2 * Copyright (c) 1989, 1993, 1994
3 * The Regents of the University of California. All rights reserved.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
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 * 4. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * @(#)slcompress.c 8.2 (Berkeley) 4/16/94
34 * Routines to compress and uncompess tcp packets (for transmission
35 * over low speed serial lines.
37 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
38 * - Initial distribution.
42 #include <sys/param.h>
44 #include <sys/systm.h>
46 #include <netinet/in.h>
47 #include <netinet/in_systm.h>
48 #include <netinet/ip.h>
49 #include <netinet/tcp.h>
51 #include <net/slcompress.h>
54 #define INCR(counter) ++comp->counter;
59 #define BCMP(p1, p2, n) bcmp((void *)(p1), (void *)(p2), (int)(n))
60 #define BCOPY(p1, p2, n) bcopy((void *)(p1), (void *)(p2), (int)(n))
63 sl_compress_init(comp
, max_state
)
64 struct slcompress
*comp
;
68 register struct cstate
*tstate
= comp
->tstate
;
70 if (max_state
== -1) {
71 max_state
= MAX_STATES
- 1;
72 bzero((char *)comp
, sizeof(*comp
));
74 /* Don't reset statistics */
75 bzero((char *)comp
->tstate
, sizeof(comp
->tstate
));
76 bzero((char *)comp
->rstate
, sizeof(comp
->rstate
));
78 for (i
= max_state
; i
> 0; --i
) {
80 tstate
[i
].cs_next
= &tstate
[i
- 1];
82 tstate
[0].cs_next
= &tstate
[max_state
];
84 comp
->last_cs
= &tstate
[0];
85 comp
->last_recv
= 255;
86 comp
->last_xmit
= 255;
87 comp
->flags
= SLF_TOSS
;
91 /* ENCODE encodes a number that is known to be non-zero. ENCODEZ
92 * checks for zero (since zero has to be encoded in the long, 3 byte
96 if ((u_int16_t)(n) >= 256) { \
105 #define ENCODEZ(n) { \
106 if ((u_int16_t)(n) >= 256 || (u_int16_t)(n) == 0) { \
116 #define DECODEL(f) { \
118 (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
121 (f) = htonl(ntohl(f) + (u_int32_t)*cp++); \
125 #define DECODES(f) { \
127 (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
130 (f) = htons(ntohs(f) + (u_int32_t)*cp++); \
134 #define DECODEU(f) { \
136 (f) = htons((cp[1] << 8) | cp[2]); \
139 (f) = htons((u_int32_t)*cp++); \
144 * Attempt to compress an outgoing TCP packet and return the type of
145 * the result. The caller must have already verified that the protocol
146 * is TCP. The first mbuf must contain the complete IP and TCP headers,
147 * and "ip" must be == mtod(m, struct ip *). "comp" supplies the
148 * compression state, and "compress_cid" tells us whether it is OK
149 * to leave out the CID field when feasible.
151 * The caller is responsible for adjusting m->m_pkthdr.len upon return,
152 * if m is an M_PKTHDR mbuf.
155 sl_compress_tcp(m
, ip
, comp
, compress_cid
)
157 register struct ip
*ip
;
158 struct slcompress
*comp
;
161 register struct cstate
*cs
= comp
->last_cs
->cs_next
;
162 register u_int hlen
= ip
->ip_hl
;
163 register struct tcphdr
*oth
;
164 register struct tcphdr
*th
;
165 register u_int deltaS
, deltaA
;
166 register u_int changes
= 0;
168 register u_char
*cp
= new_seq
;
171 * Bail if this is an IP fragment or if the TCP packet isn't
172 * `compressible' (i.e., ACK isn't set or some other control bit is
173 * set). (We assume that the caller has already made sure the
174 * packet is IP proto TCP).
176 if ((ip
->ip_off
& htons(0x3fff)) || m
->m_len
< 40)
179 th
= (struct tcphdr
*)&((int32_t *)ip
)[hlen
];
180 if ((th
->th_flags
& (TH_SYN
|TH_FIN
|TH_RST
|TH_ACK
)) != TH_ACK
)
183 * Packet is compressible -- we're going to send either a
184 * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
185 * to locate (or create) the connection state. Special case the
186 * most recently used connection since it's most likely to be used
187 * again & we don't have to do any reordering if it's used.
