Adding upstream version 86.0.1.upstream/86.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1004 insertions, 0 deletions

diff --git a/third_party/rust/bytes/src/bytes.rs b/third_party/rust/bytes/src/bytes.rs
new file mode 100644
index 0000000000..e2f08b57e5
--- /dev/null
+++ b/third_party/rust/bytes/src/bytes.rs
@@ -0,0 +1,1004 @@
+use core::{cmp, fmt, hash, mem, ptr, slice, usize};
+use core::iter::{FromIterator};
+use core::ops::{Deref, RangeBounds};
+
+use alloc::{vec::Vec, string::String, boxed::Box, borrow::Borrow};
+
+use crate::Buf;
+use crate::buf::IntoIter;
+use crate::debug;
+use crate::loom::sync::atomic::{self, AtomicPtr, AtomicUsize, Ordering};
+
+/// A reference counted contiguous slice of memory.
+///
+/// `Bytes` is an efficient container for storing and operating on contiguous
+/// slices of memory. It is intended for use primarily in networking code, but
+/// could have applications elsewhere as well.
+///
+/// `Bytes` values facilitate zero-copy network programming by allowing multiple
+/// `Bytes` objects to point to the same underlying memory. This is managed by
+/// using a reference count to track when the memory is no longer needed and can
+/// be freed.
+///
+/// ```
+/// use bytes::Bytes;
+///
+/// let mut mem = Bytes::from("Hello world");
+/// let a = mem.slice(0..5);
+///
+/// assert_eq!(a, "Hello");
+///
+/// let b = mem.split_to(6);
+///
+/// assert_eq!(mem, "world");
+/// assert_eq!(b, "Hello ");
+/// ```
+///
+/// # Memory layout
+///
+/// The `Bytes` struct itself is fairly small, limited to 4 `usize` fields used
+/// to track information about which segment of the underlying memory the
+/// `Bytes` handle has access to.
+///
+/// `Bytes` keeps both a pointer to the shared `Arc` containing the full memory
+/// slice and a pointer to the start of the region visible by the handle.
+/// `Bytes` also tracks the length of its view into the memory.
+///
+/// # Sharing
+///
+/// The memory itself is reference counted, and multiple `Bytes` objects may
+/// point to the same region. Each `Bytes` handle point to different sections within
+/// the memory region, and `Bytes` handle may or may not have overlapping views
+/// into the memory.
+///
+///
+/// ```text
+///
+///    Arc ptrs                   +---------+
+///    ________________________ / | Bytes 2 |
+///   /                           +---------+
+///  /          +-----------+     |         |
+/// |_________/ |  Bytes 1  |     |         |
+/// |           +-----------+     |         |
+/// |           |           | ___/ data     | tail
+/// |      data |      tail |/              |
+/// v           v           v               v
+/// +-----+---------------------------------+-----+
+/// | Arc |     |           |               |     |
+/// +-----+---------------------------------+-----+
+/// ```
+pub struct Bytes {
+    ptr: *const u8,
+    len: usize,
+    // inlined "trait object"
+    data: AtomicPtr<()>,
+    vtable: &'static Vtable,
+}
+
+pub(crate) struct Vtable {
+    /// fn(data, ptr, len)
+    pub clone: unsafe fn(&AtomicPtr<()>, *const u8, usize) -> Bytes,
+    /// fn(data, ptr, len)
+    pub drop: unsafe fn(&mut AtomicPtr<()>, *const u8, usize),
+}
+
+impl Bytes {
+    /// Creates a new empty `Bytes`.
+    ///
+    /// This will not allocate and the returned `Bytes` handle will be empty.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bytes::Bytes;
+    ///
+    /// let b = Bytes::new();
+    /// assert_eq!(&b[..], b"");
+    /// ```
+    #[inline]
+    pub fn new() -> Bytes {
+        Bytes::from_static(b"")
+    }
+
+    /// Creates a new `Bytes` from a static slice.
