Handling multiple connections in python with sockets

Question

I have a code which works perfectly for one connection. I have seen two options for multi-client handling but I don't really understand it. Here is the server socket code:

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as listening_sock:
    listening_sock.bind(('', port))
    listening_sock.listen()
    client_soc, client_address = listening_sock.accept()
    client_soc.sendall('200#Welcome to my server!'.encode())
    print(f'Address {client_soc.getsockname()[0]} connected with port {client_soc.getsockname()[1]}')
    while True:
        # get message
        msg = client_soc.recv(1024).decode()
        # receive log print:
        print(f'"{msg}" sent from {client_soc.getsockname()[0]}')
        if 'Quit' in msg:
            client_soc.sendall('200#Thanks for using my server!'.encode())
            client_soc.close()
        elif '0' < msg.split('#')[0] <= '9':  # one of the valid actions
            answer = call_action(msg.split('#')[0], db, msg.split('#')[1])  # the answer for given parameter
            client_soc.sendall("200#".encode() + answer.encode())

If I have only one connection it works good and last thing I need to add is option for multiple-client handling. What is the shortest and easiest way to do it?

Mark Tolonen · Accepted Answer · 2025-04-10 22:24:50Z

The code only calls accept once. Instead, call accept in a while loop and create a thread for each client connection so they are handled in parallel. Use the following pattern as an example:

import socket
import threading

# Thread to handle each "client_soc" connection
def handler(client_soc):
    with client_soc:  # closes socket when with block exits
        ...

with socket.socket() as listening_sock:
    listening_sock.bind(('', 8000))
    listening_sock.listen()
    while True:
        client_soc, client_address = listening_sock.accept()
        # Send each "client_soc" connection as a parameter to a thread.
        threading.Thread(target=handler, args=(client_soc,), daemon=True).start()

There is also a built-in socket server that simplifies this process. Here's a tested example echo server that echoes back newline-terminated data:

from socketserver import ThreadingTCPServer, StreamRequestHandler

class echohandler(StreamRequestHandler):
    def handle(self):
        print(f'Connected: {self.client_address[0]}:{self.client_address[1]}')
        while True:
            # rfile and wfile are created with socket.makefile()
            # and wrap the socket in file-like objects for reading and
            # writing the socket.
            #
            # Get newline-terminated message.
            msg = self.rfile.readline()
            if not msg:
                print(f'Disconnected: {self.client_address[0]}:{self.client_address[1]}')
                break # exits handler, framework closes socket
            print(f'Received: {msg}')
            self.wfile.write(msg)
            self.wfile.flush()  # file-like object must be flushed to ensure send.

server = ThreadingTCPServer(('', 8000), echohandler)
server.serve_forever()

Andrey · Accepted Answer · 2020-05-20 11:02:44Z

2

Your code blocks itself.

For instance: client_soc, client_address = listening_sock.accept() Accepts client, then while True: runs forever, so you can work with 1 connection only, because socket.accept() is called once. You should learn some of these to solve your problem: asyncio, threading, multiprocessing. These libraries will help your code to accept and work with clients concurrently. Sockets can use every, but often they are paired with asyncio: https://asyncio.readthedocs.io/

answered May 20, 2020 at 11:02

Andrey

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2 Comments

Ilan Yashuk Over a year ago

Should I make a function that works with a single socket and use it multiple times or something similiar?

Andrey Over a year ago

Yes, you can do something like this def handle_client(): your code for client # after accept import threading threading.Thread(target=handle_client, args=(client_soc,)).start() That will run new thread, but there are so many things to learn, and you should watch videos on youtube on these topics or read documentation.

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