mpdnotify: Daemonize at startup

Unless the `--no-fork` option is given, the program will fork into the
background and return immediately to the caller.

Makefile.am

@@ -13,7 +13,8 @@ mpdnotify_VALAFLAGS = \
 	--pkg json-glib-1.0 \
 	--pkg libmpdclient \
 	--pkg libnotify \
-	--pkg libsoup-2.4
+	--pkg libsoup-2.4 \
+	--pkg posix
 
 LIBS = @LIBS@ \
 	@glib_LIBS@ \

src/mpdnotify.vala

@@ -4,12 +4,15 @@ namespace MpdNotify {
 
     private static string host;
     private static int port;
+    private static bool no_fork;
 
     private const OptionEntry[] options = {
         {"host", 'h', 0, OptionArg.STRING, ref host,
             "MPD server hostname/address", "HOST" },
         {"port", 'p', 0, OptionArg.INT, ref port,
             "MPD server port", "PORT" },
+        {"no-fork", 'f', 0, OptionArg.NONE, ref no_fork,
+            "Do not fork into the background", null },
         { null }
     };
 
@@ -34,6 +37,30 @@ namespace MpdNotify {
         ctx.parse(ref args);
     }
 
+    void daemonize() {
+        Posix.pid_t pid;
+        pid = Posix.fork();
+        if (pid < 0) {
+            stderr.printf("Unable to fork: %s", Posix.strerror(errno));
+            Posix.exit(1);
+        } else if (pid > 0) {
+            Posix.exit(0);
+        }
+        Posix.pid_t sid = Posix.setsid();
+        if (sid < 0) {
+            stderr.printf("Unable to create new session: %s",
+                Posix.strerror(errno));
+            Posix.exit(1);
+        }
+        pid = Posix.fork();
+        if (pid < 0) {
+            stderr.printf("Unable to fork: %s", Posix.strerror(errno));
+            Posix.exit(1);
+        } else if (pid > 0) {
+            Posix.exit(0);
+        }
+    }
+
     int main(string[] args) {
         try {
             parse_args(args);
@@ -42,6 +69,10 @@ namespace MpdNotify {
             return 2;
         }
 
+        if (!no_fork) {
+            daemonize();
+        }
+
         var loop = new MainLoop();
         Unix.signal_add(2, () => {
             loop.quit();