Lib.rs

Effortless JS Integration for Rust

rustyscript provides a quick and simple way to integrate a runtime javascript or typescript component from within Rust. It uses the v8 engine through the deno_core.

I have attempted to abstract away the v8 engine details so you can for the most part operate directly on rust types.

Sandboxed

By default, the code being run is entirely sandboxed from the host, having no filesystem or network access. extensions can be added to grant additional capabilities that may violate sandboxing

Flexible

The runtime is designed to be as flexible as possible, allowing you to modify capabilities, the module loader, and more.

• Asynchronous JS is fully supported, and the runtime can be configured to run in a multithreaded environment.
• Typescript is supported, and will be transpired into JS for execution.
• Node JS is supported experimentally, but is not yet fully compatible.

Unopinionated

Rustyscript is designed to be a thin wrapper over the Deno runtime, to remove potential pitfalls and simplify the API without sacrificing flexibility or performance.

A draft version of the rustyscript user guide can be found here: https://rscarson.github.io/rustyscript-book/

Here is a very basic use of this crate to execute a JS module. It will:

• Create a basic runtime
• Load a javascript module,
• Call a function registered as the entrypoint
• Return the resulting value

use rustyscript::{json_args, Runtime, Module, Error};

let module = Module::new(
    "test.js",
    "
    export default (string, integer) => {
        console.log(`Hello world: string=${string}, integer=${integer}`);
        return 2;
    }
    "
);

let value: usize = Runtime::execute_module(
    &module, vec![],
    Default::default(),
    json_args!("test", 5)
)?;

assert_eq!(value, 2);

Modules can also be loaded from the filesystem with Module::load or Module::load_dir if you want to collect all modules in a given directory.

If all you need is the result of a single javascript expression, you can use:

let result: i64 = rustyscript::evaluate("5 + 5").expect("The expression was invalid!");

Or to just import a single module for use:

use rustyscript::{json_args, import};
let mut module = import("js/my_module.js").expect("Something went wrong!");
let value: String = module.call("exported_function_name", json_args!()).expect("Could not get a value!");

There are a few other utilities included, such as validate and resolve_path

A more detailed version of the crate's usage can be seen below, which breaks down the steps instead of using the one-liner Runtime::execute_module:

use rustyscript::{json_args, Runtime, RuntimeOptions, Module, Error, Undefined};
use std::time::Duration;

let module = Module::new(
    "test.js",
    "
    let internalValue = 0;
    export const load = (value) => internalValue = value;
    export const getValue = () => internalValue;
    "
);

// Create a new runtime
let mut runtime = Runtime::new(RuntimeOptions {
    timeout: Duration::from_millis(50), // Stop execution by force after 50ms
    default_entrypoint: Some("load".to_string()), // Run this as the entrypoint function if none is registered
    ..Default::default()
})?;

// The handle returned is used to get exported functions and values from that module.
// We then call the entrypoint function, but do not need a return value.
//Load can be called multiple times, and modules can import other loaded modules
// Using `import './filename.js'`
let module_handle = runtime.load_module(&module)?;
runtime.call_entrypoint::<Undefined>(&module_handle, json_args!(2))?;

// Functions don't need to be the entrypoint to be callable!
let internal_value: i64 = runtime.call_function(Some(&module_handle), "getValue", json_args!())?;

There are also '_async' and 'immediate' versions of most runtime functions; '_async' functions return a future that resolves to the result of the operation, while '_immediate' functions will make no attempt to wait for the event loop, making them suitable for using crate::js_value::Promise

Rust functions can also be registered to be called from javascript:

use rustyscript::{ Runtime, Module, serde_json::Value };

let module = Module::new("test.js", " rustyscript.functions.foo(); ");
let mut runtime = Runtime::new(Default::default())?;
runtime.register_function("foo", |args| {
    if let Some(value) = args.get(0) {
        println!("called with: {}", value);
    }
    Ok(Value::Null)
})?;
runtime.load_module(&module)?;

