流 ¶

源代码： Lib/asyncio/streams.py

---

流是操控网络连接的高级 async/await 就绪原语。流允许发送和接收数据，在不使用回调 (或低级协议) 和传输的情况下。

这里是使用 asyncio 流编写的 TCP 回显客户端范例：

import asyncio
async def tcp_echo_client(message):
    reader, writer = await asyncio.open_connection(
        '127.0.0.1', 8888)
    print(f'Send: {message!r}')
    writer.write(message.encode())
    await writer.drain()
    data = await reader.read(100)
    print(f'Received: {data.decode()!r}')
    print('Close the connection')
    writer.close()
    await writer.wait_closed()
asyncio.run(tcp_echo_client('Hello World!'))
					

另请参阅 范例 以下章节。

流函数

The following top-level asyncio functions can be used to create and work with streams:

协程 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 ) ¶

Establish a network connection and return a pair of (reader, writer) 对象。

返回的 reader and writer objects are instances of StreamReader and StreamWriter 类。

The loop argument is optional and can always be determined automatically when this function is awaited from a coroutine.

limit determines the buffer size limit used by the returned StreamReader instance. By default the limit is set to 64 KiB.

The rest of the arguments are passed directly to loop.create_connection() .

3.7 版新增： The ssl_handshake_timeout 参数。

协程 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 ) ¶

启动套接字服务器。

The client_connected_cb callback is called whenever a new client connection is established. It receives a (reader, writer) pair as two arguments, instances of the StreamReader and StreamWriter 类。

client_connected_cb can be a plain callable or a 协程函数 ; if it is a coroutine function, it will be automatically scheduled as a Task .

The loop argument is optional and can always be determined automatically when this method is awaited from a coroutine.

limit determines the buffer size limit used by the returned StreamReader instance. By default the limit is set to 64 KiB.

The rest of the arguments are passed directly to loop.create_server() .

3.7 版新增： The ssl_handshake_timeout and start_serving 参数。

Unix Sockets

协程 asyncio. open_unix_connection ( path=None , * , loop=None , limit=None , ssl=None , sock=None , server_hostname=None , ssl_handshake_timeout=None ) ¶

Establish a Unix socket connection and return a pair of (reader, writer) .

类似于 open_connection() 但运转于 Unix 套接字。

另请参阅文档编制为 loop.create_unix_connection() .

可用性 ：Unix。

3.7 版新增： The ssl_handshake_timeout 参数。

3.7 版改变： The path parameter can now be a 像路径对象

协程 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 ) ¶

启动 Unix 套接字服务器。

类似于 start_server() 但能操控 Unix 套接字。

另请参阅文档编制为 loop.create_unix_server() .

可用性 ：Unix。

3.7 版新增： The ssl_handshake_timeout and start_serving 参数。

3.7 版改变： The path parameter can now be a 像路径对象 .

StreamReader ¶

class asyncio. StreamReader ¶

Represents a reader object that provides APIs to read data from the IO stream.

It is not recommended to instantiate StreamReader objects directly; use open_connection() and start_server() 代替。

协程 read ( n=-1 ) ¶

读取直到 n 字节。若 n is not provided, or set to -1 , read until EOF and return all read bytes.

If EOF was received and the internal buffer is empty, return an empty bytes 对象。

协程 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 returns partially read data.

If EOF is received and the internal buffer is empty, return an empty bytes 对象。

协程 readexactly ( n ) ¶

准确读取 n 字节。

引发 IncompleteReadError if EOF is reached before n can be read. Use the IncompleteReadError.partial attribute to get the partially read data.

协程 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.

If the amount of data read exceeds the configured stream limit, a LimitOverrunError exception is raised, and the data is left in the internal buffer and can be read again.

If EOF is reached before the complete separator is found, an IncompleteReadError exception is raised, and the internal buffer is reset. The IncompleteReadError.partial attribute may contain a portion of the separator.

3.5.2 版新增。

at_eof ( ) ¶

返回 True if the buffer is empty and feed_eof() was called.

StreamWriter ¶

class asyncio. StreamWriter ¶

Represents a writer object that provides APIs to write data to the IO stream.

It is not recommended to instantiate StreamWriter objects directly; use open_connection() and start_server() 代替。

write ( data ) ¶

The method attempts to write the data to the underlying socket immediately. If that fails, the data is queued in an internal write buffer until it can be sent.

The method should be used along with the drain() 方法：

stream.write(data)
await stream.drain()
						

writelines ( data ) ¶

The method writes a list (or any iterable) of bytes to the underlying socket immediately. If that fails, the data is queued in an internal write buffer until it can be sent.

