Zero copy Sequence

[edgarriba]

Hi! we are working on a zenoh / ros2 bridge and for some conversion messages we need to implement a Sequence type from an owned Vec (e.g images). How can we make it zero-copy or in the worst case what would be the most memory efficient method ?

[esteve]

@edgarriba sorry for the slow reponse, I completely missed this ticket. I've been thinking about it, and without more details, my first approach would be to probably:

• add a RcUtilsBuffer<T> or similar,
• allocate with rcutils_get_default_allocator()
• then expose as_mut_slice()

With that you could convert it into a Sequence<T> without copying. I'm going to write some code to see if that could work. Is that something that would work for you? It's not a Vec per se, but it's the closest I can think of to avoid any copying.

[esteve]

Another option I just thought, and I don't know if it's feasible or not, would be to write a custom allocator in Rust, expose it via FFI and pass it to ROS, so the Vec and the underlying sequence would have the same allocator, but honestly I really don't know if it'd work.