[lifthrasiir]

As someone seriously trying to develop a compressed archive format with WebAssembly, sandboxing is actually easy and that's indeed why WebAssembly was chosen. The real problem is determinism, which WebAssembly does technically support but actual implementations may vary significantly. And even when WebAssembly can be made fully deterministic, function calls made to those WebAssembly modules may still be undeterministic! I tried very hard to avoid such pitfalls in my design, and it is entirely reasonable to avoid WebAssembly due to these issues.

[bangaladore]

I'm confused why determinism is a problem here? You write an algorithm that should produce the same output for a given input. How does WASM make that not deterministic?

[lifthrasiir]

Assume that I have 120 MB of data to process. Since this is quite large, implementations may want to process them in chunks (say, 50 MB). Now those implementations would call the WebAssembly module multiple times with different arguments, and input sizes would depend on the chunk size. Even though each call is deterministic, if you vary arguments non-deterministically then you lose any benefit of determinism: any bug in the WebAssembly module will corrupt data.

[bangaladore]

But that is the case in any language and runtime? There is nothing unique about WASM here.

[lifthrasiir]

Yes and that's exactly my point. It is not enough to make the execution deterministic.

Thinking about that, you may have been confused why I said it's reasonable to avoid WebAssembly for that. I meant that a full Turing-complete execution might not be necessary if that makes it easier to ensure the correctness; OpenZL graphs are not even close to a Turing-complete language for example.