Event hook on redirect request not being called twice

[kummerer94]

Hi!

Thanks for the brillant library! I love the flexibility it offers when compared to aiohttp. It was much easier setting up something like a requests HTTPAdapter with this library than with aiohttp.

But I think that there could be some issue with the event hook or at least it would be great to clarify this in the documentation. Let's look at this example:

import asyncio

import httpx


class AsyncTokenTransport(httpx.AsyncHTTPTransport):
    async def handle_async_request(self, method, url, headers, stream, extensions):
        print(f"Intercepted {url[1].decode()}")
        return await super().handle_async_request(
            method, url, headers, stream, extensions
        )


async def test_hook(request: httpx.Request) -> None:
    print(f"Called for request to {request.url}")


async def main():
    async with httpx.AsyncClient(
        transport=AsyncTokenTransport(), event_hooks={"request": [test_hook]}
    ) as client:
        # URL is the one of my last school which was handy because it has a redirect configured
        r = await client.get("http://cogym.de")
        print(r.status_code)


loop = asyncio.get_event_loop()
loop.run_until_complete(main())

The output is

Called for request to http://cogym.de
Intercepted cogym.de
Intercepted www.carl-orff-gym.de
200

This means, while the transport will be called for both requests, the hook will only be called once.

I have a use case where I need to attach an authentication token in the header for every request that needs to be unique for every request. Unfortunately, if I call an API route that redirects me (and attach the token via the event hook), httpx will automatically follow the redirect but reuse the previous headers. Therefore, I use the same authentication token twice, which leads to an auth error.

Could you clarify if this is the intended behaviour? Do you want the event hook to only be called once if we follow the redirect and make another request? That definitely was new to me and the requests HTTPAdapter that I used previously would have been called twice here.

If this is the intended behaviour, I think it would be great to clarify this in the docs. I am happy to contribute a PR.

PS:

As my example shows, you can do the thing that I want to do with a custom Transport. But this is not as easy or convenient as the event hook. In the event hook, I can work with the nice top-level Request instance (including the URL instance).

[tomchristie]

Hola!

Could you clarify if this is the intended behaviour? Do you want the event hook to only be called once if we follow the redirect and make another request? That definitely was new to me and the requests HTTPAdapter that I used previously would have been called twice here.

So... we've got a choice here, which I think is either...

• Include separate event hooks for redirects.
• Change the behaviour so that it fires the request/response event hooks, for all requests including redirects.

I had been planning on the first, but looking at it right now, today, I'd expect the second to feel more obvious, and it's certainly less complex to describe and is a simpler, smaller surface-area API.

Either way around we ought to document the behaviour.

It would also be a good idea for us to review what event_hooks behaviour requests has here.

[kummerer94]

Hi,

Thank you for the response! I really appreciate the time you invest into this.

I looked into your question around requests. I found that requests has no request hook but only a response hook.

Something similar to what you have implemented with the httpx.HTTPTransport or httpx.AsyncHTTPTransport is probably the adapter logic in requests. These adapters (similar to the HTTPTransport) fire on both requests when the first one is a redirect.

What I finally did is look into the response hook that requests provides:

import requests

def response_hook(r, *args, **kwargs):
    print(f"Status {r.status_code}")

requests.get("http://cogym.de", hooks={"response": response_hook})

The output of this is then:

Status 307
Status 200
<Response [200]>

So, the response hook is indeed called twice on redirect.

I would also prefer the request hook to fire twice when it encounters a redirect, simply because these are actually two requests. But I only recently started using your library and would not consider myself involved enough to have an informed opinion.

[tomchristie]

Linking to the resolution... #1806

Kinda a shame that discussions don't get backlinks when they're referenced in pull requests.

[kummerer94]

Already updated to the newest release version, tested it and it works great! Thanks again. It's a lot easier to work with hooks than with the transport classes due to obvious reasons...