repak/README.md

# 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

## compatibility

| UE Version | Version | Version Feature       | Read               | Write              |
|------------|---------|-----------------------|--------------------|--------------------|
|            | 1       | Initial               | :grey_question:    | :grey_question:    |
| 4.0-4.2    | 2       | NoTimestamps          | :heavy_check_mark: | :heavy_check_mark: |
| 4.3-4.15   | 3       | CompressionEncryption | :heavy_check_mark: | :heavy_check_mark: |
| 4.16-4.19  | 4       | IndexEncryption       | :heavy_check_mark: | :heavy_check_mark: |
| 4.20       | 5       | RelativeChunkOffsets  | :heavy_check_mark: | :heavy_check_mark: |
|            | 6       | DeleteRecords         | :grey_question:    | :grey_question:    |
| 4.21       | 7       | EncryptionKeyGuid     | :heavy_check_mark: | :heavy_check_mark: |
| 4.22       | 8A      | FNameBasedCompression | :heavy_check_mark: | :heavy_check_mark: |
| 4.23-4.24  | 8B      | FNameBasedCompression | :heavy_check_mark: | :heavy_check_mark: |
| 4.25       | 9       | FrozenIndex           | :heavy_check_mark: | :heavy_check_mark: |
|            | 10      | PathHashIndex         | :grey_question:    | :grey_question:    |
| 4.26-4.27  | 11      | Fnv64BugFix           | :heavy_check_mark: | :heavy_check_mark: |

| Feature         | Read               | Write |
|-----------------|--------------------|-------|
| Compression     | :heavy_check_mark: | :x:   |
| Encrypted Index | :heavy_check_mark: | :x:   |
| Encrypted Data  | :heavy_check_mark: | :x:   |

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](https://github.com/bananaturtlesandwich/unpak): original crate featuring read-only pak operations
- [rust-u4pak](https://github.com/panzi/rust-u4pak)'s README detailing the pak file layout
- [jieyouxu](https://github.com/jieyouxu) for serialization implementation of the significantly more complex V11 index