Python TCP Server

Question

I wrote a simple Python 3 TCP multithreaded server and telnet to it. All seems to work until I go to close the telnet connection. When I close the telnet connection ^] and then control+d to exit telnet the server repeatedly prints ''.

Is there something trivial I am missing here to prevent this behavior?

import socket 
from threading import Thread 
from socketserver import ThreadingMixIn 
 
# Multithreaded Python server : TCP Server Socket Thread Pool
class ClientThread(Thread): 
 
    def __init__(self,ip,port): 
        Thread.__init__(self) 
        self.ip = ip 
        self.port = port 
        print ("[+] New server socket thread started for " + ip + ":" + str(port)) 
 
    def run(self): 
        while True : 
            data = conn.recv(2048) 
            #data = "Echo data: " + data.decode()
            print ("Server received data: ", data)
            conn.send(data)  # echo 
 
# Multithreaded Python server : TCP Server Socket Program Stub
TCP_IP = '0.0.0.0' 
TCP_PORT = 2004 
BUFFER_SIZE = 1024  # Usually 1024, but we need quick response 
 
tcpServer = socket.socket(socket.AF_INET, socket.SOCK_STREAM) 
tcpServer.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) 
tcpServer.bind((TCP_IP, TCP_PORT)) 
threads = [] 
 
while True: 
    tcpServer.listen(4) 
    print ("Multithreaded Python server : Waiting for connections from TCP clients...") 
    (conn, (ip,port)) = tcpServer.accept() 
    newthread = ClientThread(ip,port) 
    newthread.start() 
    threads.append(newthread) 
 
for t in threads: 
    t.join() 



Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received data:  b''
Server received da

Ruud de Jong · Accepted Answer · 2017-07-18 15:37:38Z

1

Your client thread seems to loop indefinitely. It will happily continue to (attempt to) read from the closed connection. You should add a check that the data received from the read actually contains bytes. If not, the connection is closed.

So, after

data = conn.recv(2048)

add:

if not data: break

answered Jul 18, 2017 at 15:37

Ruud de Jong

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