Python SocketServer: sending to multiple clients?

Question

Well, I\'m trying to build a small python prgram with a SocketServer that is supposed to send messages it receives to all connected clients. I\'m stuck, I don\'t know how to

Answer 1

You want to look at asyncore here. The socket operations you're calling on the client side are blocking (don't return until some data is received or a timeout occurs) which makes it hard to listen for messages sent from the host and let the client instances enqueue data to send at the same time. asyncore is supposed to abstract the timeout-based polling loop away from you.

Here's a code "sample" -- let me know if anything is unclear:

from __future__ import print_function

import asyncore
import collections
import logging
import socket


MAX_MESSAGE_LENGTH = 1024


class RemoteClient(asyncore.dispatcher):

    """Wraps a remote client socket."""

    def __init__(self, host, socket, address):
        asyncore.dispatcher.__init__(self, socket)
        self.host = host
        self.outbox = collections.deque()

    def say(self, message):
        self.outbox.append(message)

    def handle_read(self):
        client_message = self.recv(MAX_MESSAGE_LENGTH)
        self.host.broadcast(client_message)

    def handle_write(self):
        if not self.outbox:
            return
        message = self.outbox.popleft()
        if len(message) > MAX_MESSAGE_LENGTH:
            raise ValueError('Message too long')
        self.send(message)


class Host(asyncore.dispatcher):

    log = logging.getLogger('Host')

    def __init__(self, address=('localhost', 0)):
        asyncore.dispatcher.__init__(self)
        self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
        self.bind(address)
        self.listen(1)
        self.remote_clients = []

    def handle_accept(self):
        socket, addr = self.accept() # For the remote client.
        self.log.info('Accepted client at %s', addr)
        self.remote_clients.append(RemoteClient(self, socket, addr))

    def handle_read(self):
        self.log.info('Received message: %s', self.read())

    def broadcast(self, message):
        self.log.info('Broadcasting message: %s', message)
        for remote_client in self.remote_clients:
            remote_client.say(message)


class Client(asyncore.dispatcher):

    def __init__(self, host_address, name):
        asyncore.dispatcher.__init__(self)
        self.log = logging.getLogger('Client (%7s)' % name)
        self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
        self.name = name
        self.log.info('Connecting to host at %s', host_address)
        self.connect(host_address)
        self.outbox = collections.deque()

    def say(self, message):
        self.outbox.append(message)
        self.log.info('Enqueued message: %s', message)

    def handle_write(self):
        if not self.outbox:
            return
        message = self.outbox.popleft()
        if len(message) > MAX_MESSAGE_LENGTH:
            raise ValueError('Message too long')
        self.send(message)

    def handle_read(self):
        message = self.recv(MAX_MESSAGE_LENGTH)
        self.log.info('Received message: %s', message)


if __name__ == '__main__':
    logging.basicConfig(level=logging.INFO)
    logging.info('Creating host')
    host = Host()
    logging.info('Creating clients')
    alice = Client(host.getsockname(), 'Alice')
    bob = Client(host.getsockname(), 'Bob')
    alice.say('Hello, everybody!')
    logging.info('Looping')
    asyncore.loop()

Which results in the following output:

INFO:root:Creating host
INFO:root:Creating clients
INFO:Client (  Alice):Connecting to host at ('127.0.0.1', 51117)
INFO:Client (    Bob):Connecting to host at ('127.0.0.1', 51117)
INFO:Client (  Alice):Enqueued message: Hello, everybody!
INFO:root:Looping
INFO:Host:Accepted client at ('127.0.0.1', 55628)
INFO:Host:Accepted client at ('127.0.0.1', 55629)
INFO:Host:Broadcasting message: Hello, everybody!
INFO:Client (  Alice):Received message: Hello, everybody!
INFO:Client (    Bob):Received message: Hello, everybody!