check final response in poll_informational

[zh-jq]

Make sure poll_informational returns Poll::Ready(None) after the final response received. So the caller can then use the ResponseFuture::poll() method to get the final response.

The lock in OpaqueStreamRef get released when poll_informational returned, so if it didn't returns Poll::Ready(None) on received final response header, the caller has to call ResponseFuture::poll() every time to check the final response, this may get some informational response get ignored.

[seanmonstar]

Thanks for the PR!

I looked at the code already in the function, and noticed some things. Since it matches other, it will get pushed back into the queue. Are you saying that stream.state.ensure_recv_open() will be true, even though the informational events are complete?

[zh-jq]

This is the code I used:

    fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Result<Response<()>, Error>> {
        if let Some(r) = ready!(self.rsp_fut.poll_informational(cx)) {
            return Poll::Ready(r);
        }

        let r = ready!(Pin::new(&mut self.rsp_fut).poll(cx))?;
        // ...
    }

I have to know there won't be any informational headers so I can poll for the final response. I can't call poll directly when poll_informational return Poll::Pending as poll will drop informational headers silently.

[seanmonstar]

Hm, ok. I wonder, would it possible to add a test to https://github.com/hyperium/h2/blob/master/tests/h2-tests/tests/informational_responses.rs that fails without this change? 🤓

[zh-jq]

Hm, ok. I wonder, would it possible to add a test to https://github.com/hyperium/h2/blob/master/tests/h2-tests/tests/informational_responses.rs that fails without this change? 🤓

Added one here: #890

[seanmonstar]

Got it, thanks for the test!