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 /**
  * @file
  * Dynamic Host Configuration Protocol client
  *
  */
 
 /*
  *
  * Copyright (c) 2001-2004 Leon Woestenberg <leon.woestenberg@gmx.net>
  * Copyright (c) 2001-2004 Axon Digital Design B.V., The Netherlands.
  * 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. The name of the author may not be used to endorse or promote products
  *    derived from this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
  *
  * This file is a contribution to the lwIP TCP/IP stack.
  * The Swedish Institute of Computer Science and Adam Dunkels
  * are specifically granted permission to redistribute this
  * source code.
  *
  * Author: Leon Woestenberg <leon.woestenberg@gmx.net>
  *
  * This is a DHCP client for the lwIP TCP/IP stack. It aims to conform
  * with RFC 2131 and RFC 2132.
  *
  * TODO:
  * - Proper parsing of DHCP messages exploiting file/sname field overloading.
  * - Add JavaDoc style documentation (API, internals).
  * - Support for interfaces other than Ethernet (SLIP, PPP, ...)
  *
  * Please coordinate changes and requests with Leon Woestenberg
  * <leon.woestenberg@gmx.net>
  *
  * Integration with your code:
  *
  * In lwip/dhcp.h
  * #define DHCP_COARSE_TIMER_SECS (recommended 60 which is a minute)
  * #define DHCP_FINE_TIMER_MSECS (recommended 500 which equals TCP coarse timer)
  *
  * Then have your application call dhcp_coarse_tmr() and
  * dhcp_fine_tmr() on the defined intervals.
  *
  * dhcp_start(struct netif *netif);
  * starts a DHCP client instance which configures the interface by
  * obtaining an IP address lease and maintaining it.
  *
  * Use dhcp_release(netif) to end the lease and use dhcp_stop(netif)
  * to remove the DHCP client.
  *
  */
 
 #include "lwip/opt.h"
 
 #if LWIP_DHCP /* don't build if not configured for use in lwipopts.h */
 
 #include "lwip/stats.h"
 #include "lwip/mem.h"
 #include "lwip/udp.h"
 #include "lwip/ip_addr.h"
 #include "lwip/netif.h"
 #include "lwip/inet.h"
 #include "lwip/sys.h"
 #include "lwip/dhcp.h"
 #include "lwip/autoip.h"
 #include "lwip/dns.h"
 #include "netif/etharp.h"
 
 #include <string.h>
 
 /** Default for DHCP_GLOBAL_XID is 0xABCD0000
  * This can be changed by defining DHCP_GLOBAL_XID and DHCP_GLOBAL_XID_HEADER, e.g.
  *  #define DHCP_GLOBAL_XID_HEADER "stdlib.h"
  *  #define DHCP_GLOBAL_XID rand()
  */
 #ifdef DHCP_GLOBAL_XID_HEADER
 #include DHCP_GLOBAL_XID_HEADER /* include optional starting XID generation prototypes */
 #endif
 
 /** DHCP_OPTION_MAX_MSG_SIZE is set to the MTU
  * MTU is checked to be big enough in dhcp_start */
 #define DHCP_MAX_MSG_LEN(netif)        (netif->mtu)
 #define DHCP_MAX_MSG_LEN_MIN_REQUIRED  576
 /** Minimum length for reply before packet is parsed */
 #define DHCP_MIN_REPLY_LEN             44
 
 #define REBOOT_TRIES 2
 
 /* DHCP client state machine functions */
 static void dhcp_handle_ack(struct netif *netif);
 static void dhcp_handle_nak(struct netif *netif);
 static void dhcp_handle_offer(struct netif *netif);
 
 static err_t dhcp_discover(struct netif *netif);
 static err_t dhcp_select(struct netif *netif);
 static void dhcp_bind(struct netif *netif);
 #if DHCP_DOES_ARP_CHECK
 static void dhcp_check(struct netif *netif);
 static err_t dhcp_decline(struct netif *netif);
 #endif /* DHCP_DOES_ARP_CHECK */
 static err_t dhcp_rebind(struct netif *netif);
 static err_t dhcp_reboot(struct netif *netif);
 static void dhcp_set_state(struct dhcp *dhcp, u8_t new_state);
 
 /* receive, unfold, parse and free incoming messages */
 static void dhcp_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, u16_t port);
 static err_t dhcp_unfold_reply(struct dhcp *dhcp, struct pbuf *p);
 static u8_t *dhcp_get_option_ptr(struct dhcp *dhcp, u8_t option_type);
 static u8_t dhcp_get_option_byte(u8_t *ptr);
 #if 0
 static u16_t dhcp_get_option_short(u8_t *ptr);
 #endif
 static u32_t dhcp_get_option_long(u8_t *ptr);
 static void dhcp_free_reply(struct dhcp *dhcp);
 
 /* set the DHCP timers */
 static void dhcp_timeout(struct netif *netif);
 static void dhcp_t1_timeout(struct netif *netif);
 static void dhcp_t2_timeout(struct netif *netif);
 
 /* build outgoing messages */
 /* create a DHCP request, fill in common headers */
 static err_t dhcp_create_request(struct netif *netif);
 /* free a DHCP request */
 static void dhcp_delete_request(struct netif *netif);
 /* add a DHCP option (type, then length in bytes) */
 static void dhcp_option(struct dhcp *dhcp, u8_t option_type, u8_t option_len);
 /* add option values */
 static void dhcp_option_byte(struct dhcp *dhcp, u8_t value);
 static void dhcp_option_short(struct dhcp *dhcp, u16_t value);
 static void dhcp_option_long(struct dhcp *dhcp, u32_t value);
 /* always add the DHCP options trailer to end and pad */
 static void dhcp_option_trailer(struct dhcp *dhcp);
 
 /**
  * Back-off the DHCP client (because of a received NAK response).
  *
  * Back-off the DHCP client because of a received NAK. Receiving a
  * NAK means the client asked for something non-sensible, for
  * example when it tries to renew a lease obtained on another network.
  *
  * We clear any existing set IP address and restart DHCP negotiation
  * afresh (as per RFC2131 3.2.3).
  *
  * @param netif the netif under DHCP control
  */
 static void
 dhcp_handle_nak(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_handle_nak(netif=%p) %c%c%"U16_F"\n", 
     (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));
   /* Set the interface down since the address must no longer be used, as per RFC2131 */
   netif_set_down(netif);
   /* remove IP address from interface */
   netif_set_ipaddr(netif, IP_ADDR_ANY);
   netif_set_gw(netif, IP_ADDR_ANY);
   netif_set_netmask(netif, IP_ADDR_ANY); 
   /* Change to a defined state */
   dhcp_set_state(dhcp, DHCP_BACKING_OFF);
   /* We can immediately restart discovery */
   dhcp_discover(netif);
 }
 
 #if DHCP_DOES_ARP_CHECK
 /**
  * Checks if the offered IP address is already in use.
  *
  * It does so by sending an ARP request for the offered address and
  * entering CHECKING state. If no ARP reply is received within a small
  * interval, the address is assumed to be free for use by us.
  *
  * @param netif the netif under DHCP control
  */
 static void
 dhcp_check(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   err_t result;
   u16_t msecs;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_check(netif=%p) %c%c\n", (void *)netif, (s16_t)netif->name[0],
     (s16_t)netif->name[1]));
   dhcp_set_state(dhcp, DHCP_CHECKING);
   /* create an ARP query for the offered IP address, expecting that no host
      responds, as the IP address should not be in use. */
   result = etharp_query(netif, &dhcp->offered_ip_addr, NULL);
   if (result != ERR_OK) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING, ("dhcp_check: could not perform ARP query\n"));
   }
   dhcp->tries++;
   msecs = 500;
   dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_check(): set request timeout %"U16_F" msecs\n", msecs));
 }
 #endif /* DHCP_DOES_ARP_CHECK */
 
