docs: added comments

client.py

@@ -15,10 +15,11 @@
 # create default selector for handling multiple IO
 sel = selectors.DefaultSelector()
 
-# set input non blocking
+# set input non-blocking
 origFl = fcntl.fcntl(sys.stdin, fcntl.F_GETFL)
 fcntl.fcntl(sys.stdin, fcntl.F_SETFL, origFl | os.O_NONBLOCK)
 
+# the variable checks whether the client is signed in or not
 signIn = False
 
 
@@ -58,18 +59,32 @@ def read(sock):
     msg = sock.recv(BUFFER_SIZE).decode(FORMAT)
     if msg:
 
+        # When a client opens the app for the first time, the app will send
+        # their entered nickname to the server. The server has three return options:
+        # 1. 200 Registration successful
+        # 2. 401 Client already registered
+        # 3. 400 Invalid registration
+        # The following if-else block checks whether the received message
+        # contains the above control message. If there isn't a control
+        # message, print it out to the console.
+
         if msg == '200 Registration successful':
 
             msg = 'Connection to server established. Sending intro message...\nRegistration successful.  Ready for messageing!\n'
             print(msg)
 
+            # the variable checks whether the client is signed in or not
+            # (registered successfully), since the nickname is available
+            # we turn it to True
+
             global signIn
             signIn = True
 
+            # asks client for console input
             sel.register(sys.stdin, selectors.EVENT_READ, getStdinInput)
 
         elif msg in ['401 Client already registered', '400 Invalid registration']:
-            print(f'\n{msg}')
+            print(f'\n{msg} ... Please try again later ')
             sel.unregister(sock)
             sock.close()
             sys.exit(0)
@@ -99,8 +114,11 @@ def getStdinInput(stdin, conn):
 def main():
 
     # Register our signal handler for shutting down.
+
     signal.signal(signal.SIGINT, signalHandler)
 
+    # retrieves the arguments from the console
+
     NAME, HOST, PORT = getArgs()
     ADDR = (HOST, PORT)
 
@@ -116,11 +134,21 @@ def main():
     sel.register(client, selectors.EVENT_READ, read)
 
     while True:
+
+        # prompts (displays '>' sign) client input only if they are registered
+
         if signIn:
             sys.stdout.write('> ')
             sys.stdout.flush()
+
         for k, _ in sel.select(timeout=None):
+
+            # notice that k.data here is a function,
+            # since in Python, functions are first-class citizens
+            # we can assign it to a variable
+
             callback = k.data
+
             if callback == getStdinInput:
                 callback(k.fileobj, client)
             else:

server.py

@@ -51,6 +51,9 @@ def acceptWrapper(sock):
     msg = conn.recv(BUFFER_SIZE).decode(FORMAT)
     username = msg.lstrip('REGISTER ').rstrip(' CHAT/1.0')
 
+    # checks whether the entered nickname is valid 
+    # checks whether the entered nickname already exists
+
     validRegistration = True
     controlMsg = '200 Registration successful'
     if 'REGISTER ' not in msg or ' CHAT/1.0' not in msg:
@@ -63,12 +66,17 @@ def acceptWrapper(sock):
     conn.sendall(controlMsg.encode(FORMAT))
 
     if validRegistration:
+
         print(
             f'Connection to client estatblished, waiting to reveive messages from user "{username}" ... ')
 
         # add client to the dicitonary
         clients[username] = conn
 
+        # selectors module allows us store data
+        # the following code creates the data and stores it 
+        # using the register method
+
         data = types.SimpleNamespace(
             addr=addr,
             name=username
@@ -93,6 +101,8 @@ def performService(key):
 
     if message:
         print(f'Received message from user {data.name}: {message}')
+
+        # broadcast the message to everyone except self
         broadcast(data.name, message)
 
     else:
@@ -118,13 +128,15 @@ def main():
 
     sel.register(server, selectors.EVENT_READ)
 
+    # create a closure for signalHandler
     def signalHandler(sig, frame):
         """Executed when a user press control + c"""
         print('Interrupt received, shutting down ...')
         server.close()
         sys.exit(0)
 
     # Register our signal handler for shutting down.
+
     signal.signal(signal.SIGINT, signalHandler)
 
     print('Waiting for incoming client connections ...')