slcompress.c revision 1.11
1/* $NetBSD: slcompress.c,v 1.11 1995/03/28 20:01:15 jtc 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 49#include <netinet/in.h> 50#include <netinet/in_systm.h> 51#include <netinet/ip.h> 52#include <netinet/tcp.h> 53 54#include <net/slcompress.h> 55 56#ifndef SL_NO_STATS 57#define INCR(counter) ++comp->counter; 58#else 59#define INCR(counter) 60#endif 61 62#define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n)) 63#define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n)) 64#ifndef _KERNEL 65#define ovbcopy bcopy 66#endif 67 68void 69sl_compress_init(comp, max_state) 70 struct slcompress *comp; 71 int max_state; 72{ 73 register u_int i; 74 register struct cstate *tstate = comp->tstate; 75 76 if (max_state == -1) 77 max_state = MAX_STATES - 1; 78 bzero((char *)comp, sizeof(*comp)); 79 for (i = max_state; i > 0; --i) { 80 tstate[i].cs_id = i; 81 tstate[i].cs_next = &tstate[i - 1]; 82 } 83 tstate[0].cs_next = &tstate[max_state]; 84 tstate[0].cs_id = 0; 85 comp->last_cs = &tstate[0]; 86 comp->last_recv = 255; 87 comp->last_xmit = 255; 88 comp->flags = SLF_TOSS; 89} 90 91 92/* ENCODE encodes a number that is known to be non-zero. ENCODEZ 93 * checks for zero (since zero has to be encoded in the long, 3 byte 94 * form). 95 */ 96#define ENCODE(n) { \ 97 if ((u_int16_t)(n) >= 256) { \ 98 *cp++ = 0; \ 99 cp[1] = (n); \ 100 cp[0] = (n) >> 8; \ 101 cp += 2; \ 102 } else { \ 103 *cp++ = (n); \ 104 } \ 105} 106#define ENCODEZ(n) { \ 107 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \ 108 *cp++ = 0; \ 109 cp[1] = (n); \ 110 cp[0] = (n) >> 8; \ 111 cp += 2; \ 112 } else { \ 113 *cp++ = (n); \ 114 } \ 115} 116 117#define DECODEL(f) { \ 118 if (*cp == 0) {\ 119 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 120 cp += 3; \ 121 } else { \ 122 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \ 123 } \ 124} 125 126#define DECODES(f) { \ 127 if (*cp == 0) {\ 128 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 129 cp += 3; \ 130 } else { \ 131 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \ 132 } \ 133} 134 135#define DECODEU(f) { \ 136 if (*cp == 0) {\ 137 (f) = htons((cp[1] << 8) | cp[2]); \ 138 cp += 3; \ 139 } else { \ 140 (f) = htons((u_int32_t)*cp++); \ 141 } \ 142} 143 144u_int 145sl_compress_tcp(m, ip, comp, compress_cid) 146 struct mbuf *m; 147 register struct ip *ip; 148 struct slcompress *comp; 149 int compress_cid; 150{ 151 register struct cstate *cs = comp->last_cs->cs_next; 152 register u_int hlen = ip->ip_hl; 153 register struct tcphdr *oth; 154 register struct tcphdr *th; 155 register u_int deltaS, deltaA; 156 register u_int changes = 0; 157 u_char new_seq[16]; 158 register u_char *cp = new_seq; 159 160 /* 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 163 * set). (We assume that the caller has already made sure the 164 * packet is IP proto TCP). 165 */ 166 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 167 return (TYPE_IP); 168 169 th = (struct tcphdr *)&((int32_t *)ip)[hlen]; 170 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 171 return (TYPE_IP); 172 /* 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. 178 */ 179 INCR(sls_packets) 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 *(int32_t *)th != ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 183 /* 184 * Wasn't the first -- search for it. 185 * 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. 