slcompress.c revision 8876
1/*- 2 * Copyright (c) 1989, 1993, 1994 3 * The Regents of the University of California. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. All advertising materials mentioning features or use of this software 14 * must display the following acknowledgement: 15 * This product includes software developed by the University of 16 * California, Berkeley and its contributors. 17 * 4. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 * 33 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94 34 * $Id: slcompress.c,v 1.4 1994/10/08 22:38:27 phk Exp $ 35 */ 36 37/* 38 * Routines to compress and uncompess tcp packets (for transmission 39 * over low speed serial lines. 40 * 41 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 42 * - Initial distribution. 43 * 44 */ 45 46#include <sys/param.h> 47#include <sys/systm.h> 48#include <sys/mbuf.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 69void 70sl_compress_init(comp) 71 struct slcompress *comp; 72{ 73 register u_int i; 74 register struct cstate *tstate = comp->tstate; 75 76 bzero((char *)comp, sizeof(*comp)); 77 for (i = MAX_STATES - 1; i > 0; --i) { 78 tstate[i].cs_id = i; 79 tstate[i].cs_next = &tstate[i - 1]; 80 } 81 tstate[0].cs_next = &tstate[MAX_STATES - 1]; 82 tstate[0].cs_id = 0; 83 comp->last_cs = &tstate[0]; 84 comp->last_recv = 255; 85 comp->last_xmit = 255; 86 comp->flags = SLF_TOSS; 87} 88 89 90/* ENCODE encodes a number that is known to be non-zero. ENCODEZ 91 * checks for zero (since zero has to be encoded in the long, 3 byte 92 * form). 93 */ 94#define ENCODE(n) { \ 95 if ((u_short)(n) >= 256) { \ 96 *cp++ = 0; \ 97 cp[1] = (n); \ 98 cp[0] = (n) >> 8; \ 99 cp += 2; \ 100 } else { \ 101 *cp++ = (n); \ 102 } \ 103} 104#define ENCODEZ(n) { \ 105 if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \ 106 *cp++ = 0; \ 107 cp[1] = (n); \ 108 cp[0] = (n) >> 8; \ 109 cp += 2; \ 110 } else { \ 111 *cp++ = (n); \ 112 } \ 113} 114 115#define DECODEL(f) { \ 116 if (*cp == 0) {\ 117 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 118 cp += 3; \ 119 } else { \ 120 (f) = htonl(ntohl(f) + (u_long)*cp++); \ 121 } \ 122} 123 124#define DECODES(f) { \ 125 if (*cp == 0) {\ 126 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 127 cp += 3; \ 128 } else { \ 129 (f) = htons(ntohs(f) + (u_long)*cp++); \ 130 } \ 131} 132 133#define DECODEU(f) { \ 134 if (*cp == 0) {\ 135 (f) = htons((cp[1] << 8) | cp[2]); \ 136 cp += 3; \ 137 } else { \ 138 (f) = htons((u_long)*cp++); \ 139 } \ 140} 141 142u_int 143sl_compress_tcp(m, ip, comp, compress_cid) 144 struct mbuf *m; 145 register struct ip *ip; 146 struct slcompress *comp; 147 int compress_cid; 148{ 149 register struct cstate *cs = comp->last_cs->cs_next; 150 register u_int hlen = ip->ip_hl; 151 register struct tcphdr *oth; 152 register struct tcphdr *th; 153 register u_int deltaS, deltaA; 154 register u_int changes = 0; 155 u_char new_seq[16]; 156 register u_char *cp = new_seq; 157 158 /* 159 * Bail if this is an IP fragment or if the TCP packet isn't 160 * `compressible' (i.e., ACK isn't set or some other control bit is 161 * set). (We assume that the caller has already made sure the 162 * packet is IP proto TCP). 163 */ 164 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 165 return (TYPE_IP); 166 167 th = (struct tcphdr *)&((int *)ip)[hlen]; 168 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 169 return (TYPE_IP); 170 /* 171 * Packet is compressible -- we're going to send either a 172 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 173 * to locate (or create) the connection state. Special case the 174 * most recently used connection since it's most likely to be used 175 * again & we don't have to do any reordering if it's used. 176 */ 177 INCR(sls_packets) 178 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 