path: root/libdhcp/client.c

/* libdhcp/client.c - A DHCP client
 *
 * Copyright (C) 2024  Luke T. Shumaker <lukeshu@lukeshu.com>
 * SPDX-License-Identifier: AGPL-3.0-or-later
 *
 * -----------------------------------------------------------------------------
 * https://github.com/Wiznet/ioLibrary_Driver/blob/b981401e7f3d07015619adf44c13998e13e777f9/Internet/DHCP/dhcp.c
 *
 * Copyright (c)  2013, WIZnet Co., LTD.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 *     * Neither the name of the <ORGANIZATION> nor the names of its
 * contributors may be used to endorse or promote products derived
 * from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * -----------------------------------------------------------------------------
 * https://github.com/Wiznet/ioLibrary_Driver/blob/b981401e7f3d07015619adf44c13998e13e777f9/license.txt
 *
 * Copyright (c) 2014 WIZnet Co.,Ltd.
 * Copyright (c) WIZnet ioLibrary Project.
 * All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 * SPDX-License-Identifier: MIT
 */

#include <string.h> /* for strlen(), memcpy(), memset() */

#include <libmisc/endian.h>
#include <libmisc/vcall.h>

#include <libdhcp/client.h>

/* Config *********************************************************************/

#include "config.h"

#ifndef CONFIG_DHCP_DEBUG
	#define CONFIG_DHCP_DEBUG               1
#endif
#ifndef CONFIG_DHCP_HOPS
	#define CONFIG_DHCP_HOPS                0
#endif
#ifndef CONFIG_DHCP_SECS
	#define CONFIG_DHCP_SECS                0
#endif
#ifndef CONFIG_DHCP_SELECTING_NS
	#define CONFIG_DHCP_SELECTING_NS        (5*NS_PER_S)
#endif
#ifndef CONFIG_DHCP_OPT_SIZE
	#define CONFIG_DHCP_OPT_SIZE            312
#endif

/* RFC 2131 definitions *******************************************************/

/** https://datatracker.ietf.org/doc/html/rfc2131#page-9 */
struct dhcp_msg {
	uint8_t                 op;         /* DHCP_OP_{x} */
	uint8_t                 htype;      /* DHCP_HTYPE_{x} */
	uint8_t                 hlen;       /* length of ->chaddr (`sizeof(struct net_eth_addr)`) */
	uint8_t                 hops;

	uint32be_t              xid;        /* transaction ID */

	uint16be_t              secs;
	uint16be_t              flags;      /* DHCP_FLAG_{x} */

	struct net_ip4_addr     ciaddr;     /* Request IP to DHCP sever */
	struct net_ip4_addr     yiaddr;     /* Offered IP from DHCP server */
	struct net_ip4_addr     siaddr;     /* next-server IP address (not used) */
	struct net_ip4_addr     giaddr;     /* relay-agent IP address (not used) */
	uint8_t                 chaddr[16]; /* client hardware (MAC) address */
	uint8_t                 sname[64];  /* server name (not used) */
	uint8_t                 file[128];  /* boot file name (not used) */

	uint8_t                 options[CONFIG_DHCP_OPT_SIZE];
};
static_assert(offsetof(struct dhcp_msg, options) == 236);
#define DHCP_MSG_BASE_SIZE       offsetof(struct dhcp_msg, options)

/** https://datatracker.ietf.org/doc/html/rfc2131#page-10 */
#define DHCP_OP_BOOTREQUEST      1
#define DHCP_OP_BOOTREPLY        2

/** https://datatracker.ietf.org/doc/html/rfc2131#page-11 */
#define DHCP_FLAG_BROADCAST      0x8000

/** https://datatracker.ietf.org/doc/html/rfc2131#section-3 */
static const uint8_t dhcp_magic_cookie[] = {99, 130, 83, 99};

/** https://datatracker.ietf.org/doc/html/rfc2131#section-3.3 */
#define DHCP_INFINITY            0xffffffff

/* IANA assignments ***********************************************************/

/**
 * Port Numbers
 * https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml
 */
#define DHCP_PORT_SERVER                ((uint16_t)67)
#define DHCP_PORT_CLIENT                ((uint16_t)68)

/**
 * Hardware Types
 * https://www.iana.org/assignments/arp-parameters/arp-parameters.xhtml#arp-parameters-2
 */
#define DHCP_HTYPE_ETHERNET             ((uint8_t)  1)

