gzip_header/
crc_reader.rs

1//! Simple CRC wrappers backed by the crc32 crate.
2
3use core::fmt;
4#[cfg(feature = "std")]
5use std::io;
6#[cfg(feature = "std")]
7use std::io::{BufRead, Read};
8
9use crc32fast::Hasher;
10
11/// A wrapper struct containing a CRC checksum in the format used by gzip and the amount of bytes
12/// input to it mod 2^32.
13#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Hash)]
14pub struct Crc {
15    // We don't use the Digest struct from the Crc crate for now as it doesn't implement `Display`
16    // and other common traits.
17    checksum: u32,
18    amt: u32,
19}
20
21impl fmt::Display for Crc {
22    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
23        write!(f, "({:#x},{})", self.checksum, self.amt)
24    }
25}
26
27impl Crc {
28    /// Create a new empty CRC struct.
29    pub const fn new() -> Crc {
30        Crc {
31            checksum: 0,
32            amt: 0,
33        }
34    }
35
36    pub const fn with_initial(checksum: u32, amt: u32) -> Crc {
37        Crc { checksum, amt }
38    }
39
40    /// Return the current checksum value.
41    pub const fn sum(&self) -> u32 {
42        self.checksum
43    }
44
45    /// Return the number of bytes input.
46    pub const fn amt_as_u32(&self) -> u32 {
47        self.amt
48    }
49
50    /// Update the checksum and byte counter with the provided data.
51    pub fn update(&mut self, data: &[u8]) {
52        self.amt = self.amt.wrapping_add(data.len() as u32);
53        let mut h = Hasher::new_with_initial(self.checksum);
54        h.update(data);
55        self.checksum = h.finalize();
56    }
57
58    /// Reset the checksum and byte counter.
59    pub fn reset(&mut self) {
60        self.checksum = 0;
61        self.amt = 0;
62    }
63}
64
65/// A reader that updates the checksum and counter of a `Crc` struct when reading from the wrapped
66/// reader.
67#[cfg(feature = "std")]
68#[derive(Debug)]
69pub struct CrcReader<R> {
70    inner: R,
71    crc: Crc,
72}
73
74
75#[cfg(feature = "std")]
76impl<R: Read> CrcReader<R> {
77    /// Create a new `CrcReader` with a blank checksum.
78    pub fn new(r: R) -> CrcReader<R> {
79        CrcReader {
80            inner: r,
81            crc: Crc::new(),
82        }
83    }
84
85    /// Return a reference to the underlying checksum struct.
86    pub fn crc(&self) -> &Crc {
87        &self.crc
88    }
89
90    /// Consume this `CrcReader` and return the wrapped `Read` instance.
91    pub fn into_inner(self) -> R {
92        self.inner
93    }
94
95    /// Return a mutable reference to the wrapped reader.
96    pub fn inner(&mut self) -> &mut R {
97        &mut self.inner
98    }
99
100    /// Reset the checksum and counter.
101    pub fn reset(&mut self) {
102        self.crc.reset();
103    }
104}
105
106#[cfg(feature = "std")]
107impl<R: Read> Read for CrcReader<R> {
108    fn read(&mut self, into: &mut [u8]) -> io::Result<usize> {
109        let amt = self.inner.read(into)?;
110        self.crc.update(&into[..amt]);
111        Ok(amt)
112    }
113}
114
115#[cfg(feature = "std")]
116impl<R: BufRead> BufRead for CrcReader<R> {
117    fn fill_buf(&mut self) -> io::Result<&[u8]> {
118        self.inner.fill_buf()
119    }
120    fn consume(&mut self, amt: usize) {
121        if let Ok(data) = self.inner.fill_buf() {
122            self.crc.update(&data[..amt]);
123        }
124        self.inner.consume(amt);
125    }
126}
127
128#[cfg(test)]
129mod test {
130    use super::Crc;
131    #[test]
132    fn checksum_correct() {
133        let mut c = Crc::new();
134        c.update(b"abcdefg12345689\n");
135        assert_eq!(c.sum(), 0x141ddb83);
136        assert_eq!(c.amt_as_u32(), 16);
137    }
138}
gzip_header/crc_reader.rs

gzip_header/
crc_reader.rs
