/**
 * @file
 * Address Resolution Protocol module for IP over Ethernet
 *
 * Functionally, ARP is divided into two parts. The first maps an IP address
 * to a physical address when sending a packet, and the second part answers
 * requests from other machines for our physical address.
 *
 * This implementation complies with RFC 826 (Ethernet ARP). It supports
 * Gratuitious ARP from RFC3220 (IP Mobility Support for IPv4) section 4.6
 * if an interface calls etharp_query(our_netif, its_ip_addr, NULL) upon
 * address change.
 */

/*
 * Copyright (c) 2001-2003 Swedish Institute of Computer Science.
 * Copyright (c) 2003-2004 Leon Woestenberg <leon.woestenberg@axon.tv>
 * Copyright (c) 2003-2004 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 part of the lwIP TCP/IP stack.
 *
 */

#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,
 * (240 * 5) seconds = 20 minutes.
 */
#define ARP_MAXAGE 240
/** the time an ARP entry stays pending after first request,
 * (2 * 5) seconds = 10 seconds.
 * 
 * @internal Keep this number at least 2, otherwise it might
 * run out instantly if the timeout occurs directly after a request.
 */
#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,
  /** @internal transitional state used in etharp_tmr() for convenience*/
  ETHARP_STATE_EXPIRED
};

struct etharp_entry {
#if ARP_QUEUEING
  /** 
   * Pointer to queue of pending outgoing packets on this ARP entry.
   */
   struct pbuf *p;
#endif
  struct ip_addr ipaddr;
  struct eth_addr ethaddr;
  enum etharp_state state;
  u8_t ctime;
};

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

/**
 * Try hard to create a new entry - we want the IP address to appear in
 * the cache (even if this means removing an active entry or so). */
#define ETHARP_TRY_HARD 1

static s8_t find_entry(struct ip_addr *ipaddr, u8_t flags);
static err_t update_arp_entry(struct netif *netif, struct ip_addr *ipaddr, struct eth_addr *ethaddr, u8_t flags);
/**
 * 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
    arp_table[i].ctime = 0;
  }
}

/**
 * Clears expired entries in the ARP table.
 *
 * This function should be called every ETHARP_TMR_INTERVAL microseconds (5 seconds),
 * in order to expire entries in the ARP table.
 */
void
etharp_tmr(void)
{
  u8_t i;

  LWIP_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++;
    /* stable entry? */
    if ((arp_table[i].state == ETHARP_STATE_STABLE) &&
         /* entry has become old? */
        (arp_table[i].ctime >= ARP_MAXAGE)) {
      LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer: expired stable entry %u.\n", i));
      arp_table[i].state = ETHARP_STATE_EXPIRED;
    /* pending entry? */
    } else if (arp_table[i].state == ETHARP_STATE_PENDING) {
      /* entry unresolved/pending for too long? */
      if (arp_table[i].ctime >= ARP_MAXPENDING) {
        LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer: expired pending entry %u.\n", i));
        arp_table[i].state = ETHARP_STATE_EXPIRED;
#if ARP_QUEUEING
      } else if (arp_table[i].p != NULL) {
        /* resend an ARP query here */
#endif
      }
    }
    /* clean up entries that have just been expired */
    if (arp_table[i].state == ETHARP_STATE_EXPIRED) {
#if ARP_QUEUEING
      /* and empty packet queue */
      if (arp_table[i].p != NULL) {
        /* remove all queued packets */
        LWIP_DEBUGF(ETHARP_DEBUG, ("etharp_timer: freeing entry %u, packet queue %p.\n", i, (void *)(arp_table[i].p)));
        pbuf_free(arp_table[i].p);
        arp_table[i].p = NULL;
      }
#endif
      /* recycle entry for re-use */      
      arp_table[i].state = ETHARP_STATE_EMPTY;
    }
  }
}

