The bytes Crate
How BytesMut and Bytes manage memory without copying
The Problem
Why Vec<u8> copies are expensive
In Rust, the natural way to hold a buffer of bytes is Vec<u8>. It owns its memory, grows when needed, and gets freed when dropped. Simple.
But what happens when you need to split a buffer into parts, or share it across tasks?
let data: Vec<u8> = b"Hello World".to_vec();
We have a buffer with 11 bytes of data. One allocation, no copies.
The cost of copying
Every to_vec() or clone() on a Vec<u8> triggers a heap allocation + memcpy. In network code that processes thousands of messages per second, this is a serious bottleneck. The data is already in memory -- why copy it?
Key Insight
What if multiple handles could point into the same underlying allocation, each seeing only their own slice? No copies. No extra allocations. Just pointer arithmetic and a reference count to know when to free.
That's exactly what the bytes crate does. Let's see how BytesMut works under the hood.