investigate swapping out reqwest for hyper

[clux]

We are doing a whole lot of manual TLS work ourselves, along with painful re-exporting of feature sets which selects a lot of the same dependencies (which are further re-ordered by #360 where we get a second client for websockets).

It would be interesting to see how feasible it is to just run straight hyper within kube and see what the fallout of that would be.
What does this drop? What does this let us solve better?

I imagine this will force us to make a better encapsulation interface to the Client (to avoid impulses to go down #17), as we are now putting a bunch of parameters within it, making Clone more expensive, even more so after #360.

Most of the dependencies of reqwest we already have anyway; tokio, serde, various tls deps, pin, url, futures*, but there is more. What extra dependencies would this mean we would have to lift into kube?

• async gzip compression, almost certainly - probably a good default to have
• cookies, can probably drop?
• dns resolver?
• error types: ReqwestError is re-exported in kube::Error due to its nice interface. But looks like Hyper::Error could be usable unless we want to unpack the errors out out of reqwest/hyper entirely.

If anyone wants to investigate and/or provide some PoC PRs, this would be appreciated.

[kazk]

• TLS (improvement by deduplication)
  • Code in Add WebSocket connection support and implement /attach and /exec #360 was mostly taken from reqwest and we should be able to share the setup between HTTPS and WSS
  • https://github.com/hyperium/hyper-tls
  • https://github.com/ctz/hyper-rustls
• Compression: https://github.com/Nemo157/async-compression
• Proxy: https://github.com/tafia/hyper-proxy
• OAuth2: https://github.com/dermesser/yup-oauth2 (improvement?)

[jbg]

One small request regarding TLS: please expose the vendored feature on hyper-tls, as it's the easiest way to handle the openssl dependency when cross-compiling. At the moment we have to add a direct dep on reqwest with the native-tls-vendored feature in order to get this feature activated, as it's not passed through by kube.

[kazk]

@jbg Can you open a new issue for vendored? We should be able to add a feature for it later. Comments are easy to forget.