Asynchronous JS can be called in 2 ways;

The first is to use the 'async' keyword in JS, and then call the function using Runtime::call_function_async

use rustyscript::{ Runtime, Module, json_args };

let module = Module::new("test.js", "export async function foo() { return 5; }");
let mut runtime = Runtime::new(Default::default())?;

// The runtime has its own tokio runtime; you can get a handle to it with [Runtime::tokio_runtime]
// You can also build the runtime with your own tokio runtime, see [Runtime::with_tokio_runtime]
let tokio_runtime = runtime.tokio_runtime();

let result: i32 = tokio_runtime.block_on(async {
    // Top-level await is supported - we can load modules asynchronously
    let handle = runtime.load_module_async(&module).await?;

    // Call the function asynchronously
    runtime.call_function_async(Some(&handle), "foo", json_args!()).await
})?;

assert_eq!(result, 5);

The second is to use crate::js_value::Promise

use rustyscript::{ Runtime, Module, js_value::Promise, json_args };

let module = Module::new("test.js", "export async function foo() { return 5; }");

let mut runtime = Runtime::new(Default::default())?;
let handle = runtime.load_module(&module)?;

// We call the function without waiting for the event loop to run, or for the promise to resolve
// This way we can store it and wait for it later, without blocking the event loop or borrowing the runtime
let result: Promise<i32> = runtime.call_function_immediate(Some(&handle), "foo", json_args!())?;

// We can then wait for the promise to resolve
// We can do so asynchronously, using [crate::js_value::Promise::into_future]
// But we can also block the current thread:
let result = result.into_value(&mut runtime)?;
assert_eq!(result, 5);

• See Runtime::register_async_function for registering and calling async rust from JS
• See examples/async_javascript.rs for a more detailed example of using async JS

For better performance calling rust code, consider using an extension instead of a module - see the runtime_extensions example for details

A threaded worker can be used to run code in a separate thread, or to allow multiple concurrent runtimes.

the worker module provides a simple interface to create and interact with workers. The worker::InnerWorker trait can be implemented to provide custom worker behavior.

It also provides a default worker implementation that can be used without any additional setup:

use rustyscript::{Error, worker::{Worker, DefaultWorker, DefaultWorkerOptions}};
use std::time::Duration;

fn main() -> Result<(), Error> {
    let worker = DefaultWorker::new(DefaultWorkerOptions {
        default_entrypoint: None,
        timeout: Duration::from_secs(5),
    })?;

    let result: i32 = worker.eval("5 + 5".to_string())?;
    assert_eq!(result, 10);
    Ok(())
}

Utility Functions

These functions provide simple one-liner access to common features of this crate:

• evaluate; Evaluate a single JS expression and return the resulting value
• import; Get a handle to a JS module from which you can get exported values and functions
• resolve_path; Resolve a relative path to the current working dir
• validate; Validate the syntax of a JS expression
• init_platform; Initialize the V8 platform for multi-threaded applications

Commonly used features have been grouped into the following feature-sets:

• safe_extensions - On by default, these extensions are safe to use in a sandboxed environment
• network_extensions - These extensions break sandboxing by allowing network connectivity
• io_extensions - These extensions break sandboxing by allowing filesystem access (WARNING: Also allows some network access)
• all_extensions - All 3 above groups are included
• extra_features - Enables the worker feature (enabled by default), and the snapshot_builder feature
• node_experimental - HIGHLY EXPERIMENTAL nodeJS support that enables all available Deno extensions

Crate features

The table below lists the available features for this crate. Features marked at Preserves Sandbox: NO break isolation between loaded JS modules and the host system. Use with caution.

More details on the features can be found in Cargo.toml

Please note that the web feature will also enable fs_import and url_import, allowing arbitrary filesystem and network access for import statements

• This is because the deno_web crate allows both fetch and FS reads already

For an example of this crate in use, see Lavendeux