+    ///
+    /// The returned `Bytes` will point directly to the static slice. There is
+    /// no allocating or copying.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bytes::Bytes;
+    ///
+    /// let b = Bytes::from_static(b"hello");
+    /// assert_eq!(&b[..], b"hello");
+    /// ```
+    #[inline]
+    #[cfg(not(all(loom, test)))]
+    pub const fn from_static(bytes: &'static [u8]) -> Bytes {
+        Bytes {
+            ptr: bytes.as_ptr(),
+            len: bytes.len(),
+            data: AtomicPtr::new(ptr::null_mut()),
+            vtable: &STATIC_VTABLE,
+        }
+    }
+
+    #[cfg(all(loom, test))]
+    pub fn from_static(bytes: &'static [u8]) -> Bytes {
+        Bytes {
+            ptr: bytes.as_ptr(),
+            len: bytes.len(),
+            data: AtomicPtr::new(ptr::null_mut()),
+            vtable: &STATIC_VTABLE,
+        }
+    }
+
+    /// Returns the number of bytes contained in this `Bytes`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bytes::Bytes;
+    ///
+    /// let b = Bytes::from(&b"hello"[..]);
+    /// assert_eq!(b.len(), 5);
+    /// ```
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.len
+    }
+
+    /// Returns true if the `Bytes` has a length of 0.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bytes::Bytes;
+    ///
+    /// let b = Bytes::new();
+    /// assert!(b.is_empty());
+    /// ```
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.len == 0
+    }
+
+
+    ///Creates `Bytes` instance from slice, by copying it.
+    pub fn copy_from_slice(data: &[u8]) -> Self {
+        data.to_vec().into()
+    }
+
+    /// Returns a slice of self for the provided range.
+    ///
+    /// This will increment the reference count for the underlying memory and
+    /// return a new `Bytes` handle set to the slice.
+    ///
+    /// This operation is `O(1)`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bytes::Bytes;
+    ///
+    /// let a = Bytes::from(&b"hello world"[..]);
+    /// let b = a.slice(2..5);
+    ///
+    /// assert_eq!(&b[..], b"llo");
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// Requires that `begin <= end` and `end <= self.len()`, otherwise slicing
+    /// will panic.
+    pub fn slice(&self, range: impl RangeBounds<usize>) -> Bytes {
+        use core::ops::Bound;
+
+        let len = self.len();
+
+        let begin = match range.start_bound() {
+            Bound::Included(&n) => n,
+            Bound::Excluded(&n) => n + 1,
+            Bound::Unbounded => 0,
+        };
+
+        let end = match range.end_bound() {
+            Bound::Included(&n) => n + 1,
+            Bound::Excluded(&n) => n,
+            Bound::Unbounded => len,
+        };
+
+        assert!(begin <= end);
+        assert!(end <= len);
+
+        if end == begin {
+            return Bytes::new();
+        }
+
+
+        let mut ret = self.clone();
+
+        ret.len = end - begin;
+        ret.ptr = unsafe { ret.ptr.offset(begin as isize) };
+
+        ret
+    }
+
+    /// Returns a slice of self that is equivalent to the given `subset`.
+    ///
+    /// When processing a `Bytes` buffer with other tools, one often gets a
+    /// `&[u8]` which is in fact a slice of the `Bytes`, i.e. a subset of it.
+    /// This function turns that `&[u8]` into another `Bytes`, as if one had
+    /// called `self.slice()` with the offsets that correspond to `subset`.
+    ///
+    /// This operation is `O(1)`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bytes::Bytes;
+    ///
+    /// let bytes = Bytes::from(&b"012345678"[..]);
+    /// let as_slice = bytes.as_ref();
+    /// let subset = &as_slice[2..6];
+    /// let subslice = bytes.slice_ref(&subset);
+    /// assert_eq!(&subslice[..], b"2345");
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// Requires that the given `sub` slice is in fact contained within the
+    /// `Bytes` buffer; otherwise this function will panic.
+    pub fn slice_ref(&self, subset: &[u8]) -> Bytes {
+        let bytes_p = self.as_ptr() as usize;
+        let bytes_len = self.len();
+
+        let sub_p = subset.as_ptr() as usize;
+        let sub_len = subset.len();
+
+        assert!(
+            sub_p >= bytes_p,
+            "subset pointer ({:p}) is smaller than self pointer ({:p})",
+            sub_p as *const u8,
+            bytes_p as *const u8,
+        );
+        assert!(
+            sub_p + sub_len <= bytes_p + bytes_len,
+            "subset is out of bounds: self = ({:p}, {}), subset = ({:p}, {})",
+            bytes_p as *const u8,
+            bytes_len,
+            sub_p as *const u8,
+            sub_len,
+        );
+
+        let sub_offset = sub_p - bytes_p;
+
+        self.slice(sub_offset..(sub_offset + sub_len))
+    }
+
+    /// Splits the bytes into two at the given index.
