blob_frame.h File Reference

Shared framing for versioned NVS blobs: magic, body, CRC-32 (pure C++20, natively tested). More...

#include <cstddef>
#include <cstdint>
#include <optional>
#include <span>

Go to the source code of this file.

Functions
void	checksum::frame_blob (std::span< uint8_t > blob, uint32_t magic)
	Stamps magic into the first four bytes and the CRC-32 of all but the last four bytes into the last four.
std::optional< std::span< const uint8_t > >	checksum::unframe_blob (std::span< const uint8_t > blob, uint32_t magic)
	Checks the magic and the CRC; returns the body (bytes 4 .. size-4), or empty if either check fails.

Variables
constexpr size_t	checksum::kFrameOverhead = 8
	Bytes the frame adds around the body: the magic in front and the CRC behind.

Detailed Description

Shared framing for versioned NVS blobs: magic, body, CRC-32 (pure C++20, natively tested).

Layout (host byte order, little-endian on every target): magic (u32), body (any length, version and fields included), CRC-32 of everything before it (u32). The caller owns the body layout and its version byte(s).

Function Documentation

frame_blob()

void checksum::frame_blob	(	std::span< uint8_t >	blob,
		uint32_t	magic )

Stamps magic into the first four bytes and the CRC-32 of all but the last four bytes into the last four.

The caller has already written the body at offset 4. blob must be at least kFrameOverhead bytes.

unframe_blob()

std::optional< std::span< const uint8_t > > checksum::unframe_blob	(	std::span< const uint8_t >	blob,
		uint32_t	magic )

Checks the magic and the CRC; returns the body (bytes 4 .. size-4), or empty if either check fails.

Length policy stays with the caller (compare blob.size() to the expected size first).