Add --repair option for command that work with cache

[tanshihaj]

Chunks in local cache can corrupt for many reasons and by default desync fails when met them. They can be removed by running desync verify --repair --store /path/to/cache and runnnig desync untar ... again, however it is quite a long operation.
It could be convenient to repair them by redownloading invalid chunks from store when we met them during desync untar and other command which work with cache.

[folbricht]

Thanks for the PR. I do like the feature, though not a fan of passing the repair flag into so many places. You should be able to simplify that quite a bit.

If you look at https://github.com/folbricht/desync/blob/master/cmd/desync/store.go#L22, it gets cmdStoreOptions passed in. So if you added your flag here, perhaps calling it --cache-repair or similar to be more specific, then you could either pass the boolean to NewCache() here.

To avoid passing a flag to NewCache(), one could create a new object that implements the WriteStore interface and layer that on top of the store in https://github.com/folbricht/desync/blob/master/cmd/desync/store.go#L40. That way there wouldn't need to be any boolean parameter at all, though it would require implementing a store layer whose only job it is to turn InvalidChunk into ChunkNotFound basically.

[folbricht]

Thanks for the update.