190 if (ip
->ip_src
.s_addr
!= cs
->cs_ip
.ip_src
.s_addr
||
191 ip
->ip_dst
.s_addr
!= cs
->cs_ip
.ip_dst
.s_addr
||
192 *(int32_t *)th
!= ((int32_t *)&cs
->cs_ip
)[cs
->cs_ip
.ip_hl
]) {
194 * Wasn't the first -- search for it.
196 * States are kept in a circularly linked list with
197 * last_cs pointing to the end of the list. The
198 * list is kept in lru order by moving a state to the
199 * head of the list whenever it is referenced. Since
200 * the list is short and, empirically, the connection
201 * we want is almost always near the front, we locate
202 * states via linear search. If we don't find a state
203 * for the datagram, the oldest state is (re-)used.
205 register struct cstate
*lcs
;
206 register struct cstate
*lastcs
= comp
->last_cs
;
209 lcs
= cs
; cs
= cs
->cs_next
;
211 if (ip
->ip_src
.s_addr
== cs
->cs_ip
.ip_src
.s_addr
212 && ip
->ip_dst
.s_addr
== cs
->cs_ip
.ip_dst
.s_addr
214 ((int32_t *)&cs
->cs_ip
)[cs
->cs_ip
.ip_hl
])
216 } while (cs
!= lastcs
);
219 * Didn't find it -- re-use oldest cstate. Send an
220 * uncompressed packet that tells the other side what
221 * connection number we're using for this conversation.
222 * Note that since the state list is circular, the oldest
223 * state points to the newest and we only need to set
224 * last_cs to update the lru linkage.
236 * Found it -- move to the front on the connection list.
241 lcs
->cs_next
= cs
->cs_next
;
242 cs
->cs_next
= lastcs
->cs_next
;
243 lastcs
->cs_next
= cs
;
248 * Make sure that only what we expect to change changed. The first
249 * line of the `if' checks the IP protocol version, header length &
250 * type of service. The 2nd line checks the "Don't fragment" bit.
251 * The 3rd line checks the time-to-live and protocol (the protocol
252 * check is unnecessary but costless). The 4th line checks the TCP
253 * header length. The 5th line checks IP options, if any. The 6th
254 * line checks TCP options, if any. If any of these things are
255 * different between the previous & current datagram, we send the
256 * current datagram `uncompressed'.
258 oth
= (struct tcphdr
*)&((int32_t *)&cs
->cs_ip
)[hlen
];
265 if (((u_int16_t
*)ip
)[0] != ((u_int16_t
*)&cs
->cs_ip
)[0] ||
266 ((u_int16_t
*)ip
)[3] != ((u_int16_t
*)&cs
->cs_ip
)[3] ||
267 ((u_int16_t
*)ip
)[4] != ((u_int16_t
*)&cs
->cs_ip
)[4] ||
268 th
->th_off
!= oth
->th_off
||
270 BCMP(ip
+ 1, &cs
->cs_ip
+ 1, (deltaS
- 5) << 2)) ||
272 BCMP(th
+ 1, oth
+ 1, (th
->th_off
- 5) << 2)))
276 * Figure out which of the changing fields changed. The
277 * receiver expects changes in the order: urgent, window,
278 * ack, seq (the order minimizes the number of temporaries
279 * needed in this section of code).
281 if (th
->th_flags
& TH_URG
) {
282 deltaS
= ntohs(th
->th_urp
);
285 } else if (th
->th_urp
!= oth
->th_urp
)
286 /* argh! URG not set but urp changed -- a sensible
287 * implementation should never do this but RFC793
288 * doesn't prohibit the change so we have to deal
292 deltaS
= (u_int16_t
)(ntohs(th
->th_win
) - ntohs(oth
->th_win
));
298 deltaA
= ntohl(th
->th_ack
) - ntohl(oth
->th_ack
);
306 deltaS
= ntohl(th
->th_seq
) - ntohl(oth
->th_seq
);
318 * Nothing changed. If this packet contains data and the
319 * last one didn't, this is probably a data packet following
320 * an ack (normal on an interactive connection) and we send
321 * it compressed. Otherwise it's probably a retransmit,
322 * retransmitted ack or window probe. Send it uncompressed
323 * in case the other side missed the compressed version.
