How to access request_id defined in fastapi middleware in function

Question

Hi i have my middleware written like this

@app.middleware("http")
async def request_middleware(request, call_next):
    end_point = request.url.path
    global request_id
    request_id = get_request_id()
    with logger.contextualize(request_id=request_id, end_point=end_point):
        logger.info("----------Request started----------")
        try:
            response = await call_next(request)

        except Exception as ex:
            logger.error(f"Request failed: {ex}")
            response = JSONResponse()


        finally:
            response.headers["X-Request-Id"] = request_id
            logger.info("----------Request ended----------")
            return response

i want the request_id defined in middleware to be accessible in other function defined , how can we do that?

Answer 1

Instead of a global request_id, you can use a context variable, which is not shared between async tasks

from contextvars import ContextVar

req_id: ContextVar[str] = ContextVar('req_id', default='')

# Inside your middleware
req_id.set(get_request_id())

# Inside other functions, even different files, you import that variable
req_id.get()

Answer 2

Another 2 solutions:

• Store data in request.state in your middleware, and then access request.state in the view functions. More info in https://fastapi.tiangolo.com/tutorial/sql-databases/?h=request.#about-requeststate
• Or use starlette-context, just like g in flask, which is much easier

from starlette_context import context
from starlette_context.middleware import RawContextMiddleware


app.add_middleware(RawContextMiddleware)


@app.middleware("http")
async def request_middleware(request, call_next):
    request_id = get_request_id()
    context['request_id'] = request_id


@router.post('foobar')
async def foorbar():
    context['request_id']