Python sockets - keep socket alive?

Question

I'm having a little trouble with sockets in Python. Whenever someone connects it works fine but if they disconnect the server program closes. I want the server program to remain open after the client closes. I'm using a while True loop to keep the connection alive but once the client closes the connection the server closes it's connection.

Here is the client:

import socket, sys
conn = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
host = sys.argv[1]
port = int(sys.argv[2])
conn.connect((host, port))

print("Connected to host " + sys.argv[1])
td = 1
while td == 1:
   msg = raw_input('MSG:  ')

Here is the server:

import socket, sys

socket.setdefaulttimeout(150)
host = ''               
port = 50005
socksize = 1024

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((host, port))
print("Server started on port: %s" % port)
s.listen(1)
print("Now listening...\n")
conn, addr = s.accept()

while True:
    print 'New connection from %s:%d' % (addr[0], addr[1])
    data = conn.recv(socksize)
    if not data:
        break
    elif data == 'killsrv':
        conn.close()
        sys.exit()
    else:
       print(data)

Are you using n+1 sockets for n connections? You need one socket that is listening at all times. This listen socket accepts new connections and opens another socket every time a connection is requested — Penang
Can you post a short piece of code to demonstrate the problem? — SimonJ
n+1 sockets? Not sure if I'm following. Could you explain a bit more? — AustinM
If you want to get anything done use at least a socketserver. — Jochen Ritzel

Jeff Jeff · Accepted Answer · 2011-02-24T22:22:42

If a client closes a connection, you want it to close the socket.

It seems like there's a bit of a disconnect here that I'll try to elaborate on. When you create a socket, bind, and listen, you've established an open door for others to come and make connections to you.

Once a client connects to you, and you use the accept() call to accept the connection and get a new socket (conn), which is returned for you to interact with the client. Your original listening socket is still there and active, and you can still use it to accept more new connections.

Looking at your code, you probably want to do something like this:

while True:
    print("Now listening...\n")
    conn, addr = s.accept()

    print 'New connection from %s:%d' % (addr[0], addr[1])
    data = conn.recv(socksize)
    if not data:
        break
    elif data == 'killsrv':
        conn.close()
        sys.exit()
    else:
        print(data)

Please note that this is just a starting point, and as others have suggested you probably want to use select() along with forking off processes or spawning threads to service each client.

Python sockets - keep socket alive?

2 Answers