1 /*- 2 * Copyright (c) 1989, 1993, 1994 3 * The Regents of the University of California. All rights reserved. 4 * 5 * %sccs.include.redist.c% 6 * 7 * @(#)slcompress.c 8.2 (Berkeley) 04/16/94 8 */ 9 10 /* 11 * Routines to compress and uncompess tcp packets (for transmission 12 * over low speed serial lines. 13 * 14 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989: 15 * - Initial distribution. 16 * 17 * static char rcsid[] = 18 * "$Header: slcompress.c,v 1.19 89/12/31 08:52:59 van Exp $"; 19 */ 20 21 #include <sys/param.h> 22 #include <sys/mbuf.h> 23 24 #include <netinet/in.h> 25 #include <netinet/in_systm.h> 26 #include <netinet/ip.h> 27 #include <netinet/tcp.h> 28 29 #include <net/slcompress.h> 30 31 #ifndef SL_NO_STATS 32 #define INCR(counter) ++comp->counter; 33 #else 34 #define INCR(counter) 35 #endif 36 37 #define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n)) 38 #define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n)) 39 #ifndef KERNEL 40 #define ovbcopy bcopy 41 #endif 42 43 void 44 sl_compress_init(comp) 45 struct slcompress *comp; 46 { 47 register u_int i; 48 register struct cstate *tstate = comp->tstate; 49 50 bzero((char *)comp, sizeof(*comp)); 51 for (i = MAX_STATES - 1; i > 0; --i) { 52 tstate[i].cs_id = i; 53 tstate[i].cs_next = &tstate[i - 1]; 54 } 55 tstate[0].cs_next = &tstate[MAX_STATES - 1]; 56 tstate[0].cs_id = 0; 57 comp->last_cs = &tstate[0]; 58 comp->last_recv = 255; 59 comp->last_xmit = 255; 60 comp->flags = SLF_TOSS; 61 } 62 63 64 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ 65 * checks for zero (since zero has to be encoded in the long, 3 byte 66 * form). 67 */ 68 #define ENCODE(n) { \ 69 if ((u_short)(n) >= 256) { \ 70 *cp++ = 0; \ 71 cp[1] = (n); \ 72 cp[0] = (n) >> 8; \ 73 cp += 2; \ 74 } else { \ 75 *cp++ = (n); \ 76 } \ 77 } 78 #define ENCODEZ(n) { \ 79 if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \ 80 *cp++ = 0; \ 81 cp[1] = (n); \ 82 cp[0] = (n) >> 8; \ 83 cp += 2; \ 84 } else { \ 85 *cp++ = (n); \ 86 } \ 87 } 88 89 #define DECODEL(f) { \ 90 if (*cp == 0) {\ 91 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ 92 cp += 3; \ 93 } else { \ 94 (f) = htonl(ntohl(f) + (u_long)*cp++); \ 95 } \ 96 } 97 98 #define DECODES(f) { \ 99 if (*cp == 0) {\ 100 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ 101 cp += 3; \ 102 } else { \ 103 (f) = htons(ntohs(f) + (u_long)*cp++); \ 104 } \ 105 } 106 107 #define DECODEU(f) { \ 108 if (*cp == 0) {\ 109 (f) = htons((cp[1] << 8) | cp[2]); \ 110 cp += 3; \ 111 } else { \ 112 (f) = htons((u_long)*cp++); \ 113 } \ 114 } 115 116 u_int 117 sl_compress_tcp(m, ip, comp, compress_cid) 118 struct mbuf *m; 119 register struct ip *ip; 120 struct slcompress *comp; 121 int compress_cid; 122 { 123 register struct cstate *cs = comp->last_cs->cs_next; 124 register u_int hlen = ip->ip_hl; 125 register struct tcphdr *oth; 126 register struct tcphdr *th; 127 register u_int deltaS, deltaA; 128 register u_int changes = 0; 129 u_char new_seq[16]; 130 register u_char *cp = new_seq; 131 132 /* 133 * Bail if this is an IP fragment or if the TCP packet isn't 134 * `compressible' (i.e., ACK isn't set or some other control bit is 135 * set). (We assume that the caller has already made sure the 136 * packet is IP proto TCP). 