Implementing WebTransport over HTTP/2

[Daniel-Genkin-MS-2]

Is there an existing issue for this?

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Is your feature request related to a problem? Please describe the problem.

Currently WebTransport has been implemented over HTTP/3 (#42097) but there is no support for it over HTTP/2 (https://www.ietf.org/archive/id/draft-ietf-webtrans-http2-03.html). This might be a bit challenging though as I was unable to find any working client when I checked a little while ago.

Describe the solution you'd like

It would be great to implement WebTransport over HTTP/2 as a fallback for when HTTP/3 is unavailable. I believe this is the main use case for it. However, it does have support for directly initiating a connection over HTTP/2 which might also be useful for some folks.

Ideally this would use the same API as the WebTransport over HTTP3 but the underlying connection management would be different. All the WebTransport specific features in The WebTransport over HTTP/3 spec should be transferable to HTTP/2 in theory, although features that are inherited from QUIC would not.

Additional context

No response

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