README: Polkadot Type Library for Java
Introduction
This project is in a pre-inception phase (Alpha) stay tuned - More to Come
The goal of this project is to port over the Polkadot Type Library to Java, which is pre-requisite if you plan to connect from a Java Application to Polkadot.
The library was built in a reverse engineer manner by assessing three exisiting implementations:
- Parity Polkadot-JS API Library: https://github.com/polkadot-js/api/tree/master/packages/types#readme
- Polkascan Pyhton Library: https://github.com/polkascan/py-scale-codec
- Polkadot Rust Implementation
SCALE Data Format
Substrate encodes data in the "Simple Concatenated Aggregate Little-Endian" (SCALE) data format, as implemented by the parity-codec crate and several JavaScript modules.
It is an extremely light-weight encoding format designed for high-performance, copy-free encoding and decoding of data in resource-constrained execution contexts like the Substrate runtime.
It is not self-describing in any way and assumes the decoding context has all type knowledge about the encoded data.
Technical Notes
Byte Handling
A byte according to the Java language spec represents a value between -128 up to 127.
The Java language doesn't provide something like a unsigned keyword.
If a byte is cast to a int. Java will interpret the first bit as the sign and use sign
extension.
In order to calculate with the byte, we have to convert it into
an unsigned representation (int), by using the method: Byte.toUnsignedInt(byte)
https://stackoverflow.com/questions/4266756/can-we-make-unsigned-byte-in-java/4266841