/**
  * @file
 *
 * 6LowPAN output for IPv6. Uses ND tables for link-layer addressing. Fragments packets to 6LowPAN units.
 */

/*
 * Copyright (c) 2015 Inico Technologies Ltd.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. 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: Ivan Delamer <delamer@inicotech.com>
 *
 *
 * Please coordinate changes and requests with Ivan Delamer
 * <delamer@inicotech.com>
 */

#include "netif/lowpan6.h"

#if LWIP_IPV6 && LWIP_6LOWPAN

#include "lwip/ip.h"
#include "lwip/pbuf.h"
#include "lwip/ip_addr.h"
#include "lwip/netif.h"
#include "lwip/nd6.h"
#include "lwip/mem.h"
#include "lwip/udp.h"
#include "lwip/tcpip.h"

struct ieee_802154_addr {
  u8_t addr_len;
  u8_t addr[8];
};

/** This is a helper struct.
 */
struct lowpan6_reass_helper {
  struct pbuf *pbuf;
  struct lowpan6_reass_helper *next_packet;
  u8_t timer;
  struct ieee_802154_addr sender_addr;
  u16_t datagram_size;
  u16_t datagram_tag;
};

static struct lowpan6_reass_helper * reass_list;

#if LWIP_6LOWPAN_NUM_CONTEXTS > 0
static ip6_addr_t lowpan6_context[LWIP_6LOWPAN_NUM_CONTEXTS];
#endif

static u16_t ieee_802154_pan_id;

static const struct ieee_802154_addr ieee_802154_broadcast = {2, {0xff, 0xff}};

#if LWIP_6LOWPAN_INFER_SHORT_ADDRESS
static struct ieee_802154_addr short_mac_addr = {2, {0,0}};
#endif /* LWIP_6LOWPAN_INFER_SHORT_ADDRESS */

static err_t dequeue_datagram(struct lowpan6_reass_helper *lrh);

/**
 * Periodic timer for 6LowPAN functions:
 *
 * - Remove incomplete/old packets
 */
void
lowpan6_tmr(void)
{
    struct lowpan6_reass_helper *lrh, *lrh_temp;

    lrh = reass_list;
    while (lrh != NULL)
    {
        lrh_temp = lrh->next_packet;
        if ((--lrh->timer) == 0)
        {
            dequeue_datagram(lrh);
            pbuf_free(lrh->pbuf);
            mem_free(lrh);
        }
        lrh = lrh_temp;
    }
}

/**
 * Removes a datagram from the reassembly queue.
 **/
static err_t
dequeue_datagram(struct lowpan6_reass_helper *lrh)
{
    struct lowpan6_reass_helper *lrh_temp;

    if (reass_list == lrh)
    {
        reass_list = reass_list->next_packet;
    }
    else
    {
        lrh_temp = reass_list;
        while (lrh_temp != NULL)
        {
            if (lrh_temp->next_packet == lrh)
            {
                lrh_temp->next_packet = lrh->next_packet;
                break;
            }
            lrh_temp = lrh_temp->next_packet;
        }
    }

    return ERR_OK;
}

static s8_t
lowpan6_context_lookup(const ip6_addr_t *ip6addr)
{
    s8_t i;

    for (i = 0; i < LWIP_6LOWPAN_NUM_CONTEXTS; i++)
    {
        if (ip6_addr_netcmp(&lowpan6_context[i], ip6addr))
            return i;
    }

    return -1;
}

/* Determine compression mode for unicast address. */
static s8_t
lowpan6_get_address_mode(const ip6_addr_t *ip6addr, const struct ieee_802154_addr *mac_addr)
{
    if (mac_addr->addr_len == 2)
    {
        if ((ip6addr->addr[2] == (u32_t)PP_HTONL(0x000000ff)) &&
            ((ip6addr->addr[3]  & PP_HTONL(0xffff0000)) == PP_NTOHL(0xfe000000)))
        {
            if ((ip6addr->addr[3]  & PP_HTONL(0x0000ffff)) == ntohl((mac_addr->addr[0] << 8) | mac_addr->addr[1]))
            {
                return 3;
            }
        }
    }
    else if (mac_addr->addr_len == 8)
    {
        if ((ip6addr->addr[2] == ntohl(((mac_addr->addr[0] ^ 2) << 24) | (mac_addr->addr[1] << 16) | mac_addr->addr[2] << 8 | mac_addr->addr[3])) &&
            (ip6addr->addr[3] == ntohl((mac_addr->addr[4] << 24) | (mac_addr->addr[5] << 16) | mac_addr->addr[6] << 8 | mac_addr->addr[7])))
        {
            return 3;
        }
    }

    if ((ip6addr->addr[2] == PP_HTONL(0x000000ffUL)) &&
        ((ip6addr->addr[3]  & PP_HTONL(0xffff0000)) == PP_NTOHL(0xfe000000UL)))
    {
        return 2;
    }

    return 1;
}

/* Determine compression mode for multicast address. */
static s8_t
lowpan6_get_address_mode_mc(const ip6_addr_t *ip6addr)
{
    if ((ip6addr->addr[0] == PP_HTONL(0xff020000)) &&
        (ip6addr->addr[1] == 0) &&
        (ip6addr->addr[2] == 0) &&
        ((ip6addr->addr[3]  & PP_HTONL(0xffffff00)) == 0))
    {
        return 3;
    }
    else if (((ip6addr->addr[0] & PP_HTONL(0xff00ffff)) == PP_HTONL(0xff000000)) &&
             (ip6addr->addr[1] == 0))
    {
        if ((ip6addr->addr[2] == 0) &&
            ((ip6addr->addr[3]  & PP_HTONL(0xff000000)) == 0))
        {
            return 2;
        }
        else if ((ip6addr->addr[2]  & PP_HTONL(0xffffff00)) == 0)
        {
            return 1;
        }
    }


    return 0;
}

/*
 * Encapsulates data into IEEE 802.15.4 frames.
 * Fragments an IPv6 datagram into 6LowPAN units, which fit into IEEE 802.15.4 frames.
 * If configured, will compress IPv6 and or UDP headers.
 * */
static err_t
lowpan6_frag(struct netif *netif, struct pbuf *p, const struct ieee_802154_addr *src, const struct ieee_802154_addr *dst)
{
  struct pbuf * p_frag;
  u16_t frag_len, remaining_len;
  u8_t * buffer;
  u8_t ieee_header_len;
  u8_t lowpan6_header_len;
  s8_t i;
  static u8_t frame_seq_num;
  static u16_t datagram_tag;
  u16_t datagram_offset;
  err_t err = ERR_IF;

