Use MiddewareType for middlewares

Author: Viicos

starlette/applications.py

@@ -9,7 +9,7 @@
 from starlette.requests import Request
 from starlette.responses import Response
 from starlette.routing import BaseRoute, Router
-from starlette.types import ASGIApp, Receive, Scope, Send
+from starlette.types import ASGIApp, MiddewareType, Receive, Scope, Send
 
 
 class Starlette:
@@ -138,7 +138,7 @@ def host(
         self.router.host(host, app=app, name=name)
 
     def add_middleware(
-        self, middleware_class: type, **options: typing.Any
+        self, middleware_class: typing.Type[MiddewareType], **options: typing.Any
     ) -> None:  # pragma: no cover
         self.user_middleware.insert(0, Middleware(middleware_class, **options))
         self.middleware_stack = self.build_middleware_stack()

starlette/middleware/__init__.py

@@ -1,8 +1,10 @@
 import typing
 
+from starlette.types import MiddewareType
+
 
 class Middleware:
-    def __init__(self, cls: type, **options: typing.Any) -> None:
+    def __init__(self, cls: typing.Type[MiddewareType], **options: typing.Any) -> None:
         self.cls = cls
         self.options = options
 

starlette/types.py

@@ -7,3 +7,6 @@
 Send = typing.Callable[[Message], typing.Awaitable[None]]
 
 ASGIApp = typing.Callable[[Scope, Receive, Send], typing.Awaitable[None]]
+
+MiddewareType = ASGIApp
+"""Type alias used for middleware types."""

tests/middleware/test_base.py

@@ -1,4 +1,5 @@
 import contextvars
+import typing
 from contextlib import AsyncExitStack
 
 import anyio
@@ -10,7 +11,7 @@
 from starlette.middleware.base import BaseHTTPMiddleware
 from starlette.responses import PlainTextResponse, StreamingResponse
 from starlette.routing import Route, WebSocketRoute
-from starlette.types import ASGIApp, Receive, Scope, Send
+from starlette.types import ASGIApp, MiddewareType, Receive, Scope, Send
 
 
 class CustomMiddleware(BaseHTTPMiddleware):
@@ -193,7 +194,7 @@ async def dispatch(self, request, call_next):
         ),
     ],
 )
-def test_contextvars(test_client_factory, middleware_cls: type):
+def test_contextvars(test_client_factory, middleware_cls: typing.Type[MiddewareType]):
     # this has to be an async endpoint because Starlette calls run_in_threadpool
     # on sync endpoints which has it's own set of peculiarities w.r.t propagating
     # contextvars (it propagates them forwards but not backwards)

tests/middleware/test_middleware.py

@@ -1,8 +1,10 @@
 from starlette.middleware import Middleware
+from starlette.types import Receive, Scope, Send
 
 
 class CustomMiddleware:
-    pass
+    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
+        return None  # pragma: no cover
 
 
 def test_middleware_repr():