+/* slcompress.c 7.1 89/06/28 */
+
+/*
+ * THIS CODE IS NOT FOR DISTRIBUTION!
+ * KEEP YOUR GRUBBY HANDS OFF UNLESS AUTHORIZED BY VAN JACOBSON TO COPY!
+ * ASK SAM, MIKE, OR BILL ABOUT IT.
+ */
+
+/*
+ * Routines to compress and uncompess tcp packets (for transmission
+ * over low speed serial lines.
+ *
+ * Copyright (c) 1988, 1989 by Van Jacobson, Lawrence Berkeley Laboratory
+ * All rights reserved.
+ */
+
+#ifndef lint
+static char rcsid[] = "$Header: slcompress.c,v 1.7 89/03/19 18:10:19 van Locked $";
+#endif
+
+#include <sys/types.h>
+#include <sys/param.h>
+#include <sys/mbuf.h>
+#include <netinet/in.h>
+#include <netinet/in_systm.h>
+#include <netinet/ip.h>
+#include <netinet/tcp.h>
+
+#include "slcompress.h"
+
+int sls_packets;
+int sls_searches;
+int sls_misses;
+int sls_compressed;
+int sls_ipin;
+int sls_uncompressedin;
+int sls_compressedin;
+
+#define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
+#define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
+
+#ifndef KERNEL
+extern struct mbuf *m_get();
+#undef MGET
+#define MGET(m, w, t) ((m) = m_get((w), (t)))
+#endif
+
+#if BSD>=198810
+#define m_off m_data
+#endif
+
+void
+sl_compress_init(comp)
+ struct slcompress *comp;
+{
+ register u_int i;
+ register struct cstate *tstate = comp->tstate;
+
+ bzero((char *)comp, sizeof(*comp));
+ for (i = MAX_STATES - 1; i > 0; --i) {
+ tstate[i].cs_id = i;
+ tstate[i].cs_next = &tstate[i - 1];
+ }
+ tstate[0].cs_next = &tstate[MAX_STATES - 1];
+ tstate[0].cs_id = 0;
+ comp->last_cs = &tstate[0];
+ comp->last_recv = 255;
+ comp->last_xmit = 255;
+}
+
+
+/* ENCODE encodes a number that is known to be non-zero. ENCODEZ
+ * checks for zero (since zero has to be encoded in the long, 3 byte
+ * form).
+ */
+#define ENCODE(n) { \
+ if ((u_short)(n) >= 256) { \
+ *cp++ = 0; \
+ cp[1] = (n); \
+ cp[0] = (n) >> 8; \
+ cp += 2; \
+ } else { \
+ *cp++ = (n); \
+ } \
+}
+#define ENCODEZ(n) { \
+ if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
+ *cp++ = 0; \
+ cp[1] = (n); \
+ cp[0] = (n) >> 8; \
+ cp += 2; \
+ } else { \
+ *cp++ = (n); \
+ } \
+}
+
+#define DECODEL(f) { \
+ if (*cp == 0) {\
+ (f) = htonl(ntohl(f) + ((cp[1] << 8) | cp[2])); \
+ cp += 3; \
+ } else { \
+ (f) = htonl(ntohl(f) + (u_long)*cp++); \
+ } \
+}
+
+#define DECODES(f) { \
+ if (*cp == 0) {\
+ (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \
+ cp += 3; \
+ } else { \
+ (f) = htons(ntohs(f) + (u_long)*cp++); \
+ } \
+}
+
+
+u_char
+sl_compress_tcp(m, ip, comp)
+ struct mbuf *m;
+ register struct ip *ip;
+ struct slcompress *comp;
+{
+ register struct cstate *cs = comp->last_cs->cs_next;
+ register u_int hlen = ip->ip_hl;
+ register struct tcphdr *oth;
+ register struct tcphdr *th;
+ register u_int deltaS, deltaA;
+ register u_int changes = 0;
+ u_char new_seq[16];
+ register u_char *cp = new_seq;
+
+ /*
+ * Bail if this is an ip fragment or if we don't have
+ * a complete ip & tcp header in the first mbuf. Otherwise,
+ * check flags to see if this is a packet we might compress
+ * and, if so, try to locate the connection state.
