slcompress.c revision 1.5
1 /*- 2 * Copyright (c) 1989 The Regents of the University of California. 3 * 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 7.7 (Berkeley) 5/7/91 34 */ 35 36 /* 37 * Routines to compress and uncompess tcp packets (for transmission 38 * over low speed serial lines. 39 * 40 * Van Jacobson (van (at) helios.ee.lbl.gov), Dec 31, 1989: 41 * - Initial distribution. 42 * 43 * Modified June 1993 by Paul Mackerras, paulus (at) cs.anu.edu.au, 44 * so that the entire packet being decompressed doesn't have 45 * to be in contiguous memory (just the compressed header). 46 * 47 * $Id: slcompress.c,v 1.5 1993/12/18 00:41:06 mycroft Exp $ 48 */ 49 50 #include <sys/types.h> 51 #include <sys/param.h> 52 #include <sys/mbuf.h> 53 54 #include <netinet/in.h> 55 #include <netinet/in_systm.h> 56 #include <netinet/ip.h> 57 #include <netinet/tcp.h> 58 59 #include <net/slcompress.h> 60 61 #ifndef SL_NO_STATS 62 #define INCR(counter) ++comp->counter; 63 #else 64 #define INCR(counter) 65 #endif 66 67 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n)) 68 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n)) 69 #ifndef KERNEL 70 #define ovbcopy bcopy 71 #endif 72 73 74 void 75 sl_compress_init(comp) 76 struct slcompress *comp; 77 { 78 register u_int i; 79 register struct cstate *tstate = comp->tstate; 80 81 bzero((char *)comp, sizeof(*comp)); 82 for (i = MAX_STATES - 1; i > 0; --i) { 83 tstate[i].cs_id = i; 84 tstate[i].cs_next = &tstate[i - 1]; 85 } 86 tstate[0].cs_next = &tstate[MAX_STATES - 1]; 87 tstate[0].cs_id = 0; 88 comp->last_cs = &tstate[0]; 89 comp->last_recv = 255; 90 comp->last_xmit = 255; 91 comp->flags = SLF_TOSS; 92 } 93 94 95 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 96 * checks for zero (since zero has to be encoded in the long, 3 byte 97 * form). 98 */ 99 #define ENCODE(n) { \ 100 if ((u_short)(n) >= 256) { \ 101 *cp++ = 0; \ 102 cp[1] = (n); \ 103 cp[0] = (n) >> 8; \ 104 cp += 2; \ 105 } else { \ 106 *cp++ = (n); \ 107 } \ 108 } 109 #define ENCODEZ(n) { \ 110 if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \ 111 *cp++ = 0; \ 112 cp[1] = (n); \ 113 cp[0] = (n) >> 8; \ 114 cp += 2; \ 115 } else { \ 116 *cp++ = (n); \ 117 } \ 118 } 119 120 #define DECODEL(f) { \ 121 if (*cp == 0) {\ 122 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 123 cp += 3; \ 124 } else { \ 125 (f) = htonl(ntohl(f) + (u_long)*cp++); \ 126 } \ 127 } 128 129 #define DECODES(f) { \ 130 if (*cp == 0) {\ 131 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 132 cp += 3; \ 133 } else { \ 134 (f) = htons(ntohs(f) + (u_long)*cp++); \ 135 } \ 136 } 137 138 #define DECODEU(f) { \ 139 if (*cp == 0) {\ 140 (f) = htons((cp[1] << 8) | cp[2]); \ 141 cp += 3; \ 142 } else { \ 143 (f) = htons((u_long)*cp++); \ 144 } \ 145 } 146 147 148 u_char 149 sl_compress_tcp(m, ip, comp, compress_cid) 150 struct mbuf *m; 151 register struct ip *ip; 152 struct slcompress *comp; 153 int compress_cid; 154 { 155 register struct cstate *cs = comp->last_cs->cs_next; 156 register u_int hlen = ip->ip_hl; 157 register struct tcphdr *oth; 158 register struct tcphdr *th; 159 register u_int deltaS, deltaA; 160 register u_int changes = 0; 161 u_char new_seq[16]; 162 register u_char *cp = new_seq; 163 164 /* 165 * Bail if this is an IP fragment or if the TCP packet isn't 166 * `compressible' (i.e., ACK isn't set or some other control bit is 167 * set). (We assume that the caller has already made sure the 168 * packet is IP proto TCP). 