Please test this build on a local TEST SERVER before sending to your live server!
PaperMC is not responsible for any data loss to your chunks.
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The Minecraft World Region File format has a hard cap of 1MB per chunk.
This is due to the fact that the header of the file format only allocates
a single byte for sector count, meaning a maximum of 256 sectors, at 4k per sector.
This limit can be reached fairly easily with books, resulting in the chunk being unable
to save to the world. Worse off, is that nothing printed when this occured, and silently
performed a chunk rollback on next load.
This leads to security risk with duplication and is being actively exploited.
This patch catches the too large scenario, falls back and moves any large Entity
or Tile Entity into a new compound, and this compound is saved into a different file.
On Chunk Load, we check for oversized status, and if so, we load the extra file and
merge the Entities and Tile Entities from the oversized chunk back into the level to
then be loaded as normal.
Once a chunk is returned back to normal size, the oversized flag will clear, and no
extra data file will exist.
This fix maintains compatability with all existing Anvil Region Format tools as it
does not alter the save format. They will just not know about the extra entities.
This fix also maintains compatability if someone switches server jars to one without
this fix, as the data will remain in the oversized file. Once the server returns
to a jar with this fix, the data will be restored.
Aikar