• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
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 "lwip/opt.h"
32 
33 #if PPP_SUPPORT /* don't build if not configured for use in lwipopts.h */
34 
35 #include "ppp.h"
36 #include "pppdebug.h"
37 
38 #include "vj.h"
39 
40 #include <string.h>
41 
42 #if VJ_SUPPORT
43 
44 #if LINK_STATS
45 #define INCR(counter) ++comp->stats.counter
46 #else
47 #define INCR(counter)
48 #endif
49 
50 void
vj_compress_init(struct vjcompress * comp)51 vj_compress_init(struct vjcompress *comp)
52 {
53   register u_char i;
54   register struct cstate *tstate = comp->tstate;
55 
56 #if MAX_SLOTS == 0
57   memset((char *)comp, 0, sizeof(*comp));
58 #endif
59   comp->maxSlotIndex = MAX_SLOTS - 1;
60   comp->compressSlot = 0;    /* Disable slot ID compression by default. */
61   for (i = MAX_SLOTS - 1; i > 0; --i) {
62     tstate[i].cs_id = i;
63     tstate[i].cs_next = &tstate[i - 1];
64   }
65   tstate[0].cs_next = &tstate[MAX_SLOTS - 1];
66   tstate[0].cs_id = 0;
67   comp->last_cs = &tstate[0];
68   comp->last_recv = 255;
69   comp->last_xmit = 255;
70   comp->flags = VJF_TOSS;
71 }
72 
73 
74 /* ENCODE encodes a number that is known to be non-zero.  ENCODEZ
75  * checks for zero (since zero has to be encoded in the long, 3 byte
76  * form).
77  */
78 #define ENCODE(n) { \
79   if ((u_short)(n) >= 256) { \
80     *cp++ = 0; \
81     cp[1] = (u_char)(n); \
82     cp[0] = (u_char)((n) >> 8); \
83     cp += 2; \
84   } else { \
85     *cp++ = (u_char)(n); \
86   } \
87 }
88 #define ENCODEZ(n) { \
89   if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
90     *cp++ = 0; \
91     cp[1] = (u_char)(n); \
92     cp[0] = (u_char)((n) >> 8); \
93     cp += 2; \
94   } else { \
95     *cp++ = (u_char)(n); \
96   } \
97 }
98 
99 #define DECODEL(f) { \
100   if (*cp == 0) {\
101     u32_t tmp = ntohl(f) + ((cp[1] << 8) | cp[2]); \
102     (f) = htonl(tmp); \
103     cp += 3; \
104   } else { \
105     u32_t tmp = ntohl(f) + (u32_t)*cp++; \
106     (f) = htonl(tmp); \
107   } \
108 }
109 
110 #define DECODES(f) { \
111   if (*cp == 0) {\
112     u_short tmp = ntohs(f) + (((u_short)cp[1] << 8) | cp[2]); \
113     (f) = htons(tmp); \
114     cp += 3; \
115   } else { \
116     u_short tmp = ntohs(f) + (u_short)*cp++; \
117     (f) = htons(tmp); \
118   } \
119 }
120 
121 #define DECODEU(f) { \
122   if (*cp == 0) {\
123     (f) = htons(((u_short)cp[1] << 8) | cp[2]); \
124     cp += 3; \
125   } else { \
126     (f) = htons((u_short)*cp++); \
127   } \
128 }
129 
130 /*
131  * vj_compress_tcp - Attempt to do Van Jacobson header compression on a
132  * packet.  This assumes that nb and comp are not null and that the first
133  * buffer of the chain contains a valid IP header.
134  * Return the VJ type code indicating whether or not the packet was
135  * compressed.
136  */
137 u_int
vj_compress_tcp(struct vjcompress * comp,struct pbuf * pb)138 vj_compress_tcp(struct vjcompress *comp, struct pbuf *pb)
139 {
140   register struct ip_hdr *ip = (struct ip_hdr *)pb->payload;
141   register struct cstate *cs = comp->last_cs->cs_next;
142   register u_short hlen = IPH_HL(ip);
143   register struct tcp_hdr *oth;
144   register struct tcp_hdr *th;
145   register u_short deltaS, deltaA;
146   register u_long deltaL;
147   register u_int changes = 0;
148   u_char new_seq[16];
149   register u_char *cp = new_seq;
150 
151   /*
152    * Check that the packet is IP proto TCP.
