[Efficiency Improver] perf(auth): eliminate per-IP heap allocation in RateLimiter

auth/ratelimit.go

@@ -23,7 +23,7 @@ const DefaultRateLimiterMaxVisitors = 10_000
 // RateLimiter implements a per-IP token-bucket rate limiter.
 type RateLimiter struct {
 	mu             sync.Mutex
-	visitors       map[string]*visitor
+	visitors       map[string]visitor
 	nextCleanup    time.Time
 	rate           float64
 	burst          int
@@ -61,7 +61,7 @@ func newRateLimiter(rate float64, burst int, trustedProxies []*net.IPNet) *RateL
 		copy(copied, trustedProxies)
 	}
 	return &RateLimiter{
-		visitors:       make(map[string]*visitor),
+		visitors:       make(map[string]visitor),
 		nextCleanup:    time.Now().Add(cleanup),
 		rate:           rate,
 		burst:          burst,
@@ -87,7 +87,7 @@ func (rl *RateLimiter) allow(key string) bool {
 	}
 
 	if rl.visitors == nil {
-		rl.visitors = make(map[string]*visitor)
+		rl.visitors = make(map[string]visitor)
 	}
 	v, exists := rl.visitors[key]
 	if !exists {
@@ -96,7 +96,7 @@ func (rl *RateLimiter) allow(key string) bool {
 		if rl.maxVisitors > 0 && len(rl.visitors) >= rl.maxVisitors {
 			return false
 		}
-		rl.visitors[key] = &visitor{tokens: float64(rl.burst) - 1, lastSeen: now}
+		rl.visitors[key] = visitor{tokens: float64(rl.burst) - 1, lastSeen: now}
 		return true
 	}
 
@@ -107,11 +107,12 @@ func (rl *RateLimiter) allow(key string) bool {
 	}
 	v.lastSeen = now
 
-	if v.tokens < 1 {
-		return false
+	allowed := v.tokens >= 1
+	if allowed {
+		v.tokens--
 	}
-	v.tokens--
-	return true
+	rl.visitors[key] = v
+	return allowed
 }
 
 func (rl *RateLimiter) clientIP(r *http.Request) string {

auth/ratelimit_test.go

@@ -4,6 +4,7 @@ import (
 	"net"
 	"net/http"
 	"net/http/httptest"
+	"strconv"
 	"testing"
 	"time"
 
@@ -40,7 +41,9 @@ func TestRateLimiter_refillsOverTime(t *testing.T) {
 	// Manually advance the visitor's lastSeen into the past so that the next
 	// allow call sees elapsed time.
 	rl.mu.Lock()
-	rl.visitors["key"].lastSeen = time.Now().Add(-100 * time.Millisecond)
+	v := rl.visitors["key"]
+	v.lastSeen = time.Now().Add(-100 * time.Millisecond)
+	rl.visitors["key"] = v
 	rl.mu.Unlock()
 
 	require.True(t, rl.allow("key"))
@@ -79,7 +82,7 @@ func TestRateLimiter_maxVisitorsCapRestoredAfterCleanup(t *testing.T) {
 
 	// Fill the map to capacity with a stale entry.
 	rl.mu.Lock()
-	rl.visitors["stale"] = &visitor{tokens: 5, lastSeen: time.Now().Add(-rl.cleanup - time.Second)}
+	rl.visitors["stale"] = visitor{tokens: 5, lastSeen: time.Now().Add(-rl.cleanup - time.Second)}
 	rl.mu.Unlock()
 
 	// The allow call triggers cleanup (nextCleanup is in the past), evicts
@@ -101,7 +104,7 @@ func TestRateLimiter_cleanup(t *testing.T) {
 	rl := newTestRateLimiter(10, 5)
 	// Add a stale visitor.
 	rl.mu.Lock()
-	rl.visitors["stale"] = &visitor{tokens: 5, lastSeen: time.Now().Add(-rl.cleanup - time.Second)}
+	rl.visitors["stale"] = visitor{tokens: 5, lastSeen: time.Now().Add(-rl.cleanup - time.Second)}
 	rl.mu.Unlock()
 
 	// This call should trigger cleanup and remove "stale".
@@ -330,3 +333,40 @@ func TestRateLimiter_clientIP_withTrustedProxies(t *testing.T) {
 	req.Header.Set("X-Forwarded-For", "5.6.7.8")
 	require.Equal(t, "5.6.7.8", rl.clientIP(req))
 }
+
+// ---------------------------------------------------------------------------
+// Benchmarks
+// ---------------------------------------------------------------------------
+
+// BenchmarkRateLimiterAllow_existingKey measures the hot path: a key already
+// in the map being allowed repeatedly. This is the dominant case in production,
+// where the same IP sends many requests over time.
+// Run with: go test -bench=BenchmarkRateLimiterAllow_existingKey -benchmem ./auth/
+func BenchmarkRateLimiterAllow_existingKey(b *testing.B) {
+	rl := NewRateLimiter(float64(b.N)+1, b.N+1) // tokens never run out
+	const key = "192.0.2.1"
+	rl.allow(key) // prime the map entry
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		rl.allow(key)
+	}
+}
+
+// BenchmarkRateLimiterAllow_newVisitors measures the allocation cost of adding
+// new visitor entries. In the old pointer-map design, each new visitor required
+// a separate heap allocation (*visitor). The value-map design stores visitor
+// state inline in the map bucket, eliminating that per-visitor allocation.
+// Run with: go test -bench=BenchmarkRateLimiterAllow_newVisitors -benchmem ./auth/
+func BenchmarkRateLimiterAllow_newVisitors(b *testing.B) {
+	rl := NewRateLimiter(1, 1).WithMaxVisitors(b.N + 1)
+	keys := make([]string, b.N)
+	for i := range keys {
+		keys[i] = strconv.Itoa(i) // unique key per slot, allocated outside timed loop
+	}
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		rl.allow(keys[i])
+	}
+}