/**
 * Copyright (C) 2012-2014 Steven Barth <steven@midlink.org>
 * Copyright (C) 2017-2018 Hans Dedecker <dedeckeh@gmail.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License v2 as published by
 * the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 */

#include <arpa/inet.h>
#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <libubox/md5.h>
#include <limits.h>
#include <netinet/in.h>
#include <net/if.h>
#include <net/ethernet.h>
#include <resolv.h>
#include <signal.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>

#include "config.h"
#include "odhcp6c.h"

#define ALL_DHCPV6_RELAYS {{{0xff, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,\
		0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x02}}}
#define DHCPV6_CLIENT_PORT 546
#define DHCPV6_SERVER_PORT 547
#define DHCPV6_DUID_LLADDR 3

#define DHCPV6_SOL_MAX_RT_MIN 60
#define DHCPV6_SOL_MAX_RT_MAX 86400
#define DHCPV6_INF_MAX_RT_MIN 60
#define DHCPV6_INF_MAX_RT_MAX 86400

static bool dhcpv6_response_is_valid(const void *buf, ssize_t len,
		const uint8_t transaction[3], enum dhcpv6_msg req_msg_type,
		const struct in6_addr *daddr);

static unsigned int dhcpv6_parse_ia(void *opt, void *end, int *ret);

static unsigned int dhcpv6_calc_refresh_timers(void);
static void dhcpv6_handle_status_code(_o_unused const enum dhcpv6_msg orig,
		const uint16_t code, const void *status_msg, const int len,
		int *ret);
static void dhcpv6_handle_ia_status_code(const enum dhcpv6_msg orig,
		const struct dhcpv6_ia_hdr *ia_hdr, const uint16_t code,
		const void *status_msg, const int len,
		bool handled_status_codes[_DHCPV6_Status_Max],
		int *ret);
static void dhcpv6_add_server_cand(const struct dhcpv6_server_cand *cand);
static void dhcpv6_clear_all_server_cand(void);

static void dhcpv6_log_status_code(const uint16_t code, const char *scope,
		const void *status_msg, int len);

static reply_handler dhcpv6_handle_reply;
static reply_handler dhcpv6_handle_advert;
static reply_handler dhcpv6_handle_rebind_reply;
static reply_handler dhcpv6_handle_reconfigure;
static int dhcpv6_commit_advert(void);

// RFC 3315 - 5.5 Timeout and Delay values
static const struct dhcpv6_retx dhcpv6_retx_default[_DHCPV6_MSG_MAX] = {
	[DHCPV6_MSG_UNKNOWN] = {
		0,
		1,
		120,
		0,
		"<POLL>",
		dhcpv6_handle_reconfigure,
		NULL,
		false,
		0,
		0,
		0,
		{0, 0, 0},
		0,
		0,
		0,
		-1,
		0
	},
	[DHCPV6_MSG_SOLICIT] = {
		DHCPV6_MAX_DELAY,
		DHCPV6_SOL_INIT_RT,
		DHCPV6_SOL_MAX_RT,
		0,
		"SOLICIT",
		dhcpv6_handle_advert,
		dhcpv6_commit_advert,
		false,
		0,
		0,
		0,
		{0, 0, 0},
		0,
		0,
		0,
		-1,
		0
	},
	[DHCPV6_MSG_REQUEST] = {
		0,
		DHCPV6_REQ_INIT_RT,
		DHCPV6_REQ_MAX_RT,
		DHCPV6_REQ_MAX_RC,
		"REQUEST",
		dhcpv6_handle_reply,
		NULL,
		false,
		0,
		0,
		0,
		{0, 0, 0},
		0,
		0,
		0,
		-1,
		0
	},
	[DHCPV6_MSG_RENEW] = {
		0,
		DHCPV6_REN_INIT_RT,
		DHCPV6_REN_MAX_RT,
		0,
		"RENEW",
		dhcpv6_handle_reply,
		NULL,
		false,
		0,
		0,
		0,
		{0, 0, 0},
		0,
		0,
		0,
		-1,
		0
	},
	[DHCPV6_MSG_REBIND] = {
		0,
		DHCPV6_REB_INIT_RT,
		DHCPV6_REB_MAX_RT,
		0,
		"REBIND",
			dhcpv6_handle_rebind_reply,
		NULL,
		false,
		0,
		0,
		0,
		{0, 0, 0},
		0,
		0,
		0,
		-1,
		0
	},
	[DHCPV6_MSG_RELEASE] = {
		0,
		DHCPV6_REL_INIT_RT,
		0,
		DHCPV6_REL_MAX_RC,
		"RELEASE",
		NULL,
		NULL,
		false,
		0,
		0,
		0,
		{0, 0, 0},
		0,
		0,
		0,
		-1,
		0
	},
	[DHCPV6_MSG_DECLINE] = {
		0,
		DHCPV6_DEC_INIT_RT,
		0,
		DHCPV6_DEC_MAX_RC,
		"DECLINE",
		NULL,
		NULL,
		false,
		0,
		0,
		0,
		{0, 0, 0},
		0,
		0,
		0,
		-1,
		0
	},
	[DHCPV6_MSG_INFO_REQ] = {
		DHCPV6_MAX_DELAY,
		DHCPV6_INF_INIT_RT,
		DHCPV6_INF_MAX_RT,
		0,
		"INFOREQ",
		dhcpv6_handle_reply,
		NULL,
		false,
		0,
		0,
		0,
		{0, 0, 0},
		0,
		0,
		0,
		-1,
		0
	},
};
static struct dhcpv6_retx dhcpv6_retx[_DHCPV6_MSG_MAX] = {0};

// Sockets
static int sock = -1;
static int ifindex = -1;
static int64_t t1 = 0, t2 = 0, t3 = 0;

// IA states
static enum odhcp6c_ia_mode na_mode = IA_MODE_NONE, pd_mode = IA_MODE_NONE;
static bool stateful_only_mode = false;
static bool accept_reconfig = false;
// Server unicast address
static struct in6_addr server_addr = IN6ADDR_ANY_INIT;

// Initial state of the DHCPv6 service
static enum dhcpv6_state dhcpv6_state = DHCPV6_INIT;
static int dhcpv6_state_timeout = 0;

// Authentication options
static enum odhcp6c_auth_protocol auth_protocol = AUTH_PROT_RKAP;
static uint8_t reconf_key[16];

// client options
static unsigned int client_options = 0;

// counters for statistics
static struct dhcpv6_stats dhcpv6_stats = {0};

// config
static struct config_dhcp* config_dhcp = NULL;

// store unique ifname hash to use as IA->IAID
static uint32_t ifname_hash_iaid = 0;

static uint32_t ntohl_unaligned(const uint8_t *data)
{
	uint32_t buf;

	memcpy(&buf, data, sizeof(buf));
	return ntohl(buf);
}

static void dhcpv6_next_state(void)
{
	dhcpv6_state++;
	dhcpv6_reset_state_timeout();
}

static void dhcpv6_prev_state(void)
{
	dhcpv6_state--;
	dhcpv6_reset_state_timeout();
}

static void dhcpv6_inc_counter(enum dhcpv6_msg type)
{
	switch (type) {
	case DHCPV6_MSG_SOLICIT:
		dhcpv6_stats.solicit++;
		break;

	case DHCPV6_MSG_ADVERT:
		dhcpv6_stats.advertise++;
		break;

	case DHCPV6_MSG_REQUEST:
		dhcpv6_stats.request++;
		break;

	case DHCPV6_MSG_RENEW:
		dhcpv6_stats.renew++;
		break;

	case DHCPV6_MSG_REBIND:
		dhcpv6_stats.rebind++;
		break;

	case DHCPV6_MSG_REPLY:
		dhcpv6_stats.reply++;
		break;

	case DHCPV6_MSG_RELEASE:
		dhcpv6_stats.release++;
		break;

	case DHCPV6_MSG_DECLINE:
		dhcpv6_stats.decline++;
		break;

	case DHCPV6_MSG_RECONF:
		dhcpv6_stats.reconfigure++;
		break;

	case DHCPV6_MSG_INFO_REQ:
		dhcpv6_stats.information_request++;
		break;

	default:
		break;
	}
}

static char *dhcpv6_msg_to_str(enum dhcpv6_msg msg)
{
	switch (msg) {
	case DHCPV6_MSG_SOLICIT:
		return "SOLICIT";

	case DHCPV6_MSG_ADVERT:
		return "ADVERTISE";

	case DHCPV6_MSG_REQUEST:
		return "REQUEST";

	case DHCPV6_MSG_RENEW:
		return "RENEW";

	case DHCPV6_MSG_REBIND:
		return "REBIND";

	case DHCPV6_MSG_REPLY:
		return "REPLY";

	case DHCPV6_MSG_RELEASE:
		return "RELEASE";

	case DHCPV6_MSG_DECLINE:
		return "DECLINE";

	case DHCPV6_MSG_RECONF:
		return "RECONFIGURE";

	case DHCPV6_MSG_INFO_REQ:
		return "INFORMATION REQUEST";

	default:
		break;
	}

	return "UNKNOWN";
}

static char *dhcpv6_status_code_to_str(uint16_t code)
{
	switch (code) {
	case DHCPV6_Success:
		return "Success";

	case DHCPV6_UnspecFail:
		return "Unspecified Failure";

	case DHCPV6_NoAddrsAvail:
		return "No Address Available";

	case DHCPV6_NoBinding:
		return "No Binding";

	case DHCPV6_NotOnLink:
		return "Not On Link";

	case DHCPV6_UseMulticast:
		return "Use Multicast";

	case DHCPV6_NoPrefixAvail:
		return "No Prefix Available";

	default:
		break;
	}

	return "Unknown";
}

const char *dhcpv6_state_to_str(enum dhcpv6_state state)
{
	switch (state) {
	case DHCPV6_INIT:
		return "INIT";

	case DHCPV6_SOLICIT:
		return "SOLICIT";

	case DHCPV6_SOLICIT_PROCESSING:
		return "SOLICIT_PROCESSING";

	case DHCPV6_ADVERT:
		return "ADVERT";

	case DHCPV6_REQUEST:
		return "REQUEST";

	case DHCPV6_REQUEST_PROCESSING:
		return "REQUEST_PROCESSING";

	case DHCPV6_REPLY:
		return "REPLY";

	case DHCPV6_BOUND:
		return "BOUND";

	case DHCPV6_BOUND_PROCESSING:
		return "BOUND_PROCESSING";

	case DHCPV6_BOUND_REPLY:
		return "BOUND_REPLY";

	case DHCPV6_RECONF:
		return "RECONF";

	case DHCPV6_RECONF_PROCESSING:
		return "RECONF_PROCESSING";

	case DHCPV6_RECONF_REPLY:
		return "RECONF_REPLY";

	case DHCPV6_RENEW:
		return "RENEW";

	case DHCPV6_RENEW_PROCESSING:
		return "RENEW_PROCESSING";

	case DHCPV6_RENEW_REPLY:
		return "RENEW_REPLY";

	case DHCPV6_REBIND:
		return "REBIND";

	case DHCPV6_REBIND_PROCESSING:
		return "REBIND_PROCESSING";

	case DHCPV6_REBIND_REPLY:
		return "REBIND_REPLY";

	case DHCPV6_INFO:
		return "INFO";

	case DHCPV6_INFO_PROCESSING:
		return "INFO_PROCESSING";

	case DHCPV6_INFO_REPLY:
		return "INFO_REPLY";

	case DHCPV6_EXIT:
		return "EXIT";

	default:
		return "INVALID_STATE";
	}
}

static int fd_set_nonblocking(int sockfd)
{
	int flags = fcntl(sockfd, F_GETFL, 0);
	if (flags == -1) {
		error(
			"Failed to get the dhcpv6 socket flags: fcntl F_GETFL failed (%s)",
			strerror(errno));
		return -1;
	}

