lwip_vj.c

00001 /*
00002  * Routines to compress and uncompess tcp packets (for transmission
00003  * over low speed serial lines.
00004  *
00005  * Copyright (c) 1989 Regents of the University of California.
00006  * All rights reserved.
00007  *
00008  * Redistribution and use in source and binary forms are permitted
00009  * provided that the above copyright notice and this paragraph are
00010  * duplicated in all such forms and that any documentation,
00011  * advertising materials, and other materials related to such
00012  * distribution and use acknowledge that the software was developed
00013  * by the University of California, Berkeley.  The name of the
00014  * University may not be used to endorse or promote products derived
00015  * from this software without specific prior written permission.
00016  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
00017  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
00018  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
00019  *
00020  * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
00021  *   Initial distribution.
00022  *
00023  * Modified June 1993 by Paul Mackerras, paulus@cs.anu.edu.au,
00024  * so that the entire packet being decompressed doesn't have
00025  * to be in contiguous memory (just the compressed header).
00026  *
00027  * Modified March 1998 by Guy Lancaster, glanca@gesn.com,
00028  * for a 16 bit processor.
00029  */
00030 
00031 #include "netif/ppp/ppp_opts.h"
00032 #if PPP_SUPPORT && VJ_SUPPORT /* don't build if not configured for use in lwipopts.h */
00033 
00034 #include "netif/ppp/ppp_impl.h"
00035 #include "netif/ppp/pppdebug.h"
00036 
00037 #include "netif/ppp/vj.h"
00038 
00039 #include <string.h>
00040 
00041 #if LINK_STATS
00042 #define INCR(counter) ++comp->stats.counter
00043 #else
00044 #define INCR(counter)
00045 #endif
00046 
00047 void
00048 vj_compress_init(struct vjcompress *comp)
00049 {
00050   u8_t i;
00051   struct cstate *tstate = comp->tstate;
00052 
00053 #if MAX_SLOTS == 0
00054   memset((char *)comp, 0, sizeof(*comp));
00055 #endif
00056   comp->maxSlotIndex = MAX_SLOTS - 1;
00057   comp->compressSlot = 0;    /* Disable slot ID compression by default. */
00058   for (i = MAX_SLOTS - 1; i > 0; --i) {
00059     tstate[i].cs_id = i;
00060     tstate[i].cs_next = &tstate[i - 1];
00061   }
00062   tstate[0].cs_next = &tstate[MAX_SLOTS - 1];
00063   tstate[0].cs_id = 0;
00064   comp->last_cs = &tstate[0];
00065   comp->last_recv = 255;
00066   comp->last_xmit = 255;
00067   comp->flags = VJF_TOSS;
00068 }
00069 
00070 
00071 /* ENCODE encodes a number that is known to be non-zero.  ENCODEZ
00072  * checks for zero (since zero has to be encoded in the long, 3 byte
00073  * form).
00074  */
00075 #define ENCODE(n) { \
00076   if ((u16_t)(n) >= 256) { \
00077     *cp++ = 0; \
00078     cp[1] = (u8_t)(n); \
00079     cp[0] = (u8_t)((n) >> 8); \
00080     cp += 2; \
00081   } else { \
00082     *cp++ = (u8_t)(n); \
00083   } \
00084 }
00085 #define ENCODEZ(n) { \
00086   if ((u16_t)(n) >= 256 || (u16_t)(n) == 0) { \
00087     *cp++ = 0; \
00088     cp[1] = (u8_t)(n); \
00089     cp[0] = (u8_t)((n) >> 8); \
00090     cp += 2; \
00091   } else { \
00092     *cp++ = (u8_t)(n); \
00093   } \
00094 }
00095 
00096 #define DECODEL(f) { \
00097   if (*cp == 0) {\
00098     u32_t tmp_ = lwip_ntohl(f) + ((cp[1] << 8) | cp[2]); \
00099     (f) = lwip_htonl(tmp_); \
00100     cp += 3; \
00101   } else { \
00102     u32_t tmp_ = lwip_ntohl(f) + (u32_t)*cp++; \
00103     (f) = lwip_htonl(tmp_); \
00104   } \
00105 }
00106 
00107 #define DECODES(f) { \
00108   if (*cp == 0) {\
00109     u16_t tmp_ = lwip_ntohs(f) + (((u16_t)cp[1] << 8) | cp[2]); \