+ * since slip links tend to be end nodes, check the tcp ports
+ * first since the inet addresses won't usually change.
+ * special case the most recently used connection since
+ * it's most likely to be used again & we don't have to
+ * do any reordering if it's used.
+ */
+ if ((ip->ip_off & 0x3fff) || m->m_len < 40)
+ return (TYPE_IP);
+
+ th = (struct tcphdr *)&((int *)ip)[hlen];
+ if ((th->th_flags & (TH_SYN|TH_FIN|TH_RST|TH_ACK)) != TH_ACK)
+ return (TYPE_IP);
+
+ ++sls_packets;
+ if (*(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl] ||
+ ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
+ ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr) {
+ /*
+ * Wasn't the first -- search for it.
+ *
+ * States are kept in a circularly linked list with
+ * first_cs pointing to the head of the list. The
+ * list is kept in lru order by moving a state to the
+ * head of the list whenever it is referenced. Since
+ * the list is short and, empirically, the connection
+ * we want is almost always near the front, we locate
+ * states via linear search. If we don't find a state
+ * for the datagram, the oldest state is used.
+ */
+ register struct cstate *lcs;
+
+ do {
+ lcs = cs; cs = cs->cs_next;
+ ++sls_searches;
+ if (*(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]
+ && ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
+ && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr)
+ goto found;
+ } while (cs != comp->last_cs);
+ ++sls_misses;
+
+ /*
+ * Didn't find it -- re-use oldest cstate.
+ * Send an uncompressed packet that tells
+ * the other side what connection number
+ * we're using for this conversation. Note
+ * that since the state list is circular, the
+ * oldest state points to the newest and we only
+ * need to set last_cs to update the lru linkage.
+ */
+ comp->last_cs = lcs;
+ hlen += th->th_off;
+ hlen <<= 2;
+ goto uncompressed;
+
+ found:
+ /*
+ * Found it -- move to the front on the connection list.
+ */
+ if (comp->last_cs == cs)
+ comp->last_cs = lcs;
+ else {
+ lcs->cs_next = cs->cs_next;
+ cs->cs_next = comp->last_cs->cs_next;
+ comp->last_cs->cs_next = cs;
+ }
+ }
+
+ /*
+ * Make sure that only what we expect to change changed.
+ */
+ oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen];
+ deltaS = hlen;
+ hlen += th->th_off;
+ hlen <<= 2;
+
+ if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] ||
+ ((u_short *)ip)[4] != ((u_short *)&cs->cs_ip)[4] ||
+ th->th_off != oth->th_off ||
+ (deltaS > 5 &&
+ BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) ||
+ (th->th_off > 5 &&
+ BCMP(th + 1, oth + 1, (th->th_off - 5) << 2)))
+ goto uncompressed;
+
+ /*
+ * Figure out which of the changing fields changed. The
+ * receiver expects changes in the order: urgent, window,
+ * ack, seq (the order minimizes the number of temporaries
+ * needed in this section of code).
+ */
+ if (th->th_flags & TH_URG) {
+ deltaS = ntohs(th->th_urp);
+ ENCODEZ(deltaS);
+ changes |= NEW_U;
+ } else if (th->th_urp != oth->th_urp)
+ /* argh! URG not set but urp changed -- a sensible
+ * implementation should never do this but RFC793
+ * doesn't prohibit the change so we have to deal
+ * with it. */
+ goto uncompressed;
+
+ if (deltaS = (u_short)(ntohs(th->th_win) - ntohs(oth->th_win))) {
+ ENCODE(deltaS);
+ changes |= NEW_W;
+ }
+
+ if (deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack)) {
+ if (deltaA > 0xffff)
+ goto uncompressed;
+ ENCODE(deltaA);
+ changes |= NEW_A;
+ }
+
+ if (deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq)) {
+ if (deltaS > 0xffff)
+ goto uncompressed;
+ ENCODE(deltaS);
+ changes |= NEW_S;
+ }
+
+ switch(changes) {
+
+ case 0:
+ if (ip->ip_len != cs->cs_ip.ip_len && ntohs(ip->ip_len) != hlen)
+ break;
+ /*
+ * Nothing changed and this packet looks like a duplicate
+ * of the last or contains no data -- this is probably a
+ * retransmitted ack or window probe. Send it
+ * uncompressed in case the other side missed the
+ * compressed version.