153    */
154   if (IPH_PROTO(ip) != IP_PROTO_TCP) {
155     return (TYPE_IP);
156   }
157 
158   /*
159    * Bail if this is an IP fragment or if the TCP packet isn't
160    * `compressible' (i.e., ACK isn't set or some other control bit is
161    * set).
162    */
163   if ((IPH_OFFSET(ip) & PP_HTONS(0x3fff)) || pb->tot_len < 40) {
164     return (TYPE_IP);
165   }
166   th = (struct tcp_hdr *)&((long *)ip)[hlen];
167   if ((TCPH_FLAGS(th) & (TCP_SYN|TCP_FIN|TCP_RST|TCP_ACK)) != TCP_ACK) {
168     return (TYPE_IP);
169   }
170   /*
171    * Packet is compressible -- we're going to send either a
172    * COMPRESSED_TCP or UNCOMPRESSED_TCP packet.  Either way we need
173    * to locate (or create) the connection state.  Special case the
174    * most recently used connection since it's most likely to be used
175    * again & we don't have to do any reordering if it's used.
176    */
177   INCR(vjs_packets);
178   if (!ip_addr_cmp(&ip->src, &cs->cs_ip.src)
179       || !ip_addr_cmp(&ip->dest, &cs->cs_ip.dest)
180       || *(long *)th != ((long *)&cs->cs_ip)[IPH_HL(&cs->cs_ip)]) {
181     /*
182      * Wasn't the first -- search for it.
183      *
184      * States are kept in a circularly linked list with
185      * last_cs pointing to the end of the list.  The
186      * list is kept in lru order by moving a state to the
187      * head of the list whenever it is referenced.  Since
188      * the list is short and, empirically, the connection
189      * we want is almost always near the front, we locate
190      * states via linear search.  If we don't find a state
191      * for the datagram, the oldest state is (re-)used.
192      */
193     register struct cstate *lcs;
194     register struct cstate *lastcs = comp->last_cs;
195 
196     do {
197       lcs = cs; cs = cs->cs_next;
198       INCR(vjs_searches);
199       if (ip_addr_cmp(&ip->src, &cs->cs_ip.src)
200           && ip_addr_cmp(&ip->dest, &cs->cs_ip.dest)
201           && *(long *)th == ((long *)&cs->cs_ip)[IPH_HL(&cs->cs_ip)]) {
202         goto found;
203       }
204     } while (cs != lastcs);
205 
206     /*
207      * Didn't find it -- re-use oldest cstate.  Send an
208      * uncompressed packet that tells the other side what
209      * connection number we're using for this conversation.
210      * Note that since the state list is circular, the oldest
211      * state points to the newest and we only need to set
212      * last_cs to update the lru linkage.
213      */
214     INCR(vjs_misses);
215     comp->last_cs = lcs;
216     hlen += TCPH_OFFSET(th);
217     hlen <<= 2;
218     /* Check that the IP/TCP headers are contained in the first buffer. */
219     if (hlen > pb->len) {
220       return (TYPE_IP);
221     }
222     goto uncompressed;
223 
224     found:
225     /*
226      * Found it -- move to the front on the connection list.
227      */
228     if (cs == lastcs) {
229       comp->last_cs = lcs;
230     } else {
231       lcs->cs_next = cs->cs_next;
232       cs->cs_next = lastcs->cs_next;
233       lastcs->cs_next = cs;
234     }
235   }
236 
237   oth = (struct tcp_hdr *)&((long *)&cs->cs_ip)[hlen];
238   deltaS = hlen;
239   hlen += TCPH_OFFSET(th);
240   hlen <<= 2;
241   /* Check that the IP/TCP headers are contained in the first buffer. */
242   if (hlen > pb->len) {
243     PPPDEBUG(LOG_INFO, ("vj_compress_tcp: header len %d spans buffers\n", hlen));
244     return (TYPE_IP);
245   }
246 
247   /*
248    * Make sure that only what we expect to change changed. The first
249    * line of the `if' checks the IP protocol version, header length &
250    * type of service.  The 2nd line checks the "Don't fragment" bit.
