1/*
2 * Routines to compress and uncompess tcp packets (for transmission
3 * over low speed serial lines.
4 *
5 * Copyright (c) 1989 Regents of the University of California.
6 * All rights reserved.
7 *
8 * Redistribution and use in source and binary forms are permitted
9 * provided that the above copyright notice and this paragraph are
10 * duplicated in all such forms and that any documentation,
11 * advertising materials, and other materials related to such
12 * distribution and use acknowledge that the software was developed
13 * by the University of California, Berkeley.  The name of the
14 * University may not be used to endorse or promote products derived
15 * from this software without specific prior written permission.
16 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
18 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
19 *
20 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
21 *   Initial distribution.
22 *
23 * Modified June 1993 by Paul Mackerras, paulus@cs.anu.edu.au,
24 * so that the entire packet being decompressed doesn't have
25 * to be in contiguous memory (just the compressed header).
26 *
27 * Modified March 1998 by Guy Lancaster, glanca@gesn.com,
28 * for a 16 bit processor.
29 */
30
31#include "netif/ppp/ppp_opts.h"
32#if PPP_SUPPORT && VJ_SUPPORT /* don't build if not configured for use in lwipopts.h */
33
34#include "netif/ppp/ppp_impl.h"
35#include "netif/ppp/pppdebug.h"
36
37#include "netif/ppp/vj.h"
38
39#include <string.h>
40
41#if LINK_STATS
42#define INCR(counter) ++comp->stats.counter
43#else
44#define INCR(counter)
45#endif
46
47void
48vj_compress_init(struct vjcompress *comp)
49{
50  u8_t i;
51  struct cstate *tstate = comp->tstate;
52
53#if MAX_SLOTS == 0
54  memset((char *)comp, 0, sizeof(*comp));
55#endif
56  comp->maxSlotIndex = MAX_SLOTS - 1;
57  comp->compressSlot = 0;    /* Disable slot ID compression by default. */
58  for (i = MAX_SLOTS - 1; i > 0; --i) {
59    tstate[i].cs_id = i;
60    tstate[i].cs_next = &tstate[i - 1];
61  }
62  tstate[0].cs_next = &tstate[MAX_SLOTS - 1];
63  tstate[0].cs_id = 0;
64  comp->last_cs = &tstate[0];
65  comp->last_recv = 255;
66  comp->last_xmit = 255;
67  comp->flags = VJF_TOSS;
68}
69
70
71/* ENCODE encodes a number that is known to be non-zero.  ENCODEZ
72 * checks for zero (since zero has to be encoded in the long, 3 byte
73 * form).
74 */
75#define ENCODE(n) { \
76  if ((u16_t)(n) >= 256) { \
77    *cp++ = 0; \
78    cp[1] = (u8_t)(n); \
79    cp[0] = (u8_t)((n) >> 8); \
80    cp += 2; \
81  } else { \
82    *cp++ = (u8_t)(n); \
83  } \
84}
85#define ENCODEZ(n) { \
86  if ((u16_t)(n) >= 256 || (u16_t)(n) == 0) { \
87    *cp++ = 0; \
88    cp[1] = (u8_t)(n); \
89    cp[0] = (u8_t)((n) >> 8); \
90    cp += 2; \
91  } else { \
92    *cp++ = (u8_t)(n); \
93  } \
94}
95
96#define DECODEL(f) { \
97  if (*cp == 0) {\
98    u32_t tmp_ = lwip_ntohl(f) + ((cp[1] << 8) | cp[2]); \
99    (f) = lwip_htonl(tmp_); \
100    cp += 3; \
101  } else { \
102    u32_t tmp_ = lwip_ntohl(f) + (u32_t)*cp++; \
103    (f) = lwip_htonl(tmp_); \
104  } \
105}
106
107#define DECODES(f) { \
108  if (*cp == 0) {\
109    u16_t tmp_ = lwip_ntohs(f) + (((u16_t)cp[1] << 8) | cp[2]); \
