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.
39 #define INCR(counter) ++comp->stats.counter
44 #if defined(NO_CHAR_BITFIELDS)
45 #define getip_hl(base) ((base).ip_hl_v&0xf)
46 #define getth_off(base) (((base).th_x2_off&0xf0)>>4)
48 #define getip_hl(base) ((base).ip_hl)
49 #define getth_off(base) ((base).th_off)
52 void vj_compress_init(struct vjcompress *comp)
55 register struct cstate *tstate = comp->tstate;
58 memset((char *)comp, 0, sizeof(*comp));
60 comp->maxSlotIndex = MAX_SLOTS - 1;
61 comp->compressSlot = 0; /* Disable slot ID compression by default. */
62 for (i = MAX_SLOTS - 1; i > 0; --i) {
64 tstate[i].cs_next = &tstate[i - 1];
66 tstate[0].cs_next = &tstate[MAX_SLOTS - 1];
68 comp->last_cs = &tstate[0];
69 comp->last_recv = 255;
70 comp->last_xmit = 255;
71 comp->flags = VJF_TOSS;
75 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
76 * checks for zero (since zero has to be encoded in the long, 3 byte
80 if ((u_short)(n) >= 256) { \
89 #define ENCODEZ(n) { \
90 if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
100 #define DECODEL(f) { \
102 u32_t tmp = ntohl(f) + ((cp[1] << 8) | cp[2]); \
106 u32_t tmp = ntohl(f) + (u32_t)*cp++; \
111 #define DECODES(f) { \
113 u_short tmp = ntohs(f) + (((u_short)cp[1] << 8) | cp[2]); \
117 u_short tmp = ntohs(f) + (u_short)*cp++; \
122 #define DECODEU(f) { \
124 (f) = htons(((u_short)cp[1] << 8) | cp[2]); \
127 (f) = htons((u_short)*cp++); \
132 * vj_compress_tcp - Attempt to do Van Jacobsen header compression on a
133 * packet. This assumes that nb and comp are not null and that the first
134 * buffer of the chain contains a valid IP header.
135 * Return the VJ type code indicating whether or not the packet was
138 u_int vj_compress_tcp(
139 struct vjcompress *comp,
143 register struct ip *ip = (struct ip *)pb->payload;
144 register struct cstate *cs = comp->last_cs->cs_next;
145 register u_short hlen = getip_hl(*ip);
146 register struct tcphdr *oth;
147 register struct tcphdr *th;
148 register u_short deltaS, deltaA;
149 register u_long deltaL;
150 register u_int changes = 0;
152 register u_char *cp = new_seq;
155 * Check that the packet is IP proto TCP.
157 if (ip->ip_p != IPPROTO_TCP)
161 * Bail if this is an IP fragment or if the TCP packet isn't
162 * `compressible' (i.e., ACK isn't set or some other control bit is
165 if ((ip->ip_off & htons(0x3fff)) || pb->tot_len < 40)
167 th = (struct tcphdr *)&((long *)ip)[hlen];
168 if ((th->th_flags & (TCP_SYN|TCP_FIN|TCP_RST|TCP_ACK)) != TCP_ACK)
172 * Packet is compressible -- we're going to send either a
173 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
174 * to locate (or create) the connection state. Special case the
175 * most recently used connection since it's most likely to be used
176 * again & we don't have to do any reordering if it's used.
179 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr
180 || ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr
181 || *(long *)th != ((long *)&cs->cs_ip)[getip_hl(cs->cs_ip)]) {
183 * Wasn't the first -- search for it.
185 * States are kept in a circularly linked list with
186 * last_cs pointing to the end of the list. The
187 * list is kept in lru order by moving a state to the
188 * head of the list whenever it is referenced. Since
189 * the list is short and, empirically, the connection
190 * we want is almost always near the front, we locate
191 * states via linear search. If we don't find a state
192 * for the datagram, the oldest state is (re-)used.
194 register struct cstate *lcs;
195 register struct cstate *lastcs = comp->last_cs;
198 lcs = cs; cs = cs->cs_next;
200 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
201 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
202 && *(long *)th == ((long *)&cs->cs_ip)[getip_hl(cs->cs_ip)])
204 } while (cs != lastcs);
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.
216 hlen += getth_off(*th);
218 /* Check that the IP/TCP headers are contained in the first buffer. */
225 * Found it -- move to the front on the connection list.
230 lcs->cs_next = cs->cs_next;
231 cs->cs_next = lastcs->cs_next;
232 lastcs->cs_next = cs;
236 oth = (struct tcphdr *)&((long *)&cs->cs_ip)[hlen];
238 hlen += getth_off(*th);
240 /* Check that the IP/TCP headers are contained in the first buffer. */
241 if (hlen > pb->len) {
242 PPPDEBUG((LOG_INFO, "vj_compress_tcp: header len %d spans buffers\n",
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'.
