18.5.4. Transports and protocols (callback based API)¶
Source code: Lib/asyncio/transports.py
Source code: Lib/asyncio/protocols.py
18.5.4.1. 传输¶
Transports are classes provided by asyncio
in order to abstract
various kinds of communication channels. You generally won’t instantiate
a transport yourself; instead, you will call an AbstractEventLoop
method
which will create the transport and try to initiate the underlying
communication channel, calling you back when it succeeds.
Once the communication channel is established, a transport is always paired with a protocol instance. The protocol can then call the transport’s methods for various purposes.
asyncio
currently implements transports for TCP, UDP, SSL, and
subprocess pipes. The methods available on a transport depend on
the transport’s kind.
传输类属于 线程不安全 。
在 3.6 版更改: The socket option TCP_NODELAY
is now set by default.
18.5.4.1.1. BaseTransport¶
-
class
asyncio.
BaseTransport
¶ Base class for transports.
-
close
()¶ Close the transport. If the transport has a buffer for outgoing data, buffered data will be flushed asynchronously. No more data will be received. After all buffered data is flushed, the protocol’s
connection_lost()
method will be called withNone
as its argument.
-
is_closing
()¶ 返回
True
,如果传输正在关闭或已经关闭。3.5.1 新版功能.
-
get_extra_info
(name, default=None)¶ Return optional transport information. name is a string representing the piece of transport-specific information to get, default is the value to return if the information doesn’t exist.
This method allows transport implementations to easily expose channel-specific information.
套接字:
'peername'
: 套接字链接时的远端地址,socket.socket.getpeername()
方法的结果 (出错时为None
)'socket'
:socket.socket
实例'sockname'
: 套接字本地地址,socket.socket.getsockname()
方法的结果
SSL套接字
'compression'
: 用字符串指定压缩算法,或者链接没有压缩时为None
;ssl.SSLSocket.compression()
的结果。'cipher'
: 一个三值的元组,包含使用密码的名称,定义使用的SSL协议的版本,使用的加密位数。ssl.SSLSocket.cipher()
的结果。'peercert'
: 远端凭证;ssl.SSLSocket.getpeercert()
结果。'sslcontext'
:ssl.SSLContext
实例'ssl_object'
:ssl.SSLObject
或ssl.SSLSocket
实例
管道:
'pipe'
: 管道对象
子进程:
'subprocess'
:subprocess.Popen
实例
-
set_protocol
(protocol)¶ Set a new protocol. Switching protocol should only be done when both protocols are documented to support the switch.
3.5.3 新版功能.
-
get_protocol
()¶ 返回当前协议。
3.5.3 新版功能.
在 3.5.1 版更改:
'ssl_object'
info was added to SSL sockets.-
18.5.4.1.2. ReadTransport¶
-
class
asyncio.
ReadTransport
¶ Interface for read-only transports.
-
pause_reading
()¶ Pause the receiving end of the transport. No data will be passed to the protocol’s
data_received()
method untilresume_reading()
is called.在 3.6.7 版更改: 这个方法幂等的, 它可以在传输已经暂停或关闭时调用。
-
resume_reading
()¶ Resume the receiving end. The protocol’s
data_received()
method will be called once again if some data is available for reading.在 3.6.7 版更改: 这个方法幂等的, 它可以在传输已经准备好读取数据时调用。
-
18.5.4.1.3. WriteTransport¶
-
class
asyncio.
WriteTransport
¶ Interface for write-only transports.
-
abort
()¶ Close the transport immediately, without waiting for pending operations to complete. Buffered data will be lost. No more data will be received. The protocol’s
connection_lost()
method will eventually be called withNone
as its argument.
-
can_write_eof
()¶ Return
True
if the transport supportswrite_eof()
,False
if not.
-
get_write_buffer_size
()¶ 返回传输使用输出缓冲区的当前大小。
-
get_write_buffer_limits
()¶ Get the high- and low-water limits for write flow control. Return a tuple
(low, high)
where low and high are positive number of bytes.使用
set_write_buffer_limits()
设置限制。3.4.2 新版功能.
-
set_write_buffer_limits
(high=None, low=None)¶ Set the high- and low-water limits for write flow control.
