A webpack loader for Rust wasm libraries (without requiring emscripten)
rust-native-wasm-loader
This is a webpack loader that loads Rust code as a WebAssembly module. It uses the native Rust
support for compiling to wasm32
and does not require Emscripten.
If you already know how to use Rust and Webpack, read the "Short version" of this section. If you want a full example, read the "Long version."
Add both this loader and wasm-loader
to your Webpack loaders in webpack.config.js
:
module.exports = {
// ...
module: {
rules: [
{
test: /\.rs$/,
use: [{
loader: 'wasm-loader'
}, {
loader: 'rust-native-wasm-loader',
options: {
release: true
}
}]
}
]
}
}
Then, specify that your Rust library should be a cdylib
in Cargo.toml
:
[lib]
crate-type = ["cdylib"]
Now you can import any functions marked with #[no_mangle]
as WebAssembly functions:
import loadWasm from './path/to/rustlib/src/lib.rs'
loadWasm().then(result => {
const add = result.instance.exports['add'];
console.log('return value was', add(2, 3));
});
release
: boolean
; whether to compile the WebAssembly module in debug or release mode;false
.gc
: boolean
; whether to run wasm-gc
on the WebAssembly output. Reduces binary size butfalse
and is a no-op in wasmBindgen
orcargoWeb
mode.target
: string
; the Rust target to use; this defaults to wasm32-unknown-unknown
wasmBindgen
: boolean
or object
; use wasm-bindgen
to post-process the wasm file. Thisbabel-loader
as well sincewasm-bindgen
outputs ES6 (or typescript).
wasmBindgen.debug
: boolean
; run wasm-bindgen
in debug mode.wasmBindgen.wasm2es6js
: boolean
; use wasm2es6js
to inline the wasm file into generatedwasmBindgen.typescript
: boolean
; emit a typescript declaration file as part of thets-loader
will pickbabel-loader
.cargoWeb
: boolean
or object
; use cargo-web
to compile the project instead of onlywasm
module. Defaults to false
.
cargoWeb.name
: string
; the file name to use for emitting the wasm file for cargo-web
,'static/wasm/[name].[hash:8].wasm'
.cargoWeb.regExp
: string
; a regexp to extract additional variables for use in name
.First, you need Rust installed. The easiest way is to follow the instructions at rustup.rs.
Then, you need to add support for WebAssembly cross-compilation. At the time of writing, this
requires using the nightly
compiler:
rustup toolchain install nightly
rustup target add wasm32-unknown-unknown --toolchain nightly
The next step is to integrate a cargo/node project. Let's assume we don't already have one, so we create one:
cargo init add
cd add
If nightly is not your system default toolchain, create a file named rust-toolchain
containing
the toolchain name you want to associate with the project:
echo nightly > rust-toolchain
We can add the Rust code that should be available in the WebAssembly module to src/lib.rs
. All
functions that should be reachable from WebAssembly should be marked with #[no_mangle]
:
#[no_mangle]
pub fn add(a: i32, b: i32) -> i32 {
eprintln!("add({:?}, {:?}) was called", a, b);
a + b
}
Then, specify that your Rust library should be a cdylib
in Cargo.toml
:
[lib]
crate-type = ["cdylib"]
Now you can actually start to use this loader. This loader itself does not create Javascript code
for loading a WebAssembly module, so you need to compose it with another loader, like wasm-loader
:
yarn init
yarn add --dev webpack
yarn add --dev rust-native-wasm-loader wasm-loader
The loaders can be registered the usual way by adding them to your webpack.config.js
:
const path = require('path');
module.exports = {
entry: './src/index.js',
output: {
filename: 'index.js',
path: path.resolve(__dirname, 'dist')
},
module: {
rules: [
{
test: /\.rs$/,
use: [{
loader: 'wasm-loader'
}, {
loader: 'rust-native-wasm-loader',
options: {
release: true
}
}]
}
]
}
};
You can now import the WebAssembly module by using the main .rs
file from your Cargo project
(lib.rs
or main.rs
); e.g. from your index.js
:
import loadAdd from './lib.rs'
loadAdd().then(result => {
const add = result.instance.exports['add'];
console.log('return value was', add(2, 3));
});
You can now run webpack and the resulting code from node.js or a browser:
$ yarn run webpack
$ node dist/index.js
return value was 5
wasm-bindgen
experimental supportYou can use experimental wasm-bindgen
support with the following options:
{
test: /\.rs$/,
use: [
{
loader: 'babel-loader',
options: {
compact: true,
}
},
{
loader: 'rust-native-wasm-loader',
options: {
release: true,
wasmBindgen: {
wasm2es6js: true,
},
}
}
]
}
and edit your lib.rs
:
extern crate wasm_bindgen;
use wasm_bindgen::prelude::*;
#[wasm_bindgen]
pub fn add(a: i32, b: i32) -> i32 {
a + b
}
The loader now uses wasm-bindgen
to build the project. If you are using webpack 4, it has experimental native support for importing WASM files, so you probably
don't need the wasm2es6js
flag. If you are using webpack 3 (or bundling for Chrome and it's 4K limit on main thread WASM), it is needed in order to inline
the loading of the wasm file correctly. By using wasm2es6js
, the loader returns a normal Javascript module that can
be loaded like so:
import { add, wasmBooted } from './path/to/rustlib/src/lib.rs'
wasmBooted.then(() => {
console.log('return value was', add(2, 3));
});
cargo-web
experimental supportYou can use experimental cargo-web
support with the following options:
{
loader: 'rust-native-wasm-loader',
options: {
cargoWeb: true,
name: 'static/wasm/[name].[hash:8].wasm'
}
}
The loader now uses cargo-web
to build the project, and as a result needs to emit the wasm file
separately. The loader now returns a normal Javascript module that can be loaded like so:
import loadWasm from './path/to/rustlib/src/lib.rs'
loadWasm.then(module => {
console.log('return value was', module.add(2, 3));
});