--- /dev/null
+/*
+ * Routines to compress and uncompess tcp packets (for transmission
+ * over low speed serial lines.
+ *
+ * Copyright (c) 1989 Regents of the University of California.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms are permitted
+ * provided that the above copyright notice and this paragraph are
+ * duplicated in all such forms and that any documentation,
+ * advertising materials, and other materials related to such
+ * distribution and use acknowledge that the software was developed
+ * by the University of California, Berkeley. The name of the
+ * University may not be used to endorse or promote products derived
+ * from this software without specific prior written permission.
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
+ * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:
+ * - Initial distribution.
+ *
+ * Modified June 1993 by Paul Mackerras, paulus@cs.anu.edu.au,
+ * so that the entire packet being decompressed doesn't have
+ * to be in contiguous memory (just the compressed header).
+ *
+ * $Id: slcompress.c,v 1.1 1994/11/22 00:27:52 paulus Exp $
+ */
+
+#include "../h/types.h"
+#include "../h/param.h"
+#include "../h/mbuf.h"
+#include "../net/netinet/in.h"
+#include "../net/netinet/in_systm.h"
+#include "../net/netinet/ip.h"
+#include "../net/netinet/tcp.h"
+
+#include "slcompress.h"
+
+#ifndef SL_NO_STATS
+#define INCR(counter) ++comp->counter;
+#else
+#define INCR(counter)
+#endif
+
+#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
+#define ovbcopy bcopy
+#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;
+ comp->flags = SLF_TOSS;
+}
+
+
+/*
+ * Like sl_compress_init, but we get to specify the maximum connection
+ * ID to use on transmission.
+ */
+void
+sl_compress_setup(comp, max_state)
+ struct slcompress *comp;
+ int max_state;
+{
+ register u_int i;
+ register struct cstate *tstate = comp->tstate;
+
+ if ((unsigned) max_state > MAX_STATES - 1)
+ max_state = MAX_STATES - 1;
+ bzero((char *)comp, sizeof(*comp));
+ for (i = max_state; i > 0; --i) {
+ tstate[i].cs_id = i;
+ tstate[i].cs_next = &tstate[i - 1];
+ }
+ tstate[0].cs_next = &tstate[max_state];
+ tstate[0].cs_id = 0;
+ comp->last_cs = &tstate[0];
+ comp->last_recv = 255;
+ comp->last_xmit = 255;
+ comp->flags = SLF_TOSS;
+}
+
+
+/* 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++); \
+ } \
+}
+
+#define DECODEU(f) { \
+ if (*cp == 0) {\
+ (f) = htons((cp[1] << 8) | cp[2]); \
+ cp += 3; \
+ } else { \
+ (f) = htons((u_long)*cp++); \
+ } \
+}
+
+
+u_char
+sl_compress_tcp(m, ip, comp, compress_cid)
+ struct mbuf *m;
+ register struct ip *ip;
+ struct slcompress *comp;
+ int compress_cid;
+{
+ 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 the TCP packet isn't
+ * `compressible' (i.e., ACK isn't set or some other control bit is
+ * set). (We assume that the caller has already made sure the
+ * packet is IP proto TCP).
+ */
+ if ((ip->ip_off & htons(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);
+ /*
+ * Packet is compressible -- we're going to send either a
+ * COMPRESSED_TCP or UNCOMPRESSED_TCP packet. Either way we need
+ * to locate (or create) the connection state. 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.
+ */
+ INCR(sls_packets)
+ if (ip->ip_src.s_addr != cs->cs_ip.ip_src.s_addr ||
+ ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr ||
+ *(int *)th != ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl]) {
+ /*
+ * Wasn't the first -- search for it.
+ *
+ * States are kept in a circularly linked list with
+ * last_cs pointing to the end 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 (re-)used.
+ */
+ register struct cstate *lcs;
+ register struct cstate *lastcs = comp->last_cs;
+
+ do {
+ lcs = cs; cs = cs->cs_next;
+ INCR(sls_searches)
+ if (ip->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
+ && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
+ && *(int *)th == ((int *)&cs->cs_ip)[cs->cs_ip.ip_hl])
+ goto found;
+ } while (cs != lastcs);
+
+ /*
+ * 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.
+ */
+ INCR(sls_misses)
+ comp->last_cs = lcs;
+ hlen += th->th_off;
+ hlen <<= 2;
+ if (hlen > m->m_len)
+ return (TYPE_IP);
+ goto uncompressed;
+
+ found:
+ /*
+ * Found it -- move to the front on the connection list.
