dhcps.c

/*
 * Copyright (c) 2013-2019 Huawei Technologies Co., Ltd. All rights reserved.
 * Copyright (c) 2020-2021 Huawei Device 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:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this list of
 *    conditions and the following disclaimer.
 *
 * 2. 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.
 *
 * 3. Neither the name of the copyright holder 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 HOLDER 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.
 */

/**
 * @file
 * Dynamic Host Configuration Protocol Server
 *
 */

#include "../core/ipv4/dhcp.c"  /* for enum dhcp_option_idx/dhcp_option_xx/dhcp_parse_reply etc. */

#include "lwip/opt.h"

#if (LWIP_DHCP) && (LWIP_DHCPS) /* don't build if not configured for use in lwipopts.h */
#include <string.h>

#include "lwip/stats.h"
#include "lwip/mem.h"
#include "lwip/udp.h"
#include "lwip/ip_addr.h"
#include "lwip/netif.h"
#include "lwip/def.h"
#include "lwip/prot/dhcp.h"
#include "lwip/dhcp.h"
#include "lwip/dhcps.h"
#include "lwip/sys.h"
#include "netif/etharp.h"

#define DHCPS_ADDRESS_FREE 0x0
#define DHCPS_ADDRESS_OFFERRED 0x1
#define DHCPS_ADDRESS_BOUND 0x2
#define DHCPS_ADDRESS_DECLINED 0x3

#define LWIP_STATIC static
#define DHCP_OPTION_ROUTER_SIZE     4
#define DHCP_OPTION_SUBNET_MASK_SIZE 4
#define DHCP_OPTION_LEASE_TIME_SIZE 4
#define DHCP_OPTION_SERVER_ID_LEN   4
#define DHCP_OPTION_T1_LEN          4
#define DHCP_OPTION_T2_LEN          4

#define DHCP_CLIENT_PORT  68
#define DHCP_SERVER_PORT  67

#define DHCP_BROADCAST_FLAG             0x8000

struct dyn_lease_addr {
    u8_t cli_hwaddr[DHCP_CHADDR_LEN];
    u32_t flags;
    u32_t leasetime;
    u32_t proposed_leasetime;
    ip4_addr_t cli_addr;
};

struct dhcps {
    struct dhcp dhcp;
    struct udp_pcb *pcb;
    struct dyn_lease_addr leasearr[LWIP_DHCPS_MAX_LEASE];
    u8_t pcb_allocated;
    u8_t lease_num;
    struct netif *netif;
    ip4_addr_t start_addr;
    ip4_addr_t end_addr;
};

#define dhcps_option_given(dhcps, idx)          dhcp_option_given(&(dhcps)->dhcp, idx)
#define dhcps_got_option(dhcps, idx)            dhcp_got_option(&(dhcps)->dhcp, idx)
#define dhcps_clear_option(dhcps, idx)          dhcp_clear_option(&(dhcps)->dhcp, idx)
#define dhcps_clear_all_options(dhcps)          dhcp_clear_all_options(&(dhcps)->dhcp)
#define dhcps_get_option_value(dhcps, idx)      dhcp_get_option_value(&(dhcps)->dhcp, idx)
#define dhcps_set_option_value(dhcps, idx, val) dhcp_set_option_value(&(dhcps)->dhcp, idx, val)

#define netif_get_dhcps(netif) ((struct dhcps*)netif_get_client_data(netif, LWIP_NETIF_CLIENT_DATA_INDEX_DHCPS))
#define netif_set_dhcps(netif, dhcps) netif_set_client_data(netif, LWIP_NETIF_CLIENT_DATA_INDEX_DHCPS, dhcps)

LWIP_STATIC void dhcp_common_option(struct dhcp_msg *msg_out, u8_t option_type, u8_t option_len, u16_t *options_out_len);
LWIP_STATIC void dhcp_common_option_byte(struct dhcp_msg *msg_out, u8_t value, u16_t *options_out_len);
LWIP_STATIC void dhcp_common_option_long(struct dhcp_msg *msg_out, u32_t value, u16_t *options_out_len);
LWIP_STATIC void dhcp_common_option_trailer(struct dhcp_msg *msg_out, u16_t options_out_len, struct pbuf *p_out);
LWIP_STATIC err_t dhcps_parse_options(struct pbuf *p, struct dhcps *dhcps);

LWIP_STATIC struct pbuf *dhcps_create_base_msg(struct dhcp_msg *client_msg);
LWIP_STATIC void remove_stale_entries(struct dhcps *dhcps);
LWIP_STATIC void add_client_entry(struct dhcps *dhcps, unsigned int idx, struct dhcp_msg *client_msg);
LWIP_STATIC int find_free_slot(struct dhcps *dhcps);
LWIP_STATIC struct dyn_lease_addr *find_client_lease(struct dhcps *dhcps, struct dhcp_msg *client_msg);
LWIP_STATIC ip4_addr_t validate_discover(struct dhcps *dhcps, struct dhcp_msg *client_msg,
                                         struct dyn_lease_addr **client_lease);
LWIP_STATIC void handle_discover(struct netif *netif, struct dhcps *dhcps, struct dhcp_msg *client_msg,
                                 struct dyn_lease_addr *client_lease);
LWIP_STATIC ip4_addr_t validate_request_message(struct netif *netif, struct dhcp_msg *client_msg,
                                                struct dyn_lease_addr *client_lease, ip4_addr_t serverid);
LWIP_STATIC void handle_request(struct netif *netif, struct dhcps *dhcps, struct dhcp_msg *client_msg,
                                struct dyn_lease_addr *client_lease, ip4_addr_t serverid);
LWIP_STATIC void handle_decline(struct netif *netif, struct dhcps *dhcps, struct dhcp_msg *client_msg,
                                struct dyn_lease_addr *client_lease);
LWIP_STATIC void handle_inform(struct netif *netif, struct dhcps *dhcps, struct dhcp_msg *client_msg);
LWIP_STATIC void handle_client_messages(struct netif *netif, struct dhcps *dhcps,
                                        struct dhcp_msg *client_msg, ip4_addr_t serverid, u8_t msg_type);
LWIP_STATIC void dhcps_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p,
                            const ip_addr_t *ip_addr, u16_t port);