+    ///
+    /// Afterwards `self` contains elements `[0, at)`, and the returned `Bytes`
+    /// contains elements `[at, len)`.
+    ///
+    /// This is an `O(1)` operation that just increases the reference count and
+    /// sets a few indices.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bytes::Bytes;
+    ///
+    /// let mut a = Bytes::from(&b"hello world"[..]);
+    /// let b = a.split_off(5);
+    ///
+    /// assert_eq!(&a[..], b"hello");
+    /// assert_eq!(&b[..], b" world");
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// Panics if `at > len`.
+    #[must_use = "consider Bytes::truncate if you don't need the other half"]
+    pub fn split_off(&mut self, at: usize) -> Bytes {
+        assert!(at <= self.len());
+
+        if at == self.len() {
+            return Bytes::new();
+        }
+
+        if at == 0 {
+            return mem::replace(self, Bytes::new());
+        }
+
+        let mut ret = self.clone();
+
+        self.len = at;
+
+        unsafe { ret.inc_start(at) };
+
+        ret
+    }
+
+    /// Splits the bytes into two at the given index.
+    ///
+    /// Afterwards `self` contains elements `[at, len)`, and the returned
+    /// `Bytes` contains elements `[0, at)`.
+    ///
+    /// This is an `O(1)` operation that just increases the reference count and
+    /// sets a few indices.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bytes::Bytes;
+    ///
+    /// let mut a = Bytes::from(&b"hello world"[..]);
+    /// let b = a.split_to(5);
+    ///
+    /// assert_eq!(&a[..], b" world");
+    /// assert_eq!(&b[..], b"hello");
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// Panics if `at > len`.
+    #[must_use = "consider Bytes::advance if you don't need the other half"]
+    pub fn split_to(&mut self, at: usize) -> Bytes {
+        assert!(at <= self.len());
+
+        if at == self.len() {
+            return mem::replace(self, Bytes::new());
+        }
+
+        if at == 0 {
+            return Bytes::new();
+        }
+
+
+        let mut ret = self.clone();
+
+        unsafe { self.inc_start(at) };
+
+        ret.len = at;
+        ret
+    }
+
+    /// Shortens the buffer, keeping the first `len` bytes and dropping the
+    /// rest.
+    ///
+    /// If `len` is greater than the buffer's current length, this has no
+    /// effect.
+    ///
+    /// The [`split_off`] method can emulate `truncate`, but this causes the
+    /// excess bytes to be returned instead of dropped.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bytes::Bytes;
+    ///
+    /// let mut buf = Bytes::from(&b"hello world"[..]);
+    /// buf.truncate(5);
+    /// assert_eq!(buf, b"hello"[..]);
+    /// ```
+    ///
+    /// [`split_off`]: #method.split_off
+    #[inline]
+    pub fn truncate(&mut self, len: usize) {
+        if len < self.len {
+            self.len = len;
+        }
+    }
+
+    /// Clears the buffer, removing all data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use bytes::Bytes;
+    ///
+    /// let mut buf = Bytes::from(&b"hello world"[..]);
+    /// buf.clear();
+    /// assert!(buf.is_empty());
+    /// ```
+    #[inline]
+    pub fn clear(&mut self) {
+        self.truncate(0);
+    }
+
+    #[inline]
+    pub(crate) unsafe fn with_vtable(ptr: *const u8, len: usize, data: AtomicPtr<()>, vtable: &'static Vtable) -> Bytes {
+        Bytes {
+            ptr,
+            len,
+            data,
+            vtable,
+        }
+    }
+
+    // private
+
+    #[inline]
+    fn as_slice(&self) -> &[u8] {
+        unsafe {
+            slice::from_raw_parts(self.ptr, self.len)
+        }
+    }
+
+    #[inline]
+    unsafe fn inc_start(&mut self, by: usize) {
+        // should already be asserted, but debug assert for tests
+        debug_assert!(self.len >= by);
+        self.len -= by;