110    (f) = lwip_htons(tmp_); \
111    cp += 3; \
112  } else { \
113    u16_t tmp_ = lwip_ntohs(f) + (u16_t)*cp++; \
114    (f) = lwip_htons(tmp_); \
115  } \
116}
117
118#define DECODEU(f) { \
119  if (*cp == 0) {\
120    (f) = lwip_htons(((u16_t)cp[1] << 8) | cp[2]); \
121    cp += 3; \
122  } else { \
123    (f) = lwip_htons((u16_t)*cp++); \
124  } \
125}
126
127/* Helper structures for unaligned *u32_t and *u16_t accesses */
128#ifdef PACK_STRUCT_USE_INCLUDES
129#  include "arch/bpstruct.h"
130#endif
131PACK_STRUCT_BEGIN
132struct vj_u32_t {
133  PACK_STRUCT_FIELD(u32_t v);
134} PACK_STRUCT_STRUCT;
135PACK_STRUCT_END
136#ifdef PACK_STRUCT_USE_INCLUDES
137#  include "arch/epstruct.h"
138#endif
139
140#ifdef PACK_STRUCT_USE_INCLUDES
141#  include "arch/bpstruct.h"
142#endif
143PACK_STRUCT_BEGIN
144struct vj_u16_t {
145  PACK_STRUCT_FIELD(u16_t v);
146} PACK_STRUCT_STRUCT;
147PACK_STRUCT_END
148#ifdef PACK_STRUCT_USE_INCLUDES
149#  include "arch/epstruct.h"
150#endif
151
152/*
153 * vj_compress_tcp - Attempt to do Van Jacobson header compression on a
154 * packet.  This assumes that nb and comp are not null and that the first
155 * buffer of the chain contains a valid IP header.
156 * Return the VJ type code indicating whether or not the packet was
157 * compressed.
158 */
159u8_t
160vj_compress_tcp(struct vjcompress *comp, struct pbuf **pb)
161{
162  struct pbuf *np = *pb;
163  struct ip_hdr *ip = (struct ip_hdr *)np->payload;
164  struct cstate *cs = comp->last_cs->cs_next;
165  u16_t ilen = IPH_HL(ip);
166  u16_t hlen;
167  struct tcp_hdr *oth;
168  struct tcp_hdr *th;
169  u16_t deltaS, deltaA = 0;
170  u32_t deltaL;
171  u32_t changes = 0;
172  u8_t new_seq[16];
173  u8_t *cp = new_seq;
174
175  /*
176   * Check that the packet is IP proto TCP.
177   */
178  if (IPH_PROTO(ip) != IP_PROTO_TCP) {
179    return (TYPE_IP);
180  }
181
182  /*
183   * Bail if this is an IP fragment or if the TCP packet isn't
184   * `compressible' (i.e., ACK isn't set or some other control bit is
185   * set).
186   */
187  if ((IPH_OFFSET(ip) & PP_HTONS(0x3fff)) || np->tot_len < 40) {
188    return (TYPE_IP);
189  }
190  th = (struct tcp_hdr *)&((struct vj_u32_t*)ip)[ilen];
191  if ((TCPH_FLAGS(th) & (TCP_SYN|TCP_FIN|TCP_RST|TCP_ACK)) != TCP_ACK) {
192    return (TYPE_IP);
193  }
194
195  /* Check that the TCP/IP headers are contained in the first buffer. */
196  hlen = ilen + TCPH_HDRLEN(th);
197  hlen <<= 2;
198  if (np->len < hlen) {
199    PPPDEBUG(LOG_INFO, ("vj_compress_tcp: header len %d spans buffers\n", hlen));
200    return (TYPE_IP);
201  }
202
203  /* TCP stack requires that we don't change the packet payload, therefore we copy
204   * the whole packet before compression. */
205  np = pbuf_clone(PBUF_RAW, PBUF_RAM, *pb);
206  if (!np) {
207    return (TYPE_IP);
208  }
209
210  *pb = np;
211  ip = (struct ip_hdr *)np->payload;
212
213  /*
214   * Packet is compressible -- we're going to send either a
215   * COMPRESSED_TCP or UNCOMPRESSED_TCP packet.  Either way we need
216   * to locate (or create) the connection state.  Special case the
217   * most recently used connection since it's most likely to be used
218   * again & we don't have to do any reordering if it's used.
