✨ create mutex to handle concurrency problem

Author: yuanyu90221

README.md

@@ -60,4 +60,34 @@ func (r *RateLimiter) RateLimiterMiddleware(next http.Handler, limit rate.Limit,
 func NewRateLimiter() *RateLimiter {
 	return &RateLimiter{}
 }
+```
+
+## Fix Current Access with sync.Mutext
+
+```golang
+// RateLimiterMiddleware - 建立 ratelimiter middleware
+func (r *RateLimiter) RateLimiterMiddleware(next http.Handler, limit rate.Limit, burst int) http.Handler {
+	ipLimiterMap := make(map[string]*rate.Limiter)
+	var mu sync.Mutex
+	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		// Fetch IP
+		ip := r.getIP(req)
+		// Create limiter if not present for IP
+		mu.Lock()
+		limiter, exists := ipLimiterMap[ip]
+		if !exists {
+			limiter = rate.NewLimiter(limit, burst)
+			ipLimiterMap[ip] = limiter
+		}
+		mu.Unlock()
+		// return error if the limit has been reached
+		if !limiter.Allow() {
+			w.Header().Set("Content-Type", "application/json")
+			w.WriteHeader(http.StatusTooManyRequests)
+			json.NewEncoder(w).Encode(map[string]string{"error": "Too many requests"})
+			return
+		}
+		next.ServeHTTP(w, req)
+	})
+}
 ```

go.mod

@@ -1,6 +1,6 @@
 module github.com/leetcode-golang-classroom/golang-sample-with-rate-limiter
 
-go 1.22.4
+go 1.24.0
 
 require (
 	github.com/magefile/mage v1.15.0

internal/application/app.go

@@ -34,7 +34,7 @@ func New(appConfig *config.Config) *App {
 func (app *App) Start(ctx context.Context) error {
 	// setup rateLimiter
 	rateLimitMux := rateLimiter.NewRateLimiter()
-	handler := rateLimitMux.RateLimiterMiddleware(app.router, rate.Limit(1), 10)
+	handler := rateLimitMux.RateLimiterMiddleware(app.router, rate.Limit(2), 10)
 	// setup server
 	server := &http.Server{
 		Addr:    fmt.Sprintf(":%s", app.appConfig.Port),

internal/service/rate_limiter/rate-limiter.go

@@ -5,6 +5,7 @@ import (
 	"log"
 	"net"
 	"net/http"
+	"sync"
 
 	"golang.org/x/time/rate"
 )
@@ -24,15 +25,18 @@ func (r *RateLimiter) getIP(req *http.Request) string {
 // RateLimiterMiddleware - 建立 ratelimiter middleware
 func (r *RateLimiter) RateLimiterMiddleware(next http.Handler, limit rate.Limit, burst int) http.Handler {
 	ipLimiterMap := make(map[string]*rate.Limiter)
+	var mu sync.Mutex
 	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
 		// Fetch IP
 		ip := r.getIP(req)
 		// Create limiter if not present for IP
+		mu.Lock()
 		limiter, exists := ipLimiterMap[ip]
 		if !exists {
 			limiter = rate.NewLimiter(limit, burst)
 			ipLimiterMap[ip] = limiter
 		}
+		mu.Unlock()
 		// return error if the limit has been reached
 		if !limiter.Allow() {
 			w.Header().Set("Content-Type", "application/json")