Prompt for user input using python asyncio.create_server instance

Question

I\'m learning about python 3 asyncio library, and I\'ve run into a small issue. I\'m trying to adapt the EchoServer example from the python docs to prompt for user input rat

Answer 1

You can use loop.add_reader schedule a callback to run when data is available on sys.stdin, and then use an asyncio.Queue to pass the stdin data received to your data_received method:

import sys
import asyncio


def got_stdin_data(q):
    asyncio.ensure_future(q.put(sys.stdin.readline()))

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))
       fut = asyncio.ensure_future(q.get())
       fut.add_done_callback(self.write_reply)

   def write_reply(self, fut):
       reply = fut.result()
       print('Send: {!r}'.format(reply))
       self.transport.write(reply.encode())

       #print('Close the client socket')
       #self.transport.close()

q = asyncio.Queue()
loop = asyncio.get_event_loop()
loop.add_reader(sys.stdin, got_stdin_data, q)
# 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()

The only tricky bit is how we call the Queue.put/Queue.get methods; both of them are coroutines, which can't be called using yield from in the callback or the Protocol instance methods. Instead, we just schedule them with the event loop using asyncio.ensure_future, and then use the add_done_callback method to handle the reply we retrieve from the get() call.

Note: asyncio.ensure_future was introduced in Python 3.4.4. Prior to that, the method was called asyncio.async. Additionally, Python 3.7 introduced asyncio.create_task, which is now the preferred method.