	// Set the socket to non-blocking
	if (fcntl(sockfd, F_SETFL, flags | O_NONBLOCK) == -1) {
		error(
			"Failed to set the dhcpv6 socket to non-blocking: fcntl F_SETFL failed (%s)",
			strerror(errno));
		return -1;
	}

	return 0;
}

int dhcpv6_get_socket(void)
{
	return sock;
}

enum dhcpv6_state dhcpv6_get_state(void)
{
	return dhcpv6_state;
}

void dhcpv6_set_state(enum dhcpv6_state state)
{
	dhcpv6_state = state;
	dhcpv6_reset_state_timeout();
}

int dhcpv6_get_state_timeout(void)
{
	return dhcpv6_state_timeout;
}

void dhcpv6_set_state_timeout(int timeout)
{
	if (timeout > 0 && (dhcpv6_state_timeout == 0 || timeout < dhcpv6_state_timeout)) {
		dhcpv6_state_timeout = timeout;
	}
}

void dhcpv6_reset_state_timeout(void)
{
	dhcpv6_state_timeout = 0;
}

struct dhcpv6_stats dhcpv6_get_stats(void)
{
	return dhcpv6_stats;
}

void dhcpv6_reset_stats(void)
{
	memset(&dhcpv6_stats, 0, sizeof(dhcpv6_stats));
}

static uint32_t dhcpv6_generate_iface_iaid(const char *ifname) {
	uint8_t hash[16] = {0};
	uint32_t iaid;
	md5_ctx_t md5;

	md5_begin(&md5);
	md5_hash(ifname, strlen(ifname), &md5);
	md5_end(hash, &md5);

	iaid = hash[0] << 24;
	iaid |= hash[1] << 16;
	iaid |= hash[2] << 8;
	iaid |= hash[3];

	return iaid;
}

int init_dhcpv6(const char *ifname)
{
	config_dhcp = config_dhcp_get();

	memcpy(dhcpv6_retx, dhcpv6_retx_default, sizeof(dhcpv6_retx));
	config_apply_dhcp_rtx(dhcpv6_retx);

	client_options = config_dhcp->client_options;
	na_mode = config_dhcp->ia_na_mode;
	pd_mode = config_dhcp->ia_pd_mode;
	stateful_only_mode = config_dhcp->stateful_only_mode;
	auth_protocol = config_dhcp->auth_protocol;

	sock = socket(AF_INET6, SOCK_DGRAM | SOCK_CLOEXEC, IPPROTO_UDP);
	if (sock < 0)
		goto failure;

	// Detect interface
	struct ifreq ifr;
	memset(&ifr, 0, sizeof(ifr));
	strncpy(ifr.ifr_name, ifname, sizeof(ifr.ifr_name) - 1);
	if (ioctl(sock, SIOCGIFINDEX, &ifr) < 0)
		goto failure;

	ifname_hash_iaid = dhcpv6_generate_iface_iaid(ifname);

	ifindex = ifr.ifr_ifindex;

	// Set the socket to non-blocking mode
	if (fd_set_nonblocking(sock) < 0)
		goto failure;

	// Build our FQDN
	size_t fqdn_len;
	odhcp6c_get_state(STATE_OUR_FQDN, &fqdn_len);
	if(fqdn_len == 0) {
		char fqdn_buf[256];
		gethostname(fqdn_buf, sizeof(fqdn_buf));
		struct {
			uint16_t type;
			uint16_t len;
			uint8_t flags;
			uint8_t data[256];
		} fqdn = {0};
		int dn_result = dn_comp(fqdn_buf, fqdn.data,
				sizeof(fqdn.data), NULL, NULL);
		fqdn_len = 0;
		if (dn_result > 0) {
			fqdn.type = htons(DHCPV6_OPT_FQDN);
			fqdn.len = htons(1 + dn_result);
			fqdn.flags = 0;
			fqdn_len = DHCPV6_OPT_HDR_SIZE + 1 + dn_result;
		}
		odhcp6c_add_state(STATE_OUR_FQDN, &fqdn, fqdn_len);
	}

	// Create client DUID
	size_t client_id_len;
	odhcp6c_get_state(STATE_CLIENT_ID, &client_id_len);
	if (client_id_len == 0) {
		uint8_t duid[14] = {0, DHCPV6_OPT_CLIENTID, 0, 10, 0,
				DHCPV6_DUID_LLADDR, 0, 1};

		if (ioctl(sock, SIOCGIFHWADDR, &ifr) >= 0)
			memcpy(&duid[8], ifr.ifr_hwaddr.sa_data, ETHER_ADDR_LEN);

		uint8_t zero[ETHER_ADDR_LEN] = {0, 0, 0, 0, 0, 0};
		struct ifreq ifs[100], *ifp, *ifend;
		struct ifconf ifc;
		ifc.ifc_req = ifs;
		ifc.ifc_len = sizeof(ifs);

		if (!memcmp(&duid[8], zero, ETHER_ADDR_LEN) &&
				ioctl(sock, SIOCGIFCONF, &ifc) >= 0) {
			// If our interface doesn't have an address...
			ifend = ifs + (ifc.ifc_len / sizeof(struct ifreq));
			for (ifp = ifc.ifc_req; ifp < ifend &&
					!memcmp(&duid[8], zero, ETHER_ADDR_LEN); ifp++) {
				memcpy(ifr.ifr_name, ifp->ifr_name,
						sizeof(ifr.ifr_name));
				if (ioctl(sock, SIOCGIFHWADDR, &ifr) < 0)
					continue;

				memcpy(&duid[8], ifr.ifr_hwaddr.sa_data,
						ETHER_ADDR_LEN);
			}
		}

		odhcp6c_add_state(STATE_CLIENT_ID, duid, sizeof(duid));
	}

	// Create ORO
	if (!(client_options & DHCPV6_STRICT_OPTIONS)) {
		uint16_t oro[] = {
			htons(DHCPV6_OPT_SIP_SERVER_D),
			htons(DHCPV6_OPT_SIP_SERVER_A),
			htons(DHCPV6_OPT_DNS_SERVERS),
			htons(DHCPV6_OPT_DNS_DOMAIN),
			htons(DHCPV6_OPT_SNTP_SERVERS),
			htons(DHCPV6_OPT_NTP_SERVER),
			htons(DHCPV6_OPT_PD_EXCLUDE),
			/* RFC8910: Clients that support this option SHOULD include it */
			htons(DHCPV6_OPT_CAPTIVE_PORTAL),
		};
		odhcp6c_add_state(STATE_ORO, oro, sizeof(oro));
	}
	// Required ORO
	uint16_t req_oro[] = {
		htons(DHCPV6_OPT_INF_MAX_RT),
		htons(DHCPV6_OPT_SOL_MAX_RT),
		htons(DHCPV6_OPT_INFO_REFRESH),
	};
	odhcp6c_add_state(STATE_ORO, req_oro, sizeof(req_oro));

	// Configure IPv6-options
	int val = 1;
	if (setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val)) < 0)
		goto failure;

	if (setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val)) < 0)
		goto failure;

	if (setsockopt(sock, IPPROTO_IPV6, IPV6_RECVPKTINFO, &val, sizeof(val)) < 0)
		goto failure;

	if (setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, ifname, strlen(ifname)) < 0)
		goto failure;

	if (setsockopt(sock, SOL_SOCKET, SO_PRIORITY, &(config_dhcp->sk_prio), sizeof(config_dhcp->sk_prio)) < 0)
		goto failure;

	val = config_dhcp->dscp << 2;
	if (setsockopt(sock, IPPROTO_IPV6, IPV6_TCLASS, &val, sizeof(val)) < 0) {
		goto failure;
	}

	struct sockaddr_in6 client_addr = { .sin6_family = AF_INET6,
		.sin6_port = htons(DHCPV6_CLIENT_PORT), .sin6_flowinfo = 0 };

	if (bind(sock, (struct sockaddr*)&client_addr, sizeof(client_addr)) < 0)
		goto failure;

	return 0;

failure:
	if (sock >= 0)
		close(sock);

	return -1;
}

enum {
	IOV_HDR=0,
	IOV_ORO,
	IOV_CL_ID,
	IOV_SRV_ID,
	IOV_OPTS,
	IOV_RECONF_ACCEPT,
	IOV_FQDN,
	IOV_HDR_IA_NA,
	IOV_IA_NA,
	IOV_IA_PD,
	IOV_TOTAL
};

int dhcpv6_get_ia_mode(void)
{
	int mode = DHCPV6_UNKNOWN;

	if (na_mode == IA_MODE_NONE && pd_mode == IA_MODE_NONE)
		mode = DHCPV6_STATELESS;
	else if (na_mode == IA_MODE_FORCE || pd_mode == IA_MODE_FORCE)
		mode = DHCPV6_STATEFUL;

	return mode;
}

static void dhcpv6_send(enum dhcpv6_msg req_msg_type, uint8_t trid[3], uint32_t ecs)
{
	// Build FQDN
	size_t fqdn_len;
	void *fqdn = odhcp6c_get_state(STATE_OUR_FQDN, &fqdn_len);

	// Build Client ID
	size_t cl_id_len;
	void *cl_id = odhcp6c_get_state(STATE_CLIENT_ID, &cl_id_len);

	// Get Server ID
	size_t srv_id_len;
	void *srv_id = odhcp6c_get_state(STATE_SERVER_ID, &srv_id_len);