These two values (measured in number of bytes) control when the protocol’s
pause_writing()
andresume_writing()
methods are called. If specified, the low-water limit must be less than or equal to the high-water limit. Neither high nor low can be negative.pause_writing()
is called when the buffer size becomes greater than or equal to the high value. If writing has been paused,resume_writing()
is called when the buffer size becomes less than or equal to the low value.The defaults are implementation-specific. If only the high-water limit is given, the low-water limit defaults to an implementation-specific value less than or equal to the high-water limit. Setting high to zero forces low to zero as well, and causes
pause_writing()
to be called whenever the buffer becomes non-empty. Setting low to zero causesresume_writing()
to be called only once the buffer is empty. Use of zero for either limit is generally sub-optimal as it reduces opportunities for doing I/O and computation concurrently.Use
get_write_buffer_limits()
to get the limits.
-
write
(data)¶ 将一些 data 字节串写入传输。
此方法不会阻塞;它会缓冲数据并安排其被异步地发出。
-
write_eof
()¶ Close the write end of the transport after flushing buffered data. Data may still be received.
This method can raise
NotImplementedError
if the transport (e.g. SSL) doesn’t support half-closes.
-
18.5.4.1.4. DatagramTransport¶
18.5.4.1.5. BaseSubprocessTransport¶
-
class
asyncio.
BaseSubprocessTransport
¶ -
get_pid
()¶ 将子进程的进程 ID 以整数形式返回。
-
get_pipe_transport
(fd)¶ 返回对应于整数文件描述符 fd 的通信管道的传输:
-
get_returncode
()¶ Return the subprocess returncode as an integer or
None
if it hasn’t returned, similarly to thesubprocess.Popen.returncode
attribute.
-
kill
()¶ Kill the subprocess, as in
subprocess.Popen.kill()
.在 POSIX 系统中,函数会发送 SIGKILL 到子进程。 在 Windows 中,此方法是
terminate()
的别名。
-
send_signal
(signal)¶ 发送 signal 编号到子进程,与
subprocess.Popen.send_signal()
一样。
-
terminate
()¶ Ask the subprocess to stop, as in
subprocess.Popen.terminate()
. This method is an alias for theclose()
method.在 POSIX 系统中,此方法会发送 SIGTERM 到子进程。 在 Windows 中,则会调用 Windows API 函数 TerminateProcess() 来停止子进程。
-
close
()¶ Ask the subprocess to stop by calling the
terminate()
method if the subprocess hasn’t returned yet, and close transports of all pipes (stdin, stdout and stderr).
-
18.5.4.2. 协议¶
asyncio
provides base classes that you can subclass to implement
your network protocols. Those classes are used in conjunction with
transports (see below): the protocol parses incoming
data and asks for the writing of outgoing data, while the transport is
responsible for the actual I/O and buffering.
When subclassing a protocol class, it is recommended you override certain methods. Those methods are callbacks: they will be called by the transport on certain events (for example when some data is received); you shouldn’t call them yourself, unless you are implementing a transport.
注解
All callbacks have default implementations, which are empty. Therefore, you only need to implement the callbacks for the events in which you are interested.
18.5.4.2.1. Protocol classes¶
-
class
asyncio.
Protocol
¶ The base class for implementing streaming protocols (for use with e.g. TCP and SSL transports).
-
class
asyncio.
DatagramProtocol
¶ The base class for implementing datagram protocols (for use with e.g. UDP transports).
-
class
asyncio.
SubprocessProtocol
¶ The base class for implementing protocols communicating with child processes (through a set of unidirectional pipes).
18.5.4.2.2. Connection callbacks¶
These callbacks may be called on Protocol
, DatagramProtocol
and SubprocessProtocol
instances:
-
BaseProtocol.
connection_made
(transport)¶ 链接建立时被调用。
The transport argument is the transport representing the connection. You are responsible for storing it somewhere (e.g. as an attribute) if you need to.
-
BaseProtocol.
connection_lost
(exc)¶ 链接丢失或关闭时被调用。
方法的参数是一个异常对象或为
None
。 后者意味着收到了常规的 EOF,或者连接被连接的一端取消或关闭。
connection_made()
and connection_lost()
are called exactly once per successful connection. All other callbacks will be
called between those two methods, which allows for easier resource management
in your protocol implementation.
The following callbacks may be called only on SubprocessProtocol
instances:
-
SubprocessProtocol.
pipe_data_received
(fd, data)¶ Called when the child process writes data into its stdout or stderr pipe. fd is the integer file descriptor of the pipe. data is a non-empty bytes object containing the data.
