limiter

Go Rate limiter

This package allows us to have a distributed rate limiter, using Redis as a central counter.

The limits that are set are only "soft" limits, and you might end up going a bit over.

How it works

You create an instance of the rate limiter, by specifying a limit and an interval. For example, maybe you want 2000 requests per hour. Or 25000 requests per day.

When initializing, you specify a "base key". This is used in Redis as the key where we keep count of the total number of requests, across all instances.

You also specify a "flush interval", when the library will increment the Redis counter by the number each instance has counted (since the last sync) and read back the new total.

Dependencies

This package depends on garyburd/redigo.

Example

In the example below, we create a new limiter. We'll be counting the total number of requests, limiting the total to 5 within 1 minute. We'll be syncing with the Redis counter every 5 seconds.

package main

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

	"github.com/garyburd/redigo/redis"
	"github.com/manavo/go-rate-limiter"
)

type requestObject struct {
	RateLimiter *limiter.RateLimiter
}

func main() {
	redisPool := &redis.Pool{
		Dial: func() (redis.Conn, error) {
			c, err := redis.Dial("tcp", "127.0.0.1:6379")
			if err != nil {
				return nil, err
			}
			return c, err
		},
	}

	mux := http.NewServeMux()

	request := &requestObject{}

	rl := limiter.New(redisPool, "requests", 5, time.Minute, 5*time.Second)
	limiterErr := rl.Init()

	if limiterErr == nil {
		// request is a "requestObject" instance, that http.NewServeMux().Handle() accepts
		request.RateLimiter = rl
	} else {
		log.Printf("Error creating Rate Limiter: %v", limiterErr)
	}

	mux.Handle(
		"/rate",
		request,
	)

	httpserver := &http.Server{
		Addr:         "0.0.0.0:8888",
		Handler:      mux,
		ReadTimeout:  5000 * time.Millisecond,
		WriteTimeout: 5000 * time.Millisecond,
	}

	httpserver.ListenAndServe()
}

func (req *requestObject) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if req.RateLimiter != nil {
		req.RateLimiter.Increment()

		if req.RateLimiter.IsOverLimit() {
			w.Header().Set("Content-Type", "text/plain")

			// Status code 429: Too many requests
			w.WriteHeader(429)

			w.Write([]byte("Error: Reached limit of requests"))

			return
		}
	}

	w.Write([]byte("Request OK"))
}