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4fdb6e5a | 1 | /*- |
c8dfc989 KB |
2 | * Copyright (c) 1989, 1993 |
3 | * The Regents of the University of California. All rights reserved. | |
b06f22bd | 4 | * |
dbf0c423 | 5 | * %sccs.include.redist.c% |
b06f22bd | 6 | * |
c8dfc989 | 7 | * @(#)slcompress.c 8.1 (Berkeley) %G% |
4fdb6e5a KB |
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: | |
b06f22bd | 15 | * - Initial distribution. |
4fdb6e5a KB |
16 | * |
17 | * static char rcsid[] = | |
18 | * "$Header: slcompress.c,v 1.19 89/12/31 08:52:59 van Exp $"; | |
11b5360c | 19 | */ |
11b5360c | 20 | |
11b5360c SL |
21 | #include <sys/param.h> |
22 | #include <sys/mbuf.h> | |
5548a02f | 23 | |
11b5360c SL |
24 | #include <netinet/in.h> |
25 | #include <netinet/in_systm.h> | |
26 | #include <netinet/ip.h> | |
27 | #include <netinet/tcp.h> | |
28 | ||
5548a02f | 29 | #include <net/slcompress.h> |
11b5360c | 30 | |
b06f22bd | 31 | #ifndef SL_NO_STATS |
1dbf8d66 MK |
32 | #define INCR(counter) ++comp->counter; |
33 | #else | |
34 | #define INCR(counter) | |
35 | #endif | |
11b5360c SL |
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)) | |
b06f22bd SL |
39 | #ifndef KERNEL |
40 | #define ovbcopy bcopy | |
41 | #endif | |
11b5360c | 42 | |
11b5360c SL |
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 | } | |
61 | ||
62 | ||
63 | /* ENCODE encodes a number that is known to be non-zero. ENCODEZ | |
64 | * checks for zero (since zero has to be encoded in the long, 3 byte | |
65 | * form). | |
66 | */ | |
67 | #define ENCODE(n) { \ | |
68 | if ((u_short)(n) >= 256) { \ | |
69 | *cp++ = 0; \ | |
70 | cp[1] = (n); \ | |
71 | cp[0] = (n) >> 8; \ | |
72 | cp += 2; \ | |
73 | } else { \ | |
74 | *cp++ = (n); \ | |
75 | } \ | |
76 | } | |
77 | #define ENCODEZ(n) { \ | |
78 | if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \ | |
79 | *cp++ = 0; \ | |
80 | cp[1] = (n); \ | |
81 | cp[0] = (n) >> 8; \ | |
82 | cp += 2; \ | |
83 | } else { \ | |
84 | *cp++ = (n); \ | |
85 | } \ | |
86 | } | |
87 | ||
88 | #define DECODEL(f) { \ | |
89 | if (*cp == 0) {\ | |
90 | (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \ | |
91 | cp += 3; \ | |
92 | } else { \ | |
93 | (f) = htonl(ntohl(f) + (u_long)*cp++); \ | |
94 | } \ | |
95 | } | |
96 | ||
97 | #define DECODES(f) { \ | |
98 | if (*cp == 0) {\ | |
99 | (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \ | |
100 | cp += 3; \ | |
101 | } else { \ | |
102 | (f) = htons(ntohs(f) + (u_long)*cp++); \ | |
103 | } \ | |
104 | } | |
105 | ||
b06f22bd SL |
106 | #define DECODEU(f) { \ |
107 | if (*cp == 0) {\ | |
108 | (f) = htons((cp[1] << 8) | cp[2]); \ | |
109 | cp += 3; \ | |
110 | } else { \ | |
111 | (f) = htons((u_long)*cp++); \ | |
112 | } \ | |
113 | } | |
114 | ||
8e5d10ee | 115 | u_int |
b06f22bd | 116 | sl_compress_tcp(m, ip, comp, compress_cid) |
11b5360c SL |
117 | struct mbuf *m; |
118 | register struct ip *ip; | |
119 | struct slcompress *comp; | |
b06f22bd | 120 | int compress_cid; |
11b5360c SL |
121 | { |
122 | register struct cstate *cs = comp->last_cs->cs_next; | |
123 | register u_int hlen = ip->ip_hl; | |
124 | register struct tcphdr *oth; | |
125 | register struct tcphdr *th; | |
126 | register u_int deltaS, deltaA; | |
127 | register u_int changes = 0; | |
128 | u_char new_seq[16]; | |
129 | register u_char *cp = new_seq; | |
130 | ||
131 | /* | |
b06f22bd SL |
132 | * Bail if this is an IP fragment or if the TCP packet isn't |
133 | * `compressible' (i.e., ACK isn't set or some other control bit is | |
134 | * set). (We assume that the caller has already made sure the | |
