Garry's Mod Addon

Garry's Mod Addon files are used in the PC game Garry's Mod for storing downloadable game content. They store game files in a hierarchy of folders, so gma files can be created from a folder, or extracted into a hierarchy of folders.

Format
char[4] ident ("GMAD") uint8 version uint64 steam_id (unused) uint64 timestamp uint8 zero (0) char addon_name (null terminated string of variable size) char addon_description (null terminated string of variable size) char addon_author (null terminated string of variable size) ("Author Name") uint32 addon_version

struct file_table[] uint32 file_number char file_path (null terminated string of variable size) uint64 file_size uint32 file_crc

uint32 zero (0)

struct files[] byte file (file data based on information from the file table)

uint32 addon_crc

Links

 * How to create and extract gma files
 * Source code for gmad to create and extract gma files