Implement Bytes::from_raw_parts

src/bytes.rs

@@ -535,6 +535,53 @@ impl Bytes {
         self.len -= by;
         self.ptr = self.ptr.add(by);
     }
+
+    /// Creates a new `Bytes` from a raw pointer and a length.
+    ///
+    /// # Examples
+    /// To create a new `Bytes` where the start position and end position of the backing store are
+    /// aligned to 32-byte boundaries:
+    ///
+    /// ```
+    /// use bytes::Bytes;
+    /// use std::alloc::{alloc, Layout, handle_alloc_error};
+    ///
+    /// const LEN: usize = 64;
+    /// const ALIGN: usize = 32;
+    ///
+    /// let layout = Layout::from_size_align(LEN, ALIGN)
+    ///     .expect("failed to create Layout!")
+    ///     .pad_to_align();
+    /// let ptr = unsafe { alloc(layout) };
+    /// if ptr.is_null() {
+    ///     handle_alloc_error(layout);
+    /// };
+    ///
+    /// // (Not shown here: Pass `ptr` to code that will write data into the buffer.
+    /// // For example, pass `ptr` to a system call to load data from disk using `O_DIRECT`.)
+    ///
+    /// let buf = Bytes::from_raw_parts(ptr, layout.size());
+    /// assert_eq!(buf.len(), layout.size());
+    /// ```
+    pub fn from_raw_parts(ptr: *const u8, len: usize) -> Self {
+        let ptr = ptr as *mut u8;
+        if ptr as usize & 0x1 == 0 {
+            let data = ptr_map(ptr, |addr| addr | KIND_VEC);
+            Bytes {
+                ptr,
+                len,
+                data: AtomicPtr::new(data.cast()),
+                vtable: &PROMOTABLE_EVEN_VTABLE,
+            }
+        } else {
+            Bytes {
+                ptr,
+                len,
+                data: AtomicPtr::new(ptr.cast()),
+                vtable: &PROMOTABLE_ODD_VTABLE,
+            }
+        }
+    }
 }
 
 // Vtable must enforce this behavior