text: /*
   * Copyright (c) 2005, 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. Neither the name of the Institute nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``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 INSTITUTE OR CONTRIBUTORS 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 Contiki operating system.
   *
   */
  
  /**
   * \file
   * TCP/IP header compression implementation
   * \author Adam Dunkels <adam@sics.se>
   *
   */
  
  #include "net/hc.h"
  
  #include "net/uip.h"
  
  #include <string.h>
  
  #define FLAGS_COMPRESSED     0x8000
  #define FLAGS_BROADCASTDATA  0x4000
  
  struct hc_hdr {
    uint16_t flagsport;
    uip_ipaddr_t srcipaddr;
  };
  
  struct udpip_hdr {
    /* IP header. */
    uint8_t vhl,
      tos,
      len[2],
      ipid[2],
      ipoffset[2],
      ttl,
      proto;
    uint16_t ipchksum;
    uip_ipaddr_t srcipaddr, destipaddr;
    
    /* UDP header. */
    uint16_t srcport,
      destport;
    uint16_t udplen;
    uint16_t udpchksum;
  };
  
  #include <stdio.h>
  
  /*---------------------------------------------------------------------------*/
  /**
   * Initialize the header compression module.
   */
  /*---------------------------------------------------------------------------*/
  void
  hc_init(void)
  {
  
  }
  /*---------------------------------------------------------------------------*/
  /**
   * Compress a header
   *
   * This function compresses the TCP/IP headers in a buffer and
   * should be called just before sending out data on the network. A
   * pointer to the compressed header is returned, and len is
   * adjusted.
   *
   * If the header could not be compressed, the function does nothing
   * and returns a NULL pointer.
   *
   * \return A pointer to the start of the compressed header or NULL if
   * the header could not be compressed.
   */
  /*---------------------------------------------------------------------------*/
  int
  hc_compress(uint8_t *buf, int len)
  {
    struct hc_hdr *hdr;
    struct udpip_hdr *uhdr;
  
    hdr = (struct hc_hdr *)buf;
    uhdr = (struct udpip_hdr *)buf;
  
    /* Check the original TCP/IP header to see if it matches our
       pattern, and compress if it does. */
    
    if(uhdr->vhl == 0x45 &&                      /* Only IPv4 without
  						  options. */
       uhdr->len[0] == 0x00 &&                   /* Only packets < 256
  						  bytes long. */
       uhdr->ipoffset[0] == 0x00 &&              /* No fragmented IP
  						  packets. */
       uhdr->ipoffset[1] == 0x00 &&              /* No fragmented IP
  						  packets. */
       uhdr->proto == UIP_PROTO_UDP &&           /* Only UDP packets. */
       uip_ipaddr_cmp(&uhdr->destipaddr, &uip_broadcast_addr) && /* Only
  						  link-local broadcast
  						  packets. */
       uhdr->destport == uhdr->srcport &&        /* Only packets with
  						  the same destination
  						  and source port
  						  number. */
       (uhdr->destport & UIP_HTONS(0xc000)) == 0) {  /* Only packets with the two
  						  highest bits in the port
  						  number equal to zero. */
  
      hdr->flagsport = uip_htons(
  			   FLAGS_COMPRESSED    | /* Compressed header. */
  			   FLAGS_BROADCASTDATA | /* Broadcast data. */
  			   (uip_htons(uhdr->destport) & 0x3fff));
      uip_ipaddr_copy(&hdr->srcipaddr, &uhdr->srcipaddr);
  
      /* Move the packet data to the end of the compressed header. */
      memcpy((char *)hdr + HC_HLEN,
  	   &buf[UIP_IPUDPH_LEN],
  	   len - UIP_IPUDPH_LEN);
  
      /* Return the new packet length. */
      return len - (UIP_IPUDPH_LEN - HC_HLEN);
    }
  
    /* No compression possible, return NULL pointer. */
    return len;
       
  }
  /*---------------------------------------------------------------------------*/
  /**
   * Inflate (decompress) a header
   *
   * This function should be called to inflate a possibly compressed
   * packet header just after a packet has been received from the
   * network. The function will copy the packet data so that the
   * original header fits and adjusts uip_len.
   *
   */
  /*---------------------------------------------------------------------------*/
  int
  hc_inflate(uint8_t *buf, int len)
  {
    struct udpip_hdr *uhdr;
    struct hc_hdr *hdr;
    
    hdr = (struct hc_hdr *)buf;
    
    /* First, check if the header in buf is compressed or not. */
    if((hdr->flagsport & UIP_HTONS(FLAGS_COMPRESSED)) != 0 &&
       (hdr->flagsport & UIP_HTONS(FLAGS_BROADCASTDATA)) != 0) {
      
      /* Move packet data in memory to make room for the uncompressed header. */
      memmove(&buf[UIP_IPUDPH_LEN - HC_HLEN],
  	    buf, len);
      uhdr = (struct udpip_hdr *)buf;
      hdr = (struct hc_hdr *)&buf[UIP_IPUDPH_LEN - HC_HLEN];
      
      uip_ipaddr_copy(&uhdr->srcipaddr, &hdr->srcipaddr);
      uhdr->srcport = hdr->flagsport & UIP_HTONS(0x3fff);
      uhdr->destport = hdr->flagsport & UIP_HTONS(0x3fff);
      
      uhdr->udplen = len;
      
      len += UIP_IPUDPH_LEN - HC_HLEN;
  
      
      uhdr->vhl = 0x45;
      uhdr->tos = 0;
      uhdr->len[0] = 0;
      uhdr->len[1] = len;
      uhdr->ipid[0] = uhdr->ipid[1] = 0xAD;
      uhdr->ipoffset[0] = uhdr->ipoffset[1] = 0;
      uhdr->ttl = 2;
      uhdr->proto = UIP_PROTO_UDP;
      uip_ipaddr_copy(&uhdr->destipaddr, &uip_broadcast_addr);
      uhdr->udpchksum = 0;
  
      uhdr->ipchksum = 0;
      uhdr->ipchksum = ~(uip_ipchksum());
  
    }
  
    return len;
  }
  /*---------------------------------------------------------------------------*/
  