219   */
220  INCR(vjs_packets);
221  if (!ip4_addr_cmp(&ip->src, &cs->cs_ip.src)
222      || !ip4_addr_cmp(&ip->dest, &cs->cs_ip.dest)
223      || (*(struct vj_u32_t*)th).v != (((struct vj_u32_t*)&cs->cs_ip)[IPH_HL(&cs->cs_ip)]).v) {
224    /*
225     * Wasn't the first -- search for it.
226     *
227     * States are kept in a circularly linked list with
228     * last_cs pointing to the end of the list.  The
229     * list is kept in lru order by moving a state to the
230     * head of the list whenever it is referenced.  Since
231     * the list is short and, empirically, the connection
232     * we want is almost always near the front, we locate
233     * states via linear search.  If we don't find a state
234     * for the datagram, the oldest state is (re-)used.
235     */
236    struct cstate *lcs;
237    struct cstate *lastcs = comp->last_cs;
238
239    do {
240      lcs = cs; cs = cs->cs_next;
241      INCR(vjs_searches);
242      if (ip4_addr_cmp(&ip->src, &cs->cs_ip.src)
243          && ip4_addr_cmp(&ip->dest, &cs->cs_ip.dest)
244          && (*(struct vj_u32_t*)th).v == (((struct vj_u32_t*)&cs->cs_ip)[IPH_HL(&cs->cs_ip)]).v) {
245        goto found;
246      }
247    } while (cs != lastcs);
248
249    /*
250     * Didn't find it -- re-use oldest cstate.  Send an
251     * uncompressed packet that tells the other side what
252     * connection number we're using for this conversation.
253     * Note that since the state list is circular, the oldest
254     * state points to the newest and we only need to set
255     * last_cs to update the lru linkage.
256     */
257    INCR(vjs_misses);
258    comp->last_cs = lcs;
259    goto uncompressed;
260
261    found:
262    /*
263     * Found it -- move to the front on the connection list.
264     */
265    if (cs == lastcs) {
266      comp->last_cs = lcs;
267    } else {
268      lcs->cs_next = cs->cs_next;
269      cs->cs_next = lastcs->cs_next;
270      lastcs->cs_next = cs;
271    }
272  }
273
274  oth = (struct tcp_hdr *)&((struct vj_u32_t*)&cs->cs_ip)[ilen];
275  deltaS = ilen;
276
277  /*
278   * Make sure that only what we expect to change changed. The first
279   * line of the `if' checks the IP protocol version, header length &
280   * type of service.  The 2nd line checks the "Don't fragment" bit.
281   * The 3rd line checks the time-to-live and protocol (the protocol
282   * check is unnecessary but costless).  The 4th line checks the TCP
283   * header length.  The 5th line checks IP options, if any.  The 6th
284   * line checks TCP options, if any.  If any of these things are
285   * different between the previous & current datagram, we send the
286   * current datagram `uncompressed'.
287   */
288  if ((((struct vj_u16_t*)ip)[0]).v != (((struct vj_u16_t*)&cs->cs_ip)[0]).v
289      || (((struct vj_u16_t*)ip)[3]).v != (((struct vj_u16_t*)&cs->cs_ip)[3]).v
290      || (((struct vj_u16_t*)ip)[4]).v != (((struct vj_u16_t*)&cs->cs_ip)[4]).v
291      || TCPH_HDRLEN(th) != TCPH_HDRLEN(oth)
292      || (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2))
293      || (TCPH_HDRLEN(th) > 5 && BCMP(th + 1, oth + 1, (TCPH_HDRLEN(th) - 5) << 2))) {
294    goto uncompressed;
295  }
296
297  /*
298   * Figure out which of the changing fields changed.  The
299   * receiver expects changes in the order: urgent, window,
300   * ack, seq (the order minimizes the number of temporaries
301   * needed in this section of code).
