`ProxyHeadersMiddleware` not using the `X-Forwarded-Port` header

[fiannac]

Discussed in #1948

^{Originally posted by fiannac April 21, 2023}
From the documentation:
--proxy-headers / --no-proxy-headers Enable/Disable X-Forwarded-Proto, X-Forwarded-For, X-Forwarded-Port to populate remote address info.

But I've noticed that, when the flag is set, the X-Forwarded-Port is not actually used by the application, and the source port is always set to 0.
This has to do with how the `ProxyHeadersMiddleware' is implemented, which does not match the behavior described in the docs.

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[Kludex]

The discussion is already created.

[Kludex]

Is there any server implementation that uses X-Forwarded-Port?

[victor-torres]

@Kludex https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/x-forwarded-headers.html

[RussianCow]

My understanding is that, without support for X-Forwarded-Port, there is no way to host a Uvicorn server on a non-standard port if it's behind a reverse proxy such as nginx. @Kludex Is there a workaround for this issue? Otherwise, I'm happy to contribute a PR (although #2473 should be sufficient if you remove the flag).

[keatonLiu]

I finally wrote a middleware to solve this problem temporarily:

from uvicorn._types import ASGI3Application, ASGIReceiveCallable, Scope, ASGISendCallable


class ProxyHeadersMiddlewareWithPort:
    def __init__(self, app: ASGI3Application) -> None:
        self.app = app

    async def __call__(self, scope: Scope, receive: ASGIReceiveCallable, send: ASGISendCallable) -> None:
        if scope["type"] == "lifespan":
            return await self.app(scope, receive, send)

        headers = dict(scope["headers"])
        host, port = scope["client"]
        if port == 0:
            if b"x-forwarded-port" in headers:
                port = int(headers[b"x-forwarded-port"])
        scope["client"] = (host, port)

        return await self.app(scope, receive, send)

Then in your main.py:

app = FastAPI(lifespan=lifespan)
app.add_middleware(ProxyHeadersMiddlewareWithPort)