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HACKING.md

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Hacking

How does this work?

This repository contains a rust project under ./rust which builds a shared library that interfaces with the JNI. This library is then built for all the major architectures and bundled into a jar by the ./lib gradle module. The java code in ./lib then figures out which shared library to load from based on the platform it is running on. The developer should never have to think about native libraries.

The only place where this gets a bit hairy is android. The android build tools strip out the resources of dependent jars, which means we can't distribute the shared library as a resource for android. Instead the ./android gradle module creates an AAR containing the jniLibs which android expects and then we use some variant aware matching magic in ./lib to add a dependency on the android library when building for android. Again, this should mean developers never have to think about native libraries.

Testing without a full build

The complete build requires building release binaries for every architecture. This can be quite time consuming and also requries a lot of toolchain setup. If you just want to make some changes to the java/rust code and test it you can run ./gradlew lib:test -Penv=dev. The env=dev part will build a debug build of the Rust project for the current architecture and make it available on the library path of the java tests. This is much, much faster.

Building

In general you will need a toolchain set up for all the following platforms:

  • x86_64-pc-windows-gnu
  • i686-pc-windows-gnu
  • x86_64-unknown-linux-gnu
  • aarch64-unknown-linux-gnu
  • x86_64-apple-darwin
  • aarch64-apple-darwin
  • armv7-linux-androideabi
  • aarch64-linux-android
  • i686-linux-android
  • x86_64-linux-android

To build the android libs you will also need the android sdk and ndk installed with an entry in local.properties pointing at them.

Concretely what that means is that for each of the above targets you run

`rustup add <target>`

Then, you'll need to create a local.properties file in the root of this repository with the following contents:

sdk.dir=<android SDK dir>
ndkPath=<path to NDK>
aarchLinkerPath=<path>
win64LinkerPath=<path>
win32LinkerPath=<path>
x86_64LinuxLinkerPath=<path>
aarchDarwinLinkerPath=<path>
aarchDarwinLdPath=<path>
x86_64DarwinLinkerPath=<path>
x86_64DarwinLdPath=<path>

How to find these linkers for your system is your problem I'm afraid. On x64-64 arch linux you need to install the following packages:

  • aarch64-linux-gnu-gcc
  • mingw-w64-gcc
  • i686-pc-windows-gnu

Then setup osxcross. Then the contents of local.properties might look like this:

aarchLinkerPath=/usr/bin/aarch64-linux-gnu-gcc
win64LinkerPath=/usr/bin/x86_64-w64-mingw32-gcc
win32LinkerPath=/usr/bin/i686-w64-mingw32-gcc
x86_64LinuxLinkerPath=/usr/bin/gcc
aarchDarwinLinkerPath=<osxcross path>/target/bin/arm64-apple-darwin20.4-clang
aarchDarwinLdPath=<osxcross path>/target/bin/x86_64-apple-darwin20.4-ld
x86_64DarwinLinkerPath=<osxcross path>/target/bin/x86_64-apple-darwin20.4-clang
x86_64DarwinLdPath=<osxcross path>/target/bin/x86_64-apple-darwin20.4-ld