Crate indexbus_msg 

Structured message envelope for IndexBus.

This crate defines a small, versioned, bytes-on-wire header designed to live at the start of Slot.data[..].

Contracts and invariants

• The v1 envelope is little-endian and begins with MAGIC.
• The header is designed to be append-only over time. decode_header accepts header_len >= V1_HEADER_LEN and ignores any appended bytes it does not understand.
• encode_header_into currently only emits the minimum v1 header (header_len == V1_HEADER_LEN).
• header_len + payload_len is validated to be within SLOT_CAPACITY.

This crate intentionally does not interpret payload bytes. Fields such as codec_id, schema_id, and msg_type are treated as application-defined identifiers.

Error semantics

• Decode helpers validate structural properties (magic, lengths, known flags).
• Decode helpers do not attempt to authenticate the payload or validate codec-specific formats.
• flags are treated as declarative metadata; the helpers reject unknown bits for deterministic behavior.

Features

• Default: no_std.
• alloc: reserved for future heap-backed conveniences.
• std: enables std-only trait impls (e.g. std::error::Error) and implies alloc.

Minimal v1 encode/decode

use indexbus_msg::{decode_header, encode_header_into, Header, V1_HEADER_LEN};

let payload = b"hello";
let hdr = Header {
    flags: 0,
    codec_id: 0,
    header_len: V1_HEADER_LEN as u8,
    schema_id: 1,
    msg_type: 42,
    msg_version: 1,
    payload_len: payload.len() as u16,
};

let mut buf = [0u8; 64];
let n = encode_header_into(&mut buf, hdr).unwrap();
buf[n..(n + payload.len())].copy_from_slice(payload);

let (parsed, parsed_payload) = decode_header(&buf[..(n + payload.len())]).unwrap();
assert_eq!(parsed, hdr);
assert_eq!(parsed_payload, payload);

Modules

flags

Envelope flag definitions.

prelude

Curated prelude for downstream users.

Structs

Header

Parsed v1 envelope header.

Enums

Error

Errors returned by v1 envelope encode/decode helpers.

Constants

MAGIC

Envelope magic for v1 (“USM1”).

SLOT_CAPACITY

Absolute maximum bytes available per slot.

V1_HEADER_LEN

Minimum v1 header length in bytes.

Functions

decode_header

Decode a v1 header from input.

encode_header_into

Encode a v1 header into out.

max_payload_len_v1

Maximum payload length for a v1 message, excluding any optional appended fields.