+        self.ptr = self.ptr.offset(by as isize);
+    }
+}
+
+// Vtable must enforce this behavior
+unsafe impl Send for Bytes {}
+unsafe impl Sync for Bytes {}
+
+impl Drop for Bytes {
+    #[inline]
+    fn drop(&mut self) {
+        unsafe {
+            (self.vtable.drop)(&mut self.data, self.ptr, self.len)
+        }
+    }
+}
+
+impl Clone for Bytes {
+    #[inline]
+    fn clone(&self) -> Bytes {
+        unsafe {
+            (self.vtable.clone)(&self.data, self.ptr, self.len)
+        }
+    }
+}
+
+impl fmt::Debug for Bytes {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&debug::BsDebug(&self.as_slice()), f)
+    }
+}
+
+impl Buf for Bytes {
+    #[inline]
+    fn remaining(&self) -> usize {
+        self.len()
+    }
+
+    #[inline]
+    fn bytes(&self) -> &[u8] {
+        self.as_slice()
+    }
+
+    #[inline]
+    fn advance(&mut self, cnt: usize) {
+        assert!(cnt <= self.len(), "cannot advance past `remaining`");
+        unsafe {
+            self.inc_start(cnt);
+        }
+    }
+
+    fn to_bytes(&mut self) -> crate::Bytes {
+        core::mem::replace(self, Bytes::new())
+    }
+}
+
+impl Deref for Bytes {
+    type Target = [u8];
+
+    #[inline]
+    fn deref(&self) -> &[u8] {
+        self.as_slice()
+    }
+}
+
+impl AsRef<[u8]> for Bytes {
+    #[inline]
+    fn as_ref(&self) -> &[u8] {
+        self.as_slice()
+    }
+}
+
+impl hash::Hash for Bytes {
+    fn hash<H>(&self, state: &mut H) where H: hash::Hasher {
+        self.as_slice().hash(state);
+    }
+}
+
+impl Borrow<[u8]> for Bytes {
+    fn borrow(&self) -> &[u8] {
+        self.as_slice()
+    }
+}
+
+impl IntoIterator for Bytes {
+    type Item = u8;
+    type IntoIter = IntoIter<Bytes>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        IntoIter::new(self)
+    }
+}
+
+impl<'a> IntoIterator for &'a Bytes {
+    type Item = &'a u8;
+    type IntoIter = core::slice::Iter<'a, u8>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.as_slice().into_iter()
+    }
+}
+
+impl FromIterator<u8> for Bytes {
+    fn from_iter<T: IntoIterator<Item = u8>>(into_iter: T) -> Self {
+        Vec::from_iter(into_iter).into()
+    }
+}
+
+// impl Eq
+
+impl PartialEq for Bytes {
+    fn eq(&self, other: &Bytes) -> bool {
+        self.as_slice() == other.as_slice()
+    }
+}
+
+impl PartialOrd for Bytes {
+    fn partial_cmp(&self, other: &Bytes) -> Option<cmp::Ordering> {
+        self.as_slice().partial_cmp(other.as_slice())
+    }
+}
+
+impl Ord for Bytes {
+    fn cmp(&self, other: &Bytes) -> cmp::Ordering {
+        self.as_slice().cmp(other.as_slice())
+    }
+}
+
+impl Eq for Bytes {}
+
+impl PartialEq<[u8]> for Bytes {
+    fn eq(&self, other: &[u8]) -> bool {
+        self.as_slice() == other
+    }
+}
+
+impl PartialOrd<[u8]> for Bytes {
+    fn partial_cmp(&self, other: &[u8]) -> Option<cmp::Ordering> {
+        self.as_slice().partial_cmp(other)
+    }
+}
+
+impl PartialEq<Bytes> for [u8] {
+    fn eq(&self, other: &Bytes) -> bool {
+        *other == *self
+    }
+}
+
+impl PartialOrd<Bytes> for [u8] {
+    fn partial_cmp(&self, other: &Bytes) -> Option<cmp::Ordering> {
+        other.partial_cmp(self)
+    }
+}
+
+impl PartialEq<str> for Bytes {
+    fn eq(&self, other: &str) -> bool {
+        self.as_slice() == other.as_bytes()
+    }
+}
+
+impl PartialOrd<str> for Bytes {
+    fn partial_cmp(&self, other: &str) -> Option<cmp::Ordering> {
+        self.as_slice().partial_cmp(other.as_bytes())
+    }
+}
+
+impl PartialEq<Bytes> for str {
+    fn eq(&self, other: &Bytes) -> bool {
+        *other == *self
+    }
+}
+
+impl PartialOrd<Bytes> for str {
+    fn partial_cmp(&self, other: &Bytes) -> Option<cmp::Ordering> {
+        other.partial_cmp(self)
+    }
+}
+
+impl PartialEq<Vec<u8>> for Bytes {
+    fn eq(&self, other: &Vec<u8>) -> bool {
+        *self == &other[..]