135 | * packet is IP proto TCP). | |
11b5360c | 136 | */ |
b06f22bd | 137 | if ((ip->ip_off & htons(0x3fff)) || m->m_len < 40) |
11b5360c SL |
138 | return (TYPE_IP); |
139 | ||
140 | th = (struct tcphdr *)&((int *)ip)[hlen]; | |
141 | if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) | |
142 | return (TYPE_IP); | |
b06f22bd SL |
143 | /* |
144 | * Packet is compressible -- we're going to send either a | |
145 | * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need | |
146 | * to locate (or create) the connection state. Special case the | |
147 | * most recently used connection since it's most likely to be used | |
148 | * again & we don't have to do any reordering if it's used. | |
149 | */ | |
1dbf8d66 MK |
150 | INCR(sls_packets) |
151 | if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr || | |
152 | ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr || | |
153 | *(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) { | |
11b5360c SL |
154 | /* |
155 | * Wasn't the first -- search for it. | |
156 | * | |
157 | * States are kept in a circularly linked list with | |
b06f22bd | 158 | * last_cs pointing to the end of the list. The |
11b5360c SL |
159 | * list is kept in lru order by moving a state to the |
160 | * head of the list whenever it is referenced. Since | |
161 | * the list is short and, empirically, the connection | |
162 | * we want is almost always near the front, we locate | |
163 | * states via linear search. If we don't find a state | |
b06f22bd | 164 | * for the datagram, the oldest state is (re-)used. |
11b5360c SL |
165 | */ |
166 | register struct cstate *lcs; | |
b06f22bd | 167 | register struct cstate *lastcs = comp->last_cs; |
11b5360c SL |
168 | |
169 | do { | |
170 | lcs = cs; cs = cs->cs_next; | |
1dbf8d66 | 171 | INCR(sls_searches) |
b06f22bd SL |
172 | if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr |
173 | && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr | |
174 | && *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) | |
11b5360c | 175 | goto found; |
b06f22bd | 176 | } while (cs != lastcs); |
11b5360c SL |
177 | |
178 | /* | |
b06f22bd SL |
179 | * Didn't find it -- re-use oldest cstate. Send an |
180 | * uncompressed packet that tells the other side what | |
181 | * connection number we're using for this conversation. | |
182 | * Note that since the state list is circular, the oldest | |
183 | * state points to the newest and we only need to set | |
184 | * last_cs to update the lru linkage. | |
11b5360c | 185 | */ |
b06f22bd | 186 | INCR(sls_misses) |
11b5360c SL |
187 | comp->last_cs = lcs; |
188 | hlen += th->th_off; | |
189 | hlen <<= 2; | |
190 | goto uncompressed; | |
191 | ||
192 | found: | |
193 | /* | |
194 | * Found it -- move to the front on the connection list. | |
195 | */ | |
b06f22bd | 196 | if (cs == lastcs) |
11b5360c SL |
197 | comp->last_cs = lcs; |
198 | else { | |
199 | lcs->cs_next = cs->cs_next; | |
b06f22bd SL |
200 | cs->cs_next = lastcs->cs_next; |
201 | lastcs->cs_next = cs; | |
11b5360c SL |
202 | } |
203 | } | |
204 | ||
205 | /* | |
b06f22bd SL |
206 | * Make sure that only what we expect to change changed. The first |
207 | * line of the `if' checks the IP protocol version, header length & | |
208 | * type of service. The 2nd line checks the "Don't fragment" bit. | |
209 | * The 3rd line checks the time-to-live and protocol (the protocol | |
210 | * check is unnecessary but costless). The 4th line checks the TCP | |
211 | * header length. The 5th line checks IP options, if any. The 6th | |
212 | * line checks TCP options, if any. If any of these things are | |
