588 lines
15 KiB
C
588 lines
15 KiB
C
/*
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* Routines to compress and uncompess tcp packets (for transmission
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* over low speed serial lines.
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*
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* Copyright (c) 1989 Regents of the University of California.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms are permitted
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* provided that the above copyright notice and this paragraph are
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* duplicated in all such forms and that any documentation,
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* advertising materials, and other materials related to such
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* distribution and use acknowledge that the software was developed
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* by the University of California, Berkeley. The name of the
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* University may not be used to endorse or promote products derived
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* from this software without specific prior written permission.
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
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* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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*
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* $Id$
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*
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* Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
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* - Initial distribution.
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*/
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#ifndef lint
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static char const rcsid[] = "$Id$";
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#endif
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#include "defs.h"
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#include <netinet/in_systm.h>
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#include <netinet/in.h>
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#include <netinet/tcp.h>
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#include <netinet/ip.h>
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#include "slcompress.h"
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struct slstat slstat;
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#define INCR(counter) slstat.counter++;
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#define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
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#define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
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#ifndef KERNEL
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#define ovbcopy bcopy
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#endif
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void
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sl_compress_init(comp)
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struct slcompress *comp;
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{
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register u_int i;
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register struct cstate *tstate = comp->tstate;
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bzero((char *)comp, sizeof(*comp));
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for (i = MAX_STATES - 1; i > 0; --i) {
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tstate[i].cs_id = i;
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tstate[i].cs_next = &tstate[i - 1];
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}
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tstate[0].cs_next = &tstate[MAX_STATES - 1];
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tstate[0].cs_id = 0;
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comp->last_cs = &tstate[0];
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comp->last_recv = 255;
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comp->last_xmit = 255;
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comp->flags = SLF_TOSS;
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}
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/* ENCODE encodes a number that is known to be non-zero. ENCODEZ
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* checks for zero (since zero has to be encoded in the long, 3 byte
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* form).
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*/
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#define ENCODE(n) { \
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if ((u_short)(n) >= 256) { \
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*cp++ = 0; \
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cp[1] = (n); \
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cp[0] = (n) >> 8; \
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cp += 2; \
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} else { \
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*cp++ = (n); \
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} \
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}
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#define ENCODEZ(n) { \
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if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
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*cp++ = 0; \
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cp[1] = (n); \
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cp[0] = (n) >> 8; \
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cp += 2; \
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} else { \
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*cp++ = (n); \
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} \
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}
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#define DECODEL(f) { \
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if (*cp == 0) {\
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(f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
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cp += 3; \
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} else { \
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(f) = htonl(ntohl(f) + (u_long)*cp++); \
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} \
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}
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#define DECODES(f) { \
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if (*cp == 0) {\
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(f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
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cp += 3; \
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} else { \
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(f) = htons(ntohs(f) + (u_long)*cp++); \
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} \
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}
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#define DECODEU(f) { \
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if (*cp == 0) {\
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(f) = htons((cp[1] << 8) | cp[2]); \
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cp += 3; \
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} else { \
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(f) = htons((u_long)*cp++); \
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} \
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}
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u_char
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sl_compress_tcp(m, ip, comp, compress_cid)
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struct mbuf *m;
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register struct ip *ip;
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struct slcompress *comp;
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int compress_cid;
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{
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register struct cstate *cs = comp->last_cs->cs_next;
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register u_int hlen = ip->ip_hl;
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register struct tcphdr *oth;
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register struct tcphdr *th;
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register u_int deltaS, deltaA;
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register u_int changes = 0;
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u_char new_seq[16];
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register u_char *cp = new_seq;
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/*
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* Bail if this is an IP fragment or if the TCP packet isn't
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* `compressible' (i.e., ACK isn't set or some other control bit is
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* set). (We assume that the caller has already made sure the
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* packet is IP proto TCP).
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*/
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#ifdef DEBUG
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if ((ip->ip_off & htons(0x3fff)) || m->cnt < 40) {
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logprintf("??? 1 ip_off = %x, cnt = %d\n", ip->ip_off, m->cnt);
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DumpBp(m);
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return (TYPE_IP);
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}
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#else
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if ((ip->ip_off & htons(0x3fff)) || m->cnt < 40)
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return (TYPE_IP);
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#endif
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th = (struct tcphdr *)&((int *)ip)[hlen];
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#ifdef DEBUG
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if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK) {
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logprintf("??? 2 th_flags = %x\n", th->th_flags);
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DumpBp(m);
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return (TYPE_IP);
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}
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#else
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if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
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return (TYPE_IP);
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#endif
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/*
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* Packet is compressible -- we're going to send either a
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* COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
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* to locate (or create) the connection state. Special case the
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* most recently used connection since it's most likely to be used
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* again & we don't have to do any reordering if it's used.
