peek.rs

extern crate std;

const DEFAULT_BUF_SIZE: usize = 64 * 1024;

pub struct PeekReader<R> {
    inner: R,
    buf: Vec<u8>,
    pos: usize,
    cap: usize,
}

pub trait PeekRead: std::io::Read {
    fn peek(&mut self, buf: &mut [u8]) -> std::io::Result<usize>;
}

impl<R: std::io::Read> PeekReader<R> {
    pub fn new(inner: R) -> PeekReader<R> {
        PeekReader::with_capacity(DEFAULT_BUF_SIZE, inner)
    }

    pub fn with_capacity(cap: usize, inner: R) -> PeekReader<R> {
        let mut buf = Vec::with_capacity(cap);
        buf.extend(std::iter::repeat(0).take(cap));
        PeekReader {
            inner: inner,
            buf: buf,
            pos: 0,
            cap: 0,
        }
    }

    pub fn consume(&mut self, amt: usize) {
        self.pos = std::cmp::min(self.pos + amt, self.cap);
    }
}

impl <R: std::io::Read> std::io::Read for PeekReader<R> {
    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
        if self.pos == self.cap {
            return self.inner.read(buf);
        }
        let nread = try!((&self.buf[self.pos..self.cap]).read(buf));
        self.consume(nread);
        Ok(nread)
    }
}

impl <R: std::io::Read> PeekRead for PeekReader<R> {
    fn peek(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
        let b_len = buf.len();
        if b_len > self.cap - self.pos {
            if self.pos > 0 && b_len > self.buf.len() - self.pos {
                // need to read more than the size of the buffer, move items to start
                for _ in 0..self.pos {
                    self.buf.remove(0);
                }
                self.cap -= self.pos;
                self.pos = 0;
            }
            if b_len > self.buf.len() {
                // peek buffer too small, need to resize
                self.buf.resize(b_len, 0);
            }
        }
        (&self.buf[self.pos..self.cap]).read(buf)
    }
}

Error as follows:

src/parser/io.rs:65:41: 65:50 error: type `&[u8]` does not implement any method in scope named `read`
src/parser/io.rs:65         (&self.buf[self.pos..self.cap]).read(buf)
                                                            ^~~~~~~~~
src/parser/io.rs:65:50: 65:50 help: methods from traits can only be called if the trait is in scope; the following traits are implemented but not in scope, perhaps add a `use` for one of them:
src/parser/io.rs:65:50: 65:50 help: candidate #1: use `std::io::Read`
src/parser/io.rs:65:50: 65:50 help: candidate #2: use `std::old_io::Reader`
error: aborting due to previous error