NeXT/vjcompress.c

   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
  28 /*
  29  * This version is used under SunOS 4.x, Digital UNIX, AIX 4.x,
  30  * and SVR4 systems including Solaris 2.
  31  *
  32  * $Id: vjcompress.c,v 1.3 1997/04/30 05:39:44 paulus Exp $
  33  */
  34
  35 #include <sys/types.h>
  36 #include <sys/param.h>
  37
  38 #ifdef SVR4
  39 #ifndef __GNUC__
  40 #include <sys/byteorder.h>      /* for ntohl, etc. */
  41 #else
  42 /* make sure we don't get the gnu "fixed" one! */
  43 #include "/usr/include/sys/byteorder.h"
  44 #endif
  45 #endif
  46
  47 #ifdef __osf__
  48 #include <net/net_globals.h>
  49 #endif
  50 #include <netinet/in.h>
  51
  52 #ifdef AIX4
  53 #define _NETINET_IN_SYSTM_H_
  54 typedef u_long  n_long;
  55 #else
  56 #include <netinet/in_systm.h>
  57 #endif
  58
  59 #include <netinet/ip.h>
  60 #include <netinet/tcp.h>
  61
  62 #include <net/ppp_defs.h>
  63 #include <net/vjcompress.h>
  64
  65 #ifndef VJ_NO_STATS
  66 #define INCR(counter) ++comp->stats.counter
  67 #else
  68 #define INCR(counter)
  69 #endif
  70
  71 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
  72 #undef  BCOPY
  73 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
  74 #ifndef KERNEL
  75 #define ovbcopy bcopy
  76 #endif
  77
  78 #ifdef __osf__
  79 #define getip_hl(base)  (((base).ip_vhl)&0xf)
  80 #define getth_off(base) ((((base).th_xoff)&0xf0)>>4)
  81
  82 #else
  83 #define getip_hl(base)  ((base).ip_hl)
  84 #define getth_off(base) ((base).th_off)
  85 #endif
  86
  87 void
  88 vj_compress_init(comp, max_state)
  89     struct vjcompress *comp;
  90     int max_state;
  91 {
  92     register u_int i;
  93     register struct cstate *tstate = comp->tstate;
  94
  95     if (max_state == -1)
  96         max_state = MAX_STATES - 1;
  97     bzero((char *)comp, sizeof(*comp));
  98     for (i = max_state; i > 0; --i) {
  99         tstate[i].cs_id = i;
 100         tstate[i].cs_next = &tstate[i - 1];
 101     }
 102     tstate[0].cs_next = &tstate[max_state];
 103     tstate[0].cs_id = 0;
 104     comp->last_cs = &tstate[0];
 105     comp->last_recv = 255;
 106     comp->last_xmit = 255;
 107     comp->flags = VJF_TOSS;
 108 }
 109
 110
 111 /* ENCODE encodes a number that is known to be non-zero.  ENCODEZ
 112  * checks for zero (since zero has to be encoded in the long, 3 byte
 113  * form).
