feat: harden HTTP server with rate limiting, request timeouts, and sanitized error messages

src/serve/ratelimit.go

@@ -0,0 +1,86 @@
+package serve
+
+import (
+	"net/http"
+	"sync"
+	"time"
+)
+
+type visitor struct {
+	tokens   float64
+	lastSeen time.Time
+}
+
+type rateLimiter struct {
+	mu       sync.Mutex
+	visitors map[string]*visitor
+	rate     float64 // tokens per second
+	burst    float64 // max tokens
+}
+
+func newRateLimiter(rate float64, burst int) *rateLimiter {
+	rl := &rateLimiter{
+		visitors: make(map[string]*visitor),
+		rate:     rate,
+		burst:    float64(burst),
+	}
+	go rl.cleanup()
+	return rl
+}
+
+func (rl *rateLimiter) allow(ip string) bool {
+	rl.mu.Lock()
+	defer rl.mu.Unlock()
+
+	v, exists := rl.visitors[ip]
+	now := time.Now()
+	if !exists {
+		rl.visitors[ip] = &visitor{tokens: rl.burst - 1, lastSeen: now}
+		return true
+	}
+
+	elapsed := now.Sub(v.lastSeen).Seconds()
+	v.lastSeen = now
+	v.tokens += elapsed * rl.rate
+	if v.tokens > rl.burst {
+		v.tokens = rl.burst
+	}
+
+	if v.tokens < 1 {
+		return false
+	}
+	v.tokens--
+	return true
+}
+
+func (rl *rateLimiter) cleanup() {
+	for range time.Tick(time.Minute) {
+		rl.mu.Lock()
+		for ip, v := range rl.visitors {
+			if time.Since(v.lastSeen) > 5*time.Minute {
+				delete(rl.visitors, ip)
+			}
+		}
+		rl.mu.Unlock()
+	}
+}
+
+func clientIP(r *http.Request) string {
+	if ip := r.Header.Get("X-Forwarded-For"); ip != "" {
+		return ip
+	}
+	if ip := r.Header.Get("X-Real-IP"); ip != "" {
+		return ip
+	}
+	return r.RemoteAddr
+}
+
+func withRateLimit(rl *rateLimiter, next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if !rl.allow(clientIP(r)) {
+			writeError(w, http.StatusTooManyRequests, "rate limit exceeded")
+			return
+		}
+		next.ServeHTTP(w, r)
+	})
+}