1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124

//! Simple CRC wrappers backed by the crc32 crate.

use std::io::{Read, BufRead};
use std::io;

use crc::crc32;

/// A wrapper struct containing a CRC checksum in the format used by gzip and the amount of bytes
/// input to it mod 2^32.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Crc {
    // We don't use the Digest struct from the Crc crate for now as it doesn't implement `Display`
    // and other common traits.
    checksum: u32,
    amt: u32,
}

/// A reader that updates the checksum and counter of a `Crc` struct when reading from the wrapped
/// reader.
pub struct CrcReader<R> {
    inner: R,
    crc: Crc,
}

impl Crc {
    /// Create a new empty CRC struct.
    pub fn new() -> Crc {
        Crc {
            checksum: 0,
            amt: 0,
        }
    }

    pub fn with_initial(checksum: u32, amount: u32) -> Crc {
        Crc {
            checksum: checksum,
            amt: amount,
        }
    }

    /// Return the current checksum value.
    pub fn sum(&self) -> u32 {
        self.checksum
    }

    /// Return the number of bytes input.
    pub fn amt_as_u32(&self) -> u32 {
        self.amt
    }

    /// Update the checksum and byte counter with the provided data.
    pub fn update(&mut self, data: &[u8]) {
        self.amt = self.amt.wrapping_add(data.len() as u32);
        self.checksum = crc32::update(self.checksum, &crc32::IEEE_TABLE, data);
    }

    /// Reset the checksum and byte counter.
    pub fn reset(&mut self) {
        self.checksum = 0;
        self.amt = 0;
    }
}

impl<R: Read> CrcReader<R> {
    /// Create a new `CrcReader` with a blank checksum.
    pub fn new(r: R) -> CrcReader<R> {
        CrcReader {
            inner: r,
            crc: Crc::new(),
        }
    }

    /// Return a reference to the underlying checksum struct.
    pub fn crc(&self) -> &Crc {
        &self.crc
    }

    /// Consume this `CrcReader` and return the wrapped `Read` instance.
    pub fn into_inner(self) -> R {
        self.inner
    }

    /// Return a mutable reference to the wrapped reader.
    pub fn inner(&mut self) -> &mut R {
        &mut self.inner
    }

    /// Reset the checksum and counter.
    pub fn reset(&mut self) {
        self.crc.reset();
    }
}

impl<R: Read> Read for CrcReader<R> {
    fn read(&mut self, into: &mut [u8]) -> io::Result<usize> {
        let amt = try!(self.inner.read(into));
        self.crc.update(&into[..amt]);
        Ok(amt)
    }
}

impl<R: BufRead> BufRead for CrcReader<R> {
    fn fill_buf(&mut self) -> io::Result<&[u8]> {
        self.inner.fill_buf()
    }
    fn consume(&mut self, amt: usize) {
        if let Ok(data) = self.inner.fill_buf() {
            self.crc.update(&data[..amt]);
        }
        self.inner.consume(amt);
    }
}

#[cfg(test)]
mod test {
    use super::Crc;
    #[test]
    fn checksum_correct() {
        let mut c = Crc::new();
        c.update(b"abcdefg12345689\n");
        assert_eq!(c.sum(), 0x141ddb83);
        assert_eq!(c.amt_as_u32(), 16);
    }
}