2 * Routines to compress and uncompess tcp packets (for transmission
3 * over low speed serial lines.
5 * Copyright (c) 1989 Regents of the University of California.
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.
20 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
21 * - Initial distribution.
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).
27 * Modified March 1998 by Guy Lancaster, glanca@gesn.com,
28 * for a 16 bit processor.
40 #define INCR(counter) ++comp->stats.counter
45 #if defined(NO_CHAR_BITFIELDS)
46 #define getip_hl(base) ((base).ip_hl_v&0xf)
47 #define getth_off(base) (((base).th_x2_off&0xf0)>>4)
49 #define getip_hl(base) ((base).ip_hl)
50 #define getth_off(base) ((base).th_off)
53 void vj_compress_init(struct vjcompress *comp)
56 register struct cstate *tstate = comp->tstate;
59 memset((char *)comp, 0, sizeof(*comp));
61 comp->maxSlotIndex = MAX_SLOTS - 1;
62 comp->compressSlot = 0; /* Disable slot ID compression by default. */
63 for (i = MAX_SLOTS - 1; i > 0; --i) {
65 tstate[i].cs_next = &tstate[i - 1];
67 tstate[0].cs_next = &tstate[MAX_SLOTS - 1];
69 comp->last_cs = &tstate[0];
70 comp->last_recv = 255;
71 comp->last_xmit = 255;
72 comp->flags = VJF_TOSS;
76 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
77 * checks for zero (since zero has to be encoded in the long, 3 byte
81 if ((u_short)(n) >= 256) { \
90 #define ENCODEZ(n) { \
91 if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
101 #define DECODEL(f) { \
103 u32_t tmp = ntohl(f) + ((cp[1] << 8) | cp[2]); \
107 u32_t tmp = ntohl(f) + (u32_t)*cp++; \
112 #define DECODES(f) { \
114 u_short tmp = ntohs(f) + (((u_short)cp[1] << 8) | cp[2]); \
118 u_short tmp = ntohs(f) + (u_short)*cp++; \
123 #define DECODEU(f) { \
125 (f) = htons(((u_short)cp[1] << 8) | cp[2]); \
128 (f) = htons((u_short)*cp++); \
133 * vj_compress_tcp - Attempt to do Van Jacobsen header compression on a
134 * packet. This assumes that nb and comp are not null and that the first
135 * buffer of the chain contains a valid IP header.
136 * Return the VJ type code indicating whether or not the packet was
139 u_int vj_compress_tcp(
140 struct vjcompress *comp,
144 register struct ip *ip = (struct ip *)pb->payload;
145 register struct cstate *cs = comp->last_cs->cs_next;
146 register u_short hlen = getip_hl(*ip);
147 register struct tcphdr *oth;
148 register struct tcphdr *th;
149 register u_short deltaS, deltaA;
150 register u_long deltaL;
151 register u_int changes = 0;
153 register u_char *cp = new_seq;
156 * Check that the packet is IP proto TCP.
158 if (ip->ip_p != IPPROTO_TCP)
162 * Bail if this is an IP fragment or if the TCP packet isn't
163 * `compressible' (i.e., ACK isn't set or some other control bit is
166 if ((ip->ip_off & htons(0x3fff)) || pb->tot_len < 40)
168 th = (struct tcphdr *)&((long *)ip)[hlen];
169 if ((th->th_flags & (TCP_SYN|TCP_FIN|TCP_RST|TCP_ACK)) != TCP_ACK)
173 * Packet is compressible -- we're going to send either a
174 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
175 * to locate (or create) the connection state. Special case the
176 * most recently used connection since it's most likely to be used
177 * again & we don't have to do any reordering if it's used.
180 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr
181 || ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr
182 || *(long *)th != ((long *)&cs->cs_ip)[getip_hl(cs->cs_ip)]) {
184 * Wasn't the first -- search for it.
186 * States are kept in a circularly linked list with
187 * last_cs pointing to the end of the list. The
188 * list is kept in lru order by moving a state to the
189 * head of the list whenever it is referenced. Since
190 * the list is short and, empirically, the connection
191 * we want is almost always near the front, we locate
192 * states via linear search. If we don't find a state
193 * for the datagram, the oldest state is (re-)used.
195 register struct cstate *lcs;
196 register struct cstate *lastcs = comp->last_cs;
199 lcs = cs; cs = cs->cs_next;
201 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
202 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
203 && *(long *)th == ((long *)&cs->cs_ip)[getip_hl(cs->cs_ip)])
205 } while (cs != lastcs);
208 * Didn't find it -- re-use oldest cstate. Send an
209 * uncompressed packet that tells the other side what
210 * connection number we're using for this conversation.
211 * Note that since the state list is circular, the oldest
212 * state points to the newest and we only need to set
213 * last_cs to update the lru linkage.
217 hlen += getth_off(*th);
219 /* Check that the IP/TCP headers are contained in the first buffer. */
226 * Found it -- move to the front on the connection list.
