Create a network service that sits on TCP port 12321, which accepts connections on that port, and which echoes complete lines (using a carriage-return/line-feed sequence as line separator) back to clients. No error handling is required. For the purposes of testing, it is only necessary to support connections from localhost (127.0.0.1 or perhaps ::1). Logging of connection information to standard output is recommended.

The implementation must be able to handle simultaneous connections from multiple clients. A multi-threaded or multi-process solution may be used. Each connection must be able to echo more than a single line.

The implementation must not stop responding to other clients if one client sends a partial line or stops reading responses.

import SocketServer
 
HOST = "localhost"
PORT = 12321
 
# this server uses ThreadingMixIn - one thread per connection
# replace with ForkMixIn to spawn a new process per connection
 
class EchoServer(SocketServer.ThreadingMixIn, SocketServer.TCPServer):
    # no need to override anything - default behavior is just fine
    pass
 
class EchoRequestHandler(SocketServer.StreamRequestHandler):
    """
    Handles one connection to the client.
    """
    def handle(self):
        print "connection from %s" % self.client_address[0]
        while True:
            line = self.rfile.readline()
            if not line: break
            print "%s wrote: %s" % (self.client_address[0], line.rstrip())
            self.wfile.write(line)
        print "%s disconnected" % self.client_address[0]
 
 
# Create the server
server = EchoServer((HOST, PORT), EchoRequestHandler)
 
# Activate the server; this will keep running until you
# interrupt the program with Ctrl-C
print "server listening on %s:%s" % server.server_address
server.serve_forever()