Multi Threaded TCP server in Python

Question

I have created a simple multi threaded tcp server using python's threding module. This server creates a new thread each time a new client is connected.

#!/usr/bin/env python

import socket, threading

class ClientThread(threading.Thread):

    def __init__(self,ip,port):
        threading.Thread.__init__(self)
        self.ip = ip
        self.port = port
        print "[+] New thread started for "+ip+":"+str(port)


    def run(self):    
        print "Connection from : "+ip+":"+str(port)

        clientsock.send("\nWelcome to the server\n\n")

        data = "dummydata"

        while len(data):
            data = clientsock.recv(2048)
            print "Client sent : "+data
            clientsock.send("You sent me : "+data)

        print "Client disconnected..."

host = "0.0.0.0"
port = 9999

tcpsock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
tcpsock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

tcpsock.bind((host,port))
threads = []


while True:
    tcpsock.listen(4)
    print "\nListening for incoming connections..."
    (clientsock, (ip, port)) = tcpsock.accept()
    newthread = ClientThread(ip, port)
    newthread.start()
    threads.append(newthread)

for t in threads:
    t.join()

Then I opened two new terminals and connected to the server using netcat. Then, when I type and send my first data to the server using the first terminal I connected, reply from the server comes to the other terminal and first connection got disconnected. I guessed the reason but I am doubtful whether this happens because clientsock variable is overwritten so that it refers to the second connection's socket. Am I correct and then how to avoid that?

Is there a way other than using an array with limited number of socket variables and using each variable for each connection?

Answer 1

You should pass the client sock to the thread like you do with the ip address and the port:

class ClientThread(threading.Thread):

    def __init__(self, ip, port, socket):
        threading.Thread.__init__(self)
        self.ip = ip
        self.port = port
        self.socket = socket
        print "[+] New thread started for "+ip+":"+str(port)

    def run(self):
        # use self.socket to send/receive

...
(clientsock, (ip, port)) = tcpsock.accept()
newthread = ClientThread(ip, port, clientsock)
...

Answer 2

I have created this nice class you can override

import socket
import thread

class SocketServer(socket.socket):
    clients = []

    def __init__(self):
        socket.socket.__init__(self)
        #To silence- address occupied!!
        self.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        self.bind(('0.0.0.0', 8080))
        self.listen(5)

    def run(self):
        print "Server started"
        try:
            self.accept_clients()
        except Exception as ex:
            print ex
        finally:
            print "Server closed"
            for client in self.clients:
                client.close()
            self.close()

    def accept_clients(self):
        while 1:
            (clientsocket, address) = self.accept()
            #Adding client to clients list
            self.clients.append(clientsocket)
            #Client Connected
            self.onopen(clientsocket)
            #Receiving data from client
            thread.start_new_thread(self.recieve, (clientsocket,))

    def recieve(self, client):
        while 1:
            data = client.recv(1024)
            if data == '':
                break
            #Message Received
            self.onmessage(client, data)
        #Removing client from clients list
        self.clients.remove(client)
        #Client Disconnected
        self.onclose(client)
        #Closing connection with client
        client.close()
        #Closing thread
        thread.exit()
        print self.clients

    def broadcast(self, message):
        #Sending message to all clients
        for client in self.clients:
            client.send(message)

    def onopen(self, client):
        pass

    def onmessage(self, client, message):
        pass

    def onclose(self, client):
        pass

And here's an example:

class BasicChatServer(SocketServer):

    def __init__(self):
        SocketServer.__init__(self)

    def onmessage(self, client, message):
        print "Client Sent Message"
        #Sending message to all clients
        self.broadcast(message)

    def onopen(self, client):
        print "Client Connected"

    def onclose(self, client):
        print "Client Disconnected"

def main():
    server = BasicChatServer()
    server.run()

if __name__ == "__main__":
    main()

Answer 3

Python3 has ThreadingTCPServer (and others) which can do this for you

Note the threading here is per request and not per client - this has the disadvantage of a small thread-wind-up time per request, but the advantage that it scales better as the number of clients increases.