Line data Source code
1 : use tokio_epoll_uring::BoundedBuf;
2 : use tokio_epoll_uring::BoundedBufMut;
3 : use tokio_epoll_uring::IoBufMut;
4 : use tokio_epoll_uring::Slice;
5 :
6 : pub(crate) trait SliceMutExt {
7 : /// Get a `&mut[0..self.bytes_total()`] slice, for when you need to do borrow-based IO.
8 : ///
9 : /// See the test case `test_slice_full_zeroed` for the difference to just doing `&slice[..]`
10 : fn as_mut_rust_slice_full_zeroed(&mut self) -> &mut [u8];
11 : }
12 :
13 : impl<B> SliceMutExt for Slice<B>
14 : where
15 : B: IoBufMut,
16 : {
17 : #[inline(always)]
18 778297 : fn as_mut_rust_slice_full_zeroed(&mut self) -> &mut [u8] {
19 778297 : // zero-initialize the uninitialized parts of the buffer so we can create a Rust slice
20 778297 : //
21 778297 : // SAFETY: we own `slice`, don't write outside the bounds
22 778297 : unsafe {
23 778297 : let to_init = self.bytes_total() - self.bytes_init();
24 778297 : self.stable_mut_ptr()
25 778297 : .add(self.bytes_init())
26 778297 : .write_bytes(0, to_init);
27 778297 : self.set_init(self.bytes_total());
28 778297 : };
29 778297 : let bytes_total = self.bytes_total();
30 778297 : &mut self[0..bytes_total]
31 778297 : }
32 : }
33 :
34 : #[cfg(test)]
35 : mod tests {
36 : use std::io::Read;
37 :
38 : use super::*;
39 : use bytes::Buf;
40 : use tokio_epoll_uring::Slice;
41 :
42 : #[test]
43 2 : fn test_slice_full_zeroed() {
44 6 : let make_fake_file = || bytes::BytesMut::from(&b"12345"[..]).reader();
45 :
46 : // before we start the test, let's make sure we have a shared understanding of what slice_full does
47 : {
48 2 : let buf = Vec::with_capacity(3);
49 2 : let slice: Slice<_> = buf.slice_full();
50 2 : assert_eq!(slice.bytes_init(), 0);
51 2 : assert_eq!(slice.bytes_total(), 3);
52 2 : let rust_slice = &slice[..];
53 2 : assert_eq!(
54 2 : rust_slice.len(),
55 : 0,
56 0 : "Slice only derefs to a &[u8] of the initialized part"
57 : );
58 : }
59 :
60 : // and also let's establish a shared understanding of .slice()
61 : {
62 2 : let buf = Vec::with_capacity(3);
63 2 : let slice: Slice<_> = buf.slice(0..2);
64 2 : assert_eq!(slice.bytes_init(), 0);
65 2 : assert_eq!(slice.bytes_total(), 2);
66 2 : let rust_slice = &slice[..];
67 2 : assert_eq!(
68 2 : rust_slice.len(),
69 : 0,
70 0 : "Slice only derefs to a &[u8] of the initialized part"
71 : );
72 : }
73 :
74 : // the above leads to the easy mistake of using slice[..] for borrow-based IO like so:
75 : {
76 2 : let buf = Vec::with_capacity(3);
77 2 : let mut slice: Slice<_> = buf.slice_full();
78 2 : assert_eq!(slice[..].len(), 0);
79 2 : let mut file = make_fake_file();
80 2 : file.read_exact(&mut slice[..]).unwrap(); // one might think this reads 3 bytes but it reads 0
81 2 : assert_eq!(&slice[..] as &[u8], &[][..] as &[u8]);
82 : }
83 :
84 : // With owned buffers IO like with VirtualFilem, you could totally
85 : // pass in a `Slice` with bytes_init()=0 but bytes_total()=5
86 : // and it will read 5 bytes into the slice, and return a slice that has bytes_init()=5.
87 2 : {
88 2 : // TODO: demo
89 2 : }
90 2 :
91 2 : //
92 2 : // Ok, now that we have a shared understanding let's demo how to use the extension trait.
93 2 : //
94 2 :
95 2 : // slice_full()
96 2 : {
97 2 : let buf = Vec::with_capacity(3);
98 2 : let mut slice: Slice<_> = buf.slice_full();
99 2 : let rust_slice = slice.as_mut_rust_slice_full_zeroed();
100 2 : assert_eq!(rust_slice.len(), 3);
101 2 : assert_eq!(rust_slice, &[0, 0, 0]);
102 2 : let mut file = make_fake_file();
103 2 : file.read_exact(rust_slice).unwrap();
104 2 : assert_eq!(rust_slice, b"123");
105 2 : assert_eq!(&slice[..], b"123");
106 : }
107 :
108 : // .slice(..)
109 : {
110 2 : let buf = Vec::with_capacity(3);
111 2 : let mut slice: Slice<_> = buf.slice(0..2);
112 2 : let rust_slice = slice.as_mut_rust_slice_full_zeroed();
113 2 : assert_eq!(rust_slice.len(), 2);
114 2 : assert_eq!(rust_slice, &[0, 0]);
115 2 : let mut file = make_fake_file();
116 2 : file.read_exact(rust_slice).unwrap();
117 2 : assert_eq!(rust_slice, b"12");
118 2 : assert_eq!(&slice[..], b"12");
119 : }
120 2 : }
121 : }
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