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use anyhow::Result;
use log::trace;
use std::{
io::{Read, Seek, SeekFrom},
sync::{Arc, Mutex},
};
/// Splits an reader into many by seeking in between reads.
pub struct MultiReader<T> {
position: u64,
inner: Arc<Mutex<(u64, T)>>,
}
impl<T: Seek> MultiReader<T> {
pub fn new(mut inner: T) -> Result<Self> {
let position = inner.stream_position()?;
Ok(Self {
position,
inner: Arc::new(Mutex::new((position, inner))),
})
}
}
impl<T> Clone for MultiReader<T> {
fn clone(&self) -> Self {
Self {
position: self.position,
inner: self.inner.clone(),
}
}
}
impl<T: Read + Seek> Read for MultiReader<T> {
fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
let mut g = self.inner.lock().unwrap();
if g.0 != self.position {
trace!(
"seeking to match stream position ({} actual vs {} required)",
g.0, self.position
);
g.1.seek(SeekFrom::Start(self.position))?;
g.0 = self.position;
}
let size = g.1.read(buf)?;
g.0 += size as u64;
self.position += size as u64;
Ok(size)
}
}
impl<T: Seek> Seek for MultiReader<T> {
fn seek(&mut self, pos: SeekFrom) -> std::io::Result<u64> {
self.position = match pos {
SeekFrom::Start(x) => x,
SeekFrom::Current(x) => self.position.saturating_add_signed(x),
SeekFrom::End(_) => unimplemented!(),
};
Ok(self.position)
}
}
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