Weird behaviour with AsyncClient

[piermarcob]

Dear all, I hope I find you good.

I'm facing a weird behaviour with the AsyncClient. My scenario is the following

• Frontend POSTing to some backend API.
• Backend accepting the request and returning a 301, with a Location value set to a remote website: https://....
• The AsyncClient sends a GET to a local resource, which clearly does not exist: the request becomes http://localhost:8000/https://... and the response code is 404 from my local backend.

It seems the client cannot recognise whether the Location value refers to a local or a remote path, therefore a local one is always applied.

The desired outcome would be to actually redirect the client to the remote website https://..., with a response status code 200.

I hope i made myself explained.

Let me know what you think.

Regards.

[lovelydinosaur]

So I took a look at your description of this on Gitter too.

The AsyncClient sends a GET to a local resource, which clearly does not exist: the request becomes http://localhost:8000/https://... and the response code is 404 from my local backend.

So I don't think this description quite matches what's actually happening. I double checked and the URL redirection is correctly formed, and isn't to the composite URL. But I'll describe this more carefully just in case there's still any confusion.

You've got a test client, which is making requests directly to a web app rather than actual network requests.

The initial request is "to" http://localhost:8000/. The host doesn't actually matter here because you're sending the request to your Python ASGI app, not out to the network.

The redirected request is "to" https://www.google.com/. But again, the host doesn't actually matter here because you're sending requests to your ASGI app, not out to the network.

[piermarcob]

Hi Tom, thanks for the explanation, i was indeed missing things out.
The question now becomes: How should i setup my tests such that i can actually verify the redirection and that the location received in the headers gives a 200 OK back?

[lovelydinosaur]

How should i setup my tests such that i can actually verify the redirection and that the location received in the headers gives a 200 OK back?

I'll start answering that by using an explicit transport for the ASGITransport, rather than the AsyncClient(app=...) shortcut.

Here's an equivalent of what you're currently using...

transport = httpx.ASGITransport(app=app)
async with httpx.AsyncClient(transport=transport) as client:
    ...

Typically if I was writing a test like this, I wouldn't want the third party requests to actually send out to the network. You generally want to mock out that service at the test layer.

Here's the type of pattern I'd probs be looking for...

transport = httpx.ASGITransport(app=app)
mock_google_transport = httpx.ASGITransport(app=mock_service)
mounts = {
    'https://testserver': transport,
    'https://google.com': mock_google_transport
}

async with httpx.AsyncClient(mounts=mounts) as client:
    ...

[piermarcob]

Okay, so I think at this point i'll stick with just testing that a redirect came back from my backend and ensuring the redirect location matches the one i want my clients to be redirected to.