writeVarInt function

Uint8List writeVarInt(int value)

Implementation

Uint8List writeVarInt(int value) {
  if (value < 0x40) {
    // 1 byte (00 prefix)
    return Uint8List.fromList([value]);
  }
  if (value < 0x4000) {
    // 2 bytes (01 prefix)
    return Uint8List.fromList([0x40 | (value >> 8) & 0x3F, value & 0xFF]);
  }
  if (value < 0x40000000) {
    // 4 bytes (10 prefix)
    // Dart integers are 64-bit, so this is safe.
    return Uint8List.fromList([
      0x80 | (value >> 24) & 0x3F,
      (value >> 16) & 0xFF,
      (value >> 8) & 0xFF,
      value & 0xFF,
    ]);
  }

  // For 8-byte (11 prefix), you must handle the full 62 bits:
  if (value < 0x4000000000000000) {
    // Use ByteData to ensure correct 64-bit little-endian writing.
    final buffer = ByteData(8);
    buffer.setUint64(0, value, Endian.big); // Write 64-bit value

    // Dart integers up to 2^63 - 1 are safe.
    return Uint8List.fromList([
      0xC0 | (buffer.getUint8(0) & 0x3F),
      buffer.getUint8(1),
      buffer.getUint8(2),
      buffer.getUint8(3),
      buffer.getUint8(4),
      buffer.getUint8(5),
      buffer.getUint8(6),
      buffer.getUint8(7),
    ]);
  }
  throw Exception("Value too large for QUIC VarInt");
}