213 | * different between the previous & current datagram, we send the | |
214 | * current datagram `uncompressed'. | |
11b5360c SL |
215 | */ |
216 | oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen]; | |
217 | deltaS = hlen; | |
218 | hlen += th->th_off; | |
219 | hlen <<= 2; | |
220 | ||
221 | if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] || | |
b06f22bd | 222 | ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] || |
11b5360c SL |
223 | ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] || |
224 | th->th_off != oth->th_off || | |
225 | (deltaS > 5 && | |
226 | BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) || | |
227 | (th->th_off > 5 && | |
228 | BCMP(th + 1, oth + 1, (th->th_off - 5) << 2))) | |
229 | goto uncompressed; | |
230 | ||
231 | /* | |
232 | * Figure out which of the changing fields changed. The | |
233 | * receiver expects changes in the order: urgent, window, | |
234 | * ack, seq (the order minimizes the number of temporaries | |
235 | * needed in this section of code). | |
236 | */ | |
237 | if (th->th_flags & TH_URG) { | |
238 | deltaS = ntohs(th->th_urp); | |
239 | ENCODEZ(deltaS); | |
240 | changes |= NEW_U; | |
241 | } else if (th->th_urp != oth->th_urp) | |
242 | /* argh! URG not set but urp changed -- a sensible | |
243 | * implementation should never do this but RFC793 | |
244 | * doesn't prohibit the change so we have to deal | |
b06f22bd | 245 | * with it. */ |
11b5360c SL |
246 | goto uncompressed; |
247 | ||
248 | if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) { | |
249 | ENCODE(deltaS); | |
250 | changes |= NEW_W; | |
251 | } | |
252 | ||
253 | if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) { | |
254 | if (deltaA > 0xffff) | |
255 | goto uncompressed; | |
256 | ENCODE(deltaA); | |
257 | changes |= NEW_A; | |
258 | } | |
259 | ||
260 | if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) { | |
261 | if (deltaS > 0xffff) | |
262 | goto uncompressed; | |
263 | ENCODE(deltaS); | |
264 | changes |= NEW_S; | |
265 | } | |
266 | ||
267 | switch(changes) { | |
268 | ||
269 | case 0: | |
11b5360c | 270 | /* |
b06f22bd SL |
271 | * Nothing changed. If this packet contains data and the |
272 | * last one didn't, this is probably a data packet following | |
273 | * an ack (normal on an interactive connection) and we send | |
274 | * it compressed. Otherwise it's probably a retransmit, | |
275 | * retransmitted ack or window probe. Send it uncompressed | |
276 | * in case the other side missed the compressed version. | |
11b5360c | 277 | */ |
b06f22bd SL |
278 | if (ip->ip_len != cs->cs_ip.ip_len && |
279 | ntohs(cs->cs_ip.ip_len) == hlen) | |
280 | break; | |
281 | ||
282 | /* (fall through) */ | |
11b5360c SL |
283 | |
284 | case SPECIAL_I: | |
285 | case SPECIAL_D: | |
286 | /* | |
287 | * actual changes match one of our special case encodings -- | |
288 | * send packet uncompressed. | |
289 | */ | |
290 | goto uncompressed; | |
291 | ||
292 | case NEW_S|NEW_A: | |
293 | if (deltaS == deltaA && | |
294 | deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { | |
295 | /* special case for echoed terminal traffic */ | |
296 | changes = SPECIAL_I; | |
297 | cp = new_seq; | |
298 | } | |
299 | break; | |
300 | ||
301 | case NEW_S: | |
302 | if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) { | |
303 | /* special case for data xfer */ | |
304 | changes = SPECIAL_D; | |
305 | cp = new_seq; | |
306 | } | |
307 | break; | |
308 | } | |
309 | ||
310 | deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id); | |
311 | if (deltaS != 1) { | |
