toBytes method

Uint8List toBytes()

Encodes this message in the NFC Forum wire format.

Chunking is never produced: every record is written whole, which is what real readers expect and what both platforms do.

Implementation

Uint8List toBytes() {
  final out = BytesBuilder(copy: false);

  for (var i = 0; i < records.length; i++) {
    final record = records[i];
    final isShort = record.payload.length < 256;
    // The specification always writes the ID length byte for an empty record.
    final hasId = record.identifier.isNotEmpty || record.typeNameFormat == NdefTypeNameFormat.empty;

    var header = record.typeNameFormat.index & _maskTypeNameFormat;
    if (i == 0) header |= _flagMessageBegin;
    if (i == records.length - 1) header |= _flagMessageEnd;
    if (isShort) header |= _flagShortRecord;
    if (hasId) header |= _flagIdLengthPresent;

    // TYPE_LENGTH and ID_LENGTH are one byte each on the wire. The validating constructor
    // already refuses anything longer, but NdefRecord.fromParts -- the decode path, which
    // has to represent whatever a tag holds -- does not, so a hand-built record can still
    // reach here. `addByte` would take the low eight bits and produce a message that encodes
    // without complaint and that nothing can read back, which is the failure the constructor
    // rejects these lengths to prevent.
    if (record.type.length > 255) {
      throw ArgumentError.value(
        record.type.length,
        'records[$i].type',
        'does not fit the one-byte TYPE_LENGTH field',
      );
    }
    if (record.identifier.length > 255) {
      throw ArgumentError.value(
        record.identifier.length,
        'records[$i].identifier',
        'does not fit the one-byte ID_LENGTH field',
      );
    }

    out.addByte(header);
    out.addByte(record.type.length);

    if (isShort) {
      out.addByte(record.payload.length);
    } else {
      final length = record.payload.length;
      out.add([(length >> 24) & 0xFF, (length >> 16) & 0xFF, (length >> 8) & 0xFF, length & 0xFF]);
    }

    if (hasId) out.addByte(record.identifier.length);

    out.add(record.type);
    out.add(record.identifier);
    out.add(record.payload);
  }

  return out.takeBytes();
}