00110     (f) = lwip_htons(tmp_); \
00111     cp += 3; \
00112   } else { \
00113     u16_t tmp_ = lwip_ntohs(f) + (u16_t)*cp++; \
00114     (f) = lwip_htons(tmp_); \
00115   } \
00116 }
00117 
00118 #define DECODEU(f) { \
00119   if (*cp == 0) {\
00120     (f) = lwip_htons(((u16_t)cp[1] << 8) | cp[2]); \
00121     cp += 3; \
00122   } else { \
00123     (f) = lwip_htons((u16_t)*cp++); \
00124   } \
00125 }
00126 
00127 /* Helper structures for unaligned *u32_t and *u16_t accesses */
00128 #ifdef PACK_STRUCT_USE_INCLUDES
00129 #  include "arch/bpstruct.h"
00130 #endif
00131 PACK_STRUCT_BEGIN
00132 struct vj_u32_t {
00133   PACK_STRUCT_FIELD(u32_t v);
00134 } PACK_STRUCT_STRUCT;
00135 PACK_STRUCT_END
00136 #ifdef PACK_STRUCT_USE_INCLUDES
00137 #  include "arch/epstruct.h"
00138 #endif
00139 
00140 #ifdef PACK_STRUCT_USE_INCLUDES
00141 #  include "arch/bpstruct.h"
00142 #endif
00143 PACK_STRUCT_BEGIN
00144 struct vj_u16_t {
00145   PACK_STRUCT_FIELD(u16_t v);
00146 } PACK_STRUCT_STRUCT;
00147 PACK_STRUCT_END
00148 #ifdef PACK_STRUCT_USE_INCLUDES
00149 #  include "arch/epstruct.h"
00150 #endif
00151 
00152 /*
00153  * vj_compress_tcp - Attempt to do Van Jacobson header compression on a
00154  * packet.  This assumes that nb and comp are not null and that the first
00155  * buffer of the chain contains a valid IP header.
00156  * Return the VJ type code indicating whether or not the packet was
00157  * compressed.
00158  */
00159 u8_t
00160 vj_compress_tcp(struct vjcompress *comp, struct pbuf **pb)
00161 {
00162   struct pbuf *np = *pb;
00163   struct ip_hdr *ip = (struct ip_hdr *)np->payload;
00164   struct cstate *cs = comp->last_cs->cs_next;
00165   u16_t ilen = IPH_HL(ip);
00166   u16_t hlen;
00167   struct tcp_hdr *oth;
00168   struct tcp_hdr *th;
00169   u16_t deltaS, deltaA = 0;
00170   u32_t deltaL;
00171   u32_t changes = 0;
00172   u8_t new_seq[16];
00173   u8_t *cp = new_seq;
00174 
00175   /*
00176    * Check that the packet is IP proto TCP.
00177    */
00178   if (IPH_PROTO(ip) != IP_PROTO_TCP) {
00179     return (TYPE_IP);
00180   }
00181 
00182   /*
00183    * Bail if this is an IP fragment or if the TCP packet isn't
00184    * `compressible' (i.e., ACK isn't set or some other control bit is
00185    * set).
00186    */
00187   if ((IPH_OFFSET(ip) & PP_HTONS(0x3fff)) || np->tot_len < 40) {
00188     return (TYPE_IP);
00189   }
00190   th = (struct tcp_hdr *)&((struct vj_u32_t*)ip)[ilen];
00191   if ((TCPH_FLAGS(th) & (TCP_SYN|TCP_FIN|TCP_RST|TCP_ACK)) != TCP_ACK) {
00192     return (TYPE_IP);
00193   }
00194 
00195   /* Check that the TCP/IP headers are contained in the first buffer. */
00196   hlen = ilen + TCPH_HDRLEN(th);
00197   hlen <<= 2;
00198   if (np->len < hlen) {
00199     PPPDEBUG(LOG_INFO, ("vj_compress_tcp: header len %d spans buffers\n", hlen));
00200     return (TYPE_IP);
00201   }
00202 
00203   /* TCP stack requires that we don't change the packet payload, therefore we copy
00204    * the whole packet before compression. */
00205   np = pbuf_alloc(PBUF_RAW, np->tot_len, PBUF_POOL);
00206   if (!np) {
00207     return (TYPE_IP);
00208   }
00209 
00210   if (pbuf_copy(np, *pb) != ERR_OK) {
00211     pbuf_free(np);
00212     return (TYPE_IP);
00213   }
00214 
00215   *pb = np;
00216   ip = (struct ip_hdr *)np->payload;
00217 
00218   /*
00219    * Packet is compressible -- we're going to send either a
00220    * COMPRESSED_TCP or UNCOMPRESSED_TCP packet.  Either way we need
00221    * to locate (or create) the connection state.  Special case the
00222    * most recently used connection since it's most likely to be used
00223    * again & we don't have to do any reordering if it's used.
