传输和协议 ¶

前言

传输和协议用于低级事件循环 API 譬如 loop.create_connection() 。它们使用基于回调的编程风格，并支持网络或 IPC 协议 (如 HTTP) 的高性能实现。

本质上，传输和协议只应用于库和框架，且从不应该用于高级 asyncio 应用程序。

此文档编制页面涵盖传输 and 协议 .

介绍

At the highest level, the transport is concerned with how bytes are transmitted, while the protocol determines which bytes to transmit (and to some extent when).

A different way of saying the same thing: a transport is an abstraction for a socket (or similar I/O endpoint) while a protocol is an abstraction for an application, from the transport’s point of view.

Yet another view is the transport and protocol interfaces together define an abstract interface for using network I/O and interprocess I/O.

There is always a 1:1 relationship between transport and protocol objects: the protocol calls transport methods to send data, while the transport calls protocol methods to pass it data that has been received.

Most of connection oriented event loop methods (such as loop.create_connection() ) 通常接受 protocol_factory argument used to create a Protocol object for an accepted connection, represented by a Transport object. Such methods usually return a tuple of (transport, protocol) .

内容

此文档页面包含下列章节：

The 传输章节文档 asyncio BaseTransport , ReadTransport , WriteTransport , Transport , DatagramTransport ，和 SubprocessTransport 类。
The 协议章节文档 asyncio BaseProtocol , Protocol , BufferedProtocol , DatagramProtocol ，和 SubprocessProtocol 类。
The 范例 section showcases how to work with transports, protocols, and low-level event loop APIs.

传输 ¶

源代码： Lib/asyncio/transports.py

传输是类提供通过 asyncio 为抽象各种通信通道。

传输对象始终被实例化通过 asyncio 事件循环 .

asyncio implements transports for TCP, UDP, SSL, and subprocess pipes. The methods available on a transport depend on the transport’s kind.

传输类是非线程安全 .

传输层次结构 ¶

class asyncio. BaseTransport ¶: Base class for all transports. Contains methods that all asyncio transports share.

class asyncio. WriteTransport ( BaseTransport ) ¶

A base transport for write-only connections.

实例化的 WriteTransport class are returned from the loop.connect_write_pipe() event loop method and are also used by subprocess-related methods like loop.subprocess_exec() .

class asyncio. ReadTransport ( BaseTransport ) ¶

A base transport for read-only connections.

实例化的 ReadTransport class are returned from the loop.connect_read_pipe() event loop method and are also used by subprocess-related methods like loop.subprocess_exec() .

class asyncio. Transport ( WriteTransport , ReadTransport ) ¶

Interface representing a bidirectional transport, such as a TCP connection.

The user does not instantiate a transport directly; they call a utility function, passing it a protocol factory and other information necessary to create the transport and protocol.

实例化的 Transport class are returned from or used by event loop methods like loop.create_connection() , loop.create_unix_connection() , loop.create_server() , loop.sendfile() ，等。

class asyncio. DatagramTransport ( BaseTransport ) ¶

A transport for datagram (UDP) connections.

实例化的 DatagramTransport class are returned from the loop.create_datagram_endpoint() event loop method.

class asyncio. SubprocessTransport ( BaseTransport ) ¶

An abstraction to represent a connection between a parent and its child OS process.

实例化的 SubprocessTransport class are returned from event loop methods loop.subprocess_shell() and loop.subprocess_exec() .

基传输 ¶

BaseTransport. 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 protocol.connection_lost() method will be called with None as its argument. The transport should not be used once it is closed.

BaseTransport. is_closing ( ) ¶: 返回 True if the transport is closing or is closed.

BaseTransport. get_extra_info ( 名称 , default = None ) ¶

Return information about the transport or underlying resources it uses.

name is a string representing the piece of transport-specific information to get.

default is the value to return if the information is not available, or if the transport does not support querying it with the given third-party event loop implementation or on the current platform.

For example, the following code attempts to get the underlying socket object of the transport:

sock = transport.get_extra_info('socket')
if sock is not None:
    print(sock.getsockopt(...))

协议 ¶

asyncio provides a set of abstract base classes that should be used to implement network protocols. Those classes are meant to be used together with 传输 .

