mirror of
https://github.com/denoland/deno.git
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114 lines
2.7 KiB
Rust
114 lines
2.7 KiB
Rust
// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
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use std::cell::Cell;
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use std::ops::Deref;
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use std::ops::DerefMut;
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/// A ZeroCopyBuf encapsulates a slice that's been borrowed from a JavaScript
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/// ArrayBuffer object. JavaScript objects can normally be garbage collected,
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/// but the existence of a ZeroCopyBuf inhibits this until it is dropped. It
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/// behaves much like an Arc<[u8]>.
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///
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/// # Cloning
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/// Cloning a ZeroCopyBuf does not clone the contents of the buffer,
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/// it creates a new reference to that buffer.
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///
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/// To actually clone the contents of the buffer do
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/// `let copy = Vec::from(&*zero_copy_buf);`
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#[derive(Clone)]
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pub struct ZeroCopyBuf {
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backing_store: v8::SharedRef<v8::BackingStore>,
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byte_offset: usize,
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byte_length: usize,
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}
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unsafe impl Send for ZeroCopyBuf {}
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impl ZeroCopyBuf {
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pub fn new<'s>(
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scope: &mut v8::HandleScope<'s>,
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view: v8::Local<v8::ArrayBufferView>,
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) -> Self {
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Self::try_new(scope, view).unwrap()
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}
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pub fn try_new<'s>(
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scope: &mut v8::HandleScope<'s>,
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view: v8::Local<v8::ArrayBufferView>,
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) -> Result<Self, v8::DataError> {
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let backing_store = view.buffer(scope).unwrap().get_backing_store();
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if backing_store.is_shared() {
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return Err(v8::DataError::BadType {
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actual: "shared ArrayBufferView",
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expected: "non-shared ArrayBufferView",
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});
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}
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let byte_offset = view.byte_offset();
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let byte_length = view.byte_length();
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Ok(Self {
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backing_store,
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byte_offset,
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byte_length,
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})
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}
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}
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impl Deref for ZeroCopyBuf {
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type Target = [u8];
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fn deref(&self) -> &[u8] {
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unsafe {
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get_backing_store_slice(
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&self.backing_store,
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self.byte_offset,
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self.byte_length,
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)
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}
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}
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}
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impl DerefMut for ZeroCopyBuf {
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fn deref_mut(&mut self) -> &mut [u8] {
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unsafe {
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get_backing_store_slice_mut(
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&self.backing_store,
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self.byte_offset,
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self.byte_length,
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)
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}
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}
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}
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impl AsRef<[u8]> for ZeroCopyBuf {
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fn as_ref(&self) -> &[u8] {
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&*self
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}
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}
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impl AsMut<[u8]> for ZeroCopyBuf {
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fn as_mut(&mut self) -> &mut [u8] {
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&mut *self
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}
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}
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unsafe fn get_backing_store_slice(
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backing_store: &v8::SharedRef<v8::BackingStore>,
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byte_offset: usize,
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byte_length: usize,
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) -> &[u8] {
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let cells: *const [Cell<u8>] =
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&backing_store[byte_offset..byte_offset + byte_length];
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let bytes = cells as *const [u8];
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&*bytes
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}
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#[allow(clippy::mut_from_ref)]
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unsafe fn get_backing_store_slice_mut(
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backing_store: &v8::SharedRef<v8::BackingStore>,
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byte_offset: usize,
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byte_length: usize,
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) -> &mut [u8] {
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let cells: *const [Cell<u8>] =
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&backing_store[byte_offset..byte_offset + byte_length];
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let bytes = cells as *const _ as *mut [u8];
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&mut *bytes
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}
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