194 */ 195 register struct cstate *lcs; 196 register struct cstate *lastcs = comp->last_cs; 197 198 do { 199 lcs = cs; cs = cs->cs_next; 200 INCR(sls_searches) 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 && *(int32_t *)th == 204 ((int32_t *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 205 goto found; 206 } while (cs != lastcs); 207 208 /* 209 * Didn't find it -- re-use oldest cstate. Send an 210 * uncompressed packet that tells the other side what 211 * connection number we're using for this conversation. 212 * Note that since the state list is circular, the oldest 213 * state points to the newest and we only need to set 214 * last_cs to update the lru linkage. 215 */ 216 INCR(sls_misses) 217 comp->last_cs = lcs; 218 hlen += th->th_off; 219 hlen <<= 2; 220 goto uncompressed; 221 222 found: 223 /* 224 * Found it -- move to the front on the connection list. 225 */ 226 if (cs == lastcs) 227 comp->last_cs = lcs; 228 else { 229 lcs->cs_next = cs->cs_next; 230 cs->cs_next = lastcs->cs_next; 231 lastcs->cs_next = cs; 232 } 233 } 234 235 /* 236 * Make sure that only what we expect to change changed. The first 237 * line of the `if' checks the IP protocol version, header length & 238 * type of service. The 2nd line checks the "Don't fragment" bit. 239 * The 3rd line checks the time-to-live and protocol (the protocol 240 * check is unnecessary but costless). The 4th line checks the TCP 241 * header length. The 5th line checks IP options, if any. The 6th 242 * line checks TCP options, if any. If any of these things are 243 * different between the previous & current datagram, we send the 244 * current datagram `uncompressed'. 245 */ 246 oth = (struct tcphdr *)&((int32_t *)&cs->cs_ip)[hlen]; 247 deltaS = hlen; 248 hlen += th->th_off; 249 hlen <<= 2; 250 251 if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] || 252 ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] || 253 ((u_int16_t *)ip)[4] != ((u_int16_t *)&cs->cs_ip)[4] || 254 th->th_off != oth->th_off || 255 (deltaS > 5 && 256 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 257 (th->th_off > 5 && 258 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 259 goto uncompressed; 260 261 /* 262 * Figure out which of the changing fields changed. The 263 * receiver expects changes in the order: urgent, window, 264 * ack, seq (the order minimizes the number of temporaries 265 * needed in this section of code). 266 */ 267 if (th->th_flags & TH_URG) { 268 deltaS = ntohs(th->th_urp); 269 ENCODEZ(deltaS); 270 changes |= NEW_U; 271 } else if (th->th_urp != oth->th_urp) 272 /* argh! URG not set but urp changed -- a sensible 273 * implementation should never do this but RFC793 274 * doesn't prohibit the change so we have to deal 275 * with it. */ 276 goto uncompressed; 277 278 if (deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win))) { 279 ENCODE(deltaS); 280 changes |= NEW_W; 281 } 282 283 if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) { 284 if (deltaA > 0xffff) 285 goto uncompressed; 286 ENCODE(deltaA); 287 changes |= NEW_A; 288 } 289 290 if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) { 291 if (deltaS > 0xffff) 292 goto uncompressed; 293 ENCODE(deltaS); 294 changes |= NEW_S; 295 } 296 297 switch(changes) { 298 299 case 0: 300 /* 301 * Nothing changed. If this packet contains data and the 302 * last one didn't, this is probably a data packet following 303 * an ack (normal on an interactive connection) and we send 304 * it compressed. Otherwise it's probably a retransmit, 305 * retransmitted ack or window probe. Send it uncompressed 306 * in case the other side missed the compressed version. 