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//! lib-proc-macro Buffer management for same-process client<->server communication.
//!
//! Copy from <https://github.com/rust-lang/rust/blob/6050e523bae6de61de4e060facc43dc512adaccd/src/libproc_macro/bridge/buffer.rs>
//! augmented with removing unstable features
use std::io::{self, Write};
use std::mem;
use std::ops::{Deref, DerefMut};
use std::slice;
#[repr(C)]
struct Slice<'a, T> {
data: &'a [T; 0],
len: usize,
}
unsafe impl<'a, T: Sync> Sync for Slice<'a, T> {}
unsafe impl<'a, T: Sync> Send for Slice<'a, T> {}
impl<'a, T> Copy for Slice<'a, T> {}
impl<'a, T> Clone for Slice<'a, T> {
fn clone(&self) -> Self {
*self
}
}
impl<'a, T> From<&'a [T]> for Slice<'a, T> {
fn from(xs: &'a [T]) -> Self {
Slice { data: unsafe { &*(xs.as_ptr() as *const [T; 0]) }, len: xs.len() }
}
}
impl<'a, T> Deref for Slice<'a, T> {
type Target = [T];
fn deref(&self) -> &[T] {
unsafe { slice::from_raw_parts(self.data.as_ptr(), self.len) }
}
}
#[repr(C)]
pub struct Buffer<T: Copy> {
data: *mut T,
len: usize,
capacity: usize,
extend_from_slice: extern "C" fn(Buffer<T>, Slice<'_, T>) -> Buffer<T>,
drop: extern "C" fn(Buffer<T>),
}
unsafe impl<T: Copy + Sync> Sync for Buffer<T> {}
unsafe impl<T: Copy + Send> Send for Buffer<T> {}
impl<T: Copy> Default for Buffer<T> {
fn default() -> Self {
Self::from(vec![])
}
}
impl<T: Copy> Deref for Buffer<T> {
type Target = [T];
fn deref(&self) -> &[T] {
unsafe { slice::from_raw_parts(self.data as *const T, self.len) }
}
}
impl<T: Copy> DerefMut for Buffer<T> {
fn deref_mut(&mut self) -> &mut [T] {
unsafe { slice::from_raw_parts_mut(self.data, self.len) }
}
}
impl<T: Copy> Buffer<T> {
pub(super) fn new() -> Self {
Self::default()
}
pub(super) fn clear(&mut self) {
self.len = 0;
}
pub(super) fn take(&mut self) -> Self {
mem::take(self)
}
pub(super) fn extend_from_slice(&mut self, xs: &[T]) {
// Fast path to avoid going through an FFI call.
if let Some(final_len) = self.len.checked_add(xs.len()) {
if final_len <= self.capacity {
let dst = unsafe { slice::from_raw_parts_mut(self.data, self.capacity) };
dst[self.len..][..xs.len()].copy_from_slice(xs);
self.len = final_len;
return;
}
}
let b = self.take();
*self = (b.extend_from_slice)(b, Slice::from(xs));
}
}
impl Write for Buffer<u8> {
fn write(&mut self, xs: &[u8]) -> io::Result<usize> {
self.extend_from_slice(xs);
Ok(xs.len())
}
fn write_all(&mut self, xs: &[u8]) -> io::Result<()> {
self.extend_from_slice(xs);
Ok(())
}
fn flush(&mut self) -> io::Result<()> {
Ok(())
}
}
impl<T: Copy> Drop for Buffer<T> {
fn drop(&mut self) {
let b = self.take();
(b.drop)(b);
}
}
impl<T: Copy> From<Vec<T>> for Buffer<T> {
fn from(mut v: Vec<T>) -> Self {
let (data, len, capacity) = (v.as_mut_ptr(), v.len(), v.capacity());
mem::forget(v);
// This utility function is nested in here because it can *only*
// be safely called on `Buffer`s created by *this* `proc_macro`.
fn to_vec<T: Copy>(b: Buffer<T>) -> Vec<T> {
unsafe {
let Buffer { data, len, capacity, .. } = b;
mem::forget(b);
Vec::from_raw_parts(data, len, capacity)
}
}
extern "C" fn extend_from_slice<T: Copy>(b: Buffer<T>, xs: Slice<'_, T>) -> Buffer<T> {
let mut v = to_vec(b);
v.extend_from_slice(&xs);
Buffer::from(v)
}
extern "C" fn drop<T: Copy>(b: Buffer<T>) {
mem::drop(to_vec(b));
}
Buffer { data, len, capacity, extend_from_slice, drop }
}
}
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