137 */ 138 if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) 139 return (TYPE_IP); 140 141 th = (struct tcphdr *)&((int *)ip)[hlen]; 142 if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) 143 return (TYPE_IP); 144 /* 145 * Packet is compressible -- we're going to send either a 146 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need 147 * to locate (or create) the connection state. Special case the 148 * most recently used connection since it's most likely to be used 149 * again & we don't have to do any reordering if it's used. 150 */ 151 INCR(sls_packets) 152 if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || 153 ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || 154 *(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { 155 /* 156 * Wasn't the first -- search for it. 157 * 158 * States are kept in a circularly linked list with 159 * last_cs pointing to the end of the list. The 160 * list is kept in lru order by moving a state to the 161 * head of the list whenever it is referenced. Since 162 * the list is short and, empirically, the connection 163 * we want is almost always near the front, we locate 164 * states via linear search. If we don't find a state 165 * for the datagram, the oldest state is (re-)used. 166 */ 167 register struct cstate *lcs; 168 register struct cstate *lastcs = comp->last_cs; 169 170 do { 171 lcs = cs; cs = cs->cs_next; 172 INCR(sls_searches) 173 if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr 174 && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr 175 && *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) 176 goto found; 177 } while (cs != lastcs); 178 179 /* 180 * Didn't find it -- re-use oldest cstate. Send an 181 * uncompressed packet that tells the other side what 182 * connection number we're using for this conversation. 183 * Note that since the state list is circular, the oldest 184 * state points to the newest and we only need to set 185 * last_cs to update the lru linkage. 186 */ 187 INCR(sls_misses) 188 comp->last_cs = lcs; 189 hlen += th->th_off; 190 hlen <<= 2; 191 goto uncompressed; 192 193 found: 194 /* 195 * Found it -- move to the front on the connection list. 196 */ 197 if (cs == lastcs) 198 comp->last_cs = lcs; 199 else { 200 lcs->cs_next = cs->cs_next; 201 cs->cs_next = lastcs->cs_next; 202 lastcs->cs_next = cs; 203 } 204 } 205 206 /* 207 * Make sure that only what we expect to change changed. The first 208 * line of the `if' checks the IP protocol version, header length & 209 * type of service. The 2nd line checks the "Don't fragment" bit. 210 * The 3rd line checks the time-to-live and protocol (the protocol 211 * check is unnecessary but costless). The 4th line checks the TCP 212 * header length. The 5th line checks IP options, if any. The 6th 213 * line checks TCP options, if any. If any of these things are 214 * different between the previous & current datagram, we send the 215 * current datagram `uncompressed'. 216 */ 217 oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen]; 218 deltaS = hlen; 219 hlen += th->th_off; 220 hlen <<= 2; 221 222 if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] || 223 ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] || 224 ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] || 225 th->th_off != oth->th_off || 226 (deltaS > 5 && 227 BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || 228 (th->th_off > 5 && 229 BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) 230 goto uncompressed; 231 232 /* 233 * Figure out which of the changing fields changed. The 234 * receiver expects changes in the order: urgent, window, 235 * ack, seq (the order minimizes the number of temporaries 236 * needed in this section of code). 