hotspot_ynh/conf/openvpn_90-hotspot

#!/bin/bash

source /usr/share/yunohost/helpers

is_nat_set() {
  local gateway_interface=${1}
  iptables -w -nvt nat -L POSTROUTING | grep MASQUERADE | grep -q "${gateway_interface}"
}

unset_nat() {
  local gateway_interface=${1}
  iptables -w -t nat -D POSTROUTING -o "${gateway_interface}" -j MASQUERADE
}

set_nat() {
  local gateway_interface=${1}
  iptables -w -t nat -A POSTROUTING -o "${gateway_interface}" -j MASQUERADE
}

old_gateway_interface=$(ynh_app_setting_get --app=$app --key=gateway_interface)
new_gateway_interface=$(ip route get 1.2.3.4 | awk '{ print $5; }')

if [[ -n "$old_gateway_interface" ]] && [[ "$old_gateway_interface" != "$new_gateway_interface" ]] && is_nat_set "$old_gateway_interface"; then
  unset_nat "${old_gateway_interface}"
fi

set_nat "${new_gateway_interface}"

ynh_app_setting_set --app=$app --key=gateway_interface --value="${new_gateway_interface}"