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*/
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INCR(sls_packets)
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if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
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ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
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*(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
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/*
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* Wasn't the first -- search for it.
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*
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* States are kept in a circularly linked list with
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* last_cs pointing to the end of the list. The
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* list is kept in lru order by moving a state to the
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* head of the list whenever it is referenced. Since
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* the list is short and, empirically, the connection
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* we want is almost always near the front, we locate
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* states via linear search. If we don't find a state
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* for the datagram, the oldest state is (re-)used.
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*/
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register struct cstate *lcs;
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register struct cstate *lastcs = comp->last_cs;
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do {
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lcs = cs; cs = cs->cs_next;
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INCR(sls_searches)
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if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
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&& ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
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&& *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl])
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goto found;
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} while (cs != lastcs);
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/*
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* Didn't find it -- re-use oldest cstate. Send an
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* uncompressed packet that tells the other side what
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* connection number we're using for this conversation.
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* Note that since the state list is circular, the oldest
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* state points to the newest and we only need to set
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* last_cs to update the lru linkage.
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*/
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INCR(sls_misses)
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comp->last_cs = lcs;
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#define THOFFSET(th) (th->th_off)
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hlen += th->th_off;
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hlen <<= 2;
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if (hlen > m->cnt)
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return(TYPE_IP);
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goto uncompressed;
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found:
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/*
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* Found it -- move to the front on the connection list.
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*/
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if (cs == lastcs)
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comp->last_cs = lcs;
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else {
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lcs->cs_next = cs->cs_next;
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cs->cs_next = lastcs->cs_next;
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lastcs->cs_next = cs;
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}
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}
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/*
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* Make sure that only what we expect to change changed. The first
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* line of the `if' checks the IP protocol version, header length &
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* type of service. The 2nd line checks the "Don't fragment" bit.
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* The 3rd line checks the time-to-live and protocol (the protocol
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* check is unnecessary but costless). The 4th line checks the TCP
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* header length. The 5th line checks IP options, if any. The 6th
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* line checks TCP options, if any. If any of these things are
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* different between the previous & current datagram, we send the
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* current datagram `uncompressed'.
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*/
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oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen];
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deltaS = hlen;
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hlen += th->th_off;
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hlen <<= 2;
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if (hlen > m->cnt)
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return(TYPE_IP);
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if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] ||
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((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] ||
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((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] ||
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THOFFSET(th) != THOFFSET(oth) ||
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(deltaS > 5 &&
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BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
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(THOFFSET(th) > 5 &&
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BCMP(th + 1, oth + 1, (THOFFSET(th) - 5) << 2))) {
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goto uncompressed;
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}
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/*
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* Figure out which of the changing fields changed. The
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* receiver expects changes in the order: urgent, window,
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* ack, seq (the order minimizes the number of temporaries
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* needed in this section of code).
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*/
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if (th->th_flags & TH_URG) {
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deltaS = ntohs(th->th_urp);
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ENCODEZ(deltaS);
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changes |= NEW_U;
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} else if (th->th_urp != oth->th_urp) {
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/* argh! URG not set but urp changed -- a sensible
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* implementation should never do this but RFC793
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* doesn't prohibit the change so we have to deal
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* with it. */
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goto uncompressed;
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}
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deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win));
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if (deltaS) {
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ENCODE(deltaS);
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changes |= NEW_W;
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}
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deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);
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if (deltaA) {
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if (deltaA > 0xffff) {
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goto uncompressed;
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}
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ENCODE(deltaA);
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changes |= NEW_A;
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}
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deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);
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if (deltaS) {
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if (deltaS > 0xffff) {
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goto uncompressed;
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}
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ENCODE(deltaS);
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changes |= NEW_S;
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}
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switch(changes) {
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case 0:
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/*
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* Nothing changed. If this packet contains data and the
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* last one didn't, this is probably a data packet following
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* an ack (normal on an interactive connection) and we send
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* it compressed. Otherwise it's probably a retransmit,
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* retransmitted ack or window probe. Send it uncompressed
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* in case the other side missed the compressed version.
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*/
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if (ip->ip_len != cs->cs_ip.ip_len &&
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ntohs(cs->cs_ip.ip_len) == hlen)
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break;
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/* (fall through) */
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case SPECIAL_I:
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case SPECIAL_D:
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/*
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* actual changes match one of our special case encodings --
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* send packet uncompressed.
