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/**

 * @file

 * This is the IPv4 packet segmentation and reassembly implementation.

 *

 */

/*

 * Copyright (c) 2001-2004 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: Jani Monoses <jani@iv.ro>

 *         Simon Goldschmidt

 * original reassembly code by Adam Dunkels <adam@sics.se>

 *

 */

#include "lwip/opt.h"

#include "lwip/ip_frag.h"

#include "lwip/ip.h"

#include "lwip/inet.h"

#include "lwip/inet_chksum.h"

#include "lwip/netif.h"

#include "lwip/snmp.h"

#include "lwip/stats.h"

#include "lwip/icmp.h"

#include <string.h>

#if IP_REASSEMBLY

/**

 * The IP reassembly code currently has the following limitations:

 * - IP header options are not supported

 * - fragments must not overlap (e.g. due to different routes),

 *   currently, overlapping or duplicate fragments are thrown away

 *   if IP_REASS_CHECK_OVERLAP=1 (the default)!

 *

 * @todo: work with IP header options

 */

/** Setting this to 0, you can turn off checking the fragments for overlapping

 * regions. The code gets a little smaller. Only use this if you know that

 * overlapping won't occur on your network! */

#ifndef IP_REASS_CHECK_OVERLAP

#define IP_REASS_CHECK_OVERLAP 1

#endif /* IP_REASS_CHECK_OVERLAP */

/** Set to 0 to prevent freeing the oldest datagram when the reassembly buffer is

 * full (IP_REASS_MAX_PBUFS pbufs are enqueued). The code gets a little smaller.

 * Datagrams will be freed by timeout only. Especially useful when MEMP_NUM_REASSDATA

 * is set to 1, so one datagram can be reassembled at a time, only. */

#ifndef IP_REASS_FREE_OLDEST

#define IP_REASS_FREE_OLDEST 1

#endif /* IP_REASS_FREE_OLDEST */

#define IP_REASS_FLAG_LASTFRAG 0x01

/** This is a helper struct which holds the starting

 * offset and the ending offset of this fragment to

 * easily chain the fragments.

 */

struct ip_reass_helper {

  struct pbuf *next_pbuf;

  u16_t start;

  u16_t end;

};

#define IP_ADDRESSES_AND_ID_MATCH(iphdrA, iphdrB)  \

  (ip_addr_cmp(&(iphdrA)->src, &(iphdrB)->src) && \

   ip_addr_cmp(&(iphdrA)->dest, &(iphdrB)->dest) && \

   IPH_ID(iphdrA) == IPH_ID(iphdrB)) ? 1 : 0

/* global variables */

static struct ip_reassdata *reassdatagrams;

static u16_t ip_reass_pbufcount;

/* function prototypes */

static void ip_reass_dequeue_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev);

static int ip_reass_free_complete_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev);

/**

 * Reassembly timer base function

 * for both NO_SYS == 0 and 1 (!).

 *

 * Should be called every 1000 msec (defined by IP_TMR_INTERVAL).

 */

void

ip_reass_tmr(void)

{

  struct ip_reassdata *r, *prev = NULL;

  r = reassdatagrams;

  while (r != NULL) {

    /* Decrement the timer. Once it reaches 0,

     * clean up the incomplete fragment assembly */

    if (r->timer > 0) {

      r->timer--;

      LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass_tmr: timer dec %"U16_F"\n",(u16_t)r->timer));

      prev = r;

      r = r->next;

    } else {

      /* reassembly timed out */

      struct ip_reassdata *tmp;

      LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass_tmr: timer timed out\n"));

      tmp = r;

      /* get the next pointer before freeing */

      r = r->next;

      /* free the helper struct and all enqueued pbufs */

      ip_reass_free_complete_datagram(tmp, prev);

     }

   }

}

/**

 * Free a datagram (struct ip_reassdata) and all its pbufs.

 * Updates the total count of enqueued pbufs (ip_reass_pbufcount),

 * SNMP counters and sends an ICMP time exceeded packet.

