thread_rng can't get random number in a WASI module

[autodidaddict]

Runtime panic (trap) when getting random number

Rust code in the compiled WASI module: let mut rng = thread_rng();

My system:

wasmer 0.4.2 | rustc 1.34.2 (6c2484dc3 2019-05-13) | x86_64

Steps to reproduce

1. Create a Rust project
2. Have that project invoke thread_rng() to produce a RNG
3. Compile Rust target to WASI
4. attempt to run module with wasmer

Expected behavior

According to the WASI spec, there's a __wasi_rnd_get() function that I figured would be invoked underneath the rand crate's compiled WASI code.

Actual behavior

thread 'main' panicked at 'could not initialize thread_rng: All entropy sources failed (permanently unavailable); cause: OsRng: support for wasm32 requires emscripten, stdweb or wasm-bindgen (permanently unavailable)', /home/kevin/.cargo/registry/src/github.com-1ecc6299db9ec823/rand-0.6.5/src/rngs/thread.rs:80:17

This error message reads like someone's compile-time error message that doesn't take into account the shunting being done by the WASI code and its relevant imports.

If we can't use random numbers, things are going to be difficult compiling to WASI.

Additional context

I'm perfectly fine with cheap workarounds. I don't need cryptographic random, I'm just using this to shuffle a list of servers to connect with, so if there are some lines of Rust I can replace my code with that will pick a random number between 0 and n or let me invoke shuffle on a vec and not cause a wasmer-time trap, that'd be awesome.

p.s. I don't know if the problem is in the runtime wasmer's providing or in the code that Rust is generating via the wasm32-wasi target. Apologies if this is not your issue at all.

[autodidaddict]

I've completely removed all random number generation from my own code, but it looks like somewhere in the dependency tree there's still some other code using thread_rng from the rand crate.

[Hywan]

Did you consider using https://github.com/rust-random/rand to get random number with WebAssembly?

[autodidaddict]

@Hywan yeah, like I said I removed my own random code. Problem is the use of the rand crate is littered throughout my dependency tree.

[Hywan]

Try to run cargo update or even cargo clean at some point.

[autodidaddict]

I've done both. I can actually compile the wasm to the wasm32-wasi target. It just panics as soon as wasmer 's execution hits a spot that tries to invoke thread_rng()

[MarkMcCaskey]

Thanks for the report! I'll investigate and write a test covering this case

[MarkMcCaskey]

The error message is originating past the rand crate.

See rust-random/rand#769 for more information.

And no, we don't have an ETA on the Rand 0.7 release. See #715 and the milestone. Ideally it will be within a couple of months.

That was early April, so hopefully WASI support will be coming soon!

[huangjj27]

Encountering the same issue.

[jedisct1]

You can use the getrandom crate instead.

[kubkon]

The error message is originating past the rand crate.

See rust-random/rand#769 for more information.

And no, we don't have an ETA on the Rand 0.7 release. See #715 and the milestone. Ideally it will be within a couple of months.

That was early April, so hopefully WASI support will be coming soon!

Hey guys! I don't know whether this issue is still relevant, but just wanted to let you know that the prelease version 0.7.0-pre.0 of rust-random/rand comes with wasm32-wasi support :-) So you can just specify it in your Cargo.toml as:

[dependencies]                                                                                                          
rand = "0.7.0-pre.0"

[huangjj27]

Hey guys! I don't know whether this issue is still relevant, but just wanted to let you know that the prelease version 0.7.0-pre.0 of rust-random/rand comes with wasm32-wasi support

Error has changed. and I found that getrandom should support the WASI. It just doesn't support for wasm32-unknown-wasi, but works with wasm32-wasi

thread 'main' panicked at 'could not initialize thread_rng: getrandom: unavailable', C:\Users\34937\.cargo\registry\src\mirrors.sjtug.sjtu.edu.cn-7a04d2510079875b\rand-0.7.0-pre.1\src\rngs\thread.rs:67:17
thread 'main' panicked at 'wasm trap occured: unreachable', src\bin\wasmer.rs:515:51

[syrusakbary]

This is fixed in the new version of rand: 0.7
rust-random/rand#715

Closing the issue