 /**
  * Remember the configuration offered by a DHCP server.
  *
  * @param netif the netif under DHCP control
  */
 static void
 dhcp_handle_offer(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   /* obtain the server address */
   u8_t *option_ptr = dhcp_get_option_ptr(dhcp, DHCP_OPTION_SERVER_ID);
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_handle_offer(netif=%p) %c%c%"U16_F"\n",
     (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));
   if (option_ptr != NULL) {
     dhcp->server_ip_addr.addr = htonl(dhcp_get_option_long(&option_ptr[2]));
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_STATE, ("dhcp_handle_offer(): server 0x%08"X32_F"\n", dhcp->server_ip_addr.addr));
     /* remember offered address */
     ip_addr_set(&dhcp->offered_ip_addr, (struct ip_addr *)&dhcp->msg_in->yiaddr);
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_STATE, ("dhcp_handle_offer(): offer for 0x%08"X32_F"\n", dhcp->offered_ip_addr.addr));
 
     dhcp_select(netif);
   }
 }
 
 /**
  * Select a DHCP server offer out of all offers.
  *
  * Simply select the first offer received.
  *
  * @param netif the netif under DHCP control
  * @return lwIP specific error (see error.h)
  */
 static err_t
 dhcp_select(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   err_t result;
   u16_t msecs;
 #if LWIP_NETIF_HOSTNAME
   const char *p;
 #endif /* LWIP_NETIF_HOSTNAME */
 
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_select(netif=%p) %c%c%"U16_F"\n", (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));
   dhcp_set_state(dhcp, DHCP_REQUESTING);
 
   /* create and initialize the DHCP message header */
   result = dhcp_create_request(netif);
   if (result == ERR_OK) {
     dhcp_option(dhcp, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN);
     dhcp_option_byte(dhcp, DHCP_REQUEST);
 
     dhcp_option(dhcp, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
     dhcp_option_short(dhcp, DHCP_MAX_MSG_LEN(netif));
 
     /* MUST request the offered IP address */
     dhcp_option(dhcp, DHCP_OPTION_REQUESTED_IP, 4);
     dhcp_option_long(dhcp, ntohl(dhcp->offered_ip_addr.addr));
 
     dhcp_option(dhcp, DHCP_OPTION_SERVER_ID, 4);
     dhcp_option_long(dhcp, ntohl(dhcp->server_ip_addr.addr));
 
     dhcp_option(dhcp, DHCP_OPTION_PARAMETER_REQUEST_LIST, 4/*num options*/);
     dhcp_option_byte(dhcp, DHCP_OPTION_SUBNET_MASK);
     dhcp_option_byte(dhcp, DHCP_OPTION_ROUTER);
     dhcp_option_byte(dhcp, DHCP_OPTION_BROADCAST);
     dhcp_option_byte(dhcp, DHCP_OPTION_DNS_SERVER);
 
 #if LWIP_NETIF_HOSTNAME
     p = (const char*)netif->hostname;
     if (p != NULL) {
       dhcp_option(dhcp, DHCP_OPTION_HOSTNAME, strlen(p));
       while (*p) {
         dhcp_option_byte(dhcp, *p++);
       }
     }
 #endif /* LWIP_NETIF_HOSTNAME */
 
     dhcp_option_trailer(dhcp);
     /* shrink the pbuf to the actual content length */
     pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);
 
     /* send broadcast to any DHCP server */
     udp_sendto_if(dhcp->pcb, dhcp->p_out, IP_ADDR_BROADCAST, DHCP_SERVER_PORT, netif);
     dhcp_delete_request(netif);
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_select: REQUESTING\n"));
   } else {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING, ("dhcp_select: could not allocate DHCP request\n"));
   }
   dhcp->tries++;
   msecs = (dhcp->tries < 6 ? 1 << dhcp->tries : 60) * 1000;
   dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_STATE, ("dhcp_select(): set request timeout %"U16_F" msecs\n", msecs));
   return result;
 }
 
 /**
  * The DHCP timer that checks for lease renewal/rebind timeouts.
  *
  */
 void
 dhcp_coarse_tmr()
 {
   struct netif *netif = netif_list;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_coarse_tmr()\n"));
   /* iterate through all network interfaces */
   while (netif != NULL) {
     /* only act on DHCP configured interfaces */
     if (netif->dhcp != NULL) {
       /* timer is active (non zero), and triggers (zeroes) now? */
       if (netif->dhcp->t2_timeout-- == 1) {
         LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_coarse_tmr(): t2 timeout\n"));
         /* this clients' rebind timeout triggered */
         dhcp_t2_timeout(netif);
       /* timer is active (non zero), and triggers (zeroes) now */
       } else if (netif->dhcp->t1_timeout-- == 1) {
         LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_coarse_tmr(): t1 timeout\n"));
         /* this clients' renewal timeout triggered */
         dhcp_t1_timeout(netif);
       }
     }
     /* proceed to next netif */
     netif = netif->next;
   }
 }
 
 /**
  * DHCP transaction timeout handling
  *
  * A DHCP server is expected to respond within a short period of time.
  * This timer checks whether an outstanding DHCP request is timed out.
  * 
  */
 void
 dhcp_fine_tmr()
 {
   struct netif *netif = netif_list;
   /* loop through netif's */
   while (netif != NULL) {
     /* only act on DHCP configured interfaces */
     if (netif->dhcp != NULL) {
       /* timer is active (non zero), and is about to trigger now */      
       if (netif->dhcp->request_timeout > 1) {
         netif->dhcp->request_timeout--;
       }
       else if (netif->dhcp->request_timeout == 1) {
         netif->dhcp->request_timeout--;
         /* { netif->dhcp->request_timeout == 0 } */
         LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_fine_tmr(): request timeout\n"));
         /* this clients' request timeout triggered */
         dhcp_timeout(netif);
       }
     }
     /* proceed to next network interface */
     netif = netif->next;
   }
 }
 
 /**
  * A DHCP negotiation transaction, or ARP request, has timed out.
  *
  * The timer that was started with the DHCP or ARP request has
  * timed out, indicating no response was received in time.
  *
  * @param netif the netif under DHCP control
  */
 static void
 dhcp_timeout(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_timeout()\n"));
   /* back-off period has passed, or server selection timed out */
   if ((dhcp->state == DHCP_BACKING_OFF) || (dhcp->state == DHCP_SELECTING)) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_timeout(): restarting discovery\n"));
     dhcp_discover(netif);
   /* receiving the requested lease timed out */
   } else if (dhcp->state == DHCP_REQUESTING) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_timeout(): REQUESTING, DHCP request timed out\n"));
     if (dhcp->tries <= 5) {
       dhcp_select(netif);
     } else {
       LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_timeout(): REQUESTING, releasing, restarting\n"));
       dhcp_release(netif);
       dhcp_discover(netif);
     }
 #if DHCP_DOES_ARP_CHECK
   /* received no ARP reply for the offered address (which is good) */
   } else if (dhcp->state == DHCP_CHECKING) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_timeout(): CHECKING, ARP request timed out\n"));
     if (dhcp->tries <= 1) {
       dhcp_check(netif);
     /* no ARP replies on the offered address,
        looks like the IP address is indeed free */
     } else {
       /* bind the interface to the offered address */
       dhcp_bind(netif);
     }
 #endif /* DHCP_DOES_ARP_CHECK */
   }
   /* did not get response to renew request? */
   else if (dhcp->state == DHCP_RENEWING) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_timeout(): RENEWING, DHCP request timed out\n"));
     /* just retry renewal */
     /* note that the rebind timer will eventually time-out if renew does not work */
     dhcp_renew(netif);
   /* did not get response to rebind request? */
   } else if (dhcp->state == DHCP_REBINDING) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_timeout(): REBINDING, DHCP request timed out\n"));
     if (dhcp->tries <= 8) {
       dhcp_rebind(netif);
     } else {
       LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_timeout(): RELEASING, DISCOVERING\n"));
       dhcp_release(netif);
       dhcp_discover(netif);
     }
   } else if (dhcp->state == DHCP_REBOOTING) {
     if (dhcp->tries < REBOOT_TRIES) {
       dhcp_reboot(netif);
     } else {
       dhcp_discover(netif);
     }
   }
 }
 
 /**
  * The renewal period has timed out.
  *
  * @param netif the netif under DHCP control
  */
 static void
 dhcp_t1_timeout(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_STATE, ("dhcp_t1_timeout()\n"));
   if ((dhcp->state == DHCP_REQUESTING) || (dhcp->state == DHCP_BOUND) || (dhcp->state == DHCP_RENEWING)) {
     /* just retry to renew - note that the rebind timer (t2) will
      * eventually time-out if renew tries fail. */
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_t1_timeout(): must renew\n"));
     dhcp_renew(netif);
   }
 }
 