+ *
+ * (fall through)
+ */
+
+ case SPECIAL_I:
+ case SPECIAL_D:
+ /*
+ * actual changes match one of our special case encodings --
+ * send packet uncompressed.
+ */
+ goto uncompressed;
+
+ case NEW_S|NEW_A:
+ if (deltaS == deltaA &&
+ deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
+ /* special case for echoed terminal traffic */
+ changes = SPECIAL_I;
+ cp = new_seq;
+ }
+ break;
+
+ case NEW_S:
+ if (deltaS == ntohs(cs->cs_ip.ip_len) - hlen) {
+ /* special case for data xfer */
+ changes = SPECIAL_D;
+ cp = new_seq;
+ }
+ break;
+ }
+
+ deltaS = ntohs(ip->ip_id) - ntohs(cs->cs_ip.ip_id);
+ if (deltaS != 1) {
+ ENCODEZ(deltaS);
+ changes |= NEW_I;
+ }
+ if (th->th_flags & TH_PUSH)
+ changes |= TCP_PUSH_BIT;
+ /*
+ * Grab the cksum before we overwrite it below. Then update our
+ * state with this packet's header.
+ */
+ deltaA = ntohs(th->th_sum);
+ BCOPY(ip, &cs->cs_ip, hlen);
+
+ /*
+ * We want to use the original packet as our compressed packet.
+ * (cp - new_seq) is the number of bytes we need for compressed
+ * sequence numbers. In addition we need one byte for the change
+ * mask, one for the connection id and two for the tcp checksum.
+ * So, (cp - new_seq) + 4 bytes of header are needed. hlen is how
+ * many bytes of the original packet to toss so subtract the two to
+ * get the new packet size.
+ */
+ deltaS = cp - new_seq;
+ cp = (u_char *)ip;
+ if (comp->last_xmit != cs->cs_id) {
+ comp->last_xmit = cs->cs_id;
+ hlen -= deltaS + 4;
+ cp += hlen; m->m_len -= hlen; m->m_off += hlen;
+ *cp++ = changes | NEW_C;
+ *cp++ = cs->cs_id;
+ } else {
+ hlen -= deltaS + 3;
+ cp += hlen; m->m_len -= hlen; m->m_off += hlen;
+ *cp++ = changes;
+ }
+ *cp++ = deltaA >> 8;
+ *cp++ = deltaA;
+ BCOPY(new_seq, cp, deltaS);
+ ++sls_compressed;
+ /* note: low order version bits used */
+ ip = mtod(m, struct ip *);
+ ip->ip_v |= (TYPE_COMPRESSED_TCP>>4);
+ return (TYPE_COMPRESSED_TCP);
+
+ /*
+ * Update connection state cs & send uncompressed packet ('uncompressed'
+ * means a regular ip/tcp packet but with the 'conversation id' we hope
+ * to use on future compressed packets in the protocol field).