	// Build IA_PDs
	size_t ia_pd_entry_cnt = 0, ia_pd_len = 0;
	uint8_t *ia_pd;
	struct odhcp6c_entry *pd_entries = odhcp6c_get_state(STATE_IA_PD, &ia_pd_entry_cnt);
	ia_pd_entry_cnt /= sizeof(*pd_entries);

	if (req_msg_type == DHCPV6_MSG_SOLICIT || (req_msg_type == DHCPV6_MSG_REQUEST && ia_pd_entry_cnt == 0 && pd_mode != IA_MODE_NONE)) {
		odhcp6c_clear_state(STATE_IA_PD);
		size_t n_prefixes;
		struct odhcp6c_request_prefix *request_prefixes = odhcp6c_get_state(STATE_IA_PD_INIT, &n_prefixes);
		n_prefixes /= sizeof(struct odhcp6c_request_prefix);

		ia_pd = alloca(n_prefixes * (sizeof(struct dhcpv6_ia_hdr) + sizeof(struct dhcpv6_ia_prefix)));

		for (size_t i = 0; i < n_prefixes; i++) {
			struct dhcpv6_ia_hdr hdr_ia_pd = {
				htons(DHCPV6_OPT_IA_PD),
				htons(sizeof(hdr_ia_pd) - DHCPV6_OPT_HDR_SIZE +
				      sizeof(struct dhcpv6_ia_prefix) * !!request_prefixes[i].length),
				request_prefixes[i].iaid, 0, 0
			};
			struct dhcpv6_ia_prefix pref = {
				.type = htons(DHCPV6_OPT_IA_PREFIX),
				.len = htons(sizeof(pref) - DHCPV6_OPT_HDR_SIZE),
				.prefix = request_prefixes[i].length,
				.addr = request_prefixes[i].addr
			};
			memcpy(ia_pd + ia_pd_len, &hdr_ia_pd, sizeof(hdr_ia_pd));
			ia_pd_len += sizeof(hdr_ia_pd);
			if (request_prefixes[i].length) {
				memcpy(ia_pd + ia_pd_len, &pref, sizeof(pref));
				ia_pd_len += sizeof(pref);
			}
		}
	} else {
		// we're too lazy to count our distinct IAIDs,
		// so just allocate maximally needed space
		ia_pd = alloca(ia_pd_entry_cnt * (sizeof(struct dhcpv6_ia_prefix) + 10 +
					sizeof(struct dhcpv6_ia_hdr)));

		for (size_t i = 0; i < ia_pd_entry_cnt; ++i) {
			uint32_t iaid = pd_entries[i].iaid;

			// check if this is an unprocessed IAID and skip if not.
			bool new_iaid = true;
			for (int j = i-1; j >= 0; j--) {
				if (pd_entries[j].iaid == iaid) {
					new_iaid = false;
					break;
				}
			}

			if (!new_iaid)
				continue;

			// construct header
			struct dhcpv6_ia_hdr hdr_ia_pd = {
				htons(DHCPV6_OPT_IA_PD),
				htons(sizeof(hdr_ia_pd) - DHCPV6_OPT_HDR_SIZE),
				iaid, 0, 0
			};

			memcpy(ia_pd + ia_pd_len, &hdr_ia_pd, sizeof(hdr_ia_pd));
			struct dhcpv6_ia_hdr *hdr = (struct dhcpv6_ia_hdr *) (ia_pd + ia_pd_len);
			ia_pd_len += sizeof(hdr_ia_pd);

			for (size_t j = i; j < ia_pd_entry_cnt; j++) {
				if (pd_entries[j].iaid != iaid)
					continue;

				uint8_t ex_len = 0;
				if (pd_entries[j].exclusion_length > 0)
					ex_len = ((pd_entries[j].exclusion_length - pd_entries[j].length - 1) / 8) + 6;

				struct dhcpv6_ia_prefix p = {
					.type = htons(DHCPV6_OPT_IA_PREFIX),
					.len = htons(sizeof(p) - DHCPV6_OPT_HDR_SIZE_U + ex_len),
					.prefix = pd_entries[j].length,
					.addr = pd_entries[j].target
				};

				if (req_msg_type == DHCPV6_MSG_REQUEST) {
					p.preferred = htonl(pd_entries[j].preferred);
					p.valid = htonl(pd_entries[j].valid);
				}

				memcpy(ia_pd + ia_pd_len, &p, sizeof(p));
				ia_pd_len += sizeof(p);

				if (ex_len) {
					ia_pd[ia_pd_len++] = 0;
					ia_pd[ia_pd_len++] = DHCPV6_OPT_PD_EXCLUDE;
					ia_pd[ia_pd_len++] = 0;
					ia_pd[ia_pd_len++] = ex_len - DHCPV6_OPT_HDR_SIZE;
					ia_pd[ia_pd_len++] = pd_entries[j].exclusion_length;

					uint32_t excl = ntohl(pd_entries[j].router.s6_addr32[1]);
					excl >>= (64 - pd_entries[j].exclusion_length);
					excl <<= 8 - ((pd_entries[j].exclusion_length - pd_entries[j].length) % 8);

					for (size_t k = ex_len - 5; k > 0; --k, excl >>= 8)
						ia_pd[ia_pd_len + k] = excl & 0xff;

					ia_pd_len += ex_len - 5;
				}

				hdr->len = htons(ntohs(hdr->len) + ntohs(p.len) + 4U);
			}
		}
	}

	// Build IA_NAs
	size_t ia_na_entry_cnt, ia_na_len = 0;
	void *ia_na = NULL;
	struct odhcp6c_entry *ia_entries = odhcp6c_get_state(STATE_IA_NA, &ia_na_entry_cnt);
	ia_na_entry_cnt /= sizeof(*ia_entries);

	struct dhcpv6_ia_hdr hdr_ia_na = {
		.type = htons(DHCPV6_OPT_IA_NA),
		.len = htons(sizeof(hdr_ia_na) - DHCPV6_OPT_HDR_SIZE),
		.iaid = htonl(ifname_hash_iaid),
		.t1 = 0,
		.t2 = 0,
	};

	struct dhcpv6_ia_addr ia_na_array[ia_na_entry_cnt];
	for (size_t i = 0; i < ia_na_entry_cnt; ++i) {
		ia_na_array[i].type = htons(DHCPV6_OPT_IA_ADDR);
		ia_na_array[i].len = htons(sizeof(ia_na_array[i]) - DHCPV6_OPT_HDR_SIZE_U);
		ia_na_array[i].addr = ia_entries[i].target;

		if (req_msg_type == DHCPV6_MSG_REQUEST) {
			ia_na_array[i].preferred = htonl(ia_entries[i].preferred);
			ia_na_array[i].valid = htonl(ia_entries[i].valid);
		} else {
			ia_na_array[i].preferred = 0;
			ia_na_array[i].valid = 0;
		}
	}

	ia_na = ia_na_array;
	ia_na_len = sizeof(ia_na_array);
	hdr_ia_na.len = htons(ntohs(hdr_ia_na.len) + ia_na_len);

	// Reconfigure Accept
	struct {
		uint16_t type;
		uint16_t length;
	} reconf_accept = {htons(DHCPV6_OPT_RECONF_ACCEPT), 0};

	// Option list
	size_t opts_len;
	void *opts = odhcp6c_get_state(STATE_OPTS, &opts_len);

	// Option Request List
	size_t oro_entries, oro_len = 0;
	uint16_t *oro, *s_oro = odhcp6c_get_state(STATE_ORO, &oro_entries);

	oro_entries /= sizeof(*s_oro);
	oro = alloca(oro_entries * sizeof(*oro));

	for (size_t i = 0; i < oro_entries; i++) {
		struct odhcp6c_opt *opt = odhcp6c_find_opt(htons(s_oro[i]));

		if (opt) {
			if (!(opt->flags & OPT_ORO))
				continue;

			if ((opt->flags & OPT_ORO_SOLICIT) && req_msg_type != DHCPV6_MSG_SOLICIT)
				continue;

			if ((opt->flags & OPT_ORO_STATELESS) && req_msg_type != DHCPV6_MSG_INFO_REQ)
				continue;

			if ((opt->flags & OPT_ORO_STATEFUL) && req_msg_type == DHCPV6_MSG_INFO_REQ)
				continue;
		}

		oro[oro_len++] = s_oro[i];
	}
	oro_len *= sizeof(*oro);

	// Prepare Header
	struct {
		uint8_t type;
		uint8_t trid[3];
		uint16_t elapsed_type;
		uint16_t elapsed_len;
		uint16_t elapsed_value;
		uint16_t oro_type;
		uint16_t oro_len;
	} hdr = {
		req_msg_type, {trid[0], trid[1], trid[2]},
		htons(DHCPV6_OPT_ELAPSED), htons(2),
			htons((ecs > 0xffff) ? 0xffff : ecs),
		htons(DHCPV6_OPT_ORO), htons(oro_len),
	};

	struct iovec iov[IOV_TOTAL] = {
		[IOV_HDR] = {&hdr, sizeof(hdr)},
		[IOV_ORO] = {oro, oro_len},
		[IOV_CL_ID] = {cl_id, cl_id_len},
		[IOV_SRV_ID] = {srv_id, srv_id_len},
		[IOV_OPTS] = { opts, opts_len },
		[IOV_RECONF_ACCEPT] = {&reconf_accept, sizeof(reconf_accept)},
		[IOV_FQDN] = {fqdn, fqdn_len},
		[IOV_HDR_IA_NA] = {&hdr_ia_na, sizeof(hdr_ia_na)},
		[IOV_IA_NA] = {ia_na, ia_na_len},
		[IOV_IA_PD] = {ia_pd, ia_pd_len},
	};

	size_t cnt = IOV_TOTAL;
	if (req_msg_type == DHCPV6_MSG_INFO_REQ)
		cnt = IOV_HDR_IA_NA;

	// Disable IAs if not used
	if (na_mode == IA_MODE_NONE) {
		iov[IOV_HDR_IA_NA].iov_len = 0;
	} else if (ia_na_len == 0) {
		/* RFC7550 §4.2
		 *    Solution: a client SHOULD accept Advertise messages, even
		 *    when not all IA option types are being offered. And, in
		 *    this case, the client SHOULD include the not offered IA
		 *    option types in its Request. A client SHOULD only ignore
		 *    an Advertise message when none of the requested IA
		 *    options include offered addresses or delegated prefixes.
		 *    Note that ignored messages MUST still be processed for
		 *    SOL_MAX_RT and INF_MAX_RT options as specified in
		 *    [RFC7083].
		 */

		switch (req_msg_type) {
		case DHCPV6_MSG_REQUEST:
			if (!config_dhcp->strict_rfc7550) {
				/* Some broken ISPs won't behave properly if IA_NA is
				 * sent on Requests when they have provided an empty
				 * IA_NA on Advertise.
				 * Therefore we don't comply with RFC7550 and omit
				 * IA_NA as a workaround.
				 */
				iov[IOV_HDR_IA_NA].iov_len = 0;
			}
			break;
		case DHCPV6_MSG_SOLICIT:
			break;
		default:
			iov[IOV_HDR_IA_NA].iov_len = 0;
			break;
		}
	}

	if ((req_msg_type != DHCPV6_MSG_SOLICIT && req_msg_type != DHCPV6_MSG_REQUEST) ||
			!(client_options & DHCPV6_ACCEPT_RECONFIGURE))
		iov[IOV_RECONF_ACCEPT].iov_len = 0;

