I'm thinking of creating a library type modpack but the text limit in books is far too small, Is there any way to increase the text and chapter limit? (I'm unsure if this would be the proper place to add. I know java and how to create mods just not this specific type.)

I don't know if you can change the vanilla behavior, never thought about this. However one quick way I can think of is to create your own custom book item that defines how many pages or character per page to have, and of course create the GUI accordingly

The limits used by books come from the limits of NBT (used for networking and storing to file) which in turn come from legacy limits imposed by java serialization.

If you look at java's DataOutput.writeUTF() it says the maximum size is 65535 characters. Minecraft actually uses 1/2 that, 32767, presumably in case all characters are double byte?

 

If you want to increase the limits you would need to change how the page's text gets stored in NBT. e.g. using a List of Strings instead of a single String for each page.

That would change the serialization format.

For the vanilla books, that's not something Forge would do. Because Forge supports being a "vanilla" server for vanilla clients. Changing the serialization format would break the vanilla clients.

Changing other fields like the number of pages or title length would also likely break the expectations of the vanilla guis.

 

So basically if you want to do this, you would need to create your own book items and probably your own custom blocks like the Lectern and Bookshelves to support them.

The problem with doing that is that things like the (Enchanted)BookItem are hardcoded by Mojang into the enchanting code. And not just the class, the actual object instances.

There are probably other hardcodings?