HTTP QPS rate limiting in Golang

qps-rate-limiting.go

package main

import (
        "flag"
        "fmt"
        "log"
        "net/http"
        "os"
        "os/signal"
        "time"
)

type midHTTP struct {
}

const burstLimit = 100

var throttle = make(chan struct{}, burstLimit)

func (m *midHTTP) ServeHTTP(w http.ResponseWriter, r *http.Request) {
        select {
        case <-throttle:
                http.DefaultServeMux.ServeHTTP(w, r)
        default:
                w.WriteHeader(http.StatusTooManyRequests)
                return
        }
}

func main() {
        // 100 qps
        rate := time.Second / 100
        tick := time.NewTicker(rate)
        defer tick.Stop()
        go func() {
                for _ = range tick.C {
                        select {
                        case throttle <- struct{}{}:
                        default:
                        }
                } // does not exit after tick.Stop()
        }()

        http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
                fmt.Fprintln(w, "good")
        })

        flagPort := flag.String("p", "9091", "listen port")
        flag.Parse()

        mid := &midHTTP{}
        port := ":" + *flagPort
        server := http.Server{
                Addr: port,
                Handler: mid,
        }
        go func() {
                if err := server.ListenAndServe(); err != nil {
                        if err == http.ErrServerClosed {
                        } else {
                                panic(err)
                        }
                }
        }()

        sigChan := make(chan os.Signal, 2)
        signal.Notify(sigChan, os.Interrupt, os.Kill)
        log.Print("http server listen on port ", port)
        log.Print("use c-c to exit: \n")
        <-sigChan
        server.Shutdown(nil)

}

// curl http://127.0.0.1:9091
// wrk -c 10 -d 10 -t 2  http://127.0.0.1:9091