 114  */
 115 #define ENCODE(n) { \
 116         if ((u_short)(n) >= 256) { \
 117                 *cp++ = 0; \
 118                 cp[1] = (n); \
 119                 cp[0] = (n) >> 8; \
 120                 cp += 2; \
 121         } else { \
 122                 *cp++ = (n); \
 123         } \
 124 }
 125 #define ENCODEZ(n) { \
 126         if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
 127                 *cp++ = 0; \
 128                 cp[1] = (n); \
 129                 cp[0] = (n) >> 8; \
 130                 cp += 2; \
 131         } else { \
 132                 *cp++ = (n); \
 133         } \
 134 }
 135
 136 #define DECODEL(f) { \
 137         if (*cp == 0) {\
 138                 u_int32_t tmp = ntohl(f) + ((cp[1] << 8) | cp[2]); \
 139                 (f) = htonl(tmp); \
 140                 cp += 3; \
 141         } else { \
 142                 u_int32_t tmp = ntohl(f) + (u_int32_t)*cp++; \
 143                 (f) = htonl(tmp); \
 144         } \
 145 }
 146
 147 #define DECODES(f) { \
 148         if (*cp == 0) {\
 149                 u_short tmp = ntohs(f) + ((cp[1] << 8) | cp[2]); \
 150                 (f) = htons(tmp); \
 151                 cp += 3; \
 152         } else { \
 153                 u_short tmp = ntohs(f) + (u_int32_t)*cp++; \
 154                 (f) = htons(tmp); \
 155         } \
 156 }
 157
 158 #define DECODEU(f) { \
 159         if (*cp == 0) {\
 160                 (f) = htons((cp[1] << 8) | cp[2]); \
 161                 cp += 3; \
 162         } else { \
 163                 (f) = htons((u_int32_t)*cp++); \
 164         } \
 165 }
 166
 167 u_int
 168 vj_compress_tcp(ip, mlen, comp, compress_cid, vjhdrp)
 169     register struct ip *ip;
 170     u_int mlen;
 171     struct vjcompress *comp;
 172     int compress_cid;
 173     u_char **vjhdrp;
 174 {
 175     register struct cstate *cs = comp->last_cs->cs_next;
 176     register u_int hlen = getip_hl(*ip);
 177     register struct tcphdr *oth;
 178     register struct tcphdr *th;
 179     register u_int deltaS, deltaA;
 180     register u_int changes = 0;
 181     u_char new_seq[16];
 182     register u_char *cp = new_seq;
 183
 184     /*
 185      * Bail if this is an IP fragment or if the TCP packet isn't
 186      * `compressible' (i.e., ACK isn't set or some other control bit is
 187      * set).  (We assume that the caller has already made sure the
 188      * packet is IP proto TCP).
 189      */
 190     if ((ip->ip_off & htons(0x3fff)) || mlen < 40)
 191         return (TYPE_IP);
 192
 193     th = (struct tcphdr *)&((int *)ip)[hlen];
 194     if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
 195         return (TYPE_IP);
 196     /*
 197      * Packet is compressible -- we're going to send either a
 198      * COMPRESSED_TCP or UNCOMPRESSED_TCP packet.  Either way we need
 199      * to locate (or create) the connection state.  Special case the
 200      * most recently used connection since it's most likely to be used
 201      * again & we don't have to do any reordering if it's used.
 202      */
 203     INCR(vjs_packets);
 204     if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
 205         ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
 206         *(int *)th != ((int *)&cs->cs_ip)[getip_hl(cs->cs_ip)]) {
 207         /*
 208          * Wasn't the first -- search for it.
 209          *
 210          * States are kept in a circularly linked list with
 211          * last_cs pointing to the end of the list.  The
 212          * list is kept in lru order by moving a state to the
 213          * head of the list whenever it is referenced.  Since
 214          * the list is short and, empirically, the connection
 215          * we want is almost always near the front, we locate
 216          * states via linear search.  If we don't find a state
 217          * for the datagram, the oldest state is (re-)used.
 218          */
 219         register struct cstate *lcs;
 220         register struct cstate *lastcs = comp->last_cs;
 221
 222         do {
 223             lcs = cs; cs = cs->cs_next;
 224             INCR(vjs_searches);
 225             if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
 226                 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
 227                 && *(int *)th == ((int *)&cs->cs_ip)[getip_hl(cs->cs_ip)])
 228                 goto found;
 229         } while (cs != lastcs);
 230
 231         /*
 232          * Didn't find it -- re-use oldest cstate.  Send an
 233          * uncompressed packet that tells the other side what
 234          * connection number we're using for this conversation.
 235          * Note that since the state list is circular, the oldest
 236          * state points to the newest and we only need to set
 237          * last_cs to update the lru linkage.
 238          */
 239         INCR(vjs_misses);
 240         comp->last_cs = lcs;
 241         hlen += getth_off(*th);
 242         hlen <<= 2;
 243         if (hlen > mlen)
 244             return (TYPE_IP);
 245         goto uncompressed;
 246
 247     found:
 248         /*
 249          * Found it -- move to the front on the connection list.
