Parfait

Semi-automated par2 creation / management tool. This tool creates par2 data files in a hidden .par2 folder that can be used to fix the original in case of corruption.

These are the steps that are performed:

• if no .par2 folder is found then par2 files are created for every regular file
• par2 files are created for any new regular files in the folder
• regular files are checked against par2 archives and any corrupted files identified
• if -a flag specified, file recovery is attempted on corrupted files

Usage

Usage: Parfait [options] (folder) [...]
 Options:
  -t             Test mode. show info, but don't perform any actions
  -r             Recurse into sub-folders
  -hf            Include hidden files
  -hd            Include hidden folders
  -a             Enable automatic recovery
  -v             Verbose mode. show more info
  -l (log file)  Log output to this file
  -x (file)      Path to par2 executable
  -h / --help    Show this help

Design

Parchive files use Reed-Solomon codes to save file recovery information.

Parfait is a wrapper to create and manage par2 files so that recovery info can be kept for one or more folders.

Additional links / information

• http://parchive.sourceforge.net/
• https://sourceforge.net/projects/parchive/files/
• http://paulhoule.com/phpar2/index.php
• https://github.com/Parchive/par2cmdline
• https://github.com/antiduh/ErrorCorrection/tree/master/ErrorCorrection
• https://github.com/micjahn/ZXing.Net/blob/master/Source/test/src/common/reedsolomon/ReedSolomonTestCase.cs
• https://stackoverflow.com/questions/24578536/how-to-apply-reed-solomon-algorithm-using-zxing-in-c-sharp

Example command

dotnet run -p src -- -t .

Cleanup

find -H . -type d | grep -i ".par2$" | xargs -n1 -d '\n' trash

Build

You can use the regular dotnet commands for Debug builds To publish use ./make.sh publish

Native Build

Follow the CoreRT - build prerequesites

Linux

1. run ./make.sh publish

Windows

1. Launch the "x64 Native Tools Command Prompt for VS" command prompt
2. Use msys bash to execute ./make.sh publish

Mac Os-X

I don't have a Mac currently - TBD

TODO

• see if we can replace the par2 executable with https://github.com/heksesang/Parchive.NET
  • Seems to be incomplete
• add tests for file system permissions failures
  • create directory
  • delete file
  • delete folder
  • create file
• add option to only do one operation (create/verify/recreate/repair)
• Add a summary with counts of the operations performed
• add a quiet flag to suppress the summary
• add flag to turn off recreate (manual mode) and only verify
  • maybe add input file with instructions for each file specified (re-create / restore / do nothing)
• fix problem with partial par2 files being created when the operation is cancelled
  • maybe recreate if condition can be caught

Tests

• ✓ what happens if the par2 data gets corrupted ?
  • looks like any damage to par2 files reduces the amount of data that can be recovered. it seems to be proportional to how much damage was done.
• ✓ how much corruption results in the inability to recover
  • looks like it's something like (redundancy * % of par2 good data). so basically if your redundancy was 10% and 50% of par2 volume file is corrupt you can recover 10% * 50% = 5%
• ✓ does corruption result in badly restored files
  • this doesn't seem to be the case
• ∞ is there a particular corruption that restores bad files
  • not fully tested but haven't seen any yet
• ∞ add code coverate dotnet test --collect:"Code Coverage"
  • looks like microsoft hasn't implemented this for linux yet. see vstest issue 981