Add Xiaomi miIO probe detector

Detect stock Xiaomi/Mijia devices via miIO hello packet on UDP:54321.
Response magic 0x2131 uniquely identifies miIO devices.

Detector priority: ONVIF > HomeKit > Xiaomi > standard.

internal/probe/probe.go

@@ -51,6 +51,14 @@ func Init() {
 		return ""
 	})
 
+	// Xiaomi detector (miIO hello on UDP:54321)
+	detectors = append(detectors, func(r *probe.Response) string {
+		if r.Probes.Xiaomi != nil {
+			return "xiaomi"
+		}
+		return ""
+	})
+
 	api.HandleFunc("api/probe", apiProbe)
 }
 
@@ -129,12 +137,19 @@ func runProbe(parent context.Context, ip string) *probe.Response {
 		resp.Probes.ONVIF = r
 		mu.Unlock()
 	})
+	run(func() {
+		r, _ := probe.ProbeXiaomi(fastCtx, ip)
+		mu.Lock()
+		resp.Probes.Xiaomi = r
+		mu.Unlock()
+	})
 
 	wg.Wait()
 
 	// determine reachable
 	resp.Reachable = (resp.Probes.Ports != nil && len(resp.Probes.Ports.Open) > 0) ||
-		resp.Probes.MDNS != nil
+		resp.Probes.MDNS != nil ||
+		resp.Probes.Xiaomi != nil
 
 	// determine type
 	resp.Type = "standard"

pkg/probe/models.go

@@ -15,6 +15,7 @@ type Probes struct {
 	MDNS   *MDNSResult   `json:"mdns"`
 	HTTP   *HTTPResult   `json:"http"`
 	ONVIF  *ONVIFResult  `json:"onvif"`
+	Xiaomi *XiaomiResult `json:"xiaomi"`
 }
 
 type PortsResult struct {
@@ -51,3 +52,8 @@ type ONVIFResult struct {
 	Name     string `json:"name,omitempty"`
 	Hardware string `json:"hardware,omitempty"`
 }
+
+type XiaomiResult struct {
+	DeviceID uint32 `json:"device_id"`
+	Stamp    uint32 `json:"stamp"`
+}

pkg/probe/xiaomi.go

@@ -0,0 +1,60 @@
+package probe
+
+import (
+	"context"
+	"encoding/binary"
+	"net"
+	"time"
+)
+
+// miIO hello packet -- 32 bytes. Stock Xiaomi/Mijia devices listen on
+// UDP:54321 and reply with the same magic 0x2131 + their device_id + stamp.
+// Newer firmwares always return 0xFF in the token field, regardless of
+// pairing status -- real token is only available via Mi Cloud API.
+var xiaomiHello = []byte{
+	0x21, 0x31, 0x00, 0x20,
+	0xff, 0xff, 0xff, 0xff,
+	0xff, 0xff, 0xff, 0xff,
+	0xff, 0xff, 0xff, 0xff,
+	0xff, 0xff, 0xff, 0xff,
+	0xff, 0xff, 0xff, 0xff,
+	0xff, 0xff, 0xff, 0xff,
+	0xff, 0xff, 0xff, 0xff,
+}
+
+// ProbeXiaomi sends miIO hello to ip:54321 and checks the reply magic.
+// Returns nil, nil if the device is not a Xiaomi miIO device.
+func ProbeXiaomi(ctx context.Context, ip string) (*XiaomiResult, error) {
+	conn, err := net.ListenPacket("udp4", ":0")
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Close()
+
+	deadline, ok := ctx.Deadline()
+	if !ok {
+		deadline = time.Now().Add(100 * time.Millisecond)
+	}
+	_ = conn.SetDeadline(deadline)
+
+	addr := &net.UDPAddr{IP: net.ParseIP(ip), Port: 54321}
+	if _, err = conn.WriteTo(xiaomiHello, addr); err != nil {
+		return nil, err
+	}
+
+	buf := make([]byte, 64)
+	n, _, err := conn.ReadFrom(buf)
+	if err != nil || n < 32 {
+		return nil, nil
+	}
+
+	// magic must be 0x2131 -- unique miIO header
+	if buf[0] != 0x21 || buf[1] != 0x31 {
+		return nil, nil
+	}
+
+	return &XiaomiResult{
+		DeviceID: binary.BigEndian.Uint32(buf[8:12]),
+		Stamp:    binary.BigEndian.Uint32(buf[12:16]),
+	}, nil
+}