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//==========================================================================

//

//      src/slcompress.c

//

//==========================================================================

// ####ECOSGPLCOPYRIGHTBEGIN####                                            

// -------------------------------------------                              

// This file is part of eCos, the Embedded Configurable Operating System.   

// Copyright (C) 2003 Free Software Foundation, Inc.                        

//

// eCos is free software; you can redistribute it and/or modify it under    

// the terms of the GNU General Public License as published by the Free     

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//

// As a special exception, if other files instantiate templates or use      

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// ####ECOSGPLCOPYRIGHTEND####                                              

// ####BSDALTCOPYRIGHTBEGIN####                                             

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// Portions of this software may have been derived from FreeBSD, OpenBSD,   

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// ####BSDALTCOPYRIGHTEND####                                               

//==========================================================================

/*-

 * Copyright (c) 1989, 1993, 1994

 *      The Regents of the University of California.  All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 * 3. Neither the name of the University nor the names of its contributors

 *    may be used to endorse or promote products derived from this software

 *    without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND

 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE

 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

 * SUCH DAMAGE.

 *

 *      @(#)slcompress.c        8.2 (Berkeley) 4/16/94

 * $FreeBSD: src/sys/net/slcompress.c,v 1.16 1999/12/29 04:38:37 peter Exp $

 */

/*

 * Routines to compress and uncompess tcp packets (for transmission

 * over low speed serial lines.

 *

 * Van Jacobson (van@helios.ee.lbl.gov), Dec 31, 1989:

 *      - Initial distribution.

 *

 */

#define _KERNEL

#include <sys/param.h>

#include <sys/mbuf.h>

//#include <sys/systm.h>

#include <netinet/in.h>

#include <netinet/in_systm.h>

#include <netinet/ip.h>

#include <netinet/tcp.h>

#include <cyg/ppp/slcompress.h>

typedef CYG_ADDRWORD intptr_t;

#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, max_state)

        struct slcompress *comp;

        int max_state;

{

        register u_int i;

        register struct cstate *tstate = comp->tstate;

        if (max_state == -1) {

                max_state = MAX_STATES - 1;

                bzero((char *)comp, sizeof(*comp));

        } else {

                /* Don't reset statistics */

                bzero((char *)comp->tstate, sizeof(comp->tstate));

                bzero((char *)comp->rstate, sizeof(comp->rstate));

        }

        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_int16_t)(n) >= 256) { \

                *cp++ = 0; \

                cp[1] = (n); \

                cp[0] = (n) >> 8; \

                cp += 2; \

        } else { \

                *cp++ = (n); \

        } \

}

#define ENCODEZ(n) { \

        if ((u_int16_t)(n) >= 256 || (u_int16_t)(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_int32_t)*cp++); \

        } \

}

#define DECODES(f) { \

        if (*cp == 0) {\

                (f) = htons(ntohs(f) + ((cp[1] << 8) | cp[2])); \

                cp += 3; \

        } else { \

                (f) = htons(ntohs(f) + (u_int32_t)*cp++); \

        } \

}

#define DECODEU(f) { \

        if (*cp == 0) {\

                (f) = htons((cp[1] << 8) | cp[2]); \

                cp += 3; \

        } else { \

                (f) = htons((u_int32_t)*cp++); \

        } \

}

/*

 * Attempt to compress an outgoing TCP packet and return the type of

 * the result.  The caller must have already verified that the protocol

 * is TCP.  The first mbuf must contain the complete IP and TCP headers,

 * and "ip" must be == mtod(m, struct ip *).  "comp" supplies the

 * compression state, and "compress_cid" tells us whether it is OK

 * to leave out the CID field when feasible.

 *

 * The caller is responsible for adjusting m->m_pkthdr.len upon return,

 * if m is an M_PKTHDR mbuf.