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*/
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goto uncompressed;
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case NEW_S|NEW_A:
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if (deltaS == deltaA &&
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deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
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/* special case for echoed terminal traffic */
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changes = SPECIAL_I;
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cp = new_seq;
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}
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break;
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case NEW_S:
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if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
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/* special case for data xfer */
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changes = SPECIAL_D;
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cp = new_seq;
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}
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break;
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}
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deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
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if (deltaS != 1) {
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ENCODEZ(deltaS);
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changes |= NEW_I;
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}
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if (th->th_flags & TH_PUSH)
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changes |= TCP_PUSH_BIT;
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/*
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* Grab the cksum before we overwrite it below. Then update our
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* state with this packet's header.
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*/
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deltaA = ntohs(th->th_sum);
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BCOPY(ip, &cs->cs_ip, hlen);
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/*
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* We want to use the original packet as our compressed packet.
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* (cp - new_seq) is the number of bytes we need for compressed
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* sequence numbers. In addition we need one byte for the change
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* mask, one for the connection id and two for the tcp checksum.
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* So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
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* many bytes of the original packet to toss so subtract the two to
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* get the new packet size.
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*/
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deltaS = cp - new_seq;
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cp = (u_char *)ip;
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/*
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* Since fastq traffic can jump ahead of the background traffic,
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* we don't know what order packets will go on the line. In this
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* case, we always send a "new" connection id so the receiver state
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* stays synchronized.
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*/
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#ifdef SL_NOFASTQ
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if (comp->last_xmit == cs->cs_id) {
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hlen -= deltaS + 3;
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cp += hlen;
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*cp++ = changes;
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} else
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#endif
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{
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comp->last_xmit = cs->cs_id;
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hlen -= deltaS + 4;
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cp += hlen;
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*cp++ = changes | NEW_C;
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*cp++ = cs->cs_id;
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}
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m->cnt -= hlen;
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m->offset += hlen;
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*cp++ = deltaA >> 8;
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*cp++ = deltaA;
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BCOPY(new_seq, cp, deltaS);
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INCR(sls_compressed)
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return (TYPE_COMPRESSED_TCP);
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/*
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* Update connection state cs & send uncompressed packet ('uncompressed'
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* means a regular ip/tcp packet but with the 'conversation id' we hope
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* to use on future compressed packets in the protocol field).
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*/
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uncompressed:
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BCOPY(ip, &cs->cs_ip, hlen);
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ip->ip_p = cs->cs_id;
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comp->last_xmit = cs->cs_id;
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return (TYPE_UNCOMPRESSED_TCP);
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}
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int
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sl_uncompress_tcp(bufp, len, type, comp)
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u_char **bufp;
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int len;
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u_int type;
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struct slcompress *comp;
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{
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register u_char *cp;
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register u_int hlen, changes;
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register struct tcphdr *th;
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register struct cstate *cs;
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register struct ip *ip;
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switch (type) {
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case TYPE_UNCOMPRESSED_TCP:
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ip = (struct ip *) *bufp;
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if (ip->ip_p >= MAX_STATES)
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goto bad;
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cs = &comp->rstate[comp->last_recv = ip->ip_p];
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comp->flags &=~ SLF_TOSS;
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ip->ip_p = IPPROTO_TCP;
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/*
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* Calculate the size of the TCP/IP header and make sure that
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* we don't overflow the space we have available for it.
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*/
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hlen = ip->ip_hl << 2;
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if (hlen + sizeof(struct tcphdr) > len)
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goto bad;
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th = (struct tcphdr *)&((char *)ip)[hlen];
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hlen += THOFFSET(th) << 2;
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if (hlen > MAX_HDR)
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goto bad;
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BCOPY(ip, &cs->cs_ip, hlen);
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cs->cs_ip.ip_sum = 0;
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cs->cs_hlen = hlen;
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INCR(sls_uncompressedin)
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return (len);
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default:
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goto bad;
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case TYPE_COMPRESSED_TCP:
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break;
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}
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/* We've got a compressed packet. */
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INCR(sls_compressedin)
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cp = *bufp;
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changes = *cp++;
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#ifdef DEBUG
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logprintf("compressed: changes = %02x\n", changes);
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#endif
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if (changes & NEW_C) {
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/* Make sure the state index is in range, then grab the state.