	if (!(client_options & DHCPV6_CLIENT_FQDN)) {
		iov[IOV_FQDN].iov_len = 0;
	} else {
		switch (req_msg_type) {
		/*  RFC4704 §5
			A client MUST only include the Client FQDN option in SOLICIT,
			REQUEST, RENEW, or REBIND messages.
		*/
		case DHCPV6_MSG_SOLICIT:
		case DHCPV6_MSG_REQUEST:
		case DHCPV6_MSG_RENEW:
		case DHCPV6_MSG_REBIND:
		/*  RFC4704 §6
			Servers MUST only include a Client FQDN option in ADVERTISE and REPLY
			messages...
		case DHCPV6_MSG_ADVERT:
		case DHCPV6_MSG_REPLY:
		*/
			/* leave FQDN as-is */
			break;
		default:
			/* remaining MSG types cannot contain client FQDN */
			iov[IOV_FQDN].iov_len = 0;
			break;
		}
	}

	struct sockaddr_in6 srv = {AF_INET6, htons(DHCPV6_SERVER_PORT),
		0, ALL_DHCPV6_RELAYS, ifindex};
	struct msghdr msg = {.msg_name = &srv, .msg_namelen = sizeof(srv),
			.msg_iov = iov, .msg_iovlen = cnt};

	switch (req_msg_type) {
	case DHCPV6_MSG_REQUEST:
	case DHCPV6_MSG_RENEW:
	case DHCPV6_MSG_RELEASE:
	case DHCPV6_MSG_DECLINE:
		if (!IN6_IS_ADDR_UNSPECIFIED(&server_addr) &&
			odhcp6c_addr_in_scope(&server_addr)) {
			srv.sin6_addr = server_addr;
			if (!IN6_IS_ADDR_LINKLOCAL(&server_addr))
				srv.sin6_scope_id = 0;
		}
		break;
	default:
		break;
	}

	if (sendmsg(sock, &msg, 0) < 0) {
		char in6_str[INET6_ADDRSTRLEN];

		error("Failed to send %s message to %s (%s)",
			dhcpv6_msg_to_str(req_msg_type),
			inet_ntop(AF_INET6, (const void *)&srv.sin6_addr,
				in6_str, sizeof(in6_str)), strerror(errno));
		dhcpv6_stats.transmit_failures++;
	} else {
		dhcpv6_inc_counter(req_msg_type);
	}
}

static int64_t dhcpv6_rand_delay(int64_t time)
{
	int random;
	odhcp6c_random(&random, sizeof(random));

	return (time * ((int64_t)random % (config_dhcp->rand_factor*10LL))) / 10000LL;
}

// Message validation checks according to RFC3315 chapter 15
static bool dhcpv6_response_is_valid(const void *buf, ssize_t len,
		const uint8_t transaction[3], enum dhcpv6_msg req_msg_type,
		const struct in6_addr *daddr)
{
	const struct dhcpv6_header *response_buf = buf;
	if (len < (ssize_t)sizeof(*response_buf) || memcmp(response_buf->tr_id,
			transaction, sizeof(response_buf->tr_id)))
		return false; // Invalid reply

	if (req_msg_type == DHCPV6_MSG_SOLICIT) {
		if (response_buf->msg_type != DHCPV6_MSG_ADVERT &&
				response_buf->msg_type != DHCPV6_MSG_REPLY)
			return false;
	} else if (req_msg_type == DHCPV6_MSG_UNKNOWN) {
		if (!accept_reconfig || response_buf->msg_type != DHCPV6_MSG_RECONF)
			return false;
	} else if (response_buf->msg_type != DHCPV6_MSG_REPLY) {
		return false;
	}

	uint8_t *end = ((uint8_t*)buf) + len, *odata = NULL,
		rcmsg = DHCPV6_MSG_UNKNOWN;
	uint16_t otype, olen = UINT16_MAX;
	bool clientid_ok = false, serverid_ok = false, rcauth_ok = false,
		auth_present = false, ia_present = false, options_valid = true;

	size_t client_id_len, server_id_len;
	void *client_id = odhcp6c_get_state(STATE_CLIENT_ID, &client_id_len);
	void *server_id = odhcp6c_get_state(STATE_SERVER_ID, &server_id_len);

	dhcpv6_for_each_option(&response_buf[1], end, otype, olen, odata) {
		switch (otype) {
		case DHCPV6_OPT_CLIENTID:
			clientid_ok = (olen + DHCPV6_OPT_HDR_SIZE_U == client_id_len) && !memcmp(
					&odata[-DHCPV6_OPT_HDR_SIZE], client_id, client_id_len);			
			break;

		case DHCPV6_OPT_SERVERID:
			if (server_id_len)
				serverid_ok = (olen + DHCPV6_OPT_HDR_SIZE_U == server_id_len) && !memcmp(
						&odata[-DHCPV6_OPT_HDR_SIZE], server_id, server_id_len);
			else
				serverid_ok = true;
			break;

		case DHCPV6_OPT_AUTH:
			struct dhcpv6_auth *r = (void*)&odata[-DHCPV6_OPT_HDR_SIZE];
			if (auth_present) {
				options_valid = false;
				continue;
			}

			auth_present = true;
			if (auth_protocol == AUTH_PROT_RKAP) {
				struct dhcpv6_auth_reconfigure *rkap = (void*)r->data;
				if (r->protocol != AUTH_PROT_RKAP || r->algorithm != AUTH_ALG_HMACMD5 || r->len != 28 || rkap->reconf_type != RKAP_TYPE_HMACMD5)
					continue;

				md5_ctx_t md5;
				uint8_t serverhash[16], secretbytes[64];
				uint32_t hash[4];
				memcpy(serverhash, rkap->key, sizeof(serverhash));
				memset(rkap->key, 0, sizeof(rkap->key));

				memset(secretbytes, 0, sizeof(secretbytes));
				memcpy(secretbytes, reconf_key, sizeof(reconf_key));

				for (size_t i = 0; i < sizeof(secretbytes); ++i)
					secretbytes[i] ^= 0x36;

				md5_begin(&md5);
				md5_hash(secretbytes, sizeof(secretbytes), &md5);
				md5_hash(buf, len, &md5);
				md5_end(hash, &md5);

				for (size_t i = 0; i < sizeof(secretbytes); ++i) {
					secretbytes[i] ^= 0x36;
					secretbytes[i] ^= 0x5c;
				}

				md5_begin(&md5);
				md5_hash(secretbytes, sizeof(secretbytes), &md5);
				md5_hash(hash, 16, &md5);
				md5_end(hash, &md5);

				rcauth_ok = !memcmp(hash, serverhash, sizeof(hash));
			} else if (auth_protocol == AUTH_PROT_TOKEN) {
				if (r->protocol != AUTH_PROT_TOKEN || r->algorithm != AUTH_ALG_TOKEN || r->len < 12)
					continue;

				uint16_t token_len = r->len - 11;
				if (config_dhcp->auth_token == NULL || strlen(config_dhcp->auth_token) != token_len)
					continue;

				rcauth_ok = !memcmp(r->data, config_dhcp->auth_token, token_len);
			}
			break;
		case DHCPV6_OPT_RECONF_MESSAGE:
			if (olen != 1)
				return false;
			rcmsg = odata[0];
			break;

		case DHCPV6_OPT_IA_PD:
		case DHCPV6_OPT_IA_NA:
			ia_present = true;
			if (olen < sizeof(struct dhcpv6_ia_hdr) - DHCPV6_OPT_HDR_SIZE)
				options_valid = false;
			break;

		case DHCPV6_OPT_IA_ADDR:
		case DHCPV6_OPT_IA_PREFIX:
		case DHCPV6_OPT_PD_EXCLUDE:
			// Options are not allowed on global level
			options_valid = false;
			break;

		default:
			break;
		}
	}

	if (!options_valid || ((odata + olen) > end))
		return false;

	if (req_msg_type == DHCPV6_MSG_INFO_REQ && ia_present)
		return false;

	if (response_buf->msg_type == DHCPV6_MSG_RECONF) {
		if ((rcmsg != DHCPV6_MSG_RENEW && rcmsg != DHCPV6_MSG_REBIND && rcmsg != DHCPV6_MSG_INFO_REQ) ||
			(rcmsg == DHCPV6_MSG_INFO_REQ && ia_present) ||
			!rcauth_ok || IN6_IS_ADDR_MULTICAST(daddr))
			return false;
	}

	return clientid_ok && serverid_ok;
}

static int dhcpv6_handle_reconfigure(enum dhcpv6_msg orig, const int rc,
		const void *opt, const void *end, _o_unused const struct sockaddr_in6 *from)
{
	uint16_t otype, olen;
	uint8_t *odata;
	enum dhcpv6_msg msg = DHCPV6_MSG_UNKNOWN;

	dhcpv6_for_each_option(opt, end, otype, olen, odata) {
		if (otype == DHCPV6_OPT_RECONF_MESSAGE && olen == 1) {
			switch (odata[0]) {
			case DHCPV6_MSG_REBIND:
				if (t2 != UINT32_MAX)
					t2 = 0;
				_o_fallthrough;
			case DHCPV6_MSG_RENEW:
				if (t1 != UINT32_MAX)
					t1 = 0;
				_o_fallthrough;
			case DHCPV6_MSG_INFO_REQ:
				msg = odata[0];
				notice("Need to respond with %s in reply to %s",
				       dhcpv6_msg_to_str(msg), dhcpv6_msg_to_str(DHCPV6_MSG_RECONF));
				break;

			default:
				break;
			}
		}
	}

	if (msg != DHCPV6_MSG_UNKNOWN)
		dhcpv6_handle_reply(orig, rc, NULL, NULL, NULL);

	return (msg == DHCPV6_MSG_UNKNOWN? -1: (int)msg);
}

// Collect all advertised servers
static int dhcpv6_handle_advert(enum dhcpv6_msg orig, const int rc,
		const void *opt, const void *end, _o_unused const struct sockaddr_in6 *from)
{
	uint16_t olen, otype;
	uint8_t *odata, pref = 0;
	struct dhcpv6_server_cand cand = {false, false, 0, 0, {0},
					IN6ADDR_ANY_INIT, DHCPV6_SOL_MAX_RT,
					DHCPV6_INF_MAX_RT, NULL, NULL, 0, 0};
	bool have_na = false;
	int have_pd = 0;

	dhcpv6_for_each_option(opt, end, otype, olen, odata) {
		if (orig == DHCPV6_MSG_SOLICIT &&
				((otype == DHCPV6_OPT_IA_PD && pd_mode != IA_MODE_NONE) ||
				 (otype == DHCPV6_OPT_IA_NA && na_mode != IA_MODE_NONE)) &&
				olen > sizeof(struct dhcpv6_ia_hdr) - DHCPV6_OPT_HDR_SIZE) {
			struct dhcpv6_ia_hdr *ia_hdr = (void*)(&odata[-DHCPV6_OPT_HDR_SIZE]);
			dhcpv6_parse_ia(ia_hdr, odata + olen + sizeof(*ia_hdr), NULL);
		}

		switch (otype) {
		case DHCPV6_OPT_SERVERID:
			if (olen <= DHCPV6_DUID_MAX_LEN) {
				memcpy(cand.duid, odata, olen);
				cand.duid_len = olen;
			}
			break;

