deflate 1.0.0

A DEFLATE, zlib and gzip encoder written in Rust.
Documentation 
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
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147

use std::cmp;

use crate::chained_hash_table::WINDOW_SIZE;

const MAX_MATCH: usize = crate::huffman_table::MAX_MATCH as usize;

/// The maximum size of the buffer.
pub const BUFFER_SIZE: usize = (WINDOW_SIZE * 2) + MAX_MATCH;

pub struct InputBuffer {
    buffer: Vec<u8>,
}

impl InputBuffer {
    #[cfg(test)]
    pub fn new<'a>(data: &'a [u8]) -> (InputBuffer, Option<&[u8]>) {
        let mut b = InputBuffer::empty();
        let rem = b.add_data(data);
        (b, rem)
    }

    pub fn empty() -> InputBuffer {
        InputBuffer {
            buffer: Vec::with_capacity(BUFFER_SIZE),
        }
    }

    /// Add data to the buffer.
    ///
    /// Returns a slice of the data that was not added (including the lookahead if any).
    pub fn add_data<'a>(&mut self, data: &'a [u8]) -> Option<&'a [u8]> {
        debug_assert!(self.current_end() <= BUFFER_SIZE);
        if self.current_end() + data.len() > BUFFER_SIZE {
            // Add data and return how much was left.
            let consumed = {
                let space_left = BUFFER_SIZE - self.buffer.len();
                self.buffer.extend_from_slice(&data[..space_left]);
                space_left
            };
            Some(&data[consumed..])
        } else {
            // There's space for all of the data.
            self.buffer.extend_from_slice(data);
            None
        }
    }

    /// Get the current amount of data in the buffer.
    pub fn current_end(&self) -> usize {
        self.buffer.len()
    }

    /// Slide the input window and add new data.
    ///
    /// Returns a slice containing the data that did not fit, or `None` if all data was consumed.
    pub fn slide<'a>(&mut self, data: &'a [u8]) -> Option<&'a [u8]> {
        // This should only be used when the buffer is full
        assert!(self.buffer.len() > WINDOW_SIZE * 2);

        // Do this in a closure to to end the borrow of buffer.
        let (final_len, upper_len, end) = {
            // Split into lower window and upper window + lookahead
            let (lower, upper) = self.buffer.split_at_mut(WINDOW_SIZE);
            // Copy the upper window to the lower window
            lower.copy_from_slice(&upper[..WINDOW_SIZE]);
            let lookahead_len = {
                // Copy the lookahead to the start of the upper window
                let (upper_2, lookahead) = upper.split_at_mut(WINDOW_SIZE);
                let lookahead_len = lookahead.len();
                debug_assert!(lookahead_len <= MAX_MATCH);
                upper_2[..lookahead_len].copy_from_slice(lookahead);
                lookahead_len
            };

            // Length of the upper window minus the lookahead bytes
            let upper_len = upper.len() - lookahead_len;
            let end = cmp::min(data.len(), upper_len);
            upper[lookahead_len..lookahead_len + end].copy_from_slice(&data[..end]);
            // Remove unused data if any.
            (lower.len() + lookahead_len + end, upper_len, end)
        };
        // Remove unused space.
        self.buffer.truncate(final_len);

        if data.len() > upper_len {
            // Return a slice of the data that was not added
            Some(&data[end..])
        } else {
            None
        }
    }

    /// Get a mutable slice of the used part of the buffer.
    pub fn get_buffer(&mut self) -> &mut [u8] {
        &mut self.buffer
    }
}

#[cfg(test)]
mod test {
    use super::MAX_MATCH;
    use super::*;
    use crate::chained_hash_table::WINDOW_SIZE;
    #[test]
    pub fn buffer_add_full() {
        let data = [10u8; BUFFER_SIZE + 10];
        let (mut buf, extra) = InputBuffer::new(&data[..]);
        assert!(extra.unwrap() == &[10; 10]);
        let to_add = [2, 5, 3];
        let not_added = buf.add_data(&to_add);
        assert_eq!(not_added.unwrap(), to_add);
    }

    #[test]
    pub fn buffer_add_not_full() {
        let data = [10u8; BUFFER_SIZE - 5];
        let (mut buf, extra) = InputBuffer::new(&data[..]);
        assert_eq!(buf.current_end(), data.len());
        assert_eq!(extra, None);
        let to_add = [2, 5, 3];
        {
            let not_added = buf.add_data(&to_add);
            assert!(not_added.is_none());
        }
        let not_added = buf.add_data(&to_add);
        assert_eq!(not_added.unwrap()[0], 3);
    }

    #[test]
    fn slide() {
        let data = [10u8; BUFFER_SIZE];
        let (mut buf, extra) = InputBuffer::new(&data[..]);
        assert_eq!(extra, None);
        let to_add = [5; 5];
        let rem = buf.slide(&to_add);
        assert!(rem.is_none());
        {
            let slice = buf.get_buffer();
            assert!(slice[..WINDOW_SIZE + MAX_MATCH] == data[WINDOW_SIZE..]);
            assert_eq!(
                slice[WINDOW_SIZE + MAX_MATCH..WINDOW_SIZE + MAX_MATCH + 5],
                to_add
            );
        }
        assert_eq!(buf.current_end(), WINDOW_SIZE + MAX_MATCH + to_add.len());
    }
}