fix: align Go packet decoder with MeshCore firmware spec

Match the C++ firmware wire format (Packet::writeTo/readFrom):

1. Field order: transport codes are parsed BEFORE path_length byte,
   matching firmware's header → transport_codes → path_len → path → payload

2. ACK payload: just 4-byte CRC checksum, not dest+src+ackHash.
   Firmware createAck() writes only ack_crc (4 bytes).

3. TRACE payload: tag(4) + authCode(4) + flags(1) + pathData,
   matching firmware createTrace() and onRecvPacket() TRACE handler.

4. ADVERT features: parse feat1 (0x20) and feat2 (0x40) optional
   2-byte fields between location and name, matching AdvertDataBuilder
   and AdvertDataParser in the firmware.

5. Transport code naming: code1/code2 instead of nextHop/lastHop,
   matching firmware's transport_codes[0]/transport_codes[1] naming.

Fixes applied to both cmd/ingestor/decoder.go and cmd/server/decoder.go.
Tests updated to match new behavior.

cmd/ingestor/decoder.go

@@ -72,8 +72,8 @@ type Header struct {
 
 // TransportCodes are present on TRANSPORT_FLOOD and TRANSPORT_DIRECT routes.
 type TransportCodes struct {
-	NextHop string `json:"nextHop"`
-	LastHop string `json:"lastHop"`
+	Code1 string `json:"code1"`
+	Code2 string `json:"code2"`
 }
 
 // Path holds decoded path/hop information.
@@ -92,6 +92,8 @@ type AdvertFlags struct {
 	Room        bool `json:"room"`
 	Sensor      bool `json:"sensor"`
 	HasLocation bool `json:"hasLocation"`
+	HasFeat1    bool `json:"hasFeat1"`
+	HasFeat2    bool `json:"hasFeat2"`
 	HasName     bool `json:"hasName"`
 }
 
@@ -111,6 +113,8 @@ type Payload struct {
 	Lat           *float64     `json:"lat,omitempty"`
 	Lon           *float64     `json:"lon,omitempty"`
 	Name          string       `json:"name,omitempty"`
+	Feat1         *int         `json:"feat1,omitempty"`
+	Feat2         *int         `json:"feat2,omitempty"`
 	BatteryMv     *int         `json:"battery_mv,omitempty"`
 	TemperatureC  *float64     `json:"temperature_c,omitempty"`
 	ChannelHash   int          `json:"channelHash,omitempty"`
@@ -123,6 +127,8 @@ type Payload struct {
 	EphemeralPubKey string     `json:"ephemeralPubKey,omitempty"`
 	PathData      string       `json:"pathData,omitempty"`
 	Tag           uint32       `json:"tag,omitempty"`
+	AuthCode      uint32       `json:"authCode,omitempty"`
+	TraceFlags    *int         `json:"traceFlags,omitempty"`
 	RawHex        string       `json:"raw,omitempty"`
 	Error         string       `json:"error,omitempty"`
 }
@@ -199,14 +205,13 @@ func decodeEncryptedPayload(typeName string, buf []byte) Payload {
 }
 
 func decodeAck(buf []byte) Payload {
-	if len(buf) < 6 {
+	if len(buf) < 4 {
 		return Payload{Type: "ACK", Error: "too short", RawHex: hex.EncodeToString(buf)}
 	}
+	checksum := binary.LittleEndian.Uint32(buf[0:4])
 	return Payload{
 		Type:      "ACK",
-		DestHash:  hex.EncodeToString(buf[0:1]),
-		SrcHash:   hex.EncodeToString(buf[1:2]),
-		ExtraHash: hex.EncodeToString(buf[2:6]),
+		ExtraHash: fmt.Sprintf("%08x", checksum),
 	}
 }
 
@@ -231,6 +236,8 @@ func decodeAdvert(buf []byte) Payload {
 	if len(appdata) > 0 {
 		flags := appdata[0]
 		advType := int(flags & 0x0F)
+		hasFeat1 := flags&0x20 != 0
+		hasFeat2 := flags&0x40 != 0
 		p.Flags = &AdvertFlags{
 			Raw:         int(flags),
 			Type:        advType,
@@ -239,6 +246,8 @@ func decodeAdvert(buf []byte) Payload {
 			Room:        advType == 3,
 			Sensor:      advType == 4,
 			HasLocation: flags&0x10 != 0,
+			HasFeat1:    hasFeat1,
+			HasFeat2:    hasFeat2,
 			HasName:     flags&0x80 != 0,
 		}
 