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* If we have a good state index, clear the 'discard' flag. */
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if (*cp >= MAX_STATES || comp->last_recv == 255)
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goto bad;
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comp->flags &=~ SLF_TOSS;
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comp->last_recv = *cp++;
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} else {
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/* this packet has an implicit state index. If we've
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* had a line error since the last time we got an
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* explicit state index, we have to toss the packet. */
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if (comp->flags & SLF_TOSS) {
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INCR(sls_tossed)
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return (0);
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}
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}
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cs = &comp->rstate[comp->last_recv];
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hlen = cs->cs_ip.ip_hl << 2;
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th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
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th->th_sum = htons((*cp << 8) | cp[1]);
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cp += 2;
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if (changes & TCP_PUSH_BIT)
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th->th_flags |= TH_PUSH;
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else
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th->th_flags &=~ TH_PUSH;
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switch (changes & SPECIALS_MASK) {
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case SPECIAL_I:
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{
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register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
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th->th_ack = htonl(ntohl(th->th_ack) + i);
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th->th_seq = htonl(ntohl(th->th_seq) + i);
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}
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break;
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case SPECIAL_D:
|
|
th->th_seq = htonl(ntohl(th->th_seq) + ntohs(cs->cs_ip.ip_len)
|
|
- cs->cs_hlen);
|
|
break;
|
|
|
|
default:
|
|
if (changes & NEW_U) {
|
|
th->th_flags |= TH_URG;
|
|
DECODEU(th->th_urp)
|
|
} else
|
|
th->th_flags &=~ TH_URG;
|
|
if (changes & NEW_W)
|
|
DECODES(th->th_win)
|
|
if (changes & NEW_A)
|
|
DECODEL(th->th_ack)
|
|
if (changes & NEW_S) {
|
|
#ifdef DEBUG
|
|
logprintf("NEW_S: %02x, %02x, %02x\r\n", *cp, cp[1], cp[2]);
|
|
#endif
|
|
DECODEL(th->th_seq)
|
|
}
|
|
break;
|
|
}
|
|
if (changes & NEW_I) {
|
|
DECODES(cs->cs_ip.ip_id)
|
|
} else
|
|
cs->cs_ip.ip_id = htons(ntohs(cs->cs_ip.ip_id) + 1);
|
|
#ifdef DEBUG
|
|
logprintf("id = %04x, seq = %08x\r\n", cs->cs_ip.ip_id, ntohl(th->th_seq));
|
|
#endif
|
|
|
|
/*
|
|
* At this point, cp points to the first byte of data in the
|
|
* packet. If we're not aligned on a 4-byte boundary, copy the
|
|
* data down so the ip & tcp headers will be aligned. Then back up
|
|
* cp by the tcp/ip header length to make room for the reconstructed
|
|
* header (we assume the packet we were handed has enough space to
|
|
* prepend 128 bytes of header). Adjust the length to account for
|
|
* the new header & fill in the IP total length.
|
|
*/
|
|
len -= (cp - *bufp);
|
|
if (len < 0)
|
|
/* we must have dropped some characters (crc should detect
|
|
* this but the old slip framing won't) */
|
|
goto bad;
|
|
|
|
#ifdef notdef
|
|
if ((int)cp & 3) {
|
|
if (len > 0)
|
|
(void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), len);
|
|
cp = (u_char *)((int)cp &~ 3);
|
|
}
|
|
#endif
|
|
|
|
cp -= cs->cs_hlen;
|
|
len += cs->cs_hlen;
|
|
cs->cs_ip.ip_len = htons(len);
|
|
BCOPY(&cs->cs_ip, cp, cs->cs_hlen);
|
|
*bufp = cp;
|
|
|
|
/* recompute the ip header checksum */
|
|
{
|
|
register u_short *bp = (u_short *)cp;
|
|
for (changes = 0; hlen > 0; hlen -= 2)
|
|
changes += *bp++;
|
|
changes = (changes & 0xffff) + (changes >> 16);
|
|
changes = (changes & 0xffff) + (changes >> 16);
|
|
((struct ip *)cp)->ip_sum = ~ changes;
|
|
}
|
|
return (len);
|
|
bad:
|
|
comp->flags |= SLF_TOSS;
|
|
INCR(sls_errorin)
|
|
return (0);
|
|
}
|
|
|
|
int
|
|
ReportCompress()
|
|
{
|
|
printf("Out: %d (compress) / %d (total)",
|
|
slstat.sls_compressed, slstat.sls_packets);
|
|
printf(" %d (miss) / %d (search)\n",
|
|
slstat.sls_misses, slstat.sls_searches);
|
|
printf("In: %d (compress), %d (uncompress)",
|
|
slstat.sls_compressedin, slstat.sls_uncompressedin);
|
|
printf(" %d (error), %d (tossed)\n",
|
|
slstat.sls_errorin, slstat.sls_tossed);
|
|
return(1);
|
|
}
|