 /**
  * The rebind period has timed out.
  *
  * @param netif the netif under DHCP control
  */
 static void
 dhcp_t2_timeout(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_t2_timeout()\n"));
   if ((dhcp->state == DHCP_REQUESTING) || (dhcp->state == DHCP_BOUND) || (dhcp->state == DHCP_RENEWING)) {
     /* just retry to rebind */
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_t2_timeout(): must rebind\n"));
     dhcp_rebind(netif);
   }
 }
 
 /**
  * Handle a DHCP ACK packet
  *
  * @param netif the netif under DHCP control
  */
 static void
 dhcp_handle_ack(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   u8_t *option_ptr;
   /* clear options we might not get from the ACK */
   dhcp->offered_sn_mask.addr = 0;
   dhcp->offered_gw_addr.addr = 0;
   dhcp->offered_bc_addr.addr = 0;
 
   /* lease time given? */
   option_ptr = dhcp_get_option_ptr(dhcp, DHCP_OPTION_LEASE_TIME);
   if (option_ptr != NULL) {
     /* remember offered lease time */
     dhcp->offered_t0_lease = dhcp_get_option_long(option_ptr + 2);
   }
   /* renewal period given? */
   option_ptr = dhcp_get_option_ptr(dhcp, DHCP_OPTION_T1);
   if (option_ptr != NULL) {
     /* remember given renewal period */
     dhcp->offered_t1_renew = dhcp_get_option_long(option_ptr + 2);
   } else {
     /* calculate safe periods for renewal */
     dhcp->offered_t1_renew = dhcp->offered_t0_lease / 2;
   }
 
   /* renewal period given? */
   option_ptr = dhcp_get_option_ptr(dhcp, DHCP_OPTION_T2);
   if (option_ptr != NULL) {
     /* remember given rebind period */
     dhcp->offered_t2_rebind = dhcp_get_option_long(option_ptr + 2);
   } else {
     /* calculate safe periods for rebinding */
     dhcp->offered_t2_rebind = dhcp->offered_t0_lease;
   }
 
   /* (y)our internet address */
   ip_addr_set(&dhcp->offered_ip_addr, &dhcp->msg_in->yiaddr);
 
 /**
  * Patch #1308
  * TODO: we must check if the file field is not overloaded by DHCP options!
  */
 #if 0
   /* boot server address */
   ip_addr_set(&dhcp->offered_si_addr, &dhcp->msg_in->siaddr);
   /* boot file name */
   if (dhcp->msg_in->file[0]) {
     dhcp->boot_file_name = mem_malloc(strlen(dhcp->msg_in->file) + 1);
     strcpy(dhcp->boot_file_name, dhcp->msg_in->file);
   }
 #endif
 
   /* subnet mask */
   option_ptr = dhcp_get_option_ptr(dhcp, DHCP_OPTION_SUBNET_MASK);
   /* subnet mask given? */
   if (option_ptr != NULL) {
     dhcp->offered_sn_mask.addr = htonl(dhcp_get_option_long(&option_ptr[2]));
   }
 
   /* gateway router */
   option_ptr = dhcp_get_option_ptr(dhcp, DHCP_OPTION_ROUTER);
   if (option_ptr != NULL) {
     dhcp->offered_gw_addr.addr = htonl(dhcp_get_option_long(&option_ptr[2]));
   }
 
   /* broadcast address */
   option_ptr = dhcp_get_option_ptr(dhcp, DHCP_OPTION_BROADCAST);
   if (option_ptr != NULL) {
     dhcp->offered_bc_addr.addr = htonl(dhcp_get_option_long(&option_ptr[2]));
   }
   
   /* DNS servers */
   option_ptr = dhcp_get_option_ptr(dhcp, DHCP_OPTION_DNS_SERVER);
   if (option_ptr != NULL) {
     u8_t n;
     dhcp->dns_count = dhcp_get_option_byte(&option_ptr[1]) / (u32_t)sizeof(struct ip_addr);
     /* limit to at most DHCP_MAX_DNS DNS servers */
     if (dhcp->dns_count > DHCP_MAX_DNS)
       dhcp->dns_count = DHCP_MAX_DNS;
     for (n = 0; n < dhcp->dns_count; n++) {
       dhcp->offered_dns_addr[n].addr = htonl(dhcp_get_option_long(&option_ptr[2 + n * 4]));
 #if LWIP_DNS
       dns_setserver( n, (struct ip_addr *)(&(dhcp->offered_dns_addr[n].addr)));
 #endif /* LWIP_DNS */
     }
 #if LWIP_DNS
     dns_setserver( n, (struct ip_addr *)(&ip_addr_any));
 #endif /* LWIP_DNS */
   }
 }
 
 /**
  * Start DHCP negotiation for a network interface.
  *
  * If no DHCP client instance was attached to this interface,
  * a new client is created first. If a DHCP client instance
  * was already present, it restarts negotiation.
  *
  * @param netif The lwIP network interface
  * @return lwIP error code
  * - ERR_OK - No error
  * - ERR_MEM - Out of memory
  */
 err_t
 dhcp_start(struct netif *netif)
 {
   struct dhcp *dhcp;
   err_t result = ERR_OK;
 
   LWIP_ERROR("netif != NULL", (netif != NULL), return ERR_ARG;);
   dhcp = netif->dhcp;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_start(netif=%p) %c%c%"U16_F"\n", (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));
   /* Remove the flag that says this netif is handled by DHCP,
      it is set when we succeeded starting. */
   netif->flags &= ~NETIF_FLAG_DHCP;
 
   /* check MTU of the netif */
   if (netif->mtu < DHCP_MAX_MSG_LEN_MIN_REQUIRED) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): Cannot use this netif with DHCP: MTU is too small\n"));
     return ERR_MEM;
   }
 
   /* no DHCP client attached yet? */
   if (dhcp == NULL) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): starting new DHCP client\n"));
     dhcp = mem_malloc(sizeof(struct dhcp));
     if (dhcp == NULL) {
       LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): could not allocate dhcp\n"));
       return ERR_MEM;
     }
     /* store this dhcp client in the netif */
     netif->dhcp = dhcp;
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): allocated dhcp"));
   /* already has DHCP client attached */
   } else {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_start(): restarting DHCP configuration\n"));
     if (dhcp->pcb != NULL) {
       udp_remove(dhcp->pcb);
     }
     LWIP_ASSERT("pbuf p_out wasn't freed", dhcp->p_out == NULL);
     LWIP_ASSERT("reply wasn't freed", dhcp->msg_in == NULL &&
       dhcp->options_in == NULL && dhcp->options_in_len == 0);
   }
     
   /* clear data structure */
   memset(dhcp, 0, sizeof(struct dhcp));
   /* allocate UDP PCB */
   dhcp->pcb = udp_new();
   if (dhcp->pcb == NULL) {
     LWIP_DEBUGF(DHCP_DEBUG  | LWIP_DBG_TRACE, ("dhcp_start(): could not obtain pcb\n"));
     mem_free((void *)dhcp);
     netif->dhcp = dhcp = NULL;
     return ERR_MEM;
   }
 #if IP_SOF_BROADCAST
   dhcp->pcb->so_options|=SOF_BROADCAST;
 #endif /* IP_SOF_BROADCAST */
   /* set up local and remote port for the pcb */
   udp_bind(dhcp->pcb, IP_ADDR_ANY, DHCP_CLIENT_PORT);
   udp_connect(dhcp->pcb, IP_ADDR_ANY, DHCP_SERVER_PORT);
   /* set up the recv callback and argument */
   udp_recv(dhcp->pcb, dhcp_recv, netif);
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): starting DHCP configuration\n"));
   /* (re)start the DHCP negotiation */
   result = dhcp_discover(netif);
   if (result != ERR_OK) {
     /* free resources allocated above */
     dhcp_stop(netif);
     return ERR_MEM;
   }
   /* Set the flag that says this netif is handled by DHCP. */
   netif->flags |= NETIF_FLAG_DHCP;
   return result;
 }
 
 /**
  * Inform a DHCP server of our manual configuration.
  *
  * This informs DHCP servers of our fixed IP address configuration
  * by sending an INFORM message. It does not involve DHCP address
  * configuration, it is just here to be nice to the network.
  *
  * @param netif The lwIP network interface
  */
 void
 dhcp_inform(struct netif *netif)
 {
   struct dhcp *dhcp, *old_dhcp;
   err_t result = ERR_OK;
   dhcp = mem_malloc(sizeof(struct dhcp));
   if (dhcp == NULL) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("dhcp_inform(): could not allocate dhcp\n"));
     return;
   }
   memset(dhcp, 0, sizeof(struct dhcp));
 
