Update websockifyserver.py

Systemd or upstart socket detection and activation.
Ability to activate systemd or upstart socket only on-demand.

websockify/websockifyserver.py

@@ -370,6 +370,16 @@ class WebSockifyServer(object):
         if self.daemon and not resource:
             raise Exception("Module 'resource' required to daemonize")
             
+        # Systemd or upstart socket detection
+        if os.environ.get('LISTEN_PID', None) == str(os.getpid()):
+            self.listen_host = "socketfromfd"
+            self.listen_port = 3
+            self.msg("Detected systemd socket activation, listening fd %s", self.listen_port)
+        elif os.environ.get('UPSTART_EVENTS', None) == "socket":
+            self.listen_host = "socketfromfd"
+            self.listen_port = int(os.environ.get('UPSTART_FDS'))
+            self.msg("Detected upstart socket activation, listening fd %s", self.listen_port)
+
         # Show configuration
         self.msg("WebSocket server settings:")
         if self.listen_fd != None:
@@ -426,9 +436,15 @@ class WebSockifyServer(object):
         if not connect:
             flags = flags | socket.AI_PASSIVE
             
-        if not unix_socket:
+        # Starting systemd or upstart socket
+        if host == "socketfromfd":
+            sock = socket.fromfd(port, socket.AF_INET, socket.SOCK_STREAM)
+            if sys.version_info.major == 2:
+              sock = socket.socket(_sock=sock)
+        elif not unix_socket:
              addrs = socket.getaddrinfo(host, port, 0, socket.SOCK_STREAM,
                      socket.IPPROTO_TCP, flags)
+                
             if not addrs:
                 raise Exception("Could not resolve host '%s'" % host)
             addrs.sort(key=lambda x: x[0])