Question

I’m trying to make a server / client connection with sockets. But they will not close properly and I can’t wrap my head around why.

Update 1

I’ve corrected my stupid misstake below of not actually CALLING the s.close function in the question.
But it turn out this was’nt my problem.

End of updates

This is my server code:

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import socket
import sys

if __name__ == '__main__':
    # Server connection
    s = socket.socket()          # Create a socket object
    host = socket.gethostname()  # Get local machine name
    port = 12345                 # Reserve a port for your service.

    print 'Server started!'
    print 'Waiting for clients...'

    s.bind((host, port))        # Bind to the port
    s.listen(5)                 # Now wait for client connection.
    c, addr = s.accept()     # Establish connection with client.
    print 'Got connection from', addr
    msg = c.recv(1024)

    print addr, ' >> ', msg

    if msg == 'close':
        print 'Closing down'
        c.send('SENT: Closing down')

    c.shutdown(socket.SHUT_RDWR)
    c.close()

This is my client code:

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import socket

if __name__ == '__main__':
    # Server
    s = socket.socket()          # Create a socket object
    host = socket.gethostname()  # Get local machine name
    port = 12345                 # Reserve a port for your service.

    print 'Connecting to ', host, port
    s.connect((host, port))

    msg = raw_input('CLIENT >> ')
    s.send(msg)
    msg = s.recv(1024)
    print 'SERVER >> ', msg

    s.close()                     # Close the socket when done

And this is the error message it produces:

In [13]: %run cjboxd.py
Server started!
Waiting for clients...
---------------------------------------------------------------------------
error                                     Traceback (most recent call last)
/usr/lib/python2.7/dist-packages/IPython/utils/py3compat.pyc in execfile(fname, *where)
    173             else:
    174                 filename = fname
--> 175             __builtin__.execfile(filename, *where)

/home/nine/slask/cjboxd.py in <module>()
     19     print 'Waiting for clients...'
     20 
---> 21     s.bind((host, port))        # Bind to the port
     22     s.listen(5)                 # Now wait for client connection.
     23     c, addr = s.accept()     # Establish connection with client.

/usr/lib/python2.7/socket.pyc in meth(name, self, *args)
    222 
    223 def meth(name,self,*args):
--> 224     return getattr(self._sock,name)(*args)
    225 
    226 for _m in _socketmethods:

error: [Errno 98] Address already in use

It will work like a minute later.

Answer 1

you need socket.socket.setsockopt, .i.e s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

Though the socket will be closed by the os when process ended, it is a good behavior to call close() explicitly.
However, after that, the local addr(local_ip, local_port) is not avaiable until 2 MSL(maximum segment lifetime) has passed. Why? and what we can do? you can read these:

http://www.tcpipguide.com/free/t_TCPConnectionTermination-3.htm
and http://www.unixguide.net/network/socketfaq/4.5.shtml

It will be difficult to me to post it more clear than they do :).