-
SubprocessProtocol.
pipe_connection_lost
(fd, exc)¶ Called when one of the pipes communicating with the child process is closed. fd is the integer file descriptor that was closed.
-
SubprocessProtocol.
process_exited
()¶ 子进程退出时被调用。
18.5.4.2.3. Streaming protocols¶
The following callbacks are called on Protocol
instances:
-
Protocol.
data_received
(data)¶ 当收到数据时被调用。 data 为包含入站数据的非空字节串对象。
注解
Whether the data is buffered, chunked or reassembled depends on the transport. In general, you shouldn’t rely on specific semantics and instead make your parsing generic and flexible enough. However, data is always received in the correct order.
-
Protocol.
eof_received
()¶ Called when the other end signals it won’t send any more data (for example by calling
write_eof()
, if the other end also uses asyncio).This method may return a false value (including
None
), in which case the transport will close itself. Conversely, if this method returns a true value, closing the transport is up to the protocol. Since the default implementation returnsNone
, it implicitly closes the connection.注解
Some transports such as SSL don’t support half-closed connections, in which case returning true from this method will not prevent closing the connection.
data_received()
can be called an arbitrary number of times during
a connection. However, eof_received()
is called at most once
and, if called, data_received()
won’t be called after it.
状态机:
start ->
connection_made()
[->data_received()
*] [->eof_received()
?] ->connection_lost()
-> end
18.5.4.2.4. Datagram protocols¶
The following callbacks are called on DatagramProtocol
instances.
-
DatagramProtocol.
datagram_received
(data, addr)¶ 当接收到数据报时被调用。 data 是包含传入数据的字节串对象。 addr 是发送数据的对等端地址;实际的格式取决于具体传输。
18.5.4.2.5. Flow control callbacks¶
These callbacks may be called on Protocol
,
DatagramProtocol
and SubprocessProtocol
instances:
-
BaseProtocol.
pause_writing
()¶ Called when the transport’s buffer goes over the high-water mark.
-
BaseProtocol.
resume_writing
()¶ Called when the transport’s buffer drains below the low-water mark.
pause_writing()
and resume_writing()
calls are paired –
pause_writing()
is called once when the buffer goes strictly over
the high-water mark (even if subsequent writes increases the buffer size
even more), and eventually resume_writing()
is called once when the
buffer size reaches the low-water mark.
注解
If the buffer size equals the high-water mark,
pause_writing()
is not called – it must go strictly over.
Conversely, resume_writing()
is called when the buffer size is
equal or lower than the low-water mark. These end conditions
are important to ensure that things go as expected when either
mark is zero.
注解
On BSD systems (OS X, FreeBSD, etc.) flow control is not supported
for DatagramProtocol
, because send failures caused by
writing too many packets cannot be detected easily. The socket
always appears ‘ready’ and excess packets are dropped; an
OSError
with errno set to errno.ENOBUFS
may or
may not be raised; if it is raised, it will be reported to
DatagramProtocol.error_received()
but otherwise ignored.
18.5.4.2.6. Coroutines and protocols¶
Coroutines can be scheduled in a protocol method using ensure_future()
,
but there is no guarantee made about the execution order. Protocols are not
aware of coroutines created in protocol methods and so will not wait for them.
To have a reliable execution order, use stream objects in a
coroutine with yield from
. For example, the StreamWriter.drain()
coroutine can be used to wait until the write buffer is flushed.
18.5.4.3. Protocol examples¶
18.5.4.3.1. TCP echo client protocol¶
TCP echo client using the AbstractEventLoop.create_connection()
method, send
data and wait until the connection is closed:
import asyncio
class EchoClientProtocol(asyncio.Protocol):
def __init__(self, message, loop):
self.message = message
self.loop = loop
def connection_made(self, transport):
transport.write(self.message.encode())
print('Data sent: {!r}'.format(self.message))
def data_received(self, data):
print('Data received: {!r}'.format(data.decode()))
def connection_lost(self, exc):
print('The server closed the connection')
print('Stop the event loop')
self.loop.stop()
loop = asyncio.get_event_loop()
message = 'Hello World!'
coro = loop.create_connection(lambda: EchoClientProtocol(message, loop),
'127.0.0.1', 8888)
loop.run_until_complete(coro)
loop.run_forever()
loop.close()
The event loop is running twice. The
run_until_complete()
method is preferred in this short
example to raise an exception if the server is not listening, instead of
having to write a short coroutine to handle the exception and stop the
running loop. At run_until_complete()
exit, the loop is
no longer running, so there is no need to stop the loop in case of an error.
