satellite.c

// server.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <arpa/inet.h>
#include <sys/socket.h>

#define BUFSIZE 4096

int main(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <port>\n", argv[0]);
        return 1;
    }

    int port = atoi(argv[1]);
    if (port <= 0) {
        fprintf(stderr, "Invalid port: %s\n", argv[1]);
        return 1;
    }

    int sock = socket(AF_INET, SOCK_DGRAM, 0);
    if (sock < 0) {
        perror("socket");
        return 1;
    }

    struct sockaddr_in srv;
    memset(&srv, 0, sizeof(srv));
    srv.sin_family = AF_INET;
    srv.sin_addr.s_addr = htonl(INADDR_ANY);
    srv.sin_port = htons(port);

    if (bind(sock, (struct sockaddr*)&srv, sizeof(srv)) < 0) {
        perror("bind");
        close(sock);
        return 1;
    }

    printf("UDP server listening on port %d\n", port);

    for (;;) {
        char buf[BUFSIZE];
        struct sockaddr_in cli;
        socklen_t cli_len = sizeof(cli);
        ssize_t n = recvfrom(sock, buf, sizeof(buf) - 1, 0,
                             (struct sockaddr*)&cli, &cli_len);
        if (n < 0) {
            perror("recvfrom");
            continue;
        }
        buf[n] = '\0';

        char client_addr[INET_ADDRSTRLEN];
        inet_ntop(AF_INET, &cli.sin_addr, client_addr, sizeof(client_addr));
        printf("Received %zd bytes from %s:%d: %s\n",
               n, client_addr, ntohs(cli.sin_port), buf);

        // Example behavior: echo message back to sender
        ssize_t sent = sendto(sock, buf, n, 0, (struct sockaddr*)&cli, cli_len);
        if (sent < 0) {
            perror("sendto");
        } else {
            printf("Echoed %zd bytes back to %s:%d\n", sent, client_addr, ntohs(cli.sin_port));
        }
    }

    close(sock);
    return 0;
}