237 */ 238 if (th->th_flags & TH_URG) { 239 deltaS = ntohs(th->th_urp); 240 ENCODEZ(deltaS); 241 changes |= NEW_U; 242 } else if (th->th_urp != oth->th_urp) 243 /* argh! URG not set but urp changed -- a sensible 244 * implementation should never do this but RFC793 245 * doesn't prohibit the change so we have to deal 246 * with it. */ 247 goto uncompressed; 248 249 if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) { 250 ENCODE(deltaS); 251 changes |= NEW_W; 252 } 253 254 if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) { 255 if (deltaA > 0xffff) 256 goto uncompressed; 257 ENCODE(deltaA); 258 changes |= NEW_A; 259 } 260 261 if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) { 262 if (deltaS > 0xffff) 263 goto uncompressed; 264 ENCODE(deltaS); 265 changes |= NEW_S; 266 } 267 268 switch(changes) { 269 270 case 0: 271 /* 272 * Nothing changed. If this packet contains data and the 273 * last one didn't, this is probably a data packet following 274 * an ack (normal on an interactive connection) and we send 275 * it compressed. Otherwise it's probably a retransmit, 276 * retransmitted ack or window probe. Send it uncompressed 277 * in case the other side missed the compressed version. 278 */ 279 if (ip->ip_len != cs->cs_ip.ip_len && 280 ntohs(cs->cs_ip.ip_len) == hlen) 281 break; 282 283 /* (fall through) */ 284 285 case SPECIAL_I: 286 case SPECIAL_D: 287 /* 288 * actual changes match one of our special case encodings -- 289 * send packet uncompressed. 290 */ 291 goto uncompressed; 292 293 case NEW_S|NEW_A: 294 if (deltaS == deltaA && 295 deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 296 /* special case for echoed terminal traffic */ 297 changes = SPECIAL_I; 298 cp = new_seq; 299 } 300 break; 301 302 case NEW_S: 303 if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { 304 /* special case for data xfer */ 305 changes = SPECIAL_D; 306 cp = new_seq; 307 } 308 break; 309 } 310 311 deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); 312 if (deltaS != 1) { 313 ENCODEZ(deltaS); 314 changes |= NEW_I; 315 } 316 if (th->th_flags & TH_PUSH) 317 changes |= TCP_PUSH_BIT; 318 /* 319 * Grab the cksum before we overwrite it below. Then update our 320 * state with this packet's header. 321 */ 322 deltaA = ntohs(th->th_sum); 323 BCOPY(ip, &cs->cs_ip, hlen); 324 325 /* 326 * We want to use the original packet as our compressed packet. 327 * (cp - new_seq) is the number of bytes we need for compressed 328 * sequence numbers. In addition we need one byte for the change 329 * mask, one for the connection id and two for the tcp checksum. 330 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how 331 * many bytes of the original packet to toss so subtract the two to 332 * get the new packet size. 333 */ 334 deltaS = cp - new_seq; 335 cp = (u_char *)ip; 336 if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { 337 comp->last_xmit = cs->cs_id; 338 hlen -= deltaS + 4; 339 cp += hlen; 340 *cp++ = changes | NEW_C; 341 *cp++ = cs->cs_id; 342 } else { 343 hlen -= deltaS + 3; 344 cp += hlen; 345 *cp++ = changes; 346 } 347 m->m_len -= hlen; 348 m->m_data += hlen; 349 *cp++ = deltaA >> 8; 350 *cp++ = deltaA; 351 BCOPY(new_seq, cp, deltaS); 352 INCR(sls_compressed) 353 return (TYPE_COMPRESSED_TCP); 354 355 /* 356 * Update connection state cs & send uncompressed packet ('uncompressed' 357 * means a regular ip/tcp packet but with the 'conversation id' we hope 358 * to use on future compressed packets in the protocol field). 