Rune WIT Files

This repository contains the various WebAssembly Interface Types files used by the Rune project.

Getting Started (Rune)

The underlying idea behind WIT is that an API author will use a *.wit file to define the interface for how a WebAssembly module will interact with the outside world. Anyone wanting to comply with that interface can take a copy of the *.wit file and run it through a code generator like wit-bindgen to generate the appropriate language bindings.

If you have used Protocol Buffers before, *.wit is roughly analogous to a *.proto file.

The wit-bindgen CLI tool can be installed directly from GitHub.

$ cargo install --git https://github.com/bytecodealliance/wit-bindgen wit-bindgen-cli

Once wit-bindgen is installed, you will need to add this repository as a git submodule.

$ git submodule add [email protected]:hotg-ai/wit-files.git

Rust Guest

If you are writing a Rust crate that will be compiled to WebAssembly, you can have the bindings automatically generated by a procedural macro by adding the wit-bindgen-rust crate as a dependency.

$ cargo add --git https://github.com/bytecodealliance/wit-bindgen wit-bindgen-rust

Inside your crate, you can now use the wit_bindgen_rust::import!() macro to generate bindings to functions provided by the host.

The wit_bindgen_rust::export!() macro will generate a trait that is used to expose your crate's functionality to the outside world. You will need to provide an implementation of this trait.

// lib.rs

wit_bindgen_rust::import!("../wit-files/rune/runtime-v1.wit");

wit_bindgen_rust::export!("../wit-files/rune/rune-v1.wit");

pub struct Exports;

impl rune_v1::RuneV1 for Exports { ... }

JavaScript Host

We've published a JavaScript package to NPM called @hotg-ai/rune-wit-files which contains the generated bindings for loading a WebAssembly module. The package's source code is available in the rune/js/ folder.

The package's yarn build script will automatically generate any necessary glue code and compile it to a single bundle that can be published to NPM.

Under the hood, this script will first run the wit-bindgen CLI...

$ cd rune/js/
$ wit-bindgen js --export ../runtime-v1.wit --import ../rune-v1.wit --out-dir ./bindings
Generating "bindings/intrinsics.js"
Generating "bindings/rune-v1.d.ts"
Generating "bindings/rune-v1.js"
Generating "bindings/runtime-v1.d.ts"
Generating "bindings/runtime-v1.js"

Next, it uses Parcel to generate a single release bundle...

$ ./node_modules/.bin/parcel build
✨ Built in 818ms

dist/index.js      11.12 KB    20ms
dist/index.d.ts       114 B     8ms
Done in 1.02s.

$ tree dist
dist
├── index.d.ts
├── index.d.ts.map
├── index.js
└── index.js.map

0 directories, 4 files

Finally, because Parcel doesn't generate a single typings file when from the multiple generated *.d.ts files, we create the typings file ourselves by concatenating each of the generated typings files.

$ cat bindings/*.d.ts > dist/index.d.ts

The Inspection App

To make inspecting metadata a bit easier, we've created a React app that lets you upload a WebAssembly binary and extract its metadata.

You build this app similar to most React apps.

$ cd rune/inspect/
$ yarn
yarn install v1.22.17
[1/4] Resolving packages...
[2/4] Fetching packages...
[3/4] Linking dependencies...
[4/4] Building fresh packages...
Done in 1.66s.
$ yarn start
yarn run v1.22.17
$ parcel serve index.html
Server running at http://localhost:1234
✨ Built in 397ms

Note: if you see errors saying @hotg-ai/rune-wit-files couldn't be imported, you may need to build the JavaScript bindings first.

$ cd rune/js/ && yarn && yarn build