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use std::io::{self, SeekFrom};
use crate::pull_parser::ParserSource;
#[derive(Debug, Clone, Copy)]
pub struct PositionCacheReader<R> {
inner: R,
position: usize,
}
impl<R: io::Read> PositionCacheReader<R> {
pub fn new(inner: R) -> Self {
Self { inner, position: 0 }
}
pub fn with_offset(inner: R, offset: usize) -> Self {
Self {
inner,
position: offset,
}
}
pub fn into_inner(self) -> R {
self.inner
}
pub fn position(&self) -> usize {
self.position
}
pub fn skip_distance(&mut self, mut distance: u64) -> io::Result<()>
where
R: io::Seek,
{
while distance > 0 {
let part = std::cmp::min(distance, std::i64::MAX as u64);
self.inner.seek(SeekFrom::Current(part as i64))?;
self.advance(part as usize);
distance -= part;
}
Ok(())
}
#[inline]
fn advance(&mut self, n: usize) {
self.position = self.position.checked_add(n).expect("Position overflowed");
}
}
impl<R: io::Read> io::Read for PositionCacheReader<R> {
fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
let size = self.inner.read(buf)?;
self.advance(size);
Ok(size)
}
}
impl<R: io::BufRead> io::BufRead for PositionCacheReader<R> {
fn fill_buf(&mut self) -> io::Result<&[u8]> {
self.inner.fill_buf()
}
fn consume(&mut self, amt: usize) {
self.inner.consume(amt);
self.advance(amt);
}
}
impl<R: io::Read> ParserSource for PositionCacheReader<R> {
fn position(&self) -> u64 {
self.position() as u64
}
}
#[cfg(test)]
mod tests {
use super::*;
use std::io::{Cursor, Read};
fn prepare_iota() -> Cursor<Vec<u8>> {
let orig = (0..=255).collect::<Vec<u8>>();
Cursor::new(orig)
}
#[test]
fn read() {
let reader = PositionCacheReader::new(prepare_iota());
assert_eq!(
reader.position(),
0,
"`PositionCacheReader::new()` should return a reader with position 0"
);
check_read_with_offset(reader, 0);
}
#[test]
fn read_with_offset() {
const OFFSET: usize = 60;
let reader = PositionCacheReader::with_offset(prepare_iota(), OFFSET);
assert_eq!(
reader.position(),
OFFSET,
"`PositionCacheReader::with_offset()` should return a reader with the given offset"
);
check_read_with_offset(reader, OFFSET)
}
fn check_read_with_offset<R: Read>(mut reader: PositionCacheReader<R>, offset: usize) {
const BUF_SIZE: usize = 128;
let mut buf = [0; BUF_SIZE];
let size = reader
.read(&mut buf)
.expect("Read from `Cursor<Vec<u8>>` should never fail");
assert!(
size > 0,
"Read from non-empty `Cursor<Vec<u8>>` should obtain some data"
);
assert_eq!(
&buf[..size],
&(0..size as u8).into_iter().collect::<Vec<u8>>()[..],
"Read should obtain correct data"
);
assert_eq!(
reader.position(),
offset + size,
"Position should be correctly updated after a read"
);
}
}