allow-ip

#!/bin/bash

# SPDX-FileCopyrightText: 2019 - 2024 sudorook <daemon@nullcodon.com>
#
# SPDX-License-Identifier: GPL-3.0-or-later
#
# This program is free software: you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the Free
# Software Foundation, either version 3 of the License, or (at your option)
# any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
# or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
# for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program. If not, see <https://www.gnu.org/licenses/>.

set -euo pipefail

ROOT="$(dirname "${0}")"

source "${ROOT}"/globals

! check_command grep ip sed && exit 3

# Command line script to add a routing table entry for an IP address. Useful
# for accessing network printers when behind a VPN that interferes with access
# to local machines addressed by a local/internal DNS.

function print_usage {
  show_header "Usage: allow-ip -i|--ip <ip address> -m|--mask <bitmask>"
}

OPTIONS=hi:m:
LONGOPTIONS=help,ip:,mask:
PARSED=$(getopt -o "${OPTIONS}" --long "${LONGOPTIONS}" -n "${0}" -- "${@}")
eval set -- "${PARSED}"

while [ ${#} -ge 1 ]; do
  case "${1}" in
    -i | --ip)
      # If IP address given as xxx.xxx.xxx.xxx:
      if [[ "${2}" == "$(echo "${2}" |
                         sed -n "s/^\([0-9]\+\.[0-9]\+\.[0-9]\+\.[0-9]\+\)$/\1/p")" ]]; then
        IP="${2}"
      # If IP address and netmask given as xxx.xxx.xxx.xxx/xx:
      elif [[ "${2}" == "$(echo "${2}" |
                           sed -n "s/^\([0-9]\+\.[0-9]\+\.[0-9]\+\.[0-9]\+\/[0-9]\+\)$/\1/p")" ]]; then
        IP="$(echo "${2}" | cut -d"/" -f1)"
        MASK="$(echo "${2}" | cut -d"/" -f2)"
      fi
      shift 2
      ;;
    -m | --mask)
      if ((${2} >= 0 && ${2} <= 32)); then
        MASK="${2}"
      fi
      shift 2
      ;;
    -h | --help)
      print_usage
      exit
      ;;
    --)
      shift
      break
      ;;
    *)
      show_error "What was that?"
      exit 3
      ;;
  esac
done

# Exit if no ip address supplied.
if ! [[ -v IP ]]; then
  show_error "Give me the IP address."
  exit 3
fi

# If the net mask is not specified, only allow the IP address given.
MASK="${MASK:-32}"

GATEWAY=$(ip route list |
          grep -e "enp[0-9]\+s[0-9a-f]\+" -e "wlp[0-9]\+s[0-9a-f]\+" |
          sed -n "s/^default via \([0-9\.]\+\) dev .*/\1/p" | head -1)

IFACE=$(ip route show |
        grep -e "${GATEWAY}" |
        sed -n "s/^default via [0-9\.]\+ dev \([a-z0-9]\+\) .*/\1/p")

sudo ip route add "${IP}/${MASK}" via "${GATEWAY}" dev "${IFACE}"