BLTE Containers - d07RiV/blizzget GitHub Wiki
All files downloaded from /data URLs come in BLTE containers, which serve as the primary (and only) method of compression used in the CASC system.
These containers consist of the following sections:
- Header
- Chunk information (optional)
- Chunks
Data structures:
- Header (8 bytes)
| Offset | Type | Name | Description |
|---|---|---|---|
| 0x00 | char[4] | Signature | "BLTE" |
| 0x04 | uint32 [BE] | HeaderSize | Size of BLTE header + chunk information, or 0 for one-block file (big endian) |
- Chunk information (variable size)
Only present if HeaderSize is not zero.
| Offset | Type | Name | Description |
|---|---|---|---|
| 0x00 | uint16 | Flags | Unknown flags |
| 0x02 | uint16 [BE] | ChunkCount | Number of compressed chunks |
| 0x04 | ChunkInfoEntry[ChunkCount] | Chunks | Chunk information |
- ChunkInfoEntry (24 bytes)
| Offset | Type | Name | Description |
|---|---|---|---|
| 0x00 | uint32 [BE] | CompressedSize | Size of the compressed chunk (including the compression type byte) |
| 0x04 | uint32 [BE] | DecompressedSize | Size of the decompressed chunk |
| 0x08 | char[16] | Checksum | MD5 of the compressed chunk (including the compression type byte) |
- Chunk (variable size)
If HeaderSize is zero, only one chunk is present. Otherwise, ChunkCount chunks are present, their sizes are listed in ChunkInfoEntry structures.
| Offset | Type | Name | Description |
|---|---|---|---|
| 0x00 | char | EncodingType | Known values: N, Z, F, E |
| 0x01 | char[CompressedSize - 1] | Data | Encoded data |
Encoding types:
- N: Plain (uncompressed) data.
- Z: Zlib deflated data.
- F: Recursively encoded BLTE data.
- E: Encrypted data.
In order to download the game data, we will only need to decode the encoding, download and install files, which only use N and Z encoding modes. For an explanation of the other modes, visit wowdev Wiki or browse the CascLib sources.