19.5.5. Streams (coroutine based API)¶
Source code: Lib/asyncio/streams.py
19.5.5.1. Stream functions¶
備註
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.
-
coroutine
asyncio.
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
create_connection()
returning a (reader, writer) pair.The reader returned is a
StreamReader
instance; the writer is aStreamWriter
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
StreamReader
instance.The rest of the arguments are passed directly to
AbstractEventLoop.create_connection()
.This function is a coroutine.
3.7 版新加入: The ssl_handshake_timeout parameter.
-
coroutine
asyncio.
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
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
StreamReader
instance, and the second is aStreamWriter
instance.client_connected_cb accepts a plain callable or a coroutine function; if it is a coroutine function, it will be automatically converted into a
Task
.When specified, the loop argument determines which event loop to use, and the limit argument determines the buffer size limit used by the
StreamReader
instance passed to client_connected_cb.The rest of the arguments are passed directly to
create_server()
.This function is a coroutine.
3.7 版新加入: The ssl_handshake_timeout and start_serving parameters.
-
coroutine
asyncio.
open_unix_connection
(path=None, *, loop=None, limit=None, ssl=None, sock=None, server_hostname=None, ssl_handshake_timeout=None)¶ A wrapper for
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
StreamReader
instance.The rest of the arguments are passed directly to
create_unix_connection()
.This function is a coroutine.
Availability: UNIX.
3.7 版新加入: The ssl_handshake_timeout parameter.
3.7 版更變: The path parameter can now be a path-like object
-
coroutine
asyncio.
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
StreamReader
instance, and the second is aStreamWriter
instance.client_connected_cb accepts a plain callable or a coroutine function; if it is a coroutine function, it will be automatically converted into a
Task
.When specified, the loop argument determines which event loop to use, and the limit argument determines the buffer size limit used by the
StreamReader
instance passed to client_connected_cb.The rest of the arguments are passed directly to
create_unix_server()
.This function is a coroutine.
Availability: UNIX.
3.7 版新加入: The ssl_handshake_timeout and start_serving parameters.
3.7 版更變: The path parameter can now be a path-like object.
19.5.5.2. 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.
-
coroutine
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
IncompleteReadError
exception will be raised, and the internal buffer will be reset. TheIncompleteReadError.partial
attribute may contain the separator partially.If the data cannot be read because of over limit, a
LimitOverrunError
exception will be raised, and the data will be left in the internal buffer, so it can be read again.3.5.2 版新加入.
-
at_eof
()¶ Return
True
if the buffer is empty andfeed_eof()
was called.
-
19.5.5.3. 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()
.
-
is_closing
()¶ Return
True
if the writer is closing or is closed.3.7 版新加入.
-
coroutine
wait_closed
()¶ Wait until the writer is closed.
Should be called after
close()
to wait until the underlying connection (and the associated transport/protocol pair) is closed.3.7 版新加入.
-
coroutine
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
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()
.
-
19.5.5.4. 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.)
19.5.5.5. IncompleteReadError¶
19.5.5.6. LimitOverrunError¶
19.5.5.7. Stream examples¶
19.5.5.7.1. 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()
也參考
The TCP echo client protocol
example uses the AbstractEventLoop.create_connection()
method.
19.5.5.7.2. 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()
也參考
The TCP echo server protocol
example uses the AbstractEventLoop.create_server()
method.
19.5.5.7.3. 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
19.5.5.7.4. Register an open socket to wait for data using streams¶
Coroutine waiting until a socket receives data using the
open_connection()
function:
import asyncio
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()
也參考
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.