00224    */
00225   INCR(vjs_packets);
00226   if (!ip4_addr_cmp(&ip->src, &cs->cs_ip.src)
00227       || !ip4_addr_cmp(&ip->dest, &cs->cs_ip.dest)
00228       || (*(struct vj_u32_t*)th).v != (((struct vj_u32_t*)&cs->cs_ip)[IPH_HL(&cs->cs_ip)]).v) {
00229     /*
00230      * Wasn't the first -- search for it.
00231      *
00232      * States are kept in a circularly linked list with
00233      * last_cs pointing to the end of the list.  The
00234      * list is kept in lru order by moving a state to the
00235      * head of the list whenever it is referenced.  Since
00236      * the list is short and, empirically, the connection
00237      * we want is almost always near the front, we locate
00238      * states via linear search.  If we don't find a state
00239      * for the datagram, the oldest state is (re-)used.
00240      */
00241     struct cstate *lcs;
00242     struct cstate *lastcs = comp->last_cs;
00243 
00244     do {
00245       lcs = cs; cs = cs->cs_next;
00246       INCR(vjs_searches);
00247       if (ip4_addr_cmp(&ip->src, &cs->cs_ip.src)
00248           && ip4_addr_cmp(&ip->dest, &cs->cs_ip.dest)
00249           && (*(struct vj_u32_t*)th).v == (((struct vj_u32_t*)&cs->cs_ip)[IPH_HL(&cs->cs_ip)]).v) {
00250         goto found;
00251       }
00252     } while (cs != lastcs);
00253 
00254     /*
00255      * Didn't find it -- re-use oldest cstate.  Send an
00256      * uncompressed packet that tells the other side what
00257      * connection number we're using for this conversation.
00258      * Note that since the state list is circular, the oldest
00259      * state points to the newest and we only need to set
00260      * last_cs to update the lru linkage.
00261      */
00262     INCR(vjs_misses);
00263     comp->last_cs = lcs;
00264     goto uncompressed;
00265 
00266     found:
00267     /*
00268      * Found it -- move to the front on the connection list.
00269      */
00270     if (cs == lastcs) {
00271       comp->last_cs = lcs;
00272     } else {
00273       lcs->cs_next = cs->cs_next;
00274       cs->cs_next = lastcs->cs_next;
00275       lastcs->cs_next = cs;
00276     }
00277   }
00278 
00279   oth = (struct tcp_hdr *)&((struct vj_u32_t*)&cs->cs_ip)[ilen];
00280   deltaS = ilen;
00281 
00282   /*
00283    * Make sure that only what we expect to change changed. The first
00284    * line of the `if' checks the IP protocol version, header length &
00285    * type of service.  The 2nd line checks the "Don't fragment" bit.
00286    * The 3rd line checks the time-to-live and protocol (the protocol
00287    * check is unnecessary but costless).  The 4th line checks the TCP
00288    * header length.  The 5th line checks IP options, if any.  The 6th
00289    * line checks TCP options, if any.  If any of these things are
00290    * different between the previous & current datagram, we send the
00291    * current datagram `uncompressed'.
00292    */
00293   if ((((struct vj_u16_t*)ip)[0]).v != (((struct vj_u16_t*)&cs->cs_ip)[0]).v
00294       || (((struct vj_u16_t*)ip)[3]).v != (((struct vj_u16_t*)&cs->cs_ip)[3]).v
00295       || (((struct vj_u16_t*)ip)[4]).v != (((struct vj_u16_t*)&cs->cs_ip)[4]).v
00296       || TCPH_HDRLEN(th) != TCPH_HDRLEN(oth)
00297       || (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2))
00298       || (TCPH_HDRLEN(th) > 5 && BCMP(th + 1, oth + 1, (TCPH_HDRLEN(th) - 5) << 2))) {
00299     goto uncompressed;
00300   }
00301 
00302   /*
00303    * Figure out which of the changing fields changed.  The
00304    * receiver expects changes in the order: urgent, window,
00305    * ack, seq (the order minimizes the number of temporaries
00306    * needed in this section of code).