LWIP_STATIC struct pbuf *dhcps_create_base_msg(struct dhcp_msg *client_msg)
{
    struct pbuf *srvr_msg_pbuf = NULL;
    struct dhcp_msg *srvr_msg = NULL;

    srvr_msg_pbuf = pbuf_alloc(PBUF_TRANSPORT, sizeof(struct dhcp_msg), PBUF_RAM);
    if (srvr_msg_pbuf == NULL) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
                    ("dhcps_create_base_msg(): could not allocate pbuf\n"));
        return NULL;
    }

    LWIP_ASSERT("dhcps_create_base_msg: check that first pbuf can hold struct dhcp_msg",
                (srvr_msg_pbuf->len >= sizeof(struct dhcp_msg)));
#if DRIVER_STATUS_CHECK
    srvr_msg_pbuf->flags |= PBUF_FLAG_DHCP_BUF;
#endif

    srvr_msg = (struct dhcp_msg *)srvr_msg_pbuf->payload;
    srvr_msg->op = DHCP_BOOTREPLY;
    srvr_msg->htype = client_msg->htype;
    srvr_msg->hlen = client_msg->hlen;
    srvr_msg->hops = 0;
    srvr_msg->xid = client_msg->xid;
    srvr_msg->secs = 0;
    srvr_msg->flags = client_msg->flags;
    ip4_addr_set_zero(&srvr_msg->ciaddr);
    ip4_addr_set_zero(&srvr_msg->yiaddr);
    ip4_addr_set_zero(&srvr_msg->siaddr);
    ip4_addr_copy(srvr_msg->giaddr, client_msg->giaddr);
    if (memcpy_s(srvr_msg->chaddr, sizeof(srvr_msg->chaddr), client_msg->chaddr, DHCP_CHADDR_LEN) != EOK) {
        (void)pbuf_free(srvr_msg_pbuf);
        return NULL;
    }
    (void)memset_s(srvr_msg->sname, sizeof(srvr_msg->sname), 0, DHCP_SNAME_LEN);
    (void)memset_s(srvr_msg->file, sizeof(srvr_msg->file), 0, DHCP_FILE_LEN);
    srvr_msg->cookie = PP_HTONL(DHCP_MAGIC_COOKIE);

    return srvr_msg_pbuf;
}

LWIP_STATIC void remove_stale_entries(struct dhcps *dhcps)
{
    int i = 0;
    u32_t curr_time = sys_now();

    for (i = 0; i < dhcps->lease_num; i++) {
        /* Slot should not be free or have infinite lease time */
        if ((dhcps->leasearr[i].flags != DHCPS_ADDRESS_FREE) && (dhcps->leasearr[i].leasetime != (u32_t)~0)) {
            if (dhcps->leasearr[i].leasetime < curr_time) {
                LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                            ("remove_stale_entries: Removing Client Entry at Index = %"U32_F"\n", i));
                (void)memset_s(&(dhcps->leasearr[i]), sizeof(struct dyn_lease_addr), 0, sizeof(struct dyn_lease_addr));
                dhcps->leasearr[i].flags = DHCPS_ADDRESS_FREE;
            }
        }
    }
}

LWIP_STATIC void add_client_entry(struct dhcps *dhcps, unsigned int idx, struct dhcp_msg *client_msg)
{
    u32_t client_lease_time = (u32_t)(LWIP_DHCPS_LEASE_TIME);

    if ((dhcps_option_given(dhcps, DHCP_OPTION_IDX_LEASE_TIME))
#if (LWIP_DHCPS_LEASE_TIME != ~0)
        && (dhcps_get_option_value(dhcps, DHCP_OPTION_IDX_LEASE_TIME) < LWIP_DHCPS_LEASE_TIME)
#endif
        ) {
        client_lease_time = (u32_t)dhcps_get_option_value(dhcps, DHCP_OPTION_IDX_LEASE_TIME);
    }

    (void)memset_s(&(dhcps->leasearr[idx]), sizeof(struct dyn_lease_addr), 0, sizeof(struct dyn_lease_addr));
    if (memcpy_s(dhcps->leasearr[idx].cli_hwaddr, DHCP_CHADDR_LEN,
                 client_msg->chaddr, sizeof(client_msg->chaddr)) != EOK) {
        return;
    }
    /* This is called only during offer message, so adding offer time.
      This is later updated to lease time when request message is handled */
    dhcps->leasearr[idx].leasetime = sys_now() + (LWIP_DHCPS_OFFER_TIME * 1000);
    dhcps->leasearr[idx].cli_addr.addr = dhcps->start_addr.addr + idx;
    dhcps->leasearr[idx].flags = DHCPS_ADDRESS_OFFERRED;
    dhcps->leasearr[idx].proposed_leasetime = client_lease_time;
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("add_client_entry: Adding Client Entry at Index = %"U32_F"\n", idx));
}