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_inform(): allocated dhcp\n"));
   dhcp->pcb = udp_new();
   if (dhcp->pcb == NULL) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("dhcp_inform(): could not obtain pcb"));
     goto free_dhcp_and_return;
   }
   old_dhcp = netif->dhcp;
   netif->dhcp = dhcp;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_inform(): created new udp pcb\n"));
   /* create and initialize the DHCP message header */
   result = dhcp_create_request(netif);
   if (result == ERR_OK) {
 
     dhcp_option(dhcp, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN);
     dhcp_option_byte(dhcp, DHCP_INFORM);
 
     dhcp_option(dhcp, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
     dhcp_option_short(dhcp, DHCP_MAX_MSG_LEN(netif));
 
     dhcp_option_trailer(dhcp);
 
     pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);
 
 #if IP_SOF_BROADCAST
     dhcp->pcb->so_options|=SOF_BROADCAST;
 #endif /* IP_SOF_BROADCAST */
     udp_bind(dhcp->pcb, IP_ADDR_ANY, DHCP_CLIENT_PORT);
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_inform: INFORMING\n"));
     udp_sendto_if(dhcp->pcb, dhcp->p_out, IP_ADDR_BROADCAST, DHCP_SERVER_PORT, netif);
     dhcp_delete_request(netif);
   } else {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("dhcp_inform: could not allocate DHCP request\n"));
   }
 
   udp_remove(dhcp->pcb);
   dhcp->pcb = NULL;
   netif->dhcp = old_dhcp;
 free_dhcp_and_return:
   mem_free((void *)dhcp);
 }
 
 /** Handle a possible change in the network configuration.
  *
  * This enters the REBOOTING state to verify that the currently bound
  * address is still valid.
  */
 void
 dhcp_network_changed(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   if (!dhcp)
     return;
   switch (dhcp->state) {
   case DHCP_REBINDING:
   case DHCP_RENEWING:
   case DHCP_BOUND:
   case DHCP_REBOOTING:
     netif_set_down(netif);
     dhcp->tries = 0;
     dhcp_reboot(netif);
     break;
   case DHCP_OFF:
     /* stay off */
     break;
   default:
     dhcp->tries = 0;
     dhcp_discover(netif);
     break;
   }
 }
 
 #if DHCP_DOES_ARP_CHECK
 /**
  * Match an ARP reply with the offered IP address.
  *
  * @param netif the network interface on which the reply was received
  * @param addr The IP address we received a reply from
  */
 void dhcp_arp_reply(struct netif *netif, struct ip_addr *addr)
 {
   LWIP_ERROR("netif != NULL", (netif != NULL), return;);
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_arp_reply()\n"));
   /* is a DHCP client doing an ARP check? */
   if ((netif->dhcp != NULL) && (netif->dhcp->state == DHCP_CHECKING)) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_arp_reply(): CHECKING, arp reply for 0x%08"X32_F"\n", addr->addr));
     /* did a host respond with the address we
        were offered by the DHCP server? */
     if (ip_addr_cmp(addr, &netif->dhcp->offered_ip_addr)) {
       /* we will not accept the offered address */
       LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE | LWIP_DBG_LEVEL_WARNING,
         ("dhcp_arp_reply(): arp reply matched with offered address, declining\n"));
       dhcp_decline(netif);
     }
   }
 }
 
 /**
  * Decline an offered lease.
  *
  * Tell the DHCP server we do not accept the offered address.
  * One reason to decline the lease is when we find out the address
  * is already in use by another host (through ARP).
  *
  * @param netif the netif under DHCP control
  */
 static err_t
 dhcp_decline(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   err_t result = ERR_OK;
   u16_t msecs;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_decline()\n"));
   dhcp_set_state(dhcp, DHCP_BACKING_OFF);
   /* create and initialize the DHCP message header */
   result = dhcp_create_request(netif);
   if (result == ERR_OK) {
     dhcp_option(dhcp, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN);
     dhcp_option_byte(dhcp, DHCP_DECLINE);
 
     dhcp_option(dhcp, DHCP_OPTION_REQUESTED_IP, 4);
     dhcp_option_long(dhcp, ntohl(dhcp->offered_ip_addr.addr));
 
     dhcp_option_trailer(dhcp);
     /* resize pbuf to reflect true size of options */
     pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);
 
     /* per section 4.4.4, broadcast DECLINE messages */
     udp_sendto_if(dhcp->pcb, dhcp->p_out, IP_ADDR_BROADCAST, DHCP_SERVER_PORT, netif);
     dhcp_delete_request(netif);
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_decline: BACKING OFF\n"));
   } else {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
       ("dhcp_decline: could not allocate DHCP request\n"));
   }
   dhcp->tries++;
   msecs = 10*1000;
   dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_decline(): set request timeout %"U16_F" msecs\n", msecs));
   return result;
 }
 #endif
 
 
 /**
  * Start the DHCP process, discover a DHCP server.
  *
  * @param netif the netif under DHCP control
  */
 static err_t
 dhcp_discover(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   err_t result = ERR_OK;
   u16_t msecs;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_discover()\n"));
   ip_addr_set(&dhcp->offered_ip_addr, IP_ADDR_ANY);
   dhcp_set_state(dhcp, DHCP_SELECTING);
   /* create and initialize the DHCP message header */
   result = dhcp_create_request(netif);
   if (result == ERR_OK) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_discover: making request\n"));
     dhcp_option(dhcp, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN);
     dhcp_option_byte(dhcp, DHCP_DISCOVER);
 
     dhcp_option(dhcp, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
     dhcp_option_short(dhcp, DHCP_MAX_MSG_LEN(netif));
 
     dhcp_option(dhcp, DHCP_OPTION_PARAMETER_REQUEST_LIST, 4/*num options*/);
     dhcp_option_byte(dhcp, DHCP_OPTION_SUBNET_MASK);
     dhcp_option_byte(dhcp, DHCP_OPTION_ROUTER);
     dhcp_option_byte(dhcp, DHCP_OPTION_BROADCAST);
     dhcp_option_byte(dhcp, DHCP_OPTION_DNS_SERVER);
 
     dhcp_option_trailer(dhcp);
 
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_discover: realloc()ing\n"));
     pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);
 
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_discover: sendto(DISCOVER, IP_ADDR_BROADCAST, DHCP_SERVER_PORT)\n"));
     udp_sendto_if(dhcp->pcb, dhcp->p_out, IP_ADDR_BROADCAST, DHCP_SERVER_PORT, netif);
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_discover: deleting()ing\n"));
     dhcp_delete_request(netif);
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_discover: SELECTING\n"));
   } else {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("dhcp_discover: could not allocate DHCP request\n"));
   }
   dhcp->tries++;
 #if LWIP_DHCP_AUTOIP_COOP
   if(dhcp->tries >= LWIP_DHCP_AUTOIP_COOP_TRIES && dhcp->autoip_coop_state == DHCP_AUTOIP_COOP_STATE_OFF) {
     dhcp->autoip_coop_state = DHCP_AUTOIP_COOP_STATE_ON;
     autoip_start(netif);
   }
 #endif /* LWIP_DHCP_AUTOIP_COOP */
   msecs = (dhcp->tries < 6 ? 1 << dhcp->tries : 60) * 1000;
   dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_discover(): set request timeout %"U16_F" msecs\n", msecs));
   return result;
 }
 
 
 /**
  * Bind the interface to the offered IP address.
  *
  * @param netif network interface to bind to the offered address
  */
 static void
 dhcp_bind(struct netif *netif)
 {
   u32_t timeout;
   struct dhcp *dhcp;
   struct ip_addr sn_mask, gw_addr;
   LWIP_ERROR("dhcp_bind: netif != NULL", (netif != NULL), return;);
   dhcp = netif->dhcp;
   LWIP_ERROR("dhcp_bind: dhcp != NULL", (dhcp != NULL), return;);
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_bind(netif=%p) %c%c%"U16_F"\n", (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));
 
