1 /* $NetBSD: slcompress.c,v 1.15 1996/03/15 02:28:12 paulus Exp $ */ 2 3 /* 4 * Copyright (c) 1989, 1993, 1994 5 * The Regents of the University of California. All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. All advertising materials mentioning features or use of this software 16 * must display the following acknowledgement: 17 * This product includes software developed by the University of 18 * California, Berkeley and its contributors. 19 * 4. Neither the name of the University nor the names of its contributors 20 * may be used to endorse or promote products derived from this software 21 * without specific prior written permission. 22 * 23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33 * SUCH DAMAGE. 34 * 35 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94 36 */ 37 38 /* 39 * Routines to compress and uncompess tcp packets (for transmission 40 * over low speed serial lines. 41 * 42 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 43 * - Initial distribution. 44 */ 45 46 #include <sys/param.h> 47 #include <sys/mbuf.h> 48 #include <sys/systm.h> 49 50 #include <netinet/in.h> 51 #include <netinet/in_systm.h> 52 #include <netinet/ip.h> 53 #include <netinet/tcp.h> 54 55 #include <net/slcompress.h> 56 57 #ifndef SL_NO_STATS 58 #define INCR(counter) ++comp->counter; 59 #else 60 #define INCR(counter) 61 #endif 62 63 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n)) 64 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n)) 65 #ifndef _KERNEL 66 #define ovbcopy bcopy 67 #endif 68 69 void 70 sl_compress_init(comp, max_state) 71 struct slcompress *comp; 72 int max_state; 73 { 74 register u_int i; 75 register struct cstate *tstate = comp->tstate; 76 77 if (max_state == -1) { 78 max_state = MAX_STATES - 1; 79 bzero((char *)comp, sizeof(*comp)); 80 } else { 81 /* Don't reset statistics */ 82 bzero((char *)comp->tstate, sizeof(comp->tstate)); 83 bzero((char *)comp->rstate, sizeof(comp->rstate)); 84 } 85 for (i = max_state; i > 0; --i) { 86 tstate[i].cs_id = i; 87 tstate[i].cs_next = &tstate[i - 1]; 88 } 89 tstate[0].cs_next = &tstate[max_state]; 90 tstate[0].cs_id = 0; 91 comp->last_cs = &tstate[0]; 92 comp->last_recv = 255; 93 comp->last_xmit = 255; 94 comp->flags = SLF_TOSS; 95 } 96 97 98 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 99 * checks for zero (since zero has to be encoded in the long, 3 byte 100 * form). 101 */ 102 #define ENCODE(n) { \ 103 if ((u_int16_t)(n) >= 256) { \ 104 *cp++ = 0; \ 105 cp[1] = (n); \ 106 cp[0] = (n) >> 8; \ 107 cp += 2; \ 108 } else { \ 109 *cp++ = (n); \ 110 } \ 111 } 112 #define ENCODEZ(n) { \ 113 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 114 *cp++ = 0; \ 115 cp[1] = (n); \ 116 cp[0] = (n) >> 8; \ 117 cp += 2; \ 118 } else { \ 119 *cp++ = (n); \ 120 } \ 121 } 122 123 #define DECODEL(f) { \ 124 if (*cp == 0) {\ 125 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 126 cp += 3; \ 127 } else { \ 128 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 129 } \ 130 } 131 132 #define DECODES(f) { \ 133 if (*cp == 0) {\ 134 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 135 cp += 3; \ 136 } else { \ 137 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 138 } \ 139 } 140 141 #define DECODEU(f) { \ 142 if (*cp == 0) {\ 143 (f) = htons((cp[1] << 8) | cp[2]); \ 144 cp += 3; \ 145 } else { \ 146 (f) = htons((u_int32_t)*cp++); \ 147 } \ 148 } 149 150 u_int 151 sl_compress_tcp(m, ip, comp, compress_cid) 152 struct mbuf *m; 153 register struct ip *ip; 154 struct slcompress *comp; 155 int compress_cid; 156 { 157 register struct cstate *cs = comp->last_cs->cs_next; 158 register u_int hlen = ip->ip_hl; 159 register struct tcphdr *oth; 160 register struct tcphdr *th; 161 register u_int deltaS, deltaA; 162 register u_int changes = 0; 163 u_char new_seq[16]; 164 register u_char *cp = new_seq; 165 166 /* 167 * Bail if this is an IP fragment or if the TCP packet isn't 168 * `compressible' (i.e., ACK isn't set or some other control bit is 169 * set). (We assume that the caller has already made sure the 170 * packet is IP proto TCP). 