1 //! Buffer management for same-process client<->server communication. 2 3 use std::io::{self, Write}; 4 use std::mem; 5 use std::ops::{Deref, DerefMut}; 6 use std::slice; 7 8 #[repr(C)] 9 pub 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 17 unsafe impl Sync for Buffer {} 18 unsafe impl Send for Buffer {} 19 20 impl Default for Buffer { 21 #[inline] default() -> Self22 fn default() -> Self { 23 Self::from(vec![]) 24 } 25 } 26 27 impl Deref for Buffer { 28 type Target = [u8]; 29 #[inline] deref(&self) -> &[u8]30 fn deref(&self) -> &[u8] { 31 unsafe { slice::from_raw_parts(self.data as *const u8, self.len) } 32 } 33 } 34 35 impl DerefMut for Buffer { 36 #[inline] deref_mut(&mut self) -> &mut [u8]37 fn deref_mut(&mut self) -> &mut [u8] { 38 unsafe { slice::from_raw_parts_mut(self.data, self.len) } 39 } 40 } 41 42 impl Buffer { 43 #[inline] new() -> Self44 pub(super) fn new() -> Self { 45 Self::default() 46 } 47 48 #[inline] clear(&mut self)49 pub(super) fn clear(&mut self) { 50 self.len = 0; 51 } 52 53 #[inline] take(&mut self) -> Self54 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] extend_from_array<const N: usize>(&mut self, xs: &[u8; N])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] extend_from_slice(&mut self, xs: &[u8])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] push(&mut self, v: u8)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 } 101 102 impl Write for Buffer { 103 #[inline] write(&mut self, xs: &[u8]) -> io::Result<usize>104 fn write(&mut self, xs: &[u8]) -> io::Result<usize> { 105 self.extend_from_slice(xs); 106 Ok(xs.len()) 107 } 108 109 #[inline] write_all(&mut self, xs: &[u8]) -> io::Result<()>110 fn write_all(&mut self, xs: &[u8]) -> io::Result<()> { 111 self.extend_from_slice(xs); 112 Ok(()) 113 } 114 115 #[inline] flush(&mut self) -> io::Result<()>116 fn flush(&mut self) -> io::Result<()> { 117 Ok(()) 118 } 119 } 120 121 impl Drop for Buffer { 122 #[inline] drop(&mut self)123 fn drop(&mut self) { 124 let b = self.take(); 125 (b.drop)(b); 126 } 127 } 128 129 impl From<Vec<u8>> for Buffer { from(mut v: Vec<u8>) -> Self130 fn from(mut v: Vec<u8>) -> Self { 131 let (data, len, capacity) = (v.as_mut_ptr(), v.len(), v.capacity()); 132 mem::forget(v); 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 Buffer { data, len, capacity, .. } = b; 139 mem::forget(b); 140 Vec::from_raw_parts(data, len, capacity) 141 } 142 } 143 144 extern "C" fn reserve(b: Buffer, additional: usize) -> Buffer { 145 let mut v = to_vec(b); 146 v.reserve(additional); 147 Buffer::from(v) 148 } 149 150 extern "C" fn drop(b: Buffer) { 151 mem::drop(to_vec(b)); 152 } 153 154 Buffer { data, len, capacity, reserve, drop } 155 } 156 } 157