anchor.diff:        throw const FormatException('Invalid method call');
     }
   
  -
     @override
     ByteData encodeSuccessEnvelope(dynamic result) {
       final WriteBuffer buffer = new WriteBuffer();
  
positive.code:         result = buffer.getInt64();
          break;
        case _kLargeInt:
          final int length = _readSize(buffer);
          final String hex = UTF8.decoder.convert(buffer.getUint8List(length));
          result = int.parse(hex, radix: 16);
  
negative.code:   //   in the type byte (using _kNull, _kTrue, _kFalse)
    // * Integers representable in 32 bits are encoded using 4 bytes two's
    //   complement representation.
    // * Larger integers are encoded using 8 bytes two's complement
    //   representation.
    // * doubles are encoded using the IEEE 754 64-bit double-precision binary
    //   format.
    // * Strings are encoded using their UTF-8 representation. First the length
  