/**
 * DHCP Options
 * https://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml#options
 */
#define DHCP_OPT_PAD                    ((uint8_t)  0) /* RFC2132: length: 0; meaning: None */
#define DHCP_OPT_SUBNET_MASK            ((uint8_t)  1) /* RFC2132: length: 4; meaning: Subnet Mask Value */
#define DHCP_OPT_TIME_OFFSET            ((uint8_t)  2) /* RFC2132: length: 4; meaning: Time Offset in Seconds from UTC (note: deprecated by 100 and 101 */
#define DHCP_OPT_ROUTER                 ((uint8_t)  3) /* RFC2132: length: N; meaning: N/4 Router addresses */
#define DHCP_OPT_TIME_SERVER            ((uint8_t)  4) /* RFC2132: length: N; meaning: N/4 Timeserver addresses */
#define DHCP_OPT_NAME_SERVER            ((uint8_t)  5) /* RFC2132: length: N; meaning: N/4 IEN-116 Server addresses */
#define DHCP_OPT_DOMAIN_SERVER          ((uint8_t)  6) /* RFC2132: length: N; meaning: N/4 DNS Server addresses */
#define DHCP_OPT_LOG_SERVER             ((uint8_t)  7) /* RFC2132: length: N; meaning: N/4 Logging Server addresses */
#define DHCP_OPT_QUOTES_SERVER          ((uint8_t)  8) /* RFC2132: length: N; meaning: N/4 Quotes Server addresses */
#define DHCP_OPT_LPR_SERVER             ((uint8_t)  9) /* RFC2132: length: N; meaning: N/4 Printer Server addresses */
#define DHCP_OPT_IMPRESS_SERVER         ((uint8_t) 10) /* RFC2132: length: N; meaning: N/4 Impress Server addresses */
#define DHCP_OPT_RLP_SERVER             ((uint8_t) 11) /* RFC2132: length: N; meaning: N/4 RLP Server addresses */
#define DHCP_OPT_HOSTNAME               ((uint8_t) 12) /* RFC2132: length: N; meaning: Hostname string */
#define DHCP_OPT_BOOT_FILE_SIZE         ((uint8_t) 13) /* RFC2132: length: 2; meaning: Size of boot file in 512 byte chunks */
#define DHCP_OPT_MERIT_DUMP_FILE        ((uint8_t) 14) /* RFC2132: length: N; meaning: Client to dump and name the file to dump it to */
#define DHCP_OPT_DOMAIN_NAME            ((uint8_t) 15) /* RFC2132: length: N; meaning: The DNS domain name of the client */
#define DHCP_OPT_SWAP_SERVER            ((uint8_t) 16) /* RFC2132: length: N; meaning: Swap Server address */
#define DHCP_OPT_ROOT_PATH              ((uint8_t) 17) /* RFC2132: length: N; meaning: Path name for root disk */
#define DHCP_OPT_EXTENSION_FILE         ((uint8_t) 18) /* RFC2132: length: N; meaning: Path name for more BOOTP info */
#define DHCP_OPT_FORWARD_ONOFF          ((uint8_t) 19) /* RFC2132: length: 1; meaning: Enable/Disable IP Forwarding */
#define DHCP_OPT_SRCRTE_ONOFF           ((uint8_t) 20) /* RFC2132: length: 1; meaning: Enable/Disable Source Routing */
#define DHCP_OPT_POLICY_FILTER          ((uint8_t) 21) /* RFC2132: length: N; meaning: Routing Policy Filters */
#define DHCP_OPT_MAX_DG_ASSEMBLY        ((uint8_t) 22) /* RFC2132: length: 2; meaning: Max Datagram Reassembly Size */
#define DHCP_OPT_DEFAULT_IP_TTL         ((uint8_t) 23) /* RFC2132: length: 1; meaning: Default IP Time to Live */
#define DHCP_OPT_MTU_TIMEOUT            ((uint8_t) 24) /* RFC2132: length: 4; meaning: Path MTU Aging Timeout */
#define DHCP_OPT_MTU_PLATEAU            ((uint8_t) 25) /* RFC2132: length: N; meaning: Path MTU Plateau Table */
#define DHCP_OPT_MTU_INTERFACE          ((uint8_t) 26) /* RFC2132: length: 2; meaning: Interface MTU Size */
#define DHCP_OPT_MTU_SUBNET             ((uint8_t) 27) /* RFC2132: length: 1; meaning: All Subnets are Local */
#define DHCP_OPT_BROADCAST_ADDRESS      ((uint8_t) 28) /* RFC2132: length: 4; meaning: Broadcast Address */
#define DHCP_OPT_MASK_DISCOVERY         ((uint8_t) 29) /* RFC2132: length: 1; meaning: Perform Mask Discovery */
