Auto merge of #98943 - WilliamVenner:feat/bufread_skip_until, r=dtolnay
Add `BufRead::skip_until`
Alternative version of `BufRead::read_until` that simply discards data, rather than copying it into a buffer.
Useful for situations like skipping irrelevant data in a binary file format that is NUL-terminated.
<details>
<summary>Benchmark</summary>
```
running 2 tests
test bench_read_until ... bench: 123 ns/iter (+/- 6)
test bench_skip_until ... bench: 66 ns/iter (+/- 3)
```
```rs
#![feature(test)]
extern crate test;
use test::Bencher;
use std::io::{ErrorKind, BufRead};
fn skip_until<R: BufRead + ?Sized>(r: &mut R, delim: u8) -> Result<usize, std::io::Error> {
let mut read = 0;
loop {
let (done, used) = {
let available = match r.fill_buf() {
Ok(n) => n,
Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
Err(e) => return Err(e),
};
match memchr::memchr(delim, available) {
Some(i) => (true, i + 1),
None => (false, available.len()),
}
};
r.consume(used);
read += used;
if done || used == 0 {
return Ok(read);
}
}
}
const STR: &[u8] = b"Ferris\0Hello, world!\0";
#[bench]
fn bench_skip_until(b: &mut Bencher) {
b.iter(|| {
let mut io = std::io::Cursor::new(test::black_box(STR));
skip_until(&mut io, b'\0').unwrap();
let mut hello = Vec::with_capacity(b"Hello, world!\0".len());
let num_bytes = io.read_until(b'\0', &mut hello).unwrap();
assert_eq!(num_bytes, b"Hello, world!\0".len());
assert_eq!(hello, b"Hello, world!\0");
});
}
#[bench]
fn bench_read_until(b: &mut Bencher) {
b.iter(|| {
let mut io = std::io::Cursor::new(test::black_box(STR));
io.read_until(b'\0', &mut Vec::new()).unwrap();
let mut hello = Vec::with_capacity(b"Hello, world!\0".len());
let num_bytes = io.read_until(b'\0', &mut hello).unwrap();
assert_eq!(num_bytes, b"Hello, world!\0".len());
assert_eq!(hello, b"Hello, world!\0");
});
}
```
</details>
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