winter_utils/serde/
byte_writer.rs

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
163
164
165
166
167
168
169
170
171
// Copyright (c) Facebook, Inc. and its affiliates.
//
// This source code is licensed under the MIT license found in the
// LICENSE file in the root directory of this source tree.

use super::Serializable;

// BYTE WRITER TRAIT
// ================================================================================================

/// Defines how primitive values are to be written into `Self`.
pub trait ByteWriter: Sized {
    // REQUIRED METHODS
    // --------------------------------------------------------------------------------------------

    /// Writes a single byte into `self`.
    ///
    /// # Panics
    /// Panics if the byte could not be written into `self`.
    fn write_u8(&mut self, value: u8);

    /// Writes a sequence of bytes into `self`.
    ///
    /// # Panics
    /// Panics if the sequence of bytes could not be written into `self`.
    fn write_bytes(&mut self, values: &[u8]);

    // PROVIDED METHODS
    // --------------------------------------------------------------------------------------------

    /// Writes a boolean value into `self`.
    ///
    /// A boolean value is written as a single byte.
    ///
    /// # Panics
    /// Panics if the value could not be written into `self`.
    fn write_bool(&mut self, val: bool) {
        self.write_u8(val as u8);
    }

    /// Writes a u16 value in little-endian byte order into `self`.
    ///
    /// # Panics
    /// Panics if the value could not be written into `self`.
    fn write_u16(&mut self, value: u16) {
        self.write_bytes(&value.to_le_bytes());
    }

    /// Writes a u32 value in little-endian byte order into `self`.
    ///
    /// # Panics
    /// Panics if the value could not be written into `self`.
    fn write_u32(&mut self, value: u32) {
        self.write_bytes(&value.to_le_bytes());
    }

    /// Writes a u64 value in little-endian byte order into `self`.
    ///
    /// # Panics
    /// Panics if the value could not be written into `self`.
    fn write_u64(&mut self, value: u64) {
        self.write_bytes(&value.to_le_bytes());
    }

    /// Writes a u128 value in little-endian byte order into `self`.
    ///
    /// # Panics
    /// Panics if the value could not be written into `self`.
    fn write_u128(&mut self, value: u128) {
        self.write_bytes(&value.to_le_bytes());
    }

    /// Writes a usize value in [vint64](https://docs.rs/vint64/latest/vint64/) format into `self`.
    ///
    /// # Panics
    /// Panics if the value could not be written into `self`.
    fn write_usize(&mut self, value: usize) {
        // convert the value into a u64 so that we always get 8 bytes from to_le_bytes() call
        let value = value as u64;
        let length = usize_encoded_len(value);

        // 9-byte special case
        if length == 9 {
            // length byte is zero in this case
            self.write_u8(0);
            self.write(value.to_le_bytes());
        } else {
            let encoded_bytes = ((value << 1 | 1) << (length - 1)).to_le_bytes();
            self.write_bytes(&encoded_bytes[..length]);
        }
    }

    /// Writes a serializable value into `self`.
    ///
    /// # Panics
    /// Panics if the value could not be written into `self`.
    fn write<S: Serializable>(&mut self, value: S) {
        value.write_into(self)
    }

    /// Serializes all `elements` and writes the resulting bytes into `self`.
    ///
    /// This method does not write any metadata (e.g. number of serialized elements) into `self`.
    fn write_many<S, T>(&mut self, elements: T)
    where
        T: IntoIterator<Item = S>,
        S: Serializable,
    {
        for element in elements {
            element.write_into(self);
        }
    }
}

// BYTE WRITER IMPLEMENTATIONS
// ================================================================================================

#[cfg(feature = "std")]
impl<W: std::io::Write> ByteWriter for W {
    #[inline(always)]
    fn write_u8(&mut self, byte: u8) {
        <W as std::io::Write>::write_all(self, &[byte]).expect("write failed")
    }
    #[inline(always)]
    fn write_bytes(&mut self, bytes: &[u8]) {
        <W as std::io::Write>::write_all(self, bytes).expect("write failed")
    }
}

#[cfg(not(feature = "std"))]
impl ByteWriter for alloc::vec::Vec<u8> {
    fn write_u8(&mut self, value: u8) {
        self.push(value);
    }

    fn write_bytes(&mut self, values: &[u8]) {
        self.extend_from_slice(values);
    }
}

// HELPER FUNCTIONS
// ================================================================================================

/// Returns the length of the usize value in vint64 encoding.
pub(super) fn usize_encoded_len(value: u64) -> usize {
    let zeros = value.leading_zeros() as usize;
    let len = zeros.saturating_sub(1) / 7;
    9 - core::cmp::min(len, 8)
}

#[cfg(all(test, feature = "std"))]
mod tests {
    use std::io::Cursor;

    use super::*;

    #[test]
    fn write_adapter_passthrough() {
        let mut writer = Cursor::new([0u8; 128]);
        writer.write_bytes(b"nope");
        let buf = writer.get_ref();
        assert_eq!(&buf[..4], b"nope");
    }

    #[test]
    #[should_panic]
    fn write_adapter_writer_out_of_capacity() {
        let mut writer = Cursor::new([0; 2]);
        writer.write_bytes(b"nope");
    }
}