#!/bin/sh
# dhclient-script for Linux. Dan Halbert, March, 1997.
# Updated for Linux 2.[12] by Brian J. Murrell, January 1999.
# No guarantees about this. I'm a novice at the details of Linux
# networking.

# Notes:

# 0. This script is based on the netbsd script supplied with dhcp-970306.

# 1. ifconfig down apparently deletes all relevant routes and flushes
# the arp cache, so this doesn't need to be done explicitly.

# 2. The alias address handling here has not been tested AT ALL.
# I'm just going by the doc of modern Linux ip aliasing, which uses
# notations like eth0:0, eth0:1, for each alias.

# 3. I have to calculate the network address, and calculate the broadcast
# address if it is not supplied. This might be much more easily done
# by the dhclient C code, and passed on.

# 4. TIMEOUT not tested. ping has a flag I don't know, and I'm suspicious
# of the $1 in its args.

# 5. Script refresh in 2017. The aliasing code was too convoluted and needs
# to go away. Migrated DHCPv4 script to ip command from iproute2 suite.
# This is based on Debian script with some tweaks. ifconfig is no longer
# used. Everything is done using ip tool from ip-route2.

# 'ip' just looks too weird. Also, we now have unit-tests! Those unit-tests
# overwirte this line to use a fake ip-echo tool. It's also convenient
# if your system holds ip tool in a non-standard location.
ip='/sbin/ip'

# This is a dummy function to prevent shellcheck from complaining about these
# variables later in this script. It is not used during normal operation and
# should not slow down the execution of this script at all.
# If, given the above, it still bothers you, please feel free to delete it.
# SC2154: These specific variables are assigned external to this script.
# shellcheck disable=SC2154
_shellcheck_external_variables() {
    : alias_ip_address="$alias_ip_address"
    : alias_subnet_mask="$alias_subnet_mask"
    : cur_ip6_address="$cur_ip6_address"
    : cur_ip6_prefixlen="$cur_ip6_prefixlen"
    : dad_wait_time="$dad_wait_time"
    : interface="$interface"
    : new_broadcast_address="$new_broadcast_address"
    : new_dhcp6_domain_search="$new_dhcp6_domain_search"
    : new_dhcp6_name_servers="$new_dhcp6_name_servers"
    : new_domain_name="$new_domain_name"
    : new_domain_name_servers="$new_domain_name_servers"
    : new_host_name="$new_host_name"
    : new_interface_mtu="$new_interface_mtu"
    : new_ip6_address="$new_ip6_address"
    : new_ip6_prefixlen="$new_ip6_prefixlen"
    : new_ip_address="$new_ip_address"
    : new_max_life="$new_max_life"
    : new_preferred_life="$new_preferred_life"
    : new_rfc3442_classless_static_routes="$new_rfc3442_classless_static_routes"
    : new_routers="$new_routers"
    : new_subnet_mask="$new_subnet_mask"
    : old_dhcp6_domain_search="$old_dhcp6_domain_search"
    : old_dhcp6_name_servers="$old_dhcp6_name_servers"
    : old_host_name="$old_host_name"
    : old_ip6_address="$old_ip6_address"
    : old_ip6_prefixlen="$old_ip6_prefixlen"
    : old_ip_address="$old_ip_address"
    : reason="$reason"
}

print_nameservers() {
    sed -n '/^[[:space:]]*[Nn][Aa][Mm][Ee][Ss][Ee][Rr][Vv][Ee][Rr]/p' "${@}"
}

# shellcheck disable=SC2039
init_resolv_conf() {
    local tmpfile
    tmpfile="$(mktemp -q /etc/resolv.conf.dhclient-new.XXXXXXXXXX)"
    if [ -z "${tmpfile}" ]; then
        tmpfile='/etc/resolv.conf.dhclient-new'
        rm -rf "${tmpfile}"
    fi
    : >>"${tmpfile}"
    # shellcheck disable=SC2064
    trap "rm -f ${tmpfile}" EXIT
    echo "${tmpfile}"
}

# shellcheck disable=SC2039
replace_resolv_conf() {
    local src="${1}"
    local dst='/etc/resolv.conf'

    if [ -f "${dst}" ]; then
        chown --reference="${dst}" "${src}"
        chmod --reference="${dst}" "${src}"
    fi
    mv -f "${src}" "${dst}"
}

