Modify the scope to include root_path in path and raw_path

fastapi/applications.py

@@ -1050,7 +1050,20 @@ class FastAPI(Starlette):
 
     async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
         if self.root_path:
+            root_path = scope.get("root_path", "")
+            if root_path and self.root_path != root_path:
+                raise RuntimeError(
+                    f"The ASGI server is using a different root path than the one "
+                    f"configured in FastAPI. The configured root path is: "
+                    f"{self.root_path}, the ASGI server root path is: {root_path}. "
+                )
             scope["root_path"] = self.root_path
+            path = scope.get("path")
+            if path and not path.startswith(self.root_path):
+                scope["path"] = self.root_path + path
+            raw_path: bytes | None = scope.get("raw_path")
+            if raw_path and not raw_path.startswith(self.root_path.encode()):
+                scope["raw_path"] = self.root_path.encode() + raw_path
         await super().__call__(scope, receive, send)
 
     def add_api_route(