00307    */
00308   if (TCPH_FLAGS(th) & TCP_URG) {
00309     deltaS = lwip_ntohs(th->urgp);
00310     ENCODEZ(deltaS);
00311     changes |= NEW_U;
00312   } else if (th->urgp != oth->urgp) {
00313     /* argh! URG not set but urp changed -- a sensible
00314      * implementation should never do this but RFC793
00315      * doesn't prohibit the change so we have to deal
00316      * with it. */
00317     goto uncompressed;
00318   }
00319 
00320   if ((deltaS = (u16_t)(lwip_ntohs(th->wnd) - lwip_ntohs(oth->wnd))) != 0) {
00321     ENCODE(deltaS);
00322     changes |= NEW_W;
00323   }
00324 
00325   if ((deltaL = lwip_ntohl(th->ackno) - lwip_ntohl(oth->ackno)) != 0) {
00326     if (deltaL > 0xffff) {
00327       goto uncompressed;
00328     }
00329     deltaA = (u16_t)deltaL;
00330     ENCODE(deltaA);
00331     changes |= NEW_A;
00332   }
00333 
00334   if ((deltaL = lwip_ntohl(th->seqno) - lwip_ntohl(oth->seqno)) != 0) {
00335     if (deltaL > 0xffff) {
00336       goto uncompressed;
00337     }
00338     deltaS = (u16_t)deltaL;
00339     ENCODE(deltaS);
00340     changes |= NEW_S;
00341   }
00342 
00343   switch(changes) {
00344   case 0:
00345     /*
00346      * Nothing changed. If this packet contains data and the
00347      * last one didn't, this is probably a data packet following
00348      * an ack (normal on an interactive connection) and we send
00349      * it compressed.  Otherwise it's probably a retransmit,
00350      * retransmitted ack or window probe.  Send it uncompressed
00351      * in case the other side missed the compressed version.
00352      */
00353     if (IPH_LEN(ip) != IPH_LEN(&cs->cs_ip) &&
00354       lwip_ntohs(IPH_LEN(&cs->cs_ip)) == hlen) {
00355       break;
00356     }
00357     /* no break */
00358     /* fall through */
00359 
00360   case SPECIAL_I:
00361   case SPECIAL_D:
00362     /*
00363      * actual changes match one of our special case encodings --
00364      * send packet uncompressed.
00365      */
00366     goto uncompressed;
00367 
00368   case NEW_S|NEW_A:
00369     if (deltaS == deltaA && deltaS == lwip_ntohs(IPH_LEN(&cs->cs_ip)) - hlen) {
00370       /* special case for echoed terminal traffic */
00371       changes = SPECIAL_I;
00372       cp = new_seq;
00373     }
00374     break;
00375 
00376   case NEW_S:
00377     if (deltaS == lwip_ntohs(IPH_LEN(&cs->cs_ip)) - hlen) {
00378       /* special case for data xfer */
00379       changes = SPECIAL_D;
00380       cp = new_seq;
00381     }
00382     break;
00383   default:
00384      break;
00385   }
00386 
00387   deltaS = (u16_t)(lwip_ntohs(IPH_ID(ip)) - lwip_ntohs(IPH_ID(&cs->cs_ip)));
00388   if (deltaS != 1) {
00389     ENCODEZ(deltaS);
00390     changes |= NEW_I;
00391   }
00392   if (TCPH_FLAGS(th) & TCP_PSH) {
00393     changes |= TCP_PUSH_BIT;
00394   }
00395   /*
00396    * Grab the cksum before we overwrite it below.  Then update our
00397    * state with this packet's header.
00398    */
00399   deltaA = lwip_ntohs(th->chksum);
00400   MEMCPY(&cs->cs_ip, ip, hlen);
00401 
00402   /*
00403    * We want to use the original packet as our compressed packet.
