bzimage

bzimage is a small Rust crate that defines a compact on-disk container format for a gzip-compressed payload with a SHA-256 checksum. The format is deliberately simple:

• 64-byte packed header followed by the compressed payload bytes.

Header layout (in bytes, little-endian for integer fields):

• magic: 4 bytes — the ASCII magic DMNZ
• version: u32 (4 bytes) — format version (currently 1)
• reserved1: u32 (4 bytes) — reserved for future use
• uncompressed_size: u64 (8 bytes) — size of the data after decompression
• compressed_size: u64 (8 bytes) — size of the following compressed data
• checksum: 32 bytes — SHA-256 of the compressed payload
• reserved2: u32 (4 bytes) — reserved for future use

Total header size: 64 bytes.

Usage

The crate exposes BzImageHeader and helper functions to read/write headers, validate the checksum, and decompress the payload. See the tests/ directory for examples of creating a header, writing it to a buffer, and validating/decompressing the stored payload.

Example (high level):

1. Compress some bytes with gzip.
2. Compute SHA-256 of the compressed bytes and store it in the header.
3. Write the header (64 bytes) followed by the compressed bytes.
4. On read: read the header, read compressed_size bytes, validate checksum, then decompress.

See the Rust docs in src/lib.rs for API details and the test suite for concrete usage examples.