Apply middlewares only when there's request handler

sanic/sanic.py

@@ -179,6 +179,13 @@ class Sanic:
         try:
             request_started.send(request)
 
+            # Fetch handler from router
+            handler, args, kwargs = self.router.get(request)
+            if handler is None:
+                raise ServerError(
+                    ("'None' was returned while requesting a "
+                     "handler from the router"))
+
             # -------------------------------------------- #
             # Request Middleware
             # -------------------------------------------- #
@@ -196,17 +203,9 @@ class Sanic:
             # No middleware results
             if not response:
                 # -------------------------------------------- #
-                # Execute Handler
+                # Execute Response Handler
                 # -------------------------------------------- #
 
-                # Fetch handler from router
-                handler, args, kwargs = self.router.get(request)
-                if handler is None:
-                    raise ServerError(
-                        ("'None' was returned while requesting a "
-                         "handler from the router"))
-
-                # Run response handler
                 response = handler(request, *args, **kwargs)
                 if isawaitable(response):
                     response = await response

tests/test_middleware.py

@@ -71,6 +71,25 @@ def test_middleware_override_request():
     assert response.text == 'OK'
 
 
+def test_middleware_override_scope():
+    app = Sanic('test_middleware_override_scope')
+
+    @app.middleware
+    async def validate_request(request):
+        if not request.headers.get('X-REQUIRED-HEADER'):
+            return text('X-REQUIRED-HEADER is missing.', status=412)
+
+    @app.route('/')
+    async def handler(request):
+        return text('OK')
+
+    response = sanic_endpoint_test(app, uri='/', gather_request=False)
+    assert response.status == 412
+
+    response = sanic_endpoint_test(app, uri='/nothing/', gather_request=False)
+    assert response.status == 404
+
+
 def test_middleware_override_response():
     app = Sanic('test_middleware_override_response')