 250          */
 251         if (cs == lastcs)
 252             comp->last_cs = lcs;
 253         else {
 254             lcs->cs_next = cs->cs_next;
 255             cs->cs_next = lastcs->cs_next;
 256             lastcs->cs_next = cs;
 257         }
 258     }
 259
 260     /*
 261      * Make sure that only what we expect to change changed. The first
 262      * line of the `if' checks the IP protocol version, header length &
 263      * type of service.  The 2nd line checks the "Don't fragment" bit.
 264      * The 3rd line checks the time-to-live and protocol (the protocol
 265      * check is unnecessary but costless).  The 4th line checks the TCP
 266      * header length.  The 5th line checks IP options, if any.  The 6th
 267      * line checks TCP options, if any.  If any of these things are
 268      * different between the previous & current datagram, we send the
 269      * current datagram `uncompressed'.
 270      */
 271     oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen];
 272     deltaS = hlen;
 273     hlen += getth_off(*th);
 274     hlen <<= 2;
 275     if (hlen > mlen)
 276         return (TYPE_IP);
 277
 278     if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] ||
 279         ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] ||
 280         ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] ||
 281         getth_off(*th) != getth_off(*oth) ||
 282         (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
 283         (getth_off(*th) > 5 && BCMP(th + 1, oth + 1, (getth_off(*th) - 5) << 2)))
 284         goto uncompressed;
 285
 286     /*
 287      * Figure out which of the changing fields changed.  The
 288      * receiver expects changes in the order: urgent, window,
 289      * ack, seq (the order minimizes the number of temporaries
 290      * needed in this section of code).
 291      */
 292     if (th->th_flags & TH_URG) {
 293         deltaS = ntohs(th->th_urp);
 294         ENCODEZ(deltaS);
 295         changes |= NEW_U;
 296     } else if (th->th_urp != oth->th_urp)
 297         /* argh! URG not set but urp changed -- a sensible
 298          * implementation should never do this but RFC793
 299          * doesn't prohibit the change so we have to deal
 300          * with it. */
 301         goto uncompressed;
 302
 303     if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) {
 304         ENCODE(deltaS);
 305         changes |= NEW_W;
 306     }
 307
 308     if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) {
 309         if (deltaA > 0xffff)
 310             goto uncompressed;
 311         ENCODE(deltaA);
 312         changes |= NEW_A;
 313     }
 314
 315     if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) {
 316         if (deltaS > 0xffff)
 317             goto uncompressed;
 318         ENCODE(deltaS);
 319         changes |= NEW_S;
 320     }
 321
 322     switch(changes) {
 323
 324     case 0:
 325         /*
 326          * Nothing changed. If this packet contains data and the
 327          * last one didn't, this is probably a data packet following
 328          * an ack (normal on an interactive connection) and we send
 329          * it compressed.  Otherwise it's probably a retransmit,
 330          * retransmitted ack or window probe.  Send it uncompressed
 331          * in case the other side missed the compressed version.
 332          */
 333         if (ip->ip_len != cs->cs_ip.ip_len &&
 334             ntohs(cs->cs_ip.ip_len) == hlen)
 335             break;
 336
 337         /* (fall through) */
 338
 339     case SPECIAL_I:
 340     case SPECIAL_D:
 341         /*
 342          * actual changes match one of our special case encodings --
 343          * send packet uncompressed.
 344          */
 345         goto uncompressed;
 346
 347     case NEW_S|NEW_A:
 348         if (deltaS == deltaA && deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
 349             /* special case for echoed terminal traffic */
 350             changes = SPECIAL_I;
 351             cp = new_seq;
 352         }
 353         break;
 354
 355     case NEW_S:
 356         if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
 357             /* special case for data xfer */
 358             changes = SPECIAL_D;
 359             cp = new_seq;
 360         }
 361         break;
 362     }
 363
 364     deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
 365     if (deltaS != 1) {
 366         ENCODEZ(deltaS);
 367         changes |= NEW_I;
 368     }
 369     if (th->th_flags & TH_PUSH)
 370         changes |= TCP_PUSH_BIT;
 371     /*
 372      * Grab the cksum before we overwrite it below.  Then update our
 373      * state with this packet's header.
