#!/bin/bash
# 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

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

    # DHCPv4
    if [ -n "$new_domain_search" ] || [ -n "$new_domain_name" ] ||
       [ -n "$new_domain_name_servers" ]; then
        new_resolv_conf=/etc/resolv.conf.dhclient-new
        rm -f $new_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
                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
            sed -n /^\w*[Nn][Aa][Mm][Ee][Ss][Ee][Rr][Vv][Ee][Rr]/p /etc/resolv.conf >>$new_resolv_conf
        fi

	if [ -f /etc/resolv.conf ]; then
	    chown --reference=/etc/resolv.conf $new_resolv_conf
	    chmod --reference=/etc/resolv.conf $new_resolv_conf
	fi
        mv -f $new_resolv_conf /etc/resolv.conf
    # DHCPv6
    elif [ -n "$new_dhcp6_domain_search" ] || [ -n "$new_dhcp6_name_servers" ]; then
        new_resolv_conf=/etc/resolv.conf.dhclient-new
        rm -f $new_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
            sed -n /^\w*[Nn][Aa][Mm][Ee][Ss][Ee][Rr][Vv][Ee][Rr]/p /etc/resolv.conf >>$new_resolv_conf
        fi

	if [ -f /etc/resolv.conf ]; then
            chown --reference=/etc/resolv.conf $new_resolv_conf
            chmod --reference=/etc/resolv.conf $new_resolv_conf
	fi
        mv -f $new_resolv_conf /etc/resolv.conf
    fi
}

# set host name
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 "$current_hostname" ] ||
           [ "$current_hostname" = '(none)' ] ||
           [ "$current_hostname" = 'localhost' ] ||
           [ "$current_hostname" = "$old_host_name" ]; then
           if [ "$new_host_name" != "$old_host_name" ]; then
               hostname "$new_host_name"
           fi
        fi
    fi
}

# run given script
run_hook() {
    local script
    local exit_status
    script="$1"

    if [ -f $script ]; then
        . $script
    fi

    if [ -n "$exit_status" ] && [ "$exit_status" -ne 0 ]; then
        logger -p daemon.err "$script returned non-zero exit status $exit_status"
    fi

    return $exit_status
}

# run scripts in given directory
run_hookdir() {
    local dir
    local exit_status
    dir="$1"

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

    return $exit_status
}

# Must be used on exit.   Invokes the local dhcp client exit hooks, if any.
exit_with_hooks() {
    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
}

# This function was largely borrowed from dhclient-script that
# ships with Centos, authored by Jiri Popelka and David Cantrell
# of Redhat. Thanks guys.
add_ipv6_addr_with_DAD() {
    ${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=$(${ip} -6 addr show dev ${interface} \
            | grep ${new_ip6_address}/${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
            ${ip} -6 addr del ${new_ip6_address}/${new_ip6_prefixlen} \
                dev ${interface}

            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
}

# 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
        ${ip} link set dev ${interface} up

        if [ -n "$alias_ip_address" ]; then
            # flush alias IP from interface
            ${ip} -4 addr flush dev ${interface} label ${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
            ${ip} -4 addr flush dev ${interface} label ${interface}:0
        fi

        if [ -n "$old_ip_address" ] &&
           [ "$old_ip_address" != "$new_ip_address" ]; then
            # leased IP has changed => flush it
            ${ip} -4 addr flush dev ${interface} label ${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
            ${ip} -4 addr add ${new_ip_address}${new_subnet_mask:+/$new_subnet_mask} \
                ${new_broadcast_address:+broadcast $new_broadcast_address} \
                dev ${interface} label ${interface}

            if [ -n "$new_interface_mtu" ]; then
                # set MTU
                ${ip} link set dev ${interface} mtu ${new_interface_mtu}
            fi

	    # if we have $new_rfc3442_classless_static_routes then we have to
	    # ignore $new_routers entirely
	    if [ ! "$new_rfc3442_classless_static_routes" ]; then
		    # set if_metric if IF_METRIC is set or there's more than one router
		    if_metric="$IF_METRIC"
		    if [ "${new_routers%% *}" != "${new_routers}" ]; then
			if_metric=${if_metric:-1}
		    fi

		    for router in $new_routers; do
			if [ "$new_subnet_mask" = "255.255.255.255" ]; then
			    # point-to-point connection => set explicit route
			    ${ip} -4 route add ${router} dev $interface >/dev/null 2>&1
			fi