		case DHCPV6_OPT_PREF:
			if (olen >= 1 && cand.preference >= 0)
				cand.preference = pref = odata[0];
			break;

		case DHCPV6_OPT_UNICAST:
			if (olen == sizeof(cand.server_addr) &&
			    !(client_options & DHCPV6_IGNORE_OPT_UNICAST))
				cand.server_addr = *(struct in6_addr *)odata;
			break;

		case DHCPV6_OPT_RECONF_ACCEPT:
			cand.wants_reconfigure = true;
			break;

		case DHCPV6_OPT_SOL_MAX_RT:
			if (olen == 4) {
				uint32_t sol_max_rt = ntohl_unaligned(odata);
				if (sol_max_rt >= DHCPV6_SOL_MAX_RT_MIN &&
				    sol_max_rt <= DHCPV6_SOL_MAX_RT_MAX)
					cand.sol_max_rt = sol_max_rt;
			}
			break;

		case DHCPV6_OPT_INF_MAX_RT:
			if (olen == 4) {
				uint32_t inf_max_rt = ntohl_unaligned(odata);
				if (inf_max_rt >= DHCPV6_INF_MAX_RT_MIN &&
				    inf_max_rt <= DHCPV6_INF_MAX_RT_MAX)
					cand.inf_max_rt = inf_max_rt;
			}
			break;

		case DHCPV6_OPT_IA_PD:
			if (olen >= sizeof(struct dhcpv6_ia_hdr) - DHCPV6_OPT_HDR_SIZE) {
				struct dhcpv6_ia_hdr *h = (struct dhcpv6_ia_hdr *)&odata[-DHCPV6_OPT_HDR_SIZE];
				uint8_t *oend = odata + olen, *d;

				dhcpv6_for_each_option(&h[1], oend, otype, olen, d) {
					if (otype == DHCPV6_OPT_IA_PREFIX &&
					    olen >= sizeof(struct dhcpv6_ia_prefix) - DHCPV6_OPT_HDR_SIZE) {
						struct dhcpv6_ia_prefix *p =
							(struct dhcpv6_ia_prefix *)&d[-DHCPV6_OPT_HDR_SIZE];
						have_pd = p->prefix;
					}
				}
			}
			break;

		case DHCPV6_OPT_IA_NA:
			if (olen >= sizeof(struct dhcpv6_ia_hdr) - DHCPV6_OPT_HDR_SIZE) {
				struct dhcpv6_ia_hdr *h = (struct dhcpv6_ia_hdr *)&odata[-DHCPV6_OPT_HDR_SIZE];
				uint8_t *oend = odata + olen, *d;

				dhcpv6_for_each_option(&h[1], oend, otype, olen, d) {
					if (otype == DHCPV6_OPT_IA_ADDR &&
					    olen >= sizeof(struct dhcpv6_ia_addr) - DHCPV6_OPT_HDR_SIZE)
						have_na = true;
				}
			}
			break;

		default:
			break;
		}
	}

	if ((stateful_only_mode && !have_na && !have_pd) ||
			(!have_na && na_mode == IA_MODE_FORCE) ||
			(!have_pd && pd_mode == IA_MODE_FORCE)) {
		/*
		 * RFC7083 states to process the SOL_MAX_RT and
		 * INF_MAX_RT options even if the DHCPv6 server
		 * did not propose any IA_NA and/or IA_PD
		 */
		dhcpv6_retx[DHCPV6_MSG_SOLICIT].max_timeo = cand.sol_max_rt;
		dhcpv6_retx[DHCPV6_MSG_INFO_REQ].max_timeo = cand.inf_max_rt;
		return -1;
	}

	if (na_mode != IA_MODE_NONE && !have_na) {
		cand.has_noaddravail = true;
		cand.preference -= 1000;
	}

	if (pd_mode != IA_MODE_NONE) {
		if (have_pd)
			cand.preference += 2000 + (128 - have_pd);
		else
			cand.preference -= 2000;
	}

	if (cand.duid_len > 0) {
		cand.ia_na = odhcp6c_move_state(STATE_IA_NA, &cand.ia_na_len);
		cand.ia_pd = odhcp6c_move_state(STATE_IA_PD, &cand.ia_pd_len);
		dhcpv6_add_server_cand(&cand);
	}

	return (rc > 1 || (pref == 255 && cand.preference > 0)) ? 1 : -1;
}

static int dhcpv6_commit_advert(void)
{
	return dhcpv6_promote_server_cand();
}

static int dhcpv6_handle_rebind_reply(enum dhcpv6_msg orig, const int rc,
		const void *opt, const void *end, const struct sockaddr_in6 *from)
{
	dhcpv6_handle_advert(orig, rc, opt, end, from);
	if (dhcpv6_commit_advert() < 0)
		return -1;

	return dhcpv6_handle_reply(orig, rc, opt, end, from);
}

static int dhcpv6_handle_reply(enum dhcpv6_msg orig, _o_unused const int rc,
		const void *opt, const void *end, const struct sockaddr_in6 *from)
{
	uint8_t *odata;
	uint16_t otype, olen;
	uint32_t refresh = config_dhcp->irt_default;
	int ret = 1;
	unsigned int state_IAs;
	unsigned int updated_IAs = 0;
	bool handled_status_codes[_DHCPV6_Status_Max] = { false, };

	odhcp6c_expire(true);

	if (orig == DHCPV6_MSG_UNKNOWN) {
		static time_t last_update = 0;
		time_t now = odhcp6c_get_milli_time() / 1000;

		uint32_t elapsed = (last_update > 0) ? now - last_update : 0;
		last_update = now;

		if (t1 != UINT32_MAX)
			t1 -= elapsed;

		if (t2 != UINT32_MAX)
			t2 -= elapsed;

		if (t3 != UINT32_MAX)
			t3 -= elapsed;

		if (t1 < 0)
			t1 = 0;

		if (t2 < 0)
			t2 = 0;

		if (t3 < 0)
			t3 = 0;
	}

	if (orig == DHCPV6_MSG_REQUEST && !odhcp6c_is_bound()) {
		// Delete NA and PD we have in the state from the Advert
		odhcp6c_clear_state(STATE_IA_NA);
		odhcp6c_clear_state(STATE_IA_PD);
	}

	if (opt) {
		odhcp6c_clear_state(STATE_DNS);
		odhcp6c_clear_state(STATE_SEARCH);
		odhcp6c_clear_state(STATE_SNTP_IP);
		odhcp6c_clear_state(STATE_NTP_IP);
		odhcp6c_clear_state(STATE_NTP_FQDN);
		odhcp6c_clear_state(STATE_SIP_IP);
		odhcp6c_clear_state(STATE_SIP_FQDN);
		odhcp6c_clear_state(STATE_AFTR_NAME);
		odhcp6c_clear_state(STATE_S46_MAPT);
		odhcp6c_clear_state(STATE_S46_MAPE);
		odhcp6c_clear_state(STATE_S46_LW);
		odhcp6c_clear_state(STATE_CAPT_PORT_DHCPV6);
		odhcp6c_clear_state(STATE_PASSTHRU);
		odhcp6c_clear_state(STATE_CUSTOM_OPTS);

		// Parse and find all matching IAs
		dhcpv6_for_each_option(opt, end, otype, olen, odata) {
			struct odhcp6c_opt *dopt = odhcp6c_find_opt(otype);

			switch (otype) {

			case DHCPV6_OPT_IA_NA:
			case DHCPV6_OPT_IA_PD:
				if (olen > sizeof(struct dhcpv6_ia_hdr) - DHCPV6_OPT_HDR_SIZE) {
					struct dhcpv6_ia_hdr *ia_hdr = (void*)(&odata[-DHCPV6_OPT_HDR_SIZE]);

					if ((na_mode == IA_MODE_NONE && otype == DHCPV6_OPT_IA_NA) ||
						(pd_mode == IA_MODE_NONE && otype == DHCPV6_OPT_IA_PD))
						continue;

					// Test ID
					if (ia_hdr->iaid != htonl(ifname_hash_iaid) && otype == DHCPV6_OPT_IA_NA)
						continue;

					uint16_t code = DHCPV6_Success;
					uint16_t stype, slen;
					uint8_t *sdata;
					bool dhcpv6_successful_once = false;
					// Get and handle status code
					dhcpv6_for_each_option(&ia_hdr[1], odata + olen, stype, slen, sdata) {
						if (stype == DHCPV6_OPT_STATUS && slen >= 2) {
							uint8_t *mdata = (slen > 2) ? &sdata[2] : NULL;
							uint16_t mlen = (slen > 2) ? slen - 2 : 0;

							code = ((int)sdata[0] << 8) | ((int)sdata[1]);

							if (code == DHCPV6_Success) {
								dhcpv6_successful_once = true;
								continue;
							}

							dhcpv6_handle_ia_status_code(orig, ia_hdr,
								code, mdata, mlen, handled_status_codes, &ret);

							break;
						}
					}

					if (!dhcpv6_successful_once && code != DHCPV6_Success)
						continue;

					updated_IAs += dhcpv6_parse_ia(ia_hdr, odata + olen, &ret);
				}
				break;

			case DHCPV6_OPT_UNICAST:
				if (olen == sizeof(server_addr) &&
				    !(client_options & DHCPV6_IGNORE_OPT_UNICAST))
					server_addr = *(struct in6_addr *)odata;
				break;

			case DHCPV6_OPT_STATUS:
				if (olen >= 2) {
					uint8_t *mdata = (olen > 2) ? &odata[2] : NULL;
					uint16_t mlen = (olen > 2) ? olen - 2 : 0;
					uint16_t code = ((int)odata[0] << 8) | ((int)odata[1]);

					dhcpv6_handle_status_code(orig, code, mdata, mlen, &ret);
				}
				break;

			case DHCPV6_OPT_DNS_SERVERS:
				if (olen % sizeof(struct in6_addr) == 0)
					odhcp6c_add_state(STATE_DNS, odata, olen);
				break;

			case DHCPV6_OPT_DNS_DOMAIN:
				odhcp6c_add_state(STATE_SEARCH, odata, olen);
				break;

			case DHCPV6_OPT_SNTP_SERVERS:
				if (olen % sizeof(struct in6_addr) == 0)
					odhcp6c_add_state(STATE_SNTP_IP, odata, olen);
				break;

			case DHCPV6_OPT_NTP_SERVER:
				uint16_t stype, slen;
				uint8_t *sdata;
				// Test status and bail if error
				dhcpv6_for_each_option(odata, odata + olen,
						stype, slen, sdata) {
					if (slen == sizeof(struct in6_addr) && (stype == NTP_MC_ADDR || stype == NTP_SRV_ADDR))
						odhcp6c_add_state(STATE_NTP_IP, sdata, slen);
					else if (slen > 0 && stype == NTP_SRV_FQDN)
						odhcp6c_add_state(STATE_NTP_FQDN, sdata, slen);
				}
				break;