251    * The 3rd line checks the time-to-live and protocol (the protocol
252    * check is unnecessary but costless).  The 4th line checks the TCP
253    * header length.  The 5th line checks IP options, if any.  The 6th
254    * line checks TCP options, if any.  If any of these things are
255    * different between the previous & current datagram, we send the
256    * current datagram `uncompressed'.
257    */
258   if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0]
259       || ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3]
260       || ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4]
261       || TCPH_OFFSET(th) != TCPH_OFFSET(oth)
262       || (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2))
263       || (TCPH_OFFSET(th) > 5 && BCMP(th + 1, oth + 1, (TCPH_OFFSET(th) - 5) << 2))) {
264     goto uncompressed;
265   }
266 
267   /*
268    * Figure out which of the changing fields changed.  The
269    * receiver expects changes in the order: urgent, window,
270    * ack, seq (the order minimizes the number of temporaries
271    * needed in this section of code).
272    */
273   if (TCPH_FLAGS(th) & TCP_URG) {
274     deltaS = ntohs(th->urgp);
275     ENCODEZ(deltaS);
276     changes |= NEW_U;
277   } else if (th->urgp != oth->urgp) {
278     /* argh! URG not set but urp changed -- a sensible
279      * implementation should never do this but RFC793
280      * doesn't prohibit the change so we have to deal
281      * with it. */
282     goto uncompressed;
283   }
284 
285   if ((deltaS = (u_short)(ntohs(th->wnd) - ntohs(oth->wnd))) != 0) {
286     ENCODE(deltaS);
287     changes |= NEW_W;
288   }
289 
290   if ((deltaL = ntohl(th->ackno) - ntohl(oth->ackno)) != 0) {
291     if (deltaL > 0xffff) {
292       goto uncompressed;
293     }
294     deltaA = (u_short)deltaL;
295     ENCODE(deltaA);
296     changes |= NEW_A;
297   }
298 
299   if ((deltaL = ntohl(th->seqno) - ntohl(oth->seqno)) != 0) {
300     if (deltaL > 0xffff) {
301       goto uncompressed;
302     }
303     deltaS = (u_short)deltaL;
304     ENCODE(deltaS);
305     changes |= NEW_S;
306   }
307 
308   switch(changes) {
309   case 0:
310     /*
311      * Nothing changed. If this packet contains data and the
312      * last one didn't, this is probably a data packet following
313      * an ack (normal on an interactive connection) and we send
314      * it compressed.  Otherwise it's probably a retransmit,
315      * retransmitted ack or window probe.  Send it uncompressed
316      * in case the other side missed the compressed version.
317      */
318     if (IPH_LEN(ip) != IPH_LEN(&cs->cs_ip) &&
319       ntohs(IPH_LEN(&cs->cs_ip)) == hlen) {
320       break;
321     }
322 
323   /* (fall through) */
324 
325   case SPECIAL_I:
326   case SPECIAL_D:
327     /*
328      * actual changes match one of our special case encodings --
329      * send packet uncompressed.
330      */
331     goto uncompressed;
332 
333   case NEW_S|NEW_A:
334     if (deltaS == deltaA && deltaS == ntohs(IPH_LEN(&cs->cs_ip)) - hlen) {
335       /* special case for echoed terminal traffic */
336       changes = SPECIAL_I;
337       cp = new_seq;
338     }
339     break;
340 
341   case NEW_S:
342     if (deltaS == ntohs(IPH_LEN(&cs->cs_ip)) - hlen) {
343       /* special case for data xfer */
344       changes = SPECIAL_D;
345       cp = new_seq;
346     }
347     break;
348   }
349 
350   deltaS = (u_short)(ntohs(IPH_ID(ip)) - ntohs(IPH_ID(&cs->cs_ip)));
351   if (deltaS != 1) {
352     ENCODEZ(deltaS);
353     changes |= NEW_I;
354   }
355   if (TCPH_FLAGS(th) & TCP_PSH) {
356     changes |= TCP_PUSH_BIT;
357   }
358   /*
359    * Grab the cksum before we overwrite it below.  Then update our
360    * state with this packet's header.