  /* We'll use a dedicated pbuf for building 6LowPAN fragments. */
  p_frag = pbuf_alloc(PBUF_RAW, 127, PBUF_RAM);
  if (p_frag == NULL) {
      return ERR_MEM;
  }

  /* Write IEEE 802.15.4 header. */
  buffer  = (u8_t*)p_frag->payload;
  ieee_header_len = 0;
  if (dst == &ieee_802154_broadcast)
  {
      buffer[ieee_header_len++] = 0x01; /* data packet, no ack required. */
  }
  else
  {
      buffer[ieee_header_len++] = 0x21; /* data packet, ack required. */
  }
  buffer[ieee_header_len] = (0x00 << 4); /* 2003 frame version */
  buffer[ieee_header_len] |= (dst->addr_len == 2) ? (0x02 << 2) : (0x03 << 2); /* destination addressing mode  */
  buffer[ieee_header_len] |= (src->addr_len == 2) ? (0x02 << 6) : (0x03 << 6); /* source addressing mode */
  ieee_header_len++;
  buffer[ieee_header_len++] = frame_seq_num++;

  buffer[ieee_header_len++] = ieee_802154_pan_id & 0xff; /* pan id */
  buffer[ieee_header_len++] = (ieee_802154_pan_id >> 8) & 0xff; /* pan id */
  i = dst->addr_len;
  while (i-- > 0) {
      buffer[ieee_header_len++] = dst->addr[i];
  }

  buffer[ieee_header_len++] = ieee_802154_pan_id & 0xff; /* pan id */
  buffer[ieee_header_len++] = (ieee_802154_pan_id >> 8) & 0xff; /* pan id */
  i = src->addr_len;
  while (i-- > 0) {
      buffer[ieee_header_len++] = src->addr[i];
  }

#if LWIP_6LOWPAN_IPHC
  /* Perform 6LowPAN IPv6 header compression according to RFC 6282 */
  {
      struct ip6_hdr *ip6hdr;

      /* Point to ip6 header and align copies of src/dest addresses. */
      ip6hdr = (struct ip6_hdr *)p->payload;
      ip_addr_copy_from_ip6(ip_data.current_iphdr_dest, ip6hdr->dest);
      ip_addr_copy_from_ip6(ip_data.current_iphdr_src, ip6hdr->src);

      /* Basic length of 6LowPAN header, set dispatch and clear fields. */
      lowpan6_header_len = 2;
      buffer[ieee_header_len] = 0x60;
      buffer[ieee_header_len + 1] = 0;

      /* Determine whether there will be a Context Identifier Extension byte or not.
       * If so, set it already. */
#if LWIP_6LOWPAN_NUM_CONTEXTS > 0
      buffer[ieee_header_len + 2] = 0;

      i = lowpan6_context_lookup(ip_2_ip6(&ip_data.current_iphdr_src));
      if (i >= 0)
      {
          /* Stateful source address compression. */
          buffer[ieee_header_len + 1] |= 0x40;
          buffer[ieee_header_len + 2] |= (i & 0x0f) << 4;
      }

      i = lowpan6_context_lookup(ip_2_ip6(&ip_data.current_iphdr_dest));
      if (i >= 0)
      {
          /* Stateful destination address compression. */
          buffer[ieee_header_len + 1] |= 0x04;
          buffer[ieee_header_len + 2] |= i & 0x0f;
      }

      if (buffer[ieee_header_len + 2] != 0x00)
      {
          /* Context identifier extension byte is appended. */
          buffer[ieee_header_len + 1] |= 0x80;
          lowpan6_header_len++;
      }
#endif /* LWIP_6LOWPAN_NUM_CONTEXTS > 0 */

      /* Determine TF field: Traffic Class, Flow Label */
      if (IP6H_FL(ip6hdr) == 0)
      {
          /* Flow label is elided. */
          buffer[ieee_header_len] |= 0x10;
          if (IP6H_TC(ip6hdr) == 0)
          {
              /* Traffic class (ECN+DSCP) elided too. */
              buffer[ieee_header_len] |= 0x08;
          }
          else
          {
              /* Traffic class (ECN+DSCP) appended. */
              buffer[ieee_header_len + lowpan6_header_len++] = IP6H_TC(ip6hdr);
          }
      }
      else
      {
          if (((IP6H_TC(ip6hdr) & 0x3f) == 0))
          {
              /* DSCP portion of Traffic Class is elided, ECN and FL are appended (3 bytes) */
              buffer[ieee_header_len] |= 0x08;

              buffer[ieee_header_len + lowpan6_header_len] = IP6H_TC(ip6hdr) & 0xc0;
              buffer[ieee_header_len + lowpan6_header_len++] |= (IP6H_FL(ip6hdr) >> 16) & 0x0f;
              buffer[ieee_header_len + lowpan6_header_len++] = (IP6H_FL(ip6hdr) >> 8) & 0xff;
              buffer[ieee_header_len + lowpan6_header_len++] = IP6H_FL(ip6hdr) & 0xff;
          }
          else
          {
              /* Traffic class and flow label are appended (4 bytes) */
              buffer[ieee_header_len + lowpan6_header_len++] = IP6H_TC(ip6hdr);
              buffer[ieee_header_len + lowpan6_header_len++] = (IP6H_FL(ip6hdr) >> 16) & 0x0f;
              buffer[ieee_header_len + lowpan6_header_len++] = (IP6H_FL(ip6hdr) >> 8) & 0xff;
              buffer[ieee_header_len + lowpan6_header_len++] = IP6H_FL(ip6hdr) & 0xff;
          }
      }

      /* Compress NH?
       * Only if UDP for now. TODO support other NH compression. */
      if (IP6H_NEXTH(ip6hdr) == IP6_NEXTH_UDP)
      {
          buffer[ieee_header_len] |= 0x04;
      }
      else
      {
          /* append nexth. */
          buffer[ieee_header_len + lowpan6_header_len++] = IP6H_NEXTH(ip6hdr);
      }

