Add Git pre-commit hook to check for missing serial bumps in zonefiles

utils/scripts/zone-serial-number-hook.sh

@@ -0,0 +1,85 @@
+#!/bin/sh
+# zone-serial-number-hook - Check for missing serial bumps
+#
+# Written in 2020 by Lucas
+#
+# To the extent possible under law, the author(s) have dedicated all
+# copyright and related and neighboring rights to this software to the
+# public domain worldwide. This software is distributed without any
+# warranty.
+#
+# You should have received a copy of the CC0 Public Domain Dedication
+# along with this software. If not, see
+# <http://creativecommons.org/publicdomain/zero/1.0/>.
+
+# Requires:
+# - POSIX sh
+# - bc
+# - git
+# - ldns-utils
+
+# Install instructions:
+#
+#	cp zone-serial-number-hook "$myrepo/.git/hooks/pre-commit"
+#	chmod +x "$myrepo/.git/hooks/pre-commit"
+
+bc_cmp()
+{
+	_X=$1
+	_OP=$2
+	_Y=$3
+
+	_rc=$(bc <<EOF
+define t(x, y){
+	if (x $_OP y) {
+		return(0)
+	}
+	return(1)
+}
+t($_X, $_Y)
+EOF
+)
+	return $_rc
+}
+
+get_serial()
+{
+	git show "$1" 2>/dev/null | ldns-read-zone -E SOA | {
+		read -r _name _ttl _class _rrtype _rname _mname _serial _rest
+		printf "%s\n" "${_serial:-0}"
+	}
+}
+
+if git rev-parse --verify HEAD >/dev/null 2>&1; then
+	against=HEAD
+else
+	# Initial commit: diff against an empty tree object
+	against=$(git hash-object -t tree /dev/null)
+fi
+
+# Zonefiles names are matched against hooks.zonefile_regex option.
+# Defaults to `\.zone$`.
+zonefile_regex=$(git config --default '\.zone$' hooks.zonefileregex)
+
+needs_serial_bump=$(git diff-index --name-only --cached "$against" |
+    grep -E -- "$zonefile_regex" | {
+	rc=0
+	while read -r filename; do
+		old=$(get_serial "$against:$filename")
+		new=$(get_serial ":$filename")
+		if bc_cmp "$new" "<=" "$old"; then
+			printf "%s\n" "$filename"
+			rc=1
+		fi
+	done
+	return $rc
+})
+
+rc=$?
+if [ $rc -ne 0 ]; then
+	# send all output to standard error
+	exec >&2
+	printf "The following zonefiles require a serial bump:\n"
+	printf "- %s\n" $needs_serial_bump
+fi
+exit $rc