00404    * (cp - new_seq) is the number of bytes we need for compressed
00405    * sequence numbers.  In addition we need one byte for the change
00406    * mask, one for the connection id and two for the tcp checksum.
00407    * So, (cp - new_seq) + 4 bytes of header are needed.  hlen is how
00408    * many bytes of the original packet to toss so subtract the two to
00409    * get the new packet size.
00410    */
00411   deltaS = (u16_t)(cp - new_seq);
00412   if (!comp->compressSlot || comp->last_xmit != cs->cs_id) {
00413     comp->last_xmit = cs->cs_id;
00414     hlen -= deltaS + 4;
00415     if (pbuf_header(np, -(s16_t)hlen)){
00416       /* Can we cope with this failing?  Just assert for now */
00417       LWIP_ASSERT("pbuf_header failed\n", 0);
00418     }
00419     cp = (u8_t*)np->payload;
00420     *cp++ = (u8_t)(changes | NEW_C);
00421     *cp++ = cs->cs_id;
00422   } else {
00423     hlen -= deltaS + 3;
00424     if (pbuf_header(np, -(s16_t)hlen)) {
00425       /* Can we cope with this failing?  Just assert for now */
00426       LWIP_ASSERT("pbuf_header failed\n", 0);
00427     }
00428     cp = (u8_t*)np->payload;
00429     *cp++ = (u8_t)changes;
00430   }
00431   *cp++ = (u8_t)(deltaA >> 8);
00432   *cp++ = (u8_t)deltaA;
00433   MEMCPY(cp, new_seq, deltaS);
00434   INCR(vjs_compressed);
00435   return (TYPE_COMPRESSED_TCP);
00436 
00437   /*
00438    * Update connection state cs & send uncompressed packet (that is,
00439    * a regular ip/tcp packet but with the 'conversation id' we hope
00440    * to use on future compressed packets in the protocol field).
00441    */
00442 uncompressed:
00443   MEMCPY(&cs->cs_ip, ip, hlen);
00444   IPH_PROTO_SET(ip, cs->cs_id);
00445   comp->last_xmit = cs->cs_id;
00446   return (TYPE_UNCOMPRESSED_TCP);
00447 }
00448 
00449 /*
00450  * Called when we may have missed a packet.
00451  */
00452 void
00453 vj_uncompress_err(struct vjcompress *comp)
00454 {
00455   comp->flags |= VJF_TOSS;
00456   INCR(vjs_errorin);
00457 }
00458 
00459 /*
00460  * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
00461  * Return 0 on success, -1 on failure.
00462  */
00463 int
00464 vj_uncompress_uncomp(struct pbuf *nb, struct vjcompress *comp)
00465 {
00466   u32_t hlen;
00467   struct cstate *cs;
00468   struct ip_hdr *ip;
00469 
00470   ip = (struct ip_hdr *)nb->payload;
00471   hlen = IPH_HL(ip) << 2;
00472   if (IPH_PROTO(ip) >= MAX_SLOTS
00473       || hlen + sizeof(struct tcp_hdr) > nb->len
00474       || (hlen += TCPH_HDRLEN(((struct tcp_hdr *)&((char *)ip)[hlen])) << 2)
00475           > nb->len
00476       || hlen > MAX_HDR) {
00477     PPPDEBUG(LOG_INFO, ("vj_uncompress_uncomp: bad cid=%d, hlen=%d buflen=%d\n",
00478       IPH_PROTO(ip), hlen, nb->len));
00479     comp->flags |= VJF_TOSS;
00480     INCR(vjs_errorin);
00481     return -1;
00482   }
00483   cs = &comp->rstate[comp->last_recv = IPH_PROTO(ip)];
00484   comp->flags &=~ VJF_TOSS;
00485   IPH_PROTO_SET(ip, IP_PROTO_TCP);
00486   MEMCPY(&cs->cs_ip, ip, hlen);
00487   cs->cs_hlen = (u16_t)hlen;
00488   INCR(vjs_uncompressedin);
00489   return 0;
00490 }
00491 
00492 /*
00493  * Uncompress a packet of type TYPE_COMPRESSED_TCP.
00494  * The packet is composed of a buffer chain and the first buffer
00495  * must contain an accurate chain length.
00496  * The first buffer must include the entire compressed TCP/IP header.