Subclasses of abstract base protocol classes may implement some or all methods. All these methods are callbacks: they are called by transports on certain events, for example when some data is received. A base protocol method should be called by the corresponding transport.

基协议 ¶

class asyncio. BaseProtocol ¶: Base protocol with methods that all protocols share.

class asyncio. Protocol ( BaseProtocol ) ¶: The base class for implementing streaming protocols (TCP, Unix sockets, etc).

class asyncio. BufferedProtocol ( BaseProtocol ) ¶: A base class for implementing streaming protocols with manual control of the receive buffer.

class asyncio. DatagramProtocol ( BaseProtocol ) ¶: The base class for implementing datagram (UDP) protocols.

class asyncio. SubprocessProtocol ( BaseProtocol ) ¶: The base class for implementing protocols communicating with child processes (unidirectional pipes).

BaseProtocol ¶

All asyncio protocols can implement Base Protocol callbacks.

连接回调

Connection callbacks are called on all protocols, exactly once per a successful connection. All other protocol callbacks can only be called between those two methods.

BaseProtocol. connection_made ( transport ) ¶

Called when a connection is made.

The transport argument is the transport representing the connection. The protocol is responsible for storing the reference to its transport.

BaseProtocol. connection_lost ( exc ) ¶

Called when the connection is lost or closed.

The argument is either an exception object or None . The latter means a regular EOF is received, or the connection was aborted or closed by this side of the connection.

流控件回调

Flow control callbacks can be called by transports to pause or resume writing performed by the protocol.

See the documentation of the set_write_buffer_limits() method for more details.

BaseProtocol. pause_writing ( ) ¶: Called when the transport’s buffer goes over the high watermark.

BaseProtocol. resume_writing ( ) ¶: Called when the transport’s buffer drains below the low watermark.

If the buffer size equals the high watermark, pause_writing() is not called: the buffer size must go strictly over.

Conversely, resume_writing() is called when the buffer size is equal or lower than the low watermark. These end conditions are important to ensure that things go as expected when either mark is zero.

流协议 ¶

Event methods, such as loop.create_server() , loop.create_unix_server() , loop.create_connection() , loop.create_unix_connection() , loop.connect_accepted_socket() , loop.connect_read_pipe() ，和 loop.connect_write_pipe() accept factories that return streaming protocols.

Protocol. data_received ( data ) ¶

Called when some data is received. data is a non-empty bytes object containing the incoming data.

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. However, data is always received in the correct order.

The method can be called an arbitrary number of times while a connection is open.

不管怎样， protocol.eof_received() is called at most once. Once eof_received() is called, data_received() is not called anymore.

Protocol. eof_received ( ) ¶

Called when the other end signals it won’t send any more data (for example by calling transport.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, the protocol used determines whether to close the transport. Since the default implementation returns None , it implicitly closes the connection.

Some transports, including SSL, don’t support half-closed connections, in which case returning true from this method will result in the connection being closed.

State machine:

start -> connection_made
    [-> data_received]*
    [-> eof_received]?
-> connection_lost -> end

缓冲流协议 ¶

3.7 版添加。

Buffered Protocols can be used with any event loop method that supports 流协议 .

BufferedProtocol implementations allow explicit manual allocation and control of the receive buffer. Event loops can then use the buffer provided by the protocol to avoid unnecessary data copies. This can result in noticeable performance improvement for protocols that receive big amounts of data. Sophisticated protocol implementations can significantly reduce the number of buffer allocations.

The following callbacks are called on BufferedProtocol 实例：

BufferedProtocol. get_buffer ( sizehint ) ¶

Called to allocate a new receive buffer.

sizehint is the recommended minimum size for the returned buffer. It is acceptable to return smaller or larger buffers than what sizehint suggests. When set to -1, the buffer size can be arbitrary. It is an error to return a buffer with a zero size.

get_buffer() must return an object implementing the 缓冲协议 .

BufferedProtocol. buffer_updated ( nbytes ) ¶

Called when the buffer was updated with the received data.

nbytes is the total number of bytes that were written to the buffer.

BufferedProtocol. eof_received ( ) ¶: See the documentation of the protocol.eof_received() 方法。

get_buffer() can be called an arbitrary number of times during a connection. However, protocol.eof_received() is called at most once and, if called, get_buffer() and buffer_updated() won’t be called after it.