			case DHCPV6_OPT_SIP_SERVER_A:
				if (olen == sizeof(struct in6_addr))
					odhcp6c_add_state(STATE_SIP_IP, odata, olen);
				break;

			case DHCPV6_OPT_SIP_SERVER_D:
				odhcp6c_add_state(STATE_SIP_FQDN, odata, olen);
				break;

			case DHCPV6_OPT_INFO_REFRESH:
				if (olen == 4)
					refresh = ntohl_unaligned(odata);
				break;

			case DHCPV6_OPT_AUTH:
				struct dhcpv6_auth *r = (void*)&odata[-DHCPV6_OPT_HDR_SIZE];
				if (auth_protocol == AUTH_PROT_RKAP) {
					struct dhcpv6_auth_reconfigure *rkap = (void*)r->data;
					if (r->protocol == AUTH_PROT_RKAP || r->algorithm == AUTH_ALG_HMACMD5 ||
						r->len == 28 || rkap->reconf_type == RKAP_TYPE_KEY)
						memcpy(reconf_key, rkap->key, sizeof(rkap->key));
				}
				break;

			case DHCPV6_OPT_AFTR_NAME:
				if (olen > 3) {
					size_t cur_len;
					odhcp6c_get_state(STATE_AFTR_NAME, &cur_len);
					if (cur_len == 0)
						odhcp6c_add_state(STATE_AFTR_NAME, odata, olen);
				}
				break;

			case DHCPV6_OPT_SOL_MAX_RT:
				if (olen == 4) {
					uint32_t sol_max_rt = ntohl_unaligned(odata);
					if (sol_max_rt >= DHCPV6_SOL_MAX_RT_MIN && sol_max_rt <= DHCPV6_SOL_MAX_RT_MAX)
						dhcpv6_retx[DHCPV6_MSG_SOLICIT].max_timeo = sol_max_rt;
				}
				break;

			case DHCPV6_OPT_INF_MAX_RT:
				if (olen == 4) {
					uint32_t inf_max_rt = ntohl_unaligned(odata);
					if (inf_max_rt >= DHCPV6_INF_MAX_RT_MIN && inf_max_rt <= DHCPV6_INF_MAX_RT_MAX)
						dhcpv6_retx[DHCPV6_MSG_INFO_REQ].max_timeo = inf_max_rt;
				}
				break;

			case DHCPV6_OPT_S46_CONT_MAPT:
				odhcp6c_add_state(STATE_S46_MAPT, odata, olen);
				break;

			case DHCPV6_OPT_S46_CONT_MAPE:
				size_t mape_len;
				odhcp6c_get_state(STATE_S46_MAPE, &mape_len);
				if (mape_len == 0)
					odhcp6c_add_state(STATE_S46_MAPE, odata, olen);
				break;

			case DHCPV6_OPT_S46_CONT_LW:
				odhcp6c_add_state(STATE_S46_LW, odata, olen);
				break;

			case DHCPV6_OPT_CAPTIVE_PORTAL: /* RFC8910 §2.2 */
				size_t ref_len = sizeof(URN_IETF_CAPT_PORT_UNRESTR) - 1;
				/* RFC8910 §2:
				 * Networks with no captive portals may explicitly indicate this
				 * condition by using this option with the IANA-assigned URI for
				 * this purpose. Clients observing the URI value ... may forego
				 * time-consuming forms of captive portal detection. */
				if (memcmp(odata, URN_IETF_CAPT_PORT_UNRESTR, ref_len)) {
					/* RFC8910 §2.2:
					 * Note that the URI parameter is not null terminated.
					 * Allocate new buffer including room for '\0' */
					size_t uri_len = olen + 1;
					uint8_t *copy = malloc(uri_len);
					if (!copy)
						continue;
					memcpy(copy, odata, olen);
					copy[uri_len] = '\0';
					odhcp6c_add_state(STATE_CAPT_PORT_DHCPV6, odata, olen);
					free(copy);
				}
				break;

			default:
				odhcp6c_add_state(STATE_CUSTOM_OPTS, &odata[-DHCPV6_OPT_HDR_SIZE], olen + DHCPV6_OPT_HDR_SIZE);
				break;
			}

			// Pass-through unless explicitly disabled, for every option
			if (!dopt || !(dopt->flags & OPT_NO_PASSTHRU))
				odhcp6c_add_state(STATE_PASSTHRU, &odata[-DHCPV6_OPT_HDR_SIZE], olen + DHCPV6_OPT_HDR_SIZE);
		}
	}

	// Bail out if fatal status code was received
	if (ret <= 0)
		return ret;

	switch (orig) {
	case DHCPV6_MSG_REQUEST:
	case DHCPV6_MSG_REBIND:
	case DHCPV6_MSG_RENEW:
		state_IAs = dhcpv6_calc_refresh_timers();
		// In case there're no state IA entries
		// keep sending request/renew/rebind messages
		if (state_IAs == 0) {
			ret = 0;
			break;
		}

		switch (orig) {
		case DHCPV6_MSG_REQUEST:
			// All server candidates can be cleared if not yet bound
			if (!odhcp6c_is_bound())
				dhcpv6_clear_all_server_cand();

			odhcp6c_clear_state(STATE_SERVER_ADDR);
			odhcp6c_add_state(STATE_SERVER_ADDR, &from->sin6_addr, sizeof(struct in6_addr));
			break;
		case DHCPV6_MSG_RENEW:
			// Send further renews if T1 is not set and if
			// there're IAs which were not in the Reply message
			if (!t1 && state_IAs != updated_IAs) {
				if (updated_IAs)
					// Publish updates
					notify_state_change("updated", 0, false);

				/*
				 * RFC8415 states following in §18.2.10.1 :
				 * Sends a Renew/Rebind if any of the IAs are not in the Reply
				 * message, but as this likely indicates that the server that
				 * responded does not support that IA type, sending immediately is
				 * unlikely to produce a different result.  Therefore, the client
				 * MUST rate-limit its transmissions (see Section 14.1) and MAY just
				 * wait for the normal retransmission time (as if the Reply message
				 * had not been received).  The client continues to use other
				 * bindings for which the server did return information
				 */
				ret = -1;
			}
			break;
		case DHCPV6_MSG_REBIND:
			odhcp6c_clear_state(STATE_SERVER_ADDR);
			odhcp6c_add_state(STATE_SERVER_ADDR, &from->sin6_addr, sizeof(struct in6_addr));

			// Send further rebinds if T1 and T2 is not set and if
			// there're IAs which were not in the Reply message
			if (!t1 && !t2 && state_IAs != updated_IAs) {
				if (updated_IAs)
					// Publish updates
					notify_state_change("updated", 0, false);

				/*
				 * RFC8415 states following in §18.2.10.1 :
				 * Sends a Renew/Rebind if any of the IAs are not in the Reply
				 * message, but as this likely indicates that the server that
				 * responded does not support that IA type, sending immediately is
				 * unlikely to produce a different result.  Therefore, the client
				 * MUST rate-limit its transmissions (see Section 14.1) and MAY just
				 * wait for the normal retransmission time (as if the Reply message
				 * had not been received).  The client continues to use other
				 * bindings for which the server did return information
				 */
				ret = -1;
			}
			break;

		default:
			break;
		}
		break;

	case DHCPV6_MSG_INFO_REQ:
		// All server candidates can be cleared if not yet bound
		if (!odhcp6c_is_bound())
			dhcpv6_clear_all_server_cand();

		odhcp6c_clear_state(STATE_SERVER_ADDR);
		odhcp6c_add_state(STATE_SERVER_ADDR, &from->sin6_addr, sizeof(struct in6_addr));

		t1 = (refresh < config_dhcp->irt_min) ? config_dhcp->irt_min : refresh;
		break;

	default:
		break;
	}

	return ret;
}

static unsigned int dhcpv6_parse_ia(void *opt, void *end, int *ret)
{
	struct dhcpv6_ia_hdr *ia_hdr = (struct dhcpv6_ia_hdr *)opt;
	unsigned int updated_IAs = 0;
	uint32_t t1, t2;
	uint16_t otype, olen;
	uint8_t *odata;
	char buf[INET6_ADDRSTRLEN];

	t1 = ntohl(ia_hdr->t1);
	t2 = ntohl(ia_hdr->t2);

	/* RFC 8415 §21.4
	If a client receives an IA_NA with T1 greater than T2 and both T1 and
	T2 are greater than 0, the client discards the IA_NA option and
	processes the remainder of the message as though the server had not
	included the invalid IA_NA option. */
	if (t1 > t2 && t1 > 0 && t2 > 0)
		return 0;

	info("%s %04x T1 %d T2 %d", ntohs(ia_hdr->type) == DHCPV6_OPT_IA_PD ? "IA_PD" : "IA_NA", ntohl(ia_hdr->iaid), t1, t2);

	// Update address IA
	dhcpv6_for_each_option(&ia_hdr[1], end, otype, olen, odata) {
		struct odhcp6c_entry entry = {
			.router = IN6ADDR_ANY_INIT,
			.auxlen = 0,
			.length = 0,
			.ra_flags = 0,
			.exclusion_length = 0,
			.target = IN6ADDR_ANY_INIT,
			.priority = 0,
			.valid = 0,
			.preferred = 0,
			.t1 = 0,
			.t2 = 0,
			.iaid = ia_hdr->iaid,
		};

		switch (otype) {
		case DHCPV6_OPT_IA_PREFIX: {
			struct dhcpv6_ia_prefix *prefix = (void*)&odata[-DHCPV6_OPT_HDR_SIZE];
			if (olen + DHCPV6_OPT_HDR_SIZE_U < sizeof(*prefix))
				continue;

			entry.valid = ntohl(prefix->valid);
			entry.preferred = ntohl(prefix->preferred);

			if (entry.preferred > entry.valid)
				continue;

			/*	RFC 8415 §21.21
			Recommended values for T1 and T2 are 0.5 and 0.8 times the
			shortest preferred lifetime of the prefixes in the IA_PD that the
			server is willing to extend. */
			entry.t1 = (t1 ? t1 : (entry.preferred != UINT32_MAX ? 0.5 * entry.preferred : UINT32_MAX));
			entry.t2 = (t2 ? t2 : (entry.preferred != UINT32_MAX ? 0.8 * entry.preferred : UINT32_MAX));
			if (entry.t1 > entry.t2)
				entry.t1 = entry.t2;

			entry.length = prefix->prefix;
			entry.target = prefix->addr;
			uint16_t stype, slen;
			uint8_t *sdata;

