xiaomi/cs2: reduce TCP keepalive interval to 1 second

Based on PCAP analysis of official Mi Home app traffic:
- Official app sends PING every ~1 second
- Previous 5-second interval was too slow, causing connection resets

Simply reduce keepalive timeout from 5s to 1s.

pkg/xiaomi/cs2/conn.go

@@ -24,16 +24,8 @@ func Dial(host, transport string) (*Conn, error) {
 		isTCP:  isTCP,
 		rawCh0: make(chan []byte, 10),
 		rawCh2: make(chan []byte, 100),
-		done:   make(chan struct{}),
 	}
 	go c.worker()
-
-	// For TCP connections, start independent keepalive goroutine
-	// Official Mi Home app sends PING every 1 second bidirectionally
-	if isTCP {
-		go c.keepalive()
-	}
-
 	return c, nil
 }
 
@@ -46,7 +38,6 @@ type Conn struct {
 	seqCh3 uint16
 	rawCh0 chan []byte
 	rawCh2 chan []byte
-	done   chan struct{} // signals connection close to keepalive goroutine
 
 	cmdMu  sync.Mutex
 	cmdAck func()
@@ -63,7 +54,6 @@ const (
 	msgDrwAck    = 0xD1
 	msgPing      = 0xE0
 	msgPong      = 0xE1
-	msgAlive     = 0xF0 // Camera heartbeat/alive signal
 	msgClose     = 0xF1
 )
 
@@ -112,38 +102,17 @@ func handshake(host, transport string) (net.Conn, error) {
 	return conn, nil
 }
 
-// keepalive sends PING every 1 second for TCP connections.
-// Based on PCAP analysis of official Mi Home app: both sides send PING bidirectionally,
-// neither responds with PONG. This keeps the connection alive.
-func (c *Conn) keepalive() {
-	ticker := time.NewTicker(time.Second)
-	defer ticker.Stop()
-
-	ping := []byte{magic, msgPing, 0, 0}
-
-	for {
-		select {
-		case <-c.done:
-			return
-		case <-ticker.C:
-			if _, err := c.conn.Write(ping); err != nil {
-				return
-			}
-		}
-	}
-}
-
 func (c *Conn) worker() {
 	defer func() {
 		close(c.rawCh0)
 		close(c.rawCh2)
-		close(c.done) // signal keepalive goroutine to stop
 	}()
 
 	chAck := make([]uint16, 4) // only for UDP
 	buf := make([]byte, 1200)
 	var ch2WaitSize int
 	var ch2WaitData []byte
+	var keepaliveTS time.Time
 
 	for {
 		n, err := c.conn.Read(buf)
@@ -156,7 +125,14 @@ func (c *Conn) worker() {
 		case msgDrw:
 			ch := buf[5]
 
-			if !c.isTCP {
+			if c.isTCP {
+				// For TCP we should send ping every second to keep connection alive.
+				// Based on PCAP analysis: official Mi Home app sends PING every ~1s.
+				if now := time.Now(); now.After(keepaliveTS) {
+					_, _ = c.conn.Write([]byte{magic, msgPing, 0, 0})
+					keepaliveTS = now.Add(time.Second)
+				}
+			} else {
 				// For UDP we should using ack.
 				seqHI := buf[6]
 				seqLO := buf[7]
@@ -204,11 +180,7 @@ func (c *Conn) worker() {
 			}
 
 		case msgPing:
-			// Official Mi Home app: both sides send PING, neither responds with PONG
+			_, _ = c.conn.Write([]byte{magic, msgPong, 0, 0})
-			// Just acknowledge receipt, don't send PONG
-			continue
-		case msgAlive:
-			// Some cameras may send 0xF0 as heartbeat - just ignore like PING
 			continue
 		case msgPong, msgP2PRdyUDP, msgP2PRdyTCP, msgClose:
 			continue // skip it