Corrupt Revision Data error when saving documents

Reported in the forum https://forums.couchbase.com/t/corrupt-revision-data-error-when-saving-documents/34741/1.

SDK: Couchbase Lite C
Version: 3.0.2
OS: iOS & Android
Error: kCBLErrorCorruptRevisionData

This error has only been observed through error reports from user devices, and I have not been able to replicate it.

It seems that saving a document can sometimes corrupt it, since after the first time this error has been returned when saving a document, subsequent attempts to save the document always fail with the same error. The document can still be purged, though.

There are also crashes in CBLDatabase_SaveDocumentWithConcurrencyControl and CBLDocument::properties that seem related. It would make sense to me that once a document has been corrupted, invariants that certain code relies on don’t hold anymore.

The error message only contains the error code. Looking at the source code, only in a few places is a corruptRevisionData error thrown without a message. Additional logging or an error message describing the problem might be the first step to diagnose the issue.