361    */
362   deltaA = ntohs(th->chksum);
363   BCOPY(ip, &cs->cs_ip, hlen);
364 
365   /*
366    * We want to use the original packet as our compressed packet.
367    * (cp - new_seq) is the number of bytes we need for compressed
368    * sequence numbers.  In addition we need one byte for the change
369    * mask, one for the connection id and two for the tcp checksum.
370    * So, (cp - new_seq) + 4 bytes of header are needed.  hlen is how
371    * many bytes of the original packet to toss so subtract the two to
372    * get the new packet size.
373    */
374   deltaS = (u_short)(cp - new_seq);
375   if (!comp->compressSlot || comp->last_xmit != cs->cs_id) {
376     comp->last_xmit = cs->cs_id;
377     hlen -= deltaS + 4;
378     if(pbuf_header(pb, -hlen)){
379       /* Can we cope with this failing?  Just assert for now */
380       LWIP_ASSERT("pbuf_header failed\n", 0);
381     }
382     cp = (u_char *)pb->payload;
383     *cp++ = (u_char)(changes | NEW_C);
384     *cp++ = cs->cs_id;
385   } else {
386     hlen -= deltaS + 3;
387     if(pbuf_header(pb, -hlen)) {
388       /* Can we cope with this failing?  Just assert for now */
389       LWIP_ASSERT("pbuf_header failed\n", 0);
390     }
391     cp = (u_char *)pb->payload;
392     *cp++ = (u_char)changes;
393   }
394   *cp++ = (u_char)(deltaA >> 8);
395   *cp++ = (u_char)deltaA;
396   BCOPY(new_seq, cp, deltaS);
397   INCR(vjs_compressed);
398   return (TYPE_COMPRESSED_TCP);
399 
400   /*
401    * Update connection state cs & send uncompressed packet (that is,
402    * a regular ip/tcp packet but with the 'conversation id' we hope
403    * to use on future compressed packets in the protocol field).
404    */
405 uncompressed:
406   BCOPY(ip, &cs->cs_ip, hlen);
407   IPH_PROTO_SET(ip, cs->cs_id);
408   comp->last_xmit = cs->cs_id;
409   return (TYPE_UNCOMPRESSED_TCP);
410 }
411 
412 /*
413  * Called when we may have missed a packet.
414  */
415 void
vj_uncompress_err(struct vjcompress * comp)416 vj_uncompress_err(struct vjcompress *comp)
417 {
418   comp->flags |= VJF_TOSS;
419   INCR(vjs_errorin);
420 }
421 
422 /*
423  * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
424  * Return 0 on success, -1 on failure.
425  */
426 int
vj_uncompress_uncomp(struct pbuf * nb,struct vjcompress * comp)427 vj_uncompress_uncomp(struct pbuf *nb, struct vjcompress *comp)
428 {
429   register u_int hlen;
430   register struct cstate *cs;
431   register struct ip_hdr *ip;
432 
433   ip = (struct ip_hdr *)nb->payload;
434   hlen = IPH_HL(ip) << 2;
435   if (IPH_PROTO(ip) >= MAX_SLOTS
436       || hlen + sizeof(struct tcp_hdr) > nb->len
437       || (hlen += TCPH_OFFSET(((struct tcp_hdr *)&((char *)ip)[hlen])) << 2)
438           > nb->len
439       || hlen > MAX_HDR) {
440     PPPDEBUG(LOG_INFO, ("vj_uncompress_uncomp: bad cid=%d, hlen=%d buflen=%d\n",
441       IPH_PROTO(ip), hlen, nb->len));
442     comp->flags |= VJF_TOSS;
443     INCR(vjs_errorin);
444     return -1;
445   }
446   cs = &comp->rstate[comp->last_recv = IPH_PROTO(ip)];
447   comp->flags &=~ VJF_TOSS;
448   IPH_PROTO_SET(ip, IP_PROTO_TCP);
449   BCOPY(ip, &cs->cs_ip, hlen);
450   cs->cs_hlen = (u_short)hlen;
451   INCR(vjs_uncompressedin);
452   return 0;
453 }
454 
455 /*
456  * Uncompress a packet of type TYPE_COMPRESSED_TCP.
