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use std::pin::Pin;
use async_std::prelude::*;
use async_std::io::BufReader;
use async_std::io::Read;
use futures::task::{Context, Poll};
use pin_project::pin_project;
const CHUNK_SIZE: usize = 4096;
#[pin_project]
pub struct ChunkedBufReader<T>
where T: Read + Unpin {
#[pin]
reader: BufReader<T>,
}
impl<T> ChunkedBufReader<T>
where T: Read + Unpin {
pub fn new(reader: BufReader<T>) -> Self {
Self {
reader,
}
}
}
impl<T> Stream for ChunkedBufReader<T>
where T: Read + Unpin {
type Item = Vec<u8>;
fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
let this = self.project();
// This is quite wasteful, but perfomance is fine and the only real optimization (other
// than some zero-copy shenanigans) would be to not initialize this vec, with unsafe{}
let mut chunk = vec![0; CHUNK_SIZE];
match this.reader.poll_read(cx, &mut chunk[0..(CHUNK_SIZE - 1)]) {
Poll::Ready(Ok(size)) => {
if size == 0 {
Poll::Ready(None)
} else {
chunk.truncate(size);
Poll::Ready(Some(chunk))
}
},
Poll::Ready(Err(_)) => Poll::Ready(None),
Poll::Pending => Poll::Pending,
}
}
}
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