98 lines
2.6 KiB
Rust
98 lines
2.6 KiB
Rust
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use core::ops;
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/// A specialized copy-on-write byte string.
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///
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/// The purpose of this type is to permit usage of a "borrowed or owned
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/// byte string" in a way that keeps std/no-std compatibility. That is, in
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/// no-std mode, this type devolves into a simple &[u8] with no owned variant
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/// available. We can't just use a plain Cow because Cow is not in core.
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#[derive(Clone, Debug)]
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pub struct CowBytes<'a>(Imp<'a>);
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// N.B. We don't use std::borrow::Cow here since we can get away with a
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// Box<[u8]> for our use case, which is 1/3 smaller than the Vec<u8> that
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// a Cow<[u8]> would use.
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#[cfg(feature = "std")]
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#[derive(Clone, Debug)]
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enum Imp<'a> {
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Borrowed(&'a [u8]),
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Owned(Box<[u8]>),
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}
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#[cfg(not(feature = "std"))]
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#[derive(Clone, Debug)]
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struct Imp<'a>(&'a [u8]);
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impl<'a> ops::Deref for CowBytes<'a> {
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type Target = [u8];
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#[inline(always)]
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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<'a> CowBytes<'a> {
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/// Create a new borrowed CowBytes.
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#[inline(always)]
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pub fn new<B: ?Sized + AsRef<[u8]>>(bytes: &'a B) -> CowBytes<'a> {
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CowBytes(Imp::new(bytes.as_ref()))
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}
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/// Create a new owned CowBytes.
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#[cfg(feature = "std")]
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#[inline(always)]
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pub fn new_owned(bytes: Box<[u8]>) -> CowBytes<'static> {
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CowBytes(Imp::Owned(bytes))
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}
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/// Return a borrowed byte string, regardless of whether this is an owned
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/// or borrowed byte string internally.
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#[inline(always)]
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pub fn as_slice(&self) -> &[u8] {
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self.0.as_slice()
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}
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/// Return an owned version of this copy-on-write byte string.
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///
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/// If this is already an owned byte string internally, then this is a
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/// no-op. Otherwise, the internal byte string is copied.
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#[cfg(feature = "std")]
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#[inline(always)]
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pub fn into_owned(self) -> CowBytes<'static> {
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match self.0 {
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Imp::Borrowed(b) => CowBytes::new_owned(Box::from(b)),
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Imp::Owned(b) => CowBytes::new_owned(b),
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}
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}
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}
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impl<'a> Imp<'a> {
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#[cfg(feature = "std")]
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#[inline(always)]
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pub fn new(bytes: &'a [u8]) -> Imp<'a> {
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Imp::Borrowed(bytes)
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}
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#[cfg(not(feature = "std"))]
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#[inline(always)]
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pub fn new(bytes: &'a [u8]) -> Imp<'a> {
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Imp(bytes)
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}
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#[cfg(feature = "std")]
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#[inline(always)]
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pub fn as_slice(&self) -> &[u8] {
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match self {
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Imp::Owned(ref x) => x,
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Imp::Borrowed(x) => x,
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}
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}
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#[cfg(not(feature = "std"))]
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#[inline(always)]
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pub fn as_slice(&self) -> &[u8] {
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self.0
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}
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}
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