LWIP_STATIC int find_free_slot(struct dhcps *dhcps)
{
    int i;
    for (i = 0; i < dhcps->lease_num; i++) {
        if ((dhcps->leasearr[i].flags == DHCPS_ADDRESS_FREE) &&
            (htonl(dhcps->start_addr.addr + (u32_t)i) != ip_2_ip4(&dhcps->netif->ip_addr)->addr)) {
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("find_free_slot: Found Free Slot at Index = %"U32_F"\n", i));
            return i;
        }
    }

    return -1;
}

LWIP_STATIC struct dyn_lease_addr *find_client_lease(struct dhcps *dhcps, struct dhcp_msg *client_msg)
{
    int i;
    for (i = 0; i < dhcps->lease_num; i++) {
        if (dhcps->leasearr[i].flags != DHCPS_ADDRESS_FREE) {
            if (memcmp(dhcps->leasearr[i].cli_hwaddr, client_msg->chaddr, client_msg->hlen) == 0) {
                LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                            ("find_client_lease: Found Client Lease at Index = %"U32_F"\n", i));
                return &(dhcps->leasearr[i]);
            }
        }
    }

    return NULL;
}

LWIP_STATIC ip4_addr_t validate_discover(struct dhcps *dhcps, struct dhcp_msg *client_msg,
                                         struct dyn_lease_addr **client_lease)
{
    ip4_addr_t client_ip;
    int idx = -1;

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("validate_discover: Validating Discover Message\n"));

    client_ip.addr = 0;
    if (*client_lease == NULL) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("validate_discover: Existing Client Lease not Found\n"));
        if (dhcps_option_given(dhcps, DHCP_OPTION_IDX_REQUESTED_IP)) {
            client_ip.addr = (u32_t)dhcps_get_option_value(dhcps, DHCP_OPTION_IDX_REQUESTED_IP);
#ifdef  LWIP_DEV_DEBUG
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                        ("validate_discover function: Requested IP from client = %"U32_F"\n", client_ip.addr));
#endif

            if ((client_ip.addr >= dhcps->start_addr.addr) && (client_ip.addr <= dhcps->end_addr.addr)) {
                idx = (int)(client_ip.addr - dhcps->start_addr.addr);
                if ((dhcps->leasearr[idx].flags != DHCPS_ADDRESS_FREE) ||
                    (ntohl(client_ip.addr) == ip_2_ip4(&dhcps->netif->ip_addr)->addr)) {
                    /* Requested IP is not available */
#ifdef  LWIP_DEV_DEBUG
                    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                      ("validate_discover function: Requested IP from client = %"U32_F" Not available \n", client_ip.addr));
#endif
                    idx = -1;
                }
            }
        }

        if (idx == -1) {
            idx = find_free_slot(dhcps);
            if (idx == -1) {
                LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                            ("validate_discover function: No Free Slot available for Storing addresses\n"));
                client_ip.addr = 0;
                return client_ip;
            }
            client_ip.addr = dhcps->start_addr.addr + (u32_t)idx;
#ifdef  LWIP_DEV_DEBUG
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                        ("validate_discover function: New IP = %"U32_F" is being assigned\n", client_ip.addr));
#endif
        }

        add_client_entry(dhcps, (unsigned int)idx, client_msg);
        (*client_lease) = &(dhcps->leasearr[idx]);
    } else {
        client_ip.addr = (*client_lease)->cli_addr.addr;
#ifdef  LWIP_DEV_DEBUG
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                    ("validate_discover: Existing Client Lease Found. Existing IP =%"U32_F"\n", client_ip.addr));
#endif

        if ((dhcps_option_given(dhcps, DHCP_OPTION_IDX_LEASE_TIME))
#if (~0 != LWIP_DHCPS_LEASE_TIME)
            && (dhcps_get_option_value(dhcps, DHCP_OPTION_IDX_LEASE_TIME) < LWIP_DHCPS_LEASE_TIME)
#endif
            ) {
            /* Assign the newly requested time or else use the existing lease time as-is */
            (*client_lease)->proposed_leasetime = (u32_t)dhcps_get_option_value(dhcps, DHCP_OPTION_IDX_LEASE_TIME);
        }
    }

    return client_ip;
}

void dhcp_common_option(struct dhcp_msg *msg_out, u8_t option_type, u8_t option_len, u16_t *options_out_len)
{
    *options_out_len = dhcp_option(*options_out_len, msg_out->options, option_type, option_len);
}

void dhcp_common_option_byte(struct dhcp_msg *msg_out, u8_t value, u16_t *options_out_len)
{
    *options_out_len = dhcp_option_byte(*options_out_len, msg_out->options, value);
}

void dhcp_common_option_long(struct dhcp_msg *msg_out, u32_t value, u16_t *options_out_len)
{
    *options_out_len = dhcp_option_long(*options_out_len, msg_out->options, value);
}

void dhcp_common_option_trailer(struct dhcp_msg *msg_out, u16_t options_out_len, struct pbuf *p_out)
{
    dhcp_option_trailer(options_out_len, msg_out->options, p_out);
}

LWIP_STATIC void handle_discover(struct netif *netif, struct dhcps *dhcps,
                                 struct dhcp_msg *client_msg, struct dyn_lease_addr *client_lease)
{
#if !LWIP_DHCPS_DISCOVER_BROADCAST
    ip_addr_t client_ipaddr;
#endif

    ip4_addr_t client_ip;
    ip_addr_t dst_addr;
    struct pbuf *out_msg = NULL;
    struct dhcp_msg *srvr_msg = NULL;
    u16_t options_len = 0;
#if !LWIP_DHCPS_DISCOVER_BROADCAST
#if ETHARP_SUPPORT_STATIC_ENTRIES
    struct eth_addr ethaddr;
#endif
#endif
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_discover: Processing Discover Message\n"));

    client_ip = validate_discover(dhcps, client_msg, &client_lease);
    if (client_ip.addr == 0) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                    ("handle_discover: Returning as unable to get a proper address for client\n"));
        return;
    }

    out_msg = dhcps_create_base_msg(client_msg);
    if (out_msg == NULL) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                    ("handle_discover function: Memory allocation for base message failed\n"));
        return;
    }

    srvr_msg = (struct dhcp_msg *)out_msg->payload;
    // no need check msg pointer from payload here
    srvr_msg->yiaddr.addr = htonl(client_ip.addr);

    dhcp_common_option(srvr_msg, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN, &options_len);
    dhcp_common_option_byte(srvr_msg, DHCP_OFFER, &options_len);

