exif/

util.rs

//
// Copyright (c) 2016 KAMADA Ken'ichi.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
// OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
// SUCH DAMAGE.
//

use std::io;
use std::io::Read as _;

use crate::error::Error;

const ASCII_0: u8 = 0x30;
const ASCII_9: u8 = 0x39;

pub fn read8<R>(reader: &mut R) -> Result<u8, io::Error> where R: io::Read {
    let mut buf = [0u8; 1];
    reader.read_exact(&mut buf).and(Ok(buf[0]))
}

pub fn read16<R>(reader: &mut R) -> Result<u16, io::Error> where R: io::Read {
    let mut buf = [0u8; 2];
    reader.read_exact(&mut buf)?;
    Ok(u16::from_be_bytes(buf))
}

pub fn read64<R>(reader: &mut R) -> Result<u64, io::Error> where R: io::Read {
    let mut buf = [0u8; 8];
    reader.read_exact(&mut buf)?;
    Ok(u64::from_be_bytes(buf))
}

pub trait BufReadExt {
    fn discard_exact(&mut self, len: usize) -> io::Result<()>;
    fn is_eof(&mut self) -> io::Result<bool>;
}

impl<T> BufReadExt for T where T: io::BufRead {
    fn discard_exact(&mut self, mut len: usize) -> io::Result<()> {
        while len > 0 {
            let consume_len = match self.fill_buf() {
                Ok(buf) if buf.is_empty() =>
                    return Err(io::Error::new(
                        io::ErrorKind::UnexpectedEof, "unexpected EOF")),
                Ok(buf) => buf.len().min(len),
                Err(e) if e.kind() == io::ErrorKind::Interrupted => continue,
                Err(e) => return Err(e),
            };
            self.consume(consume_len);
            len -= consume_len;
        }
        Ok(())
    }

    fn is_eof(&mut self) -> io::Result<bool> {
        loop {
            match self.fill_buf() {
                Ok(buf) => return Ok(buf.is_empty()),
                Err(e) if e.kind() == io::ErrorKind::Interrupted => continue,
                Err(e) => return Err(e),
            }
        }
    }
}

pub trait ReadExt {
    fn read_exact_len(&mut self, buf: &mut Vec<u8>, len: usize)
                      -> io::Result<()>;
}

impl<T> ReadExt for T where T: io::Read {
    fn read_exact_len(&mut self, buf: &mut Vec<u8>, len: usize)
                      -> io::Result<()> {
        // Using `vec![0; len]` and `read_exact` is more efficient but
        // less robust against broken files; a small file can easily
        // trigger OOM by a huge length value without actual data.
        // When the fallible allocation feature is stabilized,
        // we could revisit this.
        if self.take(len as u64).read_to_end(buf)? != len {
            return Err(io::Error::new(
                io::ErrorKind::UnexpectedEof, "unexpected EOF"));
        }
        Ok(())
    }
}

// This function must not be called with more than 4 bytes.
pub fn atou16(bytes: &[u8]) -> Result<u16, Error> {
    debug_assert!(bytes.len() <= 4);
    if bytes.len() == 0 {
        return Err(Error::InvalidFormat("Not a number"));
    }
    let mut n = 0;
    for &c in bytes {
        if c < ASCII_0 || ASCII_9 < c {
            return Err(Error::InvalidFormat("Not a number"));
        }
        n = n * 10 + (c - ASCII_0) as u16;
    }
    Ok(n)
}

pub fn ctou32(c: u8) -> Result<u32, Error> {
    if c < ASCII_0 || ASCII_9 < c {
        return Err(Error::InvalidFormat("Not a number"));
    }
    Ok((c - ASCII_0) as u32)
}

#[cfg(test)]
mod tests {
    use std::io::ErrorKind;
    use std::io::Read;
    use super::*;

    #[test]
    fn discard_exact() {
        let mut buf = b"abc".as_ref();
        buf.discard_exact(1).unwrap();
        assert_eq!(buf, b"bc");
        buf.discard_exact(2).unwrap();
        assert_eq!(buf, b"");
        buf.discard_exact(1).unwrap_err();
    }

    #[test]
    fn read8_len() {
        let data = [];
        assert_err_kind!(read8(&mut &data[..]), ErrorKind::UnexpectedEof);
        let data = [0x01];
        assert_ok!(read8(&mut &data[..]), 0x01);
        let data = [0x01, 0x02];
        let mut reader = &data[..];
        let mut buf = Vec::new();
        assert_ok!(read8(&mut reader), 0x01);
        assert_ok!(reader.read_to_end(&mut buf), 1);
        assert_eq!(buf, [0x02]);
    }

    #[test]
    fn read16_len() {
        let data = [];
        assert_err_kind!(read16(&mut &data[..]), ErrorKind::UnexpectedEof);
        let data = [0x01];
        assert_err_kind!(read16(&mut &data[..]), ErrorKind::UnexpectedEof);
        let data = [0x01, 0x02];
        assert_ok!(read16(&mut &data[..]), 0x0102);
        let data = [0x01, 0x02, 0x03];
        let mut reader = &data[..];
        let mut buf = Vec::new();
        assert_ok!(read16(&mut reader), 0x0102);
        assert_ok!(reader.read_to_end(&mut buf), 1);
        assert_eq!(buf, [0x03]);
    }

    #[test]
    fn atou16_misc() {
        assert_ok!(atou16(b"0"), 0);
        assert_ok!(atou16(b"0010"), 10);
        assert_ok!(atou16(b"9999"), 9999);
        assert_err_pat!(atou16(b""), Error::InvalidFormat(_));
        assert_err_pat!(atou16(b"/"), Error::InvalidFormat(_));
        assert_err_pat!(atou16(b":"), Error::InvalidFormat(_));
        assert_err_pat!(atou16(b"-1"), Error::InvalidFormat(_));
    }
}