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May 14, 2021

u4pak

Unpack, pack, list, test and mount Unreal Engine 4 .pak archives.

NOTE: I've wrote an alternative version of this in Rust and compiled a self-contained binary for Windows users. So there is no hassle with installing Python, plus it adds a way to supply command line arguments via a file that you can associate with the binary so you only need to double click that. It is also faster, mainly because it uses multi-threading. (Note that it's command line arguments are sligthly different.)

Basic usage:

u4pak.py info <archive>                 - print archive summary info
u4pak.py list <archive>                 - list contens of .pak archive
u4pak.py test <archive>                 - test archive integrity
u4pak.py unpack <archive>               - extract .pak archive
u4pak.py pack <archive> <files>         - create .pak archive
u4pak.py mount <archive> <mount-point>  - mount archive as read-only file system

For unpacking only unencryped archives of version 1, 2, 3, 4, and 7 are supported, for packing only version 1, 2, and 3.

NOTE: If you know (cheap) games that use other archive versions please tell me! Especially if its 5 or 6. There is a change in how certain offsets are handled at some point, but since I only have an example file of version 7 I don't know if it happened in version 5, 6, or 7.

The mount command depends on the llfuse Python package. If it's not available the rest is still working.

This script is compatible with Python 3.7.

If you get errors saying anything about 'utf8' codec can't decode byte [...] try to use another encoding by passing --encoding=iso-8859-1 or similar.

If you get an error message about an illegal file magic try to pass --ignore-magic. If you get an error message about the archive version being 0 try to pass --force-version=1 (or a higher number).

File Format

Byte order is little endian and the character encoding of file names seems to be ASCII (or ISO-8859-1/UTF-8 that coincidentally only uses ASCII compatiple characters).

Offsets and sizes seem to be 64bit or at least unsigned 32bit integers. If interpreted as 32bit integers all sizes (except the size of file names) and offsets are followed by another 32bit integer of the value 0, which makes me guess these are 64bit values. Also some values exceed the range of signed 32bit integers, so they have to be at least unsigned 32bit integers. This information was reverse engineered from the Elemental Demo for Linux (which contains a 2.5 GB .pak file).

Basic layout:

  • Data Records
  • Index
    • Index Header
    • Index Records
  • Footer

In order to parse a file you need to read the footer first. The footer contains an offset pointer to the start of the index records. The index records then contain offset pointers to the data records.

Some games seem to zero out parts of the file. In particular the footer, which makes it pretty much impossible to read the file without manual analysis and guessing. I suspect these games have the footer included somewhere in the game binary. If it's not obfuscated one might be able to find it using the file magic (given that the file magic is even included)?

Record

Offset  Size  Type         Description
     0     8  uint64_t     offset
     8     8  uint64_t     size (N)
    16     8  uint64_t     uncompressed size
    24     4  uint32_t     compression method:
                              0x00 ... none
                              0x01 ... zlib
                              0x10 ... bias memory
                              0x20 ... bias speed
if version <= 1
    28     8  uint64_t     timestamp
end
     ?    20  uint8_t[20]  data sha1 hash
if version >= 3
 if compression method != 0x00
  ?+20     4  uint32_t     block count (M)
  ?+24  M*16  CB[M]        compression blocks
 end
     ?     1  uint8_t      is encrypted
   ?+1     4  uint32_t     The uncompressed size of each compression block.
end                        The last block can be smaller, of course.

Compression Block (CB)

Size: 16 bytes

Offset  Size  Type         Description
     0     8  uint64_t     compressed data block start offset.
                           version <= 4: offset is absolute to the file
                           version 7: offset is relative to the offset
                                      field in the corresponding Record
     8     8  uint64_t     compressed data block end offset.
                           There may or may not be a gap between blocks.
                           version <= 4: offset is absolute to the file
                           version 7: offset is relative to the offset
                                      field in the corresponding Record

Data Record

Offset  Size  Type            Description
     0     ?  Record          file metadata (offset field is 0, N = compressed_size)
     ?     N  uint8_t[N]      file data

Index Record

Offset  Size  Type            Description
     0     4  uint32_t        file name size (S)
     4     S  char[S]         file name (includes terminating null byte)
   4+S     ?  Record          file metadata

Index

Offset  Size  Type            Description
     0     4  uint32_t        mount point size (S)
     4     S  char[S]         mount point (includes terminating null byte)
   S+4     4  uint32_t        record count (N)
   S+8     ?  IndexRecord[N]  records

Footer

Size: 44 bytes

Offset  Size  Type         Description
     0     4  uint32_t     magic: 0x5A6F12E1
     4     4  uint32_t     version: 1, 2, 3, 4, or 7
     8     8  uint64_t     index offset
    16     8  uint64_t     index size
    24    20  uint8_t[20]  index sha1 hash

Related Projects

  • fezpak: pack, unpack, list and mount FEZ .pak archives
  • psypkg: pack, unpack, list and mount Psychonauts .pkg archives
  • bgebf: unpack, list and mount Beyond Good and Evil .bf archives
  • unvpk: extract, list, check and mount Valve .vpk archives
  • rust-vpk: Rust rewrite of the above
  • t2fbq: unpack, list and mount Trine 2 .fbq archives
  • rust-u4pak: not yet finished Rust rewrite of this script

BSD License

Copyright (c) 2014-2019 Mathias Panzenböck

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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