fix: 按 K-00 约定修复 Go SDK 断线重交与退避

sdk/go/transport_mqtt.go

@@ -15,15 +15,15 @@ import (
 )
 
 type mqttTransport struct {
-	mu       sync.Mutex
-	cm       *autopaho.ConnectionManager
-	cancel   context.CancelFunc
-	cfg      transportConfig
-	cred     atomic.Value // string
-	upTopic  string
+	mu        sync.Mutex
+	cm        *autopaho.ConnectionManager
+	cancel    context.CancelFunc
+	cfg       transportConfig
+	cred      atomic.Value // string
+	upTopic   string
 	downTopic string
-	stopped  atomic.Bool
-	ready    chan struct{}
+	stopped   atomic.Bool
+	ready     chan struct{}
 }
 
 func newMQTTTransport() *mqttTransport {
@@ -57,7 +57,7 @@ func (t *mqttTransport) Start(ctx context.Context, cfg transportConfig) error {
 	var sessionExpiry uint32 // 0；由 ConnectPacketBuilder 显式写入 Properties
 	cliCfg := autopaho.ClientConfig{
 		ServerUrls:                    []*url.URL{u},
-		KeepAlive:                     30,
+		KeepAlive:                     uint16(DefaultKeepAliveSeconds),
 		ConnectTimeout:                cfg.ConnectTimeout,
 		CleanStartOnInitialConnection: false, // 不要只靠这个；每次用 ConnectPacketBuilder
 		SessionExpiryInterval:         sessionExpiry,
@@ -75,8 +75,12 @@ func (t *mqttTransport) Start(ctx context.Context, cfg transportConfig) error {
 						cfg.OnAuthFailed(reason)
 					}
 					cancel()
+					return
 				}
 			}
+			if cfg.Backoff != nil {
+				cfg.Backoff.MarkOffline()
+			}
 		},
 		OnConnectionDown: func() bool {
 			if t.stopped.Load() {
@@ -113,14 +117,17 @@ func (t *mqttTransport) Start(ctx context.Context, cfg transportConfig) error {
 			}()
 		},
 		ClientConfig: paho.ClientConfig{
-			ClientID: cfg.EndpointID,
+			ClientID:      cfg.EndpointID,
+			PacketTimeout: cfg.ConnectTimeout,
 			OnServerDisconnect: func(d *paho.Disconnect) {
 				if d != nil && d.ReasonCode == 0x8E {
 					if cfg.OnKicked != nil {
 						cfg.OnKicked()
 					}
 					cancel()
+					return
 				}
+				// 0x8B 等其它原因按可重试处理，继续重连。
 			},
 			OnPublishReceived: []func(paho.PublishReceived) (bool, error){
 				func(pr paho.PublishReceived) (bool, error) {
@@ -140,6 +147,7 @@ func (t *mqttTransport) Start(ctx context.Context, cfg transportConfig) error {
 			c.Properties = &paho.ConnectProperties{}
 		}
 		c.Properties.SessionExpiryInterval = &zero
+		// 不设置 ReceiveMaximum（B-01 / K-00）。
 		pass, _ := t.cred.Load().(string)
 		c.UsernameFlag = true
 		c.Username = cfg.EndpointID