Issue 4 jwt (#24)

server/middleware/ratelimit.go

@@ -0,0 +1,92 @@
+package middleware
+
+import (
+	"net/http"
+	"sync"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+type visitor struct {
+	tokens   float64
+	lastSeen time.Time
+}
+
+// RateLimiter implements a per-IP token bucket rate limiter.
+type RateLimiter struct {
+	mu       sync.Mutex
+	visitors map[string]*visitor
+	rate     float64 // tokens per second
+	burst    int     // max tokens
+}
+
+// NewRateLimiter creates a rate limiter.
+// rate is requests per second, burst is max burst size.
+func NewRateLimiter(rate float64, burst int) *RateLimiter {
+	rl := &RateLimiter{
+		visitors: make(map[string]*visitor),
+		rate:     rate,
+		burst:    burst,
+	}
+
+	// Cleanup stale entries every 5 minutes
+	go func() {
+		for {
+			time.Sleep(5 * time.Minute)
+			rl.cleanup()
+		}
+	}()
+
+	return rl
+}
+
+// Limit returns a Gin middleware that enforces the rate limit.
+func (rl *RateLimiter) Limit() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		ip := c.ClientIP()
+
+		rl.mu.Lock()
+		v, exists := rl.visitors[ip]
+		now := time.Now()
+
+		if !exists {
+			v = &visitor{tokens: float64(rl.burst), lastSeen: now}
+			rl.visitors[ip] = v
+		}
+
+		// Refill tokens based on elapsed time
+		elapsed := now.Sub(v.lastSeen).Seconds()
+		v.tokens += elapsed * rl.rate
+		if v.tokens > float64(rl.burst) {
+			v.tokens = float64(rl.burst)
+		}
+		v.lastSeen = now
+
+		if v.tokens < 1 {
+			rl.mu.Unlock()
+			c.Header("Retry-After", "1")
+			c.AbortWithStatusJSON(http.StatusTooManyRequests, gin.H{
+				"error": "rate limit exceeded",
+			})
+			return
+		}
+
+		v.tokens--
+		rl.mu.Unlock()
+
+		c.Next()
+	}
+}
+
+func (rl *RateLimiter) cleanup() {
+	rl.mu.Lock()
+	defer rl.mu.Unlock()
+
+	cutoff := time.Now().Add(-10 * time.Minute)
+	for ip, v := range rl.visitors {
+		if v.lastSeen.Before(cutoff) {
+			delete(rl.visitors, ip)
+		}
+	}
+}