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

use std::io::Read;
use std::cmp::min;

/// Wraps a reader and escapes all bytes with special meaning as defined by
/// [conventions](https://docs.basex.org/wiki/Server_Protocol#Conventions).
///
/// All bytes that have any special meaning get prefixed by a single `0xFF` byte.
///
/// # Example
/// ## Input
/// `[0, 1, 2, 3, 4, 0xFF]`
/// ## Output
/// `[0xFF, 0, 1, 2, 3, 4, 0xFF, 0xFF]`
pub(crate) struct EscapeReader<'a, R> where R: Read {
    inner: &'a mut R,
    accumulator: Vec<u8>,
}

impl<'a, R> EscapeReader<'a, R> where R: Read {
    pub(crate) fn new(inner: &'a mut R) -> Self {
        Self { inner, accumulator: vec![], }
    }
}

impl<R> Read for EscapeReader<'_, R> where R:Read {
    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
        let accumulator_length = min(buf.len(), self.accumulator.len());

        for i in 0..accumulator_length {
            buf[i] = self.accumulator.pop().unwrap();
        }

        let stream_length = self.inner.read(&mut buf[accumulator_length..])?;
        let size = accumulator_length + stream_length;
        let escape_chars_count = buf[accumulator_length..size].iter().filter(|b| **b == 0 || **b == 0xFF).count();
        let escaped_size = size + escape_chars_count;
        let mut shift = escape_chars_count;
        let mut next_skip = false;

        for i in (accumulator_length..escaped_size).rev() {
            if next_skip {
                next_skip = false;
                continue;
            }
            if i >= buf.len() {
                self.accumulator.push(buf[i - shift]);
            } else {
                buf[i] = buf[i - shift];
            }

            if buf[i - shift] == 0xFF || buf[i - shift] == 0 {
                if i <= buf.len() {
                    buf[i - 1] = 0xFF;
                } else {
                    self.accumulator.push(0xFF);
                }
                shift -= 1;
                next_skip = true;
            }
        }

        Ok(min(buf.len(), accumulator_length + stream_length + escape_chars_count))
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::io::{Read, empty};

    #[test]
    fn test_escaping_without_escape_bytes_leaves_buffer_intact() {
        let expected_bytes = [1u8, 2, 3, 4];
        let mut slice = &expected_bytes[..];
        let mut escaped = EscapeReader::new(&mut slice);

        let mut actual_bytes = vec![];
        escaped.read_to_end(&mut actual_bytes).unwrap();

        assert_eq!(expected_bytes.to_vec(), actual_bytes);
    }

    #[test]
    fn test_escaping_with_escape_bytes() {
        let bytes = [1u8, 0, 9, 0xFF, 6];
        let mut slice = &bytes[..];
        let mut escaped = EscapeReader::new(&mut slice);

        let expected_bytes = vec![1u8, 0xFF, 0, 9, 0xFF, 0xFF, 6];
        let mut actual_bytes = vec![];
        escaped.read_to_end(&mut actual_bytes).unwrap();

        assert_eq!(expected_bytes, actual_bytes);
    }

    #[test]
    fn test_escaping_only_escape_bytes() {
        let bytes = [0u8].repeat(4);
        let mut slice = &bytes[..];
        let mut escaped = EscapeReader::new(&mut slice);

        let expected_bytes = [0xFF, 0u8].repeat(4);
        let mut actual_bytes = vec![];
        escaped.read_to_end(&mut actual_bytes).unwrap();

        assert_eq!(expected_bytes, actual_bytes);
    }

    #[test]
    fn test_escaping_only_escape_bytes_on_multiple_reading() {
        let bytes = [0u8].repeat(20);
        let mut slice = &bytes[..];
        let mut escaped = EscapeReader::new(&mut slice);

        let expected_bytes = [0xFF, 0u8].repeat(20);
        let mut actual_bytes = vec![];
        escaped.read_to_end(&mut actual_bytes).unwrap();

        assert_eq!(expected_bytes, actual_bytes);
    }

    #[test]
    fn test_escaping_from_empty_reader_does_nothing() {
        let mut bytes = empty();
        let mut escaped = EscapeReader::new(&mut bytes);

        let expected_bytes: Vec<u8> = vec![];
        let mut actual_bytes = vec![];
        escaped.read_to_end(&mut actual_bytes).unwrap();

        assert_eq!(expected_bytes, actual_bytes);
    }

    #[test]
    fn test_escaping_into_empty_buffer_does_nothing() {
        let bytes = [1u8];
        let mut slice = &bytes[..];
        let mut escaped = EscapeReader::new(&mut slice);

        let expected_bytes: [u8; 0] = [];
        let mut actual_bytes: [u8; 0] = [];
        escaped.read(&mut actual_bytes).unwrap();

        assert_eq!(expected_bytes, actual_bytes);
    }
}