darkomen 0.5.0

Warhammer: Dark Omen library and CLI in Rust
Documentation 
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use std::io::{self, Read, Take};

enum PackBitsReaderState {
    Header,
    Literal,
    Repeat { value: u8 },
}

/// Reader that unpacks Apple's `PackBits` format.
pub(crate) struct PackBitsReader<R: Read> {
    reader: Take<R>,
    state: PackBitsReaderState,
    count: usize,
}

impl<R: Read> PackBitsReader<R> {
    /// Wraps a reader.
    pub fn new(reader: R, length: u64) -> Self {
        Self {
            reader: reader.take(length),
            state: PackBitsReaderState::Header,
            count: 0,
        }
    }
}

impl<R: Read> Read for PackBitsReader<R> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        while let PackBitsReaderState::Header = self.state {
            if self.reader.limit() == 0 {
                return Ok(0);
            }
            let mut header: [u8; 1] = [0];
            self.reader.read_exact(&mut header)?;
            let h = header[0] as i8;
            if (-127..=-1).contains(&h) {
                let mut data: [u8; 1] = [0];
                self.reader.read_exact(&mut data)?;
                self.state = PackBitsReaderState::Repeat { value: data[0] };
                self.count = (1 - h as isize) as usize;
            } else if h >= 0 {
                self.state = PackBitsReaderState::Literal;
                self.count = h as usize + 1;
            } else {
                // h = -128 is a no-op.
            }
        }

        let length = buf.len().min(self.count);
        let actual = match self.state {
            PackBitsReaderState::Literal => self.reader.read(&mut buf[..length])?,
            PackBitsReaderState::Repeat { value } => {
                for b in &mut buf[..length] {
                    *b = value;
                }

                length
            }
            PackBitsReaderState::Header => unreachable!(),
        };

        self.count -= actual;
        if self.count == 0 {
            self.state = PackBitsReaderState::Header;
        }
        Ok(actual)
    }
}

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

    macro_rules! packbits_tests {
        ($($name:ident: $value:expr,)*) => {
        $(
            #[test]
            fn $name() {
                let (data, want) = $value;
                let len = data.len();
                let mut reader = PackBitsReader::new(Cursor::new(data), len as u64);
                let mut got = Vec::new();
                reader.read_to_end(&mut got).unwrap();

                assert_eq!(got, want);
            }
        )*
        }
    }

    packbits_tests! {
        single_byte: (vec![0x00, 0x3F], vec![0x3F]),
        simple: (b"\x3CThis is a string for checking various compression algorithms.", b"This is a string for checking various compression algorithms.".to_vec()),
        repeat: (b"\x06This st\xD1r\x09ing hangs.", b"This strrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrring hangs.".to_vec()),
        large_repeat_and_non_repeat: (vec![
            0x06, 0x54, 0x68, 0x69, 0x73, 0x20, 0x73, 0x74, 0x81, 0x72, 0xE3, 0x72, 0x7F, 0x69,
            0x6E, 0x67, 0x20, 0x68, 0x61, 0x6E, 0x67, 0x73, 0x2E, 0x00, 0x01, 0x02, 0x03, 0x04,
            0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10, 0x11, 0x12,
            0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x20,
            0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E,
            0x2F, 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x3B, 0x3C,
            0x3D, 0x3E, 0x3F, 0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4A,
            0x4B, 0x4C, 0x4D, 0x4E, 0x4F, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58,
            0x59, 0x5A, 0x5B, 0x5C, 0x5D, 0x5E, 0x5F, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66,
            0x67, 0x68, 0x69, 0x6A, 0x6B, 0x6C, 0x6D, 0x6E, 0x6F, 0x70, 0x71, 0x72, 0x73, 0x74,
            0x75, 0x27, 0x76, 0x77, 0x78, 0x79, 0x7A, 0x7B, 0x7C, 0x7D, 0x7E, 0x7F, 0x80, 0x81,
            0x82, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x8A, 0x8B, 0x8C, 0x8D, 0x8E, 0x8F,
            0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9A, 0x9B, 0x9C, 0x9D,
        ], {
            let mut large = b"This st".to_vec();
            large.resize(7 + 158, b'r');
            large.extend_from_slice(b"ing hangs.");
            for i in 0..158 {
                large.push(i);
            }
            large
        }),
        example_data_from_wikipedia: (b"\xfe\xaa\x02\x80\x00\x2a\xfd\xaa\x03\x80\x00\x2a\x22\xf7\xaa", b"\xaa\xaa\xaa\x80\x00\x2a\xaa\xaa\xaa\xaa\x80\x00\x2a\x22\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa".to_vec()),
    }
}