object/write/
util.rs

1use alloc::vec::Vec;
2#[cfg(feature = "std")]
3use std::{io, mem};
4
5use crate::pod::{bytes_of, bytes_of_slice, Pod};
6
7/// Trait for writable buffer.
8#[allow(clippy::len_without_is_empty)]
9pub trait WritableBuffer {
10    /// Returns position/offset for data to be written at.
11    ///
12    /// Should only be used in debug assertions
13    fn len(&self) -> usize;
14
15    /// Reserves specified number of bytes in the buffer.
16    ///
17    /// This will be called exactly once before writing anything to the buffer,
18    /// and the given size is the exact total number of bytes that will be written.
19    fn reserve(&mut self, size: usize) -> Result<(), ()>;
20
21    /// Writes zero bytes at the end of the buffer until the buffer
22    /// has the specified length.
23    fn resize(&mut self, new_len: usize);
24
25    /// Writes the specified slice of bytes at the end of the buffer.
26    fn write_bytes(&mut self, val: &[u8]);
27
28    /// Writes the specified `Pod` type at the end of the buffer.
29    fn write_pod<T: Pod>(&mut self, val: &T)
30    where
31        Self: Sized,
32    {
33        self.write_bytes(bytes_of(val))
34    }
35
36    /// Writes the specified `Pod` slice at the end of the buffer.
37    fn write_pod_slice<T: Pod>(&mut self, val: &[T])
38    where
39        Self: Sized,
40    {
41        self.write_bytes(bytes_of_slice(val))
42    }
43}
44
45impl<'a> dyn WritableBuffer + 'a {
46    /// Writes the specified `Pod` type at the end of the buffer.
47    pub fn write<T: Pod>(&mut self, val: &T) {
48        self.write_bytes(bytes_of(val))
49    }
50
51    /// Writes the specified `Pod` slice at the end of the buffer.
52    pub fn write_slice<T: Pod>(&mut self, val: &[T]) {
53        self.write_bytes(bytes_of_slice(val))
54    }
55}
56
57impl WritableBuffer for Vec<u8> {
58    #[inline]
59    fn len(&self) -> usize {
60        self.len()
61    }
62
63    #[inline]
64    fn reserve(&mut self, size: usize) -> Result<(), ()> {
65        debug_assert!(self.is_empty());
66        self.reserve(size);
67        Ok(())
68    }
69
70    #[inline]
71    fn resize(&mut self, new_len: usize) {
72        debug_assert!(new_len >= self.len());
73        self.resize(new_len, 0);
74    }
75
76    #[inline]
77    fn write_bytes(&mut self, val: &[u8]) {
78        debug_assert!(self.len() + val.len() <= self.capacity());
79        self.extend_from_slice(val)
80    }
81}
82
83/// A [`WritableBuffer`] that streams data to a [`Write`](std::io::Write) implementation.
84///
85/// [`Self::result`] must be called to determine if an I/O error occurred during writing.
86///
87/// It is advisable to use a buffered writer like [`BufWriter`](std::io::BufWriter)
88/// instead of an unbuffered writer like [`File`](std::fs::File).
89#[cfg(feature = "std")]
90#[derive(Debug)]
91pub struct StreamingBuffer<W> {
92    writer: W,
93    len: usize,
94    result: Result<(), io::Error>,
95}
96
97#[cfg(feature = "std")]
98impl<W> StreamingBuffer<W> {
99    /// Create a new `StreamingBuffer` backed by the given writer.
100    pub fn new(writer: W) -> Self {
101        StreamingBuffer {
102            writer,
103            len: 0,
104            result: Ok(()),
105        }
106    }
107
108    /// Unwraps this [`StreamingBuffer`] giving back the original writer.
109    pub fn into_inner(self) -> W {
110        self.writer
111    }
112
113    /// Returns any error that occurred during writing.
114    pub fn result(&mut self) -> Result<(), io::Error> {
115        mem::replace(&mut self.result, Ok(()))
116    }
117}
118
119#[cfg(feature = "std")]
120impl<W: io::Write> WritableBuffer for StreamingBuffer<W> {
121    #[inline]
122    fn len(&self) -> usize {
123        self.len
124    }
125
126    #[inline]
127    fn reserve(&mut self, _size: usize) -> Result<(), ()> {
128        Ok(())
129    }
130
131    #[inline]
132    fn resize(&mut self, new_len: usize) {
133        debug_assert!(self.len <= new_len);
134        while self.len < new_len {
135            let write_amt = (new_len - self.len - 1) % 1024 + 1;
136            self.write_bytes(&[0; 1024][..write_amt]);
137        }
138    }
139
140    #[inline]
141    fn write_bytes(&mut self, val: &[u8]) {
142        if self.result.is_ok() {
143            self.result = self.writer.write_all(val);
144        }
145        self.len += val.len();
146    }
147}
148
149/// A trait for mutable byte slices.