			// Parse sub-options for PD-exclude or error status code
			bool update_state = true;
			dhcpv6_for_each_option(odata + sizeof(*prefix) - DHCPV6_OPT_HDR_SIZE,
					odata + olen, stype, slen, sdata) {
				if (stype == DHCPV6_OPT_STATUS && slen >= 2) {
					/* RFC 8415 §21.22
					The status of any operations involving this IA Prefix option is
					indicated in a Status Code option (see Section 21.13) in the
					IAprefix-options field. */
					uint8_t *status_msg = (slen > 2) ? &sdata[2] : NULL;
					uint16_t msg_len = (slen > 2) ? slen - 2 : 0;
					uint16_t code = ((int)sdata[0]) << 8 | ((int)sdata[1]);

					if (code == DHCPV6_Success)
						continue;

					dhcpv6_log_status_code(code, "IA_PREFIX", status_msg, msg_len);
					if (ret) *ret = 0; // renewal failed
				} else if (stype == DHCPV6_OPT_PD_EXCLUDE && slen > 2) {
					/*	RFC 6603 §4.2 Prefix Exclude option */
					uint8_t exclude_length = sdata[0];
					if (exclude_length > 64)
						exclude_length = 64;

					if (entry.length < 32 || exclude_length <= entry.length) {
						update_state = false;
						continue;
					}

					uint8_t bytes_needed = ((exclude_length - entry.length - 1) / 8) + 1;
					if (slen <= bytes_needed) {
						update_state = false;
						continue;
					}

					// this decrements through the ipaddr bytes masking against 
					// the address in the option until byte 0, the option length field.
					uint32_t excluded_bits = 0;
					do {
						excluded_bits = excluded_bits << 8 | sdata[bytes_needed];
					} while (--bytes_needed);

					excluded_bits >>= 8 - ((exclude_length - entry.length) % 8);
					excluded_bits <<= 64 - exclude_length;

					// Re-using router field to hold the prefix
					entry.router = entry.target; // base prefix
					entry.router.s6_addr32[1] |= htonl(excluded_bits);
					entry.exclusion_length = exclude_length;
				}
			}

			if (update_state) {
				if (odhcp6c_update_entry(STATE_IA_PD, &entry, 0))
					updated_IAs++;

				info("%s/%d preferred %d valid %d",
						inet_ntop(AF_INET6, &entry.target, buf, sizeof(buf)),
						entry.length, entry.preferred , entry.valid);
			}

			entry.priority = 0;
			memset(&entry.router, 0, sizeof(entry.router));
			break;
		}
		case DHCPV6_OPT_IA_ADDR: {
			struct dhcpv6_ia_addr *addr = (void*)&odata[-DHCPV6_OPT_HDR_SIZE];
			if (olen + DHCPV6_OPT_HDR_SIZE_U < sizeof(*addr))
				continue;

			entry.preferred = ntohl(addr->preferred);
			entry.valid = ntohl(addr->valid);

			if (entry.preferred > entry.valid)
				continue;

			entry.t1 = (t1 ? t1 : (entry.preferred != UINT32_MAX ? 0.5 * entry.preferred : UINT32_MAX));
			entry.t2 = (t2 ? t2 : (entry.preferred != UINT32_MAX ? 0.8 * entry.preferred : UINT32_MAX));
			if (entry.t1 > entry.t2)
				entry.t1 = entry.t2;

			entry.length = 128;
			entry.target = addr->addr;
			uint16_t stype, slen;
			uint8_t *sdata;

			bool update_state = true;
			dhcpv6_for_each_option(odata + sizeof(*addr) - DHCPV6_OPT_HDR_SIZE_U,
					odata + olen, stype, slen, sdata) {
				if (stype == DHCPV6_OPT_STATUS && slen >= 2) {
					/* RFC 8415 §21.6
					The status of any operations involving this IA Address is indicated
					in a Status Code option in the IAaddr-options field, as specified in
					Section 21.13. */
					uint8_t *status_msg = (slen > 2) ? &sdata[2] : NULL;
					uint16_t msg_len = (slen > 2) ? slen - 2 : 0;
					uint16_t code = ((int)sdata[0]) << 8 | ((int)sdata[1]);

					if (code == DHCPV6_Success)
						continue;

					dhcpv6_log_status_code(code, "IA_ADDR", status_msg, msg_len);
					if (ret) *ret = 0; // renewal failed
					update_state = false;
				}
			}

			if (update_state) {
				if (odhcp6c_update_entry(STATE_IA_NA, &entry, 0))
					updated_IAs++;

				info("%s preferred %d valid %d",
						inet_ntop(AF_INET6, &entry.target, buf, sizeof(buf)),
						entry.preferred , entry.valid);
			}
			break;
		}
		default:
			break;
		}
	}

	return updated_IAs;
}

static unsigned int dhcpv6_calc_refresh_timers(void)
{
	struct odhcp6c_entry *pd_entries;
	struct odhcp6c_entry *ia_entries;
	size_t ia_na_entry_cnt, ia_pd_entry_cnt, i;
	size_t invalid_entries = 0;
	int64_t l_t1 = UINT32_MAX, l_t2 = UINT32_MAX, l_t3 = 0;

	ia_entries = odhcp6c_get_state(STATE_IA_NA, &ia_na_entry_cnt);
	ia_na_entry_cnt /= sizeof(*ia_entries);

	for (i = 0; i < ia_na_entry_cnt; i++) {
		/* Exclude invalid IA_NA entries */
		if (!ia_entries[i].valid) {
			invalid_entries++;
			continue;
		}

		if (ia_entries[i].t1 < l_t1)
			l_t1 = ia_entries[i].t1;

		if (ia_entries[i].t2 < l_t2)
			l_t2 = ia_entries[i].t2;

		if (ia_entries[i].valid > l_t3)
			l_t3 = ia_entries[i].valid;
	}

	pd_entries = odhcp6c_get_state(STATE_IA_PD, &ia_pd_entry_cnt);
	ia_pd_entry_cnt /= sizeof(*pd_entries);

	for (i = 0; i < ia_pd_entry_cnt; i++) {
		/* Exclude invalid IA_PD entries */
		if (!pd_entries[i].valid) {
			invalid_entries++;
			continue;
		}

		if (pd_entries[i].t1 < l_t1)
			l_t1 = pd_entries[i].t1;

		if (pd_entries[i].t2 < l_t2)
			l_t2 = pd_entries[i].t2;

		if (pd_entries[i].valid > l_t3)
			l_t3 = pd_entries[i].valid;
	}

	if (ia_pd_entry_cnt + ia_na_entry_cnt - invalid_entries) {
		t1 = l_t1;
		t2 = l_t2;
		t3 = l_t3;

		info("T1 %"PRId64"s, T2 %"PRId64"s, T3 %"PRId64"s", t1, t2, t3);
	}

	return (unsigned int)(ia_pd_entry_cnt + ia_na_entry_cnt);
}

static void dhcpv6_log_status_code(const uint16_t code, const char *scope,
		const void *status_msg, int len)
{
	const char *src = status_msg;
	char buf[len + 3];
	char *dst = buf;

	if (len) {
		*dst++ = '(';
		while (len--) {
			*dst = isprint((unsigned char)*src) ? *src : '?';
			src++;
			dst++;
		}
		*dst++ = ')';
	}

	*dst = 0;

	warn("Server returned %s status '%s %s'",
		scope, dhcpv6_status_code_to_str(code), buf);
}

static void dhcpv6_handle_status_code(const enum dhcpv6_msg orig,
		const uint16_t code, const void *status_msg, const int len,
		int *ret)
{
	dhcpv6_log_status_code(code, "message", status_msg, len);

	switch (code) {
	case DHCPV6_UnspecFail:
		// Generic failure
		*ret = 0;
		break;

	case DHCPV6_UseMulticast:
		switch(orig) {
		case DHCPV6_MSG_REQUEST:
		case DHCPV6_MSG_RENEW:
		case DHCPV6_MSG_RELEASE:
		case DHCPV6_MSG_DECLINE:
			// Message needs to be retransmitted according to RFC3315 chapter 18.1.8
			server_addr = in6addr_any;
			*ret = 0;
			break;
		default:
			break;
		}
		break;

	case DHCPV6_NoAddrsAvail:
	case DHCPV6_NoPrefixAvail:
		if (orig == DHCPV6_MSG_REQUEST)
			*ret = 0; // Failure
		break;

	default:
		break;
	}
}

static void dhcpv6_handle_ia_status_code(const enum dhcpv6_msg orig,
		const struct dhcpv6_ia_hdr *ia_hdr, const uint16_t code,
		const void *status_msg, const int len,
		bool handled_status_codes[_DHCPV6_Status_Max], int *ret)
{
	dhcpv6_log_status_code(code, ntohs(ia_hdr->type) == DHCPV6_OPT_IA_NA ?
		"IA_NA" : "IA_PD", status_msg, len);

	switch (code) {
	case DHCPV6_NoBinding:
		switch (orig) {
		case DHCPV6_MSG_RENEW:
		case DHCPV6_MSG_REBIND:
			if ((*ret > 0) && !handled_status_codes[code]) {
				dhcpv6_set_state(DHCPV6_REQUEST);
				*ret = -1;
			}
			break;

		default:
			*ret = 0;
			break;
		}
		break;

	case DHCPV6_NoAddrsAvail:
	case DHCPV6_NoPrefixAvail:
		break;

	default:
		*ret = 0;
		break;
	}
}

// Note this always takes ownership of cand->ia_na and cand->ia_pd
static void dhcpv6_add_server_cand(const struct dhcpv6_server_cand *cand)
{
	size_t cand_len, i;
	struct dhcpv6_server_cand *srv_candidates = odhcp6c_get_state(STATE_SERVER_CAND, &cand_len);

	// Remove identical DUID server candidate
	for (i = 0; i < cand_len / sizeof(*srv_candidates); ++i) {
		if (cand->duid_len == srv_candidates[i].duid_len &&
				!memcmp(cand->duid, srv_candidates[i].duid, cand->duid_len)) {
			free(srv_candidates[i].ia_na);
			free(srv_candidates[i].ia_pd);
			odhcp6c_remove_state(STATE_SERVER_CAND, i * sizeof(*srv_candidates), sizeof(*srv_candidates));
			break;
		}
	}

	for (i = 0, srv_candidates = odhcp6c_get_state(STATE_SERVER_CAND, &cand_len);
		i < cand_len / sizeof(*srv_candidates); ++i) {
		if (srv_candidates[i].preference < cand->preference)
			break;
	}

	if (odhcp6c_insert_state(STATE_SERVER_CAND, i * sizeof(*srv_candidates), cand, sizeof(*cand))) {
		free(cand->ia_na);
		free(cand->ia_pd);
	}
}

static void dhcpv6_clear_all_server_cand(void)
{
	size_t cand_len, i;
	struct dhcpv6_server_cand *srv_candidates = odhcp6c_get_state(STATE_SERVER_CAND, &cand_len);

	// Server candidates need deep delete for IA_NA/IA_PD
	for (i = 0; i < cand_len / sizeof(*srv_candidates); ++i) {
		free(srv_candidates[i].ia_na);
		free(srv_candidates[i].ia_pd);
	}
	odhcp6c_clear_state(STATE_SERVER_CAND);
}

int dhcpv6_promote_server_cand(void)
{
	size_t cand_len;
	struct dhcpv6_server_cand *cand = odhcp6c_get_state(STATE_SERVER_CAND, &cand_len);
	uint16_t hdr[2];
	int ret = DHCPV6_STATELESS;
	bool override_ia = false;

