TCP echo client (localhost)

Challenge

Implement int tcp_echo(const char *host, int port, const char *msg, char *out, size_t out_sz) that:

1. opens a TCP socket to host:port,
2. writes msg followed by \n,
3. reads up to out_sz - 1 bytes into out and NUL-terminates,
4. closes the socket and returns 0 on success.

The grader runs a tiny echo server on 127.0.0.1:<random port> — your client only talks to loopback. Do not connect anywhere else.

Starter code

#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <stddef.h>

int tcp_echo(const char *host, int port, const char *msg, char *out, size_t out_sz) {
    /* TODO */
    return -1;
}