312 | ENCODEZ(deltaS); | |
313 | changes |= NEW_I; | |
314 | } | |
315 | if (th->th_flags & TH_PUSH) | |
316 | changes |= TCP_PUSH_BIT; | |
317 | /* | |
318 | * Grab the cksum before we overwrite it below. Then update our | |
319 | * state with this packet's header. | |
320 | */ | |
321 | deltaA = ntohs(th->th_sum); | |
322 | BCOPY(ip, &cs->cs_ip, hlen); | |
323 | ||
324 | /* | |
325 | * We want to use the original packet as our compressed packet. | |
326 | * (cp - new_seq) is the number of bytes we need for compressed | |
327 | * sequence numbers. In addition we need one byte for the change | |
328 | * mask, one for the connection id and two for the tcp checksum. | |
329 | * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how | |
330 | * many bytes of the original packet to toss so subtract the two to | |
331 | * get the new packet size. | |
332 | */ | |
333 | deltaS = cp - new_seq; | |
334 | cp = (u_char *)ip; | |
b06f22bd | 335 | if (compress_cid == 0 || comp->last_xmit != cs->cs_id) { |
11b5360c SL |
336 | comp->last_xmit = cs->cs_id; |
337 | hlen -= deltaS + 4; | |
1dbf8d66 | 338 | cp += hlen; |
1dbf8d66 | 339 | *cp++ = changes | NEW_C; |
11b5360c SL |
340 | *cp++ = cs->cs_id; |
341 | } else { | |
342 | hlen -= deltaS + 3; | |
1dbf8d66 | 343 | cp += hlen; |
1dbf8d66 | 344 | *cp++ = changes; |
11b5360c | 345 | } |
b06f22bd SL |
346 | m->m_len -= hlen; |
347 | m->m_data += hlen; | |
11b5360c SL |
348 | *cp++ = deltaA >> 8; |
349 | *cp++ = deltaA; | |
350 | BCOPY(new_seq, cp, deltaS); | |
1dbf8d66 | 351 | INCR(sls_compressed) |
11b5360c SL |
352 | return (TYPE_COMPRESSED_TCP); |
353 | ||
354 | /* | |
355 | * Update connection state cs & send uncompressed packet ('uncompressed' | |
356 | * means a regular ip/tcp packet but with the 'conversation id' we hope | |
357 | * to use on future compressed packets in the protocol field). | |
358 | */ | |
359 | uncompressed: | |
360 | BCOPY(ip, &cs->cs_ip, hlen); | |
361 | ip->ip_p = cs->cs_id; | |
362 | comp->last_xmit = cs->cs_id; | |
11b5360c SL |
363 | return (TYPE_UNCOMPRESSED_TCP); |
364 | } | |
365 | ||
11b5360c | 366 | |
1dbf8d66 MK |
367 | int |
368 | sl_uncompress_tcp(bufp, len, type, comp) | |
369 | u_char **bufp; | |
370 | int len; | |
371 | u_int type; | |
11b5360c SL |
372 | struct slcompress *comp; |
373 | { | |
374 | register u_char *cp; | |
375 | register u_int hlen, changes; | |
376 | register struct tcphdr *th; | |
377 | register struct cstate *cs; | |
378 | register struct ip *ip; | |
11b5360c SL |
379 | |
380 | switch (type) { | |
381 | ||
382 | case TYPE_UNCOMPRESSED_TCP: | |
1dbf8d66 | 383 | ip = (struct ip *) *bufp; |
b06f22bd SL |
384 | if (ip->ip_p >= MAX_STATES) |
385 | goto bad; | |
11b5360c SL |
386 | cs = &comp->rstate[comp->last_recv = ip->ip_p]; |
387 | comp->flags &=~ SLF_TOSS; | |
388 | ip->ip_p = IPPROTO_TCP; | |
389 | hlen = ip->ip_hl; | |
390 | hlen += ((struct tcphdr *)&((int *)ip)[hlen])->th_off; | |
391 | hlen <<= 2; | |
392 | BCOPY(ip, &cs->cs_ip, hlen); | |
393 | cs->cs_ip.ip_sum = 0; | |
394 | cs->cs_hlen = hlen; | |
1dbf8d66 MK |
395 | INCR(sls_uncompressedin) |
396 | return (len); | |
11b5360c | 397 | |
1dbf8d66 | 398 | default: |
b06f22bd | 399 | goto bad; |
11b5360c SL |
400 | |
401 | case TYPE_COMPRESSED_TCP: | |
11b5360c SL |
402 | break; |
403 | } | |
404 | /* We've got a compressed packet. */ | |
1dbf8d66 MK |
405 | INCR(sls_compressedin) |
406 | cp = *bufp; | |
11b5360c SL |
407 | changes = *cp++; |
408 | if (changes & NEW_C) { | |
409 | /* Make sure the state index is in range, then grab the state. | |
410 | * If we have a good state index, clear the 'discard' flag. */ | |