 *

 * @param ipr datagram to free

 * @param prev the previous datagram in the linked list

 * @return the number of pbufs freed

 */

static int

ip_reass_free_complete_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev)

{

  int pbufs_freed = 0;

  struct pbuf *p;

  struct ip_reass_helper *iprh;

  LWIP_ASSERT("prev != ipr", prev != ipr);

  if (prev != NULL) {

    LWIP_ASSERT("prev->next == ipr", prev->next == ipr);

  }

  snmp_inc_ipreasmfails();

#if LWIP_ICMP

  iprh = (struct ip_reass_helper *)ipr->p->payload;

  if (iprh->start == 0) {

    /* The first fragment was received, send ICMP time exceeded. */

    /* First, de-queue the first pbuf from r->p. */

    p = ipr->p;

    ipr->p = iprh->next_pbuf;

    /* Then, copy the original header into it. */

    SMEMCPY(p->payload, &ipr->iphdr, IP_HLEN);

    icmp_time_exceeded(p, ICMP_TE_FRAG);

    pbufs_freed += pbuf_clen(p);

    pbuf_free(p);

  }

#endif /* LWIP_ICMP */

  /* First, free all received pbufs.  The individual pbufs need to be released

     separately as they have not yet been chained */

  p = ipr->p;

  while (p != NULL) {

    struct pbuf *pcur;

    iprh = (struct ip_reass_helper *)p->payload;

    pcur = p;

    /* get the next pointer before freeing */

    p = iprh->next_pbuf;

    pbufs_freed += pbuf_clen(pcur);

    pbuf_free(pcur);

  }

  /* Then, unchain the struct ip_reassdata from the list and free it. */

  ip_reass_dequeue_datagram(ipr, prev);

  LWIP_ASSERT("ip_reass_pbufcount >= clen", ip_reass_pbufcount >= pbufs_freed);

  ip_reass_pbufcount -= pbufs_freed;

  return pbufs_freed;

}

#if IP_REASS_FREE_OLDEST

/**

 * Free the oldest datagram to make room for enqueueing new fragments.

 * The datagram 'fraghdr' belongs to is not freed!

 *

 * @param fraghdr IP header of the current fragment

 * @param pbufs_needed number of pbufs needed to enqueue

 *        (used for freeing other datagrams if not enough space)

 * @return the number of pbufs freed

 */

static int

ip_reass_remove_oldest_datagram(struct ip_hdr *fraghdr, int pbufs_needed)

{

  /* @todo Can't we simply remove the last datagram in the

   *       linked list behind reassdatagrams?

   */

  struct ip_reassdata *r, *oldest, *prev;

  int pbufs_freed = 0, pbufs_freed_current;

  int other_datagrams;

  /* Free datagrams until being allowed to enqueue 'pbufs_needed' pbufs,

   * but don't free the datagram that 'fraghdr' belongs to! */

  do {

    oldest = NULL;

    prev = NULL;

    other_datagrams = 0;

    r = reassdatagrams;

    while (r != NULL) {

      if (!IP_ADDRESSES_AND_ID_MATCH(&r->iphdr, fraghdr)) {

        /* Not the same datagram as fraghdr */

        other_datagrams++;

        if (oldest == NULL) {

          oldest = r;

        } else if (r->timer <= oldest->timer) {

          /* older than the previous oldest */

          oldest = r;

        }

      }

      if (r->next != NULL) {

        prev = r;

      }

      r = r->next;

    }

    if (oldest != NULL) {

      pbufs_freed_current = ip_reass_free_complete_datagram(oldest, prev);

      pbufs_freed += pbufs_freed_current;

    }

  } while ((pbufs_freed < pbufs_needed) && (other_datagrams > 1));

  return pbufs_freed;

}

#endif /* IP_REASS_FREE_OLDEST */

/**

 * Enqueues a new fragment into the fragment queue

 * @param fraghdr points to the new fragments IP hdr

 * @param clen number of pbufs needed to enqueue (used for freeing other datagrams if not enough space)

 * @return A pointer to the queue location into which the fragment was enqueued

 */

static struct ip_reassdata*

ip_reass_enqueue_new_datagram(struct ip_hdr *fraghdr, int clen)

{

  struct ip_reassdata* ipr;

  /* No matching previous fragment found, allocate a new reassdata struct */

  ipr = memp_malloc(MEMP_REASSDATA);

  if (ipr == NULL) {

#if IP_REASS_FREE_OLDEST

    if (ip_reass_remove_oldest_datagram(fraghdr, clen) >= clen) {

      ipr = memp_malloc(MEMP_REASSDATA);

    }

    if (ipr == NULL)

#endif /* IP_REASS_FREE_OLDEST */

    {

      IPFRAG_STATS_INC(ip_frag.memerr);

      LWIP_DEBUGF(IP_REASS_DEBUG,("Failed to alloc reassdata struct\n"));

      return NULL;

    }

  }

  memset(ipr, 0, sizeof(struct ip_reassdata));

  ipr->timer = IP_REASS_MAXAGE;

  /* enqueue the new structure to the front of the list */

  ipr->next = reassdatagrams;

  reassdatagrams = ipr;

  /* copy the ip header for later tests and input */

  /* @todo: no ip options supported? */

  SMEMCPY(&(ipr->iphdr), fraghdr, IP_HLEN);

  return ipr;

}

/**

 * Dequeues a datagram from the datagram queue. Doesn't deallocate the pbufs.

