Stream: general

Topic: ✔ host?/wasi-logging

Zeeshan Lakhani (Jan 10 2024 at 17:53):

Howdy all, I've been able to implement my own host functions and use wit-deps to import them for use in a set of wasm guest functions. However, I'm trying to understand how to use wasi:logging in our embedding of wasmtime. I'm getting the classic:

called `Result::unwrap()` on an `Err` value: WasmRuntime(import `wasi:logging/logging` has the wrong type

Caused by:
    0: instance export `log` has the wrong type
    1: expected func found nothing

so I figured I'd need with on the wasmtime bindgen and point to bindings for logging in the preview, and then add to the linker? But, I'm not sure what that is for logging? Any thoughts?

Zeeshan Lakhani (Jan 10 2024 at 18:06):

I also tried to impl it for my State/Context, but ran into lifetime errors (if that were the path). I've looked at Wasiclouds's impl, but figured that's more specific to their platform. Seemingly, there's no impl of the logging interface in preview tho. Anyhow, any related examples would help.

Pat Hickey (Jan 10 2024 at 18:16):

there is no implementation of wasi:logging provided by wasmtime-wasi, you'd need to write one

Pat Hickey (Jan 10 2024 at 18:16):

where are you getting the definition of wasi:logging?

Zeeshan Lakhani (Jan 10 2024 at 18:18):

@Pat Hickey yep, seeing this too https://github.com/bytecodealliance/ComponentizeJS/issues/6, i figured ok. I was pulling via wit-deps like so:

logging = "https://github.com/WebAssembly/wasi-logging/archive/main.tar.gz"

Pat Hickey (Jan 10 2024 at 18:19):

ah, that issue is pretty far out of date, before we had set aside wasi logging for stdout/stderr in favor of using a more posix-like stream representation defined in the wasi-cli package

Pat Hickey (Jan 10 2024 at 18:19):

i'd advise not using wasi-logging if you can avoid it

Zeeshan Lakhani (Jan 10 2024 at 18:20):

@Pat Hickey should i still use the interface to be "compatible" or just use my own variation anyhow?

Pat Hickey (Jan 10 2024 at 18:20):

since, afaik, there are no runtimes providing it, nor any client code thats using it

Zeeshan Lakhani (Jan 10 2024 at 18:20):

ah interesting.

Pat Hickey (Jan 10 2024 at 18:20):

oh, so if you are looking for some logging solution, and you were just going to define something just like wasi-logging on your own and provide both the host and client side

Pat Hickey (Jan 10 2024 at 18:20):

then sure, use wasi-logging as the definition of that interface if it suits your needs

Pat Hickey (Jan 10 2024 at 18:21):

but be aware that is forging new ground, you'll be essentially the first person to do so (since very early prototypes which we since set aside to take other paths, anyway)

Zeeshan Lakhani (Jan 10 2024 at 18:22):

@Pat Hickey yep. ok. yeah, i'll go that route. That was my first intention Let me try that again (that was my first route) and see if i don't run into issues.

@Pat Hickey haha. yep. no worries. Thanks for at least re-affirming my thoughts/etc. Having you and @Alex Crichton help out is awesome. thanks beyond thanks tbh.

Pat Hickey (Jan 10 2024 at 18:24):

sure thing, happy to help

Zeeshan Lakhani (Jan 10 2024 at 18:26):

ok, so the lifetime error I run into:

/// Basic helpers interface.
interface helpers {
    record time {
        seconds: u64,
        milliseconds: u32,
        nanoseconds: u32,
    }

    /// Get current time in sub-seconds.
    get-current-time: func() -> time;
    /// Basic `print` helper.
    print: func(msg: string);
}

world imports {
    import wasi:logging/logging;
    import helpers;
}

is how i'm trying to bring in the current logging interface into my own embedding.

Zeeshan Lakhani (Jan 10 2024 at 18:27):

then:

impl wasi::logging::logging::Host for State {
    /// Log a message.
    fn log(
        &mut self,
        level: wasi::logging::logging::Level,
        context: String,
        message: String,
    ) -> wasmtime::Result<()> {
        println!("{message}");
        Ok(())
    }
}

Zeeshan Lakhani (Jan 10 2024 at 18:27):

throws me

error[E0195]: lifetime parameters or bounds on method `log` do not match the trait declaration
  --> homestar-wasm/src/wasmtime/host/helpers.rs:32:11
   |
32 |       fn log(
   |             ^ lifetimes do not match method in trait
   |
  ::: homestar-wasm/src/wasmtime/world.rs:28:1
   |
28 | / wasmtime::component::bindgen!({
29 | |     world: "imports",
30 | |     tracing: true,
31 | |     async: true
32 | | });
   | |  -
   | |  |
   | |__lifetimes in impl do not match this method in trait
   |    this bound might be missing in the impl```

Zeeshan Lakhani (Jan 10 2024 at 18:28):

so maybe how i'm using the import is wrong here?

Zeeshan Lakhani (Jan 10 2024 at 18:28):

the other implements work fine.

Zeeshan Lakhani (Jan 10 2024 at 18:28):

I would like to use the interface off deps this way without inlining it within my custom wit.

Pat Hickey (Jan 10 2024 at 18:28):

i expect that the wasmtime::component::bindgen! impl you are using with wasi-logging has async: true turned on, and you need to decorate your impl with #[async_trait] at the top and make it an async fn log

Zeeshan Lakhani (Jan 10 2024 at 18:28):

yeah, I think it errore'd w/ that as well, one sec.

Zeeshan Lakhani (Jan 10 2024 at 18:29):

ah yeah, nvm, dum, dum, that does work. @Pat Hickey :).Actually another issue crept up, but one for me to fix. Thank you.

Notification Bot (Jan 10 2024 at 18:30):

Zeeshan Lakhani has marked this topic as resolved.

Zeeshan Lakhani (Jan 10 2024 at 18:33):

got it all working. thanks again @Pat Hickey (not sure what i missed adding async before tbh, but always updating code haha).

Pat Hickey (Jan 10 2024 at 19:02):

np that one is an uncharacteristic bad error message from rustc

Last updated: Dec 23 2024 at 12:05 UTC