<aside> 🌐 https://mupdf.com/r/Change-Detection

</aside>

Detecting Changes between Incremental Saves

This is required so we can verify that the changes between different signings conform to the permissions.

Proposal

All changes in the document will take place within objects. Fields can change various different ways within an object. Therefore, we need to compare “parts” of old and new objects to see if they have changed legally or illegally. We only need to keep records at the object level though; i.e. it’s enough to know “this object has changed in an illegal way” or “a legal way”.

So, we now have all the objects changed. Now we just need to figure out which ones are OK, and which aren’t.

Thus any field with only bit 1 set, is a problem. Any field with bit 1 and bit 3 set is an illegal field change. Anything else is fine.


Robin Watts - 2019-12-06