slow-server.go

package main

import (
	"io"
	"net/http"
	"time"
)

type SlowDevNull struct {
	interval           time.Duration
	maxBitsPerInterval int64

	n int64
	t time.Time
}

func NewSlowDevNull(bitsPerSecond int64, interval time.Duration) *SlowDevNull {
	return &SlowDevNull{
		interval:           interval,
		maxBitsPerInterval: bitsPerSecond * int64(interval) / int64(time.Second),
	}
}

func (s *SlowDevNull) Write(p []byte) (n int, err error) {
	now := time.Now()
	if s.t.IsZero() {
		s.t = now
	}
	nextInterval := s.t.Add(s.interval)
	if now.After(nextInterval) {
		s.n = 0
		s.t = now
	}
	s.n += int64(len(p)) * 8
	for s.n > s.maxBitsPerInterval {
		s.n -= s.maxBitsPerInterval
		time.Sleep(time.Until(nextInterval))
		s.t = nextInterval
		nextInterval = s.t.Add(s.interval)
	}
	return len(p), nil
}

func main() {
	const Mbps = 1000 * 1000
	slowDevNull := NewSlowDevNull(5*Mbps, 10*time.Millisecond)
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		io.Copy(slowDevNull, r.Body)
		http.Error(w, "OK", http.StatusOK)
	})
	http.ListenAndServe(":8080", nil)
}