325 if (ip
->ip_len
!= cs
->cs_ip
.ip_len
&&
326 ntohs(cs
->cs_ip
.ip_len
) == hlen
)
334 * actual changes match one of our special case encodings --
335 * send packet uncompressed.
340 if (deltaS
== deltaA
&&
341 deltaS
== ntohs(cs
->cs_ip
.ip_len
) - hlen
) {
342 /* special case for echoed terminal traffic */
349 if (deltaS
== ntohs(cs
->cs_ip
.ip_len
) - hlen
) {
350 /* special case for data xfer */
357 deltaS
= ntohs(ip
->ip_id
) - ntohs(cs
->cs_ip
.ip_id
);
362 if (th
->th_flags
& TH_PUSH
)
363 changes
|= TCP_PUSH_BIT
;
365 * Grab the cksum before we overwrite it below. Then update our
366 * state with this packet's header.
368 deltaA
= ntohs(th
->th_sum
);
369 BCOPY(ip
, &cs
->cs_ip
, hlen
);
372 * We want to use the original packet as our compressed packet.
373 * (cp - new_seq) is the number of bytes we need for compressed
374 * sequence numbers. In addition we need one byte for the change
375 * mask, one for the connection id and two for the tcp checksum.
376 * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
377 * many bytes of the original packet to toss so subtract the two to
378 * get the new packet size.
380 deltaS
= cp
- new_seq
;
382 if (compress_cid
== 0 || comp
->last_xmit
!= cs
->cs_id
) {
383 comp
->last_xmit
= cs
->cs_id
;
386 *cp
++ = changes
| NEW_C
;
397 BCOPY(new_seq
, cp
, deltaS
);
399 return (TYPE_COMPRESSED_TCP
);
402 * Update connection state cs & send uncompressed packet ('uncompressed'
403 * means a regular ip/tcp packet but with the 'conversation id' we hope
404 * to use on future compressed packets in the protocol field).
407 BCOPY(ip
, &cs
->cs_ip
, hlen
);
408 ip
->ip_p
= cs
->cs_id
;
409 comp
->last_xmit
= cs
->cs_id
;
410 return (TYPE_UNCOMPRESSED_TCP
);
415 sl_uncompress_tcp(bufp
, len
, type
, comp
)
419 struct slcompress
*comp
;
424 cp
= bufp
? *bufp
: NULL
;
425 vjlen
= sl_uncompress_tcp_core(cp
, len
, len
, type
, comp
, &hdr
, &hlen
);
427 return (0); /* error */
429 return (len
); /* was uncompressed already */
435 * At this point, cp points to the first byte of data in the
436 * packet. If we're not aligned on a 4-byte boundary, copy the
437 * data down so the ip & tcp headers will be aligned. Then back up
438 * cp by the tcp/ip header length to make room for the reconstructed
439 * header (we assume the packet we were handed has enough space to
440 * prepend 128 bytes of header).
442 if ((intptr_t)cp
& 3) {
444 BCOPY(cp
, ((intptr_t)cp
&~ 3), len
);
445 cp
= (u_char
*)((intptr_t)cp
&~ 3);
449 BCOPY(hdr
, cp
, hlen
);
456 * Uncompress a packet of total length total_len. The first buflen
457 * bytes are at buf; this must include the entire (compressed or
458 * uncompressed) TCP/IP header. This procedure returns the length
459 * of the VJ header, with a pointer to the uncompressed IP header
460 * in *hdrp and its length in *hlenp.