 * @param ipr points to the queue entry to dequeue

 */

static void

ip_reass_dequeue_datagram(struct ip_reassdata *ipr, struct ip_reassdata *prev)

{

  /* dequeue the reass struct  */

  if (reassdatagrams == ipr) {

    /* it was the first in the list */

    reassdatagrams = ipr->next;

  } else {

    /* it wasn't the first, so it must have a valid 'prev' */

    LWIP_ASSERT("sanity check linked list", prev != NULL);

    prev->next = ipr->next;

  }

  /* now we can free the ip_reass struct */

  memp_free(MEMP_REASSDATA, ipr);

}

/**

 * Chain a new pbuf into the pbuf list that composes the datagram.  The pbuf list

 * will grow over time as  new pbufs are rx.

 * Also checks that the datagram passes basic continuity checks (if the last

 * fragment was received at least once).

 * @param root_p points to the 'root' pbuf for the current datagram being assembled.

 * @param new_p points to the pbuf for the current fragment

 * @return 0 if invalid, >0 otherwise

 */

static int

ip_reass_chain_frag_into_datagram_and_validate(struct ip_reassdata *ipr, struct pbuf *new_p)

{

  struct ip_reass_helper *iprh, *iprh_tmp, *iprh_prev=NULL;

  struct pbuf *q;

  u16_t offset,len;

  struct ip_hdr *fraghdr;

  int valid = 1;

  /* Extract length and fragment offset from current fragment */

  fraghdr = (struct ip_hdr*)new_p->payload;

  len = ntohs(IPH_LEN(fraghdr)) - IPH_HL(fraghdr) * 4;

  offset = (ntohs(IPH_OFFSET(fraghdr)) & IP_OFFMASK) * 8;

  /* overwrite the fragment's ip header from the pbuf with our helper struct,

   * and setup the embedded helper structure. */

  /* make sure the struct ip_reass_helper fits into the IP header */

  LWIP_ASSERT("sizeof(struct ip_reass_helper) <= IP_HLEN",

              sizeof(struct ip_reass_helper) <= IP_HLEN);

  iprh = (struct ip_reass_helper*)new_p->payload;

  iprh->next_pbuf = NULL;

  iprh->start = offset;

  iprh->end = offset + len;

  /* Iterate through until we either get to the end of the list (append),

   * or we find on with a larger offset (insert). */

  for (q = ipr->p; q != NULL;) {

    iprh_tmp = (struct ip_reass_helper*)q->payload;

    if (iprh->start < iprh_tmp->start) {

      /* the new pbuf should be inserted before this */

      iprh->next_pbuf = q;

      if (iprh_prev != NULL) {

        /* not the fragment with the lowest offset */

#if IP_REASS_CHECK_OVERLAP

        if ((iprh->start < iprh_prev->end) || (iprh->end > iprh_tmp->start)) {

          /* fragment overlaps with previous or following, throw away */

          goto freepbuf;

        }

#endif /* IP_REASS_CHECK_OVERLAP */

        iprh_prev->next_pbuf = new_p;

      } else {

        /* fragment with the lowest offset */

        ipr->p = new_p;

      }

      break;

    } else if(iprh->start == iprh_tmp->start) {

      /* received the same datagram twice: no need to keep the datagram */

      goto freepbuf;

#if IP_REASS_CHECK_OVERLAP

    } else if(iprh->start < iprh_tmp->end) {

      /* overlap: no need to keep the new datagram */

      goto freepbuf;

#endif /* IP_REASS_CHECK_OVERLAP */

    } else {

      /* Check if the fragments received so far have no wholes. */

      if (iprh_prev != NULL) {

        if (iprh_prev->end != iprh_tmp->start) {

          /* There is a fragment missing between the current

           * and the previous fragment */

          valid = 0;

        }

      }

    }

    q = iprh_tmp->next_pbuf;

    iprh_prev = iprh_tmp;

  }

  /* If q is NULL, then we made it to the end of the list. Determine what to do now */

  if (q == NULL) {

    if (iprh_prev != NULL) {

      /* this is (for now), the fragment with the highest offset:

