mdns_external.c

/*
 * mDNS registration handler. This file is part of Shairport.
 * Copyright (c) Paul Lietar 2013
 * All rights reserved.
 *
 * 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.
 */

#include <unistd.h>
#include <signal.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include "common.h"
#include "mdns.h"

int mdns_pid = 0;

/*
 * Do a fork followed by a execvp, handling execvp errors correctly.
 * Return the pid of the new process upon success, or -1 if something failed.
 * Check errno for error details.
 */
static int fork_execvp(const char *file, char *const argv[]) {
    int execpipe[2];
    int pid = 0;
    if (pipe(execpipe) < 0) {
        return -1;
    }

    if (fcntl(execpipe[1], F_SETFD, fcntl(execpipe[1], F_GETFD) | FD_CLOEXEC) < 0) {
        close(execpipe[0]);
        close(execpipe[1]);
        return -1;
    }

    pid = fork();
    if (pid < 0) {
        close(execpipe[0]);
        close(execpipe[1]);
        return -1;
    }
    else if(pid == 0) { // Child
        close(execpipe[0]); // Close the read end
        execvp(file, argv);

        // If we reach this point then execve has failed.
        // Write erno's value into the pipe and exit.
        write_unchecked(execpipe[1], &errno, sizeof(errno));

        _exit(-1);
        return 0; // Just to make the compiler happy.
    }
    else { // Parent
        close(execpipe[1]); // Close the write end

        int childErrno;
        // Block until child closes the pipe or sends errno.
        if(read(execpipe[0], &childErrno, sizeof(childErrno)) == sizeof(childErrno)) { // We received errno
            errno = childErrno;
            return -1;
        }
        else { // Child closed the pipe. execvp was successful.
            return pid;
        }
    }
}

static int mdns_external_avahi_register(char *apname, int port) {
    char mdns_port[6];
    sprintf(mdns_port, "%d", config.port);

    char *argv[] = {
        NULL, apname, "_raop._tcp", mdns_port, MDNS_RECORD, NULL
    };

    argv[0] = "avahi-publish-service";
    int pid = fork_execvp(argv[0], argv);
    if (pid >= 0) {
        mdns_pid = pid;
        return 0;
    }
    else
        debug(1, "Calling %s failed", argv[0]);

    argv[0] = "mDNSPublish";
    pid = fork_execvp(argv[0], argv);
    if (pid >= 0)
    {
        mdns_pid = pid;
        return 0;
    }
    else
        debug(1, "Calling %s failed", argv[0]);
    
    // If we reach here, both execvp calls failed.
    return -1;
}

static int mdns_external_dns_sd_register(char *apname, int port) {
    char mdns_port[6];
    sprintf(mdns_port, "%d", config.port);

    char *argv[] = {"dns-sd", "-R", apname, "_raop._tcp", ".",
                        mdns_port, MDNS_RECORD, NULL};

    int pid = fork_execvp(argv[0], argv);
    if (pid >= 0)
    {
        mdns_pid = pid;
        return 0;
    }
    else
        debug(1, "Calling %s failed", argv[0]);

    return -1;
}

static void kill_mdns_child(void) {
    if (mdns_pid)
        kill(mdns_pid, SIGTERM);
    mdns_pid = 0;
}

mdns_backend mdns_external_avahi = {
    .name = "external-avahi",
    .mdns_register = mdns_external_avahi_register,
    .mdns_unregister = kill_mdns_child
};

mdns_backend mdns_external_dns_sd = {
    .name = "external-dns-sd",
    .mdns_register = mdns_external_dns_sd_register,
    .mdns_unregister = kill_mdns_child
};