302   */
303  if (TCPH_FLAGS(th) & TCP_URG) {
304    deltaS = lwip_ntohs(th->urgp);
305    ENCODEZ(deltaS);
306    changes |= NEW_U;
307  } else if (th->urgp != oth->urgp) {
308    /* argh! URG not set but urp changed -- a sensible
309     * implementation should never do this but RFC793
310     * doesn't prohibit the change so we have to deal
311     * with it. */
312    goto uncompressed;
313  }
314
315  if ((deltaS = (u16_t)(lwip_ntohs(th->wnd) - lwip_ntohs(oth->wnd))) != 0) {
316    ENCODE(deltaS);
317    changes |= NEW_W;
318  }
319
320  if ((deltaL = lwip_ntohl(th->ackno) - lwip_ntohl(oth->ackno)) != 0) {
321    if (deltaL > 0xffff) {
322      goto uncompressed;
323    }
324    deltaA = (u16_t)deltaL;
325    ENCODE(deltaA);
326    changes |= NEW_A;
327  }
328
329  if ((deltaL = lwip_ntohl(th->seqno) - lwip_ntohl(oth->seqno)) != 0) {
330    if (deltaL > 0xffff) {
331      goto uncompressed;
332    }
333    deltaS = (u16_t)deltaL;
334    ENCODE(deltaS);
335    changes |= NEW_S;
336  }
337
338  switch(changes) {
339  case 0:
340    /*
341     * Nothing changed. If this packet contains data and the
342     * last one didn't, this is probably a data packet following
343     * an ack (normal on an interactive connection) and we send
344     * it compressed.  Otherwise it's probably a retransmit,
345     * retransmitted ack or window probe.  Send it uncompressed
346     * in case the other side missed the compressed version.
347     */
348    if (IPH_LEN(ip) != IPH_LEN(&cs->cs_ip) &&
349      lwip_ntohs(IPH_LEN(&cs->cs_ip)) == hlen) {
350      break;
351    }
352    /* no break */
353    /* fall through */
354
355  case SPECIAL_I:
356  case SPECIAL_D:
357    /*
358     * actual changes match one of our special case encodings --
359     * send packet uncompressed.
360     */
361    goto uncompressed;
362
363  case NEW_S|NEW_A:
364    if (deltaS == deltaA && deltaS == lwip_ntohs(IPH_LEN(&cs->cs_ip)) - hlen) {
365      /* special case for echoed terminal traffic */
366      changes = SPECIAL_I;
367      cp = new_seq;
368    }
369    break;
370
371  case NEW_S:
372    if (deltaS == lwip_ntohs(IPH_LEN(&cs->cs_ip)) - hlen) {
373      /* special case for data xfer */
374      changes = SPECIAL_D;
375      cp = new_seq;
376    }
377    break;
378  default:
379     break;
380  }
381
382  deltaS = (u16_t)(lwip_ntohs(IPH_ID(ip)) - lwip_ntohs(IPH_ID(&cs->cs_ip)));
383  if (deltaS != 1) {
384    ENCODEZ(deltaS);
385    changes |= NEW_I;
386  }
387  if (TCPH_FLAGS(th) & TCP_PSH) {
388    changes |= TCP_PUSH_BIT;
389  }
390  /*
391   * Grab the cksum before we overwrite it below.  Then update our
392   * state with this packet's header.
393   */
394  deltaA = lwip_ntohs(th->chksum);
395  MEMCPY(&cs->cs_ip, ip, hlen);
396
397  /*
398   * We want to use the original packet as our compressed packet.
