Add annotations

fastapi/applications.py

@@ -4515,6 +4515,7 @@ class FastAPI(Starlette):
 
         ```python
         import time
+        from typing import Awaitable, Callabe
 
         from fastapi import FastAPI, Request
 
@@ -4522,7 +4523,7 @@ class FastAPI(Starlette):
 
 
         @app.middleware("http")
-        async def add_process_time_header(request: Request, call_next):
+        async def add_process_time_header(request: Request, call_next: Callable[[Request], Awaitable[Response]):
             start_time = time.time()
             response = await call_next(request)
             process_time = time.time() - start_time