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 || getth_off(*th) != getth_off(*oth)
262 || (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2))
263 || (getth_off(*th) > 5 && BCMP(th + 1, oth + 1, (getth_off(*th) - 5) << 2)))
267 * Figure out which of the changing fields changed. The
268 * receiver expects changes in the order: urgent, window,
269 * ack, seq (the order minimizes the number of temporaries
270 * needed in this section of code).
272 if (th->th_flags & TCP_URG) {
273 deltaS = ntohs(th->th_urp);
276 } else if (th->th_urp != oth->th_urp)
277 /* argh! URG not set but urp changed -- a sensible
278 * implementation should never do this but RFC793
279 * doesn't prohibit the change so we have to deal
283 if ((deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) != 0) {
288 if ((deltaL = ntohl(th->th_ack) - ntohl(oth->th_ack)) != 0) {
291 deltaA = (u_short)deltaL;
296 if ((deltaL = ntohl(th->th_seq) - ntohl(oth->th_seq)) != 0) {
299 deltaS = (u_short)deltaL;
308 * Nothing changed. If this packet contains data and the
309 * last one didn't, this is probably a data packet following
310 * an ack (normal on an interactive connection) and we send
311 * it compressed. Otherwise it's probably a retransmit,
312 * retransmitted ack or window probe. Send it uncompressed
313 * in case the other side missed the compressed version.
315 if (ip->ip_len != cs->cs_ip.ip_len &&
316 ntohs(cs->cs_ip.ip_len) == hlen)
324 * actual changes match one of our special case encodings --
325 * send packet uncompressed.
330 if (deltaS == deltaA && deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
331 /* special case for echoed terminal traffic */
338 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
339 /* special case for data xfer */
346 deltaS = (u_short)(ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id));
351 if (th->th_flags & TCP_PSH)
352 changes |= TCP_PUSH_BIT;
354 * Grab the cksum before we overwrite it below. Then update our
355 * state with this packet's header.
357 deltaA = ntohs(th->th_sum);
358 BCOPY(ip, &cs->cs_ip, hlen);
361 * We want to use the original packet as our compressed packet.
362 * (cp - new_seq) is the number of bytes we need for compressed
363 * sequence numbers. In addition we need one byte for the change
364 * mask, one for the connection id and two for the tcp checksum.
365 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
366 * many bytes of the original packet to toss so subtract the two to
367 * get the new packet size.
369 deltaS = (u_short)(cp - new_seq);
370 if (!comp->compressSlot || comp->last_xmit != cs->cs_id) {
371 comp->last_xmit = cs->cs_id;
373 pbuf_header(pb, -hlen);
374 cp = (u_char *)pb->payload;
375 *cp++ = changes | NEW_C;
379 pbuf_header(pb, -hlen);
380 cp = (u_char *)pb->payload;
385 BCOPY(new_seq, cp, deltaS);
386 INCR(vjs_compressed);
387 return (TYPE_COMPRESSED_TCP);
390 * Update connection state cs & send uncompressed packet (that is,
391 * a regular ip/tcp packet but with the 'conversation id' we hope
392 * to use on future compressed packets in the protocol field).
395 BCOPY(ip, &cs->cs_ip, hlen);
396 ip->ip_p = cs->cs_id;
397 comp->last_xmit = cs->cs_id;
398 return (TYPE_UNCOMPRESSED_TCP);
402 * Called when we may have missed a packet.
404 void vj_uncompress_err(struct vjcompress *comp)
406 comp->flags |= VJF_TOSS;
411 * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
412 * Return 0 on success, -1 on failure.
414 int vj_uncompress_uncomp(
416 struct vjcompress *comp
420 register struct cstate *cs;
421 register struct ip *ip;
423 ip = (struct ip *)nb->payload;
424 hlen = getip_hl(*ip) << 2;
425 if (ip->ip_p >= MAX_SLOTS
426 || hlen + sizeof(struct tcphdr) > nb->len
427 || (hlen += getth_off(*((struct tcphdr *)&((char *)ip)[hlen])) << 2)
430 PPPDEBUG((LOG_INFO, "vj_uncompress_uncomp: bad cid=%d, hlen=%d buflen=%d\n",
431 ip->ip_p, hlen, nb->len));
432 comp->flags |= VJF_TOSS;
436 cs = &comp->rstate[comp->last_recv = ip->ip_p];
437 comp->flags &=~ VJF_TOSS;
438 ip->ip_p = IPPROTO_TCP;
439 BCOPY(ip, &cs->cs_ip, hlen);
441 INCR(vjs_uncompressedin);
446 * Uncompress a packet of type TYPE_COMPRESSED_TCP.
447 * The packet is composed of a buffer chain and the first buffer
448 * must contain an accurate chain length.
449 * The first buffer must include the entire compressed TCP/IP header.
