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Make the writer even more unsafe. #1830

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Merged
merged 1 commit into from
Oct 8, 2017
Merged

Make the writer even more unsafe. #1830

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21 changes: 14 additions & 7 deletions webrender_api/src/display_list.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -492,15 +492,13 @@ impl<'a, 'b> Serialize for DisplayItemRef<'a, 'b> {
// }
//

struct UnsafeVecWriter<'a>(&'a mut Vec<u8>);
struct UnsafeVecWriter(*mut u8);

impl<'a> Write for UnsafeVecWriter<'a> {
impl Write for UnsafeVecWriter {
fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
unsafe {
let old_len = self.0.len();
self.0.set_len(old_len + buf.len());
debug_assert!(self.0.len() <= self.0.capacity());
ptr::copy_nonoverlapping(buf.as_ptr(), self.0.as_mut_ptr().offset(old_len as isize), buf.len());
ptr::copy_nonoverlapping(buf.as_ptr(), self.0, buf.len());
self.0 = self.0.offset(buf.len() as isize);
}
Ok(buf.len())
}
Expand All @@ -523,7 +521,16 @@ fn serialize_fast<T: Serialize>(vec: &mut Vec<u8>, e: &T) {
bincode::serialize_into(&mut size,e , bincode::Infinite).unwrap();
vec.reserve(size.0);

bincode::serialize_into(&mut UnsafeVecWriter(vec), e, bincode::Infinite).unwrap();
let old_len = vec.len();
let ptr = unsafe { vec.as_mut_ptr().offset(old_len as isize) };
let mut w = UnsafeVecWriter(ptr);
bincode::serialize_into(&mut w, e, bincode::Infinite).unwrap();

// fix up the length
unsafe { vec.set_len(old_len + size.0); }

// make sure we wrote the right amount
debug_assert!(((w.0 as usize) - (vec.as_ptr() as usize)) == vec.len());
}

#[derive(Clone)]
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