# update /etc/resolv.conf based on received values
# This updated version mostly follows Debian script by Andrew Pollock et al.
# shellcheck disable=SC2039
make_resolv_conf() {
    local nameserver
    local new_resolv_conf

    # DHCPv4
    if [ -n "${new_domain_search}" ] ||
       [ -n "${new_domain_name}" ] ||
       [ -n "${new_domain_name_servers}" ]
    then
        new_resolv_conf="$(init_resolv_conf)"

        if [ -n "${new_domain_name}" ]; then
            echo "domain ${new_domain_name%% *}" >>"${new_resolv_conf}"
        fi

        if [ -n "${new_domain_search}" ]; then
            if [ -n "${new_domain_name}" ]; then
                local domain domain_in_search_list=''
                for domain in ${new_domain_search}; do
                    if [ "${domain}" = "${new_domain_name}" ] ||
                       [ "${domain}" = "${new_domain_name}." ]
                    then
                        domain_in_search_list='Yes'
                    fi
                done
                if [ -z "${domain_in_search_list}" ]; then
                    new_domain_search="${new_domain_name} ${new_domain_search}"
                fi
            fi
            echo "search ${new_domain_search}" >>"${new_resolv_conf}"
        elif [ -n "${new_domain_name}" ]; then
            echo "search ${new_domain_name}" >>"${new_resolv_conf}"
        fi

        if [ -n "${new_domain_name_servers}" ]; then
            for nameserver in ${new_domain_name_servers}; do
                echo "nameserver ${nameserver}" >>"${new_resolv_conf}"
            done
        else # keep 'old' nameservers
            print_nameservers /etc/resolv.conf >>"${new_resolv_conf}"
        fi

        replace_resolv_conf "${new_resolv_conf}"
    # DHCPv6
    elif [ -n "${new_dhcp6_domain_search}" ] ||
         [ -n "${new_dhcp6_name_servers}" ]
    then
        new_resolv_conf="$(init_resolv_conf)"

        if [ -n "${new_dhcp6_domain_search}" ]; then
            echo "search ${new_dhcp6_domain_search}" >>"${new_resolv_conf}"
        fi

        if [ -n "${new_dhcp6_name_servers}" ]; then
            for nameserver in ${new_dhcp6_name_servers}; do
                # append %interface to link-local-address nameservers
                if [ "${nameserver##fe80::}" != "${nameserver}" ] ||
                   [ "${nameserver##FE80::}" != "${nameserver}" ]
                then
                    nameserver="${nameserver}%${interface}"
                fi
                echo "nameserver ${nameserver}" >>"${new_resolv_conf}"
            done
        else # keep 'old' nameservers
            print_nameservers /etc/resolv.conf >>"${new_resolv_conf}"
        fi

        replace_resolv_conf "${new_resolv_conf}"
    fi
}

# set host name
# SC2039: our shell has local for function scope
# shellcheck disable=SC2039
set_hostname() {
    local current_hostname

    if [ -n "${new_host_name}" ]; then
        current_hostname="$(hostname)"

        # current host name is empty, '(none)' or 'localhost' or
        # differs from new one from DHCP
        if [ -z "${current_hostname}" ] ||
           [ '(none)' = "${current_hostname}" ] ||
           [ 'localhost' = "${current_hostname}" ] ||
           [ "${old_host_name}" = "${current_hostname}" ]
        then
           if [ "${new_host_name}" != "${old_host_name}" ]; then
               hostname "${new_host_name}"
           fi
        fi
    fi
}

# run given script
# shellcheck disable=SC2039,SC1090
run_hook() {
    local script
    local exit_status
    script="${1}"

    if [ -f "${script}" ]; then
        . "${script}"
    fi

    if [ -n "${exit_status}" ] && [ 0 != "${exit_status}" ]; then
        logger -t dhclient-script -p daemon.err \
            "run_hook: ${script} returned non-zero exit status (${exit_status})"
        [ "${exit_status}" -lt 256 ] 2>/dev/null || exit_status=255
        [ "${exit_status}" -gt 0 ] 2>/dev/null || exit_status=1
    fi

    return "${exit_status:-${?}}"
}

# run scripts in given directory
# shellcheck disable=SC2039
run_hookdir() {
    local dir
    local script
    local exit_status
    dir="${1}"

    if [ -d "${dir}" ]; then
        for script in $(run-parts --list "${dir}"); do
            if ! run_hook "${script}"; then
                exit_status="${?}"
            fi
        done
    fi

    return "${exit_status:-${?}}"
}

# Must be used on exit.   Invokes the local dhcp client exit hooks, if any.
# shellcheck disable=SC2039
exit_with_hooks() {
    local exit_status
    exit_status="${1}"

