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
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
|
// run-pass
// This test deserializes an enum in-place by transmuting to a union that
// should have the same layout, and manipulating the tag and payloads
// independently. This verifies that `repr(some_int)` has a stable representation,
// and that we don't miscompile these kinds of manipulations.
use std::time::Duration;
use std::mem;
#[repr(C, u8)]
#[derive(Copy, Clone, Eq, PartialEq, Debug)]
enum MyEnum {
A(u32), // Single primitive value
B { x: u8, y: i16, z: u8 }, // Composite, and the offsets of `y` and `z`
// depend on tag being internal
C, // Empty
D(Option<u32>), // Contains an enum
E(Duration), // Contains a struct
}
#[repr(C)]
struct MyEnumRepr {
tag: MyEnumTag,
payload: MyEnumPayload,
}
#[repr(C)]
#[allow(non_snake_case)]
union MyEnumPayload {
A: MyEnumVariantA,
B: MyEnumVariantB,
D: MyEnumVariantD,
E: MyEnumVariantE,
}
#[repr(u8)] #[derive(Copy, Clone)] enum MyEnumTag { A, B, C, D, E }
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantA(u32);
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantB {x: u8, y: i16, z: u8 }
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantD(Option<u32>);
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantE(Duration);
fn main() {
let result: Vec<Result<MyEnum, ()>> = vec![
Ok(MyEnum::A(17)),
Ok(MyEnum::B { x: 206, y: 1145, z: 78 }),
Ok(MyEnum::C),
Err(()),
Ok(MyEnum::D(Some(407))),
Ok(MyEnum::D(None)),
Ok(MyEnum::E(Duration::from_secs(100))),
Err(()),
];
// Binary serialized version of the above (little-endian)
let input: Vec<u8> = vec![
0, 17, 0, 0, 0,
1, 206, 121, 4, 78,
2,
8, /* invalid tag value */
3, 0, 151, 1, 0, 0,
3, 1,
4, 100, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, /* incomplete value */
];
let mut output = vec![];
let mut buf = &input[..];
unsafe {
// This should be safe, because we don't match on it unless it's fully formed,
// and it doesn't have a destructor.
//
// MyEnum is repr(C, u8) so it is guaranteed to have a separate discriminant and each
// variant can be zero initialized.
let mut dest: MyEnum = mem::zeroed();
while buf.len() > 0 {
match parse_my_enum(&mut dest, &mut buf) {
Ok(()) => output.push(Ok(dest)),
Err(()) => output.push(Err(())),
}
}
}
assert_eq!(output, result);
}
fn parse_my_enum<'a>(dest: &'a mut MyEnum, buf: &mut &[u8]) -> Result<(), ()> {
unsafe {
// Should be correct to do this transmute.
let dest: &'a mut MyEnumRepr = mem::transmute(dest);
let tag = read_u8(buf)?;
dest.tag = match tag {
0 => MyEnumTag::A,
1 => MyEnumTag::B,
2 => MyEnumTag::C,
3 => MyEnumTag::D,
4 => MyEnumTag::E,
_ => return Err(()),
};
match dest.tag {
MyEnumTag::A => {
dest.payload.A.0 = read_u32_le(buf)?;
}
MyEnumTag::B => {
dest.payload.B.x = read_u8(buf)?;
dest.payload.B.y = read_u16_le(buf)? as i16;
dest.payload.B.z = read_u8(buf)?;
}
MyEnumTag::C => {
/* do nothing */
}
MyEnumTag::D => {
let is_some = read_u8(buf)? == 0;
if is_some {
dest.payload.D.0 = Some(read_u32_le(buf)?);
} else {
dest.payload.D.0 = None;
}
}
MyEnumTag::E => {
let secs = read_u64_le(buf)?;
let nanos = read_u32_le(buf)?;
dest.payload.E.0 = Duration::new(secs, nanos);
}
}
Ok(())
}
}
// reader helpers
fn read_u64_le(buf: &mut &[u8]) -> Result<u64, ()> {
if buf.len() < 8 { return Err(()) }
let val = (buf[0] as u64) << 0
| (buf[1] as u64) << 8
| (buf[2] as u64) << 16
| (buf[3] as u64) << 24
| (buf[4] as u64) << 32
| (buf[5] as u64) << 40
| (buf[6] as u64) << 48
| (buf[7] as u64) << 56;
*buf = &buf[8..];
Ok(val)
}
fn read_u32_le(buf: &mut &[u8]) -> Result<u32, ()> {
if buf.len() < 4 { return Err(()) }
let val = (buf[0] as u32) << 0
| (buf[1] as u32) << 8
| (buf[2] as u32) << 16
| (buf[3] as u32) << 24;
*buf = &buf[4..];
Ok(val)
}
fn read_u16_le(buf: &mut &[u8]) -> Result<u16, ()> {
if buf.len() < 2 { return Err(()) }
let val = (buf[0] as u16) << 0
| (buf[1] as u16) << 8;
*buf = &buf[2..];
Ok(val)
}
fn read_u8(buf: &mut &[u8]) -> Result<u8, ()> {
if buf.len() < 1 { return Err(()) }
let val = buf[0];
*buf = &buf[1..];
Ok(val)
}
|
