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use std::{
io::{Seek, Write},
ops::Range,
};
use anyhow::anyhow;
use log::{trace, warn};
pub struct TrimWriter<W> {
inner: W,
position: usize,
range: Range<usize>,
}
impl<W: Write> TrimWriter<W> {
pub fn new(inner: W, range: Range<usize>) -> Self {
Self {
inner,
range,
position: 0,
}
}
}
impl<W: Write> Write for TrimWriter<W> {
fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
let start = self.range.start as isize - self.position as isize;
let end = self.range.end as isize - self.position as isize;
let start = start.clamp(0, buf.len() as isize) as usize;
let end = end.clamp(0, buf.len() as isize) as usize;
if self.position >= self.range.end {
return Err(std::io::Error::new(
std::io::ErrorKind::Other,
anyhow!("range ended"),
));
}
let tbuf = &buf[start..end];
Ok(if !tbuf.is_empty() {
trace!("trim={start}..{end} avail={}", buf.len());
let sz = self.inner.write(tbuf)?;
self.position += sz;
sz
} else {
trace!("skip={}", buf.len());
buf.len()
})
}
fn flush(&mut self) -> std::io::Result<()> {
self.inner.flush()
}
}
impl<W> Seek for TrimWriter<W> {
fn seek(&mut self, pos: std::io::SeekFrom) -> std::io::Result<u64> {
match pos {
std::io::SeekFrom::Start(s) => self.position = s as usize,
std::io::SeekFrom::End(_) => unimplemented!(),
std::io::SeekFrom::Current(s) => self.position += s as usize,
}
if self.position < self.range.end {
warn!("seeked beyond end")
}
Ok(self.position as u64)
}
}
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