parity-wasm/examples/build.rs

// Simple example of how to use parity-wasm builder api.
// Builder api introduced as a method for fast generation of
// different small wasm modules.

extern crate parity_wasm;

use std::env;

use parity_wasm::builder;
use parity_wasm::elements;

fn main() {

    // Example binary accepts one parameter which is the output file
    // where generated wasm module will be written at the end of execution
    let args = env::args().collect::<Vec<_>>();
    if args.len() != 2 {
        println!("Usage: {} output_file.wasm", args[0]);
        return;
    }

    // Main entry for the builder api is the module function
    // It returns empty module builder structure which can be further
    // appended with various wasm artefacts
    let module = builder::module()
        // Here we append function to the builder
        // function() function returns a function builder attached
        // to the module builder.
        .function()
            // We describe signature for the function via signature()
            // function. In our simple example it's just one input
            // argument of type 'i32' without return value
            .signature().with_param(elements::ValueType::I32).build()
            // body() without any further arguments means that the body
            // of the function will be empty
            .body().build()
            // This is the end of the function builder. When `build()` is
            // invoked, function builder returns original module builder
            // from which it was invoked
            .build()
        // And finally we finish our module builder to produce actual
        // wasm module.
        .build();

    // Module structure can be serialzed to produce a valid wasm file
    parity_wasm::serialize_to_file(&args[1], module).unwrap();
}