+ */
+uncompressed:
+ BCOPY(ip, &cs->cs_ip, hlen);
+ ip->ip_p = cs->cs_id;
+ comp->last_xmit = cs->cs_id;
+ ip->ip_v = (TYPE_UNCOMPRESSED_TCP>>4);
+ return (TYPE_UNCOMPRESSED_TCP);
+}
+
+int uncdeb ;
+
+struct mbuf *
+sl_uncompress_tcp(m, type, comp)
+ register struct mbuf *m;
+ u_char type;
+ struct slcompress *comp;
+{
+ register u_char *cp;
+ register u_int hlen, changes;
+ register struct tcphdr *th;
+ register struct cstate *cs;
+ register struct ip *ip;
+ register struct mbuf *m0;
+
+ switch (type) {
+
+ case TYPE_UNCOMPRESSED_TCP:
+ ip = mtod(m, struct ip *);
+ if (ip->ip_p >= MAX_STATES)
+ goto bad;
+ ip->ip_v = 4;
+
+ cs = &comp->rstate[comp->last_recv = ip->ip_p];
+ comp->flags &=~ SLF_TOSS;
+ ip->ip_p = IPPROTO_TCP;
+ hlen = ip->ip_hl;
+ hlen += ((struct tcphdr *)&((int *)ip)[hlen])->th_off;
+ hlen <<= 2;
+ BCOPY(ip, &cs->cs_ip, hlen);
+ cs->cs_ip.ip_sum = 0;
+ cs->cs_hlen = hlen;
+ ++sls_uncompressedin;
+ return (m);
+
+ default:
+ if(type&TYPE_COMPRESSED_TCP) goto compre;
+ ++sls_ipin;
+ return (m);
+
+ case TYPE_ERROR:
+ comp->flags |= SLF_TOSS;
+ return (m);
+
+ case TYPE_COMPRESSED_TCP:
+compre:
+ break;
+ }
+ /* We've got a compressed packet. */
+ ++sls_compressedin;
+ cp = mtod(m, u_char *);
+ changes = *cp++;
+ if (changes & NEW_C) {
+ /* Make sure the state index is in range, then grab the state.
+ * If we have a good state index, clear the 'discard' flag. */
+ if (*cp >= MAX_STATES)
+ goto bad;
+
+ comp->flags &=~ SLF_TOSS;
+ comp->last_recv = *cp++;
+ } else {
+ /* this packet has an implicit state index. If we've
+ * had a line error since the last time we got an
+ * explicit state index, we have to toss the packet. */
+ if (comp->flags & SLF_TOSS)
+ goto bad;
+ }
+ cs = &comp->rstate[comp->last_recv];
+ hlen = cs->cs_ip.ip_hl << 2;
+ th = (struct tcphdr *)&((u_char *)&cs->cs_ip)[hlen];
+ th->th_sum = htons((*cp << 8) | cp[1]);
+ cp += 2;
+ if (changes & TCP_PUSH_BIT)
+ th->th_flags |= TH_PUSH;
+ else
+ th->th_flags &=~ TH_PUSH;
+
+ switch (changes & SPECIALS_MASK) {
+ case SPECIAL_I:
+ {
+ register u_int i = ntohs(cs->cs_ip.ip_len) - cs->cs_hlen;
+ th->th_ack = htonl(ntohl(th->th_ack) + i);
+ th->th_seq = htonl(ntohl(th->th_seq) + i);
+ }
+ break;
+
+ 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;
+ DECODES(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)
+ 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);
+
+ /*
+ * At this point, cp points to the first byte of data in the
+ * packet (if any). Toss the compressed header from the
+ * original packet, allocatate a new mbuf for the uncompressed
+ * header (to make sure it's aligned correctly), then chain it
+ * in front of the original. Set up the ip length & ip checksum then
+ * return the rebuilt packet.
+ */
+ changes = cp - mtod(m, u_char *);
+ m->m_off += changes; m->m_len -= changes;
+ changes = cs->cs_hlen;
+ for (m0 = m; m0; m0 = m0->m_next)
+ changes += m0->m_len;
+ cs->cs_ip.ip_len = htons(changes);
+
+ /*MGET(m0, M_DONTWAIT, MT_DATA);*/
+ MGETHDR(m0, M_DONTWAIT, MT_DATA); /* XXX! */
+ if (! m0)
+ goto bad;
+
+ m0->m_next = m;
+ m0->m_pkthdr.rcvif = m->m_pkthdr.rcvif ; /* XXX! */
+ m0->m_pkthdr.len = m->m_pkthdr.len; /* XXX! */
+ m = m0;
+ m->m_len = cs->cs_hlen;
+ ip = mtod(m, struct ip *);
+ BCOPY(&cs->cs_ip, ip, cs->cs_hlen);
+
+ ip->ip_sum = in_cksum(m, hlen);
+ return (m);
+
+bad:
+ m_freem(m);
+ return ((struct mbuf *)0);
+}
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