wg-quick: allow for the hatchet, but not by default

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

contrib/dns-hatchet/README

@@ -0,0 +1,8 @@
+The DNS Hatchet
+===============
+
+This is a workaround for distributions without resolvconf or any proper
+mechanism of setting the DNS. Running 'apply.sh` in this directory will
+insert 'hatchet.bash` into the right place in 'wg-quick.bash`. It is
+recommended that distributions without any resolvconf available run this
+before calling 'make install` in their packaging scripts.

contrib/dns-hatchet/apply.sh

@@ -0,0 +1,6 @@
+#!/bin/bash
+
+ME="$(readlink -f "$(dirname "$(readlink -f "$0")")")"
+TOOLS="$ME/../../../src/tools"
+
+sed -i "/~~ function override insertion point ~~/r $ME/hatchet.bash" "$TOOLS/wg-quick.bash"

contrib/dns-hatchet/hatchet.bash

@@ -0,0 +1,39 @@
+set_dns() {
+	[[ ${#DNS[@]} -gt 0 ]] || return 0
+
+	if [[ $(resolvconf --version 2>/dev/null) == openresolv\ * ]]; then
+		printf 'nameserver %s\n' "${DNS[@]}" | cmd resolvconf -a "$INTERFACE" -m 0 -x
+	else
+		echo "[#] mount \`${DNS[*]}' /etc/resolv.conf" >&2
+		[[ -e /etc/resolv.conf ]] || touch /etc/resolv.conf
+		{ cat <<-_EOF
+			# This file was generated by wg-quick(8) for use with
+			# the WireGuard interface $INTERFACE. It cannot be
+			# removed or altered directly. You may remove this file
+			# by running \`wg-quick down $INTERFACE', or if that
+			# poses problems, run \`umount /etc/resolv.conf'.
+
+		_EOF
+		printf 'nameserver %s\n' "${DNS[@]}"
+		} | unshare -m --propagation shared bash -c "$(cat <<-_EOF
+			set -e
+			mount --make-private /dev/shm
+			mount -t tmpfs none /dev/shm
+			cat > /dev/shm/resolv.conf
+			mount -o remount,ro /dev/shm
+			mount -o bind,ro /dev/shm/resolv.conf /etc/resolv.conf
+		_EOF
+		)"
+	fi
+	HAVE_SET_DNS=1
+}
+
+unset_dns() {
+	[[ ${#DNS[@]} -gt 0 ]] || return 0
+
+	if [[ $(resolvconf --version 2>/dev/null) == openresolv\ * ]]; then
+		cmd resolvconf -d "$INTERFACE"
+	else
+		cmd umount /etc/resolv.conf
+	fi
+}

src/wg-quick.bash

@@ -264,6 +264,8 @@ cmd_down() {
 	execute_hooks "${POST_DOWN[@]}"
 }
 
+# ~~ function override insertion point ~~
+
 if [[ $# -eq 1 && ( $1 == --help || $1 == -h || $1 == help ) ]]; then
 	cmd_usage
 elif [[ $# -eq 2 && $1 == up ]]; then