添加 MQTT 消息去重队列：Hook 层基于 payload+topic hash 去重，TTL 15 秒，定时清理

internal/mqttforward/dedup_queue.go

@@ -0,0 +1,72 @@
+package mqttforward
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"sync"
+	"time"
+)
+
+const dedupTTL = 15 * time.Second
+
+type DedupQueue struct {
+	mu      sync.Mutex
+	entries map[string]time.Time
+	stopCh  chan struct{}
+}
+
+func NewDedupQueue() *DedupQueue {
+	return &DedupQueue{
+		entries: make(map[string]time.Time),
+		stopCh:  make(chan struct{}),
+	}
+}
+
+func (dq *DedupQueue) TryForward(topic string, payload []byte) bool {
+	hash := dedupHash(topic, payload)
+	now := time.Now()
+	dq.mu.Lock()
+	defer dq.mu.Unlock()
+	if expiry, ok := dq.entries[hash]; ok && now.Before(expiry) {
+		return false
+	}
+	dq.entries[hash] = now.Add(dedupTTL)
+	return true
+}
+
+func (dq *DedupQueue) Start() {
+	go func() {
+		ticker := time.NewTicker(dedupTTL)
+		defer ticker.Stop()
+		for {
+			select {
+			case <-ticker.C:
+				dq.cleanup()
+			case <-dq.stopCh:
+				return
+			}
+		}
+	}()
+}
+
+func (dq *DedupQueue) Stop() {
+	close(dq.stopCh)
+}
+
+func (dq *DedupQueue) cleanup() {
+	now := time.Now()
+	dq.mu.Lock()
+	defer dq.mu.Unlock()
+	for hash, expiry := range dq.entries {
+		if now.After(expiry) {
+			delete(dq.entries, hash)
+		}
+	}
+}
+
+func dedupHash(topic string, payload []byte) string {
+	h := sha256.New()
+	h.Write([]byte(topic))
+	h.Write(payload)
+	return hex.EncodeToString(h.Sum(nil))
+}