wakeup/wakeup.c

#include <arpa/inet.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void printUsage()
{
    puts("usage: wakeup <MAC> <BROADCAST> [PORT]");
    puts("  MAC: interface address to wakeup (e.g. ff:ff:ff:ff:ff:ff)");
    puts("  BROADCAST: broadcast address of subnet (e.g. 192.168.2.255)");
    puts("  PORT: port to send UDP packet on (default: 7)");
}

/*
Use the UDP broadcast method to send the magic wakeup packet.
*/
int bcast_wakeup(const char* macAddr, const char* broadcast, in_port_t port)
{
    int sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (sock < 1) {
        perror("could not open socket");
        exit(EXIT_FAILURE);
    }

    int opt_broadcast = 1;
    setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &opt_broadcast,
               sizeof(opt_broadcast));

    struct in_addr ip;
    if (!inet_pton(AF_INET, broadcast, &ip)) {
        fputs("could not parse broadcast IP address", stderr);
        exit(EXIT_FAILURE);
    }

    struct sockaddr_in socket_addr;
    memset(&socket_addr, 0, sizeof(socket_addr));
    socket_addr.sin_port = port;
    socket_addr.sin_family = AF_INET;
    socket_addr.sin_addr.s_addr = ip.s_addr;

    uint8_t macValues[6];
    if (sscanf(macAddr, "%2hhx:%2hhx:%2hhx:%2hhx:%2hhx:%2hhx", &macValues[0],
               &macValues[1], &macValues[2], &macValues[3], &macValues[4],
               &macValues[5]) != 6) {
        fputs("could not parse MAC address", stderr);
        exit(EXIT_FAILURE);
    }

    uint8_t data[6 + 16 * 6];
    memset(&data, 0xFF, 6); // sync stream for magic packet
    for (size_t i = 0; i < 16;
         i++) { // followed by 16 repititions of mac address
        memcpy(data + 6 + 6 * i, &macValues, 6);
    }

    if (sendto(sock, data, sizeof(data), 0, (struct sockaddr*)&socket_addr,
               sizeof(socket_addr)) < 0) {
        fputs("packet sending failed", stderr);
        perror("Error Code:");
        exit(EXIT_FAILURE);
    }
    return 1;
}

int main(int argc, char* argv[])
{
    const char* mac;
    const char* ip;
    in_port_t port = 7;
    if (argc < 3) {
        printUsage();
        exit(0);
    } else {
        mac = argv[1];
        ip = argv[2];
    }
    if (argc > 3) {
        port = atoi(argv[3]);
    }
    bcast_wakeup(mac, ip, port);
    return 0;
}