+    }
+}
+
+impl PartialOrd<Vec<u8>> for Bytes {
+    fn partial_cmp(&self, other: &Vec<u8>) -> Option<cmp::Ordering> {
+        self.as_slice().partial_cmp(&other[..])
+    }
+}
+
+impl PartialEq<Bytes> for Vec<u8> {
+    fn eq(&self, other: &Bytes) -> bool {
+        *other == *self
+    }
+}
+
+impl PartialOrd<Bytes> for Vec<u8> {
+    fn partial_cmp(&self, other: &Bytes) -> Option<cmp::Ordering> {
+        other.partial_cmp(self)
+    }
+}
+
+impl PartialEq<String> for Bytes {
+    fn eq(&self, other: &String) -> bool {
+        *self == &other[..]
+    }
+}
+
+impl PartialOrd<String> for Bytes {
+    fn partial_cmp(&self, other: &String) -> Option<cmp::Ordering> {
+        self.as_slice().partial_cmp(other.as_bytes())
+    }
+}
+
+impl PartialEq<Bytes> for String {
+    fn eq(&self, other: &Bytes) -> bool {
+        *other == *self
+    }
+}
+
+impl PartialOrd<Bytes> for String {
+    fn partial_cmp(&self, other: &Bytes) -> Option<cmp::Ordering> {
+        other.partial_cmp(self)
+    }
+}
+
+impl PartialEq<Bytes> for &[u8] {
+    fn eq(&self, other: &Bytes) -> bool {
+        *other == *self
+    }
+}
+
+impl PartialOrd<Bytes> for &[u8] {
+    fn partial_cmp(&self, other: &Bytes) -> Option<cmp::Ordering> {
+        other.partial_cmp(self)
+    }
+}
+
+impl PartialEq<Bytes> for &str {
+    fn eq(&self, other: &Bytes) -> bool {
+        *other == *self
+    }
+}
+
+impl PartialOrd<Bytes> for &str {
+    fn partial_cmp(&self, other: &Bytes) -> Option<cmp::Ordering> {
+        other.partial_cmp(self)
+    }
+}
+
+impl<'a, T: ?Sized> PartialEq<&'a T> for Bytes
+    where Bytes: PartialEq<T>
+{
+    fn eq(&self, other: &&'a T) -> bool {
+        *self == **other
+    }
+}
+
+impl<'a, T: ?Sized> PartialOrd<&'a T> for Bytes
+    where Bytes: PartialOrd<T>
+{
+    fn partial_cmp(&self, other: &&'a T) -> Option<cmp::Ordering> {
+        self.partial_cmp(&**other)
+    }
+}
+
+// impl From
+
+impl Default for Bytes {
+    #[inline]
+    fn default() -> Bytes {
+        Bytes::new()
+    }
+}
+
+impl From<&'static [u8]> for Bytes {
+    fn from(slice: &'static [u8]) -> Bytes {
+        Bytes::from_static(slice)
+    }
+}
+
+impl From<&'static str> for Bytes {
+    fn from(slice: &'static str) -> Bytes {
+        Bytes::from_static(slice.as_bytes())
+    }
+}
+
+impl From<Vec<u8>> for Bytes {
+    fn from(vec: Vec<u8>) -> Bytes {
+        // into_boxed_slice doesn't return a heap allocation for empty vectors,
+        // so the pointer isn't aligned enough for the KIND_VEC stashing to
+        // work.