      /* Compress hop limit? */
      if (IP6H_HOPLIM(ip6hdr) == 255)
      {
          buffer[ieee_header_len] |= 0x03;
      }
      else if (IP6H_HOPLIM(ip6hdr) == 64)
      {
          buffer[ieee_header_len] |= 0x02;
      }
      else if (IP6H_HOPLIM(ip6hdr) == 1)
      {
          buffer[ieee_header_len] |= 0x01;
      }
      else
      {
          /* append hop limit */
          buffer[ieee_header_len + lowpan6_header_len++] = IP6H_HOPLIM(ip6hdr);
      }

      /* Compress source address */
      if (((buffer[ieee_header_len + 1] & 0x40) != 0) || (ip6_addr_islinklocal(ip_2_ip6(&ip_data.current_iphdr_src))))
      {
          /* Context-based or link-local source address compression. */
          i = lowpan6_get_address_mode(ip_2_ip6(&ip_data.current_iphdr_src), src);
          buffer[ieee_header_len + 1] |= (i & 0x03) << 4;
          if (i == 1)
          {
              MEMCPY(buffer + ieee_header_len + lowpan6_header_len, (u8_t*)p->payload + 16, 8);
              lowpan6_header_len += 8;
          }
          else if (i == 2)
          {
              MEMCPY(buffer + ieee_header_len + lowpan6_header_len, (u8_t*)p->payload + 22, 2);
              lowpan6_header_len += 2;
          }
      }
      else if (ip6_addr_isany(ip_2_ip6(&ip_data.current_iphdr_src)))
      {
          /* Special case: mark SAC and leave SAM=0 */
          buffer[ieee_header_len + 1] |= 0x40;
      }
      else
      {
          /* Append full address. */
          MEMCPY(buffer + ieee_header_len + lowpan6_header_len, (u8_t*)p->payload + 8, 16);
          lowpan6_header_len += 16;
      }

      /* Compress destination address */
      if (ip6_addr_ismulticast(ip_2_ip6(&ip_data.current_iphdr_dest)))
      {
          /* TODO support statefull multicast address compression */

          buffer[ieee_header_len + 1] |= 0x08;

          i = lowpan6_get_address_mode_mc(ip_2_ip6(&ip_data.current_iphdr_dest));
          buffer[ieee_header_len + 1] |= i & 0x03;
          if (i == 0)
          {
              MEMCPY(buffer + ieee_header_len + lowpan6_header_len, (u8_t*)p->payload + 24, 16);
              lowpan6_header_len += 16;
          }
          else if (i == 1)
          {
              buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[25];
              MEMCPY(buffer + ieee_header_len + lowpan6_header_len, (u8_t*)p->payload + 35, 5);
              lowpan6_header_len += 5;
          }
          else if (i == 2)
          {
              buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[25];
              MEMCPY(buffer + ieee_header_len + lowpan6_header_len, (u8_t*)p->payload + 37, 3);
              lowpan6_header_len += 3;
          }
          else if (i == 3)
          {
              buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[39];
          }
      }
      else if (((buffer[ieee_header_len + 1] & 0x04) != 0) || (ip6_addr_islinklocal(ip_2_ip6(&ip_data.current_iphdr_dest))))
      {
          /* Context-based or link-local destination address compression. */
          i = lowpan6_get_address_mode(ip_2_ip6(&ip_data.current_iphdr_dest), dst);
          buffer[ieee_header_len + 1] |= i & 0x03;
          if (i == 1)
          {
              MEMCPY(buffer + ieee_header_len + lowpan6_header_len, (u8_t*)p->payload + 32, 8);
              lowpan6_header_len += 8;
          }
          else if (i == 2)
          {
              MEMCPY(buffer + ieee_header_len + lowpan6_header_len, (u8_t*)p->payload + 38, 2);
              lowpan6_header_len += 2;
          }
      }
      else
      {
          /* Append full address. */
          MEMCPY(buffer + ieee_header_len + lowpan6_header_len, (u8_t*)p->payload + 24, 16);
          lowpan6_header_len += 16;
      }

      /* Move to payload. */
      pbuf_header(p, -IP6_HLEN);

      /* Compress UDP header? */
      if (IP6H_NEXTH(ip6hdr) == IP6_NEXTH_UDP)
      {
          /* TODO support optional checksum compression */

          buffer[ieee_header_len + lowpan6_header_len] = 0xf0;

          /* determine port compression mode. */
          if ((((u8_t *)p->payload)[0] == 0xf0) && ((((u8_t *)p->payload)[1] & 0xf0) == 0xb0) &&
              (((u8_t *)p->payload)[2] == 0xf0) && ((((u8_t *)p->payload)[3] & 0xf0) == 0xb0))
          {
              /* Compress source and dest ports. */
              buffer[ieee_header_len + lowpan6_header_len++] |= 0x03;
              buffer[ieee_header_len + lowpan6_header_len++] = ((((u8_t *)p->payload)[1] & 0x0f) << 4) | (((u8_t *)p->payload)[3] & 0x0f);
          }
          else if (((u8_t *)p->payload)[0] == 0xf0)
          {
              /* Compress source port. */
              buffer[ieee_header_len + lowpan6_header_len++] |= 0x02;
              buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[1];
              buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[2];
              buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[3];
          }
          else if (((u8_t *)p->payload)[2] == 0xf0)
          {
              /* Compress dest port. */
              buffer[ieee_header_len + lowpan6_header_len++] |= 0x01;
              buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[0];
              buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[1];
              buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[3];
          }
          else
          {
              /* append full ports. */
              lowpan6_header_len++;
              buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[0];
              buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[1];
              buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[2];
              buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[3];
          }

          /* elide length and copy checksum */
          buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[6];
          buffer[ieee_header_len + lowpan6_header_len++] = ((u8_t *)p->payload)[7];

          pbuf_header(p, -UDP_HLEN);
      }
  }

#else /* LWIP_6LOWPAN_HC */
  /* Send uncompressed IPv6 header with appropriate dispatch byte. */
  lowpan6_header_len = 1;
  buffer[ieee_header_len] = 0x41; /* IPv6 dispatch */
#endif /* LWIP_6LOWPAN_HC */

  /* Calculate remaining packet length */
  remaining_len = p->tot_len;

  /* Fragment, or 1 packet? */
  if (remaining_len > (127 - ieee_header_len - lowpan6_header_len - 3)) /* 127 - header - 1 byte dispatch - 2 bytes CRC */
  {
      /* We must move the 6LowPAN header to make room for the FRAG header. */
      i = lowpan6_header_len;
      while (i-- != 0)
      {
          buffer[ieee_header_len + i + 4] = buffer[ieee_header_len + i];
      }