359 */ 360 uncompressed: 361 BCOPY(ip, &cs->cs_ip, hlen); 362 ip->ip_p = cs->cs_id; 363 comp->last_xmit = cs->cs_id; 364 return (TYPE_UNCOMPRESSED_TCP); 365 } 366 367 368 int 369 sl_uncompress_tcp(bufp, len, type, comp) 370 u_char **bufp; 371 int len; 372 u_int type; 373 struct slcompress *comp; 374 { 375 register u_char *cp; 376 register u_int hlen, changes; 377 register struct tcphdr *th; 378 register struct cstate *cs; 379 register struct ip *ip; 380 381 switch (type) { 382 383 case TYPE_UNCOMPRESSED_TCP: 384 ip = (struct ip *) *bufp; 385 if (ip->ip_p >= MAX_STATES) 386 goto bad; 387 cs = &comp->rstate[comp->last_recv = ip->ip_p]; 388 comp->flags &=~ SLF_TOSS; 389 ip->ip_p = IPPROTO_TCP; 390 hlen = ip->ip_hl; 391 hlen += ((struct tcphdr *)&((int *)ip)[hlen])->th_off; 392 hlen <<= 2; 393 BCOPY(ip, &cs->cs_ip, hlen); 394 cs->cs_ip.ip_sum = 0; 395 cs->cs_hlen = hlen; 396 INCR(sls_uncompressedin) 397 return (len); 398 399 default: 400 goto bad; 401 402 case TYPE_COMPRESSED_TCP: 403 break; 404 } 405 /* We've got a compressed packet. */ 406 INCR(sls_compressedin) 407 cp = *bufp; 408 changes = *cp++; 409 if (changes & NEW_C) { 410 /* Make sure the state index is in range, then grab the state. 411 * If we have a good state index, clear the 'discard' flag. */ 412 if (*cp >= MAX_STATES) 413 goto bad; 414 415 comp->flags &=~ SLF_TOSS; 416 comp->last_recv = *cp++; 417 } else { 418 /* this packet has an implicit state index. If we've 419 * had a line error since the last time we got an 420 * explicit state index, we have to toss the packet. */ 421 if (comp->flags & SLF_TOSS) { 422 INCR(sls_tossed) 423 return (0); 424 } 425 } 426 cs = &comp->rstate[comp->last_recv]; 427 hlen = cs->cs_ip.ip_hl << 2; 428 th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; 429 th->th_sum = htons((*cp << 8) | cp[1]); 430 cp += 2; 431 if (changes & TCP_PUSH_BIT) 432 th->th_flags |= TH_PUSH; 433 else 434 th->th_flags &=~ TH_PUSH; 435 436 switch (changes & SPECIALS_MASK) { 437 case SPECIAL_I: 438 { 439 register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; 440 th->th_ack = htonl(ntohl(th->th_ack) + i); 441 th->th_seq = htonl(ntohl(th->th_seq) + i); 442 } 443 break; 444 445 case SPECIAL_D: 446 th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) 447 - cs->cs_hlen); 448 break; 449 450 default: 451 if (changes & NEW_U) { 452 th->th_flags |= TH_URG; 453 DECODEU(th->th_urp) 454 } else 455 th->th_flags &=~ TH_URG; 456 if (changes & NEW_W) 457 DECODES(th->th_win) 458 if (changes & NEW_A) 459 DECODEL(th->th_ack) 460 if (changes & NEW_S) 461 DECODEL(th->th_seq) 462 break; 463 } 464 if (changes & NEW_I) { 465 DECODES(cs->cs_ip.ip_id) 466 } else 467 cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); 468 469 /* 470 * At this point, cp points to the first byte of data in the 471 * packet. If we're not aligned on a 4-byte boundary, copy the 472 * data down so the ip & tcp headers will be aligned. Then back up 473 * cp by the tcp/ip header length to make room for the reconstructed 474 * header (we assume the packet we were handed has enough space to 475 * prepend 128 bytes of header). Adjust the length to account for 476 * the new header & fill in the IP total length. 477 */ 478 len -= (cp - *bufp); 479 if (len < 0) 480 /* we must have dropped some characters (crc should detect 481 * this but the old slip framing won't) */ 482 goto bad; 483 484 if ((int)cp & 3) { 485 if (len > 0) 486 (void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), len); 487 cp = (u_char *)((int)cp &~ 3); 488 } 489 cp -= cs->cs_hlen; 490 len += cs->cs_hlen; 491 cs->cs_ip.ip_len = htons(len); 492 BCOPY(&cs->cs_ip, cp, cs->cs_hlen); 493 *bufp = cp; 494 495 /* recompute the ip header checksum */ 496 { 497 register u_short *bp = (u_short *)cp; 498 for (changes = 0; hlen > 0; hlen -= 2) 499 changes += *bp++; 500 changes = (changes & 0xffff) + (changes >> 16); 501 changes = (changes & 0xffff) + (changes >> 16); 502 ((struct ip *)cp)->ip_sum = ~ changes; 503 } 504 return (len); 505 bad: 506 comp->flags |= SLF_TOSS; 507 INCR(sls_errorin) 508 return (0); 509 } 510