This is a sample project for compiling a Rust module to WASM and using JCO to import it in a Node.js AWS Lambda function.

You must have the following tooling installed

• Rust
• Node.js
• cargo-component

Note: This is based on the JCO launch announcement blog post but the steps appear to be outdated so what follows is the changes required to make it work as of 2024-05-25.

The project was created by running the following cargo-component command:

cargo component new <project-name> --lib

This creates a component in src/lib.rs that has a simple Hello World function. This function was changed to one that will turn a string into upper case:

impl Guest for Component {
    fn shout(input: String) -> String {
        let mut s = input.to_uppercase();
        s.push_str("!");
        s.into()
    }
}

The wit/world.wit file which uses the [IDL(https://github.com/WebAssembly/component-model/blob/main/design/mvp/WIT.md)] that underpins the WebAssembly component model was also changed:

package component:<project-name>;

world example {
    export shout: func(input: string) -> string;
}

1. Run npm i to install the @bytecodealliance/jco and@bytecodealliance/preview2-shim dependencies aqqqlocally.
2. Run npm run build to compile the Rust module, invoke JCO and then build a zip file of the code in a folder called dist.
3. Create a blank Node.js AWS lambda function.
4. Upload the zip to the lambda function.
5. Execute the lambda function with the default test event, which should produce the following output:

"VALUE1!"