    /* hilink need this router option */
    dhcp_common_option(srvr_msg, DHCP_OPTION_ROUTER, DHCP_OPTION_ROUTER_SIZE, &options_len);
    dhcp_common_option_long(srvr_msg, ntohl(ip_2_ip4(&netif->ip_addr)->addr), &options_len);

    /* netif already holds the Server ID in network order. so, no need to convert it again */
    dhcp_common_option(srvr_msg, DHCP_OPTION_SERVER_ID, DHCP_OPTION_SERVER_ID_LEN, &options_len);
    dhcp_common_option_long(srvr_msg, ntohl(ip_2_ip4(&netif->ip_addr)->addr), &options_len);

    dhcp_common_option(srvr_msg, DHCP_OPTION_LEASE_TIME, DHCP_OPTION_LEASE_TIME_SIZE, &options_len);
    dhcp_common_option_long(srvr_msg, client_lease->proposed_leasetime, &options_len);

    dhcp_common_option(srvr_msg, DHCP_OPTION_T1, DHCP_OPTION_T1_LEN, &options_len);
    dhcp_common_option_long(srvr_msg, (client_lease->proposed_leasetime / 2), &options_len);

    dhcp_common_option(srvr_msg, DHCP_OPTION_T2, DHCP_OPTION_T2_LEN, &options_len);
    /* calculate safe periods for lease (proposed_leasetime * 0.875 -> 87.5%) */
    dhcp_common_option_long(srvr_msg, ((client_lease->proposed_leasetime * 7) / 8), &options_len);

    /* No need to convert netmask into network order as it is already stored in network order */
    dhcp_common_option(srvr_msg, DHCP_OPTION_SUBNET_MASK, DHCP_OPTION_SUBNET_MASK_SIZE, &options_len);
    dhcp_common_option_long(srvr_msg, ntohl(ip4_addr_get_u32(ip_2_ip4(&netif->netmask))), &options_len);

    dhcp_common_option_trailer(srvr_msg, options_len, out_msg);

    if (client_msg->ciaddr.addr != 0) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_discover: sendto(OFFER, ciaddr, DHCP_CLIENT_PORT)\n"));
        ip_addr_set_ip4_u32_val(dst_addr, (u32_t)(client_msg->ciaddr.addr));
        (void)udp_sendto_if_src(dhcps->pcb, out_msg, &dst_addr, DHCP_CLIENT_PORT, netif, &(netif->ip_addr));
    }
#if !LWIP_DHCPS_DISCOVER_BROADCAST
    else if (ntohs(client_msg->flags) & DHCP_BROADCAST_FLAG) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                    ("handle_discover: sendto(OFFER, IP_ADDR_BROADCAST, DHCP_CLIENT_PORT)\n"));
        (void)udp_sendto_if_src(dhcps->pcb, out_msg, IP_ADDR_BROADCAST, DHCP_CLIENT_PORT, netif, &(netif->ip_addr));
    } else {
        client_ip.addr = htonl(client_ip.addr);

#if ETHARP_SUPPORT_STATIC_ENTRIES
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_discover: Updating ARP Static Entry for unicast reply\n"));
        if (memcpy_s(ethaddr.addr, ETHARP_HWADDR_LEN, client_msg->chaddr, client_msg->hlen) != EOK) {
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("memcpy_s failed\n"));
            (void)pbuf_free(out_msg);
            return;
        }
        if (etharp_add_static_entry(&client_ip, &ethaddr) != ERR_OK) {
            (void)pbuf_free(out_msg);
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_discover: Adding static entry to arp cache failed\n"));
            return;
        }
#endif

        /* Need to check and add an arp entry to make this pass through smoothly */
        ip_addr_copy_from_ip4(client_ipaddr, client_ip);
        (void)udp_sendto_if_src(dhcps->pcb, out_msg, &client_ipaddr, DHCP_CLIENT_PORT, netif, &(netif->ip_addr));
#if ETHARP_SUPPORT_STATIC_ENTRIES
        /* We just added the entry above and checked for it's success too. so, the below function call cannot fail */
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                    ("handle_discover: Removing ARP Static Entry added for unicast reply\n"));
        (void)etharp_remove_static_entry(&client_ip);
#endif
    }
#else
    else {
      LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                  ("handle_discover: sendto(OFFER, IP_ADDR_BROADCAST, DHCP_CLIENT_PORT)\n"));
      (void)udp_sendto_if_src(dhcps->pcb, out_msg, IP_ADDR_BROADCAST, DHCP_CLIENT_PORT, netif, &(netif->ip_addr));
    }
#endif

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_discover: deleting()ing\n"));
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_discover: Sending Reply has been successful\n"));

    (void)pbuf_free(out_msg);
    return;
}

LWIP_STATIC ip4_addr_t validate_request_message(struct netif *netif, struct dhcp_msg *client_msg,
                                                struct dyn_lease_addr *client_lease, ip4_addr_t serverid)
{
    struct dhcps *dhcps = netif_get_dhcps(netif);
    ip4_addr_t requested_ip;
    requested_ip.addr = 0;

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("validate_request_message: Processing Request Message\n"));

    if ((client_lease != NULL) && (client_lease->flags == DHCPS_ADDRESS_OFFERRED)) {
        /* Now, we are in selecting state */
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("validate_request_message: In Selecting State\n"));

        if ((serverid.addr == 0) || (client_msg->ciaddr.addr != 0) ||
            (!dhcps_option_given(dhcps, DHCP_OPTION_IDX_REQUESTED_IP))) {
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                        ("Server ID or ciaddr or requested ip option is not present\n"));
            return requested_ip;
        }

        if (serverid.addr != ip_2_ip4(&netif->ip_addr)->addr) {
            /* This message is not meant for us. The client intends to talk to some other server */
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                        ("validate_request_message: Server id doesn't match with ours. Message not for us\n"));
            requested_ip.addr = 1;
            return requested_ip;
        }

        requested_ip.addr = (u32_t)dhcps_get_option_value(dhcps, DHCP_OPTION_IDX_REQUESTED_IP);
    } else {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                    ("validate_request_message: In Init-Reboot, Renew or Rebinding State\n"));