399   * (cp - new_seq) is the number of bytes we need for compressed
400   * sequence numbers.  In addition we need one byte for the change
401   * mask, one for the connection id and two for the tcp checksum.
402   * So, (cp - new_seq) + 4 bytes of header are needed.  hlen is how
403   * many bytes of the original packet to toss so subtract the two to
404   * get the new packet size.
405   */
406  deltaS = (u16_t)(cp - new_seq);
407  if (!comp->compressSlot || comp->last_xmit != cs->cs_id) {
408    comp->last_xmit = cs->cs_id;
409    hlen -= deltaS + 4;
410    if (pbuf_remove_header(np, hlen)){
411      /* Can we cope with this failing?  Just assert for now */
412      LWIP_ASSERT("pbuf_remove_header failed\n", 0);
413    }
414    cp = (u8_t*)np->payload;
415    *cp++ = (u8_t)(changes | NEW_C);
416    *cp++ = cs->cs_id;
417  } else {
418    hlen -= deltaS + 3;
419    if (pbuf_remove_header(np, hlen)) {
420      /* Can we cope with this failing?  Just assert for now */
421      LWIP_ASSERT("pbuf_remove_header failed\n", 0);
422    }
423    cp = (u8_t*)np->payload;
424    *cp++ = (u8_t)changes;
425  }
426  *cp++ = (u8_t)(deltaA >> 8);
427  *cp++ = (u8_t)deltaA;
428  MEMCPY(cp, new_seq, deltaS);
429  INCR(vjs_compressed);
430  return (TYPE_COMPRESSED_TCP);
431
432  /*
433   * Update connection state cs & send uncompressed packet (that is,
434   * a regular ip/tcp packet but with the 'conversation id' we hope
435   * to use on future compressed packets in the protocol field).
436   */
437uncompressed:
438  MEMCPY(&cs->cs_ip, ip, hlen);
439  IPH_PROTO_SET(ip, cs->cs_id);
440  comp->last_xmit = cs->cs_id;
441  return (TYPE_UNCOMPRESSED_TCP);
442}
443
444/*
445 * Called when we may have missed a packet.
446 */
447void
448vj_uncompress_err(struct vjcompress *comp)
449{
450  comp->flags |= VJF_TOSS;
451  INCR(vjs_errorin);
452}
453
454/*
455 * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
456 * Return 0 on success, -1 on failure.
457 */
458int
459vj_uncompress_uncomp(struct pbuf *nb, struct vjcompress *comp)
460{
461  u32_t hlen;
462  struct cstate *cs;
463  struct ip_hdr *ip;
464
465  ip = (struct ip_hdr *)nb->payload;
466  hlen = IPH_HL(ip) << 2;
467  if (IPH_PROTO(ip) >= MAX_SLOTS
468      || hlen + sizeof(struct tcp_hdr) > nb->len
469      || (hlen += TCPH_HDRLEN_BYTES((struct tcp_hdr *)&((char *)ip)[hlen]))
470          > nb->len
471      || hlen > MAX_HDR) {
472    PPPDEBUG(LOG_INFO, ("vj_uncompress_uncomp: bad cid=%d, hlen=%d buflen=%d\n",
473      IPH_PROTO(ip), hlen, nb->len));
474    vj_uncompress_err(comp);
475    return -1;
476  }
477  cs = &comp->rstate[comp->last_recv = IPH_PROTO(ip)];
478  comp->flags &=~ VJF_TOSS;
479  IPH_PROTO_SET(ip, IP_PROTO_TCP);
480  /* copy from/to bigger buffers checked above instead of cs->cs_ip and ip
481     just to help static code analysis to see this is correct ;-) */
482  MEMCPY(&cs->cs_hdr, nb->payload, hlen);
483  cs->cs_hlen = (u16_t)hlen;
484  INCR(vjs_uncompressedin);
485  return 0;
486}
487
488/*
489 * Uncompress a packet of type TYPE_COMPRESSED_TCP.
490 * The packet is composed of a buffer chain and the first buffer
491 * must contain an accurate chain length.