#define DHCP_OPT_MASK_SUPPLIER          ((uint8_t) 30) /* RFC2132: length: 1; meaning: Provide Mask to Others */
#define DHCP_OPT_ROUTER_DISCOVERY       ((uint8_t) 31) /* RFC2132: length: 1; meaning: Perform Router Discovery */
#define DHCP_OPT_ROUTER_REQUEST         ((uint8_t) 32) /* RFC2132: length: 4; meaning: Router Solicitation Address */
#define DHCP_OPT_STATIC_ROUTE           ((uint8_t) 33) /* RFC2132: length: N; meaning: Static Routing Table */
#define DHCP_OPT_TRAILERS               ((uint8_t) 34) /* RFC2132: length: 1; meaning: Trailer Encapsulation */
#define DHCP_OPT_ARP_TIMEOUT            ((uint8_t) 35) /* RFC2132: length: 4; meaning: ARP Cache Timeout */
#define DHCP_OPT_ETHERNET               ((uint8_t) 36) /* RFC2132: length: 1; meaning: Ethernet Encapsulation */
#define DHCP_OPT_DEFAULT_TCP_TTL        ((uint8_t) 37) /* RFC2132: length: 1; meaning: Default TCP Time to Live */
#define DHCP_OPT_KEEPALIVE_TIME         ((uint8_t) 38) /* RFC2132: length: 4; meaning: TCP Keepalive Interval */
#define DHCP_OPT_KEEPALIVE_DATA         ((uint8_t) 39) /* RFC2132: length: 1; meaning: TCP Keepalive Garbage */
#define DHCP_OPT_NIS_DOMAIN             ((uint8_t) 40) /* RFC2132: length: N; meaning: NIS Domain Name */
#define DHCP_OPT_NIS_SERVERS            ((uint8_t) 41) /* RFC2132: length: N; meaning: NIS Server Addresses */
#define DHCP_OPT_NTP_SERVERS            ((uint8_t) 42) /* RFC2132: length: N; meaning: NTP Server Addresses */
#define DHCP_OPT_VENDOR_SPECIFIC        ((uint8_t) 43) /* RFC2132: length: N; meaning: Vendor Specific Information */
#define DHCP_OPT_NETBIOS_NAME_SRV       ((uint8_t) 44) /* RFC2132: length: N; meaning: NETBIOS Name Servers */
#define DHCP_OPT_NETBIOS_DIST_SRV       ((uint8_t) 45) /* RFC2132: length: N; meaning: NETBIOS Datagram Distribution */
#define DHCP_OPT_NETBIOS_NODE_TYPE      ((uint8_t) 46) /* RFC2132: length: 1; meaning: NETBIOS Node Type */
#define DHCP_OPT_NETBIOS_SCOPE          ((uint8_t) 47) /* RFC2132: length: N; meaning: NETBIOS Scope */
#define DHCP_OPT_X_WINDOW_FONT          ((uint8_t) 48) /* RFC2132: length: N; meaning: X Window Font Server */
#define DHCP_OPT_X_WINDOW_MANAGER       ((uint8_t) 49) /* RFC2132: length: N; meaning: X Window Display Manager */
#define DHCP_OPT_ADDRESS_REQUEST        ((uint8_t) 50) /* RFC2132: length: 4; meaning: Requested IP Address */
#define DHCP_OPT_ADDRESS_TIME           ((uint8_t) 51) /* RFC2132: length: 4; meaning: IP Address Lease Time */
#define DHCP_OPT_OVERLOAD               ((uint8_t) 52) /* RFC2132: length: 1; meaning: Overload "sname" or "file */
#define DHCP_OPT_DHCP_MSG_TYPE          ((uint8_t) 53) /* RFC2132: length: 1; meaning: DHCP Message Type */
#define DHCP_OPT_DHCP_SERVER_ID         ((uint8_t) 54) /* RFC2132: length: 4; meaning: DHCP Server Identification */
#define DHCP_OPT_PARAMETER_LIST         ((uint8_t) 55) /* RFC2132: length: N; meaning: Parameter Request List */
#define DHCP_OPT_DHCP_MESSAGE           ((uint8_t) 56) /* RFC2132: length: N; meaning: DHCP Error Message */
#define DHCP_OPT_DHCP_MAX_MSG_SIZE      ((uint8_t) 57) /* RFC2132: length: 2; meaning: DHCP Maximum Message Size */
#define DHCP_OPT_RENEWAL_TIME           ((uint8_t) 58) /* RFC2132: length: 4; meaning: DHCP Renewal (T1) Time */
#define DHCP_OPT_REBINDING_TIME         ((uint8_t) 59) /* RFC2132: length: 4; meaning: DHCP Rebinding (T2) Time */
#define DHCP_OPT_CLASS_ID               ((uint8_t) 60) /* RFC2132: length: N; meaning: Class Identifier */
#define DHCP_OPT_CLIENT_ID              ((uint8_t) 61) /* RFC2132: length: N; meaning: Client Identifier */
#define DHCP_OPT_END                    ((uint8_t)255) /* RFC2132: length: 0; meaning: None */

