1//! Buffer management for same-process client<->server communication.
2
3use std::io::{self, Write};
4use std::mem::{self, ManuallyDrop};
5use std::ops::{Deref, DerefMut};
6use std::slice;
7
8#[repr(C)]
9pub struct Buffer {
10 data: *mut u8,
11 len: usize,
12 capacity: usize,
13 reserve: extern "C" fn(Buffer, usize) -> Buffer,
14 drop: extern "C" fn(Buffer),
15}
16
17unsafe impl Sync for Buffer {}
18unsafe impl Send for Buffer {}
19
20impl Default for Buffer {
21 #[inline]
22 fn default() -> Self {
23 Self::from(vec![])
24 }
25}
26
27impl Deref for Buffer {
28 type Target = [u8];
29 #[inline]
30 fn deref(&self) -> &[u8] {
31 unsafe { slice::from_raw_parts(self.data as *const u8, self.len) }
32 }
33}
34
35impl DerefMut for Buffer {
36 #[inline]
37 fn deref_mut(&mut self) -> &mut [u8] {
38 unsafe { slice::from_raw_parts_mut(self.data, self.len) }
39 }
40}
41
42impl Buffer {
43 #[inline]
44 pub(super) fn new() -> Self {
45 Self::default()
46 }
47
48 #[inline]
49 pub(super) fn clear(&mut self) {
50 self.len = 0;
51 }
52
53 #[inline]
54 pub(super) fn take(&mut self) -> Self {
55 mem::take(self)
56 }
57
58 // We have the array method separate from extending from a slice. This is
59 // because in the case of small arrays, codegen can be more efficient
60 // (avoiding a memmove call). With extend_from_slice, LLVM at least
61 // currently is not able to make that optimization.
62 #[inline]
63 pub(super) fn extend_from_array<const N: usize>(&mut self, xs: &[u8; N]) {
64 if xs.len() > (self.capacity - self.len) {
65 let b = self.take();
66 *self = (b.reserve)(b, xs.len());
67 }
68 unsafe {
69 xs.as_ptr().copy_to_nonoverlapping(self.data.add(self.len), xs.len());
70 self.len += xs.len();
71 }
72 }
73
74 #[inline]
75 pub(super) fn extend_from_slice(&mut self, xs: &[u8]) {
76 if xs.len() > (self.capacity - self.len) {
77 let b = self.take();
78 *self = (b.reserve)(b, xs.len());
79 }
80 unsafe {
81 xs.as_ptr().copy_to_nonoverlapping(self.data.add(self.len), xs.len());
82 self.len += xs.len();
83 }
84 }
85
86 #[inline]
87 pub(super) fn push(&mut self, v: u8) {
88 // The code here is taken from Vec::push, and we know that reserve()
89 // will panic if we're exceeding isize::MAX bytes and so there's no need
90 // to check for overflow.
91 if self.len == self.capacity {
92 let b = self.take();
93 *self = (b.reserve)(b, 1);
94 }
95 unsafe {
96 *self.data.add(self.len) = v;
97 self.len += 1;
98 }
99 }
100}
101
102impl Write for Buffer {
103 #[inline]
104 fn write(&mut self, xs: &[u8]) -> io::Result<usize> {
105 self.extend_from_slice(xs);
106 Ok(xs.len())
107 }
108
109 #[inline]
110 fn write_all(&mut self, xs: &[u8]) -> io::Result<()> {
111 self.extend_from_slice(xs);
112 Ok(())
113 }
114
115 #[inline]
116 fn flush(&mut self) -> io::Result<()> {
117 Ok(())
118 }
119}
120
121impl Drop for Buffer {
122 #[inline]
123 fn drop(&mut self) {
124 let b: Buffer = self.take();
125 (b.drop)(b);
126 }
127}
128
129impl From<Vec<u8>> for Buffer {
130 fn from(v: Vec<u8>) -> Self {
131 let mut v = ManuallyDrop::new(v);
132 let (data, len, capacity) = (v.as_mut_ptr(), v.len(), v.capacity());
133
134 // This utility function is nested in here because it can *only*
135 // be safely called on `Buffer`s created by *this* `proc_macro`.
136 fn to_vec(b: Buffer) -> Vec<u8> {
137 unsafe {
138 let b = ManuallyDrop::new(b);
139 Vec::from_raw_parts(b.data, b.len, b.capacity)
140 }
141 }
142
143 extern "C" fn reserve(b: Buffer, additional: usize) -> Buffer {
144 let mut v = to_vec(b);
145 v.reserve(additional);
146 Buffer::from(v)
147 }
148
149 extern "C" fn drop(b: Buffer) {
150 mem::drop(to_vec(b));
151 }
152
153 Buffer { data, len, capacity, reserve, drop }
154 }
155}
156