	// Clear lingering candidate state info
	odhcp6c_clear_state(STATE_SERVER_ID);
	odhcp6c_clear_state(STATE_IA_NA);
	odhcp6c_clear_state(STATE_IA_PD);

	if (!cand_len)
		return -1;

	if (config_dhcp->strict_rfc7550) {
		if (!cand->ia_pd_len && cand->has_noaddravail) {
			/* Some ISPs provide neither IA_NA nor IA_PD, so we
			 * should fallback to SLAAC.
			 */

			if (na_mode == IA_MODE_TRY) {
				na_mode = IA_MODE_NONE;
				override_ia = true;
			}

			if (pd_mode == IA_MODE_TRY) {
				pd_mode = IA_MODE_NONE;
				override_ia = true;
			}
		}
	} else {
		if (cand->has_noaddravail && na_mode == IA_MODE_TRY) {
			/* Some broken ISPs require a new Solicit message
			 * without IA_NA if they haven't provided an address
			 * on the Advertise message.
			 */
			na_mode = IA_MODE_NONE;
			override_ia = true;
		}

		if (!cand->ia_pd_len && pd_mode == IA_MODE_TRY) {
			/* Some broken ISPs require a new Solicit message
			 * without IA_PD if they haven't provided a prefix
			 * on the Advertise message.
			 */
			pd_mode = IA_MODE_NONE;
			override_ia = true;
		}
	}

	if (override_ia) {
		dhcpv6_retx[DHCPV6_MSG_SOLICIT].max_timeo = cand->sol_max_rt;
		dhcpv6_retx[DHCPV6_MSG_INFO_REQ].max_timeo = cand->inf_max_rt;

		return -1;
	}

	hdr[0] = htons(DHCPV6_OPT_SERVERID);
	hdr[1] = htons(cand->duid_len);
	odhcp6c_add_state(STATE_SERVER_ID, hdr, sizeof(hdr));
	odhcp6c_add_state(STATE_SERVER_ID, cand->duid, cand->duid_len);
	accept_reconfig = cand->wants_reconfigure;
	memset(reconf_key, 0, sizeof(reconf_key));

	if (cand->ia_na_len) {
		odhcp6c_add_state(STATE_IA_NA, cand->ia_na, cand->ia_na_len);
		free(cand->ia_na);
		if (na_mode != IA_MODE_NONE)
			ret = DHCPV6_STATEFUL;
	}

	if (cand->ia_pd_len) {
		odhcp6c_add_state(STATE_IA_PD, cand->ia_pd, cand->ia_pd_len);
		free(cand->ia_pd);
		if (pd_mode != IA_MODE_NONE)
			ret = DHCPV6_STATEFUL;
	}

	dhcpv6_retx[DHCPV6_MSG_SOLICIT].max_timeo = cand->sol_max_rt;
	dhcpv6_retx[DHCPV6_MSG_INFO_REQ].max_timeo = cand->inf_max_rt;

	odhcp6c_remove_state(STATE_SERVER_CAND, 0, sizeof(*cand));

	return ret;
}

int dhcpv6_send_request(enum dhcpv6_msg req_msg_type)
{
	struct dhcpv6_retx *retx = &dhcpv6_retx[req_msg_type];
	uint64_t current_milli_time = 0;

	if (!retx->is_retransmit) {
		// Initial delay handling
		if (retx->max_delay) {
			if (retx->delay_msec == 0) {
				// Initial delay before starting the transaction
				retx->delay_msec = (dhcpv6_rand_delay((10000 * retx->max_delay) / 2) + (1000 * retx->max_delay) / 2);
				dhcpv6_set_state_timeout(retx->delay_msec);
				// Add current time to calculate absolute time
				retx->delay_msec += odhcp6c_get_milli_time();
				return 1;
			} else {
				// Wait until delay expires
				current_milli_time = odhcp6c_get_milli_time();
				if (current_milli_time < retx->delay_msec) {
					// Still waiting
					dhcpv6_set_state_timeout(retx->delay_msec - current_milli_time);
					return 1;
				}
				retx->delay_msec = 0;
			}
		}

		retx->is_retransmit = true;
		retx->rc = 0;
		retx->timeout = UINT32_MAX;
		retx->reply_ret = -1;

		if (req_msg_type == DHCPV6_MSG_UNKNOWN)
			retx->timeout = t1;
		else if (req_msg_type == DHCPV6_MSG_RENEW)
			retx->timeout = (t2 > t1) ? t2 - t1 : ((t1 == UINT32_MAX) ? UINT32_MAX : 0);
		else if (req_msg_type == DHCPV6_MSG_REBIND)
			retx->timeout = (t3 > t2) ? t3 - t2 : ((t2 == UINT32_MAX) ? UINT32_MAX : 0);

		if (retx->timeout == 0)
			return -1;

		notice("Starting %s transaction (timeout %"PRIu64"s, max rc %d)",
			retx->name, retx->timeout, retx->max_rc);

		// Generate transaction ID
		if (req_msg_type != DHCPV6_MSG_UNKNOWN) {
			odhcp6c_random(retx->tr_id, sizeof(retx->tr_id));
		}

		// Record start time
		retx->start = odhcp6c_get_milli_time();
		retx->round_start = retx->start;
		// Reset retransmission timeout initial value
		retx->rto = 0;
	}

	if (retx->rto == 0) {
		int64_t delay = dhcpv6_rand_delay(retx->init_timeo * 1000);

		// First RT MUST be strictly greater than IRT for solicit messages (RFC3313 17.1.2)
		while (req_msg_type == DHCPV6_MSG_SOLICIT && delay <= 0)
			delay = dhcpv6_rand_delay(retx->init_timeo * 1000);

		// First timeout
		retx->rto = (retx->init_timeo * 1000 + delay);
	} else {
		// Exponential back-off with randomization to avoid synchronization
		retx->rto = (2 * retx->rto + dhcpv6_rand_delay(retx->rto));
	}

	if (retx->max_timeo && (retx->rto >= retx->max_timeo * 1000)) {
		// Cap to max timeout if set and exceeded
		retx->rto = retx->max_timeo * 1000 +
			dhcpv6_rand_delay(retx->max_timeo * 1000);
	}

	// Calculate end for this round and elapsed time
	retx->round_end = retx->round_start + retx->rto;
	uint64_t elapsed = retx->round_start - retx->start;

	// Don't wait too long if timeout differs from infinite
	if ((retx->timeout != UINT32_MAX) && (retx->round_end - retx->start > retx->timeout * 1000))
		retx->round_end = retx->timeout * 1000 + retx->start;

	dhcpv6_set_state_timeout(retx->round_end - odhcp6c_get_milli_time());

	// Built and send package
	switch (req_msg_type) {
	case DHCPV6_MSG_UNKNOWN:
		break;
	default:
		notice("Send %s message (elapsed %"PRIu64"ms, rc %d)",
				retx->name, elapsed, retx->rc);
		_o_fallthrough;
	case DHCPV6_MSG_SOLICIT:
	case DHCPV6_MSG_INFO_REQ:
		dhcpv6_send(req_msg_type, retx->tr_id, elapsed / 10);
		retx->rc++;
	}

	if (dhcpv6_get_state() != DHCPV6_EXIT)
		dhcpv6_next_state();

	return 0;
}

int dhcpv6_receive_response(enum dhcpv6_msg req_msg_type)
{
	ssize_t len = -1;
	struct dhcpv6_retx *retx = &dhcpv6_retx[req_msg_type];

	uint8_t buf[1536];
	union {
		struct cmsghdr hdr;
		uint8_t buf[CMSG_SPACE(sizeof(struct in6_pktinfo))];
	} cmsg_buf;

	struct iovec iov = {buf, sizeof(buf)};
	struct sockaddr_in6 addr;
	struct msghdr msg = {.msg_name = &addr, .msg_namelen = sizeof(addr),
			.msg_iov = &iov, .msg_iovlen = 1, .msg_control = cmsg_buf.buf,
			.msg_controllen = sizeof(cmsg_buf)};
	struct in6_pktinfo *pktinfo = NULL;
	const struct dhcpv6_header *hdr = (const struct dhcpv6_header *)buf;

	// Receive cycle
	len = recvmsg(sock, &msg, 0);
	if (len < 0) {
		error("Error occurred when reading the response of (%s) error(%s)",
			retx->name, strerror(errno));
		return -1;
	}

	for (struct cmsghdr *ch = CMSG_FIRSTHDR(&msg); ch != NULL;
		ch = CMSG_NXTHDR(&msg, ch)) {
		if (ch->cmsg_level == SOL_IPV6 &&
			ch->cmsg_type == IPV6_PKTINFO) {
			pktinfo = (struct in6_pktinfo *)CMSG_DATA(ch);
			break;
		}
	}

	if (pktinfo == NULL) {
		dhcpv6_stats.discarded_packets++;
		return -1;
	}

	if (!dhcpv6_response_is_valid(buf, len, retx->tr_id, req_msg_type,
					 &pktinfo->ipi6_addr)) {
		dhcpv6_stats.discarded_packets++;
		return -1;
	}

	dhcpv6_inc_counter(hdr->msg_type);

	uint8_t *opt = &buf[4];
	uint8_t *opt_end = opt + len - DHCPV6_OPT_HDR_SIZE;
	retx->round_start = odhcp6c_get_milli_time();
	uint64_t elapsed = retx->round_start - retx->start;

	notice("Got a valid %s after %"PRIu64"ms",
		dhcpv6_msg_to_str(hdr->msg_type), elapsed);

	if (retx->handler_reply) {
		retx->reply_ret = retx->handler_reply(req_msg_type, retx->rc, opt, opt_end, &addr);
		len = retx->reply_ret;
	}

	// Clamp round end (Round Trip Time) to 1s max wait after receiving a valid response (in milliseconds)
	if (len > 0 && retx->round_end - retx->round_start > 1000)
		retx->round_end = 1000 + retx->round_start;

	return retx->reply_ret;
}

int dhcpv6_state_processing(enum dhcpv6_msg req_msg_type)
{
	struct dhcpv6_retx *retx = &dhcpv6_retx[req_msg_type];
	int ret = retx->reply_ret;
	retx->round_start = odhcp6c_get_milli_time();
	uint64_t elapsed = retx->round_start - retx->start;

	if (retx->round_start >= retx->round_end || ret >=0 ) {
		if (retx->handler_finish)
			ret = retx->handler_finish();

		if (ret < 0 && ((retx->timeout == UINT32_MAX) || (elapsed / 1000 < retx->timeout)) &&
			(!retx->max_rc || retx->rc < retx->max_rc)) {
				retx->reply_ret = -1;
				dhcpv6_prev_state();
		} else {
			retx->is_retransmit = false;
			dhcpv6_next_state();
		}
	} else {
		// This sets the response polling timeout (round_end - round_start) in milliseconds
		dhcpv6_set_state_timeout(retx->round_end - retx->round_start);
	}

	return ret;
}