httprate - HTTP Rate Limiter

net/http request rate limiter based on the Sliding Window Counter pattern inspired by CloudFlare https://blog.cloudflare.com/counting-things-a-lot-of-different-things.

The sliding window counter pattern is accurate, smooths traffic and offers a simple counter design to share a rate-limit among a cluster of servers. For example, if you'd like to use redis to coordinate a rate-limit across a group of microservices you just need to implement the httprate.LimitCounter interface to support an atomic increment and get.

Backends

• Local in-memory backend (default)
• Redis backend: https://github.com/go-chi/httprate-redis

Example

package main

import (
	"net/http"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/chi/v5/middleware"
	"github.com/go-chi/httprate"
)

func main() {
	r := chi.NewRouter()
	r.Use(middleware.Logger)

	// Enable httprate request limiter of 100 requests per minute.
	//
	// In the code example below, rate-limiting is bound to the request IP address
	// via the LimitByIP middleware handler.
	//
	// To have a single rate-limiter for all requests, use httprate.LimitAll(..).
	//
	// Please see _example/main.go for other more, or read the library code.
	r.Use(httprate.LimitByIP(100, time.Minute))

	r.Get("/", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("."))
	})

	http.ListenAndServe(":3333", r)
}

Common use cases

Rate limit by IP and URL path (aka endpoint)

r.Use(httprate.Limit(
	10,             // requests
	10*time.Second, // per duration
	httprate.WithKeyFuncs(httprate.KeyByIP, httprate.KeyByEndpoint),
))

Rate limit by arbitrary keys

r.Use(httprate.Limit(
	100,
	time.Minute,
	// an oversimplified example of rate limiting by a custom header
	httprate.WithKeyFuncs(func(r *http.Request) (string, error) {
		return r.Header.Get("X-Access-Token"), nil
	}),
))

Rate limit by request payload

// Rate-limiter for login endpoint.
loginRateLimiter := httprate.NewRateLimiter(5, time.Minute)

r.Post("/login", func(w http.ResponseWriter, r *http.Request) {
	var payload struct {
		Username string `json:"username"`
		Password string `json:"password"`
	}
	err := json.NewDecoder(r.Body).Decode(&payload)
	if err != nil || payload.Username == "" || payload.Password == "" {
		w.WriteHeader(400)
		return
	}

	// Rate-limit login at 5 req/min.
	if loginRateLimiter.RespondOnLimit(w, r, payload.Username) {
		return
	}

	w.Write([]byte("login at 5 req/min\n"))
})

Send specific response for rate-limited requests

The default response is HTTP 429 with Too Many Requests body. You can override it with:

r.Use(httprate.Limit(
	10,
	time.Minute,
	httprate.WithLimitHandler(func(w http.ResponseWriter, r *http.Request) {
		http.Error(w, `{"error": "Rate-limited. Please, slow down."}`, http.StatusTooManyRequests)
	}),
))

Send specific response on errors

An error can be returned by:

• A custom key function provided by httprate.WithKeyFunc(customKeyFn)
• A custom backend provided by httprateredis.WithRedisLimitCounter(customBackend)
  • The default local in-memory counter is guaranteed not return any errors
  • Backends that fall-back to the local in-memory counter (e.g. httprate-redis) can choose not to return any errors either

r.Use(httprate.Limit(
	10,
	time.Minute,
	httprate.WithErrorHandler(func(w http.ResponseWriter, r *http.Request, err error) {
		http.Error(w, fmt.Sprintf(`{"error": %q}`, err), http.StatusPreconditionRequired)
	}),
	httprate.WithLimitCounter(customBackend),
))

Send custom response headers

r.Use(httprate.Limit(
	1000,
	time.Minute,
	httprate.WithResponseHeaders(httprate.ResponseHeaders{
		Limit:      "X-RateLimit-Limit",
		Remaining:  "X-RateLimit-Remaining",
		Reset:      "X-RateLimit-Reset",
		RetryAfter: "Retry-After",
		Increment:  "", // omit
	}),
))

Omit response headers

r.Use(httprate.Limit(
	1000,
	time.Minute,
	httprate.WithResponseHeaders(httprate.ResponseHeaders{}),
))

LICENSE

MIT