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// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
use std::cell::Cell;
use std::ops::Deref;
use std::ops::DerefMut;
/// A ZeroCopyBuf encapsulates a slice that's been borrowed from a JavaScript
/// ArrayBuffer object. JavaScript objects can normally be garbage collected,
/// but the existence of a ZeroCopyBuf inhibits this until it is dropped. It
/// behaves much like an Arc<[u8]>.
///
/// # Cloning
/// Cloning a ZeroCopyBuf does not clone the contents of the buffer,
/// it creates a new reference to that buffer.
///
/// To actually clone the contents of the buffer do
/// `let copy = Vec::from(&*zero_copy_buf);`
#[derive(Clone)]
pub struct ZeroCopyBuf {
backing_store: v8::SharedRef<v8::BackingStore>,
byte_offset: usize,
byte_length: usize,
}
unsafe impl Send for ZeroCopyBuf {}
impl ZeroCopyBuf {
pub fn new<'s>(
scope: &mut v8::HandleScope<'s>,
view: v8::Local<v8::ArrayBufferView>,
) -> Self {
Self::try_new(scope, view).unwrap()
}
pub fn try_new<'s>(
scope: &mut v8::HandleScope<'s>,
view: v8::Local<v8::ArrayBufferView>,
) -> Result<Self, v8::DataError> {
let backing_store = view.buffer(scope).unwrap().get_backing_store();
if backing_store.is_shared() {
return Err(v8::DataError::BadType {
actual: "shared ArrayBufferView",
expected: "non-shared ArrayBufferView",
});
}
let byte_offset = view.byte_offset();
let byte_length = view.byte_length();
Ok(Self {
backing_store,
byte_offset,
byte_length,
})
}
}
impl Deref for ZeroCopyBuf {
type Target = [u8];
fn deref(&self) -> &[u8] {
unsafe {
get_backing_store_slice(
&self.backing_store,
self.byte_offset,
self.byte_length,
)
}
}
}
impl DerefMut for ZeroCopyBuf {
fn deref_mut(&mut self) -> &mut [u8] {
unsafe {
get_backing_store_slice_mut(
&self.backing_store,
self.byte_offset,
self.byte_length,
)
}
}
}
impl AsRef<[u8]> for ZeroCopyBuf {
fn as_ref(&self) -> &[u8] {
&*self
}
}
impl AsMut<[u8]> for ZeroCopyBuf {
fn as_mut(&mut self) -> &mut [u8] {
&mut *self
}
}
unsafe fn get_backing_store_slice(
backing_store: &v8::SharedRef<v8::BackingStore>,
byte_offset: usize,
byte_length: usize,
) -> &[u8] {
let cells: *const [Cell<u8>] =
&backing_store[byte_offset..byte_offset + byte_length];
let bytes = cells as *const [u8];
&*bytes
}
#[allow(clippy::mut_from_ref)]
unsafe fn get_backing_store_slice_mut(
backing_store: &v8::SharedRef<v8::BackingStore>,
byte_offset: usize,
byte_length: usize,
) -> &mut [u8] {
let cells: *const [Cell<u8>] =
&backing_store[byte_offset..byte_offset + byte_length];
let bytes = cells as *const _ as *mut [u8];
&mut *bytes
}
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