Using Deno runtime as a v8 isolate runner
Deno is awesome, not just the end product but also the core runtime. I've spend the past couple of weeks off-and-on diving into the codebase and learning how the system works. It's fantastic.
I have a rust application and I would like to run arbitrary javascript code within v8 isolates. The challenge is that I would need to implement and provide all of the web runtime APIs (Fetch, Stream, etc) to support the javascript code. So I began to wonder if I could use Deno for this?
As I have ascertained thus far, the core runtime is structured to bootstrap a worker and then run a javascript module within. I'm hoping someone could simply point me in the direction for how I might do the following:
1 - Initialize a v8 isolate with the Deno runtime + ops, from a snapshot
2 - Inject javascript into the isolate that exports one or more functions
3 - Call one or more of those functions from within rust
4 - Retrieve the response
5 - Shut down the isolate
Perhaps this is already possible with the Worker api, I'm just trying to wrap my head around it.
Also, I'm not looking for this to be a supported feature and I understand that the core runtime API will change from time-to-time, use at my own risk, etc.
Much appreciation in advance!
3 Replies
Based on the documentation, it seems like you're on the right track with your approach. Deno's core runtime is indeed designed to bootstrap a worker and run a JavaScript module within it.
To achieve your goals, you might find the "Roll your own JavaScript runtime" blog post particularly useful. This post walks through creating a custom JavaScript runtime, which is essentially what you're trying to do. It demonstrates how to create a CLI that executes JavaScript files, which is similar to your goal of running arbitrary JavaScript code within V8 isolates.
Here's a rough outline of how you might approach this, based on the documentation:
1. Initialize a V8 isolate with the Deno runtime + ops, from a snapshot: The documentation explains how to add the
deno_core and tokio dependencies to your project, which are necessary for creating a JavaScript runtime. The deno_core crate abstracts away interactions with the V8 JavaScript engine, and tokio is an asynchronous Rust runtime that you can use as an event loop. Together, these allow JavaScript's Promises to be easily mapped onto Rust's Futures.
2. Inject JavaScript into the isolate that exports one or more functions: The documentation provides an example of how to write an asynchronous Rust function that creates an instance of JsRuntime, which is responsible for JavaScript execution. You can use this to inject JavaScript into the isolate.
3. Call one or more of those functions from within Rust: The documentation doesn't provide a specific example of this, but it does show how to create a console API that can be used to print messages from JavaScript. You might be able to adapt this approach to call your own functions.
4. Retrieve the response: Again, the documentation doesn't provide aspecific example of this, but the
console API example might give you some ideas. You could potentially use a similar approach to retrieve responses from your functions.
5. Shut down the isolate: The documentation doesn't provide information on this step, so you might need to refer to the deno_core and tokio documentation or source code for more details.
Remember, this is a high-level overview and the actual implementation might be more complex. But hopefully, this gives you a good starting point! 🦕The roll your own Javascript runtime is helpful, thanks for the reference! Still struggling to understand how I can call a javascript function within the isolate from the rust program.