mirror of
https://github.com/denoland/deno.git
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122 lines
2.9 KiB
Rust
122 lines
2.9 KiB
Rust
// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
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pub(crate) type AtomicPtr<T> = *mut T;
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#[allow(unused)]
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pub(crate) struct RawBytes {
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ptr: *const u8,
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len: usize,
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// inlined "trait object"
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data: AtomicPtr<()>,
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vtable: &'static Vtable,
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}
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impl RawBytes {
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pub fn new_raw(
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ptr: *const u8,
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len: usize,
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data: AtomicPtr<()>,
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vtable: &'static Vtable,
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) -> bytes::Bytes {
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RawBytes {
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ptr,
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len,
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data,
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vtable,
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}
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.into()
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}
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}
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// Validate some bytes::Bytes layout assumptions at compile time.
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const _: () = {
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assert!(
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core::mem::size_of::<RawBytes>() == core::mem::size_of::<bytes::Bytes>(),
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);
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assert!(
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core::mem::align_of::<RawBytes>() == core::mem::align_of::<bytes::Bytes>(),
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);
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};
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#[allow(unused)]
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pub(crate) struct Vtable {
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/// fn(data, ptr, len)
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pub clone: unsafe fn(&AtomicPtr<()>, *const u8, usize) -> bytes::Bytes,
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/// fn(data, ptr, len)
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///
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/// takes `Bytes` to value
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pub to_vec: unsafe fn(&AtomicPtr<()>, *const u8, usize) -> Vec<u8>,
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/// fn(data, ptr, len)
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pub drop: unsafe fn(&mut AtomicPtr<()>, *const u8, usize),
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}
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impl From<RawBytes> for bytes::Bytes {
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fn from(b: RawBytes) -> Self {
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// SAFETY: RawBytes has the same layout as bytes::Bytes
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// this is tested below, both are composed of usize-d ptrs/values
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// thus aren't currently subject to rust's field re-ordering to minimize padding
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unsafe { std::mem::transmute(b) }
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use std::mem;
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const HELLO: &str = "hello";
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// ===== impl StaticVtable =====
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const STATIC_VTABLE: Vtable = Vtable {
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clone: static_clone,
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drop: static_drop,
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to_vec: static_to_vec,
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};
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unsafe fn static_clone(
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_: &AtomicPtr<()>,
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ptr: *const u8,
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len: usize,
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) -> bytes::Bytes {
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from_static(std::slice::from_raw_parts(ptr, len)).into()
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}
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unsafe fn static_to_vec(
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_: &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 slice = std::slice::from_raw_parts(ptr, len);
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slice.to_vec()
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}
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unsafe fn static_drop(_: &mut AtomicPtr<()>, _: *const u8, _: usize) {
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// nothing to drop for &'static [u8]
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}
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fn from_static(bytes: &'static [u8]) -> RawBytes {
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RawBytes {
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ptr: bytes.as_ptr(),
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len: bytes.len(),
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data: std::ptr::null_mut(),
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vtable: &STATIC_VTABLE,
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}
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}
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#[test]
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fn bytes_identity() {
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let b1: bytes::Bytes = from_static(HELLO.as_bytes()).into();
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let b2 = bytes::Bytes::from_static(HELLO.as_bytes());
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assert_eq!(b1, b2); // Values are equal
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}
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#[test]
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fn bytes_layout() {
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let u1: [usize; 4] =
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// SAFETY: ensuring layout is the same
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unsafe { mem::transmute(from_static(HELLO.as_bytes())) };
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let u2: [usize; 4] =
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// SAFETY: ensuring layout is the same
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unsafe { mem::transmute(bytes::Bytes::from_static(HELLO.as_bytes())) };
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assert_eq!(u1[..3], u2[..3]); // Struct bytes are equal besides Vtables
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}
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}
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