rate limited http transport

[LukasJenicek]

No description provided.

[github-actions]

Benchmark Results

goos: linux
goarch: amd64
pkg: github.com/go-chi/httprate
cpu: AMD EPYC 7763 64-Core Processor                
               │ master.txt  │            pr.txt             │
               │   sec/op    │   sec/op     vs base          │
LocalCounter-4   19.90m ± 1%   19.92m ± 1%  ~ (p=0.853 n=10)

               │  master.txt  │             pr.txt             │
               │     B/op     │     B/op      vs base          │
LocalCounter-4   2.830Mi ± 0%   2.829Mi ± 0%  ~ (p=0.739 n=10)

               │ master.txt  │            pr.txt             │
               │  allocs/op  │  allocs/op   vs base          │
LocalCounter-4   121.4k ± 0%   121.4k ± 0%  ~ (p=0.753 n=10)

[VojtechVitek]

HTTP rate-limit outgoing requests. Nice 👍

This is a good start. Few notes:

• Could we reuse the existing LimitCounter implementations (same as for incoming requests), if that's possible? Meaning we would reuse the existing in-memory counter and redis counter.
• Let's hide "golang.org/x/time/rate" from the pkg API (FYI, this package doesn't use limit/burst - it uses sliding window counter instead)
• Can you think of the package API a bit?
  • Do we need to rate-limit 1) a specific domain (e.g. key: httprate:example.com); 2) or all outgoing requests made through the *http.Client? -- is (2) enough?

  •   package httprate
      
      func Client(c *http.Client, requestLimit int, windowLength time.Duration, key string, ...opts) *httprate.LimitClient 
      
      func Transport(rt http.RoundTripper, requestLimit int, windowLength time.Duration, key string, ...opts) http.RoundTripper