450 * This procedure replaces the compressed header with the uncompressed
451 * header and returns the length of the VJ header.
453 int vj_uncompress_tcp(
455 struct vjcompress *comp
462 struct pbuf *n0 = *nb;
464 u_int vjlen, hlen, changes;
466 INCR(vjs_compressedin);
467 cp = (u_char *)n0->payload;
469 if (changes & NEW_C) {
471 * Make sure the state index is in range, then grab the state.
472 * If we have a good state index, clear the 'discard' flag.
474 if (*cp >= MAX_SLOTS) {
475 PPPDEBUG((LOG_INFO, "vj_uncompress_tcp: bad cid=%d\n", *cp));
479 comp->flags &=~ VJF_TOSS;
480 comp->last_recv = *cp++;
483 * this packet has an implicit state index. If we've
484 * had a line error since the last time we got an
485 * explicit state index, we have to toss the packet.
487 if (comp->flags & VJF_TOSS) {
488 PPPDEBUG((LOG_INFO, "vj_uncompress_tcp: tossing\n"));
493 cs = &comp->rstate[comp->last_recv];
494 hlen = getip_hl(cs->cs_ip) << 2;
495 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
496 th->th_sum = htons((*cp << 8) | cp[1]);
498 if (changes & TCP_PUSH_BIT)
499 th->th_flags |= TCP_PSH;
501 th->th_flags &=~ TCP_PSH;
503 switch (changes & SPECIALS_MASK) {
506 register u32_t i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
507 /* some compilers can't nest inline assembler.. */
508 tmp = ntohl(th->th_ack) + i;
509 th->th_ack = htonl(tmp);
510 tmp = ntohl(th->th_seq) + i;
511 th->th_seq = htonl(tmp);
516 /* some compilers can't nest inline assembler.. */
517 tmp = ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
518 th->th_seq = htonl(tmp);
522 if (changes & NEW_U) {
523 th->th_flags |= TCP_URG;
526 th->th_flags &=~ TCP_URG;
535 if (changes & NEW_I) {
536 DECODES(cs->cs_ip.ip_id);
538 cs->cs_ip.ip_id = ntohs(cs->cs_ip.ip_id) + 1;
539 cs->cs_ip.ip_id = htons(cs->cs_ip.ip_id);
543 * At this point, cp points to the first byte of data in the
544 * packet. Fill in the IP total length and update the IP
547 vjlen = (u_short)(cp - (u_char*)n0->payload);
548 if (n0->len < vjlen) {
550 * We must have dropped some characters (crc should detect
551 * this but the old slip framing won't)
553 PPPDEBUG((LOG_INFO, "vj_uncompress_tcp: head buffer %d too short %d\n",
558 #if BYTE_ORDER == LITTLE_ENDIAN
559 tmp = n0->tot_len - vjlen + cs->cs_hlen;
560 cs->cs_ip.ip_len = htons(tmp);
562 cs->cs_ip.ip_len = htons(n0->tot_len - vjlen + cs->cs_hlen);
565 /* recompute the ip header checksum */
566 bp = (u_short *) &cs->cs_ip;
567 cs->cs_ip.ip_sum = 0;
568 for (tmp = 0; hlen > 0; hlen -= 2)
570 tmp = (tmp & 0xffff) + (tmp >> 16);
571 tmp = (tmp & 0xffff) + (tmp >> 16);
572 cs->cs_ip.ip_sum = (u_short)(~tmp);
574 /* Remove the compressed header and prepend the uncompressed header. */
575 pbuf_header(n0, -vjlen);
577 if(MEM_ALIGN(n0->payload) != n0->payload) {
581 np = pbuf_alloc(PBUF_RAW, n0->len + cs->cs_hlen, PBUF_POOL);
583 PPPDEBUG((LOG_WARNING, "vj_uncompress_tcp: realign failed\n"));
588 pbuf_header(np, -cs->cs_hlen);
590 bufptr = n0->payload;
591 for(q = np; q != NULL; q = q->next) {
592 memcpy(q->payload, bufptr, q->len);
597 pbuf_chain(np, n0->next);
604 if(pbuf_header(n0, cs->cs_hlen)) {
607 LWIP_ASSERT("vj_uncompress_tcp: cs->cs_hlen <= PBUF_POOL_BUFSIZE", cs->cs_hlen <= PBUF_POOL_BUFSIZE);
608 np = pbuf_alloc(PBUF_RAW, cs->cs_hlen, PBUF_POOL);
610 PPPDEBUG((LOG_WARNING, "vj_uncompress_tcp: prepend failed\n"));
617 LWIP_ASSERT("n0->len >= cs->cs_hlen", n0->len >= cs->cs_hlen);
618 memcpy(n0->payload, &cs->cs_ip, cs->cs_hlen);
625 comp->flags |= VJF_TOSS;