One-shot echo server

Challenge

Implement int echo_once(int listening_fd) that:

1. Accepts one connection on listening_fd.
2. Reads up to 256 bytes from the client.
3. Writes those bytes back unchanged.
4. Closes the client fd.
5. Returns the number of bytes echoed, or -1 on failure.

Why this matters

The traditional first server. Accept one client, read whatever they send, write it back, close.

Starter code

#include <sys/socket.h>
#include <unistd.h>
int echo_once(int listening_fd) {
    /* TODO */
    return -1;
}

Background lessons

• listen() and accept() — the server side
• send() and recv() — moving bytes
• A complete simple TCP server (localhost)

Up next

• Multi-client server with threads (3 connections)