76 lines
2.1 KiB
Rust
76 lines
2.1 KiB
Rust
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use crate::cmp;
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use crate::io::{self, Read, ReadBuf};
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use crate::mem::MaybeUninit;
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pub struct Buffer {
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buf: Box<[MaybeUninit<u8>]>,
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pos: usize,
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cap: usize,
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init: usize,
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}
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impl Buffer {
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pub fn with_capacity(capacity: usize) -> Self {
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let buf = Box::new_uninit_slice(capacity);
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Self { buf, pos: 0, cap: 0, init: 0 }
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}
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pub fn buffer(&self) -> &[u8] {
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// SAFETY: self.cap is always <= self.init, so self.buf[self.pos..self.cap] is always init
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// Additionally, both self.pos and self.cap are valid and and self.cap => self.pos, and
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// that region is initialized because those are all invariants of this type.
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unsafe { MaybeUninit::slice_assume_init_ref(&self.buf.get_unchecked(self.pos..self.cap)) }
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}
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pub fn capacity(&self) -> usize {
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self.buf.len()
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}
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pub fn cap(&self) -> usize {
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self.cap
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}
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pub fn pos(&self) -> usize {
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self.pos
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}
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pub fn discard_buffer(&mut self) {
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self.pos = 0;
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self.cap = 0;
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}
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pub fn consume(&mut self, amt: usize) {
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self.pos = cmp::min(self.pos + amt, self.cap);
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}
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pub fn unconsume(&mut self, amt: usize) {
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self.pos = self.pos.saturating_sub(amt);
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}
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pub fn fill_buf(&mut self, mut reader: impl Read) -> io::Result<&[u8]> {
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// If we've reached the end of our internal buffer then we need to fetch
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// some more data from the underlying reader.
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// Branch using `>=` instead of the more correct `==`
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// to tell the compiler that the pos..cap slice is always valid.
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if self.pos >= self.cap {
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debug_assert!(self.pos == self.cap);
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let mut readbuf = ReadBuf::uninit(&mut self.buf);
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// SAFETY: `self.init` is either 0 or set to `readbuf.initialized_len()`
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// from the last time this function was called
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unsafe {
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readbuf.assume_init(self.init);
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}
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reader.read_buf(&mut readbuf)?;
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self.cap = readbuf.filled_len();
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self.init = readbuf.initialized_len();
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self.pos = 0;
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}
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Ok(self.buffer())
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}
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}
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