#!/bin/sh
# This is a NetworkManager dispatcher script for chronyd to update
# its NTP sources with servers from DHCP options passed by NetworkManager
# in the DHCP4_NTP_SERVERS and DHCP6_DHCP6_NTP_SERVERS environment variables.

export LC_ALL=C

interface=$1
action=$2

chronyc=/usr/bin/chronyc
server_options=iburst
server_dir=/run/chrony-dhcp

dhcp_server_file=$server_dir/$interface.sources
dhcp_ntp_servers="$DHCP4_NTP_SERVERS $DHCP6_DHCP6_NTP_SERVERS"

add_servers_from_dhcp() {
    rm -f "$dhcp_server_file"
    for server in $dhcp_ntp_servers; do
        # Check for invalid characters (from the DHCPv6 NTP FQDN suboption)
        len1=$(printf '%s' "$server" | wc -c)
        len2=$(printf '%s' "$server" | tr -d -c 'A-Za-z0-9:.-' | wc -c)
        if [ "$len1" -ne "$len2" ] || [ "$len2" -lt 1 ] || [ "$len2" -gt 255 ]; then
          continue
        fi

        printf 'server %s %s\n' "$server" "$server_options" >> "$dhcp_server_file"
    done
    $chronyc reload sources > /dev/null 2>&1 || :
}

clear_servers_from_dhcp() {
    if [ -f "$dhcp_server_file" ]; then
        rm -f "$dhcp_server_file"
        $chronyc reload sources > /dev/null 2>&1 || :
    fi
}

mkdir -p $server_dir

case "$action" in
    up|dhcp4-change|dhcp6-change)
        add_servers_from_dhcp;;
    down)
        clear_servers_from_dhcp;;
esac

exit 0