State machine:

start -> connection_made
    [-> get_buffer
        [-> buffer_updated]?
    ]*
    [-> eof_received]?
-> connection_lost -> end

数据报协议 ¶

Datagram Protocol instances should be constructed by protocol factories passed to the loop.create_datagram_endpoint() 方法。

DatagramProtocol. datagram_received ( data , addr ) ¶: Called when a datagram is received. data is a bytes object containing the incoming data. addr is the address of the peer sending the data; the exact format depends on the transport.

DatagramProtocol. error_received ( exc ) ¶

Called when a previous send or receive operation raises an OSError . exc 是 OSError 实例。

This method is called in rare conditions, when the transport (e.g. UDP) detects that a datagram could not be delivered to its recipient. In many conditions though, undeliverable datagrams will be silently dropped.

注意

On BSD systems (macOS, FreeBSD, etc.) flow control is not supported for datagram protocols, because there is no reliable way to detect send failures caused by writing too many packets.

The socket always appears ‘ready’ and excess packets are dropped. An OSError with errno 设为 errno.ENOBUFS may or may not be raised; if it is raised, it will be reported to DatagramProtocol.error_received() but otherwise ignored.

子进程协议 ¶

Subprocess Protocol instances should be constructed by protocol factories passed to the loop.subprocess_exec() and loop.subprocess_shell() 方法。

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 received 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 ( ) ¶

Called when the child process has exited.

It can be called before pipe_data_received() and pipe_connection_lost() 方法。

范例 ¶

TCP 回显服务器 ¶

Create a TCP echo server using the loop.create_server() method, send back received data, and close the connection:

import asyncio
class EchoServerProtocol(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()
async def main():
    # Get a reference to the event loop as we plan to use
    # low-level APIs.
    loop = asyncio.get_running_loop()
    server = await loop.create_server(
        EchoServerProtocol,
        '127.0.0.1', 8888)
    async with server:
        await server.serve_forever()
asyncio.run(main())

另请参阅

The TCP 回显服务器使用流范例使用高级 asyncio.start_server() 函数。

TCP 回显客户端 ¶

TCP 回显客户端使用 loop.create_connection() method, sends data, and waits until the connection is closed:

import asyncio
class EchoClientProtocol(asyncio.Protocol):
    def __init__(self, message, on_con_lost):
        self.message = message
        self.on_con_lost = on_con_lost
    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')
        self.on_con_lost.set_result(True)
async def main():
    # Get a reference to the event loop as we plan to use
    # low-level APIs.
    loop = asyncio.get_running_loop()
    on_con_lost = loop.create_future()
    message = 'Hello World!'
    transport, protocol = await loop.create_connection(
        lambda: EchoClientProtocol(message, on_con_lost),
        '127.0.0.1', 8888)
    # Wait until the protocol signals that the connection
    # is lost and close the transport.
    try:
        await on_con_lost
    finally:
        transport.close()
asyncio.run(main())

另请参阅

The TCP 回显客户端使用流范例使用高级 asyncio.open_connection() 函数。

UDP 回显服务器 ¶

UDP 回显服务器，使用 loop.create_datagram_endpoint() 方法，发回收到数据：

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)
async def main():
    print("Starting UDP server")
    # Get a reference to the event loop as we plan to use
    # low-level APIs.
    loop = asyncio.get_running_loop()
    # One protocol instance will be created to serve all
    # client requests.
    transport, protocol = await loop.create_datagram_endpoint(
        EchoServerProtocol,
        local_addr=('127.0.0.1', 9999))
    try:
        await asyncio.sleep(3600)  # Serve for 1 hour.
    finally:
        transport.close()
asyncio.run(main())

UDP 回显客户端 ¶

UDP 回显客户端，使用 loop.create_datagram_endpoint() method, sends data and closes the transport when it receives the answer:

import asyncio
class EchoClientProtocol:
    def __init__(self, message, on_con_lost):
        self.message = message
        self.on_con_lost = on_con_lost
        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("Connection closed")
        self.on_con_lost.set_result(True)
async def main():
    # Get a reference to the event loop as we plan to use
    # low-level APIs.
    loop = asyncio.get_running_loop()
    on_con_lost = loop.create_future()
    message = "Hello World!"
    transport, protocol = await loop.create_datagram_endpoint(
        lambda: EchoClientProtocol(message, on_con_lost),
        remote_addr=('127.0.0.1', 9999))
    try:
        await on_con_lost
    finally:
        transport.close()
asyncio.run(main())

