gzip_header/
crc_reader.rs

1//! Simple CRC wrappers backed by the crc32 crate.
2
3use std::fmt;
4use std::io;
5use std::io::{BufRead, Read};
6
7use crc32fast::Hasher;
8
9/// A wrapper struct containing a CRC checksum in the format used by gzip and the amount of bytes
10/// input to it mod 2^32.
11#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Hash)]
12pub struct Crc {
13    // We don't use the Digest struct from the Crc crate for now as it doesn't implement `Display`
14    // and other common traits.
15    checksum: u32,
16    amt: u32,
17}
18
19impl fmt::Display for Crc {
20    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
21        write!(f, "({:#x},{})", self.checksum, self.amt)
22    }
23}
24
25/// A reader that updates the checksum and counter of a `Crc` struct when reading from the wrapped
26/// reader.
27#[derive(Debug)]
28pub struct CrcReader<R> {
29    inner: R,
30    crc: Crc,
31}
32
33impl Crc {
34    /// Create a new empty CRC struct.
35    pub const fn new() -> Crc {
36        Crc {
37            checksum: 0,
38            amt: 0,
39        }
40    }
41
42    pub const fn with_initial(checksum: u32, amt: u32) -> Crc {
43        Crc { checksum, amt }
44    }
45
46    /// Return the current checksum value.
47    pub const fn sum(&self) -> u32 {
48        self.checksum
49    }
50
51    /// Return the number of bytes input.
52    pub const fn amt_as_u32(&self) -> u32 {
53        self.amt
54    }
55
56    /// Update the checksum and byte counter with the provided data.
57    pub fn update(&mut self, data: &[u8]) {
58        self.amt = self.amt.wrapping_add(data.len() as u32);
59        let mut h = Hasher::new_with_initial(self.checksum);
60        h.update(data);
61        self.checksum = h.finalize();
62    }
63
64    /// Reset the checksum and byte counter.
65    pub fn reset(&mut self) {
66        self.checksum = 0;
67        self.amt = 0;
68    }
69}
70
71impl<R: Read> CrcReader<R> {
72    /// Create a new `CrcReader` with a blank checksum.
73    pub fn new(r: R) -> CrcReader<R> {
74        CrcReader {
75            inner: r,
76            crc: Crc::new(),
77        }
78    }
79
80    /// Return a reference to the underlying checksum struct.
81    pub fn crc(&self) -> &Crc {
82        &self.crc
83    }
84
85    /// Consume this `CrcReader` and return the wrapped `Read` instance.
86    pub fn into_inner(self) -> R {
87        self.inner
88    }
89
90    /// Return a mutable reference to the wrapped reader.
91    pub fn inner(&mut self) -> &mut R {
92        &mut self.inner
93    }
94
95    /// Reset the checksum and counter.
96    pub fn reset(&mut self) {
97        self.crc.reset();
98    }
99}
100
101impl<R: Read> Read for CrcReader<R> {
102    fn read(&mut self, into: &mut [u8]) -> io::Result<usize> {
103        let amt = self.inner.read(into)?;
104        self.crc.update(&into[..amt]);
105        Ok(amt)
106    }
107}
108
109impl<R: BufRead> BufRead for CrcReader<R> {
110    fn fill_buf(&mut self) -> io::Result<&[u8]> {
111        self.inner.fill_buf()
112    }
113    fn consume(&mut self, amt: usize) {
114        if let Ok(data) = self.inner.fill_buf() {
115            self.crc.update(&data[..amt]);
116        }
117        self.inner.consume(amt);
118    }
119}
120
121#[cfg(test)]
122mod test {
123    use super::Crc;
124    #[test]
125    fn checksum_correct() {
126        let mut c = Crc::new();
127        c.update(b"abcdefg12345689\n");
128        assert_eq!(c.sum(), 0x141ddb83);
129        assert_eq!(c.amt_as_u32(), 16);
130    }
131}
gzip_header/crc_reader.rs

gzip_header/
crc_reader.rs
