feat!: enable H2 by default

[metcoder95]

This relates to...

Closes #2750

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Features

Bug Fixes

Breaking Changes and Deprecations

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[ronag]

I'm strongly against this. I think HTTP2 for most cases is worse both in terms of performance and stability. I'm not a big fan of the quality and lack of maintenance of the http2 module in node core. I would like to even further decouple the http2 stuff from undici core. I would be happy to reconsider this position if and when James's http/3 and quic stuff lands.

[ronag]

I would suggest we enable it by default for fetch and only fetch. It's slow anyway :).

[metcoder95]

I believe that most of the inquiries come from fetch, so I am happy to scope it for it only 🙂

[metcoder95]

Hmm, taking another look that won't be that easy; as if we try to scope an Agent just for fetch, that can overlap with the getGlobalDispatcher; for instance we will need to agree if we set the global dispatcher to use H2 by default or not.

Unless there's another way I might be missing

[mcollina]

I'm -1 with this implementation.

I think a better approach would be to enable it only if the server does not advertise HTTP/1.1 in the TLS exchange. In other terms, if a server is only exposed via HTTP/2, we can support it.

[mcollina]

I think we are not ready for turning this on for all requests, there are bugs: #2801.

[metcoder95]

SGTM, let's take this back and circle once we feel we are more prepared to it; I'll revisit the bug and seek for support and possible add a fix there 👍