feat: Add route-level middleware

docs/middleware.md

@@ -41,6 +41,31 @@ application would look like this:
 * Routing
 * Endpoint
 
+Middleware can also be added at the route level, in which case it will be executed after routing ocurrs:
+
+```python
+from starlette.applications import Starlette
+from starlette.middleware.trustedhost import TrustedHostMiddleware
+
+example_route_middleware = [
+    Middleware(TrustedHostMiddleware, allowed_hosts=['example.com', '*.example.com']),
+]
+
+routes = [
+    Route(
+        "/example",
+        endpoint=...,
+        middleware=example_route_middleware,
+    )
+]
+
+middleware = [
+  Middleware(HTTPSRedirectMiddleware)
+]
+
+app = Starlette(routes=routes, middleware=middleware)
+```
+
 The following middleware implementations are available in the Starlette package:
 
 ## CORSMiddleware

starlette/routing.py

@@ -14,6 +14,7 @@
 from starlette.convertors import CONVERTOR_TYPES, Convertor
 from starlette.datastructures import URL, Headers, URLPath
 from starlette.exceptions import HTTPException
+from starlette.middleware import Middleware
 from starlette.requests import Request
 from starlette.responses import PlainTextResponse, RedirectResponse
 from starlette.types import ASGIApp, Receive, Scope, Send
@@ -191,6 +192,7 @@ def __init__(
         methods: typing.List[str] = None,
         name: str = None,
         include_in_schema: bool = True,
+        middleware: typing.Optional[typing.Sequence[Middleware]] = None,
     ) -> None:
         assert path.startswith("/"), "Routed paths must start with '/'"
         self.path = path
@@ -210,6 +212,10 @@ def __init__(
             # Endpoint is a class. Treat it as ASGI.
             self.app = endpoint
 
+        if middleware is not None:
+            for cls, options in reversed(middleware):
+                self.app = cls(app=self.app, **options)
+
         if methods is None:
             self.methods = None
         else:
@@ -329,6 +335,8 @@ def __init__(
         app: ASGIApp = None,
         routes: typing.Sequence[BaseRoute] = None,
         name: str = None,
+        *,
+        middleware: typing.Optional[typing.Sequence[Middleware]] = None,
     ) -> None:
         assert path == "" or path.startswith("/"), "Routed paths must start with '/'"
         assert (
@@ -344,6 +352,10 @@ def __init__(
             self.path + "/{path:path}"
         )
 
+        if middleware is not None:
+            for cls, options in reversed(middleware):
+                self.app = cls(app=self.app, **options)
+
     @property
     def routes(self) -> typing.List[BaseRoute]:
         return getattr(self.app, "routes", None)

tests/test_routing.py

@@ -1,11 +1,16 @@
 import functools
+import typing
 import uuid
 
 import pytest
 
 from starlette.applications import Starlette
+from starlette.middleware import Middleware
+from starlette.middleware.base import BaseHTTPMiddleware, RequestResponseEndpoint
+from starlette.requests import Request
 from starlette.responses import JSONResponse, PlainTextResponse, Response
 from starlette.routing import Host, Mount, NoMatchFound, Route, Router, WebSocketRoute
+from starlette.testclient import TestClient
 from starlette.websockets import WebSocket, WebSocketDisconnect
 
 
@@ -648,3 +653,65 @@ def test_duplicated_param_names():
         match="Duplicated param names id, name at path /{id}/{name}/{id}/{name}",
     ):
         Route("/{id}/{name}/{id}/{name}", user)
+
+
+def assert_middleware_header_route(request: Request):
+    assert getattr(request.state, "middleware_touched") == "Set by middleware"
+    return Response()
+
+
+class AddHeadersMiddleware(BaseHTTPMiddleware):
+    async def dispatch(
+        self, request: Request, call_next: RequestResponseEndpoint
+    ) -> Response:
+        setattr(request.state, "middleware_touched", "Set by middleware")
+        response: Response = await call_next(request)
+        response.headers["X-Test"] = "Set by middleware"
+        return response
+
+
+middleware_router = Router(
+    [
+        Route(
+            "/http",
+            endpoint=assert_middleware_header_route,
+            methods=["GET"],
+            middleware=[Middleware(AddHeadersMiddleware)],
+        ),
+    ]
+)
+
+
+def test_router_middleware_http(
+    test_client_factory: typing.Callable[..., TestClient]
+) -> None:
+    test_client = test_client_factory(middleware_router)
+    response = test_client.get("/http")
+    assert response.status_code == 200
+    assert response.headers["X-Test"] == "Set by middleware"
+
+
+mounted_middleware_router = Router(
+    [
+        Mount(
+            "/http",
+            routes=[
+                Route(
+                    "/",
+                    endpoint=assert_middleware_header_route,
+                    methods=["GET"],
+                ),
+            ],
+            middleware=[Middleware(AddHeadersMiddleware)],
+        )
+    ]
+)
+
+
+def test_mounted_router_middleware(
+    test_client_factory: typing.Callable[..., TestClient]
+) -> None:
+    test_client = test_client_factory(mounted_middleware_router)
+    response = test_client.get("/http")
+    assert response.status_code == 200
+    assert response.headers["X-Test"] == "Set by middleware"