+        if vec.is_empty() {
+            return Bytes::new();
+        }
+
+        let slice = vec.into_boxed_slice();
+        let len = slice.len();
+        let ptr = slice.as_ptr();
+
+        assert!(
+            ptr as usize & KIND_VEC == 0,
+            "Vec pointer should not have LSB set: {:p}",
+            ptr,
+        );
+        drop(Box::into_raw(slice));
+
+        let data = ptr as usize | KIND_VEC;
+        Bytes {
+            ptr,
+            len,
+            data: AtomicPtr::new(data as *mut _),
+            vtable: &SHARED_VTABLE,
+        }
+    }
+}
+
+impl From<String> for Bytes {
+    fn from(s: String) -> Bytes {
+        Bytes::from(s.into_bytes())
+    }
+}
+
+// ===== impl Vtable =====
+
+impl fmt::Debug for Vtable {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Vtable")
+            .field("clone", &(self.clone as *const ()))
+            .field("drop", &(self.drop as *const ()))
+            .finish()
+    }
+}
+
+// ===== impl StaticVtable =====
+
+const STATIC_VTABLE: Vtable = Vtable {
+    clone: static_clone,
+    drop: static_drop,
+};
+
+unsafe fn static_clone(_: &AtomicPtr<()>, ptr: *const u8, len: usize) -> Bytes {
+    let slice = slice::from_raw_parts(ptr, len);
+    Bytes::from_static(slice)
+}
+
+unsafe fn static_drop(_: &mut AtomicPtr<()>, _: *const u8, _: usize) {
+    // nothing to drop for &'static [u8]
+}
+
+// ===== impl SharedVtable =====
+
+struct Shared {
+    // holds vec for drop, but otherwise doesnt access it
+    _vec: Vec<u8>,
+    ref_cnt: AtomicUsize,
+}
+
+static SHARED_VTABLE: Vtable = Vtable {
+    clone: shared_clone,
+    drop: shared_drop,
+};
+
+const KIND_ARC: usize = 0b0;
+const KIND_VEC: usize = 0b1;
+const KIND_MASK: usize = 0b1;
+
+unsafe fn shared_clone(data: &AtomicPtr<()>, ptr: *const u8, len: usize) -> Bytes {
+    let shared = data.load(Ordering::Acquire);
+    let kind = shared as usize & KIND_MASK;
+
+    if kind == KIND_ARC {
+        shallow_clone_arc(shared as _, ptr, len)
+    } else {
+        debug_assert_eq!(kind, KIND_VEC);
+        shallow_clone_vec(data, shared, ptr, len)
+    }
+}
+
+unsafe fn shared_drop(data: &mut AtomicPtr<()>, ptr: *const u8, len: usize) {
+    let shared = *data.get_mut();
+    let kind = shared as usize & KIND_MASK;
+
+
+    if kind == KIND_ARC {
+        release_shared(shared as *mut Shared);
+    } else {
+        debug_assert_eq!(kind, KIND_VEC);
+
+        drop(rebuild_vec(shared, ptr, len));
+    }
+}
+
+unsafe fn rebuild_vec(shared: *const (), offset: *const u8, len: usize) -> Vec<u8> {
+    debug_assert!(
+        shared as usize & KIND_MASK == KIND_VEC,
+        "rebuild_vec should have beeen called with KIND_VEC",
+    );
+    debug_assert!(
+        shared as usize & !KIND_MASK != 0,
+        "rebuild_vec should be called with non-null pointer: {:p}",
+        shared,
+    );
+
+    let buf = (shared as usize & !KIND_MASK) as *mut u8;
+    let cap = (offset as usize - buf as usize) + len;
+    Vec::from_raw_parts(buf, cap, cap)
+}
+
+unsafe fn shallow_clone_arc(shared: *mut Shared, ptr: *const u8, len: usize) -> Bytes {
+    let old_size = (*shared).ref_cnt.fetch_add(1, Ordering::Relaxed);
+
+    if old_size > usize::MAX >> 1 {
+        crate::abort();
+    }
+
+    Bytes {
+        ptr,
+        len,
+        data: AtomicPtr::new(shared as _),
+        vtable: &SHARED_VTABLE,
+    }
+}
+
+#[cold]
+unsafe fn shallow_clone_vec(atom: &AtomicPtr<()>, ptr: *const (), offset: *const u8, len: usize) -> Bytes {
+    // If  the buffer is still tracked in a `Vec<u8>`. It is time to
+    // promote the vec to an `Arc`. This could potentially be called
+    // concurrently, so some care must be taken.
+
+    debug_assert_eq!(ptr as usize & KIND_MASK, KIND_VEC);
+
+    // First, allocate a new `Shared` instance containing the
+    // `Vec` fields. It's important to note that `ptr`, `len`,
+    // and `cap` cannot be mutated without having `&mut self`.
+    // This means that these fields will not be concurrently
+    // updated and since the buffer hasn't been promoted to an
+    // `Arc`, those three fields still are the components of the
+    // vector.
