Improve error message if restoring from JSON file

[vetleledaal]

Current state

Older versions of Tachiyomi support backing up and restoring from JSON files. If a user tries to restore from such a backup they should be nudged in correct direction. Currently the error message is very cryptic and leads to a support burden:

kotlinx.serialization.protobuf.internal.ProtobufDecodingException: Unsupported start group or end group wire type: 3

Proposed change

Users are likely to expect old JSON backups to still be usable in Mihon, unless told directly. With the proposed change there is a de minimis maintenance/performance burden as it hooks into the existing gzip signature check. The new error message:

java.lang.Exception: JSON backup not supported

Limitations

If the user picks a JSON file that is not a backup file from Tachiyomi the error message will falsely imply that the file is a valid Tachiyomi JSON backup file. Accounting for this would be non-feasible, and an unlikely scenario.

[!] I do not have an actual JSON backup file from Tachiyomi at hand, I assume it looks like a regular JSON file.

Images

Image 1	Image 2

[MajorTanya]

They hadn't been usable in Tachiyomi for quite a while either afaik

Edit: Although considering this is just an error message, I don't think it'd be a problem to have it in Mihon.

[BrutuZ]

How do people even manage to select these, aren't JSON files filtered out of the file picker already? 🤔

[vetleledaal]

They hadn't been usable in Tachiyomi for quite a while either afaik

Still, people do manage to run into these issues, and not everyone bothers asking for support.

aren't JSON files filtered out of the file picker already?

It shows every file type for me ¯\_(ツ)_/¯

[AntsyLich]

How do people even manage to select these, aren't JSON files filtered out of the file picker already? 🤔

No file is filtered out

[AntsyLich]

Think you can also do a try catch on the decode function forProtobufDecodingEception and say the backup file is corrupted?

[BrutuZ]

No file is filtered out

Could / should they be?

[vetleledaal]

I have changed it so it will throw a more generic error in all cases. Should the Full error: string and the java.io.IOException also be changed/removed?

Image 1, old JSON backup	Image 2, invalid file

[AntsyLich]

I dedicate this PR merge to @ThaDaVos