 374      */
 375     deltaA = ntohs(th->th_sum);
 376     BCOPY(ip, &cs->cs_ip, hlen);
 377
 378     /*
 379      * We want to use the original packet as our compressed packet.
 380      * (cp - new_seq) is the number of bytes we need for compressed
 381      * sequence numbers.  In addition we need one byte for the change
 382      * mask, one for the connection id and two for the tcp checksum.
 383      * So, (cp - new_seq) + 4 bytes of header are needed.  hlen is how
 384      * many bytes of the original packet to toss so subtract the two to
 385      * get the new packet size.
 386      */
 387     deltaS = cp - new_seq;
 388     cp = (u_char *)ip;
 389     if (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
 390         comp->last_xmit = cs->cs_id;
 391         hlen -= deltaS + 4;
 392         *vjhdrp = (cp += hlen);
 393         *cp++ = changes | NEW_C;
 394         *cp++ = cs->cs_id;
 395     } else {
 396         hlen -= deltaS + 3;
 397         *vjhdrp = (cp += hlen);
 398         *cp++ = changes;
 399     }
 400     *cp++ = deltaA >> 8;
 401     *cp++ = deltaA;
 402     BCOPY(new_seq, cp, deltaS);
 403     INCR(vjs_compressed);
 404     return (TYPE_COMPRESSED_TCP);
 405
 406     /*
 407      * Update connection state cs & send uncompressed packet (that is,
 408      * a regular ip/tcp packet but with the 'conversation id' we hope
 409      * to use on future compressed packets in the protocol field).
 410      */
 411  uncompressed:
 412     BCOPY(ip, &cs->cs_ip, hlen);
 413     ip->ip_p = cs->cs_id;
 414     comp->last_xmit = cs->cs_id;
 415     return (TYPE_UNCOMPRESSED_TCP);
 416 }
 417
 418 /*
 419  * Called when we may have missed a packet.
 420  */
 421 void
 422 vj_uncompress_err(comp)
 423     struct vjcompress *comp;
 424 {
 425     comp->flags |= VJF_TOSS;
 426     INCR(vjs_errorin);
 427 }
 428
 429 /*
 430  * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
 431  */
 432 int
 433 vj_uncompress_uncomp(buf, buflen, comp)
 434     u_char *buf;
 435     int buflen;
 436     struct vjcompress *comp;
 437 {
 438     register u_int hlen;
 439     register struct cstate *cs;
 440     register struct ip *ip;
 441
 442     ip = (struct ip *) buf;
 443     hlen = getip_hl(*ip) << 2;
 444     if (ip->ip_p >= MAX_STATES
 445         || hlen + sizeof(struct tcphdr) > buflen
 446         || (hlen += getth_off(*((struct tcphdr *)&((char *)ip)[hlen])) << 2)
 447             > buflen
 448         || hlen > MAX_HDR) {
 449         comp->flags |= VJF_TOSS;
 450         INCR(vjs_errorin);
 451         return (0);
 452     }
 453     cs = &comp->rstate[comp->last_recv = ip->ip_p];
 454     comp->flags &=~ VJF_TOSS;
 455     ip->ip_p = IPPROTO_TCP;
 456     BCOPY(ip, &cs->cs_ip, hlen);
 457     cs->cs_hlen = hlen;
 458     INCR(vjs_uncompressedin);
 459     return (1);
 460 }
 461
 462 /*
 463  * Uncompress a packet of type TYPE_COMPRESSED_TCP.
 464  * The packet starts at buf and is of total length total_len.
 465  * The first buflen bytes are at buf; this must include the entire
 466  * compressed TCP/IP header.  This procedure returns the length
 467  * of the VJ header, with a pointer to the uncompressed IP header
 468  * in *hdrp and its length in *hlenp.