457  * The packet is composed of a buffer chain and the first buffer
458  * must contain an accurate chain length.
459  * The first buffer must include the entire compressed TCP/IP header.
460  * This procedure replaces the compressed header with the uncompressed
461  * header and returns the length of the VJ header.
462  */
463 int
vj_uncompress_tcp(struct pbuf ** nb,struct vjcompress * comp)464 vj_uncompress_tcp(struct pbuf **nb, struct vjcompress *comp)
465 {
466   u_char *cp;
467   struct tcp_hdr *th;
468   struct cstate *cs;
469   u_short *bp;
470   struct pbuf *n0 = *nb;
471   u32_t tmp;
472   u_int vjlen, hlen, changes;
473 
474   INCR(vjs_compressedin);
475   cp = (u_char *)n0->payload;
476   changes = *cp++;
477   if (changes & NEW_C) {
478     /*
479      * Make sure the state index is in range, then grab the state.
480      * If we have a good state index, clear the 'discard' flag.
481      */
482     if (*cp >= MAX_SLOTS) {
483       PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: bad cid=%d\n", *cp));
484       goto bad;
485     }
486 
487     comp->flags &=~ VJF_TOSS;
488     comp->last_recv = *cp++;
489   } else {
490     /*
491      * this packet has an implicit state index.  If we've
492      * had a line error since the last time we got an
493      * explicit state index, we have to toss the packet.
494      */
495     if (comp->flags & VJF_TOSS) {
496       PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: tossing\n"));
497       INCR(vjs_tossed);
498       return (-1);
499     }
500   }
501   cs = &comp->rstate[comp->last_recv];
502   hlen = IPH_HL(&cs->cs_ip) << 2;
503   th = (struct tcp_hdr *)&((u_char *)&cs->cs_ip)[hlen];
504   th->chksum = htons((*cp << 8) | cp[1]);
505   cp += 2;
506   if (changes & TCP_PUSH_BIT) {
507     TCPH_SET_FLAG(th, TCP_PSH);
508   } else {
509     TCPH_UNSET_FLAG(th, TCP_PSH);
510   }
511 
512   switch (changes & SPECIALS_MASK) {
513   case SPECIAL_I:
514     {
515       register u32_t i = ntohs(IPH_LEN(&cs->cs_ip)) - cs->cs_hlen;
516       /* some compilers can't nest inline assembler.. */
517       tmp = ntohl(th->ackno) + i;
518       th->ackno = htonl(tmp);
519       tmp = ntohl(th->seqno) + i;
520       th->seqno = htonl(tmp);
521     }
522     break;
523 
524   case SPECIAL_D:
525     /* some compilers can't nest inline assembler.. */
526     tmp = ntohl(th->seqno) + ntohs(IPH_LEN(&cs->cs_ip)) - cs->cs_hlen;
527     th->seqno = htonl(tmp);
528     break;
529 
530   default:
531     if (changes & NEW_U) {
532       TCPH_SET_FLAG(th, TCP_URG);
533       DECODEU(th->urgp);
534     } else {
535       TCPH_UNSET_FLAG(th, TCP_URG);
536     }
537     if (changes & NEW_W) {
538       DECODES(th->wnd);
539     }
540     if (changes & NEW_A) {
541       DECODEL(th->ackno);
542     }
543     if (changes & NEW_S) {
544       DECODEL(th->seqno);
545     }
546     break;
547   }
548   if (changes & NEW_I) {
549     DECODES(cs->cs_ip._id);
550   } else {
551     IPH_ID_SET(&cs->cs_ip, ntohs(IPH_ID(&cs->cs_ip)) + 1);
552     IPH_ID_SET(&cs->cs_ip, htons(IPH_ID(&cs->cs_ip)));
553   }
554 
555   /*
556    * At this point, cp points to the first byte of data in the
557    * packet.  Fill in the IP total length and update the IP
558    * header checksum.
