exercise09

Exercise Sheet 9

This week we continue working with TCP sockets by implementing a simple chat application. Unlike in last week's exercise, this time we'll also create a separate client application. To initialize a TCP socket on the client, follow the same steps to create a socket and initialize the sockaddr_in structure, however this time setting

addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK); // on client

Then, use the connect function to establish a connection to the server through your socket.

Task 1

In this first step, implement a basic client/server application, where multiple clients can dynamically connect and disconnect and send messages to the server. The sever then prints the received messages to the console, similar to the "math server" of task 3 of exercise sheet 4. Your solution should consist of two executables, one for the server, and another for the client.

The server:

• Receives as a single command line argument the port it should listen on.
• After creating and binding the socket as described above, the server should spawn a listener thread for accepting incoming connections.
  • The listener thread should terminate once the /shutdown command has been received (see below). A good way of implementing this is to use the pthread_cancel() function.
• For each client that connects, a new client thread is spawned:
  • The client thread continuously waits for incoming messages, and upon receiving them, prints them to the console, in the form "<username>: <message>".
  • Additionally, a client thread should be able to detect when a client disconnects, and subsequently terminate.
• The server waits until the listener thread and all client threads have terminated, cleans up and exits.

The client:

• Receives two command line arguments: The port to connect to, as well as a username it will be identified by.
• Upon connecting, the client first sends its username to the server.
• It then continuously prompts messages from the user, and sends them to the server.

Your chat application should support two special commands:

• /quit causes a client to exit, and the server to print the message "<username> disconnected.".
• /shutdown informs the server to shut down, no longer accepting new connections. Upon receiving the command, the server prints "Server is shutting down. Waiting for <N> clients to disconnect." where N is the number of currently connected clients. It then waits for all clients to have disconnected, cleans up and exits.

Example output:

TERMINAL 1                      TERMINAL 2                      TERMINAL 3

> ./server 24831
Listening on port 24831.
                                > ./client 24831 shelly
shelly connected.
                                                                > ./client 24831 bob
bob connected.
                                > hi all
shelly: hi all
                                                                > whats up?
bob: whats up?
                                > /shutdown
shelly disconnected.
Server is shutting down. Waiting for 1 clients to disconnected.
                                                                > /quit
bob disconnected.

Additional notes & hints:

• You can assume that every message sent over a socket is exactly MSG_SIZE = 128 bytes long.
• As always, ensure proper synchronization for all shared data structures.

Task 2

Now turn you application from a "one-way shoutbox" into a real chat: Instead of printing messages on the server, each message should be forwarded to all other clients.

Notably, your client now needs to be able to both read user input, as well as receive incoming messages forwarded by the server. Use threads to implement this functionality.

Again make sure to properly synchronize access to any shared data. Don't overthink your solution, and make use of the fact that a single socket can be simultaneously used for reading and writing from within different threads.

Example output (server omitted):

TERMINAL 1                      TERMINAL 2                      TERMINAL 3

> ./client 24831 loui           > ./client 24831 shelly         > ./client 24831 bob
                                > hi all
shelly: hi all                                                  shelly: hi all
                                                                > whats up?
bob: whats up?                  bob: whats up?

Task 3

Extend your chat application to support whispering to other people. By typing /w <username> <message>, the message <message> should only be visible to <username>.

This task should not require any modifications to your client.

Example output (server omitted):

TERMINAL 1                      TERMINAL 2                      TERMINAL 3

> ./client 24831 loui           > ./client 24831 shelly         > ./client 24831 bob
                                > hi all
shelly: hi all                                                  shelly: hi all
                                > /w loui hey dude
shelly (whispers): hey dude

---

exc09_csXXXXXX.zip
├── task1/
│   ├── Makefile
│   ├── client.c
│   ├── server.c
│   └── [*.h]
├── task2/
│   ├── Makefile
│   ├── client.c
│   ├── server.c
│   └── [*.h]
└── task3/
    ├── Makefile
│   ├── client.c
│   ├── server.c
    └── [*.h]

• Check that your solution conforms to the guidelines given in these feedback documents
• Run solutions using valgrind where applicable
• Auto-format all source files
• Check your submission on ZID-GPL
• Submit zip
• Submit tally list