			# set default route
			${ip} -4 route add default via ${router} dev ${interface} \
			    ${if_metric:+metric $if_metric} >/dev/null 2>&1

			if [ -n "$if_metric" ]; then
			    if_metric=$((if_metric+1))
			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
            ${ip} -4 addr flush dev ${interface} label ${interface}:0
            ${ip} -4 addr add ${alias_ip_address}${alias_subnet_mask:+/$alias_subnet_mask} \
                dev ${interface} label ${interface}:0
            ${ip} -4 route add ${alias_ip_address} dev ${interface} >/dev/null 2>&1
        fi

        # update /etc/resolv.conf
        make_resolv_conf

        ;;

    EXPIRE|FAIL|RELEASE|STOP)
        if [ -n "$alias_ip_address" ]; then
            # flush alias IP
            ${ip} -4 addr flush dev ${interface} label ${interface}:0
        fi

        if [ -n "$old_ip_address" ]; then
            # flush leased IP
            ${ip} -4 addr flush dev ${interface} label ${interface}
        fi

        if [ -n "$alias_ip_address" ]; then
            # alias IP given => set it & add host route to it
            ${ip} -4 addr add ${alias_ip_address}${alias_subnet_mask:+/$alias_subnet_mask} \
                dev ${interface} label ${interface}:0
            ${ip} -4 route add ${alias_ip_address} dev ${interface} >/dev/null 2>&1
        fi

        ;;

    TIMEOUT)
        if [ -n "$alias_ip_address" ]; then
            # flush alias IP
            ${ip} -4 addr flush dev ${interface} label ${interface}:0
        fi

        # set IP from recorded lease
        ${ip} -4 addr add ${new_ip_address}${new_subnet_mask:+/$new_subnet_mask} \
            ${new_broadcast_address:+broadcast $new_broadcast_address} \
            dev ${interface} label ${interface}

        if [ -n "$new_interface_mtu" ]; then
            # set MTU
            ${ip} link set dev ${interface} mtu ${new_interface_mtu}
        fi

        # 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 $new_routers entirely
	    if [ ! "$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
			${ip} -4 addr add \
                              ${alias_ip_address}${alias_subnet_mask:+/$alias_subnet_mask} \
			      dev ${interface} label ${interface}:0
			${ip} -4 route add ${alias_ip_address} dev ${interface} >/dev/null 2>&1
		    fi

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

		    # set default route
		    for router in $new_routers; do
			${ip} -4 route add default via ${router} dev ${interface} \
			    ${if_metric:+metric $if_metric} >/dev/null 2>&1

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

            # update /etc/resolv.conf
            make_resolv_conf
        else
            # flush all IPs from interface
            ip -4 addr flush dev ${interface}
            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
        ${ip} link set ${interface} up

        # We need to give the kernel some time to active interface
        interface_up_wait_time=5
        for i in $(seq 0 ${interface_up_wait_time})
        do
            ifconfig ${interface} | grep RUNNING >/dev/null 2>&1
            if [ $? -eq 0 ]; then
                break;
            fi
            sleep 1
        done

        # flush any stale global permanent IPs from interface
        ${ip} -6 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.
            ${ip} addr show ${interface} | grep inet6 | grep tentative \
                &> /dev/null
            if [ $? -eq 0 ]; then
                # Wait for duplicate address detection to complete or for
                # the timeout specified as --dad-wait-time.
                for i in $(seq 0 $dad_wait_time)
                do
                    # We're going to poll for the tentative flag every second.
                    sleep 1
                    ${ip} addr show ${interface} | grep inet6 | grep tentative \
                        &> /dev/null
                    if [ $? -ne 0 ]; then
                        break;
                    fi
                done
            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
        ${ip} -6 addr del ${old_ip6_address}/${old_ip6_prefixlen} \
            dev ${interface}

        ;;
esac

exit_with_hooks 0