FastAPI middleware scoped to a router

router_middleware.py

from typing import Callable

from fastapi import FastAPI, APIRouter
from starlette.middleware.base import BaseHTTPMiddleware
from starlette.requests import Request
from starlette.routing import Match

app = FastAPI()

router = APIRouter()
another_router = APIRouter()

@router.get("/hello")
async def hello_world():
    return "world"

@another_router.get("/foo")
async def foo_bar():
    return "bar"

app.include_router(router)
app.include_router(another_router)


def router_middleware(app: FastAPI, router: APIRouter):
    """Decorator to add a router-specific middleware."""

    def deco(func: Callable) -> Callable:
        
        async def _middleware(request: Request, call_next):
            # Check if scopes match
            matches = any([route.matches(request.scope)[0] == Match.FULL for route in router.routes])
            if matches: # Run the middleware if they do
                return await func(request, call_next)
            else: # Otherwise skip the middleware
                return await call_next(request)
            
        app.add_middleware(BaseHTTPMiddleware, dispatch=_middleware)
        return func
    return deco


@router_middleware(app, router)
async def test(request: Request, call_next):
    """This middleware will execute only for routes attached to the specified router"""
    response = await call_next(request)
    print("inside middleware")
    return response