Add Support for Parity Archives (PAR/PAR2)

[qkaiser]

Description
Parchive, commonly known as PAR (v1) or PAR2, is a format for creating redundant data that helps detect and repair corrupted files. These archives typically accompany split-file sets (like multi-volume RAR or ZIP archives).

References

• Official Parchive website (archived)
• Wikipedia: Parchive
• par2cmdline on GitHub

How to Craft

1. Install par2cmdline (e.g., sudo apt-get install par2 on Debian/Ubuntu).
2. Create a PAR2 set with:

   par2 create test.par2 file_to_protect
   

3. You can verify it with:

   par2 verify test.par2
   

Magic Value / Signature

• PAR2: Often begins with PAR2\0PKT (i.e., PAR2 + 0x00 + PKT).
• PAR (v1): Older .par files don’t have a well-defined signature but may contain identifiable metadata blocks.

How to Extract / Decompress

• Tool: Use par2cmdline for verification and recovery.
• Python Library: There’s no widely adopted Python library for PAR2 extraction. Typically, par2cmdline is used.

Determining End Offset

• Each PAR2 file is composed of multiple “packets.” Each packet header includes a length field.
• Summing the lengths of these packets gives the total file size.
• In unblob, parse the packet structure to find where each one ends and the next begins.