+ */
+ if (cs == lastcs)
+ comp->last_cs = lcs;
+ else {
+ lcs->cs_next = cs->cs_next;
+ cs->cs_next = lastcs->cs_next;
+ lastcs->cs_next = cs;
+ }
+ }
+
+ /*
+ * Make sure that only what we expect to change changed. The first
+ * line of the `if' checks the IP protocol version, header length &
+ * type of service. The 2nd line checks the "Don't fragment" bit.
+ * The 3rd line checks the time-to-live and protocol (the protocol
+ * check is unnecessary but costless). The 4th line checks the TCP
+ * header length. The 5th line checks IP options, if any. The 6th
+ * line checks TCP options, if any. If any of these things are
+ * different between the previous & current datagram, we send the
+ * current datagram `uncompressed'.
+ */
+ oth = (struct tcphdr *)&((int *)&cs->cs_ip)[hlen];
+ deltaS = hlen;
+ hlen += th->th_off;
+ hlen <<= 2;
+ if (hlen > m->m_len)
+ return (TYPE_IP);
+
+ if (((u_short *)ip)[0] != ((u_short *)&cs->cs_ip)[0] ||
+ ((u_short *)ip)[3] != ((u_short *)&cs->cs_ip)[3] ||
+ ((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:
+ /*
+ * Nothing changed. If this packet contains data and the
+ * last one didn't, this is probably a data packet following
+ * an ack (normal on an interactive connection) and we send
+ * it compressed. Otherwise it's probably a retransmit,
+ * retransmitted ack or window probe. Send it uncompressed
+ * in case the other side missed the compressed version.
+ */
+ if (ip->ip_len != cs->cs_ip.ip_len &&
+ ntohs(cs->cs_ip.ip_len) == hlen)
+ break;
+
+ /* (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 (compress_cid == 0 || comp->last_xmit != cs->cs_id) {
+ comp->last_xmit = cs->cs_id;
+ hlen -= deltaS + 4;
+ cp += hlen;
+ *cp++ = changes | NEW_C;
+ *cp++ = cs->cs_id;
+ } else {
+ hlen -= deltaS + 3;
+ cp += hlen;
+ *cp++ = changes;
+ }
+ m->m_len -= hlen;
+ m->m_off += hlen;
+ *cp++ = deltaA >> 8;
+ *cp++ = deltaA;
+ BCOPY(new_seq, cp, deltaS);
+ INCR(sls_compressed)
+ 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;
+ return (TYPE_UNCOMPRESSED_TCP);
+}
+
+
+int
+sl_uncompress_tcp(bufp, len, type, comp)
+ u_char **bufp;
+ int len;
+ u_int type;
+ struct slcompress *comp;
+{
+ return sl_uncompress_tcp_part(bufp, len, len, type, comp);
+}
+
+
+/*
+ * Uncompress a packet of total length total_len. The first buflen
+ * bytes are at *bufp; this must include the entire (compressed or
+ * uncompressed) TCP/IP header. In addition, there must be enough
+ * clear space before *bufp to build a full-length TCP/IP header.
+ */
+int
+sl_uncompress_tcp_part(bufp, buflen, total_len, type, comp)
+ u_char **bufp;
+ int buflen, total_len;
+ u_int 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;
+
+ switch (type) {
+
+ case TYPE_UNCOMPRESSED_TCP:
+ ip = (struct ip *) *bufp;
+ if (ip->ip_p >= MAX_STATES)
+ goto bad;
+ 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;
+ INCR(sls_uncompressedin)
+ return (total_len);
+
+ default:
+ goto bad;
+
+ case TYPE_COMPRESSED_TCP:
+ break;
+ }
+ /* We've got a compressed packet. */
+ INCR(sls_compressedin)
+ cp = *bufp;
+ 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) {
+ INCR(sls_tossed)
+ return (0);
+ }
+ }
+ 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;
+ 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)
+ 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 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.
+ */
+ buflen -= (cp - *bufp);
+ total_len -= (cp - *bufp);
+ if (buflen < 0)
+ /* we must have dropped some characters (crc should detect
+ * this but the old slip framing won't) */
+ goto bad;
+
+ if ((int)cp & 3) {
+ if (buflen > 0)
+ (void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), buflen);
+ cp = (u_char *)((int)cp &~ 3);
+ }
+ cp -= cs->cs_hlen;
+ total_len += cs->cs_hlen;
+ cs->cs_ip.ip_len = htons(total_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 (total_len);
+bad:
+ comp->flags |= SLF_TOSS;
+ INCR(sls_errorin)
+ return (0);
+}
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