Bash script to open a port using natpmpc and update the opened port in transmission-daemon

natpmpc-transmission-update.sh

#!/bin/bash

# The gatway to send the natpmp commands
natpmp_ip="10.2.0.1"

# Path to the lock file
lock_file="/tmp/transmission_update.lock"

# Path to the Transmission settings.json file
settings_file="/etc/transmission-daemon/settings.json"

# How long to wait for an retry to open the ports
retry_wait_time=5

# Global variables to store the opened ports
new_tcp_port=""
new_udp_port=""

get_date_time() {
    date +'%d.%m.%Y %H:%M'
}

extract_port() {
    local output="$1"
    # Use grep with a regex to extract the port number
    echo "$output" | grep -oE 'Mapped public port [0-9]+' | awk '{print $4}'
}

check_transmission_peer_port() {
    local peer_port=$(jq -r '.["peer-port"]' "$settings_file")
    if [[ -z "$peer_port" ]]; then
        echo "Error: Unable to retrieve peer-port from settings.json."
        return 1
    else
        if [[ $peer_port -eq $1 ]]; then
            return 0
        else
            return 1
        fi
    fi
}

update_transmission_peer_port() {
    /usr/sbin/service transmission-daemon stop
    echo "$(get_date_time): tranmission-daemon stopped"
    local new_port=$1
    sed -i "s/\"peer-port\": [0-9]\+,\?/\"peer-port\": $new_port,/" "$settings_file"
    /usr/sbin/service transmission-daemon start
    echo "$(get_date_time): transmission-daemon started"
}


open_ports() {
    while true; do
        # Execute the main functionality
        output_tcp=$(natpmpc -a 1 0 tcp 60 -g "$natpmp_ip")
        output_udp=$(natpmpc -a 1 0 udp 60 -g "$natpmp_ip")

        # Extract the newly opened ports for TCP and UDP
        new_tcp_port=$(extract_port "$output_tcp")
        new_udp_port=$(extract_port "$output_udp")


        # Check if UDP port opening failed
        if [[ $output_udp == *"protocol UNKNOWN"* ]]; then
            echo "$(get_date_time): Failed to open UDP port. Protocol set to UNKNOWN. Retrying in $retry_wait_time seconds..."
            sleep $retry_wait_time
            continue
        fi

        # Check if TCP port opening failed
        if [[ $output_tcp == *"protocol UNKNOWN"* ]]; then
            echo "$(get_date_time): Failed to open TCP port. Protocol set to UNKNOWN. Retrying in $retry_wait_time seconds..."
            sleep $retry_wait_time
            continue
        fi


	# Check if both TCP and UDP ports are successfully opened
        if [[ -n $new_tcp_port && -n $new_udp_port ]]; then
            # Log the newly opened TCP and UDP ports along with the current date and time
            echo "$(get_date_time): Newly opened TCP port: $new_tcp_port"
            echo "$(get_date_time): Newly opened UDP port: $new_udp_port"
            return 0  # Ports successfully opened, exit loop with success status
        else
            echo "$(get_date_time): Failed to open both TCP and UDP ports."
            #sleep $retry_wait_time
	    return 1
        fi

    done
}

remove_lock_file() {
    rm -f "$lock_file"
}


####################################################################################################
# Main												   #
####################################################################################################


# Trap any signals or errors and remove the lock file before exiting
trap 'remove_lock_file' EXIT
# Check if the lock file exists
if [ -e "$lock_file" ]; then
    echo "$(get_date_time): Script is already running. Exiting."
    exit 1
fi
touch "$lock_file"


# Check if the settings_file exists
if [ ! -e "$settings_file" ]; then
    echo "$(get_date_time): ERROR - Transmission settings file '$settings_file' not found. Exiting."
    exit 1
fi


# start opening the ports
if open_ports; then
	# check tranmission port and update if needed
	if check_transmission_peer_port "$new_tcp_port"; then
	    echo "$(get_date_time): Transmission Daemon's peer_port matches the newly opened TCP port."
	else
	    echo "$(get_date_time): Transmission Daemon's peer_port does not match the newly opened TCP port. Updating settings.json..."
	    update_transmission_peer_port "$new_tcp_port"
	    echo "$(get_date_time): peer-port in settings.json updated to $new_tcp_port."
	fi
	exit 0
else
	echo "$(get_date_time): Exit script"
	exit 1
fi