      /* Now we need to fragment the packet. FRAG1 header first */
      buffer[ieee_header_len] = 0xc0 | (((p->tot_len + lowpan6_header_len) >> 8) & 0x7);
      buffer[ieee_header_len + 1] = (p->tot_len + lowpan6_header_len) & 0xff;

      datagram_tag++;
      buffer[ieee_header_len + 2] = datagram_tag & 0xff;
      buffer[ieee_header_len + 3] = (datagram_tag >> 8) & 0xff;

      /* Fragment follows. */
      frag_len = (127 - ieee_header_len - 4 - 2) & 0xf8;

      pbuf_copy_partial(p, buffer + ieee_header_len + lowpan6_header_len + 4, frag_len - lowpan6_header_len, 0);
      remaining_len -= frag_len - lowpan6_header_len;
      datagram_offset = frag_len;

      /* 2 bytes CRC */
#if LWIP_6LOWPAN_HW_CRC
      /* Leave blank, will be filled by HW. */
#else /* LWIP_6LOWPAN_HW_CRC */
      /* TODO calculate CRC */
#endif /* LWIP_6LOWPAN_HW_CRC */

      /* Calculate frame length */
      p_frag->len = p_frag->tot_len = ieee_header_len + 4 + frag_len + 2; /* add 2 dummy bytes for crc*/

      /* send the packet */
      LWIP_DEBUGF(LOWPAN6_DEBUG | LWIP_DBG_TRACE, ("lowpan6_send: sending packet %p\n", (void *)p));
      err = netif->linkoutput(netif, p_frag);

      while ((remaining_len > 0) && (err == ERR_OK))
      {
          /* new frame, new seq num for ACK */
          buffer[2] = frame_seq_num++;

          buffer[ieee_header_len] |= 0x20; /* Change FRAG1 to FRAGN */

          buffer[ieee_header_len + 4] = datagram_offset >> 3; /* datagram offset in FRAGN header */

          frag_len = (127 - ieee_header_len - 5 - 2) & 0xf8;
          if (frag_len > remaining_len)
              frag_len = remaining_len;

          pbuf_copy_partial(p, buffer + ieee_header_len + 5, frag_len, p->tot_len - remaining_len);
          remaining_len -= frag_len;
          datagram_offset += frag_len;

          /* 2 bytes CRC */
#if LWIP_6LOWPAN_HW_CRC
          /* Leave blank, will be filled by HW. */
#else /* LWIP_6LOWPAN_HW_CRC */
          /* TODO calculate CRC */
#endif /* LWIP_6LOWPAN_HW_CRC */

          /* Calculate frame length */
          p_frag->len = p_frag->tot_len = frag_len + 5 + ieee_header_len + 2;

          /* send the packet */
          LWIP_DEBUGF(LOWPAN6_DEBUG | LWIP_DBG_TRACE, ("lowpan6_send: sending packet %p\n", (void *)p));
          err = netif->linkoutput(netif, p_frag);
      }
  }
  else
  {
      /* It fits in one frame. */
      frag_len = remaining_len;

      /* Copy IPv6 packet */
      pbuf_copy_partial(p, buffer + ieee_header_len + lowpan6_header_len, frag_len, 0);
      remaining_len = 0;

      /* 2 bytes CRC */
#if LWIP_6LOWPAN_HW_CRC
      /* Leave blank, will be filled by HW. */
#else /* LWIP_6LOWPAN_HW_CRC */
      /* TODO calculate CRC */
#endif /* LWIP_6LOWPAN_HW_CRC */

      /* Calculate frame length */
      p_frag->len = p_frag->tot_len = frag_len + lowpan6_header_len + ieee_header_len + 2;

      /* send the packet */
      LWIP_DEBUGF(LOWPAN6_DEBUG | LWIP_DBG_TRACE, ("lowpan6_send: sending packet %p\n", (void *)p));
      err = netif->linkoutput(netif, p_frag);
  }


  pbuf_free(p_frag);

  return err;
}

err_t
lowpan6_set_context(u8_t idx, const ip6_addr_t * context)
{
    if (idx > LWIP_6LOWPAN_NUM_CONTEXTS)
      return ERR_ARG;

    ip6_addr_set(&lowpan6_context[idx], context);

    return ERR_OK;
}

#if LWIP_6LOWPAN_INFER_SHORT_ADDRESS
err_t
lowpan6_set_short_addr(u8_t addr_high, u8_t addr_low)
{
    short_mac_addr.addr[0] = addr_high;
    short_mac_addr.addr[1] = addr_low;

    return ERR_OK;
}
#endif /* LWIP_6LOWPAN_INFER_SHORT_ADDRESS */

#if LWIP_IPV4
err_t
lowpan4_output(struct netif *netif, struct pbuf *q, const ip4_addr_t *ipaddr)
{
    (void)netif;
    (void)q;
    (void)ipaddr;

    return ERR_IF;
}
#endif /* LWIP_IPV4 */

/**
 * Resolve and fill-in IEEE 802.15.4 address header for outgoing IPv6 packet.
 *
 * Perform Header Compression and fragment if necessary.
 *
 * @param netif The lwIP network interface which the IP packet will be sent on.
 * @param q The pbuf(s) containing the IP packet to be sent.
 * @param ip6addr The IP address of the packet destination.
 *
 * @return
 */
err_t
lowpan6_output(struct netif *netif, struct pbuf *q, const ip6_addr_t *ip6addr)
{
    s8_t i;
    struct ieee_802154_addr src, dest;
#if LWIP_6LOWPAN_INFER_SHORT_ADDRESS
    ip6_addr_t ip6_src;
    struct ip6_hdr * ip6_hdr;
#endif /* LWIP_6LOWPAN_INFER_SHORT_ADDRESS */

#if LWIP_6LOWPAN_INFER_SHORT_ADDRESS
    /* Check if we can compress source address (use aligned copy) */
    ip6_hdr = (struct ip6_hdr *)q->payload;
    ip6_addr_set(&ip6_src, &ip6_hdr->src);
    if (lowpan6_get_address_mode(&ip6_src, &short_mac_addr) == 3)
    {
        src.addr_len = 2;
        src.addr[0] = short_mac_addr.addr[0];
        src.addr[1] = short_mac_addr.addr[1];
    }
    else
#endif /* LWIP_6LOWPAN_INFER_SHORT_ADDRESS */
    {
        src.addr_len = netif->hwaddr_len;
        SMEMCPY(src.addr, netif->hwaddr, netif->hwaddr_len);
    }