@@ -252,6 +261,16 @@ func decodeAdvert(buf []byte) Payload {
 			p.Lon = &lon
 			off += 8
 		}
+		if hasFeat1 && len(appdata) >= off+2 {
+			feat1 := int(binary.LittleEndian.Uint16(appdata[off : off+2]))
+			p.Feat1 = &feat1
+			off += 2
+		}
+		if hasFeat2 && len(appdata) >= off+2 {
+			feat2 := int(binary.LittleEndian.Uint16(appdata[off : off+2]))
+			p.Feat2 = &feat2
+			off += 2
+		}
 		if p.Flags.HasName {
 			// Find null terminator to separate name from trailing telemetry bytes
 			nameEnd := len(appdata)
@@ -469,15 +488,22 @@ func decodePathPayload(buf []byte) Payload {
 }
 
 func decodeTrace(buf []byte) Payload {
-	if len(buf) < 12 {
+	if len(buf) < 9 {
 		return Payload{Type: "TRACE", Error: "too short", RawHex: hex.EncodeToString(buf)}
 	}
-	return Payload{
-		Type:     "TRACE",
-		DestHash: hex.EncodeToString(buf[5:11]),
-		SrcHash:  hex.EncodeToString(buf[11:12]),
-		Tag:      binary.LittleEndian.Uint32(buf[1:5]),
+	tag := binary.LittleEndian.Uint32(buf[0:4])
+	authCode := binary.LittleEndian.Uint32(buf[4:8])
+	flags := int(buf[8])
+	p := Payload{
+		Type:       "TRACE",
+		Tag:        tag,
+		AuthCode:   authCode,
+		TraceFlags: &flags,
 	}
+	if len(buf) > 9 {
+		p.PathData = hex.EncodeToString(buf[9:])
+	}
+	return p
 }
 
 func decodePayload(payloadType int, buf []byte, channelKeys map[string]string) Payload {
@@ -520,8 +546,7 @@ func DecodePacket(hexString string, channelKeys map[string]string) (*DecodedPack
 	}
 
 	header := decodeHeader(buf[0])
-	pathByte := buf[1]
-	offset := 2
+	offset := 1
 
 	var tc *TransportCodes
 	if isTransportRoute(header.RouteType) {
@@ -529,12 +554,18 @@ func DecodePacket(hexString string, channelKeys map[string]string) (*DecodedPack
 			return nil, fmt.Errorf("packet too short for transport codes")
 		}
 		tc = &TransportCodes{
-			NextHop: strings.ToUpper(hex.EncodeToString(buf[offset : offset+2])),
-			LastHop: strings.ToUpper(hex.EncodeToString(buf[offset+2 : offset+4])),
+			Code1: strings.ToUpper(hex.EncodeToString(buf[offset : offset+2])),
+			Code2: strings.ToUpper(hex.EncodeToString(buf[offset+2 : offset+4])),
 		}
 		offset += 4
 	}
 
+	if offset >= len(buf) {
+		return nil, fmt.Errorf("packet too short (no path byte)")
+	}
+	pathByte := buf[offset]
+	offset++
+
 	path, bytesConsumed := decodePath(pathByte, buf, offset)
 	offset += bytesConsumed
 
@@ -562,16 +593,24 @@ func ComputeContentHash(rawHex string) string {
 		return rawHex
 	}
 
-	pathByte := buf[1]
+	headerByte := buf[0]
+	offset := 1
+	if isTransportRoute(int(headerByte & 0x03)) {
+		offset += 4
+	}
+	if offset >= len(buf) {
+		if len(rawHex) >= 16 {
+			return rawHex[:16]
+		}
+		return rawHex
+	}
+	pathByte := buf[offset]
+	offset++
 	hashSize := int((pathByte>>6)&0x3) + 1
 	hashCount := int(pathByte & 0x3F)
 	pathBytes := hashSize * hashCount
 
-	headerByte := buf[0]
-	payloadStart := 2 + pathBytes
-	if isTransportRoute(int(headerByte & 0x03)) {
-		payloadStart += 4
-	}
+	payloadStart := offset + pathBytes
 	if payloadStart > len(buf) {
 		if len(rawHex) >= 16 {
 			return rawHex[:16]

