futures_util/io/
window.rs

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1use std::ops::{Bound, Range, RangeBounds};
2
3/// An owned window around an underlying buffer.
4///
5/// Normally slices work great for considering sub-portions of a buffer, but
6/// unfortunately a slice is a *borrowed* type in Rust which has an associated
7/// lifetime. When working with future and async I/O these lifetimes are not
8/// always appropriate, and are sometimes difficult to store in tasks. This
9/// type strives to fill this gap by providing an "owned slice" around an
10/// underlying buffer of bytes.
11///
12/// A `Window<T>` wraps an underlying buffer, `T`, and has configurable
13/// start/end indexes to alter the behavior of the `AsRef<[u8]>` implementation
14/// that this type carries.
15///
16/// This type can be particularly useful when working with the `write_all`
17/// combinator in this crate. Data can be sliced via `Window`, consumed by
18/// `write_all`, and then earned back once the write operation finishes through
19/// the `into_inner` method on this type.
20#[derive(Debug)]
21pub struct Window<T> {
22    inner: T,
23    range: Range<usize>,
24}
25
26impl<T: AsRef<[u8]>> Window<T> {
27    /// Creates a new window around the buffer `t` defaulting to the entire
28    /// slice.
29    ///
30    /// Further methods can be called on the returned `Window<T>` to alter the
31    /// window into the data provided.
32    pub fn new(t: T) -> Self {
33        Self { range: 0..t.as_ref().len(), inner: t }
34    }
35
36    /// Gets a shared reference to the underlying buffer inside of this
37    /// `Window`.
38    pub fn get_ref(&self) -> &T {
39        &self.inner
40    }
41
42    /// Gets a mutable reference to the underlying buffer inside of this
43    /// `Window`.
44    pub fn get_mut(&mut self) -> &mut T {
45        &mut self.inner
46    }
47
48    /// Consumes this `Window`, returning the underlying buffer.
49    pub fn into_inner(self) -> T {
50        self.inner
51    }
52
53    /// Returns the starting index of this window into the underlying buffer
54    /// `T`.
55    pub fn start(&self) -> usize {
56        self.range.start
57    }
58
59    /// Returns the end index of this window into the underlying buffer
60    /// `T`.
61    pub fn end(&self) -> usize {
62        self.range.end
63    }
64
65    /// Changes the range of this window to the range specified.
66    ///
67    /// # Panics
68    ///
69    /// This method will panic if `range` is out of bounds for the underlying
70    /// slice or if [`start_bound()`] of `range` comes after the [`end_bound()`].
71    ///
72    /// [`start_bound()`]: std::ops::RangeBounds::start_bound
73    /// [`end_bound()`]: std::ops::RangeBounds::end_bound
74    pub fn set<R: RangeBounds<usize>>(&mut self, range: R) {
75        let start = match range.start_bound() {
76            Bound::Included(n) => *n,
77            Bound::Excluded(n) => *n + 1,
78            Bound::Unbounded => 0,
79        };
80        let end = match range.end_bound() {
81            Bound::Included(n) => *n + 1,
82            Bound::Excluded(n) => *n,
83            Bound::Unbounded => self.inner.as_ref().len(),
84        };
85
86        assert!(end <= self.inner.as_ref().len());
87        assert!(start <= end);
88
89        self.range.start = start;
90        self.range.end = end;
91    }
92}
93
94impl<T: AsRef<[u8]>> AsRef<[u8]> for Window<T> {
95    fn as_ref(&self) -> &[u8] {
96        &self.inner.as_ref()[self.range.start..self.range.end]
97    }
98}
99
100impl<T: AsMut<[u8]>> AsMut<[u8]> for Window<T> {
101    fn as_mut(&mut self) -> &mut [u8] {
102        &mut self.inner.as_mut()[self.range.start..self.range.end]
103    }
104}
futures_util/io/window.rs

futures_util/io/
window.rs