    /* multicast destination IP address? */
    if (ip6_addr_ismulticast(ip6addr)) {
      /* We need to send to the broadcast address.*/
      return lowpan6_frag(netif, q, &src, &ieee_802154_broadcast);
    }

    /* We have a unicast destination IP address */
    /* TODO anycast? */

#if LWIP_6LOWPAN_INFER_SHORT_ADDRESS
    if (src.addr_len == 2)
    {
        /* If source address was compressable to short_mac_addr, and dest has same subnet and
         * is also compressable to 2-bytes, assume we can infer dest as a short address too. */
        dest.addr_len = 2;
        dest.addr[0] = ((u8_t *)q->payload)[38];
        dest.addr[1] = ((u8_t *)q->payload)[39];
        if ((src.addr_len == 2) && (ip6_addr_netcmp(&ip6_hdr->src, &ip6_hdr->dest)) && (lowpan6_get_address_mode(ip6addr, &dest) == 3))
        {
            return lowpan6_frag(netif, q, &src, &dest);
        }
    }
#endif /* LWIP_6LOWPAN_INFER_SHORT_ADDRESS */


    /* Get next hop record. */
    i = nd6_get_next_hop_entry(ip6addr, netif);
    if (i < 0) {
      /* failed to get a next hop neighbor record. */
      return ERR_MEM;
    }

    /* Now that we have a destination record, send or queue the packet. */
    if (neighbor_cache[i].state == ND6_STALE) {
      /* Switch to delay state. */
      neighbor_cache[i].state = ND6_DELAY;
      neighbor_cache[i].counter.delay_time = LWIP_ND6_DELAY_FIRST_PROBE_TIME;
    }
    /* TODO should we send or queue if PROBE? send for now, to let unicast NS pass. */
    if ((neighbor_cache[i].state == ND6_REACHABLE) ||
        (neighbor_cache[i].state == ND6_DELAY) ||
        (neighbor_cache[i].state == ND6_PROBE)) {

      /* Send out. */
      dest.addr_len = netif->hwaddr_len;
      SMEMCPY(dest.addr, neighbor_cache[i].lladdr, netif->hwaddr_len);
      return lowpan6_frag(netif, q, &src, &dest);
    }

    /* We should queue packet on this interface. */
    return nd6_queue_packet(i, q);
}

static struct pbuf *
lowpan6_decompress(struct pbuf * p, struct ieee_802154_addr * src, struct ieee_802154_addr * dest)
{
    struct pbuf * q;
    u8_t * lowpan6_buffer;
    s8_t lowpan6_offset;
    struct ip6_hdr *ip6hdr;
    s8_t i;
    s8_t ip6_offset = IP6_HLEN;


    q = pbuf_alloc(PBUF_IP, p->len + IP6_HLEN + UDP_HLEN, PBUF_POOL);
    if (q == NULL)
    {
        pbuf_free(p);
        return NULL;
    }

    lowpan6_buffer = (u8_t *)p->payload;
    ip6hdr = (struct ip6_hdr *)q->payload;

    lowpan6_offset = 2;
    if (lowpan6_buffer[1] & 0x80)
    {
        lowpan6_offset++;
    }

    /* Set IPv6 version, traffic class and flow label. */
    if ((lowpan6_buffer[0] & 0x18) == 0x00)
    {
        IP6H_VTCFL_SET(ip6hdr, 6, lowpan6_buffer[lowpan6_offset], ((lowpan6_buffer[lowpan6_offset+1] & 0x0f) << 16) | (lowpan6_buffer[lowpan6_offset + 2] << 8) | lowpan6_buffer[lowpan6_offset+3]);
        lowpan6_offset += 4;
    }
    else if ((lowpan6_buffer[0] & 0x18) == 0x08)
    {
        IP6H_VTCFL_SET(ip6hdr, 6, lowpan6_buffer[lowpan6_offset] & 0xc0, ((lowpan6_buffer[lowpan6_offset] & 0x0f) << 16) | (lowpan6_buffer[lowpan6_offset + 1] << 8) | lowpan6_buffer[lowpan6_offset+2]);
        lowpan6_offset += 3;
    }
    else if ((lowpan6_buffer[0] & 0x18) == 0x10)
    {
        IP6H_VTCFL_SET(ip6hdr, 6, lowpan6_buffer[lowpan6_offset],0);
        lowpan6_offset += 1;
    }
    else if ((lowpan6_buffer[0] & 0x18) == 0x18)
    {
        IP6H_VTCFL_SET(ip6hdr, 6, 0, 0);
    }

    /* Set Next Header */
    if ((lowpan6_buffer[0] & 0x04) == 0x00)
    {
        IP6H_NEXTH_SET(ip6hdr, lowpan6_buffer[lowpan6_offset++]);
    }
    else
    {
        /* We should fill this later with NHC decoding */
        IP6H_NEXTH_SET(ip6hdr, 0);
    }

    /* Set Hop Limit */
    if ((lowpan6_buffer[0] & 0x03) == 0x00)
    {
        IP6H_HOPLIM_SET(ip6hdr, lowpan6_buffer[lowpan6_offset++]);
    }
    else if ((lowpan6_buffer[0] & 0x03) == 0x01)
    {
        IP6H_HOPLIM_SET(ip6hdr, 1);
    }
    else if ((lowpan6_buffer[0] & 0x03) == 0x02)
    {
        IP6H_HOPLIM_SET(ip6hdr, 64);
    }
    else if ((lowpan6_buffer[0] & 0x03) == 0x03)
    {
        IP6H_HOPLIM_SET(ip6hdr, 255);
    }

