fix: align packet decoder with MeshCore firmware spec

Compared decoder.js against the MeshCore firmware source (Dispatcher.cpp,
Packet.h, Mesh.cpp, AdvertDataHelpers.h) and fixed all mismatches:

1. Field order: transport codes now parsed BEFORE path_length byte,
   matching the spec: [header][transport_codes?][path_length][path][payload]

2. ACK payload: was incorrectly decoded as dest(1)+src(1)+ackHash(4).
   Firmware shows ACK is just checksum(4) — no dest/src hashes.

3. TRACE payload: was incorrectly decoded as flags(1)+tag(4)+dest(6)+src(1).
   Firmware shows tag(4)+authCode(4)+flags(1)+pathData.

4. ADVERT appdata: added missing feature1 (0x20 flag) and feature2
   (0x40 flag) parsing — 2-byte fields between location and name.

5. Transport code field naming: renamed nextHop/lastHop to code1/code2
   to match spec terminology (transport_code_1/transport_code_2).

6. Fixed incorrect field size labels in packets.js hex breakdown:
   dest/src are 1 byte, MAC is 2 bytes (not 6B/6B/4B).

7. Fixed ANON_REQ/PATH comment typos (dest was listed as 6 bytes,
   MAC as 4 bytes — both wrong, code was already correct).

All 329 tests pass (66 decoder + 263 spec/golden).

decoder.js

@@ -2,8 +2,8 @@
  * MeshCore Packet Decoder
  * Custom implementation — does NOT use meshcore-decoder library (known path_length bug).
  *
- * Packet layout:
- *   [header(1)] [pathLength(1)] [transportCodes?] [path hops] [payload...]
+ * Packet layout (per firmware docs/packet_format.md):
+ *   [header(1)] [transportCodes?(4)] [pathLength(1)] [path hops] [payload...]
  *
  * Header byte (LSB first):
  *   bits 1-0: routeType (0=TRANSPORT_FLOOD, 1=FLOOD, 2=DIRECT, 3=TRANSPORT_DIRECT)
@@ -42,7 +42,7 @@ const PAYLOAD_TYPES = {
   0x0F: 'RAW_CUSTOM',
 };
 
-// Route types that carry transport codes (nextHop + lastHop, 2 bytes each)
+// Route types that carry transport codes (2x uint16_t, 4 bytes total)
 const TRANSPORT_ROUTES = new Set([0, 3]); // TRANSPORT_FLOOD, TRANSPORT_DIRECT
 
 // --- Header parsing ---
@@ -94,13 +94,11 @@ function decodeEncryptedPayload(buf) {
   };
 }
 
-/** ACK: dest(1) + src(1) + ack_hash(4) (per Mesh.cpp) */
+/** ACK: checksum(4) — CRC of message timestamp + text + sender pubkey (per Mesh.cpp createAck) */
 function decodeAck(buf) {
-  if (buf.length < 6) return { error: 'too short', raw: buf.toString('hex') };
+  if (buf.length < 4) return { error: 'too short', raw: buf.toString('hex') };
   return {
-    destHash: buf.subarray(0, 1).toString('hex'),
-    srcHash: buf.subarray(1, 2).toString('hex'),
-    extraHash: buf.subarray(2, 6).toString('hex'),
+    ackChecksum: buf.subarray(0, 4).toString('hex'),
   };
 }
 
@@ -125,6 +123,8 @@ function decodeAdvert(buf) {
       room: advType === 3,
       sensor: advType === 4,
       hasLocation: !!(flags & 0x10),
+      hasFeat1: !!(flags & 0x20),
+      hasFeat2: !!(flags & 0x40),
       hasName: !!(flags & 0x80),
     };
 
@@ -134,6 +134,14 @@ function decodeAdvert(buf) {
       result.lon = appdata.readInt32LE(off + 4) / 1e6;
       off += 8;
     }
+    if (result.flags.hasFeat1 && appdata.length >= off + 2) {
+      result.feat1 = appdata.readUInt16LE(off);
+      off += 2;
+    }
+    if (result.flags.hasFeat2 && appdata.length >= off + 2) {
+      result.feat2 = appdata.readUInt16LE(off);
+      off += 2;
+    }
     if (result.flags.hasName) {
       // Find null terminator to separate name from trailing telemetry bytes
       let nameEnd = appdata.length;
@@ -231,7 +239,7 @@ function decodeGrpTxt(buf, channelKeys) {
   return { type: 'GRP_TXT', channelHash, channelHashHex, decryptionStatus: 'no_key', mac, encryptedData };
 }
 
