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Move rebuild_vec into a method #659

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Move rebuild_vec into a method #659

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cb7addd
Move rebuild_vec into a method
braddunbar Jan 19, 2024
f62a4d0
add safety section to rebuild_vec
braddunbar Jan 19, 2024
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39 changes: 25 additions & 14 deletions src/bytes_mut.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -248,7 +248,7 @@ impl BytesMut {
// Just re-use `Bytes` internal Vec vtable
unsafe {
let (off, _) = self.get_vec_pos();
let vec = rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off);
let vec = self.rebuild_vec(off);
mem::forget(self);
let mut b: Bytes = vec.into();
b.advance(off);
Expand Down Expand Up @@ -629,8 +629,7 @@ impl BytesMut {
} else {
// Not enough space, or reusing might be too much overhead:
// allocate more space!
let mut v =
ManuallyDrop::new(rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off));
let mut v = ManuallyDrop::new(self.rebuild_vec(off));
v.reserve(additional);

// Update the info
Expand Down Expand Up @@ -950,7 +949,7 @@ impl BytesMut {
// `Arc`, those three fields still are the components of the
// vector.
let shared = Box::new(Shared {
vec: rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off),
vec: self.rebuild_vec(off),
original_capacity_repr,
ref_count: AtomicUsize::new(ref_cnt),
});
Comment on lines 951 to 955
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And you don't actually follow the safety requirements as stated here.

Expand Down Expand Up @@ -1035,6 +1034,26 @@ impl BytesMut {
slice::from_raw_parts_mut(ptr.cast(), len)
}
}

/// Rebuild a vec from `offset` with the existing pointer, length, and capacity.
///
/// # Safety
///
/// After calling this method, ownership of the allocation for this instance is transferred to
/// the returned `Vec` but `self.ptr` will still point into it.
///
/// The caller must ensure all of the following:
///
/// * `offset` is the number of bytes from the start of the original allocation to `self.ptr`
/// * `self.ptr` will not be dereferenced again
#[inline]
unsafe fn rebuild_vec(&self, offset: usize) -> Vec<u8> {
let ptr = self.ptr.as_ptr().offset(-(offset as isize));
let len = self.len + offset;
let cap = self.cap + offset;

Vec::from_raw_parts(ptr, len, cap)
}
}

impl Drop for BytesMut {
Expand All @@ -1046,7 +1065,7 @@ impl Drop for BytesMut {
let (off, _) = self.get_vec_pos();

// Vector storage, free the vector
let _ = rebuild_vec(self.ptr.as_ptr(), self.len, self.cap, off);
let _ = self.rebuild_vec(off);
}
} else if kind == KIND_ARC {
unsafe { release_shared(self.data) };
Expand Down Expand Up @@ -1626,7 +1645,7 @@ impl From<BytesMut> for Vec<u8> {
let mut vec = if kind == KIND_VEC {
unsafe {
let (off, _) = bytes.get_vec_pos();
rebuild_vec(bytes.ptr.as_ptr(), bytes.len, bytes.cap, off)
bytes.rebuild_vec(off)
}
} else if kind == KIND_ARC {
let shared = bytes.data as *mut Shared;
Expand Down Expand Up @@ -1695,14 +1714,6 @@ fn offset_from(dst: *mut u8, original: *mut u8) -> usize {
dst as usize - original as usize
}

unsafe fn rebuild_vec(ptr: *mut u8, mut len: usize, mut cap: usize, off: usize) -> Vec<u8> {
let ptr = ptr.offset(-(off as isize));
len += off;
cap += off;

Vec::from_raw_parts(ptr, len, cap)
}

// ===== impl SharedVtable =====

static SHARED_VTABLE: Vtable = Vtable {
Expand Down