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// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license. | ||
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use crate::error::StdAnyError; | ||
use crate::runtime::ops; | ||
use std::convert::Infallible; | ||
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/// A conversion from a rust value to a v8 value. | ||
/// | ||
/// When passing data from Rust into JS, either | ||
/// via an op or by calling a JS function directly, | ||
/// you need to serialize the data into a native | ||
/// V8 value. When using the [`op2`][deno_core::op2] macro, the return | ||
/// value is converted to a `v8::Local<Value>` automatically, | ||
/// and the strategy for conversion is controlled by attributes | ||
/// like `#[smi]`, `#[number]`, `#[string]`. For types with support | ||
/// built-in to the op2 macro, like primitives, strings, and buffers, | ||
/// these attributes are sufficient and you don't need to worry about this trait. | ||
/// | ||
/// If, however, you want to return a custom type from an op, or | ||
/// simply want more control over the conversion process, | ||
/// you can implement the `ToV8` trait. This allows you the | ||
/// choose the best serialization strategy for your specific use case. | ||
/// You can then use the `#[to_v8]` attribute to indicate | ||
/// that the `#[op2]` macro should call your implementation for the conversion. | ||
/// | ||
/// # Example | ||
/// | ||
/// ```ignore | ||
/// use deno_core::ToV8; | ||
/// use deno_core::convert::Smi; | ||
/// use deno_core::op2; | ||
/// | ||
/// struct Foo(i32); | ||
/// | ||
/// impl<'a> ToV8<'a> for Foo { | ||
/// // This conversion can never fail, so we use `Infallible` as the error type. | ||
/// // Any error type that implements `std::error::Error` can be used here. | ||
/// type Error = std::convert::Infallible; | ||
/// | ||
/// fn to_v8(self, scope: &mut v8::HandleScope<'a>) -> Result<v8::Local<'a, v8::Value>, Self::Error> { | ||
/// // For performance, pass this value as a `v8::Integer` (i.e. a `smi`). | ||
/// // The `Smi` wrapper type implements this conversion for you. | ||
/// Smi(self.0).to_v8(scope) | ||
/// } | ||
/// } | ||
/// | ||
/// // using the `#[to_v8]` attribute tells the `op2` macro to call this implementation. | ||
/// #[op2] | ||
/// #[to_v8] | ||
/// fn op_foo() -> Foo { | ||
/// Foo(42) | ||
/// } | ||
/// ``` | ||
/// | ||
/// # Performance Notes | ||
/// ## Structs | ||
/// The natural representation of a struct in JS is an object with fields | ||
/// corresponding the struct. This, however, is a performance footgun and | ||
/// you should avoid creating and passing objects to V8 whenever possible. | ||
/// In general, if you need to pass a compound type to JS, it is more performant to serialize | ||
/// to a tuple (a `v8::Array`) rather than an object. | ||
/// Object keys are V8 strings, and strings are expensive to pass to V8 | ||
/// and they have to be managed by the V8 garbage collector. | ||
/// Tuples, on the other hand, are keyed by `smi`s, which are immediates | ||
/// and don't require allocation or garbage collection. | ||
pub trait ToV8<'a> { | ||
type Error: std::error::Error + Send + Sync + 'static; | ||
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/// Converts the value to a V8 value. | ||
fn to_v8( | ||
self, | ||
scope: &mut v8::HandleScope<'a>, | ||
) -> Result<v8::Local<'a, v8::Value>, Self::Error>; | ||
} | ||
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/// A conversion from a v8 value to a rust value. | ||
/// | ||
/// When writing a op, or otherwise writing a function in Rust called | ||
/// from JS, arguments passed from JS are represented as [`v8::Local<v8::Value>>`][deno_core::v8::Value]. | ||
/// To convert these values into custom Rust types, you can implement the [`FromV8`] trait. | ||
/// | ||
/// Once you've implemented this trait, you can use the `#[from_v8]` attribute | ||
/// to tell the [`op2`][deno_core::op2] macro to use your implementation to convert the argument | ||
/// to the desired type. | ||
/// | ||
/// # Example | ||
/// | ||
/// ```ignore | ||
/// use deno_core::FromV8; | ||
/// use deno_core::convert::Smi; | ||
/// use deno_core::op2; | ||
/// | ||
/// struct Foo(i32); | ||
/// | ||
/// impl<'a> FromV8<'a> for Foo { | ||
/// // This conversion can fail, so we use `deno_core::error::StdAnyError` as the error type. | ||
/// // Any error type that implements `std::error::Error` can be used here. | ||
/// type Error = deno_core::error::StdAnyError; | ||
/// | ||
/// fn from_v8(scope: &mut v8::HandleScope<'a>, value: v8::Local<'a, v8::Value>) -> Result<Self, Self::Error> { | ||
/// /// We expect this value to be a `v8::Integer`, so we use the [`Smi`][deno_core::convert::Smi] wrapper type to convert it. | ||
/// Smi::from_v8(scope, value).map(|Smi(v)| Foo(v)) | ||
/// } | ||
/// } | ||
/// | ||
/// // using the `#[from_v8]` attribute tells the `op2` macro to call this implementation. | ||
/// #[op2] | ||
/// fn op_foo(#[from_v8] foo: Foo) { | ||
/// let Foo(_) = foo; | ||
/// } | ||
/// ``` | ||
pub trait FromV8<'a>: Sized { | ||
type Error: std::error::Error + Send + Sync + 'static; | ||
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/// Converts a V8 value to a Rust value. | ||