-/** ANON_REQ: dest(6) + ephemeral_pubkey(32) + MAC(4) + encrypted */
+/** ANON_REQ: dest(1) + ephemeral_pubkey(32) + MAC(2) + encrypted */
 function decodeAnonReq(buf) {
   if (buf.length < 35) return { error: 'too short', raw: buf.toString('hex') };
   return {
@@ -242,7 +250,7 @@ function decodeAnonReq(buf) {
   };
 }
 
-/** PATH: dest(6) + src(6) + MAC(4) + path_data */
+/** PATH: dest(1) + src(1) + MAC(2) + path_data */
 function decodePath_payload(buf) {
   if (buf.length < 4) return { error: 'too short', raw: buf.toString('hex') };
   return {
@@ -253,14 +261,14 @@ function decodePath_payload(buf) {
   };
 }
 
-/** TRACE: flags(1) + tag(4) + dest(6) + src(1) */
+/** TRACE: tag(4) + authCode(4) + flags(1) + pathData (per Mesh.cpp onRecvPacket TRACE) */
 function decodeTrace(buf) {
-  if (buf.length < 12) return { error: 'too short', raw: buf.toString('hex') };
+  if (buf.length < 9) return { error: 'too short', raw: buf.toString('hex') };
   return {
-    flags: buf[0],
-    tag: buf.readUInt32LE(1),
-    destHash: buf.subarray(5, 11).toString('hex'),
-    srcHash: buf.subarray(11, 12).toString('hex'),
+    tag: buf.readUInt32LE(0),
+    authCode: buf.subarray(4, 8).toString('hex'),
+    flags: buf[8],
+    pathData: buf.subarray(9).toString('hex'),
   };
 }
 
@@ -289,20 +297,22 @@ function decodePacket(hexString, channelKeys) {
   if (buf.length < 2) throw new Error('Packet too short (need at least header + pathLength)');
 
   const header = decodeHeader(buf[0]);
-  const pathByte = buf[1];
-  let offset = 2;
+  let offset = 1;
 
-  // Transport codes for TRANSPORT_FLOOD / TRANSPORT_DIRECT
+  // Transport codes for TRANSPORT_FLOOD / TRANSPORT_DIRECT — BEFORE path_length per spec
   let transportCodes = null;
   if (TRANSPORT_ROUTES.has(header.routeType)) {
     if (buf.length < offset + 4) throw new Error('Packet too short for transport codes');
     transportCodes = {
-      nextHop: buf.subarray(offset, offset + 2).toString('hex').toUpperCase(),
-      lastHop: buf.subarray(offset + 2, offset + 4).toString('hex').toUpperCase(),
+      code1: buf.subarray(offset, offset + 2).toString('hex').toUpperCase(),
+      code2: buf.subarray(offset + 2, offset + 4).toString('hex').toUpperCase(),
     };
     offset += 4;
   }
 
+  // Path length byte — AFTER transport codes per spec
+  const pathByte = buf[offset++];
+
   // Path
   const path = decodePath(pathByte, buf, offset);
   offset += path.bytesConsumed;
@@ -386,7 +396,7 @@ module.exports = { decodePacket, validateAdvert, hasNonPrintableChars, ROUTE_TYP
 
 // --- Tests ---
 if (require.main === module) {
-  console.log('=== Test 1: ADVERT, FLOOD, 5 hops (2-byte hashes), "Test Repeater" ===');
+  console.log('=== Test 1: ADVERT, FLOOD, 5 hops (2-byte hashes), "Kpa Roof Solar" ===');
   const pkt1 = decodePacket(
     '11451000D818206D3AAC152C8A91F89957E6D30CA51F36E28790228971C473B755F244F718754CF5EE4A2FD58D944466E42CDED140C66D0CC590183E32BAF40F112BE8F3F2BDF6012B4B2793C52F1D36F69EE054D9A05593286F78453E56C0EC4A3EB95DDA2A7543FCCC00B939CACC009278603902FC12BCF84B706120526F6F6620536F6C6172'
   );
@@ -402,7 +412,7 @@ if (require.main === module) {
   assert(pkt1.path.hops[0] === '1000', 'first hop should be 1000');
   assert(pkt1.path.hops[1] === 'D818', 'second hop should be D818');
   assert(pkt1.transportCodes === null, 'FLOOD has no transport codes');
-  assert(pkt1.payload.name === 'Test Repeater', 'name should be "Test Repeater"');
+  assert(pkt1.payload.name === 'Kpa Roof Solar', 'name should be "Kpa Roof Solar"');
   console.log('✅ Test 1 passed\n');
 
   console.log('=== Test 2: ADVERT, FLOOD, 0 hops (zero-path) ===');

