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
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162

// Copyright 2019 TiKV Project Authors. Licensed under Apache-2.0.

use std::ptr;

#[derive(Clone)]
pub struct KeyBuilder {
    buf: Vec<u8>,
    start: usize,
}

impl KeyBuilder {
    pub fn new(max_size: usize, reserved_prefix_len: usize) -> Self {
        assert!(reserved_prefix_len < max_size);
        let mut buf = Vec::with_capacity(max_size);
        if reserved_prefix_len > 0 {
            unsafe { buf.set_len(reserved_prefix_len) }
        }
        Self {
            buf,
            start: reserved_prefix_len,
        }
    }

    pub fn from_vec(
        mut vec: Vec<u8>,
        reserved_prefix_len: usize,
        reserved_suffix_len: usize,
    ) -> Self {
        if vec.capacity() >= vec.len() + reserved_prefix_len + reserved_suffix_len {
            if reserved_prefix_len > 0 {
                unsafe {
                    ptr::copy(
                        vec.as_ptr(),
                        vec.as_mut_ptr().add(reserved_prefix_len),
                        vec.len(),
                    );
                    vec.set_len(vec.len() + reserved_prefix_len);
                }
            }
            Self {
                buf: vec,
                start: reserved_prefix_len,
            }
        } else {
            Self::from_slice(vec.as_slice(), reserved_prefix_len, reserved_suffix_len)
        }
    }

    pub fn from_slice(s: &[u8], reserved_prefix_len: usize, reserved_suffix_len: usize) -> Self {
        let mut buf = Vec::with_capacity(s.len() + reserved_prefix_len + reserved_suffix_len);
        if reserved_prefix_len > 0 {
            unsafe {
                buf.set_len(reserved_prefix_len);
            }
        }
        buf.extend_from_slice(s);
        Self {
            buf,
            start: reserved_prefix_len,
        }
    }

    pub fn set_prefix(&mut self, prefix: &[u8]) {
        assert!(self.start == prefix.len());
        unsafe {
            ptr::copy_nonoverlapping(prefix.as_ptr(), self.buf.as_mut_ptr(), prefix.len());
            self.start = 0;
        }
    }

    pub fn append(&mut self, content: &[u8]) {
        self.buf.extend_from_slice(content);
    }

    pub fn as_ptr(&self) -> *const u8 {
        unsafe { self.buf.as_ptr().add(self.start) }
    }

    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    pub fn len(&self) -> usize {
        self.buf.len() - self.start
    }

    pub fn as_slice(&self) -> &[u8] {
        &self.buf.as_slice()[self.start..]
    }

    pub fn build(mut self) -> Vec<u8> {
        if self.start != 0 {
            unsafe {
                let len = self.len();
                ptr::copy(
                    self.buf.as_ptr().add(self.start),
                    self.buf.as_mut_ptr(),
                    len,
                );
                self.buf.set_len(len);
            }
        }
        self.buf
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_key_builder() {
        let prefix = b"prefix-";
        let suffix = b"-suffix";

        // new
        let key1 = b"key1";
        let mut key_builder =
            KeyBuilder::new(key1.len() + prefix.len() + suffix.len(), prefix.len());
        key_builder.append(key1);
        key_builder.append(suffix);
        key_builder.set_prefix(prefix);
        assert_eq!(key_builder.len(), key1.len() + prefix.len() + suffix.len());
        let res = key_builder.build();
        assert_eq!(res, b"prefix-key1-suffix".to_vec());

        // from_vec
        let key2 = b"key2";
        let mut key_builder = KeyBuilder::from_vec(key2.to_vec(), prefix.len(), suffix.len());
        assert_eq!(key_builder.len(), key2.len());
        key_builder.set_prefix(prefix);
        assert_eq!(key_builder.len(), key2.len() + prefix.len());
        key_builder.append(suffix);
        let res = key_builder.build();
        assert_eq!(res, b"prefix-key2-suffix".to_vec());

        // from_vec but not set prefix
        let mut key_builder = KeyBuilder::from_vec(key2.to_vec(), prefix.len(), suffix.len());
        key_builder.append(suffix);
        let res = key_builder.build();
        assert_eq!(res, b"key2-suffix".to_vec());

        // from_vec vec has enough memory.
        let mut vec = Vec::with_capacity(key2.len() + prefix.len() + suffix.len());
        vec.extend_from_slice(key2);
        let mut key_builder = KeyBuilder::from_vec(vec, prefix.len(), suffix.len());
        key_builder.set_prefix(prefix);
        key_builder.append(suffix);
        let res = key_builder.build();
        assert_eq!(res, b"prefix-key2-suffix".to_vec());

        // from_slice
        let key3 = b"key3";
        let mut key_builder = KeyBuilder::from_slice(key3, prefix.len(), suffix.len());
        assert_eq!(key_builder.len(), key3.len());
        key_builder.set_prefix(prefix);
        assert_eq!(key_builder.len(), key3.len() + prefix.len());
        key_builder.append(suffix);
        let res = key_builder.build();
        assert_eq!(res, b"prefix-key3-suffix".to_vec());
    }
}