trealla-js VS quickjs-emscripten

I think Prolog really shines as an embedded query engine (I know this is old and it's been removed since). It's perfect for declarative configuration, very easy to write powerful queries once you wrap your head around it.

The Yarn constraints plugin also used (Tau) Prolog, although it looks like it's in the process of being replaced with JS, which makes me a bit sad. The reasoning is here: https://github.com/yarnpkg/berry/issues/1276. Seems like the biggest issue is lack of a nice dev environment. I maintain the Trealla Prolog Wasm port (npm package 'trealla') and I hope some day to use it for a VSCode extension or LSP or something to provide a nice dev experience. Performance has also been cited as an issue[1] but Trealla is quite fast and I expect it could easily handle a complex Yarn workspace with tons of facts. If this sounds like something you'd be interested in helping me with, feel free to contact me or make an issue/discussion here: https://github.com/guregu/trealla-js

[1]: https://github.com/yarnpkg/berry/issues/4079#issuecomment-10...

port a C or Rust project to wasm and make a JS package for it (trealla-js is an example of such a package, porting a C Prolog interpreter to wasm)

Hey, this is mine. Thanks for submitting it. I'll answer some questions.

> Why?

I ported Trealla Prolog to WASM (WASI) and I was looking for something useful to test it against. I found Spin, which can run WASM+CGI, and landed on this. Making this project exposed a number of bugs in my port that have now been fixed, so consumers of more useful projects[1][2] benefit as well. Also, PHP style templates are just fun! There's something valuable to just being able to shove a little bit of code inside some HTML and get it up on the internet.

I started my webdev journey with PHP many many years ago, and it's nice to revisit it from a different perspective. I don't use the real (elephant) PHP anymore, but I've gained a newfound appreciation for how fun its quick & dirty development style is.

I hope this project can serve as an example of how to use Prolog for fun things. It does showcase some of the cooler dynamic aspects of the language, and the PHP parsing code is like 10 lines of DCG.

> Is it a joke?

Yes and no. The name is certainly a joke. I was pondering what 'Prolog on Rails' might be and thought calling it PHP would be funny. This led to the PHP-style templates which were quick to implement and pretty powerful. Despite the humorous presentation, it does actually work.

> Can you use Prolog for web services?

Yes! For example, SWI has a mature HTTP package: https://www.swi-prolog.org/pldoc/doc_for?object=section(%27p.... It's used to power SWISH, an online Prolog code sharing thing: https://swish.swi-prolog.org/

> Next steps?

I would like to support persistence somehow. I think it'd be really cool if you could use Prolog's dynamic database[3] as a persistent store. Spin has components for Postgres and Redis so it shouldn't be too hard to implement, but I lose the WASI compatibility if I do that... which means I can't use the binary from WAPM, etc.

I would also like to experiment with running Trealla on Cloudflare Workers. I have another project, worker-prolog[4], which uses Tau Prolog (a Prolog written in Javascript) on Workers.

On a somewhat related note, I've also been playing around with Cosmopolitan libc[5]. I got Trealla to compile to an APE executable but there's some issues with the embedded Prolog libraries getting garbled, so I need to improve my GDB skills and figure out what's going on there.

Finally, I'd like to say thanks to Andrew Davison (@infradig on GitHub), the author of Trealla Prolog, for letting me add WASM support to his project and helping me with lots of things. For example, PHP led to Andrew implementing improvements for using DCGs to parse Prolog terms, which is now super fast[6]!

[1]: https://github.com/guregu/trealla-js

[2]: https://github.com/trealla-prolog/go

[3]: https://www.swi-prolog.org/pldoc/man?predicate=assertz/1

[4]: https://github.com/guregu/worker-prolog

[5]: https://justine.lol/cosmopolitan/

[6]: https://github.com/trealla-prolog/trealla/issues/53

With trealla-prolog/go on the backend and trealla-js on the frontend, you can share the same validation code.

I found async generators to be handy while porting a C Prolog interpreter to WASM/JS. A `for await` loop is a natural way to iterate over query results, and as a bonus you can use `finally` within the iterator to automatically clean up resources (free memory). There are ways for determined users to leak (manually iterating and forgetting to call `.return()`) but I've found that setting a finalizer on a local variable inside of the generator seems to work :-). I can't say manual memory management is a common task in JS but it did the trick.

The generator in question, which is perhaps the gnarliest JS I've ever written: https://github.com/guregu/trealla-js/blob/887d200b8eecfca8ed...

Based on your comment below I think you figured out the difference - but if you're looking to execute JS, you can pick between ShadowRealm (where available, or using a polyfill) or my library quickjs-emscripten.

