/*
 * Routines to compress and uncompress 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 for KA9Q Internet Software Package by
 * Katie Stevens (dkstevens@ucdavis.edu)
 * University of California, Davis
 * Computing Services
 *  - 01-31-90  initial adaptation (from 1.19)
 *  PPP.05  02-15-90 [ks]
 *  PPP.08  05-02-90 [ks]   use PPP protocol field to signal compression
 *  PPP.15  09-90    [ks]   improve mbuf handling
 *  PPP.16  11-02    [karn] substantially rewritten to use NOS facilities
 *
 *  - Feb 1991  Bill_Simpson@um.cc.umich.edu
 *          variable number of conversation slots
 *          allow zero or one slots
 *          separate routines
 *          status display
 */
  
#ifdef MSDOS
#include <mem.h>
#endif
#include "global.h"
#include "mbuf.h"
#include "internet.h"
#include "ip.h"
#include "tcp.h"
#include "slhc.h"
  
static char *encode __ARGS((char *cp,int16 n));
static long decode __ARGS((struct mbuf **bpp));
  
  
/* Initialize compression data structure
 *  slots must be in range 0 to 255 (zero meaning no compression)
 */
struct slcompress *
slhc_init( rslots, tslots )
int rslots;
int tslots;
{
    register int16 i;
    register struct cstate *ts;
    struct slcompress *comp;
  
    comp = callocw( 1, sizeof(struct slcompress) );
  
    if ( rslots > 0  &&  rslots < 256 ) {
        comp->rstate = callocw( rslots, sizeof(struct cstate) );
        comp->rslot_limit = rslots - 1;
    }
  
    if ( tslots > 0  &&  tslots < 256 ) {
        comp->tstate = callocw( tslots, sizeof(struct cstate) );
        comp->tslot_limit = tslots - 1;
    }
  
    comp->xmit_oldest = 0;
    comp->xmit_current = 255;
    comp->recv_current = 255;
  
    if ( tslots > 0 ) {
        ts = comp->tstate;
        for(i = comp->tslot_limit; i > 0; --i){
            ts[i].this = i;
            ts[i].next = &(ts[i - 1]);
        }
        ts[0].next = &(ts[comp->tslot_limit]);
        ts[0].this = 0;
    }
    return comp;
}
  
  
/* Free a compression data structure */
void
slhc_free(comp)
struct slcompress *comp;
{
    if ( comp == NULLSLCOMPR )
        return;
  
    if ( comp->rstate != NULLSLSTATE )
        free( comp->rstate );
  
    if ( comp->tstate != NULLSLSTATE )
        free( comp->tstate );
  
    free( comp );
}
  
  
/* Encode a number */
static char *
encode(cp,n)
register char *cp;
int16 n;
{
    if(n >= 256 || n == 0){
        *cp++ = 0;
        cp = put16(cp,n);
    } else {
        *cp++ = n;
    }
    return cp;
}
  
/* Decode a number */
static long
decode(bpp)
struct mbuf **bpp;
{
    register int x;
  
    x = PULLCHAR(bpp);
    if(x == 0){
        return pull16(bpp); /* pull16 returns -1 on error */
    } else {
        return (long)x;     /* -1 if PULLCHAR returned error */
    }
}
  
int
slhc_compress(comp, bpp, compress_cid)
struct slcompress *comp;
struct mbuf **bpp;
int compress_cid;
{
    register struct cstate *ocs = &(comp->tstate[comp->xmit_oldest]);
    register struct cstate *lcs = ocs;
    register struct cstate *cs = lcs->next;
    register int16 hlen;
    register struct tcp *oth;
    register unsigned long deltaS, deltaA;
    register int16 changes = 0;
    char new_seq[16];
    register char *cp = new_seq;
    struct mbuf *bp;
    struct tcp th;
    struct ip iph;
  
    /* Extract IP header */
    hlen = ntohip(&iph,bpp);
  
    /* Bail if this packet isn't TCP, or is an IP fragment */
    if(iph.protocol != TCP_PTCL || iph.offset != 0 || iph.flags.mf){
        /* Send as regular IP */
        if(iph.protocol != TCP_PTCL)
            comp->sls_o_nontcp++;
        else
            comp->sls_o_tcp++;
        *bpp = htonip(&iph,*bpp,IP_CS_OLD);
        return SL_TYPE_IP;
    }
    /* Extract TCP header */
    hlen += ntohtcp(&th,bpp);
  
    /*  Bail if the TCP packet isn't `compressible' (i.e., ACK isn't set or
     *  some other control bit is set).
     */
    if(th.flags.syn || th.flags.fin || th.flags.rst || !th.flags.ack){
        /* TCP connection stuff; send as regular IP */
        comp->sls_o_tcp++;
        *bpp = htontcp(&th,*bpp,NULLHEADER);
        *bpp = htonip(&iph,*bpp,IP_CS_OLD);
        return SL_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.
     *
     * States are kept in a circularly linked list with
     * xmit_oldest 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.
     */
    for ( ; ; ) {
        if( iph.source == cs->cs_ip.source
            && iph.dest == cs->cs_ip.dest
            && th.source == cs->cs_tcp.source
            && th.dest == cs->cs_tcp.dest)
            goto found;
  