171 */ 172 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 173 return (TYPE_IP); 174 175 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 176 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 177 return (TYPE_IP); 178 /* 179 * Packet is compressible -- we're going to send either a 180 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 181 * to locate (or create) the connection state. Special case the 182 * most recently used connection since it's most likely to be used 183 * again & we don't have to do any reordering if it's used. 184 */ 185 INCR(sls_packets) 186 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 187 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 188 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 189 /* 190 * Wasn't the first -- search for it. 191 * 192 * States are kept in a circularly linked list with 193 * last_cs pointing to the end of the list. The 194 * list is kept in lru order by moving a state to the 195 * head of the list whenever it is referenced. Since 196 * the list is short and, empirically, the connection 197 * we want is almost always near the front, we locate 198 * states via linear search. If we don't find a state 199 * for the datagram, the oldest state is (re-)used. 200 */ 201 register struct cstate *lcs; 202 register struct cstate *lastcs = comp->last_cs; 203 204 do { 205 lcs = cs; cs = cs->cs_next; 206 INCR(sls_searches) 207 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 208 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 209 && *(int32_t *)th == 210 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 211 goto found; 212 } while (cs != lastcs); 213 214 /* 215 * Didn't find it -- re-use oldest cstate. Send an 216 * uncompressed packet that tells the other side what 217 * connection number we're using for this conversation. 218 * Note that since the state list is circular, the oldest 219 * state points to the newest and we only need to set 220 * last_cs to update the lru linkage. 221 */ 222 INCR(sls_misses) 223 comp->last_cs = lcs; 224 hlen += th->th_off; 225 hlen <<= 2; 226 goto uncompressed; 227 228 found: 229 /* 230 * Found it -- move to the front on the connection list. 231 */ 232 if (cs == lastcs) 233 comp->last_cs = lcs; 234 else { 235 lcs->cs_next = cs->cs_next; 236 cs->cs_next = lastcs->cs_next; 237 lastcs->cs_next = cs; 238 } 239 } 240 241 /* 242 * Make sure that only what we expect to change changed. The first 243 * line of the `if' checks the IP protocol version, header length & 244 * type of service. The 2nd line checks the "Don't fragment" bit. 245 * The 3rd line checks the time-to-live and protocol (the protocol 246 * check is unnecessary but costless). The 4th line checks the TCP 247 * header length. The 5th line checks IP options, if any. The 6th 248 * line checks TCP options, if any. If any of these things are 249 * different between the previous & current datagram, we send the 250 * current datagram `uncompressed'. 251 */ 252 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 253 deltaS = hlen; 254 hlen += th->th_off; 255 hlen <<= 2; 256 257 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 258 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 259 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 260 th->th_off != oth->th_off || 261 (deltaS > 5 && 262 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 263 (th->th_off > 5 && 264 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 265 goto uncompressed; 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 (th->th_flags & TH_URG) { 274 deltaS = ntohs(th->th_urp); 275 ENCODEZ(deltaS); 276 changes |= NEW_U; 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 281 * with it. */ 282 goto uncompressed; 283 284 deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win)); 285 if (deltaS) { 286 ENCODE(deltaS); 287 changes |= NEW_W; 288 } 289 290 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 291 if (deltaA) { 292 if (deltaA > 0xffff) 293 goto uncompressed; 