    /* Source address decoding. */
    if ((lowpan6_buffer[1] & 0x40) == 0x00)
    {
        /* Stateless compression */
        if ((lowpan6_buffer[1] & 0x30) == 0x00)
        {
            /* copy full address */
            MEMCPY(&ip6hdr->src.addr[0], lowpan6_buffer + lowpan6_offset, 16);
            lowpan6_offset += 16;
        }
        else if ((lowpan6_buffer[1] & 0x30) == 0x10)
        {
            ip6hdr->src.addr[0] = PP_HTONL(0xfe800000UL);
            ip6hdr->src.addr[1] = 0;
            MEMCPY(&ip6hdr->src.addr[2], lowpan6_buffer + lowpan6_offset, 8);
            lowpan6_offset += 8;
        }
        else if ((lowpan6_buffer[1] & 0x30) == 0x20)
        {
            ip6hdr->src.addr[0] = PP_HTONL(0xfe800000UL);
            ip6hdr->src.addr[1] = 0;
            ip6hdr->src.addr[2] = PP_HTONL(0x000000ffUL);
            ip6hdr->src.addr[3] = htonl(0xfe000000UL | (lowpan6_buffer[lowpan6_offset] << 8) | lowpan6_buffer[lowpan6_offset+1]);
            lowpan6_offset += 2;
        }
        else if ((lowpan6_buffer[1] & 0x30) == 0x30)
        {
            ip6hdr->src.addr[0] = PP_HTONL(0xfe800000UL);
            ip6hdr->src.addr[1] = 0;
            if (src->addr_len == 2)
            {
                ip6hdr->src.addr[2] = PP_HTONL(0x000000ffUL);
                ip6hdr->src.addr[3] = htonl(0xfe000000UL | (src->addr[0] << 8) | src->addr[1]);
            }
            else
            {
                ip6hdr->src.addr[2] = htonl(((src->addr[0] ^ 2) << 24) | (src->addr[1] << 16) | src->addr[2] << 8 | src->addr[3]);
                ip6hdr->src.addr[3] = htonl((src->addr[4] << 24) | (src->addr[5] << 16) | src->addr[6] << 8 | src->addr[7]);
            }
        }
    }
    else
    {
        /* Stateful compression */
        if ((lowpan6_buffer[1] & 0x30) == 0x00)
        {
            /* ANY address */
            ip6hdr->src.addr[0] = 0;
            ip6hdr->src.addr[1] = 0;
            ip6hdr->src.addr[2] = 0;
            ip6hdr->src.addr[3] = 0;
        }
        else
        {
            /* Set prefix from context info */
            if (lowpan6_buffer[1] & 0x80)
            {
                i = (lowpan6_buffer[2] >> 4) & 0x0f;
            }
            else
            {
                i = 0;
            }
            if (i >= LWIP_6LOWPAN_NUM_CONTEXTS)
            {
                /* Error */
                pbuf_free(p);
                pbuf_free(q);
                return NULL;
            }

            ip6hdr->src.addr[0] = lowpan6_context[i].addr[0];
            ip6hdr->src.addr[1] = lowpan6_context[i].addr[1];
        }

        if ((lowpan6_buffer[1] & 0x30) == 0x10)
        {
            MEMCPY(&ip6hdr->src.addr[2], lowpan6_buffer + lowpan6_offset, 8);
            lowpan6_offset += 8;
        }
        else if ((lowpan6_buffer[1] & 0x30) == 0x20)
        {
            ip6hdr->src.addr[2] = PP_HTONL(0x000000ffUL);
            ip6hdr->src.addr[3] = htonl(0xfe000000UL | (lowpan6_buffer[lowpan6_offset] << 8) | lowpan6_buffer[lowpan6_offset+1]);
            lowpan6_offset += 2;
        }
        else if ((lowpan6_buffer[1] & 0x30) == 0x30)
        {
            if (src->addr_len == 2)
            {
                ip6hdr->src.addr[2] = PP_HTONL(0x000000ffUL);
                ip6hdr->src.addr[3] = htonl(0xfe000000UL | (src->addr[0] << 8) | src->addr[1]);
            }
            else
            {
                ip6hdr->src.addr[2] = htonl(((src->addr[0] ^ 2) << 24) | (src->addr[1] << 16) | src->addr[2] << 8 | src->addr[3]);
                ip6hdr->src.addr[3] = htonl((src->addr[4] << 24) | (src->addr[5] << 16) | src->addr[6] << 8 | src->addr[7]);
            }
        }
    }

    /* Destination address decoding. */
    if (lowpan6_buffer[1] & 0x08)
    {
        /* Multicast destination */
        if (lowpan6_buffer[1] & 0x04)
        {
            /* TODO support stateful multicast addressing */
            pbuf_free(p);
            pbuf_free(q);
            return NULL;
        }

        if ((lowpan6_buffer[1] & 0x03) == 0x00)
        {
            /* copy full address */
            MEMCPY(&ip6hdr->dest.addr[0], lowpan6_buffer + lowpan6_offset, 16);
            lowpan6_offset += 16;
        }
        else if ((lowpan6_buffer[1] & 0x03) == 0x01)
        {
            ip6hdr->dest.addr[0] = htonl(0xff000000UL | (lowpan6_buffer[lowpan6_offset++] << 16));
            ip6hdr->dest.addr[1] = 0;
            ip6hdr->dest.addr[2] = htonl(lowpan6_buffer[lowpan6_offset++]);
            ip6hdr->dest.addr[3] = htonl((lowpan6_buffer[lowpan6_offset] << 24) | (lowpan6_buffer[lowpan6_offset + 1] << 16) | (lowpan6_buffer[lowpan6_offset + 2] << 8) | lowpan6_buffer[lowpan6_offset + 3]);
            lowpan6_offset += 4;
        }
        else if ((lowpan6_buffer[1] & 0x03) == 0x02)
        {
            ip6hdr->dest.addr[0] = htonl(0xff000000UL | lowpan6_buffer[lowpan6_offset++]);
            ip6hdr->dest.addr[1] = 0;
            ip6hdr->dest.addr[2] = 0;
            ip6hdr->dest.addr[3] = htonl((lowpan6_buffer[lowpan6_offset] << 16) | (lowpan6_buffer[lowpan6_offset + 1] << 8) | lowpan6_buffer[lowpan6_offset + 2]);
            lowpan6_offset += 3;
        }
        else if ((lowpan6_buffer[1] & 0x03) == 0x03)
        {
            ip6hdr->dest.addr[0] = PP_HTONL(0xff020000UL);
            ip6hdr->dest.addr[1] = 0;
            ip6hdr->dest.addr[2] = 0;
            ip6hdr->dest.addr[3] = htonl(lowpan6_buffer[lowpan6_offset++]);
        }