   /* temporary DHCP lease? */
   if (dhcp->offered_t1_renew != 0xffffffffUL) {
     /* set renewal period timer */
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_bind(): t1 renewal timer %"U32_F" secs\n", dhcp->offered_t1_renew));
     timeout = (dhcp->offered_t1_renew + DHCP_COARSE_TIMER_SECS / 2) / DHCP_COARSE_TIMER_SECS;
     if(timeout > 0xffff) {
       timeout = 0xffff;
     }
     dhcp->t1_timeout = (u16_t)timeout;
     if (dhcp->t1_timeout == 0) {
       dhcp->t1_timeout = 1;
     }
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_bind(): set request timeout %"U32_F" msecs\n", dhcp->offered_t1_renew*1000));
   }
   /* set renewal period timer */
   if (dhcp->offered_t2_rebind != 0xffffffffUL) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_bind(): t2 rebind timer %"U32_F" secs\n", dhcp->offered_t2_rebind));
     timeout = (dhcp->offered_t2_rebind + DHCP_COARSE_TIMER_SECS / 2) / DHCP_COARSE_TIMER_SECS;
     if(timeout > 0xffff) {
       timeout = 0xffff;
     }
     dhcp->t2_timeout = (u16_t)timeout;
     if (dhcp->t2_timeout == 0) {
       dhcp->t2_timeout = 1;
     }
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_bind(): set request timeout %"U32_F" msecs\n", dhcp->offered_t2_rebind*1000));
   }
   /* copy offered network mask */
   ip_addr_set(&sn_mask, &dhcp->offered_sn_mask);
 
   /* subnet mask not given? */
   /* TODO: this is not a valid check. what if the network mask is 0? */
   if (sn_mask.addr == 0) {
     /* choose a safe subnet mask given the network class */
     u8_t first_octet = ip4_addr1(&sn_mask);
     if (first_octet <= 127) {
       sn_mask.addr = htonl(0xff000000);
     } else if (first_octet >= 192) {
       sn_mask.addr = htonl(0xffffff00);
     } else {
       sn_mask.addr = htonl(0xffff0000);
     }
   }
 
   ip_addr_set(&gw_addr, &dhcp->offered_gw_addr);
   /* gateway address not given? */
   if (gw_addr.addr == 0) {
     /* copy network address */
     gw_addr.addr = (dhcp->offered_ip_addr.addr & sn_mask.addr);
     /* use first host address on network as gateway */
     gw_addr.addr |= htonl(0x00000001);
   }
 
 #if LWIP_DHCP_AUTOIP_COOP
   if(dhcp->autoip_coop_state == DHCP_AUTOIP_COOP_STATE_ON) {
     autoip_stop(netif);
     dhcp->autoip_coop_state = DHCP_AUTOIP_COOP_STATE_OFF;
   }
 #endif /* LWIP_DHCP_AUTOIP_COOP */
 
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_STATE, ("dhcp_bind(): IP: 0x%08"X32_F"\n", dhcp->offered_ip_addr.addr));
   netif_set_ipaddr(netif, &dhcp->offered_ip_addr);
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_STATE, ("dhcp_bind(): SN: 0x%08"X32_F"\n", sn_mask.addr));
   netif_set_netmask(netif, &sn_mask);
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_STATE, ("dhcp_bind(): GW: 0x%08"X32_F"\n", gw_addr.addr));
   netif_set_gw(netif, &gw_addr);
   /* bring the interface up */
   netif_set_up(netif);
   /* netif is now bound to DHCP leased address */
   dhcp_set_state(dhcp, DHCP_BOUND);
 }
 
 /**
  * Renew an existing DHCP lease at the involved DHCP server.
  *
  * @param netif network interface which must renew its lease
  */
 err_t
 dhcp_renew(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   err_t result;
   u16_t msecs;
 #if LWIP_NETIF_HOSTNAME
   const char *p;
 #endif /* LWIP_NETIF_HOSTNAME */
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_renew()\n"));
   dhcp_set_state(dhcp, DHCP_RENEWING);
 
   /* create and initialize the DHCP message header */
   result = dhcp_create_request(netif);
   if (result == ERR_OK) {
 
     dhcp_option(dhcp, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN);
     dhcp_option_byte(dhcp, DHCP_REQUEST);
 
     dhcp_option(dhcp, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
     dhcp_option_short(dhcp, DHCP_MAX_MSG_LEN(netif));
 
 #if LWIP_NETIF_HOSTNAME
     p = (const char*)netif->hostname;
     if (p != NULL) {
       dhcp_option(dhcp, DHCP_OPTION_HOSTNAME, strlen(p));
       while (*p) {
         dhcp_option_byte(dhcp, *p++);
       }
     }
 #endif /* LWIP_NETIF_HOSTNAME */
 
 #if 0
     dhcp_option(dhcp, DHCP_OPTION_REQUESTED_IP, 4);
     dhcp_option_long(dhcp, ntohl(dhcp->offered_ip_addr.addr));
 #endif
 
 #if 0
     dhcp_option(dhcp, DHCP_OPTION_SERVER_ID, 4);
     dhcp_option_long(dhcp, ntohl(dhcp->server_ip_addr.addr));
 #endif
     /* append DHCP message trailer */
     dhcp_option_trailer(dhcp);
 
     pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);
 
     udp_sendto_if(dhcp->pcb, dhcp->p_out, &dhcp->server_ip_addr, DHCP_SERVER_PORT, netif);
     dhcp_delete_request(netif);
 
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_renew: RENEWING\n"));
   } else {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("dhcp_renew: could not allocate DHCP request\n"));
   }
   dhcp->tries++;
   /* back-off on retries, but to a maximum of 20 seconds */
   msecs = dhcp->tries < 10 ? dhcp->tries * 2000 : 20 * 1000;
   dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_renew(): set request timeout %"U16_F" msecs\n", msecs));
   return result;
 }
 
 /**
  * Rebind with a DHCP server for an existing DHCP lease.
  *
  * @param netif network interface which must rebind with a DHCP server
  */
 static err_t
 dhcp_rebind(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   err_t result;
   u16_t msecs;
 #if LWIP_NETIF_HOSTNAME
   const char *p;
 #endif /* LWIP_NETIF_HOSTNAME */
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_rebind()\n"));
   dhcp_set_state(dhcp, DHCP_REBINDING);
 
   /* create and initialize the DHCP message header */
   result = dhcp_create_request(netif);
   if (result == ERR_OK) {
 
     dhcp_option(dhcp, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN);
     dhcp_option_byte(dhcp, DHCP_REQUEST);
 
     dhcp_option(dhcp, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
     dhcp_option_short(dhcp, DHCP_MAX_MSG_LEN(netif));
 
 #if LWIP_NETIF_HOSTNAME
     p = (const char*)netif->hostname;
     if (p != NULL) {
       dhcp_option(dhcp, DHCP_OPTION_HOSTNAME, strlen(p));
       while (*p) {
         dhcp_option_byte(dhcp, *p++);
       }
     }
 #endif /* LWIP_NETIF_HOSTNAME */
 
 #if 0
     dhcp_option(dhcp, DHCP_OPTION_REQUESTED_IP, 4);
     dhcp_option_long(dhcp, ntohl(dhcp->offered_ip_addr.addr));
 
     dhcp_option(dhcp, DHCP_OPTION_SERVER_ID, 4);
     dhcp_option_long(dhcp, ntohl(dhcp->server_ip_addr.addr));
 #endif
 
     dhcp_option_trailer(dhcp);
 
     pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);
 
     /* broadcast to server */
     udp_sendto_if(dhcp->pcb, dhcp->p_out, IP_ADDR_BROADCAST, DHCP_SERVER_PORT, netif);
     dhcp_delete_request(netif);
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_rebind: REBINDING\n"));
   } else {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("dhcp_rebind: could not allocate DHCP request\n"));
   }
   dhcp->tries++;
   msecs = dhcp->tries < 10 ? dhcp->tries * 1000 : 10 * 1000;
   dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_rebind(): set request timeout %"U16_F" msecs\n", msecs));
   return result;
 }
 
 /**
  * Enter REBOOTING state to verify an existing lease
  *
  * @param netif network interface which must reboot
  */
 static err_t
 dhcp_reboot(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   err_t result;
   u16_t msecs;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_reboot()\n"));
   dhcp_set_state(dhcp, DHCP_REBOOTING);
 
   /* create and initialize the DHCP message header */
   result = dhcp_create_request(netif);
   if (result == ERR_OK) {
 
     dhcp_option(dhcp, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN);
     dhcp_option_byte(dhcp, DHCP_REQUEST);
 
     dhcp_option(dhcp, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
     dhcp_option_short(dhcp, 576);
 
     dhcp_option(dhcp, DHCP_OPTION_REQUESTED_IP, 4);
     dhcp_option_long(dhcp, ntohl(dhcp->offered_ip_addr.addr));
 
     dhcp_option_trailer(dhcp);
 
     pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);
 