    # Source the documented exit-hook script, if it exists
    if ! run_hook /etc/dhclient-exit-hooks; then
        exit_status="${?}"
    fi

    # Now run scripts in the Debian-specific directory.
    if ! run_hookdir /etc/dhclient-exit-hooks.d; then
        exit_status="${?}"
    fi

    exit "${exit_status}"
}

ipv6_addr_del() {
    "${ip}" -6 addr del "$@" dev "${interface}"
}

# shellcheck disable=SC2039
ipv6_addr_show() {
    local dev
    dev="${1}"

    "${ip}" -6 addr show ${dev:+dev "${dev}"}
}

# shellcheck disable=SC2039
ipv6_addr_filter() {
    local dev
    dev="${1}"
    shift

    ipv6_addr_show "${dev}" | grep -F -e "${*}"
}

# shellcheck disable=SC2039
ipv6_addr_has_tentative() {
    local dev
    dev="${1}"
    shift

    ipv6_addr_filter "${dev}" "${@}" | grep -F -e tentative >/dev/null 2>&1
}

ip_link_set() {
    "${ip}" link set "${@}"
}

link_set_up() {
    ip_link_set dev "${interface}" up
}

link_set_mtu() {
    [ -n "${1}" ] || return 0

    ip_link_set dev "${interface}" mtu "${1}"
}

# shellcheck disable=SC2039
_ip_addr_flush() {
    local af
    af="${1}"
    shift

    case "${af}" in
        (4|6)
            ;;
        (*)
            return 1
            ;;
    esac

    "${ip}" "-${af}" addr flush "${@}"
}

#ip_addr_flush() {
#    "${ip}" addr flush "${@}"
#}

ipv4_addr_flush() {
    _ip_addr_flush 4 "$@"
}

ipv6_addr_flush() {
    _ip_addr_flush 6 "$@"
}

# shellcheck disable=SC2039
addr_flush() {
    local label
    label="${1}"

    if [ -n "${label}" ]; then
        ipv4_addr_flush dev "${interface}" label "${label}"
    else
        ipv4_addr_flush dev "${interface}"
    fi
}

ipv4_route_add() {
    "${ip}" -4 route add "${@}"
}

route_add() {
    ipv4_route_add "$@" dev "${interface}" >/dev/null 2>&1
}

# shellcheck disable=SC2039
route_add_default() {
    local via
    local metric
    via="${1}"
    metric="${2}"

    ipv4_route_add default via "${via}" \
        dev "${interface}" \
        ${metric:+metric "${metric}"} \
        >/dev/null 2>&1
}

# shellcheck disable=SC2039
addr_add() {
    local label
    local addr
    local mask
    local broadcast
    label="${1}"
    addr="${2}"
    mask="${3}"
    broadcast="${4}"

    "${ip}" -4 addr add \
        "${addr}${mask:+/${mask}}" \
        ${broadcast:+broadcast "${broadcast}"} \
        dev "${label%%:*}" label "${label}"
}

# This function was largely borrowed from dhclient-script that
# ships with Centos, authored by Jiri Popelka and David Cantrell
# of Redhat. Thanks guys.
# shellcheck disable=SC2039
add_ipv6_addr_with_DAD() {
    local _i
    "${ip}" -6 addr replace "${new_ip6_address}/${new_ip6_prefixlen}" \
        dev "${interface}" scope global valid_lft "${new_max_life}" \
        preferred_lft "${new_preferred_life}"

    if [ "${dad_wait_time}" -le 0 ]; then
        # if we're not waiting for DAD, assume we're good
        return 0
    fi

    # Repeatedly test whether newly added address passed
    # duplicate address detection (DAD)
    for _i in $(seq 1 "${dad_wait_time}"); do
        sleep 1 # give the DAD some time

        addr="$(ipv6_addr_filter "${interface}" \
            "${new_ip6_address}/${new_ip6_prefixlen}")"

