Cache format

This page describes the technical information about the RuneScape:Cache. The information is currently work-in-progress.

Legacy cache format

This cache format was used for builds 244 through 377.

There are 5 files as shown in the table below. The main data Cache is separated into Archives, then individual Files. The archives and files are defined by Index Files which allow individual files to be accessed individually.

File	Contents
main_file_cache.dat	Actual game data
main_file_cache.idx0	Subarchives index
main_file_cache.idx1	Model index
main_file_cache.idx2	Animation index
main_file_cache.idx3	Sound index
main_file_cache.idx4	Map index

Index files

Index files (.idx) can be thought of as large Tables of Contents like you would see in a book. The index files are a series of bytes which tell where individual files are within the main data cache so that they can be retrieved and used. Without them, the main data cache is essentially an unorganized blob of bytes. By dividing the total number of bytes in an Index by 6, you can determine to the total amount of files within.

Index Format
Each index entry is 6 bytes
Information	Type	Description
File Size	Medium (3 bytes)	The size of the file that this Index points to
Offset	Medium (3 bytes)	The first Sector of the file that this Index points to
Example: Two indexes are highlighted in main_file_cache.idx0. The second Index shows that this file is 51,973 bytes in size and starts at the second Sector in the data file.

Data files

The main data cache file (main_file_cache.dat) contains all the game files including models, textures, and maps, as a series of Sectors. A Sector is a 520 byte block of data that includes an 8 byte header and 512 bytes data. Multiple Sectors make up a single file, so the header of the Sector tells you which file it belongs to. Files can be extracted by combining all of the Sector's data for that file, then decompressing as required.

Sector Format
Information	Type	Description
File ID	Unsigned Short	The file that this Sector belongs to
Chunk ID	Unsigned Short	Which chunk of the file the data of the Sector is
Next Sector ID	Medium (3 bytes)	The next sector of data belonging to this file. A sector ID of 0 indicates end of file
Type ID	Unsigned Byte	The type of file this Sector belongs to. It is equal to the idx number + 1
Data	512 bytes	The raw data that this Section contains

Example

An Index file defined a file with size 1,561 bytes at Sector 668. The starting position of the data buffer can be found by multiplying the starting Sector by 520, position 347,360 in this case. By looping through the Sectors and copying the data bits until reaching the end of file (EOF) Next Sector ID, the total data for file 4 is obtained.

Sector Example
	Sector 0	Sector 1	Sector 2	Sector 3
File ID	4	4	4	4
Chunk ID	0	1	2	3
Next Sector ID	669	670	671	0
Type ID	1	1	1	1
Data	512 bytes	512 bytes	512 bytes	25 bytes + 487 bytes 0

Other files

flo.dat

This file defines the floors used in game.

map_index

This file defines the map coordinates and which map files are used.

Map Index Format
Information	Type	Description
X Coordinate	Unsigned Byte	X coordinate of map region
Y Coordinate	Unsigned Byte	Y coordinate of map region
File ID	Unsigned Byte	The File ID's containing the map data
Member's Flag	Unsigned Byte	0 if Member's region, 1 if F2P

Utility methods

getMedium

public static int getMedium(ByteBuffer buf) {
		return ((buf.get() & 0xFF) << 16) | ((buf.get() & 0xFF) << 8) | (buf.get() & 0xFF);
	}