00497  * This procedure replaces the compressed header with the uncompressed
00498  * header and returns the length of the VJ header.
00499  */
00500 int
00501 vj_uncompress_tcp(struct pbuf **nb, struct vjcompress *comp)
00502 {
00503   u8_t *cp;
00504   struct tcp_hdr *th;
00505   struct cstate *cs;
00506   struct vj_u16_t *bp;
00507   struct pbuf *n0 = *nb;
00508   u32_t tmp;
00509   u32_t vjlen, hlen, changes;
00510 
00511   INCR(vjs_compressedin);
00512   cp = (u8_t*)n0->payload;
00513   changes = *cp++;
00514   if (changes & NEW_C) {
00515     /*
00516      * Make sure the state index is in range, then grab the state.
00517      * If we have a good state index, clear the 'discard' flag.
00518      */
00519     if (*cp >= MAX_SLOTS) {
00520       PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: bad cid=%d\n", *cp));
00521       goto bad;
00522     }
00523 
00524     comp->flags &=~ VJF_TOSS;
00525     comp->last_recv = *cp++;
00526   } else {
00527     /*
00528      * this packet has an implicit state index.  If we've
00529      * had a line error since the last time we got an
00530      * explicit state index, we have to toss the packet.
00531      */
00532     if (comp->flags & VJF_TOSS) {
00533       PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: tossing\n"));
00534       INCR(vjs_tossed);
00535       return (-1);
00536     }
00537   }
00538   cs = &comp->rstate[comp->last_recv];
00539   hlen = IPH_HL(&cs->cs_ip) << 2;
00540   th = (struct tcp_hdr *)&((u8_t*)&cs->cs_ip)[hlen];
00541   th->chksum = lwip_htons((*cp << 8) | cp[1]);
00542   cp += 2;
00543   if (changes & TCP_PUSH_BIT) {
00544     TCPH_SET_FLAG(th, TCP_PSH);
00545   } else {
00546     TCPH_UNSET_FLAG(th, TCP_PSH);
00547   }
00548 
00549   switch (changes & SPECIALS_MASK) {
00550   case SPECIAL_I:
00551     {
00552       u32_t i = lwip_ntohs(IPH_LEN(&cs->cs_ip)) - cs->cs_hlen;
00553       /* some compilers can't nest inline assembler.. */
00554       tmp = lwip_ntohl(th->ackno) + i;
00555       th->ackno = lwip_htonl(tmp);
00556       tmp = lwip_ntohl(th->seqno) + i;
00557       th->seqno = lwip_htonl(tmp);
00558     }
00559     break;
00560 
00561   case SPECIAL_D:
00562     /* some compilers can't nest inline assembler.. */
00563     tmp = lwip_ntohl(th->seqno) + lwip_ntohs(IPH_LEN(&cs->cs_ip)) - cs->cs_hlen;
00564     th->seqno = lwip_htonl(tmp);
00565     break;
00566 
00567   default:
00568     if (changes & NEW_U) {
00569       TCPH_SET_FLAG(th, TCP_URG);
00570       DECODEU(th->urgp);
00571     } else {
00572       TCPH_UNSET_FLAG(th, TCP_URG);
00573     }
00574     if (changes & NEW_W) {
00575       DECODES(th->wnd);
00576     }
00577     if (changes & NEW_A) {
00578       DECODEL(th->ackno);
00579     }
00580     if (changes & NEW_S) {
00581       DECODEL(th->seqno);
00582     }
00583     break;
00584   }
00585   if (changes & NEW_I) {
00586     DECODES(cs->cs_ip._id);
00587   } else {
00588     IPH_ID_SET(&cs->cs_ip, lwip_ntohs(IPH_ID(&cs->cs_ip)) + 1);
00589     IPH_ID_SET(&cs->cs_ip, lwip_htons(IPH_ID(&cs->cs_ip)));
00590   }
00591 
00592   /*
00593    * At this point, cp points to the first byte of data in the
00594    * packet.  Fill in the IP total length and update the IP
00595    * header checksum.