/**
 * Search the ARP table for a matching or new entry.
 * 
 * If an IP address is given, return a pending or stable ARP entry that matches
 * the address. If no match is found, create a new entry with this address set,
 * but in state ETHARP_EMPTY. The caller must check and possibly change the
 * state of the returned entry.
 * 
 * If ipaddr is NULL, return a initialized new entry in state ETHARP_EMPTY.
 * 
 * In all cases, attempt to create new entries from an empty entry. If no
 * empty entries are available and ETHARP_TRY_HARD flag is set, recycle
 * old entries. Heuristic choose the least important entry for recycling.
 *
 * @param ipaddr IP address to find in ARP cache, or to add if not found.
 * @param flags
 * - ETHARP_TRY_HARD: Try hard to create a entry by allowing recycling of
 * active (stable or pending) entries.
 *  
 * @return The ARP entry index that matched or is created, ERR_MEM if no
 * entry is found or could be recycled.
 */
static s8_t find_entry(struct ip_addr *ipaddr, u8_t flags)
{
  s8_t old_pending = ARP_TABLE_SIZE, old_stable = ARP_TABLE_SIZE;
  s8_t empty = ARP_TABLE_SIZE;
  u8_t i = 0, age_pending = 0, age_stable = 0;
#if ARP_QUEUEING
  /* oldest entry with packets on queue */
  s8_t old_queue = ARP_TABLE_SIZE;
  /* its age */
  u8_t age_queue = 0;
#endif

  /**
   * a) do a search through the cache, remember candidates
   * b) select candidate entry
   * c) create new entry
   */

  /* a) in a single search sweep, do all of this
   * 1) remember the first empty entry (if any)
   * 2) remember the oldest stable entry (if any)
   * 3) remember the oldest pending entry without queued packets (if any)
   * 4) remember the oldest pending entry with queued packets (if any)
   * 5) search for a matching IP entry, either pending or stable
   *    until 5 matches, or all entries are searched for.
   */

  for (i = 0; i < ARP_TABLE_SIZE; ++i) {
    /* no empty entry found yet and now we do find one? */
    if ((empty == ARP_TABLE_SIZE) && (arp_table[i].state == ETHARP_STATE_EMPTY)) {
      LWIP_DEBUGF(ETHARP_DEBUG, ("find_entry: found empty entry %d\n", i));
      /* remember first empty entry */
      empty = i;
    }
    /* pending entry? */
    else if (arp_table[i].state == ETHARP_STATE_PENDING) {
      /* if given, does IP address match IP address in ARP entry? */
      if (ipaddr && ip_addr_cmp(ipaddr, &arp_table[i].ipaddr)) {
        LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("find_entry: found matching pending entry %d\n", i));
        /* found exact IP address match, simply bail out */
        return i;
#if ARP_QUEUEING
      /* pending with queued packets? */
      } else if (arp_table[i].p != NULL) {
        if (arp_table[i].ctime >= age_queue) {
          old_queue = i;
          age_queue = arp_table[i].ctime;
        }
#endif
      /* pending without queued packets? */
      } else {
        if (arp_table[i].ctime >= age_pending) {
          old_pending = i;
          age_pending = arp_table[i].ctime;
        }
      }        
    }
    /* stable entry? */
    else if (arp_table[i].state == ETHARP_STATE_STABLE) {
      /* if given, does IP address match IP address in ARP entry? */
      if (ipaddr && ip_addr_cmp(ipaddr, &arp_table[i].ipaddr)) {
        LWIP_DEBUGF(ETHARP_DEBUG | DBG_TRACE, ("find_entry: found matching stable entry %d\n", i));
        /* found exact IP address match, simply bail out */
        return i;
      /* remember entry with oldest stable entry in oldest, its age in maxtime */
      } else if (arp_table[i].ctime >= age_stable) {
        old_stable = i;
        age_stable = arp_table[i].ctime;
      }
    }
  }
  /* { we have no match } => try to create a new entry */
   
  /* no empty entry found and not allowed to recycle? */
  if ((empty == ARP_TABLE_SIZE) && ((flags & ETHARP_TRY_HARD) == 0))