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Optimize BufReader somewhat for the only used case

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`rust-bitcoin` doesn't ever actually *use* its `BufRead`
requirement when deserializing objects, and forcing it is somewhat
inefficient, so we optimize the only (actual) case here by passing
reads straight through to the backing stream.
This commit is contained in:
Matt Corallo 2024-08-16 18:47:38 +00:00
parent aadf233d6c
commit f8b7ad242d
1 changed files with 11 additions and 5 deletions
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16
lightning/src/util/ser.rs
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@ -66,6 +66,7 @@ impl<W: Write> Writer for W {
}
}
// TODO: Drop this entirely if rust-bitcoin releases a version bump with https://github.com/rust-bitcoin/rust-bitcoin/pull/3173
/// Wrap buffering support for implementations of Read.
/// A [`Read`]er which keeps an internal buffer to avoid hitting the underlying stream directly for
/// every read, implementing [`BufRead`].
@ -92,17 +93,21 @@ impl<'a, R: Read> BufReader<'a, R> {
impl<'a, R: Read> Read for BufReader<'a, R> {
#[inline]
fn read(&mut self, output: &mut [u8]) -> io::Result<usize> {
let input = self.fill_buf()?;
let count = cmp::min(input.len(), output.len());
output[..count].copy_from_slice(&input[..count]);
self.consume(count);
Ok(count)
if output.is_empty() { return Ok(0); }
let mut offset = 0;
if !self.is_consumed {
output[0] = self.buf[0];
self.is_consumed = true;
offset = 1;
}
self.inner.read(&mut output[offset..]).map(|len| len + offset)
}
}
impl<'a, R: Read> BufRead for BufReader<'a, R> {
#[inline]
fn fill_buf(&mut self) -> io::Result<&[u8]> {
debug_assert!(false, "rust-bitcoin doesn't actually use this");
if self.is_consumed {
let count = self.inner.read(&mut self.buf[..])?;
debug_assert!(count <= 1, "read gave us a garbage length");
@ -120,6 +125,7 @@ impl<'a, R: Read> BufRead for BufReader<'a, R> {
#[inline]
fn consume(&mut self, amount: usize) {
debug_assert!(false, "rust-bitcoin doesn't actually use this");
if amount >= 1 {
debug_assert_eq!(amount, 1, "Can only consume one byte");
debug_assert!(!self.is_consumed, "Cannot consume more than had been read");