169 */ 170 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 171 return (TYPE_IP); 172 173 th = (struct tcphdr *)&((int *)ip)[hlen]; 174 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 175 return (TYPE_IP); 176 /* 177 * Packet is compressible -- we're going to send either a 178 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 179 * to locate (or create) the connection state. Special case the 180 * most recently used connection since it's most likely to be used 181 * again & we don't have to do any reordering if it's used. 182 */ 183 INCR(sls_packets) 184 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 185 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 186 *(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 187 /* 188 * Wasn't the first -- search for it. 189 * 190 * States are kept in a circularly linked list with 191 * last_cs pointing to the end of the list. The 192 * list is kept in lru order by moving a state to the 193 * head of the list whenever it is referenced. Since 194 * the list is short and, empirically, the connection 195 * we want is almost always near the front, we locate 196 * states via linear search. If we don't find a state 197 * for the datagram, the oldest state is (re-)used. 198 */ 199 register struct cstate *lcs; 200 register struct cstate *lastcs = comp->last_cs; 201 202 do { 203 lcs = cs; cs = cs->cs_next; 204 INCR(sls_searches) 205 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 206 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 207 && *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 208 goto found; 209 } while (cs != lastcs); 210 211 /* 212 * Didn't find it -- re-use oldest cstate. Send an 213 * uncompressed packet that tells the other side what 214 * connection number we're using for this conversation. 215 * Note that since the state list is circular, the oldest 216 * state points to the newest and we only need to set 217 * last_cs to update the lru linkage. 218 */ 219 INCR(sls_misses) 220 comp->last_cs = lcs; 221 hlen += th->th_off; 222 hlen <<= 2; 223 if (hlen > m->m_len) 224 return (TYPE_IP); 225 goto uncompressed; 226 227 found: 228 /* 229 * Found it -- move to the front on the connection list. 230 */ 231 if (cs == lastcs) 232 comp->last_cs = lcs; 233 else { 234 lcs->cs_next = cs->cs_next; 235 cs->cs_next = lastcs->cs_next; 236 lastcs->cs_next = cs; 237 } 238 } 239 240 /* 241 * Make sure that only what we expect to change changed. The first 242 * line of the `if' checks the IP protocol version, header length & 243 * type of service. The 2nd line checks the "Don't fragment" bit. 244 * The 3rd line checks the time-to-live and protocol (the protocol 245 * check is unnecessary but costless). The 4th line checks the TCP 246 * header length. The 5th line checks IP options, if any. The 6th 247 * line checks TCP options, if any. If any of these things are 248 * different between the previous & current datagram, we send the 249 * current datagram `uncompressed'. 250 */ 251 oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen]; 252 deltaS = hlen; 253 hlen += th->th_off; 254 hlen <<= 2; 255 if (hlen > m->m_len) 256 return (TYPE_IP); 257 258 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 th->th_off != oth->th_off || 262 (deltaS > 5 && 263 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 264 (th->th_off > 5 && 265 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 266 goto uncompressed; 267 268 /* 269 * Figure out which of the changing fields changed. The 270 * receiver expects changes in the order: urgent, window, 271 * ack, seq (the order minimizes the number of temporaries 272 * needed in this section of code). 