        /* Now, we can be either in Init-reboot state or renew state or rebinding state */
        if (dhcps_option_given(dhcps, DHCP_OPTION_IDX_REQUESTED_IP)) {
            /* Requested IP option is filled in. Indicates we are mostly in Init-Reboot State */
            if (client_lease == NULL) {
                LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                            ("validate_request_message: No Configuration found corresponding to request message\n"));
                return requested_ip;
            }

            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                        ("validate_request_message: Requested IP Option is present. So, considering as Init-Reboot State\n"));

            if (client_msg->ciaddr.addr != 0) {
                LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                            ("validate_request_message: Error: ciaddr is filled in the Init-Reboot state. \n"));
                return requested_ip;
            }

            requested_ip.addr = (u32_t)dhcps_get_option_value(dhcps, DHCP_OPTION_IDX_REQUESTED_IP);
        } else {
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("validate_request_message: \
                  Requested IP Option is not present. So, considering as Renewing or Rebinding State\n"));

            if (client_msg->ciaddr.addr == 0) {
                LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                            ("validate_request_message: Error: ciaddr is not filled in the Renewing or Rebinding state. \n"));
                return requested_ip;
            }

            requested_ip.addr = ntohl(client_msg->ciaddr.addr);
        }
    }

    /* requested_ip is in host order and DHCP Server IP is in network order,
      so converting the former to network order for check */
    if (htonl(requested_ip.addr) == ip_2_ip4(&netif->ip_addr)->addr) {
        /* This requested_ip is the dhcp server is using, it is invalid */
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("validate_request_message: Requested IP addr is invalid\n"));
        requested_ip.addr = 1;
    }

    return requested_ip;
}

LWIP_STATIC void handle_request(struct netif *netif, struct dhcps *dhcps, struct dhcp_msg *client_msg,
                                struct dyn_lease_addr *client_lease, ip4_addr_t serverid)
{
    ip4_addr_t requested_ip;
    struct pbuf *out_msg = NULL;
    struct dhcp_msg *srvr_msg = NULL;
    u16_t options_len = 0;
    ip_addr_t dst_addr;
    ip_addr_t ip_send;
#if ETHARP_SUPPORT_STATIC_ENTRIES
    struct eth_addr ethaddr;
#endif

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_request: Processing Request Message\n"));

    requested_ip = validate_request_message(netif, client_msg, client_lease, serverid);
    if (requested_ip.addr == 1) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                    ("handle_request: Validation of request message failed. Dropping the packet.\n"));
        return;
    }

    out_msg = dhcps_create_base_msg(client_msg);
    if (out_msg == NULL) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_request: Creating base message failed\n"));
        return;
    }

    srvr_msg = (struct dhcp_msg *)out_msg->payload;
    dhcp_common_option(srvr_msg, DHCP_OPTION_SERVER_ID, DHCP_OPTION_SERVER_ID_LEN, &options_len);
    dhcp_common_option_long(srvr_msg, ntohl(ip_2_ip4(&netif->ip_addr)->addr), &options_len);

    /* hilink need this router option */
    dhcp_common_option(srvr_msg, DHCP_OPTION_ROUTER, DHCP_OPTION_ROUTER_SIZE, &options_len);
    dhcp_common_option_long(srvr_msg, ntohl(ip_2_ip4(&netif->ip_addr)->addr), &options_len);

    if ((client_lease != NULL) && (client_lease->cli_addr.addr == requested_ip.addr)) {
        if (client_lease->proposed_leasetime != (u32_t)(~0)) {
            if (client_lease->flags == DHCPS_ADDRESS_OFFERRED) {
                client_lease->leasetime = sys_now() + (client_lease->proposed_leasetime * 1000);
            } else {
                client_lease->leasetime += (client_lease->proposed_leasetime * 1000);
            }
        } else {
            client_lease->leasetime = client_lease->proposed_leasetime;
        }

        client_lease->flags = DHCPS_ADDRESS_BOUND;
        srvr_msg->yiaddr.addr = htonl(client_lease->cli_addr.addr);

        dhcp_common_option(srvr_msg, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN, &options_len);
        dhcp_common_option_byte(srvr_msg, DHCP_ACK, &options_len);

        dhcp_common_option(srvr_msg, DHCP_OPTION_LEASE_TIME, DHCP_OPTION_LEASE_TIME_SIZE, &options_len);
        dhcp_common_option_long(srvr_msg, client_lease->proposed_leasetime, &options_len);

        dhcp_common_option(srvr_msg, DHCP_OPTION_T1, DHCP_OPTION_T1_LEN, &options_len);
        dhcp_common_option_long(srvr_msg, (client_lease->proposed_leasetime / 2), &options_len);

        dhcp_common_option(srvr_msg, DHCP_OPTION_T2, DHCP_OPTION_T2_LEN, &options_len);
        /* calculate safe periods for lease (proposed_leasetime * 0.875 -> 87.5%) */
        dhcp_common_option_long(srvr_msg, ((client_lease->proposed_leasetime * 7) / 8), &options_len);

        dhcp_common_option(srvr_msg, DHCP_OPTION_SUBNET_MASK, DHCP_OPTION_SUBNET_MASK_SIZE, &options_len);
        dhcp_common_option_long(srvr_msg, ntohl(ip_2_ip4(&netif->netmask)->addr), &options_len);

#ifdef  LWIP_DEV_DEBUG
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                    ("handle_request: Send ACK. to=%"U32_F" lease time=%"U32_F"\n",
                    requested_ip.addr, client_lease->proposed_leasetime));
#endif
    } else {
        dhcp_common_option(srvr_msg, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN, &options_len);
        dhcp_common_option_byte(srvr_msg, DHCP_NAK, &options_len);