150///
151/// It provides convenience methods for `Pod` types.
152pub(crate) trait BytesMut {
153    fn write_at<T: Pod>(self, offset: usize, val: &T) -> Result<(), ()>;
154}
155
156impl<'a> BytesMut for &'a mut [u8] {
157    #[inline]
158    fn write_at<T: Pod>(self, offset: usize, val: &T) -> Result<(), ()> {
159        let src = bytes_of(val);
160        let dest = self.get_mut(offset..).ok_or(())?;
161        let dest = dest.get_mut(..src.len()).ok_or(())?;
162        dest.copy_from_slice(src);
163        Ok(())
164    }
165}
166
167/// Write an unsigned number using the LEB128 encoding to a buffer.
168///
169/// Returns the number of bytes written.
170#[allow(dead_code)]
171pub(crate) fn write_uleb128(buf: &mut Vec<u8>, mut val: u64) -> usize {
172    let mut len = 0;
173    loop {
174        let mut byte = (val & 0x7f) as u8;
175        val >>= 7;
176        let done = val == 0;
177        if !done {
178            byte |= 0x80;
179        }
180
181        buf.push(byte);
182        len += 1;
183
184        if done {
185            return len;
186        }
187    }
188}
189
190/// Write a signed number using the LEB128 encoding to a buffer.
191///
192/// Returns the number of bytes written.
193#[allow(dead_code)]
194pub(crate) fn write_sleb128(buf: &mut Vec<u8>, mut val: i64) -> usize {
195    let mut len = 0;
196    loop {
197        let mut byte = val as u8;
198        // Keep the sign bit for testing
199        val >>= 6;
200        let done = val == 0 || val == -1;
201        if done {
202            byte &= !0x80;
203        } else {
204            // Remove the sign bit
205            val >>= 1;
206            byte |= 0x80;
207        }
208
209        buf.push(byte);
210        len += 1;
211
212        if done {
213            return len;
214        }
215    }
216}
217
218pub(crate) fn align(offset: usize, size: usize) -> usize {
219    (offset + (size - 1)) & !(size - 1)
220}
221
222#[allow(dead_code)]
223pub(crate) fn align_u32(offset: u32, size: u32) -> u32 {
224    (offset + (size - 1)) & !(size - 1)
225}
226
227#[allow(dead_code)]
228pub(crate) fn align_u64(offset: u64, size: u64) -> u64 {
229    (offset + (size - 1)) & !(size - 1)
230}
231
232pub(crate) fn write_align(buffer: &mut dyn WritableBuffer, size: usize) {
233    let new_len = align(buffer.len(), size);
234    buffer.resize(new_len);
235}
236
237#[cfg(test)]
238mod tests {
239    use super::*;
240
241    #[test]
242    fn bytes_mut() {
243        let data = vec![0x01, 0x23, 0x45, 0x67];
244
245        let mut bytes = data.clone();
246        bytes.extend_from_slice(bytes_of(&u16::to_be(0x89ab)));
247        assert_eq!(bytes, [0x01, 0x23, 0x45, 0x67, 0x89, 0xab]);
248
249        let mut bytes = data.clone();
250        assert_eq!(bytes.write_at(0, &u16::to_be(0x89ab)), Ok(()));
251        assert_eq!(bytes, [0x89, 0xab, 0x45, 0x67]);
252
253        let mut bytes = data.clone();
254        assert_eq!(bytes.write_at(2, &u16::to_be(0x89ab)), Ok(()));
255        assert_eq!(bytes, [0x01, 0x23, 0x89, 0xab]);
256
257        assert_eq!(bytes.write_at(3, &u16::to_be(0x89ab)), Err(()));
258        assert_eq!(bytes.write_at(4, &u16::to_be(0x89ab)), Err(()));
259        assert_eq!([].write_at(0, &u32::to_be(0x89ab)), Err(()));
260    }
261}
object/write/util.rs

object/write/
util.rs
