matrix-rust-sdk

# Uniffi based bindings for the Rust SDK crypto crate

This crate contains Uniffi based bindings for the `matrix-sdk-crypto` crate. The

README mainly describes how to build and integrate the bindings into a Kotlin

based Android project, but the Android specific bits can be skipped if you are

targeting an x86 Linux project.

To build and distribute bindings for iOS projects, see a

[dedicated page](../apple/README.md)

## Prerequisites

### Rust

To build the bindings [Rust] will be needed it can be either installed using an

OS specific package manager or directly with the provided

[installer](https://rustup.rs/).

### Android NDK

The Android NDK will be required as well, it can be installed either through

Android Studio or directly using an

[installer](https://developer.android.com/ndk/downloads).

### Configuring Rust for cross compilation

First we'll need to install the Rust target for our desired Android

architecture, for example:

```text

# rustup target add aarch64-linux-android

```

This will add support to cross-compile for the aarch64-linux-android target,

Rust supports many different [targets], you'll have to make sure to pick the

right one for your device or emulator.

After this is done, we'll have to configure [Cargo] to use the correct linker

for our target, by providing the Cargo setting of

[target.<triple>.linker](https://doc.rust-lang.org/cargo/reference/config.html#targettriplelinker)

with a value of the path to an appropriate linker in your NDK installation.

This may be set through an environment variable:

```text

$ export CARGO_TARGET_AARCH64_LINUX_ANDROID_LINKER="<path-to-ndk-installation>/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android30-clang"

```

Alternatively, it may be set in the `.cargo/config.toml` file in the current

directory, any parent directory, or your home directory:

```text

[target.aarch64-linux-android]

linker = "<path-to-ndk-installation>/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android30-clang"

```

## Building

To enable cross compilation for `olm-sys` which builds our `libolm` C library

we'll need to set the `ANDROID_NDK` environment variable to the location of our

Android NDK installation.

```text

$ export ANDROID_NDK=$HOME/Android/Sdk/ndk/<some-installed-version>

```

Also, include the NDK tools directory in your `PATH`:

```text

$ export PATH="$ANDROID_NDK/toolchains/llvm/prebuilt/linux-x86_64/bin:$PATH"

```

### Building for a target

The bindings can built for the `aarch64` target with:

```text

$ cargo build --target aarch64-linux-android

```

After that, a dynamic library can be found in the

`target/aarch64-linux-android/debug` directory, under the repository root

directory. The library will be called `libmatrix_sdk_crypto_ffi.so` and needs to

be renamed and copied into the `jniLibs` directory of your Android project, for

Element Android:

```text

$ cp ../../target/aarch64-linux-android/debug/libmatrix_sdk_crypto_ffi.so \

     /home/example/matrix-sdk-android/src/main/jniLibs/aarch64/libuniffi_olm.so

```

## License

[Apache-2.0](https://www.apache.org/licenses/LICENSE-2.0)

[Rust]: https://www.rust-lang.org/

[installer]: https://rustup.rs/

[targets]: https://doc.rust-lang.org/nightly/rustc/platform-support.html

[Cargo]: https://doc.rust-lang.org/cargo/