        /* if current equal oldest, at end of list */
        if ( cs == ocs )
            break;
        lcs = cs;
        cs = cs->next;
        comp->sls_o_searches++;
    };
    /*
     * 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
     * xmit_oldest to update the lru linkage.
     */
    comp->sls_o_misses++;
    comp->xmit_oldest = lcs->this;
  
    goto uncompressed;
  
    found:
    /*
     * Found it -- move to the front on the connection list.
     */
    if(lcs == ocs) {
        /* found at most recently used */
    } else if (cs == ocs) {
        /* found at least recently used */
        comp->xmit_oldest = lcs->this;
    } else {
        /* more than 2 elements */
        lcs->next = cs->next;
        cs->next = ocs->next;
        ocs->next = cs;
    }
  
    /*
     * Make sure that only what we expect to change changed.
     * Check the following:
     * IP protocol version, header length & type of service.
     * The "Don't fragment" bit.
     * The time-to-live field.
     * The TCP header length.
     * IP options, if any.
     * TCP options, if any.
     * If any of these things are different between the previous &
     * current datagram, we send the current datagram `uncompressed'.
     */
    oth = &cs->cs_tcp;
  
    if(iph.version != cs->cs_ip.version || iph.optlen != cs->cs_ip.optlen
        || iph.tos != cs->cs_ip.tos
        || iph.flags.df != cs->cs_ip.flags.df
        || iph.ttl != cs->cs_ip.ttl
        || th.optlen != cs->cs_tcp.optlen
        || (iph.optlen > 0 && memcmp(iph.options,cs->cs_ip.options,iph.optlen) != 0)
    || (th.optlen > 0 && memcmp(th.options,cs->cs_tcp.options,th.optlen) != 0)){
        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.flags.urg){
        deltaS = th.up;
        cp = encode(cp,deltaS);
        changes |= NEW_U;
    } else if(th.up != oth->up){
        /* 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 = th.wnd - oth->wnd) != 0){
        cp = encode(cp,deltaS);
        changes |= NEW_W;
    }
    if((deltaA = th.ack - oth->ack) != 0L){
        if(deltaA > 0x0000ffff)
            goto uncompressed;
        cp = encode(cp,deltaA);
        changes |= NEW_A;
    }
    if((deltaS = th.seq - oth->seq) != 0L){
        if(deltaS > 0x0000ffff)
            goto uncompressed;
        cp = encode(cp,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(iph.length != cs->cs_ip.length && cs->cs_ip.length == hlen)
                break;
            goto uncompressed;
        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 == cs->cs_ip.length - hlen){
            /* special case for echoed terminal traffic */
                changes = SPECIAL_I;
                cp = new_seq;
            }
            break;
        case NEW_S:
            if(deltaS == cs->cs_ip.length - hlen){
            /* special case for data xfer */
                changes = SPECIAL_D;
                cp = new_seq;
            }
            break;
    }
    deltaS = iph.id - cs->cs_ip.id;
    if(deltaS != 1){
        cp = encode(cp,deltaS);
        changes |= NEW_I;
    }
    if(th.flags.psh)
        changes |= TCP_PUSH_BIT;
    /* Grab the cksum before we overwrite it below.  Then update our
     * state with this packet's header.
     */
    deltaA = th.checksum;
    ASSIGN(cs->cs_ip,iph);
    ASSIGN(cs->cs_tcp,th);
    /* 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.
     */
    deltaS = cp - new_seq;
    if(compress_cid == 0 || comp->xmit_current != cs->this){
        bp = *bpp = pushdown(*bpp,deltaS + 4);
        cp = bp->data;
        *cp++ = changes | NEW_C;
        *cp++ = cs->this;
        comp->xmit_current = cs->this;
    } else {
        bp = *bpp = pushdown(*bpp,deltaS + 3);
        cp = bp->data;
        *cp++ = changes;
    }
    cp = put16(cp,(int16)deltaA);   /* Write TCP checksum */
    memcpy(cp,new_seq,(size_t)deltaS);  /* Write list of deltas */
    comp->sls_o_compressed++;
    return SL_TYPE_COMPRESSED_TCP;
  
    /* Update connection state cs & send uncompressed packet (i.e.,
     * a regular ip/tcp packet but with the 'conversation id' we hope
     * to use on future compressed packets in the protocol field).
     */
    uncompressed:
    iph.protocol = cs->this;
    ASSIGN(cs->cs_ip,iph);
    ASSIGN(cs->cs_tcp,th);
    comp->xmit_current = cs->this;
    comp->sls_o_uncompressed++;
    *bpp = htontcp(&th,*bpp,NULLHEADER);
    *bpp = htonip(&iph,*bpp,IP_CS_OLD);
    return SL_TYPE_UNCOMPRESSED_TCP;
}
  
  
int
slhc_uncompress(comp, bpp)
struct slcompress *comp;
struct mbuf **bpp;
{
    register int changes;
    long x;
    register struct tcp *thp;
    register struct cstate *cs;
    int len;
  
