Add url_path config option (#709)

Add new --url_path command line arg and corresponding ROS param to the websocket process. This argument allows for specifying an alternative path other than the root path when running the websocket process.

rosbridge_server/scripts/rosbridge_websocket.py

@@ -124,6 +124,15 @@ def __init__(self):
                 print("--address argument provided without a value.")
                 sys.exit(-1)
 
+        url_path = self.declare_parameter("url_path", "/").value
+        if "--url_path" in sys.argv:
+            idx = sys.argv.index("--url_path") + 1
+            if idx < len(sys.argv):
+                url_path = str(sys.argv[idx])
+            else:
+                print("--url_path argument provided without a value.")
+                sys.exit(-1)
+
         retry_startup_delay = self.declare_parameter("retry_startup_delay", 2.0).value  # seconds.
         if "--retry_startup_delay" in sys.argv:
             idx = sys.argv.index("--retry_startup_delay") + 1
@@ -137,9 +146,11 @@ def __init__(self):
         # Done with parameter handling                   #
         ##################################################
 
-        application = Application(
-            [(r"/", RosbridgeWebSocket), (r"", RosbridgeWebSocket)], **tornado_settings
-        )
+        handlers = [(r"/", RosbridgeWebSocket), (r"", RosbridgeWebSocket)]
+        if url_path != "/":
+            handlers = [(rf"{url_path}", RosbridgeWebSocket)]
+
+        application = Application(handlers, **tornado_settings)
 
         connected = False
         while not connected and self.context.ok():