231 lcs->cs_next = cs->cs_next;
232 cs->cs_next = lastcs->cs_next;
233 lastcs->cs_next = cs;
237 oth = (struct tcphdr *)&((long *)&cs->cs_ip)[hlen];
239 hlen += getth_off(*th);
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",
249 * Make sure that only what we expect to change changed. The first
250 * line of the `if' checks the IP protocol version, header length &
251 * type of service. The 2nd line checks the "Don't fragment" bit.
252 * The 3rd line checks the time-to-live and protocol (the protocol
253 * check is unnecessary but costless). The 4th line checks the TCP
254 * header length. The 5th line checks IP options, if any. The 6th
255 * line checks TCP options, if any. If any of these things are
256 * different between the previous & current datagram, we send the
257 * current datagram `uncompressed'.
259 if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0]
260 || ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3]
261 || ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4]
262 || getth_off(*th) != getth_off(*oth)
263 || (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2))
264 || (getth_off(*th) > 5 && BCMP(th + 1, oth + 1, (getth_off(*th) - 5) << 2)))
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).
273 if (th->th_flags & TCP_URG) {
274 deltaS = ntohs(th->th_urp);
277 } else if (th->th_urp != oth->th_urp)
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
284 if ((deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) != 0) {
289 if ((deltaL = ntohl(th->th_ack) - ntohl(oth->th_ack)) != 0) {
292 deltaA = (u_short)deltaL;
297 if ((deltaL = ntohl(th->th_seq) - ntohl(oth->th_seq)) != 0) {
300 deltaS = (u_short)deltaL;
309 * Nothing changed. If this packet contains data and the
310 * last one didn't, this is probably a data packet following
311 * an ack (normal on an interactive connection) and we send
312 * it compressed. Otherwise it's probably a retransmit,
313 * retransmitted ack or window probe. Send it uncompressed
314 * in case the other side missed the compressed version.
316 if (ip->ip_len != cs->cs_ip.ip_len &&
317 ntohs(cs->cs_ip.ip_len) == hlen)
325 * actual changes match one of our special case encodings --
326 * send packet uncompressed.
331 if (deltaS == deltaA && deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
332 /* special case for echoed terminal traffic */
339 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
340 /* special case for data xfer */
347 deltaS = (u_short)(ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id));
352 if (th->th_flags & TCP_PSH)
353 changes |= TCP_PUSH_BIT;
355 * Grab the cksum before we overwrite it below. Then update our
356 * state with this packet's header.
358 deltaA = ntohs(th->th_sum);
359 BCOPY(ip, &cs->cs_ip, hlen);
362 * We want to use the original packet as our compressed packet.
363 * (cp - new_seq) is the number of bytes we need for compressed
364 * sequence numbers. In addition we need one byte for the change
365 * mask, one for the connection id and two for the tcp checksum.
366 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
367 * many bytes of the original packet to toss so subtract the two to
368 * get the new packet size.
370 deltaS = (u_short)(cp - new_seq);
371 if (!comp->compressSlot || comp->last_xmit != cs->cs_id) {
372 comp->last_xmit = cs->cs_id;
374 pbuf_header(pb, -hlen);
375 cp = (u_char *)pb->payload;
376 *cp++ = changes | NEW_C;
380 pbuf_header(pb, -hlen);
381 cp = (u_char *)pb->payload;
386 BCOPY(new_seq, cp, deltaS);
387 INCR(vjs_compressed);
388 return (TYPE_COMPRESSED_TCP);
391 * Update connection state cs & send uncompressed packet (that is,
392 * a regular ip/tcp packet but with the 'conversation id' we hope
393 * to use on future compressed packets in the protocol field).
396 BCOPY(ip, &cs->cs_ip, hlen);
397 ip->ip_p = cs->cs_id;
398 comp->last_xmit = cs->cs_id;
399 return (TYPE_UNCOMPRESSED_TCP);
403 * Called when we may have missed a packet.
405 void vj_uncompress_err(struct vjcompress *comp)
407 comp->flags |= VJF_TOSS;
412 * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
413 * Return 0 on success, -1 on failure.
415 int vj_uncompress_uncomp(
417 struct vjcompress *comp
421 register struct cstate *cs;
422 register struct ip *ip;
424 ip = (struct ip *)nb->payload;
425 hlen = getip_hl(*ip) << 2;
426 if (ip->ip_p >= MAX_SLOTS
427 || hlen + sizeof(struct tcphdr) > nb->len
428 || (hlen += getth_off(*((struct tcphdr *)&((char *)ip)[hlen])) << 2)
431 PPPDEBUG((LOG_INFO, "vj_uncompress_uncomp: bad cid=%d, hlen=%d buflen=%d\n",
432 ip->ip_p, hlen, nb->len));
433 comp->flags |= VJF_TOSS;
437 cs = &comp->rstate[comp->last_recv = ip->ip_p];
438 comp->flags &=~ VJF_TOSS;
439 ip->ip_p = IPPROTO_TCP;
440 BCOPY(ip, &cs->cs_ip, hlen);
442 INCR(vjs_uncompressedin);
447 * Uncompress a packet of type TYPE_COMPRESSED_TCP.