/**
 * DHCP Message Type 53 Values
 * https://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml#message-type-53
 */
#define DHCP_MSGTYP_DISCOVER            ((uint8_t)  1) /* RFC2132 */
#define DHCP_MSGTYP_OFFER               ((uint8_t)  2) /* RFC2132 */
#define DHCP_MSGTYP_REQUEST             ((uint8_t)  3) /* RFC2132 */
#define DHCP_MSGTYP_DECLINE             ((uint8_t)  4) /* RFC2132 */
#define DHCP_MSGTYP_ACK                 ((uint8_t)  5) /* RFC2132 */
#define DHCP_MSGTYP_NAK                 ((uint8_t)  6) /* RFC2132 */
#define DHCP_MSGTYP_RELEASE             ((uint8_t)  7) /* RFC2132 */
#define DHCP_MSGTYP_INFORM              ((uint8_t)  8) /* RFC2132 */

/* Implementation *************************************************************/

#if CONFIG_DHCP_DEBUG
	#include <stdio.h>
	#define debugf(fmt, ...) printf(fmt "\n" __VA_OPT__(,) __VA_ARGS__)
#else
	#define debugf(fmt, ...) ((void)0)
#endif

/* DHCP state machine.  */
#define STATE_DHCP_INIT          0  /* Initialize */
#define STATE_DHCP_DISCOVER      1  /* send DISCOVER and wait OFFER */
#define STATE_DHCP_REQUEST       2  /* send REQEUST and wait ACK or NACK */
#define STATE_DHCP_LEASED        3  /* ReceiveD ACK and IP leased */
#define STATE_DHCP_REREQUEST     4  /* send REQUEST for maintaining leased IP */
#define STATE_DHCP_RELEASE       5  /* No use */
#define STATE_DHCP_STOP          6  /* Stop processing DHCP */

/* Global state.  */
struct net_ip4_addr DHCP_SIP;                           /* DHCP Server IP address */
struct net_ip4_addr DHCP_REAL_SIP;                      /* For extract my DHCP server in a few DHCP server */
struct net_ip4_addr OLD_allocated_ip = {0};             /* Previous IP address */
struct dhcp_lease   global_lease     = {.lifetime = DHCP_INFINITY};
int8_t              dhcp_state       = STATE_DHCP_INIT; /* DHCP state */
int8_t              dhcp_retry_count = 0;
volatile uint32_t   dhcp_tick_1s     = 0;               /* unit 1 second */
uint32_t            dhcp_tick_next   = DHCP_WAIT_TIME ;
char                global_hostname[64];
struct net_eth_addr global_eth_addr;                    /* DHCP Client MAC address. */

#define mem_encode(dst, obj) ({           \
	typeof(obj) _obj = obj;           \
	memcpy(dst, &_obj, sizeof(_obj)); \
	sizeof(_obj);                     \
})

static inline size_t str_encode(void *dst, char *str) {
	size_t len = strlen(str);
	memcpy(dst, str, len);
	return len;
}

/* make the common DHCP message */
static inline void dhcp_msg_init(struct dhcp_msg *msg, size_t *optlen,
                                 struct net_eth_addr self_eth_addr,
                                 uint16_t flags, uint32_t xid) {
	size_t tmp;

	assert(msg);
	assert(optlen);

	*msg = (struct dhcp_msg){0};

	msg->op     = DHCP_OP_BOOTREQUEST;
	msg->htype  = DHCP_HTYPE_ETHERNET;
	msg->hlen   = sizeof(self_eth_addr);
	msg->hops   = CONFIG_DHCP_HOPS;
	msg->xid    = uint32be_marshal(xid);
	msg->secs   = uint16be_marshal(CONFIG_DHCP_SECS);
	msg->flags  = uint16be_marshal(flags);
	msg->ciaddr = (struct net_ip4_addr){0};
	msg->yiaddr = (struct net_ip4_addr){0};
	msg->siaddr = (struct net_ip4_addr){0};
	msg->siaddr = (struct net_ip4_addr){0};
	msg->giaddr = (struct net_ip4_addr){0};

	tmp = mem_encode(msg->chaddr, self_eth_addr);
	memset(&msg->chaddr[tmp], 0, sizeof(msg->chaddr)-tmp);

	memset(msg->sname, 0, sizeof(msg->sname));
	memset(msg->file, 0, sizeof(msg->file));

