Reorganize mDNS advertisement

mDNS is now handled more or less in the same way audio is.
Multiple mDNS backends are available, shairport tries them all until one
works.

This makes it, IMHO, cleaner, and easier to add other mDNS backends in
the future, such as using tinysvcmdns or dns-sd library.
Also it will also allow to define mDNS backends as plugins, in a similar
way it is done in PR #230.

Makefile

@@ -9,7 +9,7 @@ endif
 
 PREFIX ?= /usr/local
 
-SRCS := shairport.c daemon.c rtsp.c mdns.c common.c rtp.c player.c alac.c audio.c audio_dummy.c audio_pipe.c
+SRCS := shairport.c daemon.c rtsp.c mdns.c mdns_external.c common.c rtp.c player.c alac.c audio.c audio_dummy.c audio_pipe.c
 
 ifdef CONFIG_SNDIO
 SRCS += audio_sndio.c
@@ -28,7 +28,7 @@ SRCS += audio_alsa.c
 endif
 
 ifdef CONFIG_AVAHI
-SRCS += avahi.c
+SRCS += mdns_avahi.c
 endif
 
 ifndef CONFIG_HAVE_GETOPT_H

avahi.h

@@ -1,7 +0,0 @@
-#ifndef _AVAHI_H
-#define _AVAHI_H
-
-int avahi_register(char *srvname);
-void avahi_unregister(void);
-
-#endif // _AVAHI_H

mdns.c

@@ -25,28 +25,29 @@
  */
 
 
-#include <signal.h>
 #include <memory.h>
 #include <string.h>
-#include <unistd.h>
 #include "config.h"
 #include "common.h"
 #include "mdns.h"
+
 #ifdef CONFIG_AVAHI
-#include "avahi.h"
+extern mdns_backend mdns_avahi;
 #endif
 
-int mdns_pid = 0;
+extern mdns_backend mdns_external_avahi;
+extern mdns_backend mdns_external_dns_sd;
 
-void mdns_unregister(void) {
+static mdns_backend *mdns_backends[] = {
 #ifdef CONFIG_AVAHI
-    avahi_unregister();
+    &mdns_avahi,
 #endif
+    &mdns_external_avahi,
+    &mdns_external_dns_sd,
+    NULL
+};
 
-    if (mdns_pid)
-        kill(mdns_pid, SIGTERM);
-    mdns_pid = 0;
-}
+static mdns_backend *backend = NULL;
 
 void mdns_register(void) {
     char *mdns_apname = malloc(strlen(config.apname) + 14);
@@ -59,31 +60,26 @@ void mdns_register(void) {
     *p++ = '@';
     strcpy(p, config.apname);
 
-#ifdef CONFIG_AVAHI
-    if (avahi_register(mdns_apname))
-        return;
-    warn("avahi_register failed, falling back to external programs");
-#endif
+    backend = NULL;
+    mdns_backend **s = NULL;
+    for (s = mdns_backends; *s; s++)
+    {
+        int error = (*s)->mdns_register(mdns_apname, config.port);
+        if (error == 0)
+        {
+            backend = *s;
+            break;
+        }
+    }
 
-    if ((mdns_pid = fork()))
-        return;
-
-    char mdns_port[6];
-    sprintf(mdns_port, "%d", config.port);
-
-    char *argv[] = {
-        NULL, mdns_apname, "_raop._tcp", mdns_port, MDNS_RECORD, NULL
-    };
-
-    argv[0] = "avahi-publish-service";
-    execvp(argv[0], argv);
-
-    argv[0] = "mDNSPublish";
-    execvp(argv[0], argv);
-
-    char *mac_argv[] = {"dns-sd", "-R", mdns_apname, "_raop._tcp", ".",
-                        mdns_port, MDNS_RECORD, NULL};
-    execvp(mac_argv[0], mac_argv);
-
-    die("Could not establish mDNS advertisement!");
+    if (backend == NULL)
+        die("Could not establish mDNS advertisement!");
 }
+
+void mdns_unregister(void) {
+    if (backend) {
+        backend->mdns_unregister();
+    }
+}
+
+

mdns.h

@@ -6,6 +6,11 @@ extern int mdns_pid;
 void mdns_unregister(void);
 void mdns_register(void);
 