    }
    else
    {
        if (lowpan6_buffer[1] & 0x04)
        {
            /* Stateful destination compression */
            /* Set prefix from context info */
            if (lowpan6_buffer[1] & 0x80)
            {
                i = lowpan6_buffer[2] & 0x0f;
            }
            else
            {
                i = 0;
            }
            if (i >= LWIP_6LOWPAN_NUM_CONTEXTS)
            {
                /* Error */
                pbuf_free(p);
                pbuf_free(q);
                return NULL;
            }

            ip6hdr->dest.addr[0] = lowpan6_context[i].addr[0];
            ip6hdr->dest.addr[1] = lowpan6_context[i].addr[1];
        }
        else
        {
            /* Link local address compression */
            ip6hdr->dest.addr[0] = PP_HTONL(0xfe800000UL);
            ip6hdr->dest.addr[1] = 0;
        }

        if ((lowpan6_buffer[1] & 0x03) == 0x00)
        {
            /* copy full address */
            MEMCPY(&ip6hdr->dest.addr[0], lowpan6_buffer + lowpan6_offset, 16);
            lowpan6_offset += 16;
        }
        else if ((lowpan6_buffer[1] & 0x03) == 0x01)
        {
            MEMCPY(&ip6hdr->dest.addr[2], lowpan6_buffer + lowpan6_offset, 8);
            lowpan6_offset += 8;
        }
        else if ((lowpan6_buffer[1] & 0x03) == 0x02)
        {
            ip6hdr->dest.addr[2] = PP_HTONL(0x000000ffUL);
            ip6hdr->dest.addr[3] = htonl(0xfe000000UL | (lowpan6_buffer[lowpan6_offset] << 8) | lowpan6_buffer[lowpan6_offset + 1]);
            lowpan6_offset += 2;
        }
        else if ((lowpan6_buffer[1] & 0x03) == 0x03)
        {
            if (dest->addr_len == 2)
            {
                ip6hdr->dest.addr[2] = PP_HTONL(0x000000ffUL);
                ip6hdr->dest.addr[3] = htonl(0xfe000000UL | (dest->addr[0] << 8) | dest->addr[1]);
            }
            else
            {
                ip6hdr->dest.addr[2] = htonl(((dest->addr[0] ^ 2) << 24) | (dest->addr[1] << 16) | dest->addr[2] << 8 | dest->addr[3]);
                ip6hdr->dest.addr[3] = htonl((dest->addr[4] << 24) | (dest->addr[5] << 16) | dest->addr[6] << 8 | dest->addr[7]);
            }
        }
    }


    /* Next Header Compression (NHC) decoding? */
    if (lowpan6_buffer[0] & 0x04)
    {
        if ((lowpan6_buffer[lowpan6_offset] & 0xf8) == 0xf0)
        {
            struct udp_hdr *udphdr;

            /* UDP compression */
            IP6H_NEXTH_SET(ip6hdr, IP6_NEXTH_UDP);
            udphdr = (struct udp_hdr *)((u8_t *)q->payload + ip6_offset);

            if (lowpan6_buffer[lowpan6_offset] & 0x04)
            {
                /* TODO support checksum decompress */
                pbuf_free(p);
                pbuf_free(q);
                return NULL;
            }

            /* Decompress ports */
            i = lowpan6_buffer[lowpan6_offset++] & 0x03;
            if (i == 0)
            {
                udphdr->src = htons(lowpan6_buffer[lowpan6_offset] << 8 | lowpan6_buffer[lowpan6_offset + 1]);
                udphdr->dest = htons(lowpan6_buffer[lowpan6_offset + 2] << 8 | lowpan6_buffer[lowpan6_offset + 3]);
                lowpan6_offset += 4;
            }
            else if (i == 0x01)
            {
                udphdr->src = htons(lowpan6_buffer[lowpan6_offset] << 8 | lowpan6_buffer[lowpan6_offset + 1]);
                udphdr->dest = htons(0xf000 | lowpan6_buffer[lowpan6_offset + 2]);
                lowpan6_offset += 3;
            }
            else if (i == 0x02)
            {
                udphdr->src = htons(0xf000 | lowpan6_buffer[lowpan6_offset]);
                udphdr->dest = htons(lowpan6_buffer[lowpan6_offset + 1] << 8 | lowpan6_buffer[lowpan6_offset + 2]);
                lowpan6_offset += 3;
            }
            else if (i == 0x03)
            {
                udphdr->src = htons(0xf0b0 | ((lowpan6_buffer[lowpan6_offset] >> 4) & 0x0f));
                udphdr->dest = htons(0xf0b0 | (lowpan6_buffer[lowpan6_offset] & 0x0f));
                lowpan6_offset += 1;
            }

            udphdr->chksum = htons(lowpan6_buffer[lowpan6_offset] << 8 | lowpan6_buffer[lowpan6_offset + 1]);
            lowpan6_offset += 2;
            udphdr->len = htons(p->tot_len - lowpan6_offset + UDP_HLEN);

            ip6_offset += UDP_HLEN;
        }
        else
        {
            /* TODO support NHC other than UDP */
            pbuf_free(p);
            pbuf_free(q);
            return NULL;
        }
    }

    /* Now we copy leftover contents from p to q, so we have all L2 and L3 headers (and L4?) in a single PBUF.
     * Replace p with q, and free p */
    pbuf_header(p, -lowpan6_offset);
    MEMCPY((u8_t*)q->payload + ip6_offset, p->payload, p->len);
    q->len = q->tot_len = ip6_offset + p->len;
    if (p->next != NULL) {
        pbuf_cat(q, p->next);
    }
    p->next = NULL;
    pbuf_free(p);

    /* Infer IPv6 payload length for header */
    IP6H_PLEN_SET(ip6hdr, q->tot_len - IP6_HLEN);

    /* all done */
    return q;
}

err_t
lowpan6_input(struct pbuf * p, struct netif *netif)
{
    u8_t * puc;
    s8_t i;
    struct ieee_802154_addr src, dest;
    u16_t datagram_size, datagram_offset, datagram_tag;
    struct lowpan6_reass_helper *lrh, *lrh_temp;

