Trait wasmi_core::HostError

source ·

pub trait HostError: 'static + Display + Debug + DowncastSync { }

Expand description

Trait that allows the host to return custom error.

It should be useful for representing custom traps, troubles at instantiation time or other host specific conditions.

Types that implement this trait can automatically be converted to wasmi::Error and wasmi::Trap and will be represented as a boxed HostError. You can then use the various methods on wasmi::Error to get your custom error type back

Examples

use std::fmt;
use wasmi_core::{Trap, HostError};

#[derive(Debug)]
struct MyError {
    code: u32,
}

impl fmt::Display for MyError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "MyError, code={}", self.code)
    }
}

impl HostError for MyError { }

fn failable_fn() -> Result<(), Trap> {
    let my_error = MyError { code: 1312 };
    // Note how you can just convert your errors to `wasmi::Error`
    Err(my_error.into())
}

// Get a reference to the concrete error
match failable_fn() {
    Err(Trap::Host(host_error)) => {
        let my_error: &MyError = host_error.downcast_ref::<MyError>().unwrap();
        assert_eq!(my_error.code, 1312);
    }
    _ => panic!(),
}

// get the concrete error itself
match failable_fn() {
    Err(err) => {
        let my_error = match err {
            Trap::Host(host_error) => host_error.downcast::<MyError>().unwrap(),
            unexpected => panic!("expected host error but found: {}", unexpected),
        };
        assert_eq!(my_error.code, 1312);
    }
    _ => panic!(),
}