Exceptions raised from the middleware will be captured but the response will not be returned correctly

[superMaaax]

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Example Code

from fastapi import FastAPI

app = FastAPI()

@app.middleware("http")
async def rate_limit_middleware(request: Request, call_next):
    # Let's say it's rejecting the request no matter how, but in the end, the server will respond 500 Internal Server Error instead of 429
    raise HTTPException(status_code=status.HTTP_429_TOO_MANY_REQUESTS, detail="Rate limit exceeded") 

    # return await middleware.rate_limit(request, call_next)

Description

I'm writing a Rate Limiter as a middleware for the service I'm developing. The Exceptions raised from the API function work pretty well (raised, catched, and returned response correctly). However, I found that the HTTPException raised from the middleware will not be returned correctly. It will respond 500 Internal Server Error instead of 429. I really have to write return responses.JSONResponse(status_code=status.HTTP_429_TOO_MANY_REQUESTS, content={"detail": "Rate limit exceeded"}) when it meets the condition, instead of raise HTTPException(status_code=status.HTTP_429_TOO_MANY_REQUESTS, detail="Rate limit exceeded") to solve the problem, but that would not be consistent with what I wrote before (I was writing raise Exception on this project all the time)

Operating System

macOS

Operating System Details

No response

FastAPI Version

0.111.0

Pydantic Version

2.6.2

Python Version

Python 3.12.2

Additional Context

No response

[YuriiMotov]

You can't handle exceptions from middleware using exception handlers. Using exception handler you can only handle HTTPExceptions that were raised from endpoints and router.
You can read more in Starlette docs (https://www.starlette.io/exceptions/#httpexception):

You should only raise HTTPException inside routing or endpoints. Middleware classes should instead just return appropriate responses directly.

Instead of raising HTTPException in your middleware, you can return response:

@app.middleware("http")
async def rate_limit_middleware(request: Request, call_next):
    return JSONResponse(
        status_code=status.HTTP_429_TOO_MANY_REQUESTS,
        content={"detail": "Rate limit exceeded"}
    )