bincode/enc/
write.rs

1//! This module contains writer-based structs and traits.
2//!
3//! Because `std::io::Write` is only limited to `std` and not `core`, we provide our own [Writer].
4
5use crate::error::EncodeError;
6
7/// Trait that indicates that a struct can be used as a destination to encode data too. This is used by [Encode]
8///
9/// [Encode]: ../trait.Encode.html
10pub trait Writer {
11    /// Write `bytes` to the underlying writer. Exactly `bytes.len()` bytes must be written, or else an error should be returned.
12    fn write(&mut self, bytes: &[u8]) -> Result<(), EncodeError>;
13}
14
15impl<T: Writer> Writer for &mut T {
16    #[inline]
17    fn write(&mut self, bytes: &[u8]) -> Result<(), EncodeError> {
18        (**self).write(bytes)
19    }
20}
21
22/// A helper struct that implements `Writer` for a `&[u8]` slice.
23///
24/// ```
25/// use bincode::enc::write::{Writer, SliceWriter};
26///
27/// let destination = &mut [0u8; 100];
28/// let mut writer = SliceWriter::new(destination);
29/// writer.write(&[1, 2, 3, 4, 5]).unwrap();
30///
31/// assert_eq!(writer.bytes_written(), 5);
32/// assert_eq!(destination[0..6], [1, 2, 3, 4, 5, 0]);
33/// ```
34pub struct SliceWriter<'storage> {
35    slice: &'storage mut [u8],
36    original_length: usize,
37}
38
39impl<'storage> SliceWriter<'storage> {
40    /// Create a new instance of `SliceWriter` with the given byte array.
41    pub fn new(bytes: &'storage mut [u8]) -> SliceWriter<'storage> {
42        let original = bytes.len();
43        SliceWriter {
44            slice: bytes,
45            original_length: original,
46        }
47    }
48
49    /// Return the amount of bytes written so far.
50    pub fn bytes_written(&self) -> usize {
51        self.original_length - self.slice.len()
52    }
53}
54
55impl Writer for SliceWriter<'_> {
56    #[inline(always)]
57    fn write(&mut self, bytes: &[u8]) -> Result<(), EncodeError> {
58        if bytes.len() > self.slice.len() {
59            return Err(EncodeError::UnexpectedEnd);
60        }
61        let (a, b) = core::mem::take(&mut self.slice).split_at_mut(bytes.len());
62        a.copy_from_slice(bytes);
63        self.slice = b;
64
65        Ok(())
66    }
67}
68
69/// A writer that counts how many bytes were written. This is useful for e.g. pre-allocating buffers bfeore writing to them.
70#[derive(Default)]
71pub struct SizeWriter {
72    /// the amount of bytes that were written so far
73    pub bytes_written: usize,
74}
75impl Writer for SizeWriter {
76    #[inline(always)]
77    fn write(&mut self, bytes: &[u8]) -> Result<(), EncodeError> {
78        self.bytes_written += bytes.len();
79
80        Ok(())
81    }
82}
bincode/enc/write.rs

bincode/enc/
write.rs
