flakm/rust-assemblyscript

Showcase how to use wasmer and assemblyscript wasm binaries

Rust <-> assemblyscript example

This repository showcases the following:

1. How to ompile example assemblyscript to wasm
   • it has a function transform that takes string and returns didderent string
   • it has a host defined function called log that sends a string to rust side for logging
2. How to use WebAssembly runtime (wasmer) to setup and call this module
   • call wasm module change with http response from some json web api
   • print the output in rust side

Running instruction

Prerequisities:

• nodejs
• nix
• cargo

And then run:

cd transformation
npm install
npm run asbuild # this will create required wasm binaries

cd ..

# run the host side
cargo run
   Compiling wasm v0.1.0 (/home/flakm/programming/modivo/wasm)
    Finished dev [unoptimized + debuginfo] target(s) in 2.54s
     Running `target/debug/wasm`
Compiling module...
Creating the imported function...
[0] my_response: status: 200, body: {"name":"John", "age":30}
[1] my_response: status: 200, body: {"tag":"@John"}

TODOS

• Only basic testing support there is other project as-pect that might be awesome
• assemblyscript has to be manually installed and run because it's not packaged in nix
• cargo crane project is super basic example
• better error handling: https://docs.wasmer.io/integrations/examples/errors

Pain points

• Error handling is painful since we loose a lot of information when code throws error during serialization issue
• Sharing memory is complicated for example if we want to provide host functions to wasm module that will reach back to some memory in host from the guest it will require dereferencing a raw pointer that is leaked (kind of like with FFI) or some kind of hash map backed storage.

Interesting material

1. Wasmer rust - rust example: https://github.com/wasmerio/wasmer-rust-example/blob/master/src/main.rs

   wasmer is an open-source runtime for executing WebAssembly on the Server.

2. AssemblyScript A TypeScript-like language for WebAssembly https://www.assemblyscript.org/

• Example of importing functions into wasm

3. wasm-bindgen rust crate enabling high level interactions between wasm modules allows for similar code:

use wasm_bindgen::prelude::*;

// Import the `window.alert` function from the Web.
#[wasm_bindgen]
extern "C" {
    fn alert(s: &str);
}

// Export a `greet` function from Rust to JavaScript, that alerts a
// hello message.
#[wasm_bindgen]
pub fn greet(name: &str) {
    alert(&format!("Hello, {}!", name));
}

Set up transformation

https://www.assemblyscript.org/getting-started.html#setting-up-a-new-project