273 */ 274 if (th->th_flags & TH_URG) { 275 deltaS = ntohs(th->th_urp); 276 ENCODEZ(deltaS); 277 changes |= NEW_U; 278 } else if (th->th_urp != oth->th_urp) 279 /* argh! URG not set but urp changed -- a sensible 280 * implementation should never do this but RFC793 281 * doesn't prohibit the change so we have to deal 282 * with it. */ 283 goto uncompressed; 284 285 if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) { 286 ENCODE(deltaS); 287 changes |= NEW_W; 288 } 289 290 if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) { 291 if (deltaA > 0xffff) 292 goto uncompressed; 293 ENCODE(deltaA); 294 changes |= NEW_A; 295 } 296 297 if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) { 298 if (deltaS > 0xffff) 299 goto uncompressed; 300 ENCODE(deltaS); 301 changes |= NEW_S; 302 } 303 304 switch(changes) { 305 306 case 0: 307 /* 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. 314 */ 315 if (ip->ip_len != cs->cs_ip.ip_len && 316 ntohs(cs->cs_ip.ip_len) == hlen) 317 break; 318 319 /* (fall through) */ 320 321 case SPECIAL_I: 322 case SPECIAL_D: 323 /* 324 * actual changes match one of our special case encodings -- 325 * send packet uncompressed. 326 */ 327 goto uncompressed; 328 329 case NEW_S|NEW_A: 330 if (deltaS == deltaA && 331 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 332 /* special case for echoed terminal traffic */ 333 changes = SPECIAL_I; 334 cp = new_seq; 335 } 336 break; 337 338 case NEW_S: 339 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 340 /* special case for data xfer */ 341 changes = SPECIAL_D; 342 cp = new_seq; 343 } 344 break; 345 } 346 347 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 348 if (deltaS != 1) { 349 ENCODEZ(deltaS); 350 changes |= NEW_I; 351 } 352 if (th->th_flags & TH_PUSH) 353 changes |= TCP_PUSH_BIT; 354 /* 355 * Grab the cksum before we overwrite it below. Then update our 356 * state with this packet's header. 357 */ 358 deltaA = ntohs(th->th_sum); 359 BCOPY(ip, &cs->cs_ip, hlen); 360 361 /* 362 * We want to use the original packet as our compressed packet. 363 * (cp - new_seq) is the number of bytes we need for compressed 364 * sequence numbers. In addition we need one byte for the change 365 * mask, one for the connection id and two for the tcp checksum. 366 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 367 * many bytes of the original packet to toss so subtract the two to 368 * get the new packet size. 369 */ 370 deltaS = cp - new_seq; 371 cp = (u_char *)ip; 372 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 373 comp->last_xmit = cs->cs_id; 374 hlen -= deltaS + 4; 375 cp += hlen; 376 *cp++ = changes | NEW_C; 377 *cp++ = cs->cs_id; 378 } else { 379 hlen -= deltaS + 3; 380 cp += hlen; 381 *cp++ = changes; 382 } 383 m->m_len -= hlen; 384 m->m_data += hlen; 385 *cp++ = deltaA >> 8; 386 *cp++ = deltaA; 387 BCOPY(new_seq, cp, deltaS); 388 INCR(sls_compressed) 389 return (TYPE_COMPRESSED_TCP); 390 391 /* 392 * Update connection state cs & send uncompressed packet ('uncompressed' 393 * means a regular ip/tcp packet but with the 'conversation id' we hope 394 * to use on future compressed packets in the protocol field). 395 */ 396 uncompressed: 397 BCOPY(ip, &cs->cs_ip, hlen); 398 ip->ip_p = cs->cs_id; 399 comp->last_xmit = cs->cs_id; 400 return (TYPE_UNCOMPRESSED_TCP); 401 } 402 403 404 int 405 sl_uncompress_tcp(bufp, len, type, comp) 406 u_char **bufp; 407 int len; 408 u_int type; 409 struct slcompress *comp; 410 { 411 return sl_uncompress_tcp_part(bufp, len, len, type, comp); 412 } 413 414 415 /* 416 * Uncompress a packet of total length total_len. The first buflen 417 * bytes are at *bufp; this must include the entire (compressed or 418 * uncompressed) TCP/IP header. In addition, there must be enough 419 * clear space before *bufp to build a full-length TCP/IP header. 