492 * The first buffer must include the entire compressed TCP/IP header.
493 * This procedure replaces the compressed header with the uncompressed
494 * header and returns the length of the VJ header.
495 */
496int
497vj_uncompress_tcp(struct pbuf **nb, struct vjcompress *comp)
498{
499  u8_t *cp;
500  struct tcp_hdr *th;
501  struct cstate *cs;
502  struct vj_u16_t *bp;
503  struct pbuf *n0 = *nb;
504  u32_t tmp;
505  u32_t vjlen, hlen, changes;
506
507  INCR(vjs_compressedin);
508  cp = (u8_t*)n0->payload;
509  changes = *cp++;
510  if (changes & NEW_C) {
511    /*
512     * Make sure the state index is in range, then grab the state.
513     * If we have a good state index, clear the 'discard' flag.
514     */
515    if (*cp >= MAX_SLOTS) {
516      PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: bad cid=%d\n", *cp));
517      goto bad;
518    }
519
520    comp->flags &=~ VJF_TOSS;
521    comp->last_recv = *cp++;
522  } else {
523    /*
524     * this packet has an implicit state index.  If we've
525     * had a line error since the last time we got an
526     * explicit state index, we have to toss the packet.
527     */
528    if (comp->flags & VJF_TOSS) {
529      PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: tossing\n"));
530      INCR(vjs_tossed);
531      return (-1);
532    }
533  }
534  cs = &comp->rstate[comp->last_recv];
535  hlen = IPH_HL(&cs->cs_ip) << 2;
536  th = (struct tcp_hdr *)&((u8_t*)&cs->cs_ip)[hlen];
537  th->chksum = lwip_htons((*cp << 8) | cp[1]);
538  cp += 2;
539  if (changes & TCP_PUSH_BIT) {
540    TCPH_SET_FLAG(th, TCP_PSH);
541  } else {
542    TCPH_UNSET_FLAG(th, TCP_PSH);
543  }
544
545  switch (changes & SPECIALS_MASK) {
546  case SPECIAL_I:
547    {
548      u32_t i = lwip_ntohs(IPH_LEN(&cs->cs_ip)) - cs->cs_hlen;
549      /* some compilers can't nest inline assembler.. */
550      tmp = lwip_ntohl(th->ackno) + i;
551      th->ackno = lwip_htonl(tmp);
552      tmp = lwip_ntohl(th->seqno) + i;
553      th->seqno = lwip_htonl(tmp);
554    }
555    break;
556
557  case SPECIAL_D:
558    /* some compilers can't nest inline assembler.. */
559    tmp = lwip_ntohl(th->seqno) + lwip_ntohs(IPH_LEN(&cs->cs_ip)) - cs->cs_hlen;
560    th->seqno = lwip_htonl(tmp);
561    break;
562
563  default:
564    if (changes & NEW_U) {
565      TCPH_SET_FLAG(th, TCP_URG);
566      DECODEU(th->urgp);
567    } else {
568      TCPH_UNSET_FLAG(th, TCP_URG);
569    }
570    if (changes & NEW_W) {
571      DECODES(th->wnd);
572    }
573    if (changes & NEW_A) {
574      DECODEL(th->ackno);
575    }
576    if (changes & NEW_S) {
577      DECODEL(th->seqno);
578    }
579    break;
580  }
581  if (changes & NEW_I) {
582    DECODES(cs->cs_ip._id);
583  } else {
584    IPH_ID_SET(&cs->cs_ip, lwip_ntohs(IPH_ID(&cs->cs_ip)) + 1);
585    IPH_ID_SET(&cs->cs_ip, lwip_htons(IPH_ID(&cs->cs_ip)));
586  }
587
588  /*
589   * At this point, cp points to the first byte of data in the
590   * packet.  Fill in the IP total length and update the IP
591   * header checksum.