        # tentative flag == DAD is still not complete
        tentative="$(echo "${addr}" | grep tentative)"
        # dadfailed flag == address is already in use somewhere else
        dadfailed="$(echo "${addr}" | grep dadfailed)"

        if [ -n "${dadfailed}" ]; then
            # address was added with valid_lft/preferred_lft 'forever',
            # remove it
            ipv6_addr_del "${new_ip6_address}/${new_ip6_prefixlen}"

            exit_with_hooks 3
        fi

        if [ -z "${tentative}" ]; then
            if [ -n "${addr}" ]; then
                # DAD is over
                return 0
            else
                # address was auto-removed (or not added at all)
                exit_with_hooks 3
            fi
        fi
    done

    return 0
}

# shellcheck disable=SC2039
init_if_metric() {
    local _if_metric

    # set if_metric if IF_METRIC is set or there's more than one router
    # shellcheck disable=SC2153
    _if_metric="${IF_METRIC}"
    if [ "${new_routers%% *}" != "${new_routers}" ]; then
        _if_metric="${_if_metric:-1}"
    fi

    if_metric="${_if_metric}"
    echo "${_if_metric}"
}

# Invoke the local dhcp client enter hooks, if they exist.
run_hook /etc/dhclient-enter-hooks
run_hookdir /etc/dhclient-enter-hooks.d

# Execute the operation
case "${reason}" in

    ### DHCPv4 Handlers

    MEDIUM|ARPCHECK|ARPSEND)
        # Do nothing
        ;;
    PREINIT)
        # The DHCP client is requesting that an interface be
        # configured as required in order to send packets prior to
        # receiving an actual address. - dhclient-script(8)

        # ensure interface is up
        link_set_up

        if [ -n "${alias_ip_address}" ]; then
            # flush alias IP from interface
            addr_flush "${interface}:0"
        fi

        ;;

    BOUND|RENEW|REBIND|REBOOT)
        set_hostname

        if [ -n "${old_ip_address}" ] && [ -n "${alias_ip_address}" ] &&
           [ "${alias_ip_address}" != "${old_ip_address}" ]; then
            # alias IP may have changed => flush it
            addr_flush "${interface}:0"
        fi

        if [ -n "${old_ip_address}" ] &&
           [ "${old_ip_address}" != "${new_ip_address}" ]; then
            # leased IP has changed => flush it
            addr_flush "${interface}"
        fi

        if [ -z "${old_ip_address}" ] ||
           [ "${old_ip_address}" != "${new_ip_address}" ] ||
           [ "${reason}" = "BOUND" ] || [ "${reason}" = "REBOOT" ]; then
            # new IP has been leased or leased IP changed => set it
            addr_add "${interface}" \
                "${new_ip_address}" "${new_subnet_mask}" \
                "${new_broadcast_address}"

            link_set_mtu "${new_interface_mtu}"

            # if we have $new_rfc3442_classless_static_routes then we have to
            # ignore $new_routers entirely
            if [ -z "${new_rfc3442_classless_static_routes}" ]; then
                    if_metric="$(init_if_metric)"
                    for router in ${new_routers}; do
                        if [ "255.255.255.255" = "${new_subnet_mask}" ]; then
                            # point-to-point connection => set explicit route
                            route_add "${router}"
                        fi

                        # set default route
                        route_add_default "${router}" "${if_metric}"

                        if [ -n "${if_metric}" ]; then
                            if_metric="$((1+if_metric))"
                        fi
                    done
            fi
        fi

        if [ -n "${alias_ip_address}" ] &&
           [ "${new_ip_address}" != "${alias_ip_address}" ]
        then
            # separate alias IP given, which may have changed
            # => flush it, set it & add host route to it
            addr_flush "${interface}:0"
            addr_add "${interface}:0" \
                "${alias_ip_address}" "${alias_subnet_mask}"
            route_add "${alias_ip_address}"
        fi

        # update /etc/resolv.conf
        make_resolv_conf

        ;;

    EXPIRE|FAIL|RELEASE|STOP)
        if [ -n "${alias_ip_address}" ]; then
            # flush alias IP
            addr_flush "${interface}:0"
        fi

        if [ -n "${old_ip_address}" ]; then
            # flush leased IP
            addr_flush "${interface}"
        fi

        if [ -n "${alias_ip_address}" ]; then
            # alias IP given => set it & add host route to it
            addr_add "${interface}:0" \
                "${alias_ip_address}" "${alias_subnet_mask}"
            route_add "${alias_ip_address}"
        fi

