kbknapp/rust_wasm.md

## rust_wasm.md

      
    Raw
  

              rust_wasm.md
            
          
    wasm32-unknown-unknown

Setup


Use nightly with rustup

$ rustup update nightly
$ rustup target add wasm32-unknown-unknown --toolchain nightly 


Add the target wasm32-unknown-unknown
Install wasm-gc

$ cargo install --git https://github.com/alexcrichton/wasm-gc 
$ wasm-gc .\add.wasm small-add.wasm


Compile as a cdylib

$ rustc +nightly --target wasm32-unknown-unknown -O .\lib.rs --crate-type=cdylib 

Or using cargo and Cargo.toml
[lib]
path = "src/lib.rs"
crate-type = ["cdylib"]

Run wasm-gc to compress the code size

$ wasm-gc TARGET.wasm small-TARGET.wasm

Example

Rust Code:
// add.rs
#![feature(lang_items)]
#![no_std]

#[no_mangle]
pub fn add_one(x: i32) -> i32 {
    x + 1
}


// needed for no_std if no_std is requirement
#[lang = "panic_fmt"]
#[no_mangle]
pub extern fn rust_begin_panic(_msg: core::fmt::Arguments,
                               _file: &'static str,
                               _line: u32,
                               _column: u32) 
                               -> ! 
{
    loop {}
}
HTML:
<!DOCTYPE html>
<html lang="en">
  <head>
      <meta charset="utf-8">
      <title>wasm wasm wasm</title>
      <script>
        fetch('small-add.wasm').then(response =>
          response.arrayBuffer()
        ).then(bytes =>
          WebAssembly.instantiate(bytes, {})
        ).then(results => {
          alert(results.instance.exports.add_one(41));
        });
      </script>
  </head>
</html>
Run:
$ python -m SimpleHTTPServer

Open browser to http://localhost:8000/