How to return a string (or similar) from Rust in WebAssembly?

Question

I created a small Wasm file from this Rust code:

#[no_mangle]
pub fn hello() -> &\'static str {
    \"hello from rust\"
}

It builds

Answer 1

You cannot directly return a Rust String or an &str. Instead allocate and return a raw byte pointer containing the data which has to be then encoded as a JS string on the JavaScript side.

You can take a look at the SHA1 example here.

The functions of interest are in

• demos/bundle.js - copyCStr
• demos/sha1/sha1-digest.rs - digest

For more examples: https://www.hellorust.com/demos/sha1/index.html