public/packets.js

@@ -1512,14 +1512,12 @@
       rows += fieldRow(off + 1, 'Sender', decoded.sender || '—', '');
       if (decoded.sender_timestamp) rows += fieldRow(off + 2, 'Sender Time', decoded.sender_timestamp, '');
     } else if (decoded.type === 'ACK') {
-      rows += fieldRow(off, 'Dest Hash (6B)', decoded.destHash || '', '');
-      rows += fieldRow(off + 6, 'Src Hash (6B)', decoded.srcHash || '', '');
-      rows += fieldRow(off + 12, 'Extra (6B)', decoded.extraHash || '', '');
+      rows += fieldRow(off, 'Checksum (4B)', decoded.ackChecksum || '', '');
     } else if (decoded.destHash !== undefined) {
-      rows += fieldRow(off, 'Dest Hash (6B)', decoded.destHash || '', '');
-      rows += fieldRow(off + 6, 'Src Hash (6B)', decoded.srcHash || '', '');
-      rows += fieldRow(off + 12, 'MAC (4B)', decoded.mac || '', '');
-      rows += fieldRow(off + 16, 'Encrypted Data', truncate(decoded.encryptedData || '', 30), '');
+      rows += fieldRow(off, 'Dest Hash (1B)', decoded.destHash || '', '');
+      rows += fieldRow(off + 1, 'Src Hash (1B)', decoded.srcHash || '', '');
+      rows += fieldRow(off + 2, 'MAC (2B)', decoded.mac || '', '');
+      rows += fieldRow(off + 4, 'Encrypted Data', truncate(decoded.encryptedData || '', 30), '');
     } else {
       rows += fieldRow(off, 'Raw', truncate(buf.slice(off * 2), 40), '');
     }

test-decoder-spec.js

@@ -122,13 +122,14 @@ console.log('── Spec Tests: Transport Codes ──');
 
 {
   // Route type 0 (TRANSPORT_FLOOD) and 3 (TRANSPORT_DIRECT) should have 4-byte transport codes
-  // Route type 0: header byte = 0bPPPPPP00, e.g. 0x14 = payloadType 5 (GRP_TXT), routeType 0
-  const hex = '1400' + 'AABB' + 'CCDD' + '1A' + '00'.repeat(10); // transport codes + GRP_TXT payload
+  // Route type 0: header=0x14 = payloadType 5 (GRP_TXT), routeType 0 (TRANSPORT_FLOOD)
+  // Format: header(1) + transportCodes(4) + pathByte(1) + payload
+  const hex = '14' + 'AABB' + 'CCDD' + '00' + '1A' + '00'.repeat(10); // transport codes + pathByte + GRP_TXT payload
   const p = decodePacket(hex);
   assertEq(p.header.routeType, 0, 'transport: routeType=0 (TRANSPORT_FLOOD)');
   assert(p.transportCodes !== null, 'transport: transportCodes present for TRANSPORT_FLOOD');
-  assertEq(p.transportCodes.nextHop, 'AABB', 'transport: nextHop');
-  assertEq(p.transportCodes.lastHop, 'CCDD', 'transport: lastHop');
+  assertEq(p.transportCodes.code1, 'AABB', 'transport: code1');
+  assertEq(p.transportCodes.code2, 'CCDD', 'transport: code2');
 }
 
 {
@@ -257,13 +258,13 @@ console.log('── Spec Tests: Advert Payload ──');
 
 console.log('── Spec Tests: Encrypted Payload Format ──');
 
-// NOTE: Spec says v1 encrypted payloads have dest(1) + src(1) + MAC(2) + ciphertext
-// But decoder reads dest(6) + src(6) + MAC(4) + ciphertext
-// This is a known discrepancy — the decoder matches production behavior, not the spec.
-// The spec may describe the firmware's internal addressing while the OTA format differs,
-// or the decoder may be parsing the fields differently. Production data validates the decoder.
+// Spec says v1 encrypted payloads: dest(1)+src(1)+MAC(2)+cipher — decoder matches this.
 {
-  note('Spec says v1 encrypted payloads: dest(1)+src(1)+MAC(2)+cipher, but decoder reads dest(6)+src(6)+MAC(4)+cipher — decoder matches prod data');
+  const hex = '0100' + 'AA' + 'BB' + 'CCDD' + '00'.repeat(10);
+  const p = decodePacket(hex);
+  assertEq(p.payload.destHash, 'aa', 'encrypted payload: dest is 1 byte');
+  assertEq(p.payload.srcHash, 'bb', 'encrypted payload: src is 1 byte');
+  assertEq(p.payload.mac, 'ccdd', 'encrypted payload: MAC is 2 bytes');
 }
 
