Re-enable http/2

[willscott]

By setting a custom TLSClientConfig we remove the default of having a NextProtos set and need to add it back

[lidel]

Thanks! I suspect it is not that easy, we miss something:

failed to resolve /ipfs/bafybeigdyrzt5sfp7udm7hu76uh7y26nf3efuylqabf3oclgtqy55fbzdi: Bad Gateway: http request failed: Get "https://38.93.247.224/ipfs/bafybeigdyrzt5sfp7udm7hu76uh7y26nf3efuylqabf3oclgtqy55fbzdi?format=raw": http2: no cached connection was available

Unless you get to this first, I can look into this after IPFS Thing.

Quick thoughts:

• good opportunity to clean up and move generic client things to http_client.go so HTTP2-enabled client can be reused by blockstore_proxy.go and routing.go, ensuring we benefit from HTTP/2 everywhere
  • caveat: non-HTTPS endpoints like PROXY_GATEWAY_URL=http://127.0.0.1:8080 need to work, this is what we use in conformance test on CI, and using the same HTTP client there will be a good idea
    • Maybe http2.Transport{AllowHTTP: true will do the trick?

[willscott]

explanation potentially around context of the 'no cached connection available' at golang/go#16582

[willscott]

@lidel - i think we want ahttp2.Transport at the basis instead of a an http.Transport. That means a custom DialTLSContext method to make use of the cached DNS dialer, unfortunately.
See if this basic structure seems plausible.

[willscott]

It looks like we could potentially just set ForceAttemptHTTP2 on the standard http transport. I'll try simplifying to that
https://go.googlesource.com/go/+/master/src/net/http/transport.go#288