        /* Just set this here, so that the NAK message is brcasted.
        The correct flags has already been added in the respose message during base message creation */
        client_msg->flags |= htons(DHCP_BROADCAST_FLAG);
        client_msg->ciaddr.addr = 0; /* This is done so that NAK Gets brcasted */
#ifdef  LWIP_DEV_DEBUG
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                    ("handle_request: Send NAK. Requested from=%"U32_F"\n", requested_ip.addr));
#endif
    }

    requested_ip.addr = htonl(requested_ip.addr);
    dhcp_common_option_trailer(srvr_msg, options_len, out_msg);

    if (client_msg->ciaddr.addr != 0) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_request: sendto(ACK, ciaddr, DHCP_CLIENT_PORT)\n"));
        ip_addr_set_ip4_u32_val(dst_addr, (u32_t)(client_msg->ciaddr.addr));
        (void)udp_sendto_if_src(dhcps->pcb, out_msg, &dst_addr, DHCP_CLIENT_PORT, netif, &(netif->ip_addr));
    } else if (ntohs(client_msg->flags) & DHCP_BROADCAST_FLAG) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_request: sending reply using brdcast \n"));
        (void)udp_sendto_if_src(dhcps->pcb, out_msg, IP_ADDR_BROADCAST, DHCP_CLIENT_PORT, netif, &(netif->ip_addr));
    } else {
#if ETHARP_SUPPORT_STATIC_ENTRIES
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_request: Updating ARP Static Entry for unicast reply\n"));
        if (memcpy_s(ethaddr.addr, ETHARP_HWADDR_LEN, client_msg->chaddr, client_msg->hlen) != EOK) {
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_request: Copy chaddr failed\n"));
            (void)pbuf_free(out_msg);
            return;
        }
        if (ERR_OK != etharp_add_static_entry(&requested_ip, &ethaddr)) {
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_request: Adding static entry to arp cache failed\n"));
            (void)pbuf_free(out_msg);
            return;
        }
#endif
        /* Need to check and add an arp entry to make this pass through smoothly */
#ifdef  LWIP_DEV_DEBUG
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                    ("handle_request: sending reply using unicast Client IP =%"U32_F"\n", requested_ip.addr));
#endif
        ip_send.u_addr.ip4.addr = requested_ip.addr;
        ip_send.type = IPADDR_TYPE_V4;
        (void)udp_sendto_if_src(dhcps->pcb, out_msg, &ip_send, DHCP_CLIENT_PORT, netif, &(netif->ip_addr));

#if ETHARP_SUPPORT_STATIC_ENTRIES
        /* We just added the entry above and checked for it's success too. so, the below function call cannot fail */
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                    ("handle_request: Removing ARP Static Entry added for unicast reply\n"));
        (void)etharp_remove_static_entry(&requested_ip);
#endif
    }
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_request: deleting\n"));

    (void)pbuf_free(out_msg);
    return;
}

LWIP_STATIC void handle_decline(struct netif *netif, struct dhcps *dhcps, struct dhcp_msg *client_msg,
                                struct dyn_lease_addr *client_lease)
{
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_decline: Processing Decline Message\n"));

    if ((client_lease != NULL) && (dhcps_option_given(dhcps, DHCP_OPTION_IDX_REQUESTED_IP)) &&
        (client_msg->ciaddr.addr == 0)) {
        if (client_lease->cli_addr.addr == (u32_t)dhcps_get_option_value(dhcps, DHCP_OPTION_IDX_REQUESTED_IP)) {
#ifdef  LWIP_DEV_DEBUG
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                        ("handle_decline: Marking Client Entry as declined. Client IP =%"U32_F"\n",
                        client_lease->cli_addr.addr));
#endif
            (void)memset_s(client_lease->cli_hwaddr, sizeof(client_lease->cli_hwaddr), 0, DHCP_CHADDR_LEN);
            client_lease->proposed_leasetime = 0;
            client_lease->leasetime = sys_now() + (LWIP_DHCPS_DECLINE_TIME * 1000);
            client_lease->flags = DHCPS_ADDRESS_DECLINED;
        }
    }
}

LWIP_STATIC void handle_inform(struct netif *netif, struct dhcps *dhcps, struct dhcp_msg *client_msg)
{
    struct pbuf *out_msg = NULL;
    struct dhcp_msg *srvr_msg = NULL;
    u16_t options_len = 0;
    ip_addr_t dst_addr;

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_inform: Processing Inform Message\n"));

    if (client_msg->ciaddr.addr == 0) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_inform: ciaddr is empty. Can't send back a response\n"));
        return;
    }

    out_msg = dhcps_create_base_msg(client_msg);
    if (out_msg == NULL) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_inform: Creating base message failed\n"));
        return;
    }

    srvr_msg = (struct dhcp_msg *)out_msg->payload;
    dhcp_common_option(srvr_msg, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN, &options_len);
    dhcp_common_option_byte(srvr_msg, DHCP_ACK, &options_len);

    dhcp_common_option_trailer(srvr_msg, options_len, out_msg);

#ifdef  LWIP_DEV_DEBUG
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
               ("handle_inform: Send ACK to Client. Client is=%"U32_F"\n", client_msg->ciaddr.addr));
#endif
    ip_addr_set_ip4_u32_val(dst_addr, client_msg->ciaddr.addr);
    (void)udp_sendto_if_src(dhcps->pcb, out_msg, &dst_addr, DHCP_CLIENT_PORT, netif, &(netif->ip_addr));