 console.log('── Spec Tests: validateAdvert ──');

test-decoder.js

@@ -28,22 +28,22 @@ test('FLOOD + ADVERT = 0x11', () => {
 });
 
 test('TRANSPORT_FLOOD = routeType 0', () => {
-  // 0x00 = TRANSPORT_FLOOD + REQ(0), needs transport codes + 16 byte payload
-  const hex = '0000' + 'AABB' + 'CCDD' + '00'.repeat(16);
+  // header=0x00 (TRANSPORT_FLOOD + REQ), transportCodes=AABB+CCDD, pathByte=0x00, payload
+  const hex = '00' + 'AABB' + 'CCDD' + '00' + '00'.repeat(16);
   const p = decodePacket(hex);
   assert.strictEqual(p.header.routeType, 0);
   assert.strictEqual(p.header.routeTypeName, 'TRANSPORT_FLOOD');
   assert.notStrictEqual(p.transportCodes, null);
-  assert.strictEqual(p.transportCodes.nextHop, 'AABB');
-  assert.strictEqual(p.transportCodes.lastHop, 'CCDD');
+  assert.strictEqual(p.transportCodes.code1, 'AABB');
+  assert.strictEqual(p.transportCodes.code2, 'CCDD');
 });
 
 test('TRANSPORT_DIRECT = routeType 3', () => {
-  const hex = '0300' + '1122' + '3344' + '00'.repeat(16);
+  const hex = '03' + '1122' + '3344' + '00' + '00'.repeat(16);
   const p = decodePacket(hex);
   assert.strictEqual(p.header.routeType, 3);
   assert.strictEqual(p.header.routeTypeName, 'TRANSPORT_DIRECT');
-  assert.strictEqual(p.transportCodes.nextHop, '1122');
+  assert.strictEqual(p.transportCodes.code1, '1122');
 });
 
 test('DIRECT = routeType 2, no transport codes', () => {
@@ -358,9 +358,7 @@ test('ACK decode', () => {
   const hex = '0D00' + '00'.repeat(18);
   const p = decodePacket(hex);
   assert.strictEqual(p.payload.type, 'ACK');
-  assert(p.payload.destHash);
-  assert(p.payload.srcHash);
-  assert(p.payload.extraHash);
+  assert(p.payload.ackChecksum);
 });
 
 test('ACK too short', () => {
@@ -424,9 +422,9 @@ test('TRACE decode', () => {
   const hex = '2500' + '00'.repeat(12);
   const p = decodePacket(hex);
   assert.strictEqual(p.payload.type, 'TRACE');
-  assert.strictEqual(p.payload.flags, 0);
   assert(p.payload.tag !== undefined);
-  assert(p.payload.destHash);
+  assert(p.payload.authCode !== undefined);
+  assert.strictEqual(p.payload.flags, 0);
 });
 
 test('TRACE too short', () => {
@@ -460,16 +458,18 @@ test('Transport route too short throws', () => {
   assert.throws(() => decodePacket('0000'), /too short for transport/);
 });
 
-test('Corrupt packet #183 — path overflow capped to buffer', () => {
+test('Corrupt packet #183 — TRANSPORT_DIRECT with correct field order', () => {
   const hex = 'BBAD6797EC8751D500BF95A1A776EF580E665BCBF6A0BBE03B5E730707C53489B8C728FD3FB902397197E1263CEC21E52465362243685DBBAD6797EC8751C90A75D9FD8213155D';
   const p = decodePacket(hex);
   assert.strictEqual(p.header.routeType, 3, 'routeType should be TRANSPORT_DIRECT');
   assert.strictEqual(p.header.payloadTypeName, 'UNKNOWN');
-  // pathByte 0xAD claims 45 hops × 3 bytes = 135, but only 65 bytes available
+  // transport codes are bytes 1-4, pathByte=0x87 at byte 5
+  assert.strictEqual(p.transportCodes.code1, 'AD67');
+  assert.strictEqual(p.transportCodes.code2, '97EC');
+  // pathByte 0x87: hashSize=3, hashCount=7
   assert.strictEqual(p.path.hashSize, 3);
-  assert.strictEqual(p.path.hashCount, 21, 'hashCount capped to fit buffer');
-  assert.strictEqual(p.path.hops.length, 21);
-  assert.strictEqual(p.path.truncated, true);
+  assert.strictEqual(p.path.hashCount, 7);
+  assert.strictEqual(p.path.hops.length, 7);
   // No empty strings in hops
   assert(p.path.hops.every(h => h.length > 0), 'no empty hops');
 });