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Encoding file
Encoding file contains the mapping from content hashes to CDN (file) hashes, and defines the compression layout for files.
This binary file can be obtained from the CDN data URL, using the second encoding hash found in the build-config file. Example URL:
http://blzddist1-a.akamaihd.net/tpr/d3/data/1d/d1/1dd1cf5ae8b9fd3f6c14ad12bc8406a6
Encoding files have the following structure:
- Header
- Layout string block
- Key table index (table A)
- Key table entries
- Layout table index (table B)
- Layout table entries
- Encoding file layout string
- Header (22 bytes)
| Offset | Type | Name | Description |
|---|---|---|---|
| 0x00 | char[2] | Signature | "EN" |
| 0x02 | uint8 | Unknown | ??? |
| 0x03 | uint8 | HashSizeA | Always 0x10 (16 bytes) |
| 0x04 | uint8 | HashSizeB | Always 0x10 (16 bytes) |
| 0x05 | uint16 | FlagsA | Unknown flags |
| 0x07 | uint16 | FlagsB | Unknown flags |
| 0x09 | uint32 [BE] | SizeA | Number of key table entries |
| 0x0D | uint32 [BE] | SizeB | Number of layout table entries |
| 0x11 | uint8 | Unknown | ??? |
| 0x12 | uint32 [BE] | StringSize | Size of the layout string block, in bytes |
- Layout string block
Consists of a list of null-terminated strings describing the possible file compression layouts - see Layout string.
- Key table index (32 bytes, array)
Consists of SizeA entries of the following format:
| Offset | Type | Name | Description |
|---|---|---|---|
| 0x00 | char[16] | FirstHash | Hash of the first file in the entry |
| 0x10 | char[16] | EntryHash | MD5 checksum of the entire entry |
- Key table entries (variable size, padded array)
Consists of SizeA zero-padded blocks of 4096 bytes each, filled with the following (variable size) entries:
| Offset | Type | Name | Description |
|---|---|---|---|
| 0x00 | uint16 [LE] | KeyCount | Number of CDN keys |
| 0x02 | uint32 [BE] | DecompressedSize | Size of the decompressed file |
| 0x06 | char[16] | Hash | Content hash of the file |
| 0x16 | char[KeyCount][16] | Keys | Array of file CDN keys |
- Layout table index (32 bytes, array)
Consists of SizeB entries of the following format:
| Offset | Type | Name | Description |
|---|---|---|---|
| 0x00 | char[16] | FirstKey | Key of the first file in the entry |
| 0x10 | char[16] | EntryHash | MD5 checksum of the entire entry |
- Layout table entries (25 bytes, padded array)
Consists of SizeB zero-padded blocks of 4096 bytes each, filled with the following entries:
| Offset | Type | Name | Description |
|---|---|---|---|
| 0x00 | char[16] | Key | CDN key of the file |
| 0x10 | uint32 [BE] | StringIndex | Index of the layout string in the table |
| 0x14 | uint8 | Unknown | ??? |
| 0x15 | uint32 [BE] | CompressedSize | Size of the compressed file |
- Encoding file layout string
Layout string describing the encoding file itself.
The key table defines the mapping from content hashes to CDN hashes. The entries within the file are sorted by the hash, which allows searching for them using two binary searches if one doesn't wish to create a secondary hash structure.
Each file can theoretically have multiple CDN keys, but it is rarely observed in practice.
Layout table can be used to find the compressed size and compression layout of individual files by their CDN key.
Layout strings describe the chunks into which the file is broken down in BLTE containers. This information is only necessary to compress the files, as BLTE containers contain sufficient information to decompress files without having to parse these strings. A description of the string format can be found on wowdev Wiki.