    /* We've got a compressed packet; read the change byte */
    comp->sls_i_compressed++;
    if(len_p(*bpp) < 3){
        comp->sls_i_error++;
        return 0;
    }
    changes = PULLCHAR(bpp);    /* "Can't fail" */
    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.
         */
        x = PULLCHAR(bpp);  /* Read conn index */
        if(x < 0 || x > comp->rslot_limit)
            goto bad;
  
        comp->flags &=~ SLF_TOSS;
        comp->recv_current = x;
    } 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){
            comp->sls_i_tossed++;
            return 0;
        }
    }
    cs = &comp->rstate[comp->recv_current];
    thp = &cs->cs_tcp;
  
    if((x = pull16(bpp)) == -1) /* Read the TCP checksum */
        goto bad;
    thp->checksum = x;
  
    thp->flags.psh = (changes & TCP_PUSH_BIT) ? 1 : 0;
  
    switch(changes & SPECIALS_MASK){
        case SPECIAL_I:     /* Echoed terminal traffic */
        {
            register int16 i;
            i = cs->cs_ip.length;
            i -= (cs->cs_ip.optlen + IPLEN + TCPLEN);
            thp->ack += i;
            thp->seq += i;
        }
            break;
  
        case SPECIAL_D:         /* Unidirectional data */
            thp->seq += cs->cs_ip.length - (cs->cs_ip.optlen +IPLEN + TCPLEN);
            break;
  
        default:
            if(changes & NEW_U){
                thp->flags.urg = 1;
                if((x = decode(bpp)) == -1)
                    goto bad;
                thp->up = x;
            } else
                thp->flags.urg = 0;
            if(changes & NEW_W){
                if((x = decode(bpp)) == -1)
                    goto bad;
                thp->wnd += x;
            }
            if(changes & NEW_A){
                if((x = decode(bpp)) == -1)
                    goto bad;
                thp->ack += x;
            }
            if(changes & NEW_S){
                if((x = decode(bpp)) == -1)
                    goto bad;
                thp->seq += x;
            }
            break;
    }
    if(changes & NEW_I){
        if((x = decode(bpp)) == -1)
            goto bad;
        cs->cs_ip.id += x;
    } else
        cs->cs_ip.id++;
  
    /*
     * At this point, bpp points to the first byte of data in the
     * packet.  Put the reconstructed TCP and IP headers back on the
     * packet.  Recalculate IP checksum (but not TCP checksum).
     */
    len = len_p(*bpp) + IPLEN + TCPLEN + cs->cs_ip.optlen;
    cs->cs_ip.length = len;
  
    *bpp = htontcp(thp,*bpp,NULLHEADER);
    *bpp = htonip(&cs->cs_ip,*bpp,IP_CS_NEW);
    return len;
    bad:
    comp->sls_i_error++;
    return slhc_toss( comp );
}
  
  
int
slhc_remember(comp, bpp)
struct slcompress *comp;
struct mbuf **bpp;
{
    register struct cstate *cs;
    struct ip iph;
    struct tcp th;
  
    /* Extract IP and TCP headers and verify conn ID */
    ntohip(&iph,bpp);
    ntohtcp(&th,bpp);
    if(uchar(iph.protocol) > comp->rslot_limit) {
        comp->sls_i_error++;
        return slhc_toss(comp);
    }
  
    /* Update local state */
    cs = &comp->rstate[comp->recv_current = uchar(iph.protocol)];
    comp->flags &=~ SLF_TOSS;
    iph.protocol = TCP_PTCL;
    ASSIGN(cs->cs_ip,iph);
    ASSIGN(cs->cs_tcp,th);
  
    /* Put headers back on packet
     * Neither header checksum is recalculated
     */
    *bpp = htontcp(&th,*bpp,NULLHEADER);
    *bpp = htonip(&iph,*bpp,IP_CS_OLD);
    comp->sls_i_uncompressed++;
    return len_p(*bpp);
}
  
  
int
slhc_toss(comp)
struct slcompress *comp;
{
    if ( comp == NULLSLCOMPR )
        return 0;
  
    comp->flags |= SLF_TOSS;
    return 0;
}
  
  
void slhc_i_status(comp)
struct slcompress *comp;
{
    if (comp != NULLSLCOMPR) {
        tprintf("\t%10ld Cmp,"
        " %10ld Uncmp,"
        " %10ld Bad, "
        " %10ld Tossed\n",
        comp->sls_i_compressed,
        comp->sls_i_uncompressed,
        comp->sls_i_error,
        comp->sls_i_tossed);
    }
}
  
  
void slhc_o_status(comp)
struct slcompress *comp;
{
    if (comp != NULLSLCOMPR) {
        tprintf("\t%10ld Cmp,"
        " %10ld Uncmp,"
        " %10ld AsIs,"
        " %10ld NotTCP\n",
        comp->sls_o_compressed,
        comp->sls_o_uncompressed,
        comp->sls_o_tcp,
        comp->sls_o_nontcp);
        tprintf("\t%10ld Searches,"
        " %10ld Misses\n",
        comp->sls_o_searches,
        comp->sls_o_misses);
    }
}
  
  