307 */ 308 if (ip->ip_len != cs->cs_ip.ip_len && 309 ntohs(cs->cs_ip.ip_len) == hlen) 310 break; 311 312 /* (fall through) */ 313 314 case SPECIAL_I: 315 case SPECIAL_D: 316 /* 317 * actual changes match one of our special case encodings -- 318 * send packet uncompressed. 319 */ 320 goto uncompressed; 321 322 case NEW_S|NEW_A: 323 if (deltaS == deltaA && 324 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 325 /* special case for echoed terminal traffic */ 326 changes = SPECIAL_I; 327 cp = new_seq; 328 } 329 break; 330 331 case NEW_S: 332 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 333 /* special case for data xfer */ 334 changes = SPECIAL_D; 335 cp = new_seq; 336 } 337 break; 338 } 339 340 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 341 if (deltaS != 1) { 342 ENCODEZ(deltaS); 343 changes |= NEW_I; 344 } 345 if (th->th_flags & TH_PUSH) 346 changes |= TCP_PUSH_BIT; 347 /* 348 * Grab the cksum before we overwrite it below. Then update our 349 * state with this packet's header. 350 */ 351 deltaA = ntohs(th->th_sum); 352 BCOPY(ip, &cs->cs_ip, hlen); 353 354 /* 355 * We want to use the original packet as our compressed packet. 356 * (cp - new_seq) is the number of bytes we need for compressed 357 * sequence numbers. In addition we need one byte for the change 358 * mask, one for the connection id and two for the tcp checksum. 359 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 360 * many bytes of the original packet to toss so subtract the two to 361 * get the new packet size. 362 */ 363 deltaS = cp - new_seq; 364 cp = (u_char *)ip; 365 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 366 comp->last_xmit = cs->cs_id; 367 hlen -= deltaS + 4; 368 cp += hlen; 369 *cp++ = changes | NEW_C; 370 *cp++ = cs->cs_id; 371 } else { 372 hlen -= deltaS + 3; 373 cp += hlen; 374 *cp++ = changes; 375 } 376 m->m_len -= hlen; 377 m->m_data += hlen; 378 *cp++ = deltaA >> 8; 379 *cp++ = deltaA; 380 BCOPY(new_seq, cp, deltaS); 381 INCR(sls_compressed) 382 return (TYPE_COMPRESSED_TCP); 383 384 /* 385 * Update connection state cs & send uncompressed packet ('uncompressed' 386 * means a regular ip/tcp packet but with the 'conversation id' we hope 387 * to use on future compressed packets in the protocol field). 388 */ 389uncompressed: 390 BCOPY(ip, &cs->cs_ip, hlen); 391 ip->ip_p = cs->cs_id; 392 comp->last_xmit = cs->cs_id; 393 return (TYPE_UNCOMPRESSED_TCP); 394} 395 396 397int 398sl_uncompress_tcp(bufp, len, type, comp) 399 u_char **bufp; 400 int len; 401 u_int type; 402 struct slcompress *comp; 403{ 404 405 return sl_uncompress_tcp_part(bufp, len, len, type, comp); 406} 407 408/* 409 * Uncompress a packet of total length total_len. The first buflen 410 * bytes are at *bufp; this must include the entire (compressed or 411 * uncompressed) TCP/IP header. In addition, there must be enough 412 * clear space before *bufp to build a full-length TCP/IP header. 