/**
 * @file
 * Address Resolution Protocol module for IP over Ethernet
 *
 */

/*
 * Copyright (c) 2001-2003 Swedish Institute of Computer Science.
 * 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 part of the lwIP TCP/IP stack.
 * 
 * Author: Adam Dunkels <adam@sics.se>
 *
 */
 
/*
 * TODO:
 *
RFC 3220 4.6          IP Mobility Support for IPv4          January 2002 

      -  A Gratuitous ARP [45] is an ARP packet sent by a node in order 
         to spontaneously cause other nodes to update an entry in their 
         ARP cache.  A gratuitous ARP MAY use either an ARP Request or 
         an ARP Reply packet.  In either case, the ARP Sender Protocol 
         Address and ARP Target Protocol Address are both set to the IP 
         address of the cache entry to be updated, and the ARP Sender 
         Hardware Address is set to the link-layer address to which this 
         cache entry should be updated.  When using an ARP Reply packet, 
         the Target Hardware Address is also set to the link-layer 
         address to which this cache entry should be updated (this field 
         is not used in an ARP Request packet). 

         In either case, for a gratuitous ARP, the ARP packet MUST be 
         transmitted as a local broadcast packet on the local link.  As 
         specified in [36], any node receiving any ARP packet (Request 
         or Reply) MUST update its local ARP cache with the Sender 
         Protocol and Hardware Addresses in the ARP packet, if the 
         receiving node has an entry for that IP address already in its 
         ARP cache.  This requirement in the ARP protocol applies even 
         for ARP Request packets, and for ARP Reply packets that do not 
         match any ARP Request transmitted by the receiving node [36]. 
*
  My suggestion would be to send a ARP request for our newly obtained
  address upon configuration of an Ethernet interface.

*/

#include "lwip/opt.h"
#include "lwip/inet.h"
#include "netif/etharp.h"
#include "lwip/ip.h"
#include "lwip/stats.h"

/* ARP needs to inform DHCP of any ARP replies? */
#if (LWIP_DHCP && DHCP_DOES_ARP_CHECK)
#  include "lwip/dhcp.h"
#endif

/** the time an ARP entry stays valid after its last update, (120 * 10) seconds = 20 minutes. */
#define ARP_MAXAGE 120  
/** the time an ARP entry stays pending after first request, (2 * 10) seconds = 20 seconds. */
#define ARP_MAXPENDING 2 

#define HWTYPE_ETHERNET 1

/** ARP message types */
#define ARP_REQUEST 1
#define ARP_REPLY 2

#define ARPH_HWLEN(hdr) (ntohs((hdr)->_hwlen_protolen) >> 8)
#define ARPH_PROTOLEN(hdr) (ntohs((hdr)->_hwlen_protolen) & 0xff)

#define ARPH_HWLEN_SET(hdr, len) (hdr)->_hwlen_protolen = htons(ARPH_PROTOLEN(hdr) | ((len) << 8))
#define ARPH_PROTOLEN_SET(hdr, len) (hdr)->_hwlen_protolen = htons((len) | (ARPH_HWLEN(hdr) << 8))

enum etharp_state {
  ETHARP_STATE_EMPTY,
  ETHARP_STATE_PENDING,
  ETHARP_STATE_STABLE
};

struct etharp_entry {
  struct ip_addr ipaddr;
  struct eth_addr ethaddr;
  enum etharp_state state;
#if ARP_QUEUEING
  struct pbuf *p;
#endif
  u8_t ctime;
};

static const struct eth_addr ethbroadcast = {{0xff,0xff,0xff,0xff,0xff,0xff}};
static struct etharp_entry arp_table[ARP_TABLE_SIZE];

static struct pbuf *update_arp_entry(struct netif *netif, struct ip_addr *ipaddr, struct eth_addr *ethaddr, u8_t flags);
#define ARP_INSERT_FLAG 1

/**
 * Initializes ARP module.
 */
void
etharp_init(void)
{
  u8_t i;
  /* clear ARP entries */
  for(i = 0; i < ARP_TABLE_SIZE; ++i) {
    arp_table[i].state = ETHARP_STATE_EMPTY;
#if ARP_QUEUEING
    arp_table[i].p = NULL;
#endif
  }
}

/**
 * Clears expired entries in the ARP table.
 *
 * This function should be called every ETHARP_TMR_INTERVAL microseconds (10 seconds),
 * in order to expire entries in the ARP table.
 */
void
etharp_tmr(void)
{
  u8_t i;
  
