Launch with `flock -n /var/run/torrent_vpn_control.pid /root/torrent_vpn_control.sh` out of crontab every minute

torrent_vpn_control.sh

#!/bin/ash

last_vpn_up=-1
count=0

while :; do
  ip route list | grep -q "default via .* dev tun0"
  vpn_up=$?
  count=$(($count+1))

  if [[ $last_vpn_up -ne $vpn_up ]] || [[ $count -ge 60 ]]; then
    if [[ $vpn_up -eq 0 ]]; then
      echo "VPN just connected, resuming torrents..."
      while :; do
        paused_jobs=`/root/node_modules/syno/bin/syno.js dl listTasks | jq '[.tasks[]|select(.status=="paused").id]'`
        if [[ "$paused_jobs" == "[]" ]]; then
          break
        fi
        /root/node_modules/syno/bin/syno.js dl resumeTasks --payload "{\"id\": $paused_jobs}"
        sleep 1
      done
    else
      echo "VPN just disconnected, pausing torrents..."
      while :; do
        unpaused_jobs=`/root/node_modules/syno/bin/syno.js dl listTasks | jq '[.tasks[]|select(.status!="paused").id]'`
        if [[ "$unpaused_jobs" == "[]" ]]; then
          break
        fi
        /root/node_modules/syno/bin/syno.js dl pauseTasks --payload "{\"id\": $unpaused_jobs}"
        sleep 1
      done
    fi
    count=0
  fi

  last_vpn_up=$vpn_up
  sleep 1
done