	*optlen = 0;
	msg->options[*optlen++] = dhcp_magic_cookie[0];
	msg->options[*optlen++] = dhcp_magic_cookie[1];
	msg->options[*optlen++] = dhcp_magic_cookie[2];
	msg->options[*optlen++] = dhcp_magic_cookie[3];
}

static void dhcp_send_DISCOVER(implements_net_packet_conn *sock) {
	struct dhcp_msg msg;
	size_t k;

	dhcp_msg_init(&msg, &k, DHCP_FLAG_BROADCAST);
	DHCP_SIP = (struct net_ip4_addr){0};
	DHCP_REAL_SIP = (struct net_ip4_addr){0};

	/* Message type.  */
	msg->options[k++] = DHCP_OPT_DHCP_MSG_TYPE;
	msg->options[k++] = 1;
	msg->options[k++] = DHCP_MSGTYP_DISCOVER;

	/* Our Client ID.  */
	msg->options[k++] = DHCP_OPT_CLIENT_ID;
	msg->options[k++] = 1+sizeof(self_eth_addr);
	msg->options[k++] = DHCP_HTYPE_ETHERNET;
	k += mem_encode(&msg->options[k], self_eth_addr);

	/* Our requested hostname.  */
	msg->options[k++] = DHCP_OPT_HOSTNAME;
	msg->options[k++] = strlen(global_hostname);
	k += str_encode(&msg->options[k], global_hostname);

	/* Which parameters we want back.  */
	msg->options[k++] = DHCP_OPT_PARAMETER_LIST;
	msg->options[k++] = 6;
	msg->options[k++] = DHCP_OPT_SUBNET_MASK;    /* 1 */
	msg->options[k++] = DHCP_OPT_ROUTER;         /* 2 */
	msg->options[k++] = DHCP_OPT_DOMAIN_SERVER;  /* 3 */
	msg->options[k++] = DHCP_OPT_DOMAIN_NAME;    /* 4 */
	msg->options[k++] = DHCP_OPT_RENEWAL_TIME;   /* 5 */
	msg->options[k++] = DHCP_OPT_REBINDING_TIME; /* 6 */

	/* End.  */
	msg->options[k++] = DHCP_OPT_END;
	assert(k <= CONFIG_DHCP_OPT_SIZE);

	/* Send. */
	debugf("> Send DHCP_DISCOVER");
	VCALL(sock, sendto, msg, DHCP_MSG_BASE_SIZE + k, net_ip4_addr_broadcast, DHCP_PORT_SERVER);
}

static void dhcp_send_REQUEST(implements_net_packet_conn *sock) {
	struct net_ip4_addr ip;
	struct dhcp_msg msg;
	size_t k;

	dhcp_msg_init(msg, &k,
	              (dhcp_state != STATE_DHCP_LEASED && dhcp_state != STATE_DHCP_REREQUEST) ? DHCP_FLAG_BROADCAST : 0);

	switch (dhcp_state) {
	case STATE_DHCP_LEASED:
	case STATE_DHCP_REREQUEST:
		msg->ciaddr = global_lease.addr;
		ip = DHCP_SIP;
		break;
	default:
		ip = net_ip4_addr_broadcast;
	}

	/* Message type.  */
	msg->options[k++] = DHCP_OPT_DHCP_MSG_TYPE;
	msg->options[k++] = 1;
	msg->options[k++] = DHCP_MSGTYP_REQUEST;

	/* Our Client ID.  */
	msg->options[k++] = DHCP_OPT_CLIENT_ID;
	msg->options[k++] = 1+sizeof(self_eth_addr);
	msg->options[k++] = DHCP_HTYPE_ETHERNET;
	k += mem_encode(&msg->options[k], self_eth_addr);

	switch (dhcp_state) {
	case STATE_DHCP_LEASED:
	case STATE_DHCP_REREQUEST:
		/* Our current IP address.  */
		msg->options[k++] = DHCP_OPT_ADDRESS_REQUEST;
		msg->options[k++] = sizeof(global_lease.addr);
		k += mem_encode(&msg->options[k], global_lease.addr);

		/* The server we got it from.  */
		msg->options[k++] = DHCP_OPT_DHCP_SERVER_ID;
		msg->options[k++] = sizeof(DHCP_SIP);
		k += mem_encode(&msg->options[k], DHCP_SIP);
	}

