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hc.c

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00001 /*
00002  * Copyright (c) 2005, Swedish Institute of Computer Science
00003  * All rights reserved.
00004  *
00005  * Redistribution and use in source and binary forms, with or without
00006  * modification, are permitted provided that the following conditions
00007  * are met:
00008  * 1. Redistributions of source code must retain the above copyright
00009  *    notice, this list of conditions and the following disclaimer.
00010  * 2. Redistributions in binary form must reproduce the above copyright
00011  *    notice, this list of conditions and the following disclaimer in the
00012  *    documentation and/or other materials provided with the distribution.
00013  * 3. Neither the name of the Institute nor the names of its contributors
00014  *    may be used to endorse or promote products derived from this software
00015  *    without specific prior written permission.
00016  *
00017  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
00018  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
00019  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
00020  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
00021  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
00022  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
00023  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
00024  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
00025  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
00026  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
00027  * SUCH DAMAGE.
00028  *
00029  * This file is part of the Contiki operating system.
00030  *
00031  * @(#)$Id: hc.c,v 1.5 2010/10/19 18:29:04 adamdunkels Exp $
00032  */
00033 
00034 /**
00035  * \file
00036  * TCP/IP header compression implementation
00037  * \author Adam Dunkels <adam@sics.se>
00038  *
00039  */
00040 
00041 #include "net/hc.h"
00042 
00043 #include "net/uip.h"
00044 
00045 #include <string.h>
00046 
00047 #define FLAGS_COMPRESSED     0x8000
00048 #define FLAGS_BROADCASTDATA  0x4000
00049 
00050 struct hc_hdr {
00051   uint16_t flagsport;
00052   uip_ipaddr_t srcipaddr;
00053 };
00054 
00055 struct udpip_hdr {
00056   /* IP header. */
00057   uint8_t vhl,
00058     tos,
00059     len[2],
00060     ipid[2],
00061     ipoffset[2],
00062     ttl,
00063     proto;
00064   uint16_t ipchksum;
00065   uip_ipaddr_t srcipaddr, destipaddr;
00066   
00067   /* UDP header. */
00068   uint16_t srcport,
00069     destport;
00070   uint16_t udplen;
00071   uint16_t udpchksum;
00072 };
00073 
00074 #include <stdio.h>
00075 
00076 /*---------------------------------------------------------------------------*/
00077 /**
00078  * Initialize the header compression module.
00079  */
00080 /*---------------------------------------------------------------------------*/
00081 void
00082 hc_init(void)
00083 {
00084 
00085 }
00086 /*---------------------------------------------------------------------------*/
00087 /**
00088  * Compress a header
00089  *
00090  * This function compresses the TCP/IP headers in a buffer and
00091  * should be called just before sending out data on the network. A
00092  * pointer to the compressed header is returned, and len is
00093  * adjusted.
00094  *
00095  * If the header could not be compressed, the function does nothing
00096  * and returns a NULL pointer.
00097  *
00098  * \return A pointer to the start of the compressed header or NULL if
00099  * the header could not be compressed.