The method should be used along with the drain() 方法：

stream.writelines(lines)
await stream.drain()
						

close ( ) ¶

The method closes the stream and the underlying socket.

The method should be used along with the wait_closed() 方法：

stream.close()
await stream.wait_closed()
					

can_write_eof ( ) ¶

返回 True if the underlying transport supports the write_eof() 方法， False 否则。

write_eof ( ) ¶

Close the write end of the stream after the buffered write data is flushed.

transport ¶

Return the underlying asyncio transport.

get_extra_info ( name , default=None ) ¶

Access optional transport information; see BaseTransport.get_extra_info() 了解细节。

协程 drain ( ) ¶

Wait until it is appropriate to resume writing to the stream. Example:

writer.write(data)
await writer.drain()
						

This is a flow control method that interacts with the underlying IO write buffer. When the size of the buffer reaches the high watermark, drain() blocks until the size of the buffer is drained down to the low watermark and writing can be resumed. When there is nothing to wait for, the drain() returns immediately.

is_closing ( ) ¶

返回 True if the stream is closed or in the process of being closed.

3.7 版新增。

协程 wait_closed ( ) ¶

等待直到流被关闭。

Should be called after close() to wait until the underlying connection is closed.

3.7 版新增。

范例 ¶

TCP 回显客户端使用流 ¶

TCP 回显客户端使用 asyncio.open_connection() 函数：

import asyncio
async def tcp_echo_client(message):
    reader, writer = await asyncio.open_connection(
        '127.0.0.1', 8888)
    print(f'Send: {message!r}')
    writer.write(message.encode())
    data = await reader.read(100)
    print(f'Received: {data.decode()!r}')
    print('Close the connection')
    writer.close()
asyncio.run(tcp_echo_client('Hello World!'))
						

另请参阅

The TCP 回显客户端协议 范例使用低级 loop.create_connection() 方法。

TCP 回显服务器使用流 ¶

TCP 回显服务器使用 asyncio.start_server() 函数：

import asyncio
async def handle_echo(reader, writer):
    data = await reader.read(100)
    message = data.decode()
    addr = writer.get_extra_info('peername')
    print(f"Received {message!r} from {addr!r}")
    print(f"Send: {message!r}")
    writer.write(data)
    await writer.drain()
    print("Close the connection")
    writer.close()
async def main():
    server = await asyncio.start_server(
        handle_echo, '127.0.0.1', 8888)
    addr = server.sockets[0].getsockname()
    print(f'Serving on {addr}')
    async with server:
        await server.serve_forever()
asyncio.run(main())
						

另请参阅

The TCP 回显服务器协议 范例使用 loop.create_server() 方法。

获取 HTTP 头 ¶

查询命令行传递的 HTTP URL 头的简单范例：

import asyncio
import urllib.parse
import sys
async def print_http_headers(url):
    url = urllib.parse.urlsplit(url)
    if url.scheme == 'https':
        reader, writer = await asyncio.open_connection(
            url.hostname, 443, ssl=True)
    else:
        reader, writer = await asyncio.open_connection(
            url.hostname, 80)
    query = (
        f"HEAD {url.path or '/'} HTTP/1.0\r\n"
        f"Host: {url.hostname}\r\n"
        f"\r\n"
    )
    writer.write(query.encode('latin-1'))
    while True:
        line = await reader.readline()
        if not line:
            break
        line = line.decode('latin1').rstrip()
        if line:
            print(f'HTTP header> {line}')
    # Ignore the body, close the socket
    writer.close()
url = sys.argv[1]
asyncio.run(print_http_headers(url))
						

用法：

python example.py http://example.com/path/page.html
						

或采用 HTTPS：

python example.py https://example.com/path/page.html
			
						

注册打开套接字以使用流等待数据 ¶

协程等待直到套接字接收数据使用 open_connection() 函数：

import asyncio
import socket
async def wait_for_data():
    # Get a reference to the current event loop because
    # we want to access low-level APIs.
    loop = asyncio.get_running_loop()
    # Create a pair of connected sockets.
    rsock, wsock = socket.socketpair()
    # Register the open socket to wait for data.
    reader, writer = await asyncio.open_connection(sock=rsock)
    # 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()
asyncio.run(wait_for_data())
						

另请参阅

The 注册打开套接字等待使用协议的数据 范例使用低级协议和 loop.create_connection() 方法。

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

内容表

• 流
  • StreamReader
  • StreamWriter
  • 范例
    • TCP 回显客户端使用流
    • TCP 回显服务器使用流
    • 获取 HTTP 头
    • 注册打开套接字以使用流等待数据

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