448 * The packet is composed of a buffer chain and the first buffer
449 * must contain an accurate chain length.
450 * The first buffer must include the entire compressed TCP/IP header.
451 * This procedure replaces the compressed header with the uncompressed
452 * header and returns the length of the VJ header.
454 int vj_uncompress_tcp(
456 struct vjcompress *comp
463 struct pbuf *n0 = *nb;
465 u_int vjlen, hlen, changes;
467 INCR(vjs_compressedin);
468 cp = (u_char *)n0->payload;
470 if (changes & NEW_C) {
472 * Make sure the state index is in range, then grab the state.
473 * If we have a good state index, clear the 'discard' flag.
475 if (*cp >= MAX_SLOTS) {
476 PPPDEBUG((LOG_INFO, "vj_uncompress_tcp: bad cid=%d\n", *cp));
480 comp->flags &=~ VJF_TOSS;
481 comp->last_recv = *cp++;
484 * this packet has an implicit state index. If we've
485 * had a line error since the last time we got an
486 * explicit state index, we have to toss the packet.
488 if (comp->flags & VJF_TOSS) {
489 PPPDEBUG((LOG_INFO, "vj_uncompress_tcp: tossing\n"));
494 cs = &comp->rstate[comp->last_recv];
495 hlen = getip_hl(cs->cs_ip) << 2;
496 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
497 th->th_sum = htons((*cp << 8) | cp[1]);
499 if (changes & TCP_PUSH_BIT)
500 th->th_flags |= TCP_PSH;
502 th->th_flags &=~ TCP_PSH;
504 switch (changes & SPECIALS_MASK) {
507 register u32_t i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
508 /* some compilers can't nest inline assembler.. */
509 tmp = ntohl(th->th_ack) + i;
510 th->th_ack = htonl(tmp);
511 tmp = ntohl(th->th_seq) + i;
512 th->th_seq = htonl(tmp);
517 /* some compilers can't nest inline assembler.. */
518 tmp = ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
519 th->th_seq = htonl(tmp);
523 if (changes & NEW_U) {
524 th->th_flags |= TCP_URG;
527 th->th_flags &=~ TCP_URG;
536 if (changes & NEW_I) {
537 DECODES(cs->cs_ip.ip_id);
539 cs->cs_ip.ip_id = ntohs(cs->cs_ip.ip_id) + 1;
540 cs->cs_ip.ip_id = htons(cs->cs_ip.ip_id);
544 * At this point, cp points to the first byte of data in the
545 * packet. Fill in the IP total length and update the IP
548 vjlen = (u_short)(cp - (u_char*)n0->payload);
549 if (n0->len < vjlen) {
551 * We must have dropped some characters (crc should detect
552 * this but the old slip framing won't)
554 PPPDEBUG((LOG_INFO, "vj_uncompress_tcp: head buffer %d too short %d\n",
559 #if BYTE_ORDER == LITTLE_ENDIAN
560 tmp = n0->tot_len - vjlen + cs->cs_hlen;
561 cs->cs_ip.ip_len = htons(tmp);
563 cs->cs_ip.ip_len = htons(n0->tot_len - vjlen + cs->cs_hlen);
566 /* recompute the ip header checksum */
567 bp = (u_short *) &cs->cs_ip;
568 cs->cs_ip.ip_sum = 0;
569 for (tmp = 0; hlen > 0; hlen -= 2)
571 tmp = (tmp & 0xffff) + (tmp >> 16);
572 tmp = (tmp & 0xffff) + (tmp >> 16);
573 cs->cs_ip.ip_sum = (u_short)(~tmp);
575 /* Remove the compressed header and prepend the uncompressed header. */
576 pbuf_header(n0, -vjlen);
578 if(MEM_ALIGN(n0->payload) != n0->payload) {
582 np = pbuf_alloc(PBUF_RAW, n0->len + cs->cs_hlen, PBUF_POOL);
584 PPPDEBUG((LOG_WARNING, "vj_uncompress_tcp: realign failed\n"));
589 pbuf_header(np, -cs->cs_hlen);
591 bufptr = n0->payload;
592 for(q = np; q != NULL; q = q->next) {
593 memcpy(q->payload, bufptr, q->len);
598 pbuf_chain(np, n0->next);
605 if(pbuf_header(n0, cs->cs_hlen)) {
608 LWIP_ASSERT("vj_uncompress_tcp: cs->cs_hlen <= PBUF_POOL_BUFSIZE", cs->cs_hlen <= PBUF_POOL_BUFSIZE);
609 np = pbuf_alloc(PBUF_RAW, cs->cs_hlen, PBUF_POOL);
611 PPPDEBUG((LOG_WARNING, "vj_uncompress_tcp: prepend failed\n"));
618 LWIP_ASSERT("n0->len >= cs->cs_hlen", n0->len >= cs->cs_hlen);
619 memcpy(n0->payload, &cs->cs_ip, cs->cs_hlen);
626 comp->flags |= VJF_TOSS;