     /* broadcast to server */
     udp_sendto_if(dhcp->pcb, dhcp->p_out, IP_ADDR_BROADCAST, DHCP_SERVER_PORT, netif);
     dhcp_delete_request(netif);
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_reboot: REBOOTING\n"));
   } else {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("dhcp_reboot: could not allocate DHCP request\n"));
   }
   dhcp->tries++;
   msecs = dhcp->tries < 10 ? dhcp->tries * 1000 : 10 * 1000;
   dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_reboot(): set request timeout %"U16_F" msecs\n", msecs));
   return result;
 }
 
 
 /**
  * Release a DHCP lease.
  *
  * @param netif network interface which must release its lease
  */
 err_t
 dhcp_release(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   err_t result;
   u16_t msecs;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_release()\n"));
 
   /* idle DHCP client */
   dhcp_set_state(dhcp, DHCP_OFF);
   /* clean old DHCP offer */
   dhcp->server_ip_addr.addr = 0;
   dhcp->offered_ip_addr.addr = dhcp->offered_sn_mask.addr = 0;
   dhcp->offered_gw_addr.addr = dhcp->offered_bc_addr.addr = 0;
   dhcp->offered_t0_lease = dhcp->offered_t1_renew = dhcp->offered_t2_rebind = 0;
   dhcp->dns_count = 0;
   
   /* create and initialize the DHCP message header */
   result = dhcp_create_request(netif);
   if (result == ERR_OK) {
     dhcp_option(dhcp, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN);
     dhcp_option_byte(dhcp, DHCP_RELEASE);
 
     dhcp_option_trailer(dhcp);
 
     pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);
 
     udp_sendto_if(dhcp->pcb, dhcp->p_out, &dhcp->server_ip_addr, DHCP_SERVER_PORT, netif);
     dhcp_delete_request(netif);
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_release: RELEASED, DHCP_OFF\n"));
   } else {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("dhcp_release: could not allocate DHCP request\n"));
   }
   dhcp->tries++;
   msecs = dhcp->tries < 10 ? dhcp->tries * 1000 : 10 * 1000;
   dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_release(): set request timeout %"U16_F" msecs\n", msecs));
   /* bring the interface down */
   netif_set_down(netif);
   /* remove IP address from interface */
   netif_set_ipaddr(netif, IP_ADDR_ANY);
   netif_set_gw(netif, IP_ADDR_ANY);
   netif_set_netmask(netif, IP_ADDR_ANY);
   
   /* TODO: netif_down(netif); */
   return result;
 }
 
 /**
  * Remove the DHCP client from the interface.
  *
  * @param netif The network interface to stop DHCP on
  */
 void
 dhcp_stop(struct netif *netif)
 {
   struct dhcp *dhcp = netif->dhcp;
   LWIP_ERROR("dhcp_stop: netif != NULL", (netif != NULL), return;);
   /* Remove the flag that says this netif is handled by DHCP. */
   netif->flags &= ~NETIF_FLAG_DHCP;
 
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_stop()\n"));
   /* netif is DHCP configured? */
   if (dhcp != NULL) {
 #if LWIP_DHCP_AUTOIP_COOP
   if(dhcp->autoip_coop_state == DHCP_AUTOIP_COOP_STATE_ON) {
     autoip_stop(netif);
     dhcp->autoip_coop_state = DHCP_AUTOIP_COOP_STATE_OFF;
   }
 #endif /* LWIP_DHCP_AUTOIP_COOP */
 
     if (dhcp->pcb != NULL) {
       udp_remove(dhcp->pcb);
       dhcp->pcb = NULL;
     }
     LWIP_ASSERT("reply wasn't freed", dhcp->msg_in == NULL &&
       dhcp->options_in == NULL && dhcp->options_in_len == 0);
     mem_free((void *)dhcp);
     netif->dhcp = NULL;
   }
 }
 
 /*
  * Set the DHCP state of a DHCP client.
  *
  * If the state changed, reset the number of tries.
  *
  * TODO: we might also want to reset the timeout here?
  */
 static void
 dhcp_set_state(struct dhcp *dhcp, u8_t new_state)
 {
   if (new_state != dhcp->state) {
     dhcp->state = new_state;
     dhcp->tries = 0;
   }
 }
 
 /*
  * Concatenate an option type and length field to the outgoing
  * DHCP message.
  *
  */
 static void
 dhcp_option(struct dhcp *dhcp, u8_t option_type, u8_t option_len)
 {
   LWIP_ASSERT("dhcp_option: dhcp->options_out_len + 2 + option_len <= DHCP_OPTIONS_LEN", dhcp->options_out_len + 2U + option_len <= DHCP_OPTIONS_LEN);
   dhcp->msg_out->options[dhcp->options_out_len++] = option_type;
   dhcp->msg_out->options[dhcp->options_out_len++] = option_len;
 }
 /*
  * Concatenate a single byte to the outgoing DHCP message.
  *
  */
 static void
 dhcp_option_byte(struct dhcp *dhcp, u8_t value)
 {
   LWIP_ASSERT("dhcp_option_byte: dhcp->options_out_len < DHCP_OPTIONS_LEN", dhcp->options_out_len < DHCP_OPTIONS_LEN);
   dhcp->msg_out->options[dhcp->options_out_len++] = value;
 }
 
 static void
 dhcp_option_short(struct dhcp *dhcp, u16_t value)
 {
   LWIP_ASSERT("dhcp_option_short: dhcp->options_out_len + 2 <= DHCP_OPTIONS_LEN", dhcp->options_out_len + 2U <= DHCP_OPTIONS_LEN);
   dhcp->msg_out->options[dhcp->options_out_len++] = (u8_t)((value & 0xff00U) >> 8);
   dhcp->msg_out->options[dhcp->options_out_len++] = (u8_t) (value & 0x00ffU);
 }
 
 static void
 dhcp_option_long(struct dhcp *dhcp, u32_t value)
 {
   LWIP_ASSERT("dhcp_option_long: dhcp->options_out_len + 4 <= DHCP_OPTIONS_LEN", dhcp->options_out_len + 4U <= DHCP_OPTIONS_LEN);
   dhcp->msg_out->options[dhcp->options_out_len++] = (u8_t)((value & 0xff000000UL) >> 24);
   dhcp->msg_out->options[dhcp->options_out_len++] = (u8_t)((value & 0x00ff0000UL) >> 16);
   dhcp->msg_out->options[dhcp->options_out_len++] = (u8_t)((value & 0x0000ff00UL) >> 8);
   dhcp->msg_out->options[dhcp->options_out_len++] = (u8_t)((value & 0x000000ffUL));
 }
 
 /**
  * Extract the DHCP message and the DHCP options.
  *
  * Extract the DHCP message and the DHCP options, each into a contiguous
  * piece of memory. As a DHCP message is variable sized by its options,
  * and also allows overriding some fields for options, the easy approach
  * is to first unfold the options into a conitguous piece of memory, and
  * use that further on.
  *
  */
 static err_t
 dhcp_unfold_reply(struct dhcp *dhcp, struct pbuf *p)
 {
   u16_t ret;
   LWIP_ERROR("dhcp != NULL", (dhcp != NULL), return ERR_ARG;);
   /* free any left-overs from previous unfolds */
   dhcp_free_reply(dhcp);
   /* options present? */
   if (p->tot_len > (sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN)) {
     dhcp->options_in_len = p->tot_len - (sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN);
     dhcp->options_in = mem_malloc(dhcp->options_in_len);
     if (dhcp->options_in == NULL) {
       LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
         ("dhcp_unfold_reply(): could not allocate dhcp->options\n"));
       dhcp->options_in_len = 0;
       return ERR_MEM;
     }
   }
   dhcp->msg_in = mem_malloc(sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN);
   if (dhcp->msg_in == NULL) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
       ("dhcp_unfold_reply(): could not allocate dhcp->msg_in\n"));
     if (dhcp->options_in != NULL) {
       mem_free(dhcp->options_in);
       dhcp->options_in = NULL;
       dhcp->options_in_len = 0;
     }
     return ERR_MEM;
   }
 
