wasm: aws-config uses fastrand, which needs a feature patch for WASM compatibility

[simbleau]

Describe the bug

To be fixed with #59.

Attempting to compile anything using aws-config on WASM will fail since it uses fastrand.

See the Cargo.toml.

fastrand has a dependency on rand, and rand uses getrandom. getrandom needs to be compiled with the js feature.

Fortunately, fastrand has the undocumented js feature flag to fix this for us. We just need to include it for wasm.

Expected Behavior

Successful compile.

Current Behavior

Fails to compile.

14:35 simbleau on main ~ wasm-pack test --node
[INFO]: 🎯  Checking for the Wasm target...
   Compiling getrandom v0.2.10
error: the wasm*-unknown-unknown targets are not supported by default, you may need to enable the "js" feature. For more information see: https://docs.rs/getrandom/#webassembly-support
   --> /Users/simbleau/.cargo/registry/src/index.crates.io-6f17d22bba15001f/getrandom-0.2.10/src/lib.rs:285:9
    |
285 | /         compile_error!("the wasm*-unknown-unknown targets are not supported by \
286 | |                         default, you may need to enable the \"js\" feature. \
287 | |                         For more information see: \
288 | |                         https://docs.rs/getrandom/#webassembly-support");
    | |________________________________________________________________________^

Reproduction Steps

• Create a rust lib project.
• Include in cargo.toml deps: aws-config = { version = "0.55", default-features = false }
• Compile.

Possible Solution

Here's the fix to the Cargo.toml:

[target.'cfg(all(any(target_arch = "wasm32", target_arch = "wasm64"), target_os = "unknown"))'.dependencies]
fastrand = { version = "2", features = ["js"] }

[target.'cfg(not(any(target_arch = "wasm32", target_arch = "wasm64"), target_os = "unknown"))'.dependencies]
fastrand = "2"

Additional Information/Context

No response

Version

Main

Environment details (OS name and version, etc.)

MacOS Ventura

Logs

No response

[Velfi]

Hey @simbleau, thanks for submitting this issue. We'll add it to our backlog.

To whomever picks this one up: It looks like we should consider making the source of randomness configurable, just like we did for the async sleep impl and the time source.

[jdisanti]

getrandom is also an optional dependency for fastrand, so we could consider disabling it as well. I ran into other issues with getrandom last week and started removing it. I'll check to see if it's completely gone for the next release.

[jdisanti]

It looks like in the latest code, rand and getrandom are no longer pulled in, so this should be resolved with the next release.

[jdisanti]

I think you can work around this in the current release of aws-config by setting no-default-features.

[simbleau]

I think you can work around this in the current release of aws-config by setting no-default-features.

By current release, do you mean 0.55?

If so, then that is not correct. I didn't have default features (in the reproduction steps).

[jdisanti]

Hmmm. OK, I didn't look into that thoroughly enough. I saw that our integration test for webassembly was depending on aws-config with no default features, and it is currently passing, but that may be a more recent development.

Edit: I think I see why: the test is specifically targeting wasm32-wasi. We need to have one for wasm32-unknown-unknown.

[jdisanti]

This has been fixed in the August 3rd release.

[github-actions]

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