http3: add support for RFC8878 `Content-Encoding: zstd` to `RoundTripper`

[Jorropo]

See rational here: golang/go#62492
TL;DR: zstd is a better gzip in about all ways and is being added to browsers.

Support for gzip would be kept and both would be supported.

After discussing with other peoples it make sense to wait for compress/zstd proposal golang/go#62513 to continue quic-go not requiring any third party dependency.

This would do nothing when DisableCompression is set to true.

[marten-seemann]

This doesn't only apply to the RoundTripper, it would also need to be supported on the server side, right?

After discussing with other peoples it make sense to wait for compress/zstd proposal golang/go#62513 to continue quic-go not requiring any third party dependency.

I assume you mean discussing this with me? 🤣
Yes, I'd prefer to keep quic-go free of any third-party dependencies (outside of testing and qlog).

[Jorropo]

This doesn't only apply to the RoundTripper, it would also need to be supported on the server side, right?

The default net/http servers do not support compression due to the more complex tradeoffs and Side Channel Attacks issue. Wrappers handlers exists and are easy to use.
Similar wrappers also exists on for the client and handle decompression themselves but this is about providing good modern defaults.
Due to how internet is rigged and how HTTP is commonly used (you pay for upload traffic but not download traffic and responses are far bigger than requests) the server side peoples have more incentive to go figure it out, so I think it's fine leaving them to figure out.

In my use-case I'll manually handle crafted zstd archives, seek at premade cut points and .WriteTo various regions for example, so if the server had compression support I would turn it off anyway.

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I assume you mean discussing this with me?

Yes.

[marten-seemann]

@Jorropo is right. This only needs to be supported on the client side.

I love Zstd, but I think it would be silly to add this, given the basically solid red here:

https://caniuse.com/zstd

[marten-seemann]

Related: https://groups.google.com/a/chromium.org/g/blink-dev/c/GFFOLCF12a4/m/crdNkVeaAQAJ