API rate-limiting in go

main.go

package main

import (
	"fmt"
	"log"
	"net/http"
	"sync"
	"time"

	"github.com/gorilla/mux"
)

type limit struct {
	max      int
	interval time.Duration
	counter  int
	mux      sync.Mutex
}

func main() {
	r := mux.NewRouter()

	limits := &limit{
		max:      100,
		interval: 10 * time.Second,
	}
	// set max to 3 and keep hitting localhost:8000
	// ab from apache package can also used to test

	go limits.start()
	r.Use(limits.toLimit)
	r.HandleFunc("/", hello)

	srv := &http.Server{
		Addr:         "127.0.0.1:8000",
		Handler:      r,
		ReadTimeout:  5 * time.Second,
		WriteTimeout: 10 * time.Second,
	}

	log.Fatal(srv.ListenAndServe())
}

func hello(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "Hello %s!", r.RemoteAddr)
}

func (l *limit) pass() bool {
	l.mux.Lock()
	defer l.mux.Unlock()
	if l.counter >= l.max {
		return false
	}
	l.counter++
	return true
}

func (l *limit) start() {
	ticker := time.NewTicker(l.interval)
	defer ticker.Stop()
	// precious resources must not be leaked
	for {
		select {
		case <-ticker.C:
			l.mux.Lock()
			l.counter = 0
			l.mux.Unlock()
		}
	}
}

func (l *limit) toLimit(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if !l.pass() {
			http.Error(w, "Rate limiting", http.StatusTooManyRequests)
			return
		}
		next.ServeHTTP(w, r)
	})
}