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use core::{marker::PhantomData, mem::MaybeUninit};
use crate::{allocate::Allocator, weak_slice::WeakSliceMut};
pub struct Pending<'a> {
/// start of the allocation
buf: WeakSliceMut<'a, MaybeUninit<u8>>,
/// next pending byte to output to the stream
out: usize,
/// number of bytes in the pending buffer
pub(crate) pending: usize,
/// semantically we're storing a mutable slice of bytes
_marker: PhantomData<&'a mut [u8]>,
}
impl<'a> Pending<'a> {
pub fn reset_keep(&mut self) {
// keep the buffer as it is
self.pending = 0;
}
pub fn pending(&self) -> &[u8] {
let slice = &self.buf.as_slice()[self.out..][..self.pending];
// SAFETY: the slice contains initialized bytes.
unsafe { &*(slice as *const [MaybeUninit<u8>] as *const [u8]) }
}
/// Number of bytes that can be added to the pending buffer until it is full
pub(crate) fn remaining(&self) -> usize {
self.buf.len() - (self.out + self.pending)
}
/// Total number of bytes that can be stored in the pending buffer
pub(crate) fn capacity(&self) -> usize {
self.buf.len()
}
#[inline(always)]
#[track_caller]
/// Mark a number of pending bytes as no longer pending
pub fn advance(&mut self, number_of_bytes: usize) {
debug_assert!(self.pending >= number_of_bytes);
self.out = self.out.wrapping_add(number_of_bytes);
self.pending -= number_of_bytes;
if self.pending == 0 {
self.out = 0;
}
}
#[inline(always)]
#[track_caller]
pub fn rewind(&mut self, n: usize) {
assert!(n <= self.pending, "rewinding past then start");
self.pending -= n;
if self.pending == 0 {
self.out = 0;
}
}
#[inline(always)]
#[track_caller]
pub fn extend(&mut self, buf: &[u8]) {
assert!(
self.remaining() >= buf.len(),
"buf.len() must fit in remaining()"
);
// SAFETY: [u8] is valid [MaybeUninit<u8>]
let buf = unsafe { &*(buf as *const [u8] as *const [MaybeUninit<u8>]) };
self.buf.as_mut_slice()[self.out + self.pending..][..buf.len()].copy_from_slice(buf);
self.pending += buf.len();
}
pub(crate) fn new_in(alloc: &Allocator<'a>, len: usize) -> Option<Self> {
let ptr = alloc.allocate_slice_raw::<MaybeUninit<u8>>(len)?;
// SAFETY: freshly allocated buffer
let buf = unsafe { WeakSliceMut::from_raw_parts_mut(ptr.as_ptr(), len) };
Some(Self {
buf,
out: 0,
pending: 0,
_marker: PhantomData,
})
}
pub(crate) fn clone_in(&self, alloc: &Allocator<'a>) -> Option<Self> {
let mut clone = Self::new_in(alloc, self.buf.len())?;
clone
.buf
.as_mut_slice()
.copy_from_slice(self.buf.as_slice());
clone.out = self.out;
clone.pending = self.pending;
Some(clone)
}
/// # Safety
///
/// [`Self`] must not be used after calling this function.
pub(crate) unsafe fn drop_in(&mut self, alloc: &Allocator) {
unsafe { alloc.deallocate(self.buf.as_mut_ptr(), self.buf.len()) };
}
}