zonefiles in map format larger than 2 GiB cannot be read but can be written (data loss)

Summary

Large zones written in masterfile-format map; with files larger than 2 GiB cannot be read.

BIND version used

It affects latest commits on all supported branches:

• main 042d206b
• v9_16 713ded2c
• v9_11 0480e212

Steps to reproduce

1. Generate a zone file which results in map file larger than 2 GiB:

perl bin/tests/startperf/mkzonefile.pl test 8000000 > /tmp/text

2. Convert text zone file into map format:

named-compilezone -i none -k ignore -m ignore -M ignore -n ignore -r ignore -S ignore -T ignore -W ignore -f text -F map -o /tmp/map test /tmp/text

3. Attempt to read the zone:

named-checkzone -i none -k ignore -m ignore -M ignore -n ignore -r ignore -S ignore -T ignore -W ignore -f map test /tmp/map

What is the current bug behavior?

zone test/IN: loading from master file /tmp/map failed: invalid file
zone test/IN: not loaded due to errors.

What is the expected correct behavior?

Zone can be read and the data are intact, obviously.

Possible fixes

The main question is how much we want to invest into the map format. If we decide to remove RBTDB map format in favor of a different data structure, we might consider a low-cost option: Limit file size to make it "safe" and remove the format a bit later.