# Title               : get-static-ipv4-addrs
# Last modified date  : 11.02.2023
# Author              : Martin Tonusoo
# Description         : Finds the permanent IPv4 addresses configured on the
#                       interface and stores those to a variable, which is later
#                       processed by dhclient restore-static-ipv4-addrs exit
#                       hook script.
#                       For example, in case the leased IPv4 address changes or the IPv4
#                       address is released by the client(dhclient -r) or the lease
#                       expires, then dhclient-script called by dhclient flushes all
#                       the IPv4 addresses configured on the interface. This includes
#                       IPv4 addresses defined in /etc/network/interfaces or conf
#                       files in interfaces.d directory. This script finds the non-dynamic
#                       IPv4 addresses configured on the interface and populates the
#                       "perm_addrs" variable. Exit hook "restore-static-ipv4-addrs" adds
#                       those addresses back to interface based on the content of the
#                       "perm_addrs" variable.
# Options             :
# Notes               : Script is meant to be run as a dhclient enter hook.
#                       Script is POSIX sh compliant.
#
#                       Routes and aliases("ALIAS DECLARATIONS" in dhclient.conf man)
#                       are not touched.
#
#                       Dhclient-script called by dhclient binary always adds IPv4 addresses
#                       to non-alias interface with "valid_lft" and "preferred_lft" set
#                       which results with a "dynamic" flag set in the output of "ip addr".
#
#                       This script can't help in case the manually configured address is
#                       from the same network as the address leased by the DHCP server AND
#                       the manually configured address is a secondary one- if the dynamic
#                       primary address expires, then both the dynamic primary and all
#                       the secondary manually configured addresses are removed by the
#                       kernel automatically.

perm_addrs=""

while read -r _ _ _ perm_addr _; do

    # Sanity check.
    case "$perm_addr" in
        *.*.*.*/*)
            perm_addrs="$perm_addrs $perm_addr"
            ;;
        esac

done <<-EOF
	$(ip -oneline -4 addr show dev "$interface" permanent label "$interface" 2>/dev/null)
EOF