how to handle tcp client socket auto reconnect in python asyncio?

Question

I am using python asyncio streams to connect to several socket servers, but when the server is down, my code can't auto reconnect.

What I need is that, when the server is down, my script will try to reconnect every 5 seconds, until connected and start to parse the data again.

import asyncio

server1 = {'host': '192.168.1.51', 'port': 11110}
server2 = {'host': '192.168.1.52', 'port': 11110}


async def tcp_client(host, port, loop):
    print('connect to server {} {}'.format(host, str(port)))
    reader, writer = await asyncio.open_connection(host, port, loop=loop)

    while True:
        data = await reader.read(100)
        print('raw data received: {}'.format(data))

        await asyncio.sleep(0.1)


loop = asyncio.get_event_loop()
try:
    for server in [server1, server2]:
        loop.run_until_complete(tcp_client(server['host'], server['port'], loop))
        print('task added: connect to server {} {}'.format(server['host'], server['port']))
finally:
    loop.close()
    print('loop closed')

Answer 1

You can handle reconnection by simply looping over a try/except statement.

Additionally, asyncio.wait_for can be used to set a timeout on the read operation.

Consider this working example:

import asyncio

async def tcp_client(host, port):
    reader, writer = await asyncio.open_connection(host, port)
    try:
        while not reader.at_eof():
            data = await asyncio.wait_for(reader.read(100), 3.0)
            print('raw data received: {}'.format(data))
    finally:
        writer.close()

async def tcp_reconnect(host, port):
    server = '{} {}'.format(host, port)
    while True:
        print('Connecting to server {} ...'.format(server))
        try:
            await tcp_client(host, port)
        except ConnectionRefusedError:
            print('Connection to server {} failed!'.format(server))
        except asyncio.TimeoutError:
            print('Connection to server {} timed out!'.format(server))
        else:
            print('Connection to server {} is closed.'.format(server))
        await asyncio.sleep(2.0)

async def main():
    servers = [('localhost', 8888), ('localhost', 9999)]
    coros = [tcp_reconnect(host, port) for host, port in servers]
    await asyncio.gather(*coros)

if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(main())
    loop.close()