179 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 180 *(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 181 /* 182 * Wasn't the first -- search for it. 183 * 184 * States are kept in a circularly linked list with 185 * last_cs pointing to the end of the list. The 186 * list is kept in lru order by moving a state to the 187 * head of the list whenever it is referenced. Since 188 * the list is short and, empirically, the connection 189 * we want is almost always near the front, we locate 190 * states via linear search. If we don't find a state 191 * for the datagram, the oldest state is (re-)used. 192 */ 193 register struct cstate *lcs; 194 register struct cstate *lastcs = comp->last_cs; 195 196 do { 197 lcs = cs; cs = cs->cs_next; 198 INCR(sls_searches) 199 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 200 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 201 && *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 202 goto found; 203 } while (cs != lastcs); 204 205 /* 206 * Didn't find it -- re-use oldest cstate. Send an 207 * uncompressed packet that tells the other side what 208 * connection number we're using for this conversation. 209 * Note that since the state list is circular, the oldest 210 * state points to the newest and we only need to set 211 * last_cs to update the lru linkage. 212 */ 213 INCR(sls_misses) 214 comp->last_cs = lcs; 215 hlen += th->th_off; 216 hlen <<= 2; 217 goto uncompressed; 218 219 found: 220 /* 221 * Found it -- move to the front on the connection list. 222 */ 223 if (cs == lastcs) 224 comp->last_cs = lcs; 225 else { 226 lcs->cs_next = cs->cs_next; 227 cs->cs_next = lastcs->cs_next; 228 lastcs->cs_next = cs; 229 } 230 } 231 232 /* 233 * Make sure that only what we expect to change changed. The first 234 * line of the `if' checks the IP protocol version, header length & 235 * type of service. The 2nd line checks the "Don't fragment" bit. 236 * The 3rd line checks the time-to-live and protocol (the protocol 237 * check is unnecessary but costless). The 4th line checks the TCP 238 * header length. The 5th line checks IP options, if any. The 6th 239 * line checks TCP options, if any. If any of these things are 240 * different between the previous & current datagram, we send the 241 * current datagram `uncompressed'. 242 */ 243 oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen]; 244 deltaS = hlen; 245 hlen += th->th_off; 246 hlen <<= 2; 247 248 if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] || 249 ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] || 250 ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] || 251 th->th_off != oth->th_off || 252 (deltaS > 5 && 253 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 254 (th->th_off > 5 && 255 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 256 goto uncompressed; 257 258 /* 259 * Figure out which of the changing fields changed. The 260 * receiver expects changes in the order: urgent, window, 261 * ack, seq (the order minimizes the number of temporaries 262 * needed in this section of code). 263 */ 264 if (th->th_flags & TH_URG) { 265 deltaS = ntohs(th->th_urp); 266 ENCODEZ(deltaS); 267 changes |= NEW_U; 268 } else if (th->th_urp != oth->th_urp) 269 /* argh! URG not set but urp changed -- a sensible 270 * implementation should never do this but RFC793 271 * doesn't prohibit the change so we have to deal 272 * with it. */ 273 goto uncompressed; 274 275 deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win)); 276 if (deltaS) { 277 ENCODE(deltaS); 278 changes |= NEW_W; 279 } 280 281 deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack); 282 if (deltaA) { 283 if (deltaA > 0xffff) 284 goto uncompressed; 285 ENCODE(deltaA); 286 changes |= NEW_A; 287 } 288 289 deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq); 290 