b06f22bd SL |
411 | if (*cp >= MAX_STATES) |
412 | goto bad; | |
413 | ||
11b5360c SL |
414 | comp->flags &=~ SLF_TOSS; |
415 | comp->last_recv = *cp++; | |
416 | } else { | |
417 | /* this packet has an implicit state index. If we've | |
418 | * had a line error since the last time we got an | |
419 | * explicit state index, we have to toss the packet. */ | |
1dbf8d66 MK |
420 | if (comp->flags & SLF_TOSS) { |
421 | INCR(sls_tossed) | |
422 | return (0); | |
423 | } | |
11b5360c SL |
424 | } |
425 | cs = &comp->rstate[comp->last_recv]; | |
426 | hlen = cs->cs_ip.ip_hl << 2; | |
427 | th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen]; | |
428 | th->th_sum = htons((*cp << 8) | cp[1]); | |
429 | cp += 2; | |
430 | if (changes & TCP_PUSH_BIT) | |
431 | th->th_flags |= TH_PUSH; | |
432 | else | |
433 | th->th_flags &=~ TH_PUSH; | |
434 | ||
435 | switch (changes & SPECIALS_MASK) { | |
436 | case SPECIAL_I: | |
437 | { | |
438 | register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen; | |
439 | th->th_ack = htonl(ntohl(th->th_ack) + i); | |
440 | th->th_seq = htonl(ntohl(th->th_seq) + i); | |
441 | } | |
442 | break; | |
443 | ||
444 | case SPECIAL_D: | |
445 | th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len) | |
446 | - cs->cs_hlen); | |
447 | break; | |
448 | ||
449 | default: | |
450 | if (changes & NEW_U) { | |
451 | th->th_flags |= TH_URG; | |
b06f22bd | 452 | DECODEU(th->th_urp) |
11b5360c SL |
453 | } else |
454 | th->th_flags &=~ TH_URG; | |
455 | if (changes & NEW_W) | |
456 | DECODES(th->th_win) | |
457 | if (changes & NEW_A) | |
458 | DECODEL(th->th_ack) | |
459 | if (changes & NEW_S) | |
460 | DECODEL(th->th_seq) | |
461 | break; | |
462 | } | |
463 | if (changes & NEW_I) { | |
464 | DECODES(cs->cs_ip.ip_id) | |
465 | } else | |
466 | cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1); | |
467 | ||
468 | /* | |
469 | * At this point, cp points to the first byte of data in the | |
1dbf8d66 MK |
470 | * packet. If we're not aligned on a 4-byte boundary, copy the |
471 | * data down so the ip & tcp headers will be aligned. Then back up | |
472 | * cp by the tcp/ip header length to make room for the reconstructed | |
473 | * header (we assume the packet we were handed has enough space to | |
b06f22bd | 474 | * prepend 128 bytes of header). Adjust the length to account for |
1dbf8d66 | 475 | * the new header & fill in the IP total length. |
11b5360c | 476 | */ |
1dbf8d66 | 477 | len -= (cp - *bufp); |
b06f22bd | 478 | if (len < 0) |
1dbf8d66 MK |
479 | /* we must have dropped some characters (crc should detect |
480 | * this but the old slip framing won't) */ | |
b06f22bd SL |
481 | goto bad; |
482 | ||
26fea0bf SL |
483 | if ((int)cp & 3) { |
484 | if (len > 0) | |
b06f22bd | 485 | (void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), len); |
1dbf8d66 MK |
486 | cp = (u_char *)((int)cp &~ 3); |
487 | } | |
488 | cp -= cs->cs_hlen; | |
489 | len += cs->cs_hlen; | |
490 | cs->cs_ip.ip_len = htons(len); | |
491 | BCOPY(&cs->cs_ip, cp, cs->cs_hlen); | |
492 | *bufp = cp; | |
493 | ||
494 | /* recompute the ip header checksum */ | |
495 | { | |
496 | register u_short *bp = (u_short *)cp; | |
497 | for (changes = 0; hlen > 0; hlen -= 2) | |
498 | changes += *bp++; | |
499 | changes = (changes & 0xffff) + (changes >> 16); | |
500 | changes = (changes & 0xffff) + (changes >> 16); | |
501 | ((struct ip *)cp)->ip_sum = ~ changes; | |
502 | } | |
503 | return (len); | |
b06f22bd SL |
504 | bad: |
505 | comp->flags |= SLF_TOSS; | |
506 | INCR(sls_errorin) | |
507 | return (0); | |
11b5360c | 508 | } |