参见
The TCP echo client using streams
example uses the asyncio.open_connection()
function.
18.5.4.3.2. TCP echo server protocol¶
TCP echo server using the AbstractEventLoop.create_server()
method, send back
received data and close the connection:
import asyncio
class EchoServerClientProtocol(asyncio.Protocol):
def connection_made(self, transport):
peername = transport.get_extra_info('peername')
print('Connection from {}'.format(peername))
self.transport = transport
def data_received(self, data):
message = data.decode()
print('Data received: {!r}'.format(message))
print('Send: {!r}'.format(message))
self.transport.write(data)
print('Close the client socket')
self.transport.close()
loop = asyncio.get_event_loop()
# Each client connection will create a new protocol instance
coro = loop.create_server(EchoServerClientProtocol, '127.0.0.1', 8888)
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()
Transport.close()
can be called immediately after
WriteTransport.write()
even if data are not sent yet on the socket: both
methods are asynchronous. yield from
is not needed because these transport
methods are not coroutines.
参见
The TCP echo server using streams
example uses the asyncio.start_server()
function.
18.5.4.3.3. UDP echo client protocol¶
UDP echo client using the AbstractEventLoop.create_datagram_endpoint()
method, send data and close the transport when we received the answer:
import asyncio
class EchoClientProtocol:
def __init__(self, message, loop):
self.message = message
self.loop = loop
self.transport = None
def connection_made(self, transport):
self.transport = transport
print('Send:', self.message)
self.transport.sendto(self.message.encode())
def datagram_received(self, data, addr):
print("Received:", data.decode())
print("Close the socket")
self.transport.close()
def error_received(self, exc):
print('Error received:', exc)
def connection_lost(self, exc):
print("Socket closed, stop the event loop")
loop = asyncio.get_event_loop()
loop.stop()
loop = asyncio.get_event_loop()
message = "Hello World!"
connect = loop.create_datagram_endpoint(
lambda: EchoClientProtocol(message, loop),
remote_addr=('127.0.0.1', 9999))
transport, protocol = loop.run_until_complete(connect)
loop.run_forever()
transport.close()
loop.close()
18.5.4.3.4. UDP echo server protocol¶
UDP echo server using the AbstractEventLoop.create_datagram_endpoint()
method, send back received data:
import asyncio
class EchoServerProtocol:
def connection_made(self, transport):
self.transport = transport
def datagram_received(self, data, addr):
message = data.decode()
print('Received %r from %s' % (message, addr))
print('Send %r to %s' % (message, addr))
self.transport.sendto(data, addr)
loop = asyncio.get_event_loop()
print("Starting UDP server")
# One protocol instance will be created to serve all client requests
listen = loop.create_datagram_endpoint(
EchoServerProtocol, local_addr=('127.0.0.1', 9999))
transport, protocol = loop.run_until_complete(listen)
try:
loop.run_forever()
except KeyboardInterrupt:
pass
transport.close()
loop.close()
18.5.4.3.5. Register an open socket to wait for data using a protocol¶
Wait until a socket receives data using the
AbstractEventLoop.create_connection()
method with a protocol, and then close
the event loop
import asyncio
try:
from socket import socketpair
except ImportError:
from asyncio.windows_utils import socketpair
# Create a pair of connected sockets
rsock, wsock = socketpair()
loop = asyncio.get_event_loop()
class MyProtocol(asyncio.Protocol):
transport = None
def connection_made(self, transport):
self.transport = transport
def data_received(self, data):
print("Received:", data.decode())
# We are done: close the transport (it will call connection_lost())
self.transport.close()
def connection_lost(self, exc):
# The socket has been closed, stop the event loop
loop.stop()
# Register the socket to wait for data
connect_coro = loop.create_connection(MyProtocol, sock=rsock)
transport, protocol = loop.run_until_complete(connect_coro)
# Simulate the reception of data from the network
loop.call_soon(wsock.send, 'abc'.encode())
# Run the event loop
loop.run_forever()
# We are done, close sockets and the event loop
rsock.close()
wsock.close()
loop.close()
参见
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.
The register an open socket to wait for data using streams example uses high-level streams
created by the open_connection()
function in a coroutine.