Feature Request: Dealing with missing or damaged *.par2 files

[ramboman]

All files can be subjected to corruption, including *.par2 files. It would be great if par2cmdline can deal with corruptions over the original file and also over *.par2 files as a whole.

Example:

a.img <- Damaged requiring 1 block
a.img.par2
a.img.vol000+01.par2 <- Missing
a.img.vol001+02.par2
a.img.vol003+04.par2
a.img.vol007+08.par2 <- Damaged

Legend:
[x] means what par2cmdline can already do
[ ] means a feature request

$ par2 verify *.par2
[ ] Show missing *.par2 files
[ ] Be explicit about damaged *.par2 files

$ par2 repair *.par2
[x] If there are enough healthy *.par2 files to repair a.img, repair it
[ ] Use the now healthy a.img file to regenerate the missing and damaged *.par2 files

[animetosho]

[ ] Show missing *.par2 files

Unfortunately there's no way to know this. Your example seems logical with default settings, but it's possible to generate that set without the file you marked as missing.

[ ] Be explicit about damaged *.par2 files

This one can be a little tricky because it may be difficult to tell if something is damaged data, or something extraneous that the application doesn't understand (e.g. a new unrecognised packet).
par2cmdline could be more explicit if it encounters something odd though (e.g. hash mismatch, or number of found recovery packets doesn't match what the filename declares), just note that it's not a guarantee.

[ ] Use the now healthy a.img file to regenerate the missing and damaged *.par2 files

Once you've recovered a.img, you can just re-create the PAR2 set and delete the old one.
So technically, this can already be done, but a "PAR2 repair" function could make this faster by re-using known good recovery instead of recomputing them.