1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
pub(crate) type AtomicPtr<T> = *mut T;
#[allow(unused)]
pub(crate) struct RawBytes {
ptr: *const u8,
len: usize,
data: AtomicPtr<()>,
vtable: &'static Vtable,
}
impl RawBytes {
pub fn new_raw(
ptr: *const u8,
len: usize,
data: AtomicPtr<()>,
vtable: &'static Vtable,
) -> bytes::Bytes {
RawBytes {
ptr,
len,
data,
vtable,
}
.into()
}
}
const _: () = {
assert!(
core::mem::size_of::<RawBytes>() == core::mem::size_of::<bytes::Bytes>(),
);
assert!(
core::mem::align_of::<RawBytes>() == core::mem::align_of::<bytes::Bytes>(),
);
};
#[allow(unused)]
pub(crate) struct Vtable {
pub clone: unsafe fn(&AtomicPtr<()>, *const u8, usize) -> bytes::Bytes,
pub to_vec: unsafe fn(&AtomicPtr<()>, *const u8, usize) -> Vec<u8>,
pub drop: unsafe fn(&mut AtomicPtr<()>, *const u8, usize),
}
impl From<RawBytes> for bytes::Bytes {
fn from(b: RawBytes) -> Self {
unsafe { std::mem::transmute(b) }
}
}
#[cfg(test)]
mod tests {
use super::*;
use std::mem;
const HELLO: &str = "hello";
const STATIC_VTABLE: Vtable = Vtable {
clone: static_clone,
drop: static_drop,
to_vec: static_to_vec,
};
unsafe fn static_clone(
_: &AtomicPtr<()>,
ptr: *const u8,
len: usize,
) -> bytes::Bytes {
from_static(std::slice::from_raw_parts(ptr, len)).into()
}
unsafe fn static_to_vec(
_: &AtomicPtr<()>,
ptr: *const u8,
len: usize,
) -> Vec<u8> {
let slice = std::slice::from_raw_parts(ptr, len);
slice.to_vec()
}
unsafe fn static_drop(_: &mut AtomicPtr<()>, _: *const u8, _: usize) {
}
fn from_static(bytes: &'static [u8]) -> RawBytes {
RawBytes {
ptr: bytes.as_ptr(),
len: bytes.len(),
data: std::ptr::null_mut(),
vtable: &STATIC_VTABLE,
}
}
#[test]
fn bytes_identity() {
let b1: bytes::Bytes = from_static(HELLO.as_bytes()).into();
let b2 = bytes::Bytes::from_static(HELLO.as_bytes());
assert_eq!(b1, b2); }
#[test]
fn bytes_layout() {
let u1: [usize; 4] =
unsafe { mem::transmute(from_static(HELLO.as_bytes())) };
let u2: [usize; 4] =
unsafe { mem::transmute(bytes::Bytes::from_static(HELLO.as_bytes())) };
assert_eq!(u1[..3], u2[..3]); }
}