Python 3.4+Async programmingfunction

asyncio.start_server()

streams

Starts a TCP server: for each incoming connection it calls a callback with a (StreamReader, StreamWriter) pair.

Syntax

server = await asyncio.start_server(client_connected_cb, host=None, port=None, *, limit=2**16, **kwds)

The server accepts connections right after the await; serve_forever() merely keeps the program alive. If the callback is a coroutine, each client gets its own task; an exception there does not crash the server, it is only logged, so handler errors are easy to miss. port=0 asks the OS for a free port; read the real one from server.sockets[0].getsockname(). async with server closes it on exit.

Examples

import asyncio
async def handle(reader, writer):
    data = await reader.read(100)
    writer.write(data.upper())
    await writer.drain()
    writer.close()
async def main():
    server = await asyncio.start_server(handle, '127.0.0.1', 0)
    host, port = server.sockets[0].getsockname()[:2]
    print(host, port > 0)  # → 127.0.0.1 True
    async with server:
        reader, writer = await asyncio.open_connection(host, port)
        writer.write(b'abc')
        print(await reader.read(100))  # → b'ABC'
        writer.close()
        await writer.wait_closed()
asyncio.run(main())

See also

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