ldk-swift

Automatic Swift bindings generation for rust-lightning.

Installation

In order to use the automatically generated bindings, simply drag *.xcframework file into an Xcode project.

The *.xcframework files are either available on the Releases page, or can be compiled from scratch.

Compilation

Prerequisites

A Mac with Xcode 13.2.1 or lower (this is because there is a bug with cc that prevents it from compiling for Mac Catalyst targets with clang 13)
Python3
Rust
gnu-sed (optional; but will cut your compile times significantly!)

For Rust specifically, there are a couple additional requirements that can be installed once the Rust toolchain is set up:

rustup toolchain install nightly
rustup target add aarch64-apple-darwin aarch64-apple-ios x86_64-apple-ios
cargo install cbindgen

Cloning Dependencies

In order to generate these bindings from scratch, you will need to clone two dependency repositories:

rust-lightning, (a specific branch built for bindings compatibility)

git clone --branch 2022-06-108-java-bindings https://github.com/TheBlueMatt/rust-lightning /path/to/rust-lightning

ldk-c-bindings

git clone --branch v0.0.108.2 https://github.com/lightningdevkit/ldk-c-bindings /path/to/ldk-c-bindings

Take note of where you clone these directories, it's best you save the absolute path somewhere handy for the rest of the remaining steps.

Generating Rust-to-C-bindings

Now, navigate to the ldk-c-bindings directory and run the genbindings.sh script:

pushd path/to/ldk-c-bindings
./genbindings.sh /path/to/rust-lightning true
popd

Generating C-to-Swift-bindings

If using Docker

If you're using Docker to generate the Swift bindings, navigate (if you're not already there from the previous step) to the ldk-c-bindings directory and open the file located here:

/path/to/ldk-c-bindings/lightning-c-bindings/Cargo.toml

In that file, you will see four lines specifying the lightning, lightning-persister, lightning-invoice, and lightning-background-processor dependencies. They will most likely show local paths to the rust-lightning folder due to the previous genbindings.sh step. As Docker won't have access to local paths, replace those lines with the following:

lightning = { git = "https://github.com/thebluematt/rust-lightning", branch = "2021-03-java-bindings-base", default-features = false }
lightning-persister = { git = "https://github.com/thebluematt/rust-lightning", branch = "2021-03-java-bindings-base", default-features = false }
lightning-invoice = { git = "https://github.com/thebluematt/rust-lightning", branch = "2021-03-java-bindings-base", default-features = false }
lightning-background-processor = { git = "https://github.com/thebluematt/rust-lightning", branch = "2021-03-java-bindings-base", default-features = false }

You will note that the revision is unspecified and is currently just placeholder xxxs. To obtain the revision, just navigate to the just clone custom rust-lightning directory and run:

cd /path/to/rust-lightning
git rev-parse HEAD

Take that commit hash and replace the xxx instances with it.

Generating the Swift files

To generate the Swift files, navigate to the ldk-swift repository and run the following:

export LDK_SWIFT_GENERATOR_INPUT_HEADER_PATH="/path/to/ldk-c-bindings/lightning-c-bindings/include/lightning.h"
python3 ./

Now, the contents of the bindings/LDK folder will have been completely regenerated.

Configuring Xcode for Framework Compilation

Go to the xcode folder and open LDKFramework.xcworkspace.

Then, navigate to the "LDKFramework" project and click on the LDKFramework project target:

Search for LDK_C_BINDINGS_BASE:

Here, enter the absolute path, pointing to your ldk-c-bindings.

You will now also have to do the same for LDK_C_BINDINGS_BINARY_DIRECTORY, and enter any directory you wish. We like to use just bin/.

Generating the *.xcframework files

With all the bindings generated, you will just have to run two commands to generate the xcframework:

cd xcode
./build_framework.sh

Once the script finishes running, you should see LDKFramework.xcframework in the xcode/build folder. Drag that into your project, and you're done!

SparrowTek / ldk-swift