Stream: wasi

Topic: ✔ Trampoline::{Future,Stream}{Read,Write} canon opts

Victor Adossi (Sep 03 2025 at 17:33):

Hey all, quick question -- it seems like wasmtime_environ::Trampoline::StreamWrite and friends have async_ set in theircanon opts (via the options: OptionsIndex member).

I'm pulling the opts like this:

                let options = self
                    .component // &wasmtime_environ::Component
                    .options
                    .get(*options)
                    .expect("failed to find options");

When I get the CanonicalOptions object out, it's got async_ set and no callback (which is invalid)

Intuitively, the canon functions are clearly not async, so I'm thinking the issue here is that async_ is set on the CanonicalOptions that got created?

Alternatively, if I read this line in the canonopt validation section a bit differently:

• :shuffle: callback - the function has type (func (param i32 i32 i32) (result i32)) and cannot be present without async and is only allowed with canon lift

Maybe the intent was that it's fine for async_ to be set, but callback can be missing (and I should basically only check that non-async things don't have a callback, not that all async things must have a callback).

Obviously during canon_lift the callback is quite required, but the canon function is a little blurrier...

I'm leaning towards the idea that the CanonicalOptions being set/saved for the relevant Trampoline:: members should not have async_ set in the first place.

Alex Crichton (Sep 03 2025 at 17:39):

ah yeah this is where each option is a bit overloaded in the context of each intrinsic

Alex Crichton (Sep 03 2025 at 17:40):

but async_ means whether these intrinsics are blocking or not basically for stream/future read/write

Alex Crichton (Sep 03 2025 at 17:40):

and the validation is different from canon lift'd functions for now (in the future though we might allow just-async_ on functions)

Victor Adossi (Sep 03 2025 at 17:40):

Ah OK, I thought that might be the case -- that somehow async_ meant something different in this context

Victor Adossi (Sep 03 2025 at 17:41):

OK, great, I've got that implemented -- I just disabled that last check for stream.write/etc and kept all the other ones on

Alex Crichton (Sep 03 2025 at 17:41):

FWIW you can skip all the validation bits in jco b/c wasmparser/wasmtime-environ do all that for you

Victor Adossi (Sep 03 2025 at 17:42):

Even better, I'll do that!

Victor Adossi (Sep 03 2025 at 17:44):

Thanks for the help! I think this makes sense now

Notification Bot (Sep 03 2025 at 17:44):

Victor Adossi has marked this topic as resolved.

Last updated: Dec 06 2025 at 06:05 UTC