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https://github.com/denoland/deno.git
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192 lines
6 KiB
Rust
192 lines
6 KiB
Rust
// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
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use std::ops::Deref;
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use std::ops::DerefMut;
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use std::ops::Range;
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use std::rc::Rc;
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use crate::error::value_to_type_str;
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use super::rawbytes;
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use super::transl8::FromV8;
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/// A V8Slice 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 V8Slice 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 V8Slice 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 V8Slice {
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pub(crate) store: v8::SharedRef<v8::BackingStore>,
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pub(crate) range: Range<usize>,
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}
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// SAFETY: unsafe trait must have unsafe implementation
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unsafe impl Send for V8Slice {}
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impl V8Slice {
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pub fn from_buffer(
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buffer: v8::Local<v8::ArrayBuffer>,
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range: Range<usize>,
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) -> Result<Self, v8::DataError> {
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let store = buffer.get_backing_store();
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if 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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Ok(Self { store, range })
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}
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fn as_slice(&self) -> &[u8] {
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// SAFETY: v8::SharedRef<v8::BackingStore> is similar to Arc<[u8]>,
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// it points to a fixed continuous slice of bytes on the heap.
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// We assume it's initialized and thus safe to read (though may not contain meaningful data)
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unsafe { &*(&self.store[self.range.clone()] as *const _ as *const [u8]) }
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}
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fn as_slice_mut(&mut self) -> &mut [u8] {
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#[allow(clippy::cast_ref_to_mut)]
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// SAFETY: v8::SharedRef<v8::BackingStore> is similar to Arc<[u8]>,
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// it points to a fixed continuous slice of bytes on the heap.
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// It's safe-ish to mutate concurrently because it can not be
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// shrunk/grown/moved/reallocated, thus avoiding dangling refs (unlike a Vec).
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// Concurrent writes can't lead to meaningful structural invalidation
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// since we treat them as opaque buffers / "bags of bytes",
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// concurrent mutation is simply an accepted fact of life.
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// And in practice V8Slices also do not have overallping read/write phases.
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// TLDR: permissive interior mutability on slices of bytes is "fine"
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unsafe {
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&mut *(&self.store[self.range.clone()] as *const _ as *mut [u8])
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}
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}
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}
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pub(crate) fn to_ranged_buffer<'s>(
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scope: &mut v8::HandleScope<'s>,
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value: v8::Local<v8::Value>,
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) -> Result<(v8::Local<'s, v8::ArrayBuffer>, Range<usize>), v8::DataError> {
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if let Ok(view) = v8::Local::<v8::ArrayBufferView>::try_from(value) {
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let (offset, len) = (view.byte_offset(), view.byte_length());
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let buffer = view.buffer(scope).ok_or(v8::DataError::NoData {
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expected: "view to have a buffer",
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})?;
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let buffer = v8::Local::new(scope, buffer); // recreate handle to avoid lifetime issues
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return Ok((buffer, offset..offset + len));
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}
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let b: v8::Local<v8::ArrayBuffer> = value.try_into()?;
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let b = v8::Local::new(scope, b); // recreate handle to avoid lifetime issues
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Ok((b, 0..b.byte_length()))
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}
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impl FromV8 for V8Slice {
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fn from_v8(
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scope: &mut v8::HandleScope,
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value: v8::Local<v8::Value>,
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) -> Result<Self, crate::Error> {
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match to_ranged_buffer(scope, value) {
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Ok((b, r)) => {
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if b.get_backing_store().is_resizable_by_user_javascript() {
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return Err(crate::Error::ResizableBackingStoreNotSupported);
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}
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Self::from_buffer(b, r)
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.map_err(|_| crate::Error::ExpectedBuffer(value_to_type_str(value)))
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}
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Err(_) => Err(crate::Error::ExpectedBuffer(value_to_type_str(value))),
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}
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}
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}
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impl Deref for V8Slice {
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type Target = [u8];
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fn deref(&self) -> &[u8] {
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self.as_slice()
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}
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}
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impl DerefMut for V8Slice {
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fn deref_mut(&mut self) -> &mut [u8] {
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self.as_slice_mut()
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}
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}
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impl AsRef<[u8]> for V8Slice {
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fn as_ref(&self) -> &[u8] {
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self.as_slice()
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}
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}
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impl AsMut<[u8]> for V8Slice {
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fn as_mut(&mut self) -> &mut [u8] {
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self.as_slice_mut()
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}
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}
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// Implement V8Slice -> bytes::Bytes
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impl V8Slice {
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fn rc_into_byte_parts(self: Rc<Self>) -> (*const u8, usize, *mut V8Slice) {
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let (ptr, len) = {
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let slice = self.as_ref();
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(slice.as_ptr(), slice.len())
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};
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let rc_raw = Rc::into_raw(self);
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let data = rc_raw as *mut V8Slice;
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(ptr, len, data)
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}
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}
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impl From<V8Slice> for bytes::Bytes {
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fn from(v8slice: V8Slice) -> Self {
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let (ptr, len, data) = Rc::new(v8slice).rc_into_byte_parts();
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rawbytes::RawBytes::new_raw(ptr, len, data.cast(), &V8SLICE_VTABLE)
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}
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}
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// NOTE: in the limit we could avoid extra-indirection and use the C++ shared_ptr
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// but we can't store both the underlying data ptr & ctrl ptr ... so instead we
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// use a shared rust ptr (Rc/Arc) that itself controls the C++ shared_ptr
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const V8SLICE_VTABLE: rawbytes::Vtable = rawbytes::Vtable {
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clone: v8slice_clone,
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drop: v8slice_drop,
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to_vec: v8slice_to_vec,
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};
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unsafe fn v8slice_clone(
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data: &rawbytes::AtomicPtr<()>,
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ptr: *const u8,
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len: usize,
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) -> bytes::Bytes {
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let rc = Rc::from_raw(*data as *const V8Slice);
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let (_, _, data) = rc.clone().rc_into_byte_parts();
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std::mem::forget(rc);
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// NOTE: `bytes::Bytes` does bounds checking so we trust its ptr, len inputs
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// and must use them to allow cloning Bytes it has sliced
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rawbytes::RawBytes::new_raw(ptr, len, data.cast(), &V8SLICE_VTABLE)
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}
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unsafe fn v8slice_to_vec(
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data: &rawbytes::AtomicPtr<()>,
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ptr: *const u8,
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len: usize,
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) -> Vec<u8> {
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let rc = Rc::from_raw(*data as *const V8Slice);
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std::mem::forget(rc);
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// NOTE: `bytes::Bytes` does bounds checking so we trust its ptr, len inputs
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// and must use them to allow cloning Bytes it has sliced
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Vec::from_raw_parts(ptr as _, len, len)
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}
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unsafe fn v8slice_drop(
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data: &mut rawbytes::AtomicPtr<()>,
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_: *const u8,
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_: usize,
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) {
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drop(Rc::from_raw(*data as *const V8Slice))
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}
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