Comment by sd2k | Hacker News Reader

Comment by sd2k | Hacker News Reader

Cool to see more projects in this space! I think Wasm is a great way to do secure sandboxing here. How does Amla handle commands like grep/jq/curl etc which make AI agents so effective at bash but require recompilation to WASI (which is kinda impractical for so many projects)?

I've been working on a couple of things which take a very similar approach, with what seem to be some different tradeoffs:

- eryx [1], which uses a WASI build of CPython to provide a true Python sandbox (similar to componentize-py but supports some form of 'dynamic linking' with either pure Python packages or WASI-compiled native wheels) - conch [2], which embeds the `brush` Rust reimplementation of Bash to provide a similar bash sandbox. This is where I've been struggling with figuring out the best way to do subcommands, right now they just have to be rewritten and compiled in but I'd like to find a way to dynamically link them in similar to the Python package approach...

One other note, WASI's VFS support has been great, I just wish there was more progress on `wasi-tls`, it's tricky to get network access working otherwise...

[1] https://github.com/eryx-org/eryx [2] https://github.com/sd2k/conch

Great question. We cheated a bit; we didn't compile the GNU coreutils to wasm. Instead, we have Rust reimplementations of common shell commands. It allows us to focus on the use cases agents actually care about instead of reimplementing all of the corner cases exactly.

For `jq` specifically we use the excellent `jaq_interpret` crate: https://crates.io/crates/jaq-interpret

curl is interesting. We don't include it currently but we could do it without too much additional effort.

Networking isn't done within the wasm sandbox; we "yield" back to the the caller using what we call "host operations" in order to perform any IO. This keeps the Wasm sandbox minimal and as close to "pure compute" as possible. In fact, the only capabilities we give the WASI runtime is a method to get the current time and to generate random numbers. Since we intercept all external IO, random number generation, time, and the Wasm runtime is just for pure computation, we also get perfect reproducibility. We can replay anything within the sandbox exactly.

Your approach with brush is interesting. Having actual bash semantics rather than "bash-like" is a real advantage for complex scripts. The dynamic linking problem for subcommands is a tough one; have you looked at WASI components for this? Feels like that's where it'll eventually land but the tooling isn't there yet.

Will check out eryx and conch. Thanks for sharing!

Hah, that is exactly the same approach I landed on. Fortunately the most common tools either seem to have Rust ports or are fairly easy to port 80% of the functionality! Conch's Wasm file is around ~3.5MB and only has a few tools though so I can see it growing. I think for the places where size really matters (e.g. the web) it should be possible to split it using the component model and `jco` (which I think splits Wasm components into modules along interface boundaries, and could defer loading of unused modules) but I haven't got that far yet.

I did something very similar to you for networking in eryx too (no networking in conch yet); defined an `eryx:net` interface in WIT and reimplemented the `urllib` module using host networking, which most downstream packages (httpx, requests, etc) use far enough down the stack. It's a tradeoff but I think it's pretty much good enough for most use cases like this, and gives the host full control which is great.

Oh full transparency, the vast majority of conch and eryx were written by Opus 4.5. Being backed by wasmtime and the rather strict Rust compiler is definitely a boon here!

The opus 4.5 confession is great haha. We have found Claude Code + Opus 4.5 + Rust with miri/cargo-deny/cargo-check/cargo-fmt + Python with strict type checking/pedantic lint rules/comprehensive test suites to be a winning combination. It makes AI-assisted development surprisingly viable for systems work.

Good to see that you chose a similar path for networking in eryx!

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