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.

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

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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

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

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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

Feature	Description	Preserves Sandbox	Dependencies
broadcast_channel	Implements the web-messaging API for Deno	NO	deno_broadcast_channel, deno_web, deno_webidl
cache	Implements the Cache API for Deno	NO	deno_cache, deno_webidl, deno_web, deno_crypto, deno_fetch, deno_url, deno_net
console	Provides console.* functionality from JS	yes	deno_console, deno_terminal
cron	Implements scheduled tasks (crons) API	NO	deno_cron, deno_console
crypto	Provides crypto.* functionality from JS	yes	deno_crypto, deno_webidl
ffi	Dynamic library ffi features	NO	deno_ffi
fs	Provides ops for interacting with the file system.	NO	deno_fs, web, io
http	Implements the fetch standard	NO	deno_http, web, websocket
kv	Implements the Deno KV Connect protocol	NO	deno_kv, web, console
url	Provides the URL, and URLPattern APIs from within JS	yes	deno_webidl, deno_url
io	Provides IO primitives such as stdio streams and abstraction over File System files.	NO	deno_io, rustyline, winapi, nix, libc, once_cell
web	Provides the Event, TextEncoder, TextDecoder, File, Web Cryptography, and fetch APIs from within JS	NO	deno_webidl, deno_web, deno_crypto, deno_fetch, deno_url, deno_net
webgpu	Implements the WebGPU API	NO	deno_webgpu, web
webstorage	Provides the WebStorage API	NO	deno_webidl, deno_webstorage
websocket	Provides the WebSocket API	NO	deno_web, deno_websocket
webidl	Provides the webidl API	yes	deno_webidl
default	Provides only those extensions that preserve sandboxing	yes	deno_console, deno_crypto, deno_webidl, deno_url
no_extensions	Disables all extensions to the JS runtime - you can still add your own extensions in this mode	yes	None
all	Provides all available functionality	NO	deno_console, deno_webidl, deno_web, deno_net, deno_crypto, deno_fetch, deno_url
fs_import	Enables importing arbitrary code from the filesystem through JS	NO	None
url_import	Enables importing arbitrary code from network locations through JS	NO	reqwest
node_experimental	HIGHLY EXPERIMENTAL nodeJS support that enables all available Deno extensions	NO	For complete list, see Cargo.toml
worker	Enables access to the threaded worker API [worker]	yes	None
snapshot_builder	Enables access to [SnapshotBuilder], a runtime for creating snapshots that can improve start-times	yes	None
web_stub	Enables a subset of web features that do not break sandboxing	yes	deno_webidl

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For an example of this crate in use, see Lavendeux