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("handle_inform: deleting pbuf\n"));
    (void)pbuf_free(out_msg);

    return;
}

LWIP_STATIC void handle_client_messages(struct netif *netif, struct dhcps *dhcps,
                                        struct dhcp_msg *client_msg, ip4_addr_t serverid, u8_t msg_type)
{
    struct dyn_lease_addr *client_lease = NULL;

    client_lease = find_client_lease(dhcps, client_msg);
    switch (msg_type) {
        case DHCP_DISCOVER:
            handle_discover(netif, dhcps, client_msg, client_lease);
            break;
        case DHCP_REQUEST:
            handle_request(netif, dhcps, client_msg, client_lease, serverid);
            break;
        case DHCP_DECLINE:
            handle_decline(netif, dhcps, client_msg, client_lease);
            break;
        case DHCP_RELEASE:
            if ((client_lease != NULL) && (client_lease->cli_addr.addr == ntohl(client_msg->ciaddr.addr))) {
#ifdef  LWIP_DEV_DEBUG
                LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("DHCP Release: Client IPAdd =%"U32_F"\n", client_msg->ciaddr.addr));
#endif
                (void)memset_s(client_lease, sizeof(struct dyn_lease_addr), 0, sizeof(struct dyn_lease_addr));
                client_lease->flags = DHCPS_ADDRESS_FREE;
            }
            break;
        case DHCP_INFORM:
            handle_inform(netif, dhcps, client_msg);
            break;
        default:
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
                        ("DHCP Server. Invalid message type received %d\n", msg_type));
    }
}

err_t dhcps_parse_options(struct pbuf *p, struct dhcps *dhcps)
{
    return dhcp_parse_reply(p, &dhcps->dhcp);
}

LWIP_STATIC void dhcps_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, const ip_addr_t *ip_addr, u16_t port)
{
    struct netif *netif = (struct netif *)arg;
    struct dhcps *dhcps = netif_get_dhcps(netif);
    struct dhcp_msg *client_msg = (struct dhcp_msg *)p->payload;
    u8_t msg_type;
    ip4_addr_t serverid;
    ip4_addr_t addr;

    if (client_msg == NULL) {
        return;
    }
    addr.addr = ip_addr->u_addr.ip4.addr;
    serverid.addr = 0;
#ifdef  LWIP_DEV_DEBUG
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                ("dhcps_recv(pbuf = %p) from DHCP Client %"U16_F".%"U16_F".%"U16_F".%"U16_F" port %"U16_F"\n", (void*)p,
                ip4_addr1_16(&addr), ip4_addr2_16(&addr), ip4_addr3_16(&addr), ip4_addr4_16(&addr), port));
#endif
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("pbuf->len = %"U16_F"\n", p->len));
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("pbuf->tot_len = %"U16_F"\n", p->tot_len));
    /* prevent warnings about unused arguments */
    LWIP_UNUSED_ARG(pcb);
    LWIP_UNUSED_ARG(addr);
    LWIP_UNUSED_ARG(port);

    dhcps_clear_all_options(dhcps);

    /* Check and remove old entries on each call to dhcp_recv. This way, we don't need to maintain timers */
    remove_stale_entries(dhcps);

    if (p->len < DHCP_OPTIONS_OFS) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
                    ("DHCP client message or pbuf too short. pbuf len =%"U16_F" DHCP MIN Reply Len = %"U32_F"\n",
                        p->len, DHCP_MIN_REPLY_LEN));
        goto free_pbuf_and_return;
    }

    if (client_msg->op != DHCP_BOOTREQUEST) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
                    ("Not a DHCP reply message, Type %"U16_F"\n", (u16_t)client_msg->op));
        goto free_pbuf_and_return;
    }

    if (client_msg->cookie != PP_HTONL(DHCP_MAGIC_COOKIE)) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
                    ("DHCP Server. Cookie Value is incorrect. %"U32_F"\n", (u32_t)client_msg->cookie));
        goto free_pbuf_and_return;
    }

    if (client_msg->hlen != ETHARP_HWADDR_LEN) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
                    ("DHCP Server. Invalid hardware address length %"U16_F"\n", (u16_t)client_msg->hlen));
        goto free_pbuf_and_return;
    }

    if (dhcps_parse_options(p, dhcps) != ERR_OK) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
                    ("Parsing of Options failed in DHCP Client Message\n"));
        goto free_pbuf_and_return;
    }

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("Searching DHCP_OPTION_MESSAGE_TYPE\n"));
    /* obtain pointer to DHCP message type */
    if (!dhcps_option_given(dhcps, DHCP_OPTION_IDX_MSG_TYPE)) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
                    ("DHCP_OPTION_MESSAGE_TYPE option not found\n"));
        goto free_pbuf_and_return;
    }

    /* read DHCP message type */
    msg_type = (u8_t)dhcps_get_option_value(dhcps, DHCP_OPTION_IDX_MSG_TYPE);

    if (dhcps_option_given(dhcps, DHCP_OPTION_IDX_SERVER_ID)) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
                    ("DHCP_OPTION_SERVER_ID option found\n"));
        /* Parse options would have changed it to host order. But, we have our IP stored in netif in network order */
        serverid.addr = htonl((u32_t)dhcps_get_option_value(dhcps, DHCP_OPTION_IDX_SERVER_ID));
    }

    if ((serverid.addr != 0) && ((msg_type == DHCP_DISCOVER) || (msg_type == DHCP_INFORM))) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
                    ("Serverid present in DHCP_DISCOVER and DHCP_INFORM messages\n"));
        goto free_pbuf_and_return;
    }

    if ((!ip4_addr_cmp(&serverid, ip_2_ip4(&netif->ip_addr))) &&
        ((msg_type == DHCP_DECLINE) || (msg_type == DHCP_RELEASE))) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
                    ("Serverid not present in DHCP_RELEASE and DHCP_DECLINE messages\n"));
        goto free_pbuf_and_return;
    }

    handle_client_messages(netif, dhcps, client_msg, serverid, msg_type);

free_pbuf_and_return:
    (void)pbuf_free(p);
}

err_t dhcps_start(struct netif *netif, const char *start_ip, u16_t ip_num)
{
    struct dhcps *dhcps = NULL;
    ip4_addr_t address_in_hton;
    int err;

