Merge pull request #1 from leetcode-golang-classroom/sync-map-solution

✨ handle concurrency with sync.Map

Author: yuanyu90221

README.md

@@ -91,3 +91,32 @@ func (r *RateLimiter) RateLimiterMiddleware(next http.Handler, limit rate.Limit,
 	})
 }
 ```
+
+
+## handle concurrency problem with sync.Map
+
+```golang
+var ipLimiterMap sync.Map
+
+// RateLimiterMiddleware - 建立 ratelimiter middleware
+func (r *RateLimiter) RateLimiterMiddleware(next http.Handler, limit rate.Limit, burst int) http.Handler {
+
+	// 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
+		limiterAny, _ := ipLimiterMap.LoadOrStore(ip, rate.NewLimiter(limit, burst))
+		limiter := limiterAny.(*rate.Limiter)
+		// 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)
+	})
+}
+```
+

internal/service/rate_limiter/rate-limiter.go

@@ -22,21 +22,18 @@ func (r *RateLimiter) getIP(req *http.Request) string {
 	return host
 }
 
+var ipLimiterMap sync.Map
+
 // 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
+
+	// 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()
+		limiterAny, _ := ipLimiterMap.LoadOrStore(ip, rate.NewLimiter(limit, burst))
+		limiter := limiterAny.(*rate.Limiter)
 		// return error if the limit has been reached
 		if !limiter.Allow() {
 			w.Header().Set("Content-Type", "application/json")