420 */ 421 int 422 sl_uncompress_tcp_part(bufp, buflen, total_len, type, comp) 423 u_char **bufp; 424 int buflen, total_len; 425 u_int type; 426 struct slcompress *comp; 427 { 428 register u_char *cp; 429 register u_int hlen, changes; 430 register struct tcphdr *th; 431 register struct cstate *cs; 432 register struct ip *ip; 433 434 switch (type) { 435 436 case TYPE_UNCOMPRESSED_TCP: 437 ip = (struct ip *) *bufp; 438 if (ip->ip_p >= MAX_STATES) 439 goto bad; 440 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 441 comp->flags &=~ SLF_TOSS; 442 ip->ip_p = IPPROTO_TCP; 443 hlen = ip->ip_hl; 444 hlen += ((struct tcphdr *)&((int *)ip)[hlen])->th_off; 445 hlen <<= 2; 446 BCOPY(ip, &cs->cs_ip, hlen); 447 cs->cs_ip.ip_sum = 0; 448 cs->cs_hlen = hlen; 449 INCR(sls_uncompressedin) 450 return (total_len); 451 452 default: 453 goto bad; 454 455 case TYPE_COMPRESSED_TCP: 456 break; 457 } 458 /* We've got a compressed packet. */ 459 INCR(sls_compressedin) 460 cp = *bufp; 461 changes = *cp++; 462 if (changes & NEW_C) { 463 /* Make sure the state index is in range, then grab the state. 464 * If we have a good state index, clear the 'discard' flag. */ 465 if (*cp >= MAX_STATES) 466 goto bad; 467 468 comp->flags &=~ SLF_TOSS; 469 comp->last_recv = *cp++; 470 } else { 471 /* this packet has an implicit state index. If we've 472 * had a line error since the last time we got an 473 * explicit state index, we have to toss the packet. */ 474 if (comp->flags & SLF_TOSS) { 475 INCR(sls_tossed) 476 return (0); 477 } 478 } 479 cs = &comp->rstate[comp->last_recv]; 480 hlen = cs->cs_ip.ip_hl << 2; 481 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 482 th->th_sum = htons((*cp << 8) | cp[1]); 483 cp += 2; 484 if (changes & TCP_PUSH_BIT) 485 th->th_flags |= TH_PUSH; 486 else 487 th->th_flags &=~ TH_PUSH; 488 489 switch (changes & SPECIALS_MASK) { 490 case SPECIAL_I: 491 { 492 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 493 th->th_ack = htonl(ntohl(th->th_ack) + i); 494 th->th_seq = htonl(ntohl(th->th_seq) + i); 495 } 496 break; 497 498 case SPECIAL_D: 499 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 500 - cs->cs_hlen); 501 break; 502 503 default: 504 if (changes & NEW_U) { 505 th->th_flags |= TH_URG; 506 DECODEU(th->th_urp) 507 } else 508 th->th_flags &=~ TH_URG; 509 if (changes & NEW_W) 510 DECODES(th->th_win) 511 if (changes & NEW_A) 512 DECODEL(th->th_ack) 513 if (changes & NEW_S) 514 DECODEL(th->th_seq) 515 break; 516 } 517 if (changes & NEW_I) { 518 DECODES(cs->cs_ip.ip_id) 519 } else 520 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 521 522 /* 523 * At this point, cp points to the first byte of data in the 524 * packet. If we're not aligned on a 4-byte boundary, copy the 525 * data down so the ip & tcp headers will be aligned. Then back up 526 * cp by the tcp/ip header length to make room for the reconstructed 527 * header (we assume the packet we were handed has enough space to 528 * prepend 128 bytes of header). Adjust the length to account for 529 * the new header & fill in the IP total length. 530 */ 531 buflen -= (cp - *bufp); 532 total_len -= (cp - *bufp); 533 if (buflen < 0) 534 /* we must have dropped some characters (crc should detect 535 * this but the old slip framing won't) */ 536 goto bad; 537 538 if ((int)cp & 3) { 539 if (buflen > 0) 540 (void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), buflen); 541 cp = (u_char *)((int)cp &~ 3); 542 } 543 cp -= cs->cs_hlen; 544 total_len += cs->cs_hlen; 545 cs->cs_ip.ip_len = htons(total_len); 546 BCOPY(&cs->cs_ip, cp, cs->cs_hlen); 547 *bufp = cp; 548 549 /* recompute the ip header checksum */ 550 { 551 register u_short *bp = (u_short *)cp; 552 for (changes = 0; hlen > 0; hlen -= 2) 553 changes += *bp++; 554 changes = (changes & 0xffff) + (changes >> 16); 555 changes = (changes & 0xffff) + (changes >> 16); 556 ((struct ip *)cp)->ip_sum = ~ changes; 557 } 558 return (total_len); 559 bad: 560 comp->flags |= SLF_TOSS; 561 INCR(sls_errorin) 562 return (0); 563 } 564
Indexes created Wed Sep 24 05:09:52 GMT 2025