/*
 * Half-Life Linux dedicated server Checker
 * Part of dedtools
 * Code by Tomas Janousek <tomi@nomi.cz>
 *
 * Returns success if the server is not living.
 * Returns failure if the server is ok or an error occurs.
 */

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/select.h>
#include <stdlib.h>
#include <linux/types.h>
#include <linux/errqueue.h>

static char infostring[] = "\xff\xff\xff\xffinfostring\0";
static int infostring_sz = sizeof(infostring) / sizeof(*infostring);
static char infostring2[] = "\xFF\xFF\xFF\xFF\x54Source Engine Query";
static int infostring2_sz = sizeof(infostring2) / sizeof(*infostring2);

int main(int argc, char *argv[])
{
    int sock, salen, i;
    struct sockaddr_in sa, sa2;
    char buffer[4096];

    if (argc != 2) {
	puts("Usage: ./hlds_check <port>");
	return -1;
    }

    sa.sin_family = AF_INET;
    sa.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
    sa.sin_port = htons(atol(argv[1]));

    sock = socket(AF_INET, SOCK_DGRAM, 0);
    if (sock == -1)
	return -1;

    int set_opt = 1;
    setsockopt(sock, SOL_IP, IP_RECVERR, &set_opt, sizeof(set_opt));

    for (i = 0; i < 30; i++) {
	fd_set fd;
	struct timeval timeout;
	FD_ZERO(&fd);
	FD_SET(sock, &fd);

	timeout.tv_sec = 0;
	timeout.tv_usec = 500000;

	if (sendto(sock, infostring, infostring_sz, 0, &sa, sizeof(sa)) != infostring_sz) {
	    select(0, 0, 0, 0, &timeout);
	    continue;
	}

	if (sendto(sock, infostring2, infostring2_sz, 0, &sa, sizeof(sa)) != infostring2_sz) {
	    select(0, 0, 0, 0, &timeout);
	    continue;
	}

	if (select(sock + 1, &fd, 0, 0, &timeout) > 0) {
	    salen = sizeof(sa2);
	    recvfrom(sock, buffer, 4096, 0, &sa2, &salen);
	    return -1;
	}
    }

    return 0;
}