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✏️ Editing: resolvconf

#!/bin/sh
#
# This file is part of the resolvconf package.
#

set -e

echo_usage() { echo "Usage: resolvconf (-d IFACE|-a IFACE|-u|--enable-updates|--disable-updates|--updates-are-enabled)" ; }

PATH=/sbin:/bin:/usr/sbin:/usr/bin
MYNAME="${0##*/}"
RUN_DIR=/run/resolvconf
ENABLE_UPDATES_FLAGFILE="${RUN_DIR}/enable-updates"
POSTPONED_UPDATE_FLAGFILE="${RUN_DIR}/postponed-update"

report_err() { echo "${MYNAME}: Error: $*" >&2 ; }

# Check arguments
CMD="$1"
case "$CMD" in
  -a|-d)
	IFACE="$2"
	if [ ! "$IFACE" ] ; then
		report_err "No interface name specified"
		echo_usage >&2
		exit 1
	fi
	report_iface_err() {
		report_err "$* not allowed in interface record name"
	}
	case "$IFACE" in
	  */*) report_iface_err "Slash" ; exit 1 ;;
	  *" "*) report_iface_err "Space" ; exit 1 ;;
	  .*) report_iface_err "Initial dot" ; exit 1 ;;
	  -*) report_iface_err "Initial hyphen" ; exit 1 ;;
	  \~*) report_iface_err "Initial tilde" ; exit 1 ;;
	esac
	;;
  -u|--enable-updates|--disable-updates|--updates-are-enabled)
  	if [ "$2" ] ; then
		report_err "The $CMD option does not take an argument"
		echo_usage >&2
		exit 1
	fi
	;;
  *)
	report_err "Command not recognized"
	echo_usage >&2
	exit 99
	;;
esac

[ -d "${RUN_DIR}/interface" ] || { mkdir -p "${RUN_DIR}/interface" ; }
[ -d "${RUN_DIR}/interface" ] || { report_err "${RUN_DIR}/interface either does not exist or is not a directory" ; exit 1 ; }
cd "${RUN_DIR}/interface"

{
# Make sure that we do not end up with a broken resolv.conf if resolvconf
# is invoked in parallel.
LOCK_WAIT_S=10
flock -w $LOCK_WAIT_S 9 ||
	{ report_err "Run lock held by another process for longer than $LOCK_WAIT_S seconds"; exit 1; }

update_and_exit()
{
	rm -f "$POSTPONED_UPDATE_FLAGFILE"
	exec run-parts ${1:+--arg="$1"} ${2:+--arg="$2"} /etc/resolvconf/update.d
}

# Handle commands that don't require normalized_stdin()

case "$CMD" in
  -d)
	if [ ! -e "$IFACE" ] ; then
		exit 0
	fi
	if [ ! -s "$IFACE" ] ; then
		rm -f "$IFACE"
		exit 0
	fi
	rm -f "$IFACE"
	if [ -e "$ENABLE_UPDATES_FLAGFILE" ] ; then
		update_and_exit -d "$IFACE"
	else
		: >| "$POSTPONED_UPDATE_FLAGFILE"
		exit 0
	fi
	;;
  -u)
	if [ -e "$ENABLE_UPDATES_FLAGFILE" ] ; then
		update_and_exit -u
	else
		: >| "$POSTPONED_UPDATE_FLAGFILE"
		exit 0
	fi
	;;
  --enable-updates)
	: >| "$ENABLE_UPDATES_FLAGFILE" || exit 1
	if [ -e "$POSTPONED_UPDATE_FLAGFILE" ] ; then
		(update_and_exit -u) || :
	fi
	exit 0
	;;
  --disable-updates)
	rm -f "$POSTPONED_UPDATE_FLAGFILE" || :
	rm -f "$ENABLE_UPDATES_FLAGFILE" || exit 1
	exit 0
	;;
  --updates-are-enabled)
	if [ -e "$ENABLE_UPDATES_FLAGFILE" ] ; then
		exit 0
	else
		exit 1
	fi
	;;
esac

#	
# The following function must EXACTLY the same in the resolvconf
# and test-normalization scripts. And the test must pass!
#
### BEGIN FUNCTION TO COPY TO THE test-normalization SCRIPT ###
#
# Echo stdin with:
#	comments removed;
#	initial and terminal whitespace removed;
#	whitespace strings replaced by single blanks;
#	leading zeroes removed from nameserver address fields;
#	first set of zero fields in an IPv6 address collapsed to '::';
#	empty lines removed.
normalized_stdin() {
	sed                                                                        \
		-e 's/#.*$//'                                                      \
		-e 's/[[:blank:]]\+$//'                                            \
		-e 's/^[[:blank:]]\+//'                                            \
		-e 's/[[:blank:]]\+/ /g'                                           \
		-e '/^nameserver/!b ENDOFCYCLE'                                    \
		-e 's/$/ /'                                                        \
		-e 's/$[:. ]$0\+/\10/g'                                          \
		-e 's/$[:. ]$0$[123456789abcdefABCDEF][[:xdigit:]]*$/\1\2/g'   \
		-e '/::/b ENDOFCYCLE; s/ $0[: ]$\+/ ::/'                         \
		-e '/::/b ENDOFCYCLE; s/:$0[: ]$\+/::/'                          \
		-e ': ENDOFCYCLE'                                                  \
		- |                                                                \
	sed                                                                        \
		-e 's/[[:blank:]]\+$//'                                            \
		-e '/^$/d'
}
### END FUNCTION TO COPY TO THE test-normalization SCRIPT ###

case "$CMD" in
  -a)
	OLD_CONTENT=""
	[ -f "$IFACE" ] && OLD_CONTENT="$(cat "$IFACE")"
	NEW_CONTENT="$(normalized_stdin)"
	# Proceed only if content has changed. The test here can't
	# eliminate 100% of redundant invocations of update scripts
	# because we don't do any locking; however it certainly does
	# eliminate most of them.
	if [ "$NEW_CONTENT" = "$OLD_CONTENT" ] ; then 
		exit 0
	fi
	IFACE_TMPFILE="${IFACE}_new.$$"
	cleanup() { rm -f "$IFACE_TMPFILE" ; }
	trap cleanup EXIT
	echo "$NEW_CONTENT" > "$IFACE_TMPFILE"
	mv -f "$IFACE_TMPFILE" "$IFACE"

if [ -e "$ENABLE_UPDATES_FLAGFILE" ] ; then
		update_and_exit -a "$IFACE"
	else
		: >| "$POSTPONED_UPDATE_FLAGFILE"
		exit 0
	fi
	;;
esac

# Don't reach here
exit 99

} 9>"${RUN_DIR}/run-lock"

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