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use std::io::{Read, Result as IoResult}; use std::io::Seek; use std::io::SeekFrom; #[derive(Debug)] pub struct PeekReader<R: Read> { pub inner: R, pub peeked: Option<u8>, } impl<R: Read> Read for PeekReader<R> { fn read(&mut self, buf: &mut [u8]) -> IoResult<usize> { if buf.is_empty() { return Ok(0); } if let Some(b) = self.peeked { buf[0] = b; self.peeked = None; self.inner.read(&mut buf[1..]).map(|x| x+1) } else { self.inner.read(buf) } } } impl<R: Read + Seek> Seek for PeekReader<R> { fn seek(&mut self, pos: SeekFrom) -> ::std::io::Result<u64> { if let Some(_) = self.peeked { self.inner.seek(SeekFrom::Current(-1))?; self.peeked = None; } self.inner.seek(pos) } } impl<R: Read> PeekReader<R> { pub fn new(inner: R) -> PeekReader<R> { PeekReader { inner, peeked: None } } pub fn is_empty(&mut self) -> IoResult<bool> { if self.peeked.is_some() { return Ok(false); } let mut buf = [0; 1]; let nb_read = self.read(&mut buf)?; Ok( match nb_read { 0 => true, 1 => { self.peeked = Some(buf[0]); false }, _ => unreachable!(), } ) } }