/*
 * 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.
 */

#ifndef lint
static char rcsid[] = "$Header: HOG:Other/networking/sana2/src/slip/RCS/slcompress.c,v 38.1 94/02/17 14:14:37 kcd Exp $";
#endif

#include <exec/types.h>
#include <sys/types.h>
#include "param.h"
#include "mbuf.h"
#include "in.h"
#include "in_systm.h"
#include "ip.h"
#include "tcp.h"
#include "string.h"
#include "slcompress.h"
#include "slcompress_protos.h"

#ifndef SL_NO_STATS
#define INCR(counter) ++comp->counter;
#else
#define INCR(counter)
#endif

#define BCMP(p1, p2, n) memcmp((char *)(p1), (char *)(p2), (int)(n))
#define BCOPY(p1, p2, n) movmem((char *)(p1), (char *)(p2), (int)(n))
#ifndef KERNEL
#define ovbcopy movmem
#endif

typedef	char *	caddr_t;

extern struct Library *SysBase;

void
 sl_compress_init(comp)
    struct slcompress *comp;
{
    register u_int i;
    register struct cstate *tstate = comp->tstate;

    setmem((char *) comp, sizeof(*comp), 0);
    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++); \
        } \
}

#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;
    ULONG 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;
        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 (((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);
}


ULONG
 sl_uncompress_tcp(bufp, len, type, comp)
    u_char **bufp;
    ULONG len;
    ULONG 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 (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.
     */
    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;

    if ((int) cp & 3)
    {
        if (len > 0)
            (void) ovbcopy(cp, (caddr_t) ((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);
  bad:
    comp->flags |= SLF_TOSS;
    INCR(sls_errorin)
        return (0);
}
