Maps network ports thru NAT-PMP and refreshes that mapping automatically

natpmprfr.sh

#!/usr/bin/env bash

# natpmprfr.sh: Maps network ports thru NAT-PMP and refreshes that mapping automatically
# (https://en.wikipedia.org/wiki/NAT_Port_Mapping_Protocol)
#
# Useful for applications with poor or without NAT-PMP implementation
# (http://miniupnp.free.fr/libnatpmp.html)
#
# Script can set UFW rules according to mapped/unmapped local ports
# (https://help.ubuntu.com/community/UFW)
#
# Requirements: sudo, natpmpc, ufw (optional)
# Tested on Ubuntu 22.04 LTS

gateway="192.168.1.1"                   # mat-pmp gateway
private_port="0"                        # set 0 to obtain from natpmpc
protocols="tcp"                         # "tcp" "udp" "tcp udp"
refresh_timeout="40"                    # seconds
port_file="/tmp/nat-pmp_local_port.txt" # leave "" to disable
set_ufw_rules=true                      # requires root permissions

map_port() {
	if [[ "$protocols" == *"tcp"* ]]; then
		natpmc_out=$(sudo -u nobody natpmpc -g "$gateway" -a 0 "$local_port" tcp 60)
		local_port=$(echo "$natpmc_out" | grep -Po 'local\sport\s\K\d{0,65535}')
		public_port=$(echo "$natpmc_out" | grep -Po 'public\sport\s\K\d{0,65535}')
		echo "💻 Local  TCP port: $local_port" >/dev/tty
		echo "🌐 Public TCP port: $public_port" >/dev/tty
	fi
	if [[ "$protocols" == *"udp"* ]]; then
		natpmc_out=$(sudo -u nobody natpmpc -g "$gateway" -a 0 "$local_port" udp 60)
		local_port=$(echo "$natpmc_out" | grep -Po 'local\sport\s\K\d{0,65535}')
		public_port=$(echo "$natpmc_out" | grep -Po 'public\sport\s\K\d{0,65535}')
		echo "💻 Local  UDP port: $local_port" >/dev/tty
		echo "🌐 Public UDP port: $public_port" >/dev/tty
	fi
	if [ -n "$local_port" ]; then
		echo "$local_port"
	fi
}

ufw_open_port() {
	if [ "$set_ufw_rules" = true ]; then
		echo ""
		echo "🧱 UFW says:"
		if [ "$local_port" = "0" ]; then
			ufw allow "$1"
		else
			ufw allow "$local_port"
		fi
	fi
}

ufw_close_port() {
	if [ "$set_ufw_rules" = true ]; then
		echo ""
		echo "🧱 UFW says:"
		if [ "$local_port" = "0" ]; then
			ufw delete allow "$1"
		else
			ufw delete allow "$local_port"
		fi
	fi
}

write_port_to_file() {
	if [ -n "$port_file" ]; then
		echo "$1" | sudo -u nobody tee "$port_file" 1>/dev/null
	fi
}

unmap_ports() {
	echo ""
	echo "🌊 Unmapping port(s)..."
	if [ -n "$cached_local_port" ]; then
		if [[ "$protocols" == *"tcp"* ]]; then
			sudo -u nobody natpmpc -g "$gateway" -a "$cached_local_port" "$local_port" tcp 0 1>/dev/null
		fi
		if [[ "$protocols" == *"udp"* ]]; then
			sudo -u nobody natpmpc -g "$gateway" -a "$cached_local_port" "$local_port" udp 0 1>/dev/null
		fi
		ufw_close_port "$cached_local_port"
	fi
}

terminate() {
	unmap_ports
	rm -f "$port_file"
	exit
}

if [ "$set_ufw_rules" = true ]; then
	if [ "$EUID" -ne 0 ]; then
		echo "Please run as root"
		exit
	fi
fi

trap terminate SIGINT SIGTERM SIGQUIT SIGABRT

echo "🌎 Getting info..."
if sudo -u nobody natpmpc -g "$gateway"; then
	while true; do
		echo ""
		echo "🔌 Mapping ${protocols^^} port(s)..."
		local_port=$(map_port)
		if [ -n "$local_port" ]; then
			ufw_open_port "$local_port"
			write_port_to_file "$local_port"
			cached_local_port="$local_port"
		else
			echo ""
			echo "💢 Something went wrong..."
			if [ -n "$cached_local_port" ]; then
				unmap_ports
				cached_local_port=""
				rm -f "$port_file"
			fi
		fi
		echo ""
		echo "🔄 Refreshing ($(date))..."
		sleep "$refresh_timeout"
	done
else
	exit
fi