    LWIP_ERROR("netif != NULL", (netif != NULL), return ERR_ARG);
    dhcps = netif_get_dhcps(netif);

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
                ("dhcps_start(netif=%p) %s\n", (void *)netif, netif_get_name(netif)));

    if (netif->mtu < DHCP_MAX_MSG_LEN_MIN_REQUIRED) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                    ("MTU =%"U16_F",DHCP Msg Len Required =%"U32_F"\n", netif->mtu, DHCP_MAX_MSG_LEN_MIN_REQUIRED));
        return ERR_MEM;
    }

    if (dhcps != NULL) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcps_start(): DHCP Server is already started\n"));
        return ERR_MEM;
    }

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcps_start(): starting new DHCP Server\n"));
    dhcps = (struct dhcps *)mem_malloc(sizeof(struct dhcps));
    if (dhcps == NULL) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcps_start(): could not allocate dhcp\n"));
        return ERR_MEM;
    }

    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcps_start(): allocated dhcp"));

    (void)memset_s(dhcps, sizeof(struct dhcps), 0, sizeof(struct dhcps));

    dhcps->pcb = udp_new();
    if (dhcps->pcb == NULL) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): could not allocate pcb\n"));
        mem_free((void *)dhcps);
        return ERR_MEM;
    }

#if LWIP_SO_BINDTODEVICE
    /* bind dhcp udp_pcb to specific netif, this could make dhcp server start on multiple netif */
    dhcps->pcb->ifindex = netif->ifindex;
#endif
    if ((start_ip == NULL) || (ip_num == 0)) {
        /* use default ip lease configuration. */
        dhcps->start_addr.addr = ntohl(ip_2_ip4(&netif->ip_addr)->addr & ip_2_ip4(&netif->netmask)->addr) + 1;
        dhcps->end_addr.addr = ntohl(ip_2_ip4(&netif->ip_addr)->addr | (~ip_2_ip4(&netif->netmask)->addr)) - 1;
        dhcps->lease_num = (u8_t)(dhcps->end_addr.addr - dhcps->start_addr.addr + 1);
        if (dhcps->lease_num > LWIP_DHCPS_MAX_LEASE) {
            dhcps->lease_num = LWIP_DHCPS_MAX_LEASE;
            dhcps->end_addr.addr = dhcps->start_addr.addr + LWIP_DHCPS_MAX_LEASE - 1;
        }
    } else {
        dhcps->start_addr.addr = ntohl(ipaddr_addr(start_ip));
        dhcps->end_addr.addr = (u32_t)(dhcps->start_addr.addr +
                                       (u32_t)(LWIP_MIN(ip_num - 1, LWIP_DHCPS_MAX_LEASE - 1)));

        ip4_addr_set_hton(&address_in_hton, &dhcps->start_addr);

        if (!ip4_addr_netcmp((&address_in_hton), ip_2_ip4(&netif->ip_addr), ip_2_ip4(&netif->netmask)) ||
            ip4_addr_isbroadcast((&address_in_hton), netif)) {
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): %s in not a valid ip lease\n", start_ip));
            udp_remove(dhcps->pcb);
            mem_free((void *)dhcps);
            return ERR_ARG;
        }

        ip4_addr_set_hton(&address_in_hton, &dhcps->end_addr);

        if (!ip4_addr_netcmp((&address_in_hton), ip_2_ip4(&netif->ip_addr), ip_2_ip4(&netif->netmask)) ||
            ip4_addr_isbroadcast((&address_in_hton), netif)) {
            dhcps->end_addr.addr = ntohl(ip_2_ip4(&netif->ip_addr)->addr | (~ip_2_ip4(&netif->netmask)->addr)) - 1;
        }
        dhcps->lease_num = (u8_t)(dhcps->end_addr.addr - dhcps->start_addr.addr + 1);
    }

    dhcps->netif = netif;
    dhcps->pcb->so_options |= SOF_BROADCAST;
    err = udp_bind(dhcps->pcb, IP_ADDR_ANY, DHCP_SERVER_PORT);
    if (err != ERR_OK) {
        udp_remove(dhcps->pcb);
        mem_free((void *)dhcps);
        return ERR_MEM;
    }

    err = udp_connect(dhcps->pcb, IP_ADDR_ANY, DHCP_CLIENT_PORT);
    if (err != ERR_OK) {
        udp_remove(dhcps->pcb);
        mem_free((void *)dhcps);
        return ERR_MEM;
    }
    udp_recv(dhcps->pcb, dhcps_recv, netif);
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcps_start(): starting DHCPS Successfully\n"));
#ifdef  LWIP_DEV_DEBUG
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                ("dhcps_start(): DHCPS Conf:: netif addr = %"U32_F" dhcps start addr%"U32_F" dhcp end addr%"U32_F"\n",
                ip_2_ip4(&netif->ip_addr)->addr, dhcps->start_addr.addr, dhcps->end_addr.addr));
#endif
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
                ("dhcps_start(): DHCPS Lease Conf:: Lease Time = %"U32_F" Offer Time = %"U32_F"\n",
                    LWIP_DHCPS_LEASE_TIME, LWIP_DHCPS_OFFER_TIME));
    netif_set_dhcps(netif, dhcps);
    return ERR_OK;
}

void dhcps_stop(struct netif *netif)
{
    LWIP_ERROR("dhcps_stop: netif != NULL", (netif != NULL), return);
    struct dhcps *dhcps = netif_get_dhcps(netif);
    if (dhcps != NULL) {
        LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcps_stop(): Stopping DHCP Server\n"));
        if (dhcps->pcb != NULL) {
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcps_stop(): Removing UDP PCB\n"));
            udp_remove(dhcps->pcb);
            dhcps->pcb = NULL;
        }

        mem_free(dhcps);
        netif_set_dhcps(netif, NULL);
    }
}

#endif