meshcore: support for multibyte path hashes

protocol/meshcore/packet.go

@@ -38,7 +38,14 @@ type Packet struct {
 	// TransportCodes are set by transport route types.
 	TransportCodes []uint16 `json:"transport_codes,omitempty"`
 
-	// Path are repeater hashes.
+	// PathHashSize is the number of bytes per node in the path hash.
+	PathHashSize int `json:"path_hash_size"`
+
+	// PathHashCount is the number of nodes in the path hash.
+	PathHashCount int `json:"path_hash_count"`
+
+	// Path are repeater hashes. The first hash is the source node, the last hash is the destination node, and the middle hashes are repeaters.
+	// The path is empty for direct packets.
 	Path []byte `json:"path"`
 
 	// Payload is the raw (encoded) payload.
@@ -158,14 +165,21 @@ func (packet *Packet) UnmarshalBytes(data []byte) error {
 		packet.TransportCodes = nil
 	}
 
-	pathLength := int(data[offset])
+	var (
+		pathLength     = int(data[offset])
+		pathHashSize   = pathLength>>6 + 1
+		pathHashCount  = pathLength & 63
+		pathByteLength = pathHashSize * pathHashCount
+	)
 	offset += 1
-	if pathLength > maxPathSize {
-		return fmt.Errorf("meshcore: path length %d exceeds maximum of %d", pathLength, maxPathSize)
-	} else if pathLength > len(data[offset:]) {
+	if pathByteLength > maxPathSize {
+		return fmt.Errorf("meshcore: path length %d exceeds maximum of %d", pathByteLength, maxPathSize)
+	} else if pathByteLength > len(data[offset:]) {
 		return io.ErrUnexpectedEOF
 	}
-	packet.Path = make([]byte, pathLength)
+	packet.Path = make([]byte, pathByteLength)
+	packet.PathHashSize = pathHashSize
+	packet.PathHashCount = pathHashCount
 	offset += copy(packet.Path, data[offset:])
 
 	payloadLength := len(data[offset:])