/*
 * Copyright (C) 2012 Andrew Ayer
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * Except as contained in this notice, the name(s) of the above copyright
 * holders shall not be used in advertising or otherwise to promote the
 * sale, use or other dealings in this Software without prior written
 * authorization.
 */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>

#define XDMCP_TIMEOUT 3
static const char xdmcp_query_packet[] = { 0, 1, 0, 2, 0, 1, 0 };

/* returns: 1 == willing, 0 == unwilling, <0 == timeout/error */
static int xdmcp_status (void)
{
	struct timeval timeout = { XDMCP_TIMEOUT, 0 };
	char reply[128];
	int sock = socket(AF_INET, SOCK_DGRAM, 0);
	struct sockaddr_in addr;
	ssize_t res;
	fd_set read_fds;
	if (sock == -1) {
		return -errno;
	}

	memset(&addr, '\0', sizeof(addr));
	addr.sin_family = AF_INET;
	addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
	addr.sin_port = htons(177);

	res = sendto(sock, xdmcp_query_packet, sizeof(xdmcp_query_packet), 0, (struct sockaddr*)&addr, sizeof(addr));
	if (res == -1) {
		res = -errno;
		close(sock);
		return res;
	}

	FD_ZERO(&read_fds);
	FD_SET(sock, &read_fds);

	res = select(sock + 1, &read_fds, NULL, NULL, &timeout);
	if (res == -1) {
		res = -errno;
		close(sock);
		return res;
	} else if (res == 0) {
		close(sock);
		return -ETIMEDOUT;
	}

	res = recvfrom(sock, reply, sizeof(reply), 0, NULL, NULL);
	if (res == -1) {
		res = -errno;
		close(sock);
		return res;
	}
	close(sock);

	if (res >= 4 && reply[2] == 0 && reply[3] == 5) {
		/* Willing */
		return 1;
	}
	if (res >= 4 && reply[2] == 0 && reply[3] == 6) {
		/* Unwilling */
		return 0;
	}

	return -EIO;
}

int main (int argc, char** argv)
{
	int quiet = 0;
	int silent = 0;
	int res;

	if (argc >= 2 && strcmp(argv[1], "-q") == 0) { /* Quiet - only print error messages */
		quiet = 1;
	} else if (argc >= 2 && strcmp(argv[1], "-s") == 0) { /* Silent - print nothing */
		quiet = 1;
		silent = 1;
	}

	res = xdmcp_status();
	if (res < 0) {
		if (!silent) {
			fprintf(stdout, "Error: %s\n", strerror(-res));
		}
		return 3;
	} else if (res == 0) {
		if (!silent) {
			fprintf(stdout, "Unwilling\n");
		}
		return 1;
	} else {
		if (!quiet) {
			fprintf(stdout, "Willing\n");
		}
		return 0;
	}
}