Heatshrink-compressed Tarball Format {#heatshrink_file_format}

Flipper supports the use of Heatshrink compression library for .tar archives. This allows for smaller file sizes and faster OTA updates.

Heatshrink specification does not define a container format for storing compression parameters. This document describes the format used by Flipper to store Heatshrink-compressed data streams.

Header begins with a magic value, followed by a version number and compression parameters - window size and lookahead size.

Magic value consists of 4 bytes: 0x48 0x53 0x44 0x53 (ASCII "HSDS", HeatShrink DataStream).

Version number is a single byte, currently set to 0x01.

Window size is a single byte, representing the size of the sliding window used by the compressor. It corresponds to -w parameter in Heatshrink CLI.

Lookahead size is a single byte, representing the size of the lookahead buffer used by the compressor. It corresponds to -l parameter in Heatshrink CLI.

Total header size is 7 bytes. Header is followed by compressed data.