must handle alignment for packets w/o data

[unix-history] / usr / src / sys / net / slcompress.c

/*
*      @(#)slcompress.c        7.4 (Berkeley) %G%
*
*                      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.
*/

#include "sl.h"
#if NSL > 0
#ifndef lint
static char rcsid[] = "$Header: slcompress.c,v 1.10 89/06/05 08:28:52 van Exp $";
#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"

#ifndef NO_SL_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))


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.
        * 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);

       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
                * 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;
                       INCR(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);
               INCR(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_data += hlen;
               *cp++ = changes | NEW_C;
               *cp++ = cs->cs_id;
       } else {
               hlen -= deltaS + 3;
               cp += hlen;
               m->m_len -= hlen;
               m->m_data += hlen;
               *cp++ = changes;
       }
       *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;
{
       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) {
                       INCR(sls_errorin)
                       return (0);
               }
               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 (len);

       case TYPE_ERROR:
               comp->flags |= SLF_TOSS;
       default:
               INCR(sls_errorin)
               return (0);

       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) {
                       INCR(sls_errorin)
                       return (0);
               }
               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;
                       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 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 lenth 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) */
               INCR(sls_errorin)
               return (0);
       }
       if ((int)cp & 3) {
               if (len > 0)
                       BCOPY(cp, (int)cp &~ 3, len);
               cp = (u_char *)((int)cp &~ 3);
       }
       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);
}
#endif