       * chain it to the last fragment */

#if IP_REASS_CHECK_OVERLAP

      LWIP_ASSERT("check fragments don't overlap", iprh_prev->end <= iprh->start);

#endif /* IP_REASS_CHECK_OVERLAP */

      iprh_prev->next_pbuf = new_p;

      if (iprh_prev->end != iprh->start) {

        valid = 0;

      }

    } else {

#if IP_REASS_CHECK_OVERLAP

      LWIP_ASSERT("no previous fragment, this must be the first fragment!",

        ipr->p == NULL);

#endif /* IP_REASS_CHECK_OVERLAP */

      /* this is the first fragment we ever received for this ip datagram */

      ipr->p = new_p;

    }

  }

  /* At this point, the validation part begins: */

  /* If we already received the last fragment */

  if ((ipr->flags & IP_REASS_FLAG_LASTFRAG) != 0) {

    /* and had no wholes so far */

    if (valid) {

      /* then check if the rest of the fragments is here */

      /* Check if the queue starts with the first datagram */

      if (((struct ip_reass_helper*)ipr->p->payload)->start != 0) {

        valid = 0;

      } else {

        /* and check that there are no wholes after this datagram */

        iprh_prev = iprh;

        q = iprh->next_pbuf;

        while (q != NULL) {

          iprh = (struct ip_reass_helper*)q->payload;

          if (iprh_prev->end != iprh->start) {

            valid = 0;

            break;

          }

          iprh_prev = iprh;

          q = iprh->next_pbuf;

        }

        /* if still valid, all fragments are received

         * (because to the MF==0 already arrived */

        if (valid) {

          LWIP_ASSERT("sanity check", ipr->p != NULL);

          LWIP_ASSERT("sanity check",

            ((struct ip_reass_helper*)ipr->p->payload) != iprh);

          LWIP_ASSERT("validate_datagram:next_pbuf!=NULL",

            iprh->next_pbuf == NULL);

          LWIP_ASSERT("validate_datagram:datagram end!=datagram len",

            iprh->end == ipr->datagram_len);

        }

      }

    }

    /* If valid is 0 here, there are some fragments missing in the middle

     * (since MF == 0 has already arrived). Such datagrams simply time out if

     * no more fragments are received... */

    return valid;

  }

  /* If we come here, not all fragments were received, yet! */

  return 0; /* not yet valid! */

#if IP_REASS_CHECK_OVERLAP

freepbuf:

  ip_reass_pbufcount -= pbuf_clen(new_p);

  pbuf_free(new_p);

  return 0;

#endif /* IP_REASS_CHECK_OVERLAP */

}

/**

 * Reassembles incoming IP fragments into an IP datagram.

 *

 * @param p points to a pbuf chain of the fragment

 * @return NULL if reassembly is incomplete, ? otherwise

 */

struct pbuf *

ip_reass(struct pbuf *p)

{

  struct pbuf *r;

  struct ip_hdr *fraghdr;

  struct ip_reassdata *ipr;

  struct ip_reass_helper *iprh;

  u16_t offset, len;

  u8_t clen;

  struct ip_reassdata *ipr_prev = NULL;

  IPFRAG_STATS_INC(ip_frag.recv);

  snmp_inc_ipreasmreqds();

  fraghdr = (struct ip_hdr*)p->payload;

  if ((IPH_HL(fraghdr) * 4) != IP_HLEN) {

    LWIP_DEBUGF(IP_REASS_DEBUG,("ip_reass: IP options currently not supported!\n"));

    IPFRAG_STATS_INC(ip_frag.err);

    goto nullreturn;

  }

  offset = (ntohs(IPH_OFFSET(fraghdr)) & IP_OFFMASK) * 8;

  len = ntohs(IPH_LEN(fraghdr)) - IPH_HL(fraghdr) * 4;

  /* Check if we are allowed to enqueue more datagrams. */

  clen = pbuf_clen(p);

  if ((ip_reass_pbufcount + clen) > IP_REASS_MAX_PBUFS) {

#if IP_REASS_FREE_OLDEST

    if (!ip_reass_remove_oldest_datagram(fraghdr, clen) ||

        ((ip_reass_pbufcount + clen) > IP_REASS_MAX_PBUFS))