463 sl_uncompress_tcp_core(buf
, buflen
, total_len
, type
, comp
, hdrp
, hlenp
)
465 int buflen
, total_len
;
467 struct slcompress
*comp
;
472 register u_int hlen
, changes
;
473 register struct tcphdr
*th
;
474 register struct cstate
*cs
;
475 register struct ip
*ip
;
476 register u_int16_t
*bp
;
477 register u_int vjlen
;
481 case TYPE_UNCOMPRESSED_TCP
:
482 ip
= (struct ip
*) buf
;
483 if (ip
->ip_p
>= MAX_STATES
)
485 cs
= &comp
->rstate
[comp
->last_recv
= ip
->ip_p
];
486 comp
->flags
&=~ SLF_TOSS
;
487 ip
->ip_p
= IPPROTO_TCP
;
489 * Calculate the size of the TCP/IP header and make sure that
490 * we don't overflow the space we have available for it.
492 hlen
= ip
->ip_hl
<< 2;
493 if (hlen
+ sizeof(struct tcphdr
) > buflen
)
495 hlen
+= ((struct tcphdr
*)&((char *)ip
)[hlen
])->th_off
<< 2;
496 if (hlen
> MAX_HDR
|| hlen
> buflen
)
498 BCOPY(ip
, &cs
->cs_ip
, hlen
);
500 INCR(sls_uncompressedin
)
501 *hdrp
= (u_char
*) &cs
->cs_ip
;
508 case TYPE_COMPRESSED_TCP
:
511 /* We've got a compressed packet. */
512 INCR(sls_compressedin
)
515 if (changes
& NEW_C
) {
516 /* Make sure the state index is in range, then grab the state.
517 * If we have a good state index, clear the 'discard' flag. */
518 if (*cp
>= MAX_STATES
)
521 comp
->flags
&=~ SLF_TOSS
;
522 comp
->last_recv
= *cp
++;
524 /* this packet has an implicit state index. If we've
525 * had a line error since the last time we got an
526 * explicit state index, we have to toss the packet. */
527 if (comp
->flags
& SLF_TOSS
) {
532 cs
= &comp
->rstate
[comp
->last_recv
];
533 hlen
= cs
->cs_ip
.ip_hl
<< 2;
534 th
= (struct tcphdr
*)&((u_char
*)&cs
->cs_ip
)[hlen
];
535 th
->th_sum
= htons((*cp
<< 8) | cp
[1]);
537 if (changes
& TCP_PUSH_BIT
)
538 th
->th_flags
|= TH_PUSH
;
540 th
->th_flags
&=~ TH_PUSH
;
542 switch (changes
& SPECIALS_MASK
) {
545 register u_int i
= ntohs(cs
->cs_ip
.ip_len
) - cs
->cs_hlen
;
546 th
->th_ack
= htonl(ntohl(th
->th_ack
) + i
);
547 th
->th_seq
= htonl(ntohl(th
->th_seq
) + i
);
552 th
->th_seq
= htonl(ntohl(th
->th_seq
) + ntohs(cs
->cs_ip
.ip_len
)
557 if (changes
& NEW_U
) {
558 th
->th_flags
|= TH_URG
;
561 th
->th_flags
&=~ TH_URG
;
570 if (changes
& NEW_I
) {
571 DECODES(cs
->cs_ip
.ip_id
)
573 cs
->cs_ip
.ip_id
= htons(ntohs(cs
->cs_ip
.ip_id
) + 1);
576 * At this point, cp points to the first byte of data in the
577 * packet. Fill in the IP total length and update the IP
583 /* we must have dropped some characters (crc should detect
584 * this but the old slip framing won't) */
587 total_len
+= cs
->cs_hlen
- vjlen
;
588 cs
->cs_ip
.ip_len
= htons(total_len
);
590 /* recompute the ip header checksum */
591 bp
= (u_int16_t
*) &cs
->cs_ip
;
592 cs
->cs_ip
.ip_sum
= 0;
593 for (changes
= 0; hlen
> 0; hlen
-= 2)
595 changes
= (changes
& 0xffff) + (changes
>> 16);
596 changes
= (changes
& 0xffff) + (changes
>> 16);
597 cs
->cs_ip
.ip_sum
= ~ changes
;
599 *hdrp
= (u_char
*) &cs
->cs_ip
;
600 *hlenp
= cs
->cs_hlen
;
604 comp
->flags
|= SLF_TOSS
;