Crate prefix_arena 

Prefix-oriented arena utilities for caller-provided byte buffers.

prefix-arena is a small no_std crate for working with a mutable byte buffer as a prefix-growing arena. It is designed for cases where allocation must stay explicit and bounded, such as embedded systems, protocol parsing, serializers, and staging temporary output into preallocated storage.

The crate exposes two primary types:

• PrefixArena: detaches prefixes from a backing buffer while keeping the remaining capacity available for later use.
• StagingBuffer: writes into the current arena prefix and detaches only the bytes that were actually produced.

Examples

Reserve a prefix directly from the arena:

use prefix_arena::PrefixArena;

let mut storage = [0u8; 8];
let arena = PrefixArena::new(&mut storage);

let prefix = arena
    .init_prefix_with(|buffer| {
        buffer[..3].copy_from_slice(b"abc");
        Ok::<usize, core::convert::Infallible>(3)
    })
    .unwrap();

assert_eq!(prefix, b"abc");

Stage bytes first and detach them once complete:

use prefix_arena::{PrefixArena, StagingBuffer};

let mut storage = [0u8; 16];
let mut arena = PrefixArena::new(&mut storage);
let mut staging = StagingBuffer::new(&mut arena);

staging.extend_from_slice(b"hello").unwrap();
staging.push_byte(b'!').unwrap();

let written = staging.into_written_slice();
assert_eq!(written, b"hello!");
assert_eq!(arena.len(), 10);

Safety model

The safe API only returns initialized &[u8] or &mut [u8] values after the caller reports how many bytes were written. Unsafe methods exist for treating the remaining arena bytes as initialized data; those methods require the caller to uphold initialization guarantees.

Structs

ArenaView

A temporary view over the remaining bytes of a PrefixArena.

PrefixArena

A bump-style arena over caller-provided byte storage.

StagingBuffer

A staging buffer over the remaining bytes of a PrefixArena.

StagingBufferError