if (deltaS) { 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 register u_char *cp; 405 register u_int hlen, changes; 406 register struct tcphdr *th; 407 register struct cstate *cs; 408 register struct ip *ip; 409 410 switch (type) { 411 412 case TYPE_UNCOMPRESSED_TCP: 413 ip = (struct ip *) *bufp; 414 if (ip->ip_p >= MAX_STATES) 415 goto bad; 416 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 417 comp->flags &=~ SLF_TOSS; 418 ip->ip_p = IPPROTO_TCP; 419 hlen = ip->ip_hl; 420 hlen += ((struct tcphdr *)&((int *)ip)[hlen])->th_off; 421 hlen <<= 2; 422 BCOPY(ip, &cs->cs_ip, hlen); 423 cs->cs_ip.ip_sum = 0; 424 cs->cs_hlen = hlen; 425 INCR(sls_uncompressedin) 426 return (len); 427 428 default: 429 goto bad; 430 431 case TYPE_COMPRESSED_TCP: 432 break; 433 } 434 /* We've got a compressed packet. */ 435 INCR(sls_compressedin) 436 cp = *bufp; 437 changes = *cp++; 438 if (changes & NEW_C) { 439 /* Make sure the state index is in range, then grab the state. 440 * If we have a good state index, clear the 'discard' flag. */ 441 if (*cp >= MAX_STATES) 442 goto bad; 443 444 comp->flags &=~ SLF_TOSS; 445 comp->last_recv = *cp++; 446 } else { 447 /* this packet has an implicit state index. If we've 448 * had a line error since the last time we got an 449 * explicit state index, we have to toss the packet. */ 450 if (comp->flags & SLF_TOSS) { 451 INCR(sls_tossed) 452 return (0); 453 } 454 } 455 cs = &comp->rstate[comp->last_recv]; 456 hlen = cs->cs_ip.ip_hl << 2; 457 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 458 th->th_sum = htons((*cp << 8) | cp[1]); 459 cp += 2; 460 if (changes & TCP_PUSH_BIT) 461 th->th_flags |= TH_PUSH; 462 else 463 th->th_flags &=~ TH_PUSH; 464 465 switch (changes & SPECIALS_MASK) { 466 case SPECIAL_I: 467 { 468 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 469 th->th_ack = htonl(ntohl(th->th_ack) + i); 470 th->th_seq = htonl(ntohl(th->th_seq) + i); 471 } 472 break; 473 474 case SPECIAL_D: 475 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 476 - cs->cs_hlen); 477 break; 478 479 default: 480 if (changes & NEW_U) { 481 th->th_flags |= TH_URG; 482 DECODEU(th->th_urp) 483 } else 484 th->th_flags &=~ TH_URG; 485 if (changes & NEW_W) 486 DECODES(th->th_win) 487 if (changes & NEW_A) 488 DECODEL(th->th_ack) 489 if (changes & NEW_S) 490 DECODEL(th->th_seq) 491 break; 492 } 493 if (changes & NEW_I) { 494 DECODES(cs->cs_ip.ip_id) 495 } else 496 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 497 498 /* 499 * At this point, cp points to the first byte of data in the 500 * packet. If we're not aligned on a 4-byte boundary, copy the 501 * data down so the ip & tcp headers will be aligned. Then back up 502 * cp by the tcp/ip header length to make room for the reconstructed 503 * header (we assume the packet we were handed has enough space to 504 * prepend 128 bytes of header). Adjust the length to account for 505 * the new header & fill in the IP total length. 506 */ 507 len -= (cp - *bufp); 508 if (len < 0) 509 /* we must have dropped some characters (crc should detect 510 * this but the old slip framing won't) */ 511 goto bad; 512 513 if ((int)cp & 3) { 514 if (len > 0) 515 (void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), len); 516 cp = (u_char *)((int)cp &~ 3); 517 } 518 cp -= cs->cs_hlen; 519 len += cs->cs_hlen; 520 cs->cs_ip.ip_len = htons(len); 521 BCOPY(&cs->cs_ip, cp, cs->cs_hlen); 522 *bufp = cp; 523 524 /* recompute the ip header checksum */ 525 { 526 register u_short *bp = (u_short *)cp; 527 for (changes = 0; hlen > 0; hlen -= 2) 528 changes += *bp++; 529 changes = (changes & 0xffff) + (changes >> 16); 530 changes = (changes & 0xffff) + (changes >> 16); 531 ((struct ip *)cp)->ip_sum = ~ changes; 532 } 533 return (len); 534bad: 535 comp->flags |= SLF_TOSS; 536 INCR(sls_errorin) 537 return (0); 538} 539