cowbytes

A clone-on-write bytes type whose non-borrowed variant is bytes::Bytes.

pub enum CowBytes<'a> {
    Borrowed(&'a [u8]),
    Shared(Bytes),
}

Unlike Cow<'a, [u8]>, whose owned side is a Vec<u8>, cloning and slicing a shared value are reference count operations rather than copies.

Unlike Bytes, which can only borrow &'static data, an arbitrary slice can be held without copying it, at the cost of a lifetime.

Example

use cowbytes::CowBytes;

// Borrowing does not allocate.
let borrowed: CowBytes<'_> = CowBytes::from(&[1u8, 2, 3][..]);

// A `Vec` is adopted without copying.
let shared: CowBytes<'_> = CowBytes::from(vec![1u8, 2, 3]);

// Equality is by contents, not by variant.
assert_eq!(borrowed, shared);

// Slicing shared bytes keeps the same allocation.
let sliced: CowBytes<'_> = shared.slice(1..3);
assert_eq!(sliced, [2u8, 3]);

// `into_vec` hands the allocation back while it is unshared, rather than copying.
let bytes = vec![1u8, 2, 3];
let ptr = bytes.as_ptr();
let owned: Vec<u8> = CowBytes::from(bytes).into_vec();
assert_eq!(owned.as_ptr(), ptr);

Feature flags

• std (default) — enables bytes/std. Disable for no_std (requires alloc).
• serde — implements Serialize and Deserialize. Add #[serde(borrow)] to struct fields holding CowBytes<'a> to allow zero-copy deserialization from input data.

Licence

Licensed under either of

• Apache Licence, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT Licence (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.