mirror of
https://github.com/element-hq/element-android
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97 lines
3 KiB
Markdown
97 lines
3 KiB
Markdown
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# Kotlin bindings for the Rust SDK crypto layer.
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## Prerequisites
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### Rust
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To build the bindings [Rust] will be needed it can be either installed using an
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OS specific package manager or directly with the provided [installer](https://rustup.rs/).
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### Android NDK
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The Android NDK will be required as well, it can be installed either through
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Android Studio or directly using an [installer](https://developer.android.com/ndk/downloads).
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### Uniffi
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The bindings are using [uniffi] to generate the C translation layer between Rust
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and Kotlin. Uniffi is a Rust project and can be installed with our freshly
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installed Rust setup using:
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```
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$ cargo install uniffi_bindgen
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```
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### Configuring Rust for cross compilation
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First we'll need to install the Rust target for our desired Android architecture,
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for example:
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```
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# rustup target add aarch64-linux-android
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```
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This will add support to cross-compile for the aarch64-linux-android target,
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Rust supports many different [targets], you'll have to make sure to pick the
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right one for your device or emulator.
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After this is done, we'll have to configure [Cargo] to use the correct linker
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for our target. Cargo is configured using a TOML file that will be found in
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`%USERPROFILE%\.cargo\config.toml` on Windows or `$HOME/.cargo/config` on Unix
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platforms. More details and configuration options for Cargo can be found in the
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official docs over [here](https://doc.rust-lang.org/cargo/reference/config.html).
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```
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[target.aarch64-linux-android]
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ar = "NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin/ar"
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linker = "NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android30-clang"
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```
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## Building
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A `Makefile` is provided that builds and installs the dynamic library into the
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appropriate target specific `jniLibs` directory. But before we can get started
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we'll need to tweak our Rust setup to allow cross compilation.
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To enable cross compilation fro `olm-sys` which builds our libolm C library
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we'll need to set the `ANDROID_NDK` environment variable to the location of our
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Android NDK installation.
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```
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$ export ANDROID_NDK=$HOME/Android/Sdk/ndk/22.0.7026061/
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```
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### Makefile build
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After the prerequisites have been installed and the environment variable has
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been set a build for the `aarch64` target can be build using:
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```
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make aarch64
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```
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### Manual build
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If the `Makefile` doesn't work on your system, the bindings can built for the `aarch64`
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target with:
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```
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$ cargo build --target aarch64-linux-android
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```
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After that, a dynamic library can be found in the `target/aarch64-linux-android/debug` directory.
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The library will be called `libmatrix_crypto.so` and needs to be renamed and
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copied into the `jniLibs` directory:
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```
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$ cp target/aarch64-linux-android/debug/libmatrix_crypto.so \
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../matrix-sdk-android/src/main/jniLibs/aarch64/libuniffi_olm.so
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```
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[Rust]: https://www.rust-lang.org/
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[installer]: https://rustup.rs/
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[targets]: https://doc.rust-lang.org/nightly/rustc/platform-support.html
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[Cargo]: https://doc.rust-lang.org/cargo/
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[uniffi]: https://github.com/mozilla/uniffi-rs/
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