src/libproc_macro/bridge/buffer.rs

   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 struct Slice<'a, T> {
  10     data: &'a [T; 0],
  11     len: usize,
  12 }
  13
  14 unsafe impl<'a, T: Sync> Sync for Slice<'a, T> {}
  15 unsafe impl<'a, T: Sync> Send for Slice<'a, T> {}
  16
  17 impl<T> Copy for Slice<'a, T> {}
  18 impl<T> Clone for Slice<'a, T> {
  19     fn clone(&self) -> Self {
  20         *self
  21     }
  22 }
  23
  24 impl<T> From<&'a [T]> for Slice<'a, T> {
  25     fn from(xs: &'a [T]) -> Self {
  26         Slice {
  27             data: unsafe { &*(xs.as_ptr() as *const [T; 0]) },
  28             len: xs.len(),
  29         }
  30     }
  31 }
  32
  33 impl<T> Deref for Slice<'a, T> {
  34     type Target = [T];
  35     fn deref(&self) -> &[T] {
  36         unsafe { slice::from_raw_parts(self.data.as_ptr(), self.len) }
  37     }
  38 }
  39
  40 #[repr(C)]
  41 pub struct Buffer<T: Copy> {
  42     data: *mut T,
  43     len: usize,
  44     capacity: usize,
  45     extend_from_slice: extern "C" fn(Buffer<T>, Slice<'_, T>) -> Buffer<T>,
  46     drop: extern "C" fn(Buffer<T>),
  47 }
  48
  49 unsafe impl<T: Copy + Sync> Sync for Buffer<T> {}
  50 unsafe impl<T: Copy + Send> Send for Buffer<T> {}
  51
  52 impl<T: Copy> Default for Buffer<T> {
  53     fn default() -> Self {
  54         Self::from(vec![])
  55     }
  56 }
  57
  58 impl<T: Copy> Deref for Buffer<T> {
  59     type Target = [T];
  60     fn deref(&self) -> &[T] {
  61         unsafe { slice::from_raw_parts(self.data as *const T, self.len) }
  62     }
  63 }
  64
  65 impl<T: Copy> DerefMut for Buffer<T> {
  66     fn deref_mut(&mut self) -> &mut [T] {
  67         unsafe { slice::from_raw_parts_mut(self.data, self.len) }
  68     }
  69 }
  70
  71 impl<T: Copy> Buffer<T> {
  72     pub(super) fn new() -> Self {
  73         Self::default()
  74     }
  75
  76     pub(super) fn clear(&mut self) {
  77         self.len = 0;
  78     }
  79
  80     pub(super) fn take(&mut self) -> Self {
  81         mem::take(self)
  82     }
  83
  84     pub(super) fn extend_from_slice(&mut self, xs: &[T]) {
  85         // Fast path to avoid going through an FFI call.
  86         if let Some(final_len) = self.len.checked_add(xs.len()) {
  87             if final_len <= self.capacity {
  88                 let dst = unsafe { slice::from_raw_parts_mut(self.data, self.capacity) };
  89                 dst[self.len..][..xs.len()].copy_from_slice(xs);
  90                 self.len = final_len;
  91                 return;
  92             }
  93         }
  94         let b = self.take();
  95         *self = (b.extend_from_slice)(b, Slice::from(xs));
  96     }
  97 }
  98
  99 impl Write for Buffer<u8> {
 100     fn write(&mut self, xs: &[u8]) -> io::Result<usize> {
 101         self.extend_from_slice(xs);
 102         Ok(xs.len())
 103     }
 104
 105     fn write_all(&mut self, xs: &[u8]) -> io::Result<()> {
 106         self.extend_from_slice(xs);
 107         Ok(())
 108     }
 109
 110     fn flush(&mut self) -> io::Result<()> {
 111         Ok(())
 112     }
 113 }
 114
 115 impl<T: Copy> Drop for Buffer<T> {
 116     fn drop(&mut self) {
 117         let b = self.take();
 118         (b.drop)(b);
 119     }
 120 }
 121
 122 impl<T: Copy> From<Vec<T>> for Buffer<T> {
 123     fn from(mut v: Vec<T>) -> Self {
 124         let (data, len, capacity) = (v.as_mut_ptr(), v.len(), v.capacity());
 125         mem::forget(v);
 126
 127         // This utility function is nested in here because it can *only*
 128         // be safely called on `Buffer`s created by *this* `proc_macro`.
 129         fn to_vec<T: Copy>(b: Buffer<T>) -> Vec<T> {
 130             unsafe {
 131                 let Buffer {
 132                     data,
 133                     len,
 134                     capacity,
 135                     ..
 136                 } = b;
 137                 mem::forget(b);
 138                 Vec::from_raw_parts(data, len, capacity)
 139             }
 140         }
 141
 142         extern "C" fn extend_from_slice<T: Copy>(b: Buffer<T>, xs: Slice<'_, T>) -> Buffer<T> {
 143             let mut v = to_vec(b);
 144             v.extend_from_slice(&xs);
 145             Buffer::from(v)
 146         }
 147
 148         extern "C" fn drop<T: Copy>(b: Buffer<T>) {
 149             mem::drop(to_vec(b));
 150         }
 151
 152         Buffer {
 153             data,
 154             len,
 155             capacity,
 156             extend_from_slice,
 157             drop,
 158         }
 159     }
 160 }