Create a file called 1.2-echo_client-uni.py and save the following code in it:

import sys, socket
import tincanchat

HOST = sys.argv[-1] if len(sys.argv) > 1 else '127.0.0.1'
PORT = tincanchat.PORT

if __name__ == '__main__':
    while True:
        try:
            sock = socket.socket(socket.AF_INET,
                                 socket.SOCK_STREAM)
            sock.connect((HOST, PORT))
            print('
Connected to {}:{}'.format(HOST, PORT))
            print("Type message, enter to send, 'q' to quit")
            msg = input()
            if msg == 'q': break
            tincanchat.send_msg(sock, msg)  # Blocks until sent
            print('Sent message: {}'.format(msg))
            msg = tincanchat.recv_msg(sock)  # Block until
                                             # received complete
                                             # message
            print('Received echo: ' + msg)
        except ConnectionError:
            print('Socket error')
            break
        finally:
            sock.close()
            print('Closed connection to server
')

If we're running our server on a different machine from the one on which we are running the client, then we can supply the IP address or the hostname of the server as a command line argument to the client program. If we don't, then it will default to trying to connect to the localhost.

The third and forth lines of the code check the command line arguments for a server address. Once we've determined which server to connect to, we enter our main loop, which loops forever until we kill the client by entering q as a message. Within the main loop, we first create a connection to the server. Second, we prompt the user to enter the message to send and then we send the message using the tincanchat.send_msg() function. We then wait for the server's reply. Once we get the reply, we print it and then we close the connection as per our protocol.

Give our client and server a try. Run the server in a terminal by using the following command:

$ python 1.1-echo_server-uni.py
Listening on ('0.0.0.0', 4040)

In another terminal, run the client and note that you will need to specify the server if you need to connect to another computer, as shown here:

$ python 1.2-echo_client.py 192.168.0.7
Type message, enter to send, 'q' to quit

Running the terminals side by side is a good idea, because you can simultaneously see how the programs behave.

Type a few messages into the client and see how the server picks them up and sends them back. Disconnecting with the client should also prompt a notification on the server.