Pros of quickjs-emscripten over ShadowRealm:

- You can use quickjs today in any browser with WASM. ShadowRealm isn't available yet, and polyfills have had security issues in the past. See https://www.figma.com/blog/an-update-on-plugin-security/

- In ShadowRealm eval, untrusted code can consume arbitrary CPU cycles. With QuickJS, you can control the CPU time used during an `eval` using an [interrupt handler] that's called periodically during the eval.

- In ShadowRealm eval, untrusted code can allocate arbitrary amounts of memory. With QuickJS, you can control both the [stack size] and the [heap size] available inside the runtime.

- quickjs-emscripten can do interesting things with custom module loaders and facades that allow synchronous code inside the runtime to call async code on the host.

Pros of ShadowRealm over QuickJS:

- ShadowRealm will (presumably?) execute code using your native runtime, probably v8, JavaScriptCore, or SpiderMonkey. Quickjs is orders of magnitude slower than JIT'd javascript performance of v8 etc. It's also slower than v8/JSC's interpreters, although not by a huge amount. See [benchmarks] from 2019.

- You can easily call and pass values to ShadowRealm imported functions. Talking to quickjs-emscripten guest code requires a lot of fiddly and manual object building.

- Overall the quickjs(-emscripten) API is verbose, and requires manual memory management of references to values inside the quickjs runtime.

[interrupt handler]: https://github.com/justjake/quickjs-emscripten/blob/main/doc...

[stack size]: https://github.com/justjake/quickjs-emscripten/blob/main/doc...

[heap size]: https://github.com/justjake/quickjs-emscripten/blob/main/doc...

[benchmarks]: https://bellard.org/quickjs/bench.html

The thing I want to achieve with WebAssembly is still proving a lot harder than I had anticipated.

I want to be able to take strings of untrusted code provided by users and execute them in a safe sandbox.

I have all sorts of things I want this for - think custom templates for a web application, custom workflow automation scripts (Zapier-style), running transformations against JSON data.

When you're dealing with untrusted code you need a really robust sandbox. WebAssembly really should be that sandbox.

I'd like to support Python, JavaScript and maybe other languages too. I want to take a user-provided string of code in one of those languages and execute that in a sandbox with a strict limit on both memory usage and time taken (so I can't be crashed by a "while True" loop). If memory or time limit are exceeded, I want to get an exception which I can catch and return an error message to the user.

I've been exploring options for this for quite a while now. The furthest I've got was running Pyodide inside of Deno: https://til.simonwillison.net/deno/pyodide-sandbox

Surprisingly I've not found a good pattern for running a JavaScript interpreter in a WASM sandbox yet. https://github.com/justjake/quickjs-emscripten looks promising but I've not found the right recipe to call it from server-side Python or Deno yet.

Can Extism help with this? I'm confident I'm not the only person who's looking for a solution here!

"Safely execute untrusted Javascript in your Javascript, and execute synchronous code that uses async functions" quickjs-emscripten, NPM

This maybe, as a start?

https://github.com/justjake/quickjs-emscripten

QuickJS Running in WebAssembly\ (17 comments)

The library was inspired by Figma’s blog posts about their plug-in system: https://github.com/justjake/quickjs-emscripten#background

If you need to call into user-generated Javascript synchronously or have greater control over the sandbox environment, you can use WebAssembly to run a Javascript interpreter: https://github.com/justjake/quickjs-emscripten#quickjs-emscr...

QuickJS in WebAssembly is much slower than your browser's native Javascript runtime, but possibly faster than async calls using postMessage. As an added bonus, it can make async functions in the host appear to be synchronous inside the sandbox using asyncify: https://emscripten.org/docs/porting/asyncify.html.

You can use One Weird Trick with generator functions to make your code "generic" over synchronicity. I use this technique to avoid needing to implement both sync and async versions of some functions in my quickjs-emscripten library.

The great part about this technique as a library author is that unlike choosing to use a Promise return type, this technique is invisible in my public API. I can write a function like `export function coolAlgorithm(getData: (request: I) => O | Promise): R | Promise`, and we get automatic performance improvement if the user's function happens to return synchronously, without mystery generator stuff showing up in the function signature.

Helper to make a function that can be either sync or async: https://github.com/justjake/quickjs-emscripten/blob/ff211447...

Uses: https://cs.github.com/justjake/quickjs-emscripten?q=yield*+l...

This seems like a pretty nice, recently enabled way of getting a sandboxed js environment: QuickJS compiled to WASM: https://github.com/justjake/quickjs-emscripten.