repak

Library and CLI tool for working with Unreal Engine .pak files.

• Supports reading and writing a wide range of versions
• Easy to use API while providing low level control:
  • Only parses index initially and reads file data upon request
  • Can rewrite index in place to perform append or delete operations without rewriting entire pak

repak CLI

• Sane handling of mount points: defaults to ../../../ but can be configured via flag
• 2x faster unpacking over UnrealPak. As much as 30x faster has been observed (on Linux unpacked to ramdisk)
• Unpacking is guarded against malicious pak that attempt to write to parent directories

cli

$ repak --help
Usage: repak [OPTIONS] <COMMAND>

Commands:
  info       Print .pak info
  list       List .pak files
  hash-list  List .pak files and the SHA256 of their contents. Useful for finding differences between paks
  unpack     Unpack .pak file
  pack       Pack directory into .pak file
  get        Reads a single file to stdout
  help       Print this message or the help of the given subcommand(s)

Options:
  -a, --aes-key <AES_KEY>  256 bit AES encryption key as base64 or hex string if the pak is encrypted
  -h, --help               Print help
  -V, --version            Print version

packing

$ find mod
mod
mod/assets
mod/assets/AssetA.uasset
mod/assets/AssetA.uexp

$ repak pack -v mod
packing assets/AssetA.uasset
packing assets/AssetA.uexp
Packed 4 files to mod.pak

$ repak list mod.pak
assets/AssetA.uasset
assets/AssetA.uexp

unpacking

$ repak --aes-key 0x12345678 unpack MyEncryptedGame.pak
Unpacked 12345 files to MyEncryptedGame from MyEncryptedGame.pak

compatibility

UE Version	Version	Version Feature	Read	Write
	1	Initial	❔	❔
4.0-4.2	2	NoTimestamps	✔️	✔️
4.3-4.15	3	CompressionEncryption	✔️	✔️
4.16-4.19	4	IndexEncryption	✔️	✔️
4.20	5	RelativeChunkOffsets	✔️	✔️
	6	DeleteRecords	❔	❔
4.21	7	EncryptionKeyGuid	✔️	✔️
4.22	8A	FNameBasedCompression	✔️	✔️
4.23-4.24	8B	FNameBasedCompression	✔️	✔️
4.25	9	FrozenIndex	✔️	✔️1
	10	PathHashIndex	❔	❔
4.26-5.32	11	Fnv64BugFix	✔️	✔️

Feature	Read	Write
Compression	✔️	〰️3
Encrypted Index	✔️	❌
Encrypted Data	✔️	❌

Supports reading encrypted (both index and/or data) and compressed paks. Writing does not support compression or encryption yet.

notes

determinism

As far as I can tell, the index is not necessarily written deterministically by UnrealPak. repak uses BTreeMap in place of HashMap to deterministically write the index and happens to rewrite the test paks in the same order, but this more likely than not stops happening on larger pak files.

full directory index

UnrealPak includes a directory entry in the full directory index for all parent directories back to the pak root for a given file path regardless of whether those directories contain any files or just other directories. repak only includes directories that contain files. So far no functional differences have been observed as a result.

acknowledgements

• unpak: original crate featuring read-only pak operations
• rust-u4pak's README detailing the pak file layout
• jieyouxu for serialization implementation of the significantly more complex V11 index

Footnotes

1. Except for paks compressed using frozen index which has significant complexity and only existed for UE 4.25 anyway. ↩

2. As of writing. Later versions are likely supported but untested. ↩

3. Zlib, Gzip, and Zstd are supported. Not all compression algorithms are available in all games. ↩