fn from_v8( | ||
scope: &mut v8::HandleScope<'a>, | ||
value: v8::Local<'a, v8::Value>, | ||
) -> Result<Self, Self::Error>; | ||
} | ||
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// impls | ||
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#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)] | ||
/// Marks a numeric type as being serialized as a v8 `smi` in a `v8::Integer`. | ||
#[repr(transparent)] | ||
pub struct Smi<T: SmallInt>(pub T); | ||
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/// A trait for types that can represent a JS `smi`. | ||
pub trait SmallInt { | ||
const NAME: &'static str; | ||
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#[allow(clippy::wrong_self_convention)] | ||
fn as_i32(self) -> i32; | ||
fn from_i32(value: i32) -> Self; | ||
} | ||
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macro_rules! impl_smallint { | ||
(for $($t:ty),*) => { | ||
$( | ||
impl SmallInt for $t { | ||
const NAME: &'static str = stringify!($t); | ||
#[allow(clippy::wrong_self_convention)] | ||
#[inline(always)] | ||
fn as_i32(self) -> i32 { | ||
self as _ | ||
} | ||
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#[inline(always)] | ||
fn from_i32(value: i32) -> Self { | ||
value as _ | ||
} | ||
} | ||
)* | ||
}; | ||
} | ||
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impl_smallint!(for u8, u16, u32, u64, usize, i8, i16, i32, i64, isize); | ||
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impl<'a, T: SmallInt> ToV8<'a> for Smi<T> { | ||
type Error = Infallible; | ||
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#[inline] | ||
fn to_v8( | ||
self, | ||
scope: &mut v8::HandleScope<'a>, | ||
) -> Result<v8::Local<'a, v8::Value>, Self::Error> { | ||
Ok(v8::Integer::new(scope, self.0.as_i32()).into()) | ||
} | ||
} | ||
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impl<'a, T: SmallInt> FromV8<'a> for Smi<T> { | ||
type Error = StdAnyError; | ||
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#[inline] | ||
fn from_v8( | ||
_scope: &mut v8::HandleScope<'a>, | ||
value: v8::Local<'a, v8::Value>, | ||
) -> Result<Self, Self::Error> { | ||
let v = crate::runtime::ops::to_i32_option(&value).ok_or_else(|| { | ||
crate::error::type_error(format!("Expected {}", T::NAME)) | ||
})?; | ||
Ok(Smi(T::from_i32(v))) | ||
} | ||
} | ||
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#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)] | ||
/// Marks a numeric type as being serialized as a v8 `number` in a `v8::Number`. | ||
#[repr(transparent)] | ||
pub struct Number<T: Numeric>(pub T); | ||
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/// A trait for types that can represent a JS `number`. | ||
pub trait Numeric: Sized { | ||
const NAME: &'static str; | ||
#[allow(clippy::wrong_self_convention)] | ||
fn as_f64(self) -> f64; | ||
fn from_value(value: &v8::Value) -> Option<Self>; | ||
} | ||
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macro_rules! impl_numeric { | ||
($($t:ty : $from: path ),*) => { | ||
$( | ||
impl Numeric for $t { | ||
const NAME: &'static str = stringify!($t); | ||
#[inline(always)] | ||
fn from_value(value: &v8::Value) -> Option<Self> { | ||
$from(value).map(|v| v as _) | ||
} | ||
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#[allow(clippy::wrong_self_convention)] | ||
#[inline(always)] | ||
fn as_f64(self) -> f64 { | ||
self as _ | ||
} | ||
} | ||
)* | ||
}; | ||
} | ||
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impl_numeric!( | ||
f32 : ops::to_f32_option, | ||
f64 : ops::to_f64_option, | ||
u32 : ops::to_u32_option, | ||
u64 : ops::to_u64_option, | ||
usize : ops::to_u64_option, | ||
i32 : ops::to_i32_option, | ||
i64 : ops::to_i64_option, | ||
isize : ops::to_i64_option | ||
); | ||
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impl<'a, T: Numeric> ToV8<'a> for Number<T> { | ||
type Error = Infallible; | ||
#[inline] | ||
fn to_v8( | ||
self, | ||
scope: &mut v8::HandleScope<'a>, | ||
) -> Result<v8::Local<'a, v8::Value>, Self::Error> { | ||
Ok(v8::Number::new(scope, self.0.as_f64()).into()) | ||
} | ||
} | ||
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impl<'a, T: Numeric> FromV8<'a> for Number<T> { | ||
type Error = StdAnyError; | ||
#[inline] | ||
fn from_v8( | ||
_scope: &mut v8::HandleScope<'a>, | ||
value: v8::Local<'a, v8::Value>, | ||
) -> Result<Self, Self::Error> { | ||
T::from_value(&value).map(Number).ok_or_else(|| { | ||
crate::error::type_error(format!("Expected {}", T::NAME)).into() | ||
}) | ||
} | ||
} | ||
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impl<'a> ToV8<'a> for bool { | ||
type Error = Infallible; | ||
#[inline] | ||
fn to_v8( | ||
self, | ||
scope: &mut v8::HandleScope<'a>, | ||
) -> Result<v8::Local<'a, v8::Value>, Self::Error> { | ||
Ok(v8::Boolean::new(scope, self).into()) | ||
} | ||
} | ||
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impl<'a> FromV8<'a> for bool { | ||
type Error = Infallible; | ||
#[inline] | ||
fn from_v8( | ||
_scope: &mut v8::HandleScope<'a>, | ||
value: v8::Local<'a, v8::Value>, | ||
) -> Result<Self, Self::Error> { | ||
Ok(value.is_true()) | ||
} | ||
} |
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