buffer.rs - source
Description: Source of the Rust file `library/proc_macro/src/bridge/buffer.rs`.

#
proc_macro/bridge/
buffer.rs

    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 = 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}