Add InvalidResourceError exception type, fix #393.

Author: T4rk1n

dash/dash.py

@@ -218,6 +218,10 @@ def add_url(name, view_func, methods=('GET',)):
         self._cached_layout = None
         self.routes = []
 
+        # add a handler for components suites errors to return 404
+        self.server.errorhandler(exceptions.InvalidResourceError)(
+            self._invalid_resources_handler)
+
     @property
     def layout(self):
         return self._layout
@@ -400,14 +404,14 @@ def _generate_meta_html(self):
     # Serve the JS bundles for each package
     def serve_component_suites(self, package_name, path_in_package_dist):
         if package_name not in self.registered_paths:
-            raise Exception(
+            raise exceptions.InvalidResourceError(
                 'Error loading dependency.\n'
                 '"{}" is not a registered library.\n'
                 'Registered libraries are: {}'
                 .format(package_name, list(self.registered_paths.keys())))
 
         elif path_in_package_dist not in self.registered_paths[package_name]:
-            raise Exception(
+            raise exceptions.InvalidResourceError(
                 '"{}" is registered but the path requested is not valid.\n'
                 'The path requested: "{}"\n'
                 'List of registered paths: {}'
@@ -944,6 +948,9 @@ def add_resource(p, filepath):
                 elif f == 'favicon.ico':
                     self._favicon = path
 
+    def _invalid_resources_handler(self, err):
+        return err.args[0], 404
+
     def get_asset_url(self, path):
         asset = _get_asset_path(
             self.config.requests_pathname_prefix,

dash/exceptions.py

@@ -60,3 +60,7 @@ class InvalidCallbackReturnValue(CallbackException):
 
 class InvalidConfig(DashException):
     pass
+
+
+class InvalidResourceError(DashException):
+    pass