compio_io\util/
repeat.rs

1use std::mem::MaybeUninit;
2
3use compio_buf::{BufResult, IoVectoredBufMut, SetLenExt};
4
5use crate::{AsyncBufRead, AsyncRead, IoResult};
6
7/// A reader that infinitely repeats one byte constructed via [`repeat`].
8///
9/// All reads from this reader will succeed by filling the specified buffer with
10/// the given byte.
11///
12/// # Examples
13///
14/// ```rust
15/// # futures_executor::block_on(async {
16/// use compio_io::{self, AsyncRead, AsyncReadExt};
17///
18/// let (len, buffer) = compio_io::repeat(42)
19///     .read(Vec::with_capacity(3))
20///     .await
21///     .unwrap();
22///
23/// assert_eq!(buffer.as_slice(), [42, 42, 42]);
24/// assert_eq!(len, 3);
25/// # })
26/// ```
27pub struct Repeat(u8);
28
29impl AsyncRead for Repeat {
30    async fn read<B: compio_buf::IoBufMut>(
31        &mut self,
32        mut buf: B,
33    ) -> compio_buf::BufResult<usize, B> {
34        let slice = buf.as_uninit();
35
36        let len = slice.len();
37        slice.fill(MaybeUninit::new(self.0));
38        // SAFETY: we just initialized exactly `len` bytes in `buf` from index
39        // 0.
40        unsafe { buf.advance(len) };
41
42        BufResult(Ok(len), buf)
43    }
44
45    async fn read_vectored<V: IoVectoredBufMut>(&mut self, mut buf: V) -> BufResult<usize, V> {
46        let mut len: usize = 0;
47        for slice in buf.iter_uninit_slice() {
48            len = len
49                .checked_add(slice.len())
50                .expect("total vectored buffer length overflow");
51            slice.fill(MaybeUninit::new(self.0));
52        }
53        debug_assert_eq!(len, buf.total_capacity());
54        // SAFETY: every byte counted in `len` is initialized in the loop above.
55        unsafe { buf.advance_vec_to(len) };
56
57        BufResult(Ok(len), buf)
58    }
59}
60
61impl AsyncBufRead for Repeat {
62    async fn fill_buf(&mut self) -> IoResult<&'_ [u8]> {
63        Ok(std::slice::from_ref(&self.0))
64    }
65
66    fn consume(&mut self, _: usize) {}
67}
68
69/// Creates a reader that infinitely repeats one byte.
70///
71/// All reads from this reader will succeed by filling the specified buffer with
72/// the given byte.
73///
74/// # Examples
75///
76/// ```rust
77/// # futures_executor::block_on(async {
78/// use compio_io::{self, AsyncRead, AsyncReadExt};
79///
80/// let ((), buffer) = compio_io::repeat(42)
81///     .read_exact(Vec::with_capacity(3))
82///     .await
83///     .unwrap();
84///
85/// assert_eq!(buffer.as_slice(), [42, 42, 42]);
86/// # })
87/// ```
88pub fn repeat(byte: u8) -> Repeat {
89    Repeat(byte)
90}
compio_io\util/repeat.rs

compio_io\util/
repeat.rs