 469  */
 470 int
 471 vj_uncompress_tcp(buf, buflen, total_len, comp, hdrp, hlenp)
 472     u_char *buf;
 473     int buflen, total_len;
 474     struct vjcompress *comp;
 475     u_char **hdrp;
 476     u_int *hlenp;
 477 {
 478     register u_char *cp;
 479     register u_int hlen, changes;
 480     register struct tcphdr *th;
 481     register struct cstate *cs;
 482     register u_short *bp;
 483     register u_int vjlen;
 484     register u_int32_t tmp;
 485
 486     INCR(vjs_compressedin);
 487     cp = buf;
 488     changes = *cp++;
 489     if (changes & NEW_C) {
 490         /* Make sure the state index is in range, then grab the state.
 491          * If we have a good state index, clear the 'discard' flag. */
 492         if (*cp >= MAX_STATES)
 493             goto bad;
 494
 495         comp->flags &=~ VJF_TOSS;
 496         comp->last_recv = *cp++;
 497     } else {
 498         /* this packet has an implicit state index.  If we've
 499          * had a line error since the last time we got an
 500          * explicit state index, we have to toss the packet. */
 501         if (comp->flags & VJF_TOSS) {
 502             INCR(vjs_tossed);
 503             return (-1);
 504         }
 505     }
 506     cs = &comp->rstate[comp->last_recv];
 507     hlen = getip_hl(cs->cs_ip) << 2;
 508     th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
 509     th->th_sum = htons((*cp << 8) | cp[1]);
 510     cp += 2;
 511     if (changes & TCP_PUSH_BIT)
 512         th->th_flags |= TH_PUSH;
 513     else
 514         th->th_flags &=~ TH_PUSH;
 515
 516     switch (changes & SPECIALS_MASK) {
 517     case SPECIAL_I:
 518         {
 519             register u_int32_t i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
 520             /* some compilers can't nest inline assembler.. */
 521             tmp = ntohl(th->th_ack) + i;
 522             th->th_ack = htonl(tmp);
 523             tmp = ntohl(th->th_seq) + i;
 524             th->th_seq = htonl(tmp);
 525         }
 526         break;
 527
 528     case SPECIAL_D:
 529         /* some compilers can't nest inline assembler.. */
 530         tmp = ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
 531         th->th_seq = htonl(tmp);
 532         break;
 533
 534     default:
 535         if (changes & NEW_U) {
 536             th->th_flags |= TH_URG;
 537             DECODEU(th->th_urp);
 538         } else
 539             th->th_flags &=~ TH_URG;
 540         if (changes & NEW_W)
 541             DECODES(th->th_win);
 542         if (changes & NEW_A)
 543             DECODEL(th->th_ack);
 544         if (changes & NEW_S)
 545             DECODEL(th->th_seq);
 546         break;
 547     }
 548     if (changes & NEW_I) {
 549         DECODES(cs->cs_ip.ip_id);
 550     } else {
 551         cs->cs_ip.ip_id = ntohs(cs->cs_ip.ip_id) + 1;
 552         cs->cs_ip.ip_id = htons(cs->cs_ip.ip_id);
 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 = cp - buf;
 561     buflen -= vjlen;
 562     if (buflen < 0)
 563         /* we must have dropped some characters (crc should detect
 564          * this but the old slip framing won't) */
 565         goto bad;
 566
 567     total_len += cs->cs_hlen - vjlen;
 568     cs->cs_ip.ip_len = htons(total_len);
 569
 570     /* recompute the ip header checksum */
 571     bp = (u_short *) &cs->cs_ip;
 572     cs->cs_ip.ip_sum = 0;
 573     for (changes = 0; hlen > 0; hlen -= 2)
 574         changes += *bp++;
 575     changes = (changes & 0xffff) + (changes >> 16);
 576     changes = (changes & 0xffff) + (changes >> 16);
 577     cs->cs_ip.ip_sum = ~ changes;
 578
 579     *hdrp = (u_char *) &cs->cs_ip;
 580     *hlenp = cs->cs_hlen;
 581     return vjlen;
 582
 583  bad:
 584     comp->flags |= VJF_TOSS;
 585     INCR(vjs_errorin);
 586     return (-1);
 587 }