294 ENCODE(deltaA); 295 changes |= NEW_A; 296 } 297 298 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 299 if (deltaS) { 300 if (deltaS > 0xffff) 301 goto uncompressed; 302 ENCODE(deltaS); 303 changes |= NEW_S; 304 } 305 306 switch(changes) { 307 308 case 0: 309 /* 310 * Nothing changed. If this packet contains data and the 311 * last one didn't, this is probably a data packet following 312 * an ack (normal on an interactive connection) and we send 313 * it compressed. Otherwise it's probably a retransmit, 314 * retransmitted ack or window probe. Send it uncompressed 315 * in case the other side missed the compressed version. 316 */ 317 if (ip->ip_len != cs->cs_ip.ip_len && 318 ntohs(cs->cs_ip.ip_len) == hlen) 319 break; 320 321 /* (fall through) */ 322 323 case SPECIAL_I: 324 case SPECIAL_D: 325 /* 326 * actual changes match one of our special case encodings -- 327 * send packet uncompressed. 328 */ 329 goto uncompressed; 330 331 case NEW_S|NEW_A: 332 if (deltaS == deltaA && 333 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 334 /* special case for echoed terminal traffic */ 335 changes = SPECIAL_I; 336 cp = new_seq; 337 } 338 break; 339 340 case NEW_S: 341 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 342 /* special case for data xfer */ 343 changes = SPECIAL_D; 344 cp = new_seq; 345 } 346 break; 347 } 348 349 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 350 if (deltaS != 1) { 351 ENCODEZ(deltaS); 352 changes |= NEW_I; 353 } 354 if (th->th_flags & TH_PUSH) 355 changes |= TCP_PUSH_BIT; 356 /* 357 * Grab the cksum before we overwrite it below. Then update our 358 * state with this packet's header. 359 */ 360 deltaA = ntohs(th->th_sum); 361 BCOPY(ip, &cs->cs_ip, hlen); 362 363 /* 364 * We want to use the original packet as our compressed packet. 365 * (cp - new_seq) is the number of bytes we need for compressed 366 * sequence numbers. In addition we need one byte for the change 367 * mask, one for the connection id and two for the tcp checksum. 368 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 369 * many bytes of the original packet to toss so subtract the two to 370 * get the new packet size. 371 */ 372 deltaS = cp - new_seq; 373 cp = (u_char *)ip; 374 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 375 comp->last_xmit = cs->cs_id; 376 hlen -= deltaS + 4; 377 cp += hlen; 378 *cp++ = changes | NEW_C; 379 *cp++ = cs->cs_id; 380 } else { 381 hlen -= deltaS + 3; 382 cp += hlen; 383 *cp++ = changes; 384 } 385 m->m_len -= hlen; 386 m->m_data += hlen; 387 *cp++ = deltaA >> 8; 388 *cp++ = deltaA; 389 BCOPY(new_seq, cp, deltaS); 390 INCR(sls_compressed) 391 return (TYPE_COMPRESSED_TCP); 392 393 /* 394 * Update connection state cs & send uncompressed packet ('uncompressed' 395 * means a regular ip/tcp packet but with the 'conversation id' we hope 396 * to use on future compressed packets in the protocol field). 397 */ 398 uncompressed: 399 BCOPY(ip, &cs->cs_ip, hlen); 400 ip->ip_p = cs->cs_id; 401 comp->last_xmit = cs->cs_id; 402 return (TYPE_UNCOMPRESSED_TCP); 403 } 404 405 406 int 407 sl_uncompress_tcp(bufp, len, type, comp) 408 u_char **bufp; 409 int len; 410 u_int type; 411 struct slcompress *comp; 412 { 413 u_char *hdr, *cp; 414 int hlen, vjlen; 415 416 cp = bufp? *bufp: NULL; 417 vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen); 418 if (vjlen < 0) 419 return (0); /* error */ 420 if (vjlen == 0) 421 return (len); /* was uncompressed already */ 422 423 cp += vjlen; 424 len -= vjlen; 425 426 /* 427 * At this point, cp points to the first byte of data in the 428 * packet. If we're not aligned on a 4-byte boundary, copy the 429 * data down so the ip & tcp headers will be aligned. Then back up 430 * cp by the tcp/ip header length to make room for the reconstructed 431 * header (we assume the packet we were handed has enough space to 432 * prepend 128 bytes of header). 