559    */
560   vjlen = (u_short)(cp - (u_char*)n0->payload);
561   if (n0->len < vjlen) {
562     /*
563      * We must have dropped some characters (crc should detect
564      * this but the old slip framing won't)
565      */
566     PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: head buffer %d too short %d\n",
567           n0->len, vjlen));
568     goto bad;
569   }
570 
571 #if BYTE_ORDER == LITTLE_ENDIAN
572   tmp = n0->tot_len - vjlen + cs->cs_hlen;
573   IPH_LEN_SET(&cs->cs_ip, htons((u_short)tmp));
574 #else
575   IPH_LEN_SET(&cs->cs_ip, htons(n0->tot_len - vjlen + cs->cs_hlen));
576 #endif
577 
578   /* recompute the ip header checksum */
579   bp = (u_short *) &cs->cs_ip;
580   IPH_CHKSUM_SET(&cs->cs_ip, 0);
581   for (tmp = 0; hlen > 0; hlen -= 2) {
582     tmp += *bp++;
583   }
584   tmp = (tmp & 0xffff) + (tmp >> 16);
585   tmp = (tmp & 0xffff) + (tmp >> 16);
586   IPH_CHKSUM_SET(&cs->cs_ip,  (u_short)(~tmp));
587 
588   /* Remove the compressed header and prepend the uncompressed header. */
589   if(pbuf_header(n0, -((s16_t)(vjlen)))) {
590     /* Can we cope with this failing?  Just assert for now */
591     LWIP_ASSERT("pbuf_header failed\n", 0);
592     goto bad;
593   }
594 
595   if(LWIP_MEM_ALIGN(n0->payload) != n0->payload) {
596     struct pbuf *np, *q;
597     u8_t *bufptr;
598 
599     np = pbuf_alloc(PBUF_RAW, n0->len + cs->cs_hlen, PBUF_POOL);
600     if(!np) {
601       PPPDEBUG(LOG_WARNING, ("vj_uncompress_tcp: realign failed\n"));
602       goto bad;
603     }
604 
605     if(pbuf_header(np, -cs->cs_hlen)) {
606       /* Can we cope with this failing?  Just assert for now */
607       LWIP_ASSERT("pbuf_header failed\n", 0);
608       goto bad;
609     }
610 
611     bufptr = n0->payload;
612     for(q = np; q != NULL; q = q->next) {
613       MEMCPY(q->payload, bufptr, q->len);
614       bufptr += q->len;
615     }
616 
617     if(n0->next) {
618       pbuf_chain(np, n0->next);
619       pbuf_dechain(n0);
620     }
621     pbuf_free(n0);
622     n0 = np;
623   }
624 
625   if(pbuf_header(n0, cs->cs_hlen)) {
626     struct pbuf *np;
627 
628     LWIP_ASSERT("vj_uncompress_tcp: cs->cs_hlen <= PBUF_POOL_BUFSIZE", cs->cs_hlen <= PBUF_POOL_BUFSIZE);
629     np = pbuf_alloc(PBUF_RAW, cs->cs_hlen, PBUF_POOL);
630     if(!np) {
631       PPPDEBUG(LOG_WARNING, ("vj_uncompress_tcp: prepend failed\n"));
632       goto bad;
633     }
634     pbuf_cat(np, n0);
635     n0 = np;
636   }
637   LWIP_ASSERT("n0->len >= cs->cs_hlen", n0->len >= cs->cs_hlen);
638   MEMCPY(n0->payload, &cs->cs_ip, cs->cs_hlen);
639 
640   *nb = n0;
641 
642   return vjlen;
643 
644 bad:
645   comp->flags |= VJF_TOSS;
646   INCR(vjs_errorin);
647   return (-1);
648 }
649 
650 #endif /* VJ_SUPPORT */
651 
652 #endif /* PPP_SUPPORT */
653