Then what you need is search the Internet for ideas of extracting objects(text resources, 2D texture, etc.) from Unity assets. With sufficient information we retrieved, we were able to extract raw asset files from a UnityFS bundle. Each file information contains file offset we need( BE UInt64), the decompressed size( BE UInt64), a BE UInt32 flag and a Null-Terminated string of file name. Then a BE UInt32 value represents file count in a single package. Each block information contains a Big-Endian UInt32 decompressed size, a Big-Endian UInt32 compressed size and a flag that we might not interested in. There we go…block and file information!įollowing a unknown 16 bytes block, there’s a Big-Endian UInt32 value represents block count in a single package. You can implement your own block-based reader - but my time budget didn’t allow me to do this. But I just wanted these bundle files, so I decided to read all blocks at once and decompress into a single memory stream.ĭecompressed size should match what you get. The Unity’s proprietary parser and Disunity respects this design. Both LZMA and LZ4* (LZ4Hc, etc.) are supported. UnityFS uses optional block-based compression for streaming (you can read a specific bundle without downloading the whole file).
Length of each data type matters - but that’s a basic stuff for CS students.Ĭode snippet of my simple parser Compression For the sake of convenience, I extended the original BinaryReader for these support. Unity utilizes both Big Endian and Little Endian in a single file and personally I didn’t get this. But it can be improved for better Null-terminated String and Big Endian support.
(Flags & 0x80) says whether the block and directory list is at the end of this bundle file.Ĭ# provides a good BinaryReader that makes things a bit easy. (Flags & 0x40) says whether the bundle has directory info. 0 means no compression, 1 means LZMA and 2/3 means LZ4/LZ4HC. There’s a DWORD flags data that matters - it contains some critical information required for decompression and directory parsing. Look into the old Disunity source code for some idea. There’s bunch of documentation about this.
You have to parse asset files in order to extract what you need. UnityFS follows a standard Unity file header structure. 2D texture, text resources, scene objects, etc.). Each asset contains a collection of serialized Unity objects (e.g. UnityFS is just bundle of several Unity assets. I am not a Unit圓D developer, and I absolutely didn’t know why Unity introduce a new bundle format. UnityFS was a new asset bundle format introduced in Unity 5. Special thank to the UABE project - without these generous header, I would not be able to implement my own parsing and compose this article. And I was too lazy to write a C wrapper for P/Invoke. But these C++ header files point to a perfect solution - parse file and implement my own UnityFS parser/reader. Since it was compiled with Microsoft Visual C++ 2010, I was unable to use it directly(C++ ABI constantly changes with every MSVC release). Luckily this toolkit provides some API and documentation. I tried the command line support but failed (maybe I was too stupid). However, acquiring thousands of texture assets from 2000+ isolated files is not an easy job. It did a great job extracting resources I needed graphically. Then I turned to a tool called Unity Assets Bundle Extractor. Since resource extraction has not been implemented at this moment, Disunity couldn’t be my choice. Disunity has been refactored, and remaining work is still in progress (at least the moment I write this article). I thought I could extract assets I needed with existing tools (e.g. DISCLAIMER: I will not tell you details about encryption. Original assets were encrypted with known algorithm and key. I accepted the challenge, but things were far more complicated than I expected. Someone asked me if I could extract some images from a popular Chinese mobile game. Posted at Comments Learn something Project. Deep dive into UnityFS: structure and implementation
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