	/* Our requested hostname.  */
	msg->options[k++] = DHCP_OPT_HOSTNAME;
	msg->options[k++] = strlen(global_hostname);
	k += str_encode(&msg->options[k], global_hostname);

	/* Which parameters we want back.  */
	msg->options[k++] = DHCP_OPT_PARAMETER_LIST;
	msg->options[k++] = 8;
	msg->options[k++] = DHCP_OPT_SUBNET_MASK;      /* 1 */
	msg->options[k++] = DHCP_OPT_ROUTER;           /* 2 */
	msg->options[k++] = DHCP_OPT_DOMAIN_SERVER;    /* 3 */
	msg->options[k++] = DHCP_OPT_DOMAIN_NAME;      /* 4 */
	msg->options[k++] = DHCP_OPT_RENEWAL_TIME;     /* 5 */
	msg->options[k++] = DHCP_OPT_REBINDING_TIME;   /* 6 */
	msg->options[k++] = DHCP_OPT_ROUTER_DISCOVERY; /* 7 */
	msg->options[k++] = DHCP_OPT_STATIC_ROUTE;     /* 8 */

	/* End.  */
	msg->options[k++] = DHCP_OPT_END;
	assert(k <= CONFIG_DHCP_OPT_SIZE);

	debugf("> Send DHCP_REQUEST");
	VCALL(sock, sendto, msg, DHCP_MSG_BASE_SIZE + k, ip, DHCP_PORT_SERVER);
}

static void dhcp_send_DECLINE(implements_net_packet_conn *sock) {
	size_t k;

	dhcp_msg_init(pDHCPMSG, &k, DHCP_FLAG_BROADCAST);
	pDHCPMSG->flags = uint16be_marshal(0);

	/* Option Request Param. */
	pDHCPMSG->options[k++] = DHCP_OPT_DHCP_MSG_TYPE;
	pDHCPMSG->options[k++] = 1;
	pDHCPMSG->options[k++] = DHCP_MSGTYP_DECLINE;

	/* Our Client ID.  */
	pDHCPMSG->options[k++] = DHCP_OPT_CLIENT_ID;
	pDHCPMSG->options[k++] = 1+sizeof(self_eth_addr);
	pDHCPMSG->options[k++] = DHCP_HTYPE_ETHERNET;
	memcpy(&pDHCPMSG->options[k], self_eth_addr.octets, sizeof(self_eth_addr));
	k += sizeof(self_eth_addr);

	/* Our current IP address.  */
	pDHCPMSG->options[k++] = DHCP_OPT_ADDRESS_REQUEST;
	pDHCPMSG->options[k++] = sizeof(global_lease.addr);
	k += mem_encode(&pDHCPMSG->options[k], global_lease.addr);

	/* The server we got it from.  */
	pDHCPMSG->options[k++] = DHCP_OPT_DHCP_SERVER_ID;
	pDHCPMSG->options[k++] = sizeof(DHCP_SIP);
	k += mem_encode(&pDHCPMSG->options[k], DHCP_SIP);

	/* End.  */
	pDHCPMSG->options[k++] = DHCP_OPT_END;

	debugf("> Send DHCP_DECLINE");
	assert(k <= CONFIG_DHCP_OPT_SIZE);
	VCALL(sock, sendto, pDHCPMSG, DHCP_MSG_BASE_SIZE + k, net_ip4_addr_broadcast, DHCP_PORT_SERVER);
}

/**
 * @return
 *   - <0: -errno
 *   -  0: ???
 *   - >0 && <= UINT8_MAX: msgtyp
 *   - >UINT8_MAX: ???
 */
static int dhcp_recv_msg(implements_net_packet_conn *sock) {
	struct net_ip4_addr srv_addr;
	uint16_t            srv_port;
	ssize_t             msg_len;
 restart:
	msg_len = VCALL(sock, recvfrom, pDHCPMSG, sizeof(*pDHCPMSG), &srv_addr, &srv_port);
	if (msg_len < 0)
		return msg_len;
	debugf("DHCP message : %d.%d.%d.%d(%d) %d received.",
	       srv_addr.octets[0], srv_addr.octets[1], srv_addr.octets[2], srv_addr.octets[3], srv_port, msg_len);
	/* Compare server port.  */
	if (srv_port != DHCP_PORT_SERVER) {
		goto restart;
	}
	/* Compare our MAC address.  */
	if (memcmp(pDHCPMSG->chaddr, self_eth_addr.octets, sizeof(self_eth_addr))) {
		debugf("Not my DHCP Message.  This message is ignored.");
		goto restart;
	}
	/* Compare server IP address.  */
	if (memcmp(DHCP_SIP.octets, ((struct net_ip4_addr){0}).octets, sizeof(struct net_ip4_addr))) {
		if ( memcmp(srv_addr.octets, DHCP_SIP.octets, sizeof(srv_addr)) &&
		     memcmp(srv_addr.octets, DHCP_REAL_SIP.octets, sizeof(srv_addr)) ) {
			debugf("Another DHCP sever send a response message. This is ignored.");
			goto restart;
		}
	}