592   */
593  vjlen = (u16_t)(cp - (u8_t*)n0->payload);
594  if (n0->len < vjlen) {
595    /*
596     * We must have dropped some characters (crc should detect
597     * this but the old slip framing won't)
598     */
599    PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: head buffer %d too short %d\n",
600          n0->len, vjlen));
601    goto bad;
602  }
603
604#if BYTE_ORDER == LITTLE_ENDIAN
605  tmp = n0->tot_len - vjlen + cs->cs_hlen;
606  IPH_LEN_SET(&cs->cs_ip, lwip_htons((u16_t)tmp));
607#else
608  IPH_LEN_SET(&cs->cs_ip, lwip_htons(n0->tot_len - vjlen + cs->cs_hlen));
609#endif
610
611  /* recompute the ip header checksum */
612  bp = (struct vj_u16_t*) &cs->cs_ip;
613  IPH_CHKSUM_SET(&cs->cs_ip, 0);
614  for (tmp = 0; hlen > 0; hlen -= 2) {
615    tmp += (*bp++).v;
616  }
617  tmp = (tmp & 0xffff) + (tmp >> 16);
618  tmp = (tmp & 0xffff) + (tmp >> 16);
619  IPH_CHKSUM_SET(&cs->cs_ip,  (u16_t)(~tmp));
620
621  /* Remove the compressed header and prepend the uncompressed header. */
622  if (pbuf_remove_header(n0, vjlen)) {
623    /* Can we cope with this failing?  Just assert for now */
624    LWIP_ASSERT("pbuf_remove_header failed\n", 0);
625    goto bad;
626  }
627
628  if(LWIP_MEM_ALIGN(n0->payload) != n0->payload) {
629    struct pbuf *np;
630
631#if IP_FORWARD
632    /* If IP forwarding is enabled we are using a PBUF_LINK packet type so
633     * the packet is being allocated with enough header space to be
634     * forwarded (to Ethernet for example).
635     */
636    np = pbuf_alloc(PBUF_LINK, n0->len + cs->cs_hlen, PBUF_POOL);
637#else /* IP_FORWARD */
638    np = pbuf_alloc(PBUF_RAW, n0->len + cs->cs_hlen, PBUF_POOL);
639#endif /* IP_FORWARD */
640    if(!np) {
641      PPPDEBUG(LOG_WARNING, ("vj_uncompress_tcp: realign failed\n"));
642      goto bad;
643    }
644
645    if (pbuf_remove_header(np, cs->cs_hlen)) {
646      /* Can we cope with this failing?  Just assert for now */
647      LWIP_ASSERT("pbuf_remove_header failed\n", 0);
648      goto bad;
649    }
650
651    pbuf_take(np, n0->payload, n0->len);
652
653    if(n0->next) {
654      pbuf_chain(np, n0->next);
655      pbuf_dechain(n0);
656    }
657    pbuf_free(n0);
658    n0 = np;
659  }
660
661  if (pbuf_add_header(n0, cs->cs_hlen)) {
662    struct pbuf *np;
663
664    LWIP_ASSERT("vj_uncompress_tcp: cs->cs_hlen <= PBUF_POOL_BUFSIZE", cs->cs_hlen <= PBUF_POOL_BUFSIZE);
665    np = pbuf_alloc(PBUF_RAW, cs->cs_hlen, PBUF_POOL);
666    if(!np) {
667      PPPDEBUG(LOG_WARNING, ("vj_uncompress_tcp: prepend failed\n"));
668      goto bad;
669    }
670    pbuf_cat(np, n0);
671    n0 = np;
672  }
673  LWIP_ASSERT("n0->len >= cs->cs_hlen", n0->len >= cs->cs_hlen);
674  MEMCPY(n0->payload, &cs->cs_ip, cs->cs_hlen);
675
676  *nb = n0;
677
678  return vjlen;
679
680bad:
681  vj_uncompress_err(comp);
682  return (-1);
683}
684
685#endif /* PPP_SUPPORT && VJ_SUPPORT */
686