#endif /* IP_REASS_FREE_OLDEST */

    {

      /* No datagram could be freed and still too many pbufs enqueued */

      LWIP_DEBUGF(IP_REASS_DEBUG,("ip_reass: Overflow condition: pbufct=%d, clen=%d, MAX=%d\n",

        ip_reass_pbufcount, clen, IP_REASS_MAX_PBUFS));

      IPFRAG_STATS_INC(ip_frag.memerr);

      /* @todo: send ICMP time exceeded here? */

      /* drop this pbuf */

      goto nullreturn;

    }

  }

  /* Look for the datagram the fragment belongs to in the current datagram queue,

   * remembering the previous in the queue for later dequeueing. */

  for (ipr = reassdatagrams; ipr != NULL; ipr = ipr->next) {

    /* Check if the incoming fragment matches the one currently present

       in the reassembly buffer. If so, we proceed with copying the

       fragment into the buffer. */

    if (IP_ADDRESSES_AND_ID_MATCH(&ipr->iphdr, fraghdr)) {

      LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_reass: matching previous fragment ID=%"X16_F"\n",

        ntohs(IPH_ID(fraghdr))));

      IPFRAG_STATS_INC(ip_frag.cachehit);

      break;

    }

    ipr_prev = ipr;

  }

  if (ipr == NULL) {

  /* Enqueue a new datagram into the datagram queue */

    ipr = ip_reass_enqueue_new_datagram(fraghdr, clen);

    /* Bail if unable to enqueue */

    if(ipr == NULL) {

      goto nullreturn;

    }

  } else {

    if (((ntohs(IPH_OFFSET(fraghdr)) & IP_OFFMASK) == 0) &&

      ((ntohs(IPH_OFFSET(&ipr->iphdr)) & IP_OFFMASK) != 0)) {

      /* ipr->iphdr is not the header from the first fragment, but fraghdr is

       * -> copy fraghdr into ipr->iphdr since we want to have the header

       * of the first fragment (for ICMP time exceeded and later, for copying

       * all options, if supported)*/

      SMEMCPY(&ipr->iphdr, fraghdr, IP_HLEN);

    }

  }

  /* Track the current number of pbufs current 'in-flight', in order to limit

  the number of fragments that may be enqueued at any one time */

  ip_reass_pbufcount += clen;

  /* At this point, we have either created a new entry or pointing

   * to an existing one */

  /* check for 'no more fragments', and update queue entry*/

  if ((ntohs(IPH_OFFSET(fraghdr)) & IP_MF) == 0) {

    ipr->flags |= IP_REASS_FLAG_LASTFRAG;

    ipr->datagram_len = offset + len;

    LWIP_DEBUGF(IP_REASS_DEBUG,

     ("ip_reass: last fragment seen, total len %"S16_F"\n",

      ipr->datagram_len));

  }

  /* find the right place to insert this pbuf */

  /* @todo: trim pbufs if fragments are overlapping */

  if (ip_reass_chain_frag_into_datagram_and_validate(ipr, p)) {

    /* the totally last fragment (flag more fragments = 0) was received at least

     * once AND all fragments are received */

    ipr->datagram_len += IP_HLEN;

    /* save the second pbuf before copying the header over the pointer */

    r = ((struct ip_reass_helper*)ipr->p->payload)->next_pbuf;

    /* copy the original ip header back to the first pbuf */

    fraghdr = (struct ip_hdr*)(ipr->p->payload);

    SMEMCPY(fraghdr, &ipr->iphdr, IP_HLEN);

    IPH_LEN_SET(fraghdr, htons(ipr->datagram_len));

    IPH_OFFSET_SET(fraghdr, 0);

    IPH_CHKSUM_SET(fraghdr, 0);

    /* @todo: do we need to set calculate the correct checksum? */

    IPH_CHKSUM_SET(fraghdr, inet_chksum(fraghdr, IP_HLEN));

    p = ipr->p;

    /* chain together the pbufs contained within the reass_data list. */

    while(r != NULL) {

      iprh = (struct ip_reass_helper*)r->payload;

      /* hide the ip header for every succeding fragment */

      pbuf_header(r, -IP_HLEN);

      pbuf_cat(p, r);

      r = iprh->next_pbuf;

    }

    /* release the sources allocate for the fragment queue entry */

    ip_reass_dequeue_datagram(ipr, ipr_prev);

    /* and adjust the number of pbufs currently queued for reassembly. */

    ip_reass_pbufcount -= pbuf_clen(p);

    /* Return the pbuf chain */

    return p;

  }

  /* the datagram is not (yet?) reassembled completely */

  LWIP_DEBUGF(IP_REASS_DEBUG,("ip_reass_pbufcount: %d out\n", ip_reass_pbufcount));

  return NULL;

nullreturn:

  LWIP_DEBUGF(IP_REASS_DEBUG,("ip_reass: nullreturn\n"));

  IPFRAG_STATS_INC(ip_frag.drop);

  pbuf_free(p);

  return NULL;

}

#endif /* IP_REASSEMBLY */

#if IP_FRAG

#if IP_FRAG_USES_STATIC_BUF

static u8_t buf[LWIP_MEM_ALIGN_SIZE(IP_FRAG_MAX_MTU)];

#endif /* IP_FRAG_USES_STATIC_BUF */

/**

 * Fragment an IP datagram if too large for the netif.

 *

 * Chop the datagram in MTU sized chunks and send them in order

 * by using a fixed size static memory buffer (PBUF_REF) or

 * point PBUF_REFs into p (depending on IP_FRAG_USES_STATIC_BUF).

 *

 * @param p ip packet to send

 * @param netif the netif on which to send

 * @param dest destination ip address to which to send

 *

 * @return ERR_OK if sent successfully, err_t otherwise

 */

err_t

ip_frag(struct pbuf *p, struct netif *netif, struct ip_addr *dest)

{

  struct pbuf *rambuf;

#if IP_FRAG_USES_STATIC_BUF

  struct pbuf *header;

#else

  struct pbuf *newpbuf;

  struct ip_hdr *original_iphdr;

#endif

  struct ip_hdr *iphdr;

  u16_t nfb;

  u16_t left, cop;

  u16_t mtu = netif->mtu;

  u16_t ofo, omf;

  u16_t last;

  u16_t poff = IP_HLEN;

  u16_t tmp;

#if !IP_FRAG_USES_STATIC_BUF

  u16_t newpbuflen = 0;

  u16_t left_to_copy;

#endif

  /* Get a RAM based MTU sized pbuf */

#if IP_FRAG_USES_STATIC_BUF

  /* When using a static buffer, we use a PBUF_REF, which we will

   * use to reference the packet (without link header).

   * Layer and length is irrelevant.

   */

  rambuf = pbuf_alloc(PBUF_LINK, 0, PBUF_REF);

  if (rambuf == NULL) {

    LWIP_DEBUGF(IP_REASS_DEBUG, ("ip_frag: pbuf_alloc(PBUF_LINK, 0, PBUF_REF) failed\n"));

    return ERR_MEM;

  }

  rambuf->tot_len = rambuf->len = mtu;

  rambuf->payload = LWIP_MEM_ALIGN((void *)buf);

  /* Copy the IP header in it */

  iphdr = rambuf->payload;

  SMEMCPY(iphdr, p->payload, IP_HLEN);

#else /* IP_FRAG_USES_STATIC_BUF */

  original_iphdr = p->payload;

  iphdr = original_iphdr;

#endif /* IP_FRAG_USES_STATIC_BUF */

  /* Save original offset */

  tmp = ntohs(IPH_OFFSET(iphdr));

  ofo = tmp & IP_OFFMASK;

  omf = tmp & IP_MF;

  left = p->tot_len - IP_HLEN;

  nfb = (mtu - IP_HLEN) / 8;

  while (left) {

    last = (left <= mtu - IP_HLEN);

    /* Set new offset and MF flag */

    tmp = omf | (IP_OFFMASK & (ofo));

    if (!last)

      tmp = tmp | IP_MF;

    /* Fill this fragment */

    cop = last ? left : nfb * 8;

#if IP_FRAG_USES_STATIC_BUF

    poff += pbuf_copy_partial(p, (u8_t*)iphdr + IP_HLEN, cop, poff);

#else /* IP_FRAG_USES_STATIC_BUF */

    /* When not using a static buffer, create a chain of pbufs.

     * The first will be a PBUF_RAM holding the link and IP header.

     * The rest will be PBUF_REFs mirroring the pbuf chain to be fragged,

     * but limited to the size of an mtu.

     */

    rambuf = pbuf_alloc(PBUF_LINK, IP_HLEN, PBUF_RAM);

    if (rambuf == NULL) {

      return ERR_MEM;

    }

    LWIP_ASSERT("this needs a pbuf in one piece!",

                (p->len >= (IP_HLEN)));

    SMEMCPY(rambuf->payload, original_iphdr, IP_HLEN);

    iphdr = rambuf->payload;

    /* Can just adjust p directly for needed offset. */

    p->payload = (u8_t *)p->payload + poff;