	uint8_t msg_type = 0;
	for (size_t k = 4, k_max = msg_len - DHCP_MSG_BASE_SIZE, opt_len; k < k_max; k += opt_len) {
		uint8_t opt_typ;
		opt_typ = pDHCPMSG->options[k++];
		switch (opt_typ) {
		case DHCP_OPT_END:
			opt_len = k_max - k;
			break;
		case DHCP_OPT_PAD:
			opt_len = 0;
			break;
		default:
			opt_len = pDHCPMSG->options[k++];
			xhandle(opt_typ, opt_len, &pDHCPMSG->options[k]);
		}
		switch (opt_typ) {
		case DHCP_OPT_DHCP_MSG_TYPE:
			if (opt_len != 1)
				continue;
			msg_type = pDHCPMSG->options[k];
			break;
		case DHCP_OPT_ADDRESS_TIME:
			if (opt_len != 4)
				continue;
			global_lease.lifetime = uint32be_decode(&pDHCPMSG->options[k]);
#if CONFIG_DHCP_DEBUG
			global_lease.lifetime = 10;
#endif
			break;
		case DHCP_OPT_DHCP_SERVER_ID:
			if (opt_len != 4)
				continue;
			DHCP_SIP.octets[0] = pDHCPMSG->options[k+0];
			DHCP_SIP.octets[1] = pDHCPMSG->options[k+1];
			DHCP_SIP.octets[2] = pDHCPMSG->options[k+2];
			DHCP_SIP.octets[3] = pDHCPMSG->options[k+3];
			DHCP_REAL_SIP = srv_addr;
			break;
		}
	}
	return msg_type;
}

static void dhcp_reset_timeout(void) {
	dhcp_tick_1s = 0;
	dhcp_tick_next = DHCP_WAIT_TIME;
	dhcp_retry_count = 0;
}

static uint8_t dhcp_check_timeout(implements_net_packet_conn *sock) {
	uint8_t ret = DHCP_RET_RUNNING;

	if (dhcp_retry_count < MAX_DHCP_RETRY) {
		if (dhcp_tick_next < dhcp_tick_1s) {

			switch ( dhcp_state ) {
			case STATE_DHCP_DISCOVER :
				/*debugf("<<timeout>> state : STATE_DHCP_DISCOVER");*/
				dhcp_send_DISCOVER(sock);
				break;

			case STATE_DHCP_REQUEST :
				/*debugf("<<timeout>> state : STATE_DHCP_REQUEST");*/
				dhcp_send_REQUEST(sock);
				break;

			case STATE_DHCP_REREQUEST :
				/*debugf("<<timeout>> state : STATE_DHCP_REREQUEST");*/
				dhcp_send_REQUEST(sock);
				break;

			default :
				break;
			}

			dhcp_tick_1s = 0;
			dhcp_tick_next = dhcp_tick_1s + DHCP_WAIT_TIME;
			dhcp_retry_count++;
		}
	} else { /* timeout occurred */

		switch(dhcp_state) {
		case STATE_DHCP_DISCOVER:
			dhcp_state = STATE_DHCP_INIT;
			ret = DHCP_RET_FAILED;
			break;
		case STATE_DHCP_REQUEST:
		case STATE_DHCP_REREQUEST:
			dhcp_send_DISCOVER(sock);
			dhcp_state = STATE_DHCP_DISCOVER;
			break;
		default :
			break;
		}
		dhcp_reset_timeout();
	}
	return ret;
}

static int8_t dhcp_check_leasedIP(implements_net_packet_conn *sock) {
	int32_t ret;

	/* IP conflict detection : ARP request - ARP reply */
	/* Broadcasting ARP Request for check the IP conflict using UDP sendto() function */
	ret = VCALL(sock, sendto, "CHECK_IP_CONFLICT", 17, global_lease.addr, 5000);

	if (ret == NET_ETIMEDOUT) {
		/* UDP send Timeout occurred : allocated IP address is unique, DHCP Success */
		debugf("\r\n> Check leased IP - OK");
		return 1;
	}