cmd/ingestor/decoder_test.go

@@ -129,7 +129,8 @@ func TestDecodePath3ByteHashes(t *testing.T) {
 
 func TestTransportCodes(t *testing.T) {
 	// Route type 0 (TRANSPORT_FLOOD) should have transport codes
-	hex := "1400" + "AABB" + "CCDD" + "1A" + strings.Repeat("00", 10)
+	// Firmware order: header + transport_codes(4) + path_len + path + payload
+	hex := "14" + "AABB" + "CCDD" + "00" + strings.Repeat("00", 10)
 	pkt, err := DecodePacket(hex, nil)
 	if err != nil {
 		t.Fatal(err)
@@ -140,11 +141,11 @@ func TestTransportCodes(t *testing.T) {
 	if pkt.TransportCodes == nil {
 		t.Fatal("transportCodes should not be nil for TRANSPORT_FLOOD")
 	}
-	if pkt.TransportCodes.NextHop != "AABB" {
-		t.Errorf("nextHop=%s, want AABB", pkt.TransportCodes.NextHop)
+	if pkt.TransportCodes.Code1 != "AABB" {
+		t.Errorf("code1=%s, want AABB", pkt.TransportCodes.Code1)
 	}
-	if pkt.TransportCodes.LastHop != "CCDD" {
-		t.Errorf("lastHop=%s, want CCDD", pkt.TransportCodes.LastHop)
+	if pkt.TransportCodes.Code2 != "CCDD" {
+		t.Errorf("code2=%s, want CCDD", pkt.TransportCodes.Code2)
 	}
 
 	// Route type 1 (FLOOD) should NOT have transport codes
@@ -537,10 +538,11 @@ func TestDecodeTraceShort(t *testing.T) {
 
 func TestDecodeTraceValid(t *testing.T) {
 	buf := make([]byte, 16)
-	buf[0] = 0x00
-	buf[1] = 0x01 // tag LE uint32 = 1
-	buf[5] = 0xAA // destHash start
-	buf[11] = 0xBB
+	// tag(4) + authCode(4) + flags(1) + pathData
+	binary.LittleEndian.PutUint32(buf[0:4], 1)          // tag = 1
+	binary.LittleEndian.PutUint32(buf[4:8], 0xDEADBEEF) // authCode
+	buf[8] = 0x02                                         // flags
+	buf[9] = 0xAA                                         // path data
 	p := decodeTrace(buf)
 	if p.Error != "" {
 		t.Errorf("unexpected error: %s", p.Error)
@@ -548,9 +550,18 @@ func TestDecodeTraceValid(t *testing.T) {
 	if p.Tag != 1 {
 		t.Errorf("tag=%d, want 1", p.Tag)
 	}
+	if p.AuthCode != 0xDEADBEEF {
+		t.Errorf("authCode=%d, want 0xDEADBEEF", p.AuthCode)
+	}
+	if p.TraceFlags == nil || *p.TraceFlags != 2 {
+		t.Errorf("traceFlags=%v, want 2", p.TraceFlags)
+	}
 	if p.Type != "TRACE" {
 		t.Errorf("type=%s, want TRACE", p.Type)
 	}
+	if p.PathData == "" {
+		t.Error("pathData should not be empty")
+	}
 }
 
 func TestDecodeAdvertShort(t *testing.T) {
@@ -833,10 +844,9 @@ func TestComputeContentHashShortHex(t *testing.T) {
 }
 
 func TestComputeContentHashTransportRoute(t *testing.T) {
-	// Route type 0 (TRANSPORT_FLOOD) with no path hops + 4 transport code bytes
-	// header=0x14 (TRANSPORT_FLOOD, ADVERT), path=0x00 (0 hops)
-	// transport codes = 4 bytes, then payload
-	hex := "1400" + "AABBCCDD" + strings.Repeat("EE", 10)
+	// Route type 0 (TRANSPORT_FLOOD) with transport codes then path=0x00 (0 hops)
+	// header=0x14 (TRANSPORT_FLOOD, ADVERT), transport(4), path=0x00
+	hex := "14" + "AABBCCDD" + "00" + strings.Repeat("EE", 10)
 	hash := ComputeContentHash(hex)
 	if len(hash) != 16 {
 		t.Errorf("hash length=%d, want 16", len(hash))
@@ -870,12 +880,10 @@ func TestComputeContentHashPayloadBeyondBufferLongHex(t *testing.T) {
 
