can i raise exception from inside a function in the 'try:' block when client disconnects from the server?

Question

im trying to build a simple server-client chatroom with python socket.

i have the following code:

def handle_connection(client):
    while(1):
        try:
            message = receive_message()
            broadcast(message["data"])
        except:     # for now i don't mind which exception
              print("client disconnected")


def receive_message(client_socket):
    try:
        message_header = client_socket.recv(HEADER)
        if len(message_header) == 0:
            return False
        message_length = int(message_header.decode("utf-8"))

        message = client_socket.recv(message_length).decode("utf-8")
        return {"header": message_header, "data": message}

    except:  # most likely will trigger when a client disconnects
        return False

where receive_message() calls inside of it to client.recv(HEADER) and returns either False when there is no message, or {"header": msg_header, "data": msg} when everything is ok.

my question is: if client.recv() fails inside of receive_message() due to the client CLI closing, will it raise the exception and print "client disconnected" , or not?

i did come up with the following solution i think works:

i defined a function called handle_disconnection() that handles all the content inside of the except in the code above.

def handle_connection(client_socket):
    while 1:
        try:
            message = receive_message()
            if not message:
                handle_disconnection(client_socket)
                break
            broadcast(message["data"])

        except:     # client disconnected
            handle_disconnection(client_socket)
            break

is this a valid and/or right programming approach to the problem? if this approach is wrong, how can i handle it correctly?

Answer 1

If client.recv() will raise an exception you will handle it inside of receive_message() and handle_connection() will not receive the exception.

I suggest you to identify situations when you want to control the flow with exceptions or with if-else. I think receive_message() should return a value of message or throw ConnectionError when there are connection issues. In case when there are no messages from the socket you can return None or raise NoMessagesAvailableError .

There is also a rule that tells you should catch specified exceptions, not all of them. Your code will print client disconnected when you are out of memory.