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Overview

This is a binding to the Signal client code in rust/, implemented on top of the C FFI produced by rust/bridge/ffi/. It's set up as a CocoaPod for integration into the Signal iOS client and as a Swift Package for local development.

Use as CocoaPod

  1. Make sure you are using use_frameworks! in your Podfile. LibSignalClient is a Swift pod and as such cannot be compiled as a plain library.

  2. Add 'LibSignalClient' as a dependency in your Podfile, as well as the prebuild checksum for the latest release. You can find the checksum in the GitHub Releases for the project.

     pod 'LibSignalClient', git: 'https://github.com/signalapp/libsignal.git'
 ENV['LIBSIGNAL_FFI_PREBUILD_CHECKSUM'] = '...'

  3. Use pod install or pod update to build the Rust library for all targets. You may be prompted to install Rust dependencies (cbindgen, rust-src).

  4. Build as usual. The Rust library will automatically be linked into the built LibSignalClient.framework.

Development as a CocoaPod

Instead of a git-based dependency, use a path-based dependency to treat LibSignalClient as a development pod. Since prepare_commands are not run for path-based dependencies, you will need to build the Rust library yourself. (Xcode should prompt you to do this if you forget.)

CARGO_BUILD_TARGET=x86_64-apple-ios swift/build_ffi.sh --release
CARGO_BUILD_TARGET=aarch64-apple-ios-sim swift/build_ffi.sh --release
CARGO_BUILD_TARGET=aarch64-apple-ios swift/build_ffi.sh --release

The CocoaPod is configured to use the release build of the Rust library. Use pod lib lint to validate locally. You can pass --debug-level-logs to build_ffi.sh to turn on debug- and verbose-level logs.

When exposing new APIs to Swift, you will need to add the --generate-ffi flag to your build_ffi.sh invocation.

Development as a Swift Package

  1. Build the Rust library using swift/build_ffi.sh. The Swift Package.swift is configured to use the debug build of the Rust library.

  2. Use swift build and swift test as usual from within the swift/ directory.

When exposing new APIs to Swift, you will need to add the --generate-ffi flag to your build_ffi.sh invocation. This requires installing the cbindgen Rust tool:

$ cargo +stable install cbindgen

Use as a Swift Package

...is not supported. In theory we could make this work through the use of a custom pkg-config file and requiring clients to set PKG_CONFIG_PATH (or install the Rust build products), but since Signal itself does not use this configuration it's considered extra maintenance burden. Development as a package is supported as a lightweight convenience (as well as a cross-platform one), but the CocoaPods build is considered the canonical one.

Benchmarks

The package in Benchmarks is set up for relative benchmarking on a build machine (rather than on iOS devices). This is mostly interesting to test that the bridging layer is not imposing undue overhead. Best results will come from testing on an Apple Silicon Mac, since that's closest in system libraries to an iOS device.

  1. Build the Rust library using swift/build_ffi.sh --release.

  2. swift run -c release from within the swift/Benchmarks/ directory.

SwiftPM hides the executable in .build/release/, but you can find it there to run profiling tools on it.

Catalyst Support

Mac Catalyst is not supported by this repository, but we've done experiments with it in the past. Rust targets for Catalyst are still in tier 3 support, so we use the experimental -Zbuild-std flag to build the standard library.

In order to compile for Catalyst you will need to:

  • Install the standard library component with rustup component add rust-src
  • Add the --build-std flag to your build_ffi.sh invocation

There may be other issues. For example, at one point the cmake crate had trouble compiling for Catalyst; you can try downgrading to version 0.1.48 if that's affecting you.