#!/bin/sh
# vim: set ts=4 et:

# This script should be installed as symlinks in
#   /etc/udhcpc/<hook>/eth-eni-hook
# <hook> :-
#   post-bound  - after udhcpc binds an IP to the interface
#   post-renew  - after udhcpc renews the lease for the IP
#
# udhcpc provides via ENV...
#   IFACE  - eth0, etc.
#   mask   - bits in IPv4 subnet mask

set -e

HOOK="$(basename "$(dirname "$0")")"

DEBUG=

log() {
    [ -z "$DEBUG" ] && [ "$1" = "debug" ] && return
    FACILITY="daemon.$1"
    shift
    logger -s -p "$FACILITY" -t "udhcpc/${HOOK}[$$]" -- "$@"
}

if [ -z "$IFACE" ] || [ -z "$mask" ]; then
    log err "Missing 'IFACE' or 'mask' ENV from udhcpc"
    exit 1
fi

# route table number
RTABLE="${IFACE#eth}"
let RTABLE+=1000

IMDS=X-aws-ec2-metadata-token
IMDS_IP=169.254.169.254
IMDS_MAC="http://$IMDS_IP/latest/meta-data/network/interfaces/macs/$(
    cat "/sys/class/net/$IFACE/address")"

get_imds_token() {
    IMDS_TOKEN="$(echo -ne \
        "PUT /latest/api/token HTTP/1.0\r\n$IMDS-ttl-seconds: 60\r\n\r\n" |
        nc "$IMDS_IP" 80 | tail -n 1)"
}

mac_meta() {
    wget -qO - --header "$IMDS: $IMDS_TOKEN" "$IMDS_MAC/$1" 2>/dev/null \
        || true  # when no ipv6s attached (yet), IMDS returns 404 error
}

ip() {
    FAIL_OK=
    if [ "$1" = '+F' ]; then
        FAIL_OK=1
        shift
    fi
    v=-4
    if [ "$1" = '-4' ] || [ "$1" = '-6' ]; then
        v="$1"
        shift
    fi
    OP="$2"
    [ "$OP" = show ] && LEV=debug || LEV=info
    if /sbin/ip "$v" "$@" || [ -n "$FAIL_OK" ]; then
        log "$LEV" "OK: ip $v $*"
    else
        log err "FAIL: ip $v $*"
    fi
}

iface_ip4s() {
    ip -4 addr show "$IFACE" secondary |
        sed -E -e '/inet /!d' -e 's/.*inet ([0-9.]+).*/\1/'
}

iface_ip6s() {
    ip -6 addr show "$IFACE" scope global |
        sed -E -e '/inet6/!d' -e 's/.*inet6 ([0-9a-f:]+).*/\1/'
}

ec2_ip4s() {
    get_imds_token
    # NOTE: metadata for ENI arrives later than hotplug events
    TRIES=60
    while true; do
        IP4="$(mac_meta local-ipv4s)"
        [ -n "$IP4" ] && break
        let TRIES--
        if [ "$TRIES" -eq 0 ]; then
            log err "Unable to get IPv4 addresses for $IFACE after 30s"
            exit 1
        fi
        sleep 0.5
    done
    IP4S="$(echo "$IP4" | tail +2)" # secondary IPs (udhcpc handles primary)

    # non-eth0 interfaces need custom route tables
    #
    if [ "$IFACE" != eth0 ] && [ -n "$IP4S" ] &&
            [ -z "$(ip +F -4 route show table "$RTABLE")" ]; then
        IP4P="$(echo "$IP4" | head -1)" # primary IP
        IP4_CIDR="$(mac_meta subnet-ipv4-cidr-block)"
        IP4_GW="$(echo "$IP4_CIDR" | cut -d/ -f1 |
            awk -F. '{ print $1"."$2"."$3"."$4+1 }')"
        ip -4 route add default via "$IP4_GW" dev "$IFACE" table "$RTABLE"
        ip -4 route add "$IP4_CIDR" dev "$IFACE" proto kernel scope link \
            src "$IP4P" table "$RTABLE"
    fi
    echo "$IP4S"
}

ec2_ip6s() {
    get_imds_token
    # NOTE: IPv6 metadata (if any) may arrive later than IPv4 metadata
    TRIES=60
    while true; do
        IP6S="$(mac_meta ipv6s)"
        [ -n "$IP6S" ] && break
        let TRIES--
        if [ "$TRIES" -eq 0 ]; then
            log warn "Unable to get IPv6 addresses for $IFACE after 30s"
            break
        fi
        sleep 0.5
    done

    # non-eth0 interfaces need custom route tables
    #
    # NOTE: busybox iproute2 doesn't do 'route show table' properly for IPv6,
    #       so iproute2-minimal package is required!
    #
    if [ "$IFACE" != eth0 ] && [ -n "$IP6S" ] &&
            [ -z "$(ip +F -6 route show table "$RTABLE")" ]; then
        TRIES=20
        while true; do
            GW="$(ip -6 route show dev "$IFACE" default | awk '{ print $3 }')"
            [ -n "$GW" ] && break
            let TRIES--
            if [ "$TRIES" -eq 0 ]; then
                log warn "Unable to get IPv6 gateway RA after 10s"
                break
            fi
            sleep 0.5
        done
        ip -6 route add default via "$GW" dev "$IFACE" table "$RTABLE"
    fi
    echo "$IP6S"
}

in_list() {
    echo "$2" | grep -q "^$1$"
}

# ip_addr {4|6} {add|del} <ip>
ip_addr() {
    [ "$1" -eq 6 ] && MASK=128 || MASK="$mask"  # IP6s are always /128
    ip -"$1" addr "$2" "$3/$MASK" dev "$IFACE"
    [ "$IFACE" = eth0 ] && return

    # non-eth0 interfaces get rules associating IPs with route tables
    ip -"$1" rule "$2" from "$3" lookup "$RTABLE"
}

# sync_ips {4|6} "<ec2-ips>" "<iface-ips>"
sync_ips() {
    # remove extra IPs
    for i in $3; do
        in_list "$i" "$2" || ip_addr "$1" del "$i"
    done
    # add missing IPs
    for i in $2; do
        in_list "$i" "$3" || ip_addr "$1" add "$i"
    done
}

log info "STARTING: $IFACE"

if [ "$HOOK" != post-bound ] && [ "$HOOK" != post-renew ]; then
    log err "Unhandled udhcpc hook '$HOOK'"
    exit 1
fi

sync_ips 4 "$(ec2_ip4s)" "$(iface_ip4s)"
sync_ips 6 "$(ec2_ip6s)" "$(iface_ip6s)"

log info "FINISHED: $IFACE"