Crate bytearray_ringbuffer 

Bytearray-Ringbuffer

An embedded-friendly VecDeque<Vec<u8>>.

BytearrayRingbuffer stores byte slices in a fixed-size array, similar to heapless::Vec. However, the elements in BytearrayRingbuffer are not required to have a fixed size. Instead, information about each slice (ie. length) is stored alongside the payload. Each slice data uses up data.len() + 8 bytes in the buffer.

This is useful for efficiently storing elements of very different lengths, as short elements do not have to be padded.

One downside is that elements may wrap around at the end of the buffer. For pop_front, iter, iter_backwards, nth, and nth_reverse, each element is returned as a Packet with fields a and b. If the element does not wrap around, a will contain all data and b will be empty. Otherwise, a and b have to be concatenated to yield the full result. Packet::len returns the total payload length (a.len() + b.len()), Packet::copy_into copies the full payload into a flat &mut [u8], Packet::copy_part_into copies a sub-range, and Packet::extend_into appends the payload into any Extend<u8> collection such as Vec<u8>. nth_contiguous is the exception: it returns a single &[u8] and may rotate the backing array so that slice is contiguous. It returns None if the queue is empty or if n >= count().

MSRV

Rust 1.85 or later (edition = "2024").

Usage

use bytearray_ringbuffer::BytearrayRingbuffer;
// Create a buffer with a capacity of 64 bytes.
let mut buffer = BytearrayRingbuffer::<64>::new();
// Store some packets.
buffer.push(b"hello world").unwrap();
buffer.push(b"").unwrap();
buffer.push(b"testing").unwrap();
// Number of packets currently stored.
assert_eq!(buffer.count(), 3);

// Pop the oldest packet and copy it into a flat Vec<u8>.
let p = buffer.pop_front().unwrap();
assert_eq!(p.len(), 11); // "hello world"
let mut out = vec![0u8; p.len()];
p.copy_into(&mut out);
assert_eq!(out, b"hello world");

// Iterate oldest-first without removing entries; extend into a Vec<u8>.
for p in buffer.iter() {
    let mut collected = Vec::new();
    p.extend_into(&mut collected); // works with any Extend<u8>
    // `collected` now contains the full packet payload
}

Multipart push

When the full payload is not available up-front, use push_multipart (or push_multipart_force) to build a packet incrementally:

use bytearray_ringbuffer::BytearrayRingbuffer;
let mut buffer = BytearrayRingbuffer::<64>::new();
// begin an in-progress packet
let mut mp = buffer.push_multipart().unwrap();
mp.push(b"hello").unwrap();
mp.push(b" world").unwrap();
drop(mp); // commits the packet "hello world"
assert_eq!(buffer.count(), 1);

// or discard the in-progress write:
let mut mp = buffer.push_multipart().unwrap();
mp.push(b"discarded").unwrap();
mp.cancel(); // head is rewound; count is unchanged
assert_eq!(buffer.count(), 1);

Performance

The tradeoff here is that random access by index (nth, nth_reverse, nth_contiguous) walks packets from an end of the queue, so it is linear in the number of packets skipped.

operation	time complexity
push()	O(1)
push_force()	O(1) amortized per push; worst case O(m) if m oldest packets are dropped to make room
push_multipart()	O(1) to create the guard; each push call is O(1); drop/cancel is O(1)
push_multipart_force()	O(1) to create the guard; each push call is O(1) amortized; drop/cancel is O(1)
pop_front()	O(1)
iter() / iter_backwards()	O(1) to create the iterator; O(1) per next(); O(k) to visit all k packets
count()	O(1)
nth(n) / nth_reverse(n)	O(n) in the index n (packets walked)
nth_contiguous(n)	O(n) to locate the packet, plus O(N) if the buffer is rotated

Changelog

See CHANGELOG.md in the repository.

Structs

BytearrayRingbuffer

Fixed-capacity FIFO of variable-length byte slices, backed by [u8; N] with no heap allocation.

Iter

Iterator over packets from oldest to newest. See BytearrayRingbuffer::iter.

IterBackwards

Iterator over packets from newest to oldest. See BytearrayRingbuffer::iter_backwards.

MultipartPush

Guard returned by BytearrayRingbuffer::push_multipart and BytearrayRingbuffer::push_multipart_force.

NotEnoughSpaceError

Returned when a BytearrayRingbuffer::push cannot store data without dropping older packets.

Packet

A borrowed view of a single packet from the ring buffer.