
if the buffer is empty andfeed_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()
andclose()
. It addsdrain()
which returns an optionalFuture
on which you can wait for flow control. It also adds a transport attribute which references theTransport
directly.This class is not thread safe.
-
transport
Transport.
-
can_write_eof
() Return
True
if the transport supportswrite_eof()
,False
if not. SeeWriteTransport.can_write_eof()
.
-
close
() Close the transport: see
BaseTransport.close()
.
-
coroutine
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
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 towrite()
.This method is a coroutine.
-
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
andStreamReader
. Sublclass ofProtocol
.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 aProtocol
subclass, because theStreamReader
has other potential uses, and to prevent the user of theStreamReader
to accidentally call inappropriate methods of the protocol.)
18.5.5.5. IncompleteReadError
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.