00596    */
00597   vjlen = (u16_t)(cp - (u8_t*)n0->payload);
00598   if (n0->len < vjlen) {
00599     /*
00600      * We must have dropped some characters (crc should detect
00601      * this but the old slip framing won't)
00602      */
00603     PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: head buffer %d too short %d\n",
00604           n0->len, vjlen));
00605     goto bad;
00606   }
00607 
00608 #if BYTE_ORDER == LITTLE_ENDIAN
00609   tmp = n0->tot_len - vjlen + cs->cs_hlen;
00610   IPH_LEN_SET(&cs->cs_ip, lwip_htons((u16_t)tmp));
00611 #else
00612   IPH_LEN_SET(&cs->cs_ip, lwip_htons(n0->tot_len - vjlen + cs->cs_hlen));
00613 #endif
00614 
00615   /* recompute the ip header checksum */
00616   bp = (struct vj_u16_t*) &cs->cs_ip;
00617   IPH_CHKSUM_SET(&cs->cs_ip, 0);
00618   for (tmp = 0; hlen > 0; hlen -= 2) {
00619     tmp += (*bp++).v;
00620   }
00621   tmp = (tmp & 0xffff) + (tmp >> 16);
00622   tmp = (tmp & 0xffff) + (tmp >> 16);
00623   IPH_CHKSUM_SET(&cs->cs_ip,  (u16_t)(~tmp));
00624 
00625   /* Remove the compressed header and prepend the uncompressed header. */
00626   if (pbuf_header(n0, -(s16_t)vjlen)) {
00627     /* Can we cope with this failing?  Just assert for now */
00628     LWIP_ASSERT("pbuf_header failed\n", 0);
00629     goto bad;
00630   }
00631 
00632   if(LWIP_MEM_ALIGN(n0->payload) != n0->payload) {
00633     struct pbuf *np, *q;
00634     u8_t *bufptr;
00635 
00636 #if IP_FORWARD
00637     /* If IP forwarding is enabled we are using a PBUF_LINK packet type so
00638      * the packet is being allocated with enough header space to be
00639      * forwarded (to Ethernet for example).
00640      */
00641     np = pbuf_alloc(PBUF_LINK, n0->len + cs->cs_hlen, PBUF_POOL);
00642 #else /* IP_FORWARD */
00643     np = pbuf_alloc(PBUF_RAW, n0->len + cs->cs_hlen, PBUF_POOL);
00644 #endif /* IP_FORWARD */
00645     if(!np) {
00646       PPPDEBUG(LOG_WARNING, ("vj_uncompress_tcp: realign failed\n"));
00647       goto bad;
00648     }
00649 
00650     if (pbuf_header(np, -(s16_t)cs->cs_hlen)) {
00651       /* Can we cope with this failing?  Just assert for now */
00652       LWIP_ASSERT("pbuf_header failed\n", 0);
00653       goto bad;
00654     }
00655 
00656     bufptr = (u8_t*)n0->payload;
00657     for(q = np; q != NULL; q = q->next) {
00658       MEMCPY(q->payload, bufptr, q->len);
00659       bufptr += q->len;
00660     }
00661 
00662     if(n0->next) {
00663       pbuf_chain(np, n0->next);
00664       pbuf_dechain(n0);
00665     }
00666     pbuf_free(n0);
00667     n0 = np;
00668   }
00669 
00670   if (pbuf_header(n0, (s16_t)cs->cs_hlen)) {
00671     struct pbuf *np;
00672 
00673     LWIP_ASSERT("vj_uncompress_tcp: cs->cs_hlen <= PBUF_POOL_BUFSIZE", cs->cs_hlen <= PBUF_POOL_BUFSIZE);
00674     np = pbuf_alloc(PBUF_RAW, cs->cs_hlen, PBUF_POOL);
00675     if(!np) {
00676       PPPDEBUG(LOG_WARNING, ("vj_uncompress_tcp: prepend failed\n"));
00677       goto bad;
00678     }
00679     pbuf_cat(np, n0);
00680     n0 = np;
00681   }
00682   LWIP_ASSERT("n0->len >= cs->cs_hlen", n0->len >= cs->cs_hlen);
00683   MEMCPY(n0->payload, &cs->cs_ip, cs->cs_hlen);
00684 
00685   *nb = n0;
00686 
00687   return vjlen;
00688 
00689 bad:
00690   comp->flags |= VJF_TOSS;
00691   INCR(vjs_errorin);
00692   return (-1);
00693 }
00694 
00695 #endif /* PPP_SUPPORT && VJ_SUPPORT */