    /* Analyze header. TODO validate. */
    puc = (u8_t*)p->payload;
    datagram_offset = 5;
    if ((puc[1] & 0x0c) == 0x0c)
    {
        dest.addr_len = 8;
        for (i = 0; i < 8; i++)
        {
            dest.addr[i] = puc[datagram_offset + 7 - i];
        }
        datagram_offset += 8;
    }
    else
    {
        dest.addr_len = 2;
        dest.addr[0] = puc[datagram_offset + 1];
        dest.addr[1] = puc[datagram_offset];
        datagram_offset += 2;
    }

    datagram_offset += 2; /* skip PAN ID. */

    if ((puc[1] & 0xc0) == 0xc0)
    {
        src.addr_len = 8;
        for (i = 0; i < 8; i++)
        {
            src.addr[i] = puc[datagram_offset + 7 - i];
        }
        datagram_offset += 8;
    }
    else
    {
        src.addr_len = 2;
        src.addr[0] = puc[datagram_offset + 1];
        src.addr[1] = puc[datagram_offset];
        datagram_offset += 2;
    }

    pbuf_header(p, -datagram_offset); /* hide IEEE802.15.4 header. */

    /* Check dispatch. */
    puc = (u8_t*)p->payload;

    if ((*puc & 0xf8) == 0xc0)
    {
        /* FRAG1 dispatch. add this packet to reassembly list. */
        datagram_size = ((u16_t)(puc[0] & 0x07) << 8) | (u16_t)puc[1];
        datagram_tag = ((u16_t)puc[2] << 8) | (u16_t)puc[3];

        /* check for duplicate */
        lrh = reass_list;
        while (lrh != NULL)
        {
            if ((lrh->sender_addr.addr_len == src.addr_len) &&
                (memcmp(lrh->sender_addr.addr, src.addr, src.addr_len) == 0))
            {
                /* address match with packet in reassembly. */
                if ((datagram_tag == lrh->datagram_tag) && (datagram_size == lrh->datagram_size)) {
                    /* duplicate fragment. */
                    pbuf_free(p);
                    return ERR_OK;
                }
                else {
                    /* We are receiving the start of a new datagram. Discard old one (incomplete). */
                    lrh_temp = lrh->next_packet;
                    dequeue_datagram(lrh);
                    pbuf_free(lrh->pbuf);
                    mem_free(lrh);

                    /* Check next datagram in queue. */
                    lrh = lrh_temp;
                }
            }
            else {
                /* Check next datagram in queue. */
                lrh = lrh->next_packet;
            }
        }

        pbuf_header(p, -4); /* hide frag1 dispatch */

        lrh = (struct lowpan6_reass_helper *) mem_malloc(sizeof(struct lowpan6_reass_helper));
        if (lrh == NULL) {
            pbuf_free(p);
            return ERR_MEM;
        }

        lrh->sender_addr.addr_len = src.addr_len;
        for (i = 0; i < src.addr_len; i++) {
            lrh->sender_addr.addr[i] = src.addr[i];
        }
        lrh->datagram_size = datagram_size;
        lrh->datagram_tag = datagram_tag;
        lrh->pbuf = p;
        lrh->next_packet = reass_list;
        lrh->timer = 2;
        reass_list = lrh;

        return ERR_OK;
    }
    else if ((*puc & 0xf8) == 0xe0)
    {
        /* FRAGN dispatch, find packet being reassembled. */
        datagram_size = ((u16_t)(puc[0] & 0x07) << 8) | (u16_t)puc[1];
        datagram_tag = ((u16_t)puc[2] << 8) | (u16_t)puc[3];
        datagram_offset = (u16_t)puc[4] << 3;
        pbuf_header(p, -5); /* hide frag1 dispatch */

        for (lrh = reass_list; lrh != NULL; lrh = lrh->next_packet)
        {
            if (
                (lrh->sender_addr.addr_len == src.addr_len) &&
                (memcmp(lrh->sender_addr.addr, src.addr, src.addr_len) == 0) &&
                (datagram_tag == lrh->datagram_tag) &&
                (datagram_size == lrh->datagram_size)
                )
            {
                break;
            }
        }
        if (lrh == NULL)
        {
            /* rogue fragment */
            pbuf_free(p);
            return ERR_OK;
        }

        if (lrh->pbuf->tot_len < datagram_offset)
        {
            /* duplicate, ignore. */
            pbuf_free(p);
            return ERR_OK;
        }
        else if (lrh->pbuf->tot_len > datagram_offset)
        {
            /* We have missed a fragment. Delete whole reassembly. */
            dequeue_datagram(lrh);
            pbuf_free(lrh->pbuf);
            mem_free(lrh);
            pbuf_free(p);
            return ERR_OK;
        }
        pbuf_cat(lrh->pbuf, p);
        p = NULL;

        /* is packet now complete?*/
        if (lrh->pbuf->tot_len >= lrh->datagram_size)
        {
            /* dequeue from reass list. */
            dequeue_datagram(lrh);

            /* get pbuf */
            p = lrh->pbuf;

            /* release helper */
            mem_free(lrh);
        }
        else
        {
            return ERR_OK;
        }
    }

    if (p == NULL) return ERR_OK;

    /* We have a complete packet, check dispatch for headers. */
    puc = (u8_t*)p->payload;

    if (*puc == 0x41)
    {
        /* This is a complete IPv6 packet, just skip dispatch byte. */
        pbuf_header(p, -1); /* hide dispatch byte. */
    }
    else if ((*puc & 0xe0 )== 0x60)
    {
        /* IPv6 headers are compressed using IPHC. */
        p = lowpan6_decompress(p, &src, &dest);
        if (p == NULL) return ERR_OK;
    }
    else
    {
        pbuf_free(p);
        return ERR_OK;
    }

    return ip6_input(p, netif);
}

err_t
lowpan6_if_init(struct netif *netif)
{
    netif->name[0] = 'L';
    netif->name[1] = '6';
#if LWIP_IPV4
    netif->output = lowpan4_output;
#endif /* LWIP_IPV4 */
    netif->output_ip6 = lowpan6_output;

    /* maximum transfer unit */
    netif->mtu = 1280;

    /* broadcast capability */
    netif->flags = NETIF_FLAG_BROADCAST /* | NETIF_FLAG_LOWPAN6 */;

    return ERR_OK;
}

err_t
lowpan6_set_pan_id(u16_t pan_id)
{
    ieee_802154_pan_id = pan_id;

    return ERR_OK;
}

/**
 * Pass a received packet to tcpip_thread for input processing
 *
 * @param p the received packet, p->payload pointing to the
 *          IEEE 802.15.4 header.
 * @param inp the network interface on which the packet was received
 */
err_t
tcpip_6lowpan_input(struct pbuf *p, struct netif *inp)
{
  return tcpip_inpkt(p, inp, lowpan6_input);
}

#endif /* LWIP_IPV6 && LWIP_6LOWPAN */