	/* Received ARP reply or etc : IP address conflict occur, DHCP Failed */
	dhcp_send_DECLINE(sock);

	ret = dhcp_tick_1s;
	while ((dhcp_tick_1s - ret) < 2) {} /* wait for 1s over; wait to complete to send DECLINE message; */

	return 0;
}

COROUTINE dhcp_client_cr(struct w5500 *chip, uint8_t socknum,
                         struct net_eth_addr self_eth_addr,
                         char *self_hostname,
                         dhcp_callback_t cb) {
	uint32_t xid;
	implements_net_packet_conn *sock;

	xid = 0x12345678;
	xid += self_eth_addr.octets[3];
	xid += self_eth_addr.octets[4];
	xid += self_eth_addr.octets[5];
	xid += (self_eth_addr.octets[3] ^
	        self_eth_addr.octets[4] ^
	        self_eth_addr.octets[5]);

	dhcp_tick_1s = 0;
	dhcp_tick_next = DHCP_WAIT_TIME;
	dhcp_retry_count = 0;

	sock = w5500_udp_conn(chip, socknum, DHCP_PORT_CLIENT);

	int r;

	dhcp_state = STATE_DHCP_INIT;
	uint64_t time_ns_init;

	for (;;) {
		/* State transition diagram: https://datatracker.ietf.org/doc/html/rfc2131#page-35 */
		switch (state) {
		case STATE_DHCP_INIT:
			dhcp_send_DISCOVER(sock);
			time_ns_init = VCALL(bootclock, get_time_ns);
			VCALL(sock, set_read_deadline(time_ns_init+CONFIG_DHCP_SELECTING_NS));
			dhcp_state = STATE_DHCP_SELECTING;
			break;
		case STATE_DHCP_SELECTING :
			switch ((r = dhcp_recv_msg(sock))) {
			case DHCP_MSGTYP_OFFER:
				debugf("> Receive DHCP_OFFER");
				global_lease.addr = pDHCPMSG->yiaddr;
				dhcp_send_REQUEST(sock);
				dhcp_state = STATE_DHCP_REQUEST;
				break;
			case -NET_ETIMEDOUT:
				break;
			default:
				debugf("unexpected error: %d", r);
			}
			break;

		case STATE_DHCP_REQUEST :
			if (msg_type == DHCP_MSGTYP_ACK) {
				debugf("> Receive DHCP_ACK");
				if (dhcp_check_leasedIP(sock)) {
					/* Network info assignment from DHCP */
					cb(DHCP_ASSIGN, global_lease);
					dhcp_reset_timeout();

					dhcp_state = STATE_DHCP_LEASED;
				} else {
					/* IP address conflict occurred */
					dhcp_reset_timeout();
					cb(DHCP_CONFLICT, global_lease);
					dhcp_state = STATE_DHCP_INIT;
				}
			} else if (msg_type == DHCP_MSGTYP_NAK) {
				debugf("> Receive DHCP_NACK");

				dhcp_reset_timeout();

				dhcp_state = STATE_DHCP_DISCOVER;
			} else
				ret = dhcp_check_timeout(sock);
			break;

		case STATE_DHCP_LEASED :
			ret = DHCP_RET_IP_LEASED;
		if ((global_lease.lifetime != DHCP_INFINITY) && ((global_lease.lifetime/2) < dhcp_tick_1s)) {
			debugf("> Maintains the IP address");

			msg_type = 0;
			OLD_allocated_ip = global_lease.addr;

			xid++;

			dhcp_send_REQUEST(sock);

			dhcp_reset_timeout();

			dhcp_state = STATE_DHCP_REREQUEST;
		}
		break;

	case STATE_DHCP_REREQUEST :
		ret = DHCP_RET_IP_LEASED;
		if (msg_type == DHCP_MSGTYP_ACK) {
			dhcp_retry_count = 0;
			if (memcmp(OLD_allocated_ip.octets, global_lease.addr.octets, sizeof(global_lease.addr))) {
				ret = DHCP_RET_IP_CHANGED;
				cb(DHCP_UPDATE, global_lease);
				debugf(">IP changed.");
			} else {
				debugf(">IP is continued.");
			}
			dhcp_reset_timeout();
			dhcp_state = STATE_DHCP_LEASED;
		} else if (msg_type == DHCP_MSGTYP_NAK) {
			debugf("> Receive DHCP_NACK, Failed to maintain ip");
			dhcp_reset_timeout();

			dhcp_state = STATE_DHCP_DISCOVER;
		} else
			ret = dhcp_check_timeout(sock);
		break;
	default :
		break;
	}

	return ret;
}