连接现有套接字 ¶

等待直到套接字接收数据使用 loop.create_connection() 方法采用协议：

import asyncio
import socket
class MyProtocol(asyncio.Protocol):
    def __init__(self, on_con_lost):
        self.transport = None
        self.on_con_lost = on_con_lost
    def connection_made(self, transport):
        self.transport = transport
    def data_received(self, data):
        print("Received:", data.decode())
        # We are done: close the transport;
        # connection_lost() will be called automatically.
        self.transport.close()
    def connection_lost(self, exc):
        # The socket has been closed
        self.on_con_lost.set_result(True)
async def main():
    # Get a reference to the event loop as we plan to use
    # low-level APIs.
    loop = asyncio.get_running_loop()
    on_con_lost = loop.create_future()
    # Create a pair of connected sockets
    rsock, wsock = socket.socketpair()
    # Register the socket to wait for data.
    transport, protocol = await loop.create_connection(
        lambda: MyProtocol(on_con_lost), sock=rsock)
    # Simulate the reception of data from the network.
    loop.call_soon(wsock.send, 'abc'.encode())
    try:
        await protocol.on_con_lost
    finally:
        transport.close()
        wsock.close()
asyncio.run(main())

另请参阅

The 为读取事件看守文件描述符范例使用低级 loop.add_reader() 方法以注册 FD (文件描述符)。

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.

loop.subprocess_exec() 和 SubprocessProtocol ¶

An example of a subprocess protocol used to get the output of a subprocess and to wait for the subprocess exit.

子进程的创建通过 loop.subprocess_exec() 方法：

import asyncio
import sys
class DateProtocol(asyncio.SubprocessProtocol):
    def __init__(self, exit_future):
        self.exit_future = exit_future
        self.output = bytearray()
        self.pipe_closed = False
        self.exited = False
    def pipe_connection_lost(self, fd, exc):
        self.pipe_closed = True
        self.check_for_exit()
    def pipe_data_received(self, fd, data):
        self.output.extend(data)
    def process_exited(self):
        self.exited = True
        # process_exited() method can be called before
        # pipe_connection_lost() method: wait until both methods are
        # called.
        self.check_for_exit()
    def check_for_exit(self):
        if self.pipe_closed and self.exited:
            self.exit_future.set_result(True)
async def get_date():
    # Get a reference to the event loop as we plan to use
    # low-level APIs.
    loop = asyncio.get_running_loop()
    code = 'import datetime; print(datetime.datetime.now())'
    exit_future = asyncio.Future(loop=loop)
    # Create the subprocess controlled by DateProtocol;
    # redirect the standard output into a pipe.
    transport, protocol = await loop.subprocess_exec(
        lambda: DateProtocol(exit_future),
        sys.executable, '-c', code,
        stdin=None, stderr=None)
    # Wait for the subprocess exit using the process_exited()
    # method of the protocol.
    await exit_future
    # Close the stdout pipe.
    transport.close()
    # Read the output which was collected by the
    # pipe_data_received() method of the protocol.
    data = bytes(protocol.output)
    return data.decode('ascii').rstrip()
date = asyncio.run(get_date())
print(f"Current date: {date}")

另请参阅相同范例使用高级 API 编写。

传输和协议 ¶

传输 ¶

传输层次结构 ¶

基传输 ¶

只读传输 ¶

只写传输 ¶

数据报传输 ¶

子进程传输 ¶

协议 ¶

基协议 ¶

BaseProtocol ¶

流协议 ¶

缓冲流协议 ¶

数据报协议 ¶

子进程协议 ¶

范例 ¶

TCP 回显服务器 ¶

TCP 回显客户端 ¶

UDP 回显服务器 ¶

UDP 回显客户端 ¶

连接现有套接字 ¶

loop.subprocess_exec() 和 SubprocessProtocol ¶

内容表

上一话题

下一话题

本页