+typedef struct {
+    int (*mdns_register)(char *apname, int port);
+    void (*mdns_unregister)(void);
+} mdns_backend;
+
 #define MDNS_RECORD  "tp=UDP", "sm=false", "ek=1", "et=0,1", "cn=0,1", "ch=2", \
                 "ss=16", "sr=44100", "vn=3", "txtvers=1", \
                 config.password ? "pw=true" : "pw=false"

mdns_avahi.c

@@ -38,6 +38,7 @@ static AvahiEntryGroup *group = NULL;
 static AvahiThreadedPoll *tpoll = NULL;
 
 static char *name = NULL;
+static int port = 0;
 
 static void egroup_callback(AvahiEntryGroup *g,
                             AvahiEntryGroupState state,
@@ -67,7 +68,7 @@ static void register_service(AvahiClient *c) {
                                         "_raop._tcp",
                                         NULL,
                                         NULL,
-                                        config.port,
+                                        port,
                                         MDNS_RECORD,
                                         NULL);
     if (ret < 0)
@@ -100,14 +101,15 @@ static void client_callback(AvahiClient *c,
     }
 }
 
-int avahi_register(char *srvname) {
+static int avahi_register(char *srvname, int srvport) {
     debug(1, "avahi: avahi_register\n");
     name = strdup(srvname);
+    port = srvport;
 
     int err;
     if (!(tpoll = avahi_threaded_poll_new())) {
         warn("couldn't create avahi threaded tpoll!");
-        return 0;
+        return -1;
     }
     if (!(client = avahi_client_new(avahi_threaded_poll_get(tpoll), 
                                     0,
@@ -115,18 +117,18 @@ int avahi_register(char *srvname) {
                                     NULL,
                                     &err))) {
         warn("couldn't create avahi client: %s!", avahi_strerror(err));
-        return 0;
+        return -1;
     }
 
     if (avahi_threaded_poll_start(tpoll) < 0) {
         warn("couldn't start avahi tpoll thread");
-        return 0;
+        return -1;
     }
 
-    return 1;
+    return 0;
 }
 
-void avahi_unregister(void) {
+static void avahi_unregister(void) {
     debug(1, "avahi: avahi_unregister\n");
     if (tpoll)
         avahi_threaded_poll_stop(tpoll);
@@ -137,4 +139,9 @@ void avahi_unregister(void) {
     name = NULL;
 }
 
+mdns_backend mdns_avahi = 
+{
+    .mdns_register = avahi_register,
+    .mdns_unregister = avahi_unregister
+};
 

mdns_external.c

@@ -0,0 +1,144 @@
+/*
+ * 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(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";
+    mdns_pid = fork_execvp(argv[0], argv);
+    if (mdns_pid > 0)
+        return 0;
+    else
+        warn("Calling %s failed !", argv[0]);
+
+    argv[0] = "mDNSPublish";
+    mdns_pid = fork_execvp(argv[0], argv);
+    if (mdns_pid > 0)
+        return 0;
+    else
+        warn("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};
+
+    mdns_pid = fork_execvp(argv[0], argv);
+    if (mdns_pid > 0)
+        return 0;
+    else
+        warn("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 = {
+    .mdns_register = mdns_external_avahi_register,
+    .mdns_unregister = kill_mdns_child
+};
+
+mdns_backend mdns_external_dns_sd = {
+    .mdns_register = mdns_external_dns_sd_register,
+    .mdns_unregister = kill_mdns_child
+};
+

shairport.c

@@ -187,7 +187,7 @@ void signal_setup(void) {
     // setting this to SIG_IGN would prevent signalling any threads.
     struct sigaction sa;
     memset(&sa, 0, sizeof(sa));
-    sa.sa_flags = SA_SIGINFO;
+    sa.sa_flags = SA_SIGINFO | SA_RESTART;
     sa.sa_sigaction = &sig_ignore;
     sigaction(SIGUSR1, &sa, NULL);
 
@@ -198,7 +198,6 @@ void signal_setup(void) {
     sa.sa_sigaction = &sig_logrotate;
     sigaction(SIGHUP, &sa, NULL);
 
-    sa.sa_flags = SA_SIGINFO;
     sa.sa_sigaction = &sig_child;
     sigaction(SIGCHLD, &sa, NULL);
 }