   /** copy the DHCP message without options */
   ret = pbuf_copy_partial(p, dhcp->msg_in, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN, 0);
   LWIP_ASSERT("ret == sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN", ret == sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN);
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_unfold_reply(): copied %"U16_F" bytes into dhcp->msg_in[]\n",
      sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN));
 
   if (dhcp->options_in != NULL) {
     /** copy the DHCP options */
     ret = pbuf_copy_partial(p, dhcp->options_in, dhcp->options_in_len, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN);
     LWIP_ASSERT("ret == dhcp->options_in_len", ret == dhcp->options_in_len);
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_unfold_reply(): copied %"U16_F" bytes to dhcp->options_in[]\n",
       dhcp->options_in_len));
   }
   LWIP_UNUSED_ARG(ret);
   return ERR_OK;
 }
 
 /**
  * Free the incoming DHCP message including contiguous copy of
  * its DHCP options.
  */
 static void dhcp_free_reply(struct dhcp *dhcp)
 {
   if (dhcp->msg_in != NULL) {
     mem_free((void *)dhcp->msg_in);
     dhcp->msg_in = NULL;
   }
   if (dhcp->options_in) {
     mem_free(dhcp->options_in);
     dhcp->options_in = NULL;
     dhcp->options_in_len = 0;
   }
   LWIP_DEBUGF(DHCP_DEBUG, ("dhcp_free_reply(): free'd\n"));
 }
 
 /**
  * If an incoming DHCP message is in response to us, then trigger the state machine
  */
 static void dhcp_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, u16_t port)
 {
   struct netif *netif = (struct netif *)arg;
   struct dhcp *dhcp = netif->dhcp;
   struct dhcp_msg *reply_msg = (struct dhcp_msg *)p->payload;
   u8_t *options_ptr;
   u8_t msg_type;
   u8_t i;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_recv(pbuf = %p) from DHCP server %"U16_F".%"U16_F".%"U16_F".%"U16_F" port %"U16_F"\n", (void*)p,
     (u16_t)(ntohl(addr->addr) >> 24 & 0xff), (u16_t)(ntohl(addr->addr) >> 16 & 0xff),
     (u16_t)(ntohl(addr->addr) >>  8 & 0xff), (u16_t)(ntohl(addr->addr) & 0xff), port));
   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);
 
   LWIP_ASSERT("reply wasn't freed", dhcp->msg_in == NULL &&
     dhcp->options_in == NULL && dhcp->options_in_len == 0);
 
   if (p->len < DHCP_MIN_REPLY_LEN) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING, ("DHCP reply message too short\n"));
     goto free_pbuf_and_return;
   }
 
   if (reply_msg->op != DHCP_BOOTREPLY) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING, ("not a DHCP reply message, but type %"U16_F"\n", (u16_t)reply_msg->op));
     goto free_pbuf_and_return;
   }
   /* iterate through hardware address and match against DHCP message */
   for (i = 0; i < netif->hwaddr_len; i++) {
     if (netif->hwaddr[i] != reply_msg->chaddr[i]) {
       LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
         ("netif->hwaddr[%"U16_F"]==%02"X16_F" != reply_msg->chaddr[%"U16_F"]==%02"X16_F"\n",
         (u16_t)i, (u16_t)netif->hwaddr[i], (u16_t)i, (u16_t)reply_msg->chaddr[i]));
       goto free_pbuf_and_return;
     }
   }
   /* match transaction ID against what we expected */
   if (ntohl(reply_msg->xid) != dhcp->xid) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
       ("transaction id mismatch reply_msg->xid(%"X32_F")!=dhcp->xid(%"X32_F")\n",ntohl(reply_msg->xid),dhcp->xid));
     goto free_pbuf_and_return;
   }
   /* option fields could be unfold? */
   if (dhcp_unfold_reply(dhcp, p) != ERR_OK) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
       ("problem unfolding DHCP message - too short on memory?\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 */
   options_ptr = dhcp_get_option_ptr(dhcp, DHCP_OPTION_MESSAGE_TYPE);
   if (options_ptr == NULL) {
     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 = dhcp_get_option_byte(options_ptr + 2);
   /* message type is DHCP ACK? */
   if (msg_type == DHCP_ACK) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("DHCP_ACK received\n"));
     /* in requesting state? */
     if (dhcp->state == DHCP_REQUESTING) {
       dhcp_handle_ack(netif);
       dhcp->request_timeout = 0;
 #if DHCP_DOES_ARP_CHECK
       /* check if the acknowledged lease address is already in use */
       dhcp_check(netif);
 #else
       /* bind interface to the acknowledged lease address */
       dhcp_bind(netif);
 #endif
     }
     /* already bound to the given lease address? */
     else if ((dhcp->state == DHCP_REBOOTING) || (dhcp->state == DHCP_REBINDING) || (dhcp->state == DHCP_RENEWING)) {
       dhcp->request_timeout = 0;
       dhcp_bind(netif);
     }
   }
   /* received a DHCP_NAK in appropriate state? */
   else if ((msg_type == DHCP_NAK) &&
     ((dhcp->state == DHCP_REBOOTING) || (dhcp->state == DHCP_REQUESTING) ||
      (dhcp->state == DHCP_REBINDING) || (dhcp->state == DHCP_RENEWING  ))) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("DHCP_NAK received\n"));
     dhcp->request_timeout = 0;
     dhcp_handle_nak(netif);
   }
   /* received a DHCP_OFFER in DHCP_SELECTING state? */
   else if ((msg_type == DHCP_OFFER) && (dhcp->state == DHCP_SELECTING)) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("DHCP_OFFER received in DHCP_SELECTING state\n"));
     dhcp->request_timeout = 0;
     /* remember offered lease */
     dhcp_handle_offer(netif);
   }
 free_pbuf_and_return:
   dhcp_free_reply(dhcp);
   pbuf_free(p);
 }
 
 /**
  * Create a DHCP request, fill in common headers
  *
  * @param netif the netif under DHCP control
  */
 static err_t
 dhcp_create_request(struct netif *netif)
 {
   struct dhcp *dhcp;
   u16_t i;
 #ifndef DHCP_GLOBAL_XID
   /** default global transaction identifier starting value (easy to match
    *  with a packet analyser). We simply increment for each new request.
    *  Predefine DHCP_GLOBAL_XID to a better value or a function call to generate one
    *  at runtime, any supporting function prototypes can be defined in DHCP_GLOBAL_XID_HEADER */
   static u32_t xid = 0xABCD0000;
 #else
   static u32_t xid;
   static u8_t xid_initialised = 0;
   if (!xid_initialised) {
     xid = DHCP_GLOBAL_XID;
     xid_initialised = !xid_initialised;
   }
 #endif
   LWIP_ERROR("dhcp_create_request: netif != NULL", (netif != NULL), return ERR_ARG;);
   dhcp = netif->dhcp;
   LWIP_ERROR("dhcp_create_request: dhcp != NULL", (dhcp != NULL), return ERR_VAL;);
   LWIP_ASSERT("dhcp_create_request: dhcp->p_out == NULL", dhcp->p_out == NULL);
   LWIP_ASSERT("dhcp_create_request: dhcp->msg_out == NULL", dhcp->msg_out == NULL);
   dhcp->p_out = pbuf_alloc(PBUF_TRANSPORT, sizeof(struct dhcp_msg), PBUF_RAM);
   if (dhcp->p_out == NULL) {
     LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
       ("dhcp_create_request(): could not allocate pbuf\n"));
     return ERR_MEM;
   }
   LWIP_ASSERT("dhcp_create_request: check that first pbuf can hold struct dhcp_msg",
            (dhcp->p_out->len >= sizeof(struct dhcp_msg)));
 