 func TestComputeContentHashTransportBeyondBuffer(t *testing.T) {
 	// Transport route (0x00 = TRANSPORT_FLOOD) with path claiming some bytes
-	// total buffer too short for transport codes + path
-	// header=0x00, pathByte=0x02 (2 hops, 1-byte hash), then only 2 more bytes
-	// payloadStart = 2 + 2 + 4(transport) = 8, but buffer only 6 bytes
-	hex := "0002" + "AABB" + strings.Repeat("CC", 6) // 20 chars = 10 bytes
+	// header=0x00, transport(4), pathByte=0x02 (2 hops, 1-byte hash)
+	// offset=1+4+1+2=8, buffer needs to be >= 8
+	hex := "00" + "AABB" + "CCDD" + "02" + strings.Repeat("CC", 6) // 20 chars = 10 bytes  
 	hash := ComputeContentHash(hex)
-	// payloadStart = 2 + 2 + 4 = 8, buffer is 10 bytes → should work
 	if len(hash) != 16 {
 		t.Errorf("hash length=%d, want 16", len(hash))
 	}
@@ -913,8 +921,8 @@ func TestDecodePacketWithNewlines(t *testing.T) {
 }
 
 func TestDecodePacketTransportRouteTooShort(t *testing.T) {
-	// TRANSPORT_FLOOD (route=0) but only 3 bytes total → too short for transport codes
-	_, err := DecodePacket("140011", nil)
+	// TRANSPORT_FLOOD (route=0) but only 2 bytes total → too short for transport codes
+	_, err := DecodePacket("1400", nil)
 	if err == nil {
 		t.Error("expected error for transport route with too-short buffer")
 	}
@@ -931,16 +939,19 @@ func TestDecodeAckShort(t *testing.T) {
 }
 
 func TestDecodeAckValid(t *testing.T) {
-	buf := []byte{0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF}
+	buf := []byte{0xAA, 0xBB, 0xCC, 0xDD}
 	p := decodeAck(buf)
 	if p.Error != "" {
 		t.Errorf("unexpected error: %s", p.Error)
 	}
-	if p.DestHash != "aa" {
-		t.Errorf("destHash=%s, want aa", p.DestHash)
+	if p.ExtraHash != "ddccbbaa" {
+		t.Errorf("extraHash=%s, want ddccbbaa", p.ExtraHash)
 	}
-	if p.ExtraHash != "ccddeeff" {
-		t.Errorf("extraHash=%s, want ccddeeff", p.ExtraHash)
+	if p.DestHash != "" {
+		t.Errorf("destHash should be empty, got %s", p.DestHash)
+	}
+	if p.SrcHash != "" {
+		t.Errorf("srcHash should be empty, got %s", p.SrcHash)
 	}
 }
 

cmd/server/decoder.go

@@ -54,8 +54,8 @@ type Header struct {
 
 // TransportCodes are present on TRANSPORT_FLOOD and TRANSPORT_DIRECT routes.
 type TransportCodes struct {
-	NextHop string `json:"nextHop"`
-	LastHop string `json:"lastHop"`
+	Code1 string `json:"code1"`
+	Code2 string `json:"code2"`
 }
 
 // Path holds decoded path/hop information.
@@ -74,6 +74,8 @@ type AdvertFlags struct {
 	Room        bool `json:"room"`
 	Sensor      bool `json:"sensor"`
 	HasLocation bool `json:"hasLocation"`
+	HasFeat1    bool `json:"hasFeat1"`
+	HasFeat2    bool `json:"hasFeat2"`
 	HasName     bool `json:"hasName"`
 }
 
@@ -97,6 +99,8 @@ type Payload struct {
 	EphemeralPubKey string       `json:"ephemeralPubKey,omitempty"`
 	PathData        string       `json:"pathData,omitempty"`
 	Tag             uint32       `json:"tag,omitempty"`
+	AuthCode        uint32       `json:"authCode,omitempty"`
+	TraceFlags      *int         `json:"traceFlags,omitempty"`
 	RawHex          string       `json:"raw,omitempty"`
 	Error           string       `json:"error,omitempty"`
 }
@@ -173,14 +177,13 @@ func decodeEncryptedPayload(typeName string, buf []byte) Payload {
 }
 
 func decodeAck(buf []byte) Payload {
-	if len(buf) < 6 {
+	if len(buf) < 4 {
 		return Payload{Type: "ACK", Error: "too short", RawHex: hex.EncodeToString(buf)}
 	}
+	checksum := binary.LittleEndian.Uint32(buf[0:4])
 	return Payload{
 		Type:      "ACK",
-		DestHash:  hex.EncodeToString(buf[0:1]),
-		SrcHash:   hex.EncodeToString(buf[1:2]),
-		ExtraHash: hex.EncodeToString(buf[2:6]),
+		ExtraHash: fmt.Sprintf("%08x", checksum),
 	}
 }
 