  DEBUGF(ETHARP_DEBUG, ("etharp_timer\n"));
  /* remove expired entries from the ARP table */
  for(i = 0; i < ARP_TABLE_SIZE; ++i) {
    arp_table[i].ctime++;	  
    if((arp_table[i].state == ETHARP_STATE_STABLE) &&       
       (arp_table[i].ctime >= ARP_MAXAGE)) {
      DEBUGF(ETHARP_DEBUG, ("etharp_timer: expired stable entry %u.\n", i));
      arp_table[i].state = ETHARP_STATE_EMPTY;
#if ARP_QUEUEING
      /* remove any queued packet */
      pbuf_free(arp_table[i].p);      
      arp_table[i].p = NULL;
#endif
    } else if((arp_table[i].state == ETHARP_STATE_PENDING) &&
	      (arp_table[i].ctime >= ARP_MAXPENDING)) {
      arp_table[i].state = ETHARP_STATE_EMPTY;
#if ARP_QUEUEING
      DEBUGF(ETHARP_DEBUG, ("etharp_timer: expired pending entry %u - dequeueing %p.\n", i, (void *)(arp_table[i].p)));
      /* remove any queued packet */
      pbuf_free(arp_table[i].p);      
      arp_table[i].p = NULL;
#else
      DEBUGF(ETHARP_DEBUG, ("etharp_timer: expired pending entry %u.\n", i));
#endif
    }
  }  
}

/**
 * Return an empty ARP entry or, if the table is full, ARP_TABLE_SIZE if all
 * entries are pending, otherwise the oldest entry.
 *
 * @return The ARP entry index that is available, ARP_TABLE_SIZE if no usable
 * entry is found.
 */
static u8_t
find_arp_entry(void)
{
  u8_t i, j, maxtime;
  
  /* Try to find an unused entry in the ARP table. */
  for(i = 0; i < ARP_TABLE_SIZE; ++i) {
    if(arp_table[i].state == ETHARP_STATE_EMPTY) {
      DEBUGF(ETHARP_DEBUG, ("find_arp_entry: found empty entry %u\n", i));
      break;
    }
  }
  
  /* If no unused entry is found, we try to find the oldest entry and
     throw it away. If all entries are new and have 0 ctime drop one  */
  if(i == ARP_TABLE_SIZE) {
    maxtime = 0;
    j = ARP_TABLE_SIZE;
    for(i = 0; i < ARP_TABLE_SIZE; ++i) {
      /* remember entry with oldest stable entry in j*/
      if((arp_table[i].state == ETHARP_STATE_STABLE) &&
#if ARP_QUEUEING /* do not want to re-use an entry with queued packets */
      (arp_table[i].p == NULL) &&
#endif
      (arp_table[i].ctime >= maxtime)) {
        maxtime = arp_table[i].ctime;
	      j = i;
      }
    }
    DEBUGF(ETHARP_DEBUG, ("find_arp_entry: found oldest stable entry %u\n", j));
    i = j;
  }
  DEBUGF(ETHARP_DEBUG, ("find_arp_entry: returning %u, state %u\n", i, arp_table[i].state));
  return i;
}

/**
 * Update (or insert) a IP/MAC address pair in the ARP cache.
 *
 * @param ipaddr IP address of the inserted ARP entry.
 * @param ethaddr Ethernet address of the inserted ARP entry.
 * @param flags Defines behaviour:
 * - ARP_INSERT_FLAG Allows ARP to insert this as a new item. If not specified,
 * only existing ARP entries will be updated.
 *
 * @return pbuf If non-NULL, a packet that was queued on a pending entry.
 * You should sent it and must call pbuf_free() afterwards.
 *
 * @see pbuf_free()
 */
static struct pbuf *
update_arp_entry(struct netif *netif, struct ip_addr *ipaddr, struct eth_addr *ethaddr, u8_t flags)
{
  u8_t i, k;
#if ARP_QUEUEING
  struct pbuf *p;
  struct eth_hdr *ethhdr;
#endif
  DEBUGF(ETHARP_DEBUG | DBG_TRACE | 3, ("update_arp_entry()\n"));
  DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: %u.%u.%u.%u - %02x:%02x:%02x:%02x:%02x:%02x\n", ip4_addr1(ipaddr), ip4_addr2(ipaddr), ip4_addr3(ipaddr), ip4_addr4(ipaddr),
  ethaddr->addr[0], ethaddr->addr[1], ethaddr->addr[2], ethaddr->addr[3], ethaddr->addr[4], ethaddr->addr[5]));
  /* do not update for 0.0.0.0 addresses */
  if (ipaddr->addr == 0) {
    DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: will not add 0.0.0.0 to ARP cache\n"));
    return NULL;
  }
  /* Walk through the ARP mapping table and try to find an entry to
  update. If none is found, the IP -> MAC address mapping is
  inserted in the ARP table. */
  for(i = 0; i < ARP_TABLE_SIZE; ++i) {
    /* Check if the source IP address of the incoming packet matches
    the IP address in this ARP table entry. */
    if(ip_addr_cmp(ipaddr, &arp_table[i].ipaddr)) {
      /* pending entry? */
      if(arp_table[i].state == ETHARP_STATE_PENDING) {
        DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: pending entry %u goes stable\n", i));
        /* A pending entry was found, mark it stable */
        arp_table[i].state = ETHARP_STATE_STABLE;
        /* fall-through to next if */
      }
      /* stable entry? (possible just marked to become stable) */
      if(arp_table[i].state == ETHARP_STATE_STABLE) {
        DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: updating stable entry %u\n", i));
        /* An old entry found, update this and return. */
        for(k = 0; k < netif->hwaddr_len; ++k) {
          arp_table[i].ethaddr.addr[k] = ethaddr->addr[k];
        }
        /* reset time stamp */
        arp_table[i].ctime = 0;
#if ARP_QUEUEING
        /* queued packet present? */
        if((p = arp_table[i].p) != NULL) {
          /* Null out attached buffer immediately */
          arp_table[i].p = NULL;
          /* fill-in Ethernet header */
          ethhdr = p->payload;
          for(k = 0; k < netif->hwaddr_len; ++k) {
            ethhdr->dest.addr[k] = ethaddr->addr[k];
          }
          ethhdr->type = htons(ETHTYPE_IP);	  	 	  
          DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: sending queued IP packet.\n"));
          /* send the queued IP packet */
          netif->linkoutput(netif, p);
          /* free the queued IP packet */
          pbuf_free(p);
        }
#endif
        return NULL;
      }
    } /* if */
  } /* for */