   /* reuse transaction identifier in retransmissions */
   if (dhcp->tries==0)
       xid++;
   dhcp->xid = xid;
   LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
               ("transaction id xid(%"X32_F")\n", xid));
 
   dhcp->msg_out = (struct dhcp_msg *)dhcp->p_out->payload;
 
   dhcp->msg_out->op = DHCP_BOOTREQUEST;
   /* TODO: make link layer independent */
   dhcp->msg_out->htype = DHCP_HTYPE_ETH;
   /* TODO: make link layer independent */
   dhcp->msg_out->hlen = DHCP_HLEN_ETH;
   dhcp->msg_out->hops = 0;
   dhcp->msg_out->xid = htonl(dhcp->xid);
   dhcp->msg_out->secs = 0;
   dhcp->msg_out->flags = 0;
   dhcp->msg_out->ciaddr.addr = 0;
   if (dhcp->state==DHCP_BOUND || dhcp->state==DHCP_RENEWING || dhcp->state==DHCP_REBINDING) {
     dhcp->msg_out->ciaddr.addr = netif->ip_addr.addr;
   }
   dhcp->msg_out->yiaddr.addr = 0;
   dhcp->msg_out->siaddr.addr = 0;
   dhcp->msg_out->giaddr.addr = 0;
   for (i = 0; i < DHCP_CHADDR_LEN; i++) {
     /* copy netif hardware address, pad with zeroes */
     dhcp->msg_out->chaddr[i] = (i < netif->hwaddr_len) ? netif->hwaddr[i] : 0/* pad byte*/;
   }
   for (i = 0; i < DHCP_SNAME_LEN; i++) {
     dhcp->msg_out->sname[i] = 0;
   }
   for (i = 0; i < DHCP_FILE_LEN; i++) {
     dhcp->msg_out->file[i] = 0;
   }
   dhcp->msg_out->cookie = htonl(0x63825363UL);
   dhcp->options_out_len = 0;
   /* fill options field with an incrementing array (for debugging purposes) */
   for (i = 0; i < DHCP_OPTIONS_LEN; i++) {
     dhcp->msg_out->options[i] = (u8_t)i; /* for debugging only, no matter if truncated */
   }
   return ERR_OK;
 }
 
 /**
  * Free previously allocated memory used to send a DHCP request.
  *
  * @param netif the netif under DHCP control
  */
 static void
 dhcp_delete_request(struct netif *netif)
 {
   struct dhcp *dhcp;
   LWIP_ERROR("dhcp_delete_request: netif != NULL", (netif != NULL), return;);
   dhcp = netif->dhcp;
   LWIP_ERROR("dhcp_delete_request: dhcp != NULL", (dhcp != NULL), return;);
   LWIP_ASSERT("dhcp_delete_request: dhcp->p_out != NULL", dhcp->p_out != NULL);
   LWIP_ASSERT("dhcp_delete_request: dhcp->msg_out != NULL", dhcp->msg_out != NULL);
   if (dhcp->p_out != NULL) {
     pbuf_free(dhcp->p_out);
   }
   dhcp->p_out = NULL;
   dhcp->msg_out = NULL;
 }
 
 /**
  * Add a DHCP message trailer
  *
  * Adds the END option to the DHCP message, and if
  * necessary, up to three padding bytes.
  *
  * @param dhcp DHCP state structure
  */
 static void
 dhcp_option_trailer(struct dhcp *dhcp)
 {
   LWIP_ERROR("dhcp_option_trailer: dhcp != NULL", (dhcp != NULL), return;);
   LWIP_ASSERT("dhcp_option_trailer: dhcp->msg_out != NULL\n", dhcp->msg_out != NULL);
   LWIP_ASSERT("dhcp_option_trailer: dhcp->options_out_len < DHCP_OPTIONS_LEN\n", dhcp->options_out_len < DHCP_OPTIONS_LEN);
   dhcp->msg_out->options[dhcp->options_out_len++] = DHCP_OPTION_END;
   /* packet is too small, or not 4 byte aligned? */
   while ((dhcp->options_out_len < DHCP_MIN_OPTIONS_LEN) || (dhcp->options_out_len & 3)) {
     /* LWIP_DEBUGF(DHCP_DEBUG,("dhcp_option_trailer:dhcp->options_out_len=%"U16_F", DHCP_OPTIONS_LEN=%"U16_F, dhcp->options_out_len, DHCP_OPTIONS_LEN)); */
     LWIP_ASSERT("dhcp_option_trailer: dhcp->options_out_len < DHCP_OPTIONS_LEN\n", dhcp->options_out_len < DHCP_OPTIONS_LEN);
     /* add a fill/padding byte */
     dhcp->msg_out->options[dhcp->options_out_len++] = 0;
   }
 }
 
 /**
  * Find the offset of a DHCP option inside the DHCP message.
  *
  * @param dhcp DHCP client
  * @param option_type
  *
  * @return a byte offset into the UDP message where the option was found, or
  * zero if the given option was not found.
  */
 static u8_t *dhcp_get_option_ptr(struct dhcp *dhcp, u8_t option_type)
 {
   u8_t overload = DHCP_OVERLOAD_NONE;
 
   /* options available? */
   if ((dhcp->options_in != NULL) && (dhcp->options_in_len > 0)) {
     /* start with options field */
     u8_t *options = (u8_t *)dhcp->options_in;
     u16_t offset = 0;
     /* at least 1 byte to read and no end marker, then at least 3 bytes to read? */
     while ((offset < dhcp->options_in_len) && (options[offset] != DHCP_OPTION_END)) {
       /* LWIP_DEBUGF(DHCP_DEBUG, ("msg_offset=%"U16_F", q->len=%"U16_F, msg_offset, q->len)); */
       /* are the sname and/or file field overloaded with options? */
       if (options[offset] == DHCP_OPTION_OVERLOAD) {
         LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("overloaded message detected\n"));
         /* skip option type and length */
         offset += 2;
         overload = options[offset++];
       }
       /* requested option found */
       else if (options[offset] == option_type) {
         LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("option found at offset %"U16_F" in options\n", offset));
         return &options[offset];
       /* skip option */
       } else {
          LWIP_DEBUGF(DHCP_DEBUG, ("skipping option %"U16_F" in options\n", options[offset]));
         /* skip option type */
         offset++;
         /* skip option length, and then length bytes */
         offset += 1 + options[offset];
       }
     }
     /* is this an overloaded message? */
     if (overload != DHCP_OVERLOAD_NONE) {
       u16_t field_len;
       if (overload == DHCP_OVERLOAD_FILE) {
         LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("overloaded file field\n"));
         options = (u8_t *)&dhcp->msg_in->file;
         field_len = DHCP_FILE_LEN;
       } else if (overload == DHCP_OVERLOAD_SNAME) {
         LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("overloaded sname field\n"));
         options = (u8_t *)&dhcp->msg_in->sname;
         field_len = DHCP_SNAME_LEN;
       /* TODO: check if else if () is necessary */
       } else {
         LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("overloaded sname and file field\n"));
         options = (u8_t *)&dhcp->msg_in->sname;
         field_len = DHCP_FILE_LEN + DHCP_SNAME_LEN;
       }
       offset = 0;
 
       /* at least 1 byte to read and no end marker */
       while ((offset < field_len) && (options[offset] != DHCP_OPTION_END)) {
         if (options[offset] == option_type) {
            LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("option found at offset=%"U16_F"\n", offset));
           return &options[offset];
         /* skip option */
         } else {
           LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("skipping option %"U16_F"\n", options[offset]));
           /* skip option type */
           offset++;
           offset += 1 + options[offset];
         }
       }
     }
   }
   return NULL;
 }
 
 /**
  * Return the byte of DHCP option data.
  *
  * @param client DHCP client.
  * @param ptr pointer obtained by dhcp_get_option_ptr().
  *
  * @return byte value at the given address.
  */
 static u8_t
 dhcp_get_option_byte(u8_t *ptr)
 {
   LWIP_DEBUGF(DHCP_DEBUG, ("option byte value=%"U16_F"\n", (u16_t)(*ptr)));
   return *ptr;
 }
 
 #if 0 /* currently unused */
 /**
  * Return the 16-bit value of DHCP option data.
  *
  * @param client DHCP client.
  * @param ptr pointer obtained by dhcp_get_option_ptr().
  *
  * @return byte value at the given address.
  */
 static u16_t
 dhcp_get_option_short(u8_t *ptr)
 {
   u16_t value;
   value = *ptr++ << 8;
   value |= *ptr;
   LWIP_DEBUGF(DHCP_DEBUG, ("option short value=%"U16_F"\n", value));
   return value;
 }
 #endif
 
 /**
  * Return the 32-bit value of DHCP option data.
  *
  * @param client DHCP client.
  * @param ptr pointer obtained by dhcp_get_option_ptr().
  *
  * @return byte value at the given address.
  */
 static u32_t dhcp_get_option_long(u8_t *ptr)
 {
   u32_t value;
   value = (u32_t)(*ptr++) << 24;
   value |= (u32_t)(*ptr++) << 16;
   value |= (u32_t)(*ptr++) << 8;
   value |= (u32_t)(*ptr++);
   LWIP_DEBUGF(DHCP_DEBUG, ("option long value=%"U32_F"\n", value));
   return value;
 }
 
 #endif /* LWIP_DHCP */