wasmi/src/host.rs

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use std::any::TypeId;
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use value::{RuntimeValue, TryInto};
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use Error;
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/// Safe wrapper for list of arguments.
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#[derive(Debug)]
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pub struct RuntimeArgs<'a>(&'a [RuntimeValue]);
impl<'a> From<&'a [RuntimeValue]> for RuntimeArgs<'a> {
fn from(inner: &'a [RuntimeValue]) -> Self {
RuntimeArgs(inner)
}
}
impl<'a> RuntimeArgs<'a> {
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/// Extract argument by index `idx` returning error if cast is invalid or not enough arguments
pub fn nth<T>(&self, idx: usize) -> Result<T, Error> where RuntimeValue: TryInto<T, Error> {
Ok(self.nth_value(idx)?.try_into().map_err(|_| Error::Value("Invalid argument cast".to_owned()))?)
}
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/// Extract argument as a runtime value by index `idx` returning error is not enough arguments
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pub fn nth_value(&self, idx: usize) -> Result<RuntimeValue, Error> {
if self.0.len() <= idx {
return Err(Error::Value("Invalid argument index".to_owned()));
}
Ok(self.0[idx])
}
/// Total number of arguments
pub fn len(&self) -> usize {
self.0.len()
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}
}
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/// Custom user error.
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pub trait HostError: 'static + ::std::fmt::Display + ::std::fmt::Debug + Send + Sync {
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#[doc(hidden)]
fn __private_get_type_id__(&self) -> TypeId {
TypeId::of::<Self>()
}
}
impl HostError {
/// Attempt to downcast this `HostError` to a concrete type by reference.
pub fn downcast_ref<T: HostError>(&self) -> Option<&T> {
if self.__private_get_type_id__() == TypeId::of::<T>() {
unsafe { Some(&*(self as *const HostError as *const T)) }
} else {
None
}
}
/// Attempt to downcast this `HostError` to a concrete type by mutable
/// reference.
pub fn downcast_mut<T: HostError>(&mut self) -> Option<&mut T> {
if self.__private_get_type_id__() == TypeId::of::<T>() {
unsafe { Some(&mut *(self as *mut HostError as *mut T)) }
} else {
None
}
}
}
pub trait Externals {
fn invoke_index(
&mut self,
index: usize,
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args: RuntimeArgs,
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) -> Result<Option<RuntimeValue>, Error>;
}
pub struct NopExternals;
impl Externals for NopExternals {
fn invoke_index(
&mut self,
_index: usize,
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_args: RuntimeArgs,
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) -> Result<Option<RuntimeValue>, Error> {
Err(Error::Trap("invoke index on no-op externals".into()))
}
}
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#[cfg(test)]
mod tests {
use value::RuntimeValue;
use super::RuntimeArgs;
#[test]
fn i32_runtime_args() {
let args: RuntimeArgs = (&[RuntimeValue::I32(0)][..]).into();
let val: i32 = args.nth(0).unwrap();
assert_eq!(val, 0);
}
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#[test]
fn i64_invalid_arg_cast() {
let args: RuntimeArgs = (&[RuntimeValue::I64(90534534545322)][..]).into();
assert!(args.nth::<i32>(0).is_err());
}
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}