18.5.5. Streams (coroutine based API)¶
Source code: Lib/asyncio/streams.py
18.5.5.1. Stream functions¶
注解
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, **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
AbstractEventLoop.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
).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=_DEFAULT_LIMIT, loop=None)¶ This class is not thread safe.
The limit argument’s default value is set to _DEFAULT_LIMIT which is 2**16 (64 KiB)
-
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)¶ 读取 n 个byte. 如果没有设置 n , 则自动置为
-1
,读至 EOF 并返回所有读取的byte。If the EOF was received and the internal buffer is empty, return an empty
bytes
object.This method is a coroutine.
-
coroutine
readline
()¶ 读取一行,其中“行”指的是以
\n
结尾的字节序列。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.成功后,数据和指定的separator将从内部缓冲区中删除(或者说被消费掉)。返回的数据将包括在末尾的指定separator。
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 新版功能.
-
at_eof
()¶ 如果缓冲区为空并且
feed_eof()
被调用,则返回True
。
-
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
. 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.)
18.5.5.5. IncompleteReadError¶
18.5.5.6. LimitOverrunError¶
18.5.5.7. Stream examples¶
18.5.5.7.1. 使用流的 TCP 回显客户端¶
使用 asyncio.open_connection()
函数的 TCP 回显客户端:
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()
参见
The TCP echo client protocol
example uses the AbstractEventLoop.create_connection()
method.
18.5.5.7.2. 使用流的 TCP 回显服务器¶
TCP 回显服务器使用 asyncio.start_server()
函数:
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()
参见
The TCP echo server protocol
example uses the AbstractEventLoop.create_server()
method.
18.5.5.7.3. 获取 HTTP 标头¶
查询命令行传入 URL 的 HTTP 标头的简单示例:
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()
用法:
python example.py http://example.com/path/page.html
或使用 HTTPS:
python example.py https://example.com/path/page.html
18.5.5.7.4. 注册一个打开的套接字以等待使用流的数据¶
使用 open_connection()
函数实现等待直到套接字接收到数据的协程:
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()
参见
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.