Objective

Write a TCP chat relay that listens on 127.0.0.1, accepts many clients at once, and forwards every message it receives to all the other connected clients. A single thread must stay responsive at all times, so the program is built around one I/O multiplexing loop and never blocks on a slow peer.

Steps

• The program takes exactly one argument: the port number to listen on. With any other argument count, write "Invalid argument count" followed by a newline to standard error and exit with status 1.
• Bind and listen on the loopback address 127.0.0.1 using the given port. If a socket setup, bind, or listen call fails, write "Server setup failed" followed by a newline to standard error and exit with status 1.
• Give each accepted connection an id. The first client to connect gets id 0, and every later client gets the previous id plus one. Ids are never reused, even after a client leaves.
• When a client connects, broadcast "relay: peer %d joined\n" (with its id) to every other client. When a client disconnects, broadcast "relay: peer %d left\n" to every other client.
• When a client sends data, forward it to all other clients line by line. Each forwarded line is prefixed with "peer %d says: " (the sender's id). The sender never receives its own messages.
• Treat input as a byte stream, not as framed messages. Buffer whatever arrives until a newline completes a line, then emit that line with its prefix. Hold an unfinished fragment until the rest of the line shows up.
• Use a single non-blocking event loop (for example select or poll). A client that stops reading must never stall traffic for the others. Release every buffer and close every descriptor you own when a client leaves or the program ends.

Objective

Write a TCP chat relay that listens on 127.0.0.1, accepts many clients at once, and forwards every message it receives to all the other connected clients. A single thread must stay responsive at all times, so the program is built around one I/O multiplexing loop and never blocks on a slow peer.

Steps

• The program takes exactly one argument: the port number to listen on. With any other argument count, write "Invalid argument count" followed by a newline to standard error and exit with status 1.
• Bind and listen on the loopback address 127.0.0.1 using the given port. If a socket setup, bind, or listen call fails, write "Server setup failed" followed by a newline to standard error and exit with status 1.
• Give each accepted connection an id. The first client to connect gets id 0, and every later client gets the previous id plus one. Ids are never reused, even after a client leaves.
• When a client connects, broadcast "relay: peer %d joined\n" (with its id) to every other client. When a client disconnects, broadcast "relay: peer %d left\n" to every other client.
• When a client sends data, forward it to all other clients line by line. Each forwarded line is prefixed with "peer %d says: " (the sender's id). The sender never receives its own messages.
• Treat input as a byte stream, not as framed messages. Buffer whatever arrives until a newline completes a line, then emit that line with its prefix. Hold an unfinished fragment until the rest of the line shows up.
• Use a single non-blocking event loop (for example select or poll). A client that stops reading must never stall traffic for the others. Release every buffer and close every descriptor you own when a client leaves or the program ends.