ipratelimit.go

// The MIT License (MIT)

// Copyright (c) 2019 Anurag Patel (anuragpatel.optnio@gmail.com)

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package ipratelimit // import "github.com/geekfarmer/ipratelimit"

import (
	"net/http"
	"sync"

	"golang.org/x/time/rate"
)

// Limiter is used to rate-limit http-request for user's IP address
// rate.Limiter provides token button algorithm and controls how frequently events are allowed to be happen
// b -> token bucket size (maxium events) (initially full)
// r -> rate/second by which token bucket will refill
// ips -> maintain a map of limiters for each ip address
type Limiter struct {
	ips map[string]*rate.Limiter
	mu  *sync.RWMutex
	r   rate.Limit
	b   int
}

// New create an instance of ip rate limiter
// returns a Limiter that will limit to the given RPS.
func New(r rate.Limit, b int) *Limiter {
	i := &Limiter{
		ips: make(map[string]*rate.Limiter),
		mu:  &sync.RWMutex{},
		r:   r,
		b:   b,
	}

	return i
}

// AddIP creates a new rate limiter and adds it to the ips map,
// using the IP address as the key
func (i *Limiter) AddIP(ip string) *rate.Limiter {
	i.mu.Lock()
	defer i.mu.Unlock()

	limiter := rate.NewLimiter(i.r, i.b)

	i.ips[ip] = limiter

	return limiter
}

// GetLimiter returns the rate limiter for the provided IP address if it exists.
// Otherwise calls AddIP to add IP address to the map
func (i *Limiter) GetLimiter(ip string) *rate.Limiter {
	i.mu.Lock()
	limiter, exists := i.ips[ip]

	if !exists {
		i.mu.Unlock()
		return i.AddIP(ip)
	}

	i.mu.Unlock()

	return limiter
}

// IPRateLimitMiddleware -> we will add this middleware to all endpoints
// if ip reached max bucket size (b) it will respond toomany requests
// else it will process next request
func (i *Limiter) IPRateLimitMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		limiter := i.GetLimiter(r.RemoteAddr)
		if !limiter.Allow() {
			http.Error(w, http.StatusText(http.StatusTooManyRequests), http.StatusTooManyRequests)
			return
		}

		next.ServeHTTP(w, r)
	})
}