  /* no matching ARP entry was found */
  LWIP_ASSERT("update_arp_entry: i == ARP_TABLE_SIZE", i == ARP_TABLE_SIZE);

  DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: IP address not yet in table\n"));
  /* allowed to insert an entry? */
  if ((ETHARP_ALWAYS_INSERT) || (flags & ARP_INSERT_FLAG))
  {
    DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: adding entry to table\n"));
    /* find an empty or old entry. */
    i = find_arp_entry();
    if(i == ARP_TABLE_SIZE) {
      DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: no available entry found\n"));
      return NULL;
    }
    /* see if find_arp_entry() gave us an old stable, or empty entry to re-use */
    if (arp_table[i].state == ETHARP_STATE_STABLE) {
      DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: overwriting old stable entry %u\n", i));
      /* stable entries should have no queued packets (TODO: allow later) */
#if ARP_QUEUEING
      LWIP_ASSERT("update_arp_entry: arp_table[i].p == NULL", arp_table[i].p == NULL);
#endif
    } else {
      DEBUGF(ETHARP_DEBUG | DBG_TRACE | DBG_STATE, ("update_arp_entry: filling empty entry %u with state %u\n", i, arp_table[i].state));
      LWIP_ASSERT("update_arp_entry: arp_table[i].state == ETHARP_STATE_EMPTY", arp_table[i].state == ETHARP_STATE_EMPTY);
    }
    /* set IP address */  
    ip_addr_set(&arp_table[i].ipaddr, ipaddr);
    /* set Ethernet hardware address */  
    for(k = 0; k < netif->hwaddr_len; ++k) {
      arp_table[i].ethaddr.addr[k] = ethaddr->addr[k];
    }
    /* reset time-stamp */  
    arp_table[i].ctime = 0;
    /* mark as stable */  
    arp_table[i].state = ETHARP_STATE_STABLE;
    /* no queued packet */  
#if ARP_QUEUEING
    arp_table[i].p = NULL;
#endif
  }
  else
  {
    DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("update_arp_entry: no matching stable entry to update\n"));
  }
  return NULL;
}

/**
 * Updates the ARP table using the given packet.
 *
 * Uses the incoming IP packet's source address to update the
 * ARP cache for the local network. The function does not alter
 * or free the packet. This function must be called before the
 * packet p is passed to the IP layer.
 *
 * @param netif The lwIP network interface on which the IP packet pbuf arrived.
 * @param pbuf The IP packet that arrived on netif.
 * 
 * @return NULL
 *
 * @see pbuf_free()
 */
struct pbuf *
etharp_ip_input(struct netif *netif, struct pbuf *p)
{
  struct ethip_hdr *hdr;
  
  /* Only insert an entry if the source IP address of the
     incoming IP packet comes from a host on the local network. */
  hdr = p->payload;
  /* source is on local network? */
  if(!ip_addr_maskcmp(&(hdr->ip.src), &(netif->ip_addr), &(netif->netmask))) {
    /* do nothing */
    return NULL;
  }
  
  DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("etharp_ip_input: updating ETHARP table.\n"));
  /* update ARP table, ask to insert entry */
  update_arp_entry(netif, &(hdr->ip.src), &(hdr->eth.src), ARP_INSERT_FLAG);
  return NULL;
}


/**
 * Responds to ARP requests, updates ARP entries and sends queued IP packets.
 * 
 * Should be called for incoming ARP packets. The pbuf in the argument
 * is freed by this function.
 *
 * @param netif The lwIP network interface on which the ARP packet pbuf arrived.
 * @param pbuf The ARP packet that arrived on netif. Is freed by this function.
 * @param ethaddr Ethernet address of netif.
 *
 * @return NULL
 *
 * @see pbuf_free()
 */
struct pbuf *
etharp_arp_input(struct netif *netif, struct eth_addr *ethaddr, struct pbuf *p)
{
  struct etharp_hdr *hdr;