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.
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 andfeed_eof()
was called.
-
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()
.
-
is_closing
()¶ Return
True
if the writer is closing or is closed.New in version 3.7.
-
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()
.
-
StreamReaderProtocol¶
-
class
asyncio.
StreamReaderProtocol
(stream_reader, client_connected_cb=None, loop=None)¶ Trivial helper class to adapt between
Protocol
andStreamReader
. Subclass 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
from accidentally calling inappropriate methods of the protocol.)
IncompleteReadError¶
LimitOverrunError¶
Stream examples¶
TCP echo client using streams¶
TCP echo client using the 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()
See also
The TCP echo client protocol
example uses the AbstractEventLoop.create_connection()
method.
TCP echo server using streams¶
TCP echo server using the 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()
See also
The TCP echo server protocol
example uses the 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
@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 = 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
Register an open socket to wait for data using streams¶
Coroutine waiting until a socket receives data using the
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()
See also
The register an open socket to wait for data using a protocol example uses a low-level protocol created by the
AbstractEventLoop.create_connection()
method.
The watch a file descriptor for read events example uses the low-level
AbstractEventLoop.add_reader()
method to register the file descriptor of a
socket.