+    let vec = rebuild_vec(ptr as *const (), offset, len);
+    let shared = Box::new(Shared {
+        _vec: vec,
+        // Initialize refcount to 2. One for this reference, and one
+        // for the new clone that will be returned from
+        // `shallow_clone`.
+        ref_cnt: AtomicUsize::new(2),
+    });
+
+    let shared = Box::into_raw(shared);
+
+    // The pointer should be aligned, so this assert should
+    // always succeed.
+    debug_assert!(0 == (shared as usize & KIND_MASK));
+
+    // Try compare & swapping the pointer into the `arc` field.
+    // `Release` is used synchronize with other threads that
+    // will load the `arc` field.
+    //
+    // If the `compare_and_swap` fails, then the thread lost the
+    // race to promote the buffer to shared. The `Acquire`
+    // ordering will synchronize with the `compare_and_swap`
+    // that happened in the other thread and the `Shared`
+    // pointed to by `actual` will be visible.
+    let actual = atom.compare_and_swap(ptr as _, shared as _, Ordering::AcqRel);
+
+    if actual as usize == ptr as usize {
+        // The upgrade was successful, the new handle can be
+        // returned.
+        return Bytes {
+            ptr: offset,
+            len,
+            data: AtomicPtr::new(shared as _),
+            vtable: &SHARED_VTABLE,
+        };
+    }
+
+    // The upgrade failed, a concurrent clone happened. Release
+    // the allocation that was made in this thread, it will not
+    // be needed.
+    let shared = Box::from_raw(shared);
+    mem::forget(*shared);
+
+    // Buffer already promoted to shared storage, so increment ref
+    // count.
+    shallow_clone_arc(actual as _, offset, len)
+}
+
+unsafe fn release_shared(ptr: *mut Shared) {
+    // `Shared` storage... follow the drop steps from Arc.
+    if (*ptr).ref_cnt.fetch_sub(1, Ordering::Release) != 1 {
+        return;
+    }
+
+    // This fence is needed to prevent reordering of use of the data and
+    // deletion of the data.  Because it is marked `Release`, the decreasing
+    // of the reference count synchronizes with this `Acquire` fence. This
+    // means that use of the data happens before decreasing the reference
+    // count, which happens before this fence, which happens before the
+    // deletion of the data.
+    //
+    // As explained in the [Boost documentation][1],
+    //
+    // > It is important to enforce any possible access to the object in one
+    // > thread (through an existing reference) to *happen before* deleting
+    // > the object in a different thread. This is achieved by a "release"
+    // > operation after dropping a reference (any access to the object
+    // > through this reference must obviously happened before), and an
+    // > "acquire" operation before deleting the object.
+    //
+    // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
+    atomic::fence(Ordering::Acquire);
+
+    // Drop the data
+    Box::from_raw(ptr);
+}
+
+// compile-fails
+
+/// ```compile_fail
+/// use bytes::Bytes;
+/// #[deny(unused_must_use)]
+/// {
+///     let mut b1 = Bytes::from("hello world");
+///     b1.split_to(6);
+/// }
+/// ```
+fn _split_to_must_use() {}
+
+/// ```compile_fail
+/// use bytes::Bytes;
+/// #[deny(unused_must_use)]
+/// {
+///     let mut b1 = Bytes::from("hello world");
+///     b1.split_off(6);
+/// }
+/// ```
+fn _split_off_must_use() {}
+
+// fuzz tests
+#[cfg(all(test, loom))]
+mod fuzz {
+    use std::sync::Arc;
+    use loom::thread;
+
+    use super::Bytes;
+    #[test]
+    fn bytes_cloning_vec() {
+        loom::model(|| {
+            let a = Bytes::from(b"abcdefgh".to_vec());
+            let addr = a.as_ptr() as usize;
+
+            // test the Bytes::clone is Sync by putting it in an Arc
+            let a1 = Arc::new(a);
+            let a2 = a1.clone();
+
+            let t1 = thread::spawn(move || {
+                let b: Bytes = (*a1).clone();
+                assert_eq!(b.as_ptr() as usize, addr);
+            });
+
+            let t2 = thread::spawn(move || {
+                let b: Bytes = (*a2).clone();
+                assert_eq!(b.as_ptr() as usize, addr);
+            });
+
+            t1.join().unwrap();
+            t2.join().unwrap();
+        });
+    }
+}