433 */ 434 if ((long)cp & 3) { 435 if (len > 0) 436 (void) ovbcopy(cp, (caddr_t)((long)cp &~ 3), len); 437 cp = (u_char *)((long)cp &~ 3); 438 } 439 cp -= hlen; 440 len += hlen; 441 BCOPY(hdr, cp, hlen); 442 443 *bufp = cp; 444 return (len); 445 } 446 447 /* 448 * Uncompress a packet of total length total_len. The first buflen 449 * bytes are at buf; this must include the entire (compressed or 450 * uncompressed) TCP/IP header. This procedure returns the length 451 * of the VJ header, with a pointer to the uncompressed IP header 452 * in *hdrp and its length in *hlenp. 453 */ 454 int 455 sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp) 456 u_char *buf; 457 int buflen, total_len; 458 u_int type; 459 struct slcompress *comp; 460 u_char **hdrp; 461 u_int *hlenp; 462 { 463 register u_char *cp; 464 register u_int hlen, changes; 465 register struct tcphdr *th; 466 register struct cstate *cs; 467 register struct ip *ip; 468 register u_int16_t *bp; 469 register u_int vjlen; 470 471 switch (type) { 472 473 case TYPE_UNCOMPRESSED_TCP: 474 ip = (struct ip *) buf; 475 if (ip->ip_p >= MAX_STATES) 476 goto bad; 477 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 478 comp->flags &=~ SLF_TOSS; 479 ip->ip_p = IPPROTO_TCP; 480 hlen = ip->ip_hl; 481 hlen += ((struct tcphdr *)&((int32_t *)ip)[hlen])->th_off; 482 hlen <<= 2; 483 BCOPY(ip, &cs->cs_ip, hlen); 484 cs->cs_hlen = hlen; 485 INCR(sls_uncompressedin) 486 *hdrp = (u_char *) &cs->cs_ip; 487 *hlenp = hlen; 488 return (0); 489 490 default: 491 goto bad; 492 493 case TYPE_COMPRESSED_TCP: 494 break; 495 } 496 /* We've got a compressed packet. */ 497 INCR(sls_compressedin) 498 cp = buf; 499 changes = *cp++; 500 if (changes & NEW_C) { 501 /* Make sure the state index is in range, then grab the state. 502 * If we have a good state index, clear the 'discard' flag. */ 503 if (*cp >= MAX_STATES) 504 goto bad; 505 506 comp->flags &=~ SLF_TOSS; 507 comp->last_recv = *cp++; 508 } else { 509 /* this packet has an implicit state index. If we've 510 * had a line error since the last time we got an 511 * explicit state index, we have to toss the packet. */ 512 if (comp->flags & SLF_TOSS) { 513 INCR(sls_tossed) 514 return (-1); 515 } 516 } 517 cs = &comp->rstate[comp->last_recv]; 518 hlen = cs->cs_ip.ip_hl << 2; 519 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 520 th->th_sum = htons((*cp << 8) | cp[1]); 521 cp += 2; 522 if (changes & TCP_PUSH_BIT) 523 th->th_flags |= TH_PUSH; 524 else 525 th->th_flags &=~ TH_PUSH; 526 527 switch (changes & SPECIALS_MASK) { 528 case SPECIAL_I: 529 { 530 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 531 th->th_ack = htonl(ntohl(th->th_ack) + i); 532 th->th_seq = htonl(ntohl(th->th_seq) + i); 533 } 534 break; 535 536 case SPECIAL_D: 537 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 538 - cs->cs_hlen); 539 break; 540 541 default: 542 if (changes & NEW_U) { 543 th->th_flags |= TH_URG; 544 DECODEU(th->th_urp) 545 } else 546 th->th_flags &=~ TH_URG; 547 if (changes & NEW_W) 548 DECODES(th->th_win) 549 if (changes & NEW_A) 550 DECODEL(th->th_ack) 551 if (changes & NEW_S) 552 DECODEL(th->th_seq) 553 break; 554 } 555 if (changes & NEW_I) { 556 DECODES(cs->cs_ip.ip_id) 557 } else 558 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 559 560 /* 561 * At this point, cp points to the first byte of data in the 562 * packet. Fill in the IP total length and update the IP 563 * header checksum. 564 */ 565 vjlen = cp - buf; 566 buflen -= vjlen; 567 if (buflen < 0) 568 /* we must have dropped some characters (crc should detect 569 * this but the old slip framing won't) */ 570 goto bad; 571 572 total_len += cs->cs_hlen - vjlen; 573 cs->cs_ip.ip_len = htons(total_len); 574 575 /* recompute the ip header checksum */ 576 bp = (u_int16_t *) &cs->cs_ip; 577 cs->cs_ip.ip_sum = 0; 578 for (changes = 0; hlen > 0; hlen -= 2) 579 changes += *bp++; 580 changes = (changes & 0xffff) + (changes >> 16); 581 changes = (changes & 0xffff) + (changes >> 16); 582 cs->cs_ip.ip_sum = ~ changes; 583 584 *hdrp = (u_char *) &cs->cs_ip; 585 *hlenp = cs->cs_hlen; 586 return vjlen; 587 588 bad: 589 comp->flags |= SLF_TOSS; 590 INCR(sls_errorin) 591 return (-1); 592 } 593