@@ -205,6 +208,8 @@ func decodeAdvert(buf []byte) Payload {
 	if len(appdata) > 0 {
 		flags := appdata[0]
 		advType := int(flags & 0x0F)
+		hasFeat1 := flags&0x20 != 0
+		hasFeat2 := flags&0x40 != 0
 		p.Flags = &AdvertFlags{
 			Raw:         int(flags),
 			Type:        advType,
@@ -213,6 +218,8 @@ func decodeAdvert(buf []byte) Payload {
 			Room:        advType == 3,
 			Sensor:      advType == 4,
 			HasLocation: flags&0x10 != 0,
+			HasFeat1:    hasFeat1,
+			HasFeat2:    hasFeat2,
 			HasName:     flags&0x80 != 0,
 		}
 
@@ -226,6 +233,12 @@ func decodeAdvert(buf []byte) Payload {
 			p.Lon = &lon
 			off += 8
 		}
+		if hasFeat1 && len(appdata) >= off+2 {
+			off += 2  // skip feat1 bytes (reserved for future use)
+		}
+		if hasFeat2 && len(appdata) >= off+2 {
+			off += 2  // skip feat2 bytes (reserved for future use)
+		}
 		if p.Flags.HasName {
 			name := string(appdata[off:])
 			name = strings.TrimRight(name, "\x00")
@@ -276,15 +289,22 @@ func decodePathPayload(buf []byte) Payload {
 }
 
 func decodeTrace(buf []byte) Payload {
-	if len(buf) < 12 {
+	if len(buf) < 9 {
 		return Payload{Type: "TRACE", Error: "too short", RawHex: hex.EncodeToString(buf)}
 	}
-	return Payload{
-		Type:     "TRACE",
-		DestHash: hex.EncodeToString(buf[5:11]),
-		SrcHash:  hex.EncodeToString(buf[11:12]),
-		Tag:      binary.LittleEndian.Uint32(buf[1:5]),
+	tag := binary.LittleEndian.Uint32(buf[0:4])
+	authCode := binary.LittleEndian.Uint32(buf[4:8])
+	flags := int(buf[8])
+	p := Payload{
+		Type:       "TRACE",
+		Tag:        tag,
+		AuthCode:   authCode,
+		TraceFlags: &flags,
 	}
+	if len(buf) > 9 {
+		p.PathData = hex.EncodeToString(buf[9:])
+	}
+	return p
 }
 
 func decodePayload(payloadType int, buf []byte) Payload {
@@ -327,8 +347,7 @@ func DecodePacket(hexString string) (*DecodedPacket, error) {
 	}
 
 	header := decodeHeader(buf[0])
-	pathByte := buf[1]
-	offset := 2
+	offset := 1
 
 	var tc *TransportCodes
 	if isTransportRoute(header.RouteType) {
@@ -336,12 +355,18 @@ func DecodePacket(hexString string) (*DecodedPacket, error) {
 			return nil, fmt.Errorf("packet too short for transport codes")
 		}
 		tc = &TransportCodes{
-			NextHop: strings.ToUpper(hex.EncodeToString(buf[offset : offset+2])),
-			LastHop: strings.ToUpper(hex.EncodeToString(buf[offset+2 : offset+4])),
+			Code1: strings.ToUpper(hex.EncodeToString(buf[offset : offset+2])),
+			Code2: strings.ToUpper(hex.EncodeToString(buf[offset+2 : offset+4])),
 		}
 		offset += 4
 	}
 
+	if offset >= len(buf) {
+		return nil, fmt.Errorf("packet too short (no path byte)")
+	}
+	pathByte := buf[offset]
+	offset++
+
 	path, bytesConsumed := decodePath(pathByte, buf, offset)
 	offset += bytesConsumed
 
@@ -367,16 +392,24 @@ func ComputeContentHash(rawHex string) string {
 		return rawHex
 	}
 
-	pathByte := buf[1]
+	headerByte := buf[0]
+	offset := 1
+	if isTransportRoute(int(headerByte & 0x03)) {
+		offset += 4
+	}
+	if offset >= len(buf) {
+		if len(rawHex) >= 16 {
+			return rawHex[:16]
+		}
+		return rawHex
+	}
+	pathByte := buf[offset]
+	offset++
 	hashSize := int((pathByte>>6)&0x3) + 1
 	hashCount := int(pathByte & 0x3F)
 	pathBytes := hashSize * hashCount
 
-	headerByte := buf[0]
-	payloadStart := 2 + pathBytes
-	if isTransportRoute(int(headerByte & 0x03)) {
-		payloadStart += 4
-	}
+	payloadStart := offset + pathBytes
 	if payloadStart > len(buf) {
 		if len(rawHex) >= 16 {
 			return rawHex[:16]