00100  */
00101 /*---------------------------------------------------------------------------*/
00102 int
00103 hc_compress(uint8_t *buf, int len)
00104 {
00105   struct hc_hdr *hdr;
00106   struct udpip_hdr *uhdr;
00107 
00108   hdr = (struct hc_hdr *)buf;
00109   uhdr = (struct udpip_hdr *)buf;
00110 
00111   /* Check the original TCP/IP header to see if it matches our
00112      pattern, and compress if it does. */
00113   
00114   if(uhdr->vhl == 0x45 &&                      /* Only IPv4 without
00115                                                   options. */
00116      uhdr->len[0] == 0x00 &&                   /* Only packets < 256
00117                                                   bytes long. */
00118      uhdr->ipoffset[0] == 0x00 &&              /* No fragmented IP
00119                                                   packets. */
00120      uhdr->ipoffset[1] == 0x00 &&              /* No fragmented IP
00121                                                   packets. */
00122      uhdr->proto == UIP_PROTO_UDP &&           /* Only UDP packets. */
00123      uip_ipaddr_cmp(&uhdr->destipaddr, &uip_broadcast_addr) && /* Only
00124                                                   link-local broadcast
00125                                                   packets. */
00126      uhdr->destport == uhdr->srcport &&        /* Only packets with
00127                                                   the same destination
00128                                                   and source port
00129                                                   number. */
00130      (uhdr->destport & UIP_HTONS(0xc000)) == 0) {  /* Only packets with the two
00131                                                   highest bits in the port
00132                                                   number equal to zero. */
00133 
00134     hdr->flagsport = uip_htons(
00135                            FLAGS_COMPRESSED    | /* Compressed header. */
00136                            FLAGS_BROADCASTDATA | /* Broadcast data. */
00137                            (uip_htons(uhdr->destport) & 0x3fff));
00138     uip_ipaddr_copy(&hdr->srcipaddr, &uhdr->srcipaddr);
00139 
00140     /* Move the packet data to the end of the compressed header. */
00141     memcpy((char *)hdr + HC_HLEN,
00142            &buf[UIP_IPUDPH_LEN],
00143            len - UIP_IPUDPH_LEN);
00144 
00145     /* Return the new packet length. */
00146     return len - (UIP_IPUDPH_LEN - HC_HLEN);
00147   }
00148 
00149   /* No compression possible, return NULL pointer. */
00150   return len;
00151      
00152 }
00153 /*---------------------------------------------------------------------------*/
00154 /**
00155  * Inflate (decompress) a header
00156  *
00157  * This function should be called to inflate a possibly compressed
00158  * packet header just after a packet has been received from the
00159  * network. The function will copy the packet data so that the
00160  * original header fits and adjusts uip_len.
00161  *
00162  */
00163 /*---------------------------------------------------------------------------*/
00164 int
00165 hc_inflate(uint8_t *buf, int len)
00166 {
00167   struct udpip_hdr *uhdr;
00168   struct hc_hdr *hdr;
00169   
00170   hdr = (struct hc_hdr *)buf;
00171   
00172   /* First, check if the header in buf is compressed or not. */
00173   if((hdr->flagsport & UIP_HTONS(FLAGS_COMPRESSED)) != 0 &&
00174      (hdr->flagsport & UIP_HTONS(FLAGS_BROADCASTDATA)) != 0) {
00175     
00176     /* Move packet data in memory to make room for the uncompressed header. */
00177     memmove(&buf[UIP_IPUDPH_LEN - HC_HLEN],
00178             buf, len);
00179     uhdr = (struct udpip_hdr *)buf;
00180     hdr = (struct hc_hdr *)&buf[UIP_IPUDPH_LEN - HC_HLEN];
00181     
00182     uip_ipaddr_copy(&uhdr->srcipaddr, &hdr->srcipaddr);
00183     uhdr->srcport = hdr->flagsport & UIP_HTONS(0x3fff);
00184     uhdr->destport = hdr->flagsport & UIP_HTONS(0x3fff);
00185     
00186     uhdr->udplen = len;
00187     
00188     len += UIP_IPUDPH_LEN - HC_HLEN;
00189 
00190     
00191     uhdr->vhl = 0x45;
00192     uhdr->tos = 0;
00193     uhdr->len[0] = 0;
00194     uhdr->len[1] = len;
00195     uhdr->ipid[0] = uhdr->ipid[1] = 0xAD;
00196     uhdr->ipoffset[0] = uhdr->ipoffset[1] = 0;
00197     uhdr->ttl = 2;
00198     uhdr->proto = UIP_PROTO_UDP;
00199     uip_ipaddr_copy(&uhdr->destipaddr, &uip_broadcast_addr);
00200     uhdr->udpchksum = 0;
00201 
00202     uhdr->ipchksum = 0;
00203     uhdr->ipchksum = ~(uip_ipchksum());
00204 
00205   }
00206 
00207   return len;
00208 }
00209 /*---------------------------------------------------------------------------*/