        ;;

    TIMEOUT)
        if [ -n "${alias_ip_address}" ]; then
            # flush alias IP
            addr_flush "${interface}:0"
        fi

        # set IP from recorded lease
        addr_add "${interface}" \
            "${new_ip_address}" "${new_subnet_mask}" \
            "${new_broadcast_address}"

        link_set_mtu "${new_interface_mtu}"

        # if there is no router recorded in the lease
        # or the 1st router answers pings
        if [ -z "${new_routers}" ] || ping -q -c 1 "${new_routers%% *}"; then
            # if we have $new_rfc3442_classless_static_routes then we have to
            # ignore $new_routers entirely
            if [ -z "${new_rfc3442_classless_static_routes}" ]; then
                if [ -n "${alias_ip_address}" ] &&
                   [ "${new_ip_address}" != "${alias_ip_address}" ]
                then
                    # separate alias IP given => set up the alias IP & add host route to it
                    addr_add "${interface}:0" \
                        "${alias_ip_address}" "${alias_subnet_mask}"
                    route_add "${alias_ip_address}"
                fi

                if_metric="$(init_if_metric)"
                for router in ${new_routers}; do
                    # set default route
                    route_add_default "${router}" "${if_metric}"

                    if [ -n "${if_metric}" ]; then
                        if_metric="$((1+if_metric))"
                    fi
                done
            fi

            # update /etc/resolv.conf
            make_resolv_conf
        else
            # flush all IPs from interface
            addr_flush
            exit_with_hooks 2
        fi

        ;;

    ### DHCPv6 Handlers
    # TODO handle prefix change: ?based on ${old_ip6_prefix} and ${new_ip6_prefix}?

    PREINIT6)
        # ensure interface is up
        link_set_up

        # We need to give the kernel some time to active interface
        interface_up_wait_time=5
        # shellcheck disable=SC2034
        for _i in $(seq 0 ${interface_up_wait_time}); do
            if ifconfig "${interface}" | grep RUNNING >/dev/null 2>&1; then
                break
            fi
            sleep 1
        done; unset -v _i

        # flush any stale global permanent IPs from interface
        ipv6_addr_flush dev "${interface}" scope global permanent

        # Wait for duplicate address detection for this interface if the
        # --dad-wait-time parameter has been specified and is greater than
        # zero.
        if [ "${dad_wait_time}" -gt 0 ]; then
            # Check if any IPv6 address on this interface is marked as
            # tentative.
            if ipv6_addr_has_tentative "${interface}" inet6; then
                # Wait for duplicate address detection to complete or for
                # the timeout specified as --dad-wait-time.
                # shellcheck disable=SC2034
                for _i in $(seq 0 "${dad_wait_time}"); do
                    # We're going to poll for the tentative flag every second.
                    sleep 1
                    if ! ipv6_addr_has_tentative "${interface}" inet6; then
                        break
                    fi
                done; unset -v _i
            fi
        fi

        ;;

    BOUND6|RENEW6|REBIND6)
        if [ "${new_ip6_address}" ] && [ "${new_ip6_prefixlen}" ]; then
            # set leased IP
            add_ipv6_addr_with_DAD
        fi

        # update /etc/resolv.conf
        if [ "${reason}" = BOUND6 ] ||
           [ "${new_dhcp6_name_servers}" != "${old_dhcp6_name_servers}" ] ||
           [ "${new_dhcp6_domain_search}" != "${old_dhcp6_domain_search}" ]; then
            make_resolv_conf
        fi

        ;;

    DEPREF6)
        if [ -z "${cur_ip6_prefixlen}" ]; then
            exit_with_hooks 2
        fi

        # set preferred lifetime of leased IP to 0
        "${ip}" -6 addr change "${cur_ip6_address}/${cur_ip6_prefixlen}" \
            dev "${interface}" scope global preferred_lft 0

        ;;

    EXPIRE6|RELEASE6|STOP6)
        if [ -z "${old_ip6_address}" ] || [ -z "${old_ip6_prefixlen}" ]; then
            exit_with_hooks 2
        fi

        # delete leased IP
        ipv6_addr_del "${old_ip6_address}/${old_ip6_prefixlen}"

        ;;
esac

exit_with_hooks 0