413 */ 414int 415sl_uncompress_tcp_part(bufp, buflen, total_len, type, comp) 416 u_char **bufp; 417 int buflen, total_len; 418 u_int type; 419 struct slcompress *comp; 420{ 421 register u_char *cp; 422 register u_int hlen, changes; 423 register struct tcphdr *th; 424 register struct cstate *cs; 425 register struct ip *ip; 426 427 switch (type) { 428 429 case TYPE_UNCOMPRESSED_TCP: 430 ip = (struct ip *) *bufp; 431 if (ip->ip_p >= MAX_STATES) 432 goto bad; 433 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 434 comp->flags &=~ SLF_TOSS; 435 ip->ip_p = IPPROTO_TCP; 436 hlen = ip->ip_hl; 437 hlen += ((struct tcphdr *)&((int32_t *)ip)[hlen])->th_off; 438 hlen <<= 2; 439 BCOPY(ip, &cs->cs_ip, hlen); 440 cs->cs_ip.ip_sum = 0; 441 cs->cs_hlen = hlen; 442 INCR(sls_uncompressedin) 443 return (total_len); 444 445 default: 446 goto bad; 447 448 case TYPE_COMPRESSED_TCP: 449 break; 450 } 451 /* We've got a compressed packet. */ 452 INCR(sls_compressedin) 453 cp = *bufp; 454 changes = *cp++; 455 if (changes & NEW_C) { 456 /* Make sure the state index is in range, then grab the state. 457 * If we have a good state index, clear the 'discard' flag. */ 458 if (*cp >= MAX_STATES) 459 goto bad; 460 461 comp->flags &=~ SLF_TOSS; 462 comp->last_recv = *cp++; 463 } else { 464 /* this packet has an implicit state index. If we've 465 * had a line error since the last time we got an 466 * explicit state index, we have to toss the packet. */ 467 if (comp->flags & SLF_TOSS) { 468 INCR(sls_tossed) 469 return (0); 470 } 471 } 472 cs = &comp->rstate[comp->last_recv]; 473 hlen = cs->cs_ip.ip_hl << 2; 474 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 475 th->th_sum = htons((*cp << 8) | cp[1]); 476 cp += 2; 477 if (changes & TCP_PUSH_BIT) 478 th->th_flags |= TH_PUSH; 479 else 480 th->th_flags &=~ TH_PUSH; 481 482 switch (changes & SPECIALS_MASK) { 483 case SPECIAL_I: 484 { 485 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 486 th->th_ack = htonl(ntohl(th->th_ack) + i); 487 th->th_seq = htonl(ntohl(th->th_seq) + i); 488 } 489 break; 490 491 case SPECIAL_D: 492 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 493 - cs->cs_hlen); 494 break; 495 496 default: 497 if (changes & NEW_U) { 498 th->th_flags |= TH_URG; 499 DECODEU(th->th_urp) 500 } else 501 th->th_flags &=~ TH_URG; 502 if (changes & NEW_W) 503 DECODES(th->th_win) 504 if (changes & NEW_A) 505 DECODEL(th->th_ack) 506 if (changes & NEW_S) 507 DECODEL(th->th_seq) 508 break; 509 } 510 if (changes & NEW_I) { 511 DECODES(cs->cs_ip.ip_id) 512 } else 513 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 514 515 /* 516 * At this point, cp points to the first byte of data in the 517 * packet. If we're not aligned on a 4-byte boundary, copy the 518 * data down so the ip & tcp headers will be aligned. Then back up 519 * cp by the tcp/ip header length to make room for the reconstructed 520 * header (we assume the packet we were handed has enough space to 521 * prepend 128 bytes of header). Adjust the length to account for 522 * the new header & fill in the IP total length. 523 */ 524 buflen -= (cp - *bufp); 525 total_len -= (cp - *bufp); 526 if (buflen < 0) 527 /* we must have dropped some characters (crc should detect 528 * this but the old slip framing won't) */ 529 goto bad; 530 531 if ((long)cp & 3) { 532 if (buflen > 0) 533 (void) ovbcopy(cp, (caddr_t)((long)cp &~ 3), buflen); 534 cp = (u_char *)((long)cp &~ 3); 535 } 536 cp -= cs->cs_hlen; 537 total_len += cs->cs_hlen; 538 cs->cs_ip.ip_len = htons(total_len); 539 BCOPY(&cs->cs_ip, cp, cs->cs_hlen); 540 *bufp = cp; 541 542 /* recompute the ip header checksum */ 543 { 544 register u_int16_t *bp = (u_int16_t *)cp; 545 for (changes = 0; hlen > 0; hlen -= 2) 546 changes += *bp++; 547 changes = (changes & 0xffff) + (changes >> 16); 548 changes = (changes & 0xffff) + (changes >> 16); 549 ((struct ip *)cp)->ip_sum = ~ changes; 550 } 551 return (total_len); 552bad: 553 comp->flags |= SLF_TOSS; 554 INCR(sls_errorin) 555 return (0); 556} 557