 */

u_int

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 *)&((int32_t *)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 ||

            *(int32_t *)th != ((int32_t *)&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

                            && *(int32_t *)th ==

                            ((int32_t *)&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 *)&((int32_t *)&cs->cs_ip)[hlen];

        deltaS = hlen;

        hlen += th->th_off;

        hlen <<= 2;

        if (hlen > m->m_len)

            return TYPE_IP;

        if (((u_int16_t *)ip)[0] != ((u_int16_t *)&cs->cs_ip)[0] ||

            ((u_int16_t *)ip)[3] != ((u_int16_t *)&cs->cs_ip)[3] ||

            ((u_int16_t *)ip)[4] != ((u_int16_t *)&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;

        deltaS = (u_int16_t)(ntohs(th->th_win) - ntohs(oth->th_win));

        if (deltaS) {

                ENCODE(deltaS);

                changes |= NEW_W;

        }

        deltaA = ntohl(th->th_ack) - ntohl(oth->th_ack);

        if (deltaA) {

                if (deltaA > 0xffff)

                        goto uncompressed;

                ENCODE(deltaA);

                changes |= NEW_A;

        }

        deltaS = ntohl(th->th_seq) - ntohl(oth->th_seq);

        if (deltaS) {

                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_data += 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;

{

        u_char *hdr, *cp;

        unsigned int hlen;

        int vjlen;

        cp = bufp? *bufp: NULL;

        vjlen = sl_uncompress_tcp_core(cp, len, len, type, comp, &hdr, &hlen);

        if (vjlen < 0)

                return (0);      /* error */

        if (vjlen == 0)

                return (len);   /* was uncompressed already */

        cp += vjlen;

        len -= vjlen;

        /*

         * 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).

         */

        if ((intptr_t)cp & 3) {

                if (len > 0)

                        (void) ovbcopy(cp, (caddr_t)((intptr_t)cp &~ 3), len);

                cp = (u_char *)((intptr_t)cp &~ 3);

        }

        cp -= hlen;

        len += hlen;

        BCOPY(hdr, cp, hlen);

        *bufp = cp;

        return (len);

}

/*

 * Uncompress a packet of total length total_len.  The first buflen

 * bytes are at buf; this must include the entire (compressed or

 * uncompressed) TCP/IP header.  This procedure returns the length

 * of the VJ header, with a pointer to the uncompressed IP header

 * in *hdrp and its length in *hlenp.

 */

int

sl_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp)

        u_char *buf;

        int buflen, total_len;

        u_int type;

        struct slcompress *comp;

        u_char **hdrp;

        u_int *hlenp;

{

        register u_char *cp;

        register u_int hlen, changes;

        register struct tcphdr *th;

        register struct cstate *cs;

        register struct ip *ip;

        register u_int16_t *bp;

        register u_int vjlen;

        switch (type) {

        case TYPE_UNCOMPRESSED_TCP:

                ip = (struct ip *) buf;

                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;

                /*

                 * Calculate the size of the TCP/IP header and make sure that

                 * we don't overflow the space we have available for it.

                 */

                hlen = ip->ip_hl << 2;

                if (hlen + sizeof(struct tcphdr) > buflen)

                        goto bad;

                hlen += ((struct tcphdr *)&((char *)ip)[hlen])->th_off << 2;

                if (hlen > MAX_HDR || hlen > buflen)

                        goto bad;

                BCOPY(ip, &cs->cs_ip, hlen);

                cs->cs_hlen = hlen;

                INCR(sls_uncompressedin)

                *hdrp = (u_char *) &cs->cs_ip;

                *hlenp = hlen;

                return (0);

        default:

                goto bad;

        case TYPE_COMPRESSED_TCP:

                break;

        }

        /* We've got a compressed packet. */

        INCR(sls_compressedin)

        cp = buf;

        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 (-1);

                }

        }

        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.  Fill in the IP total length and update the IP

         * header checksum.

         */

        vjlen = cp - buf;

        buflen -= vjlen;

        if (buflen < 0)

                /* we must have dropped some characters (crc should detect

                 * this but the old slip framing won't) */

                goto bad;

        total_len += cs->cs_hlen - vjlen;

        cs->cs_ip.ip_len = htons(total_len);

        /* recompute the ip header checksum */

        bp = (u_int16_t *) &cs->cs_ip;

        cs->cs_ip.ip_sum = 0;

                for (changes = 0; hlen > 0; hlen -= 2)

                        changes += *