codeq 0.5.2

Codec trait
Documentation 
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use std::io;

/// A reader that tracks the number of bytes read.
///
/// This reader wraps any type implementing [`io::Read`] and transparently tracks
/// the number of bytes read through it. The current offset can be retrieved using
/// the [`offset()`](Self::offset) method.
///
/// Example:
/// ```rust
/// # use std::io::Read;
/// # use codeq::OffsetReader;
///
/// let data = b"hello";
/// let mut reader = OffsetReader::new(data.as_ref());
/// let mut buf = [0; 3];
/// reader.read_exact(&mut buf).unwrap();
/// assert_eq!(reader.offset(), 3);
/// ```
pub struct OffsetReader<R> {
    inner: R,
    offset: usize,
}

impl<R: io::Read> OffsetReader<R> {
    /// Creates a new `OffsetReader` wrapping the provided reader.
    pub fn new(inner: R) -> Self {
        Self { inner, offset: 0 }
    }

    /// Returns the current offset of the reader.
    ///
    /// # Returns
    /// The current offset in bytes
    pub fn offset(&self) -> usize {
        self.offset
    }
}

impl<R: io::Read> io::Read for OffsetReader<R> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let n = self.inner.read(buf)?;
        self.offset += n;
        Ok(n)
    }
}

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

    use crate::offset_reader::OffsetReader;

    #[test]
    fn test_offset_reader() -> Result<(), io::Error> {
        let data = b"hello";
        let mut reader = OffsetReader::new(data.as_ref());
        let mut buf = [0; 3];
        reader.read_exact(&mut buf)?;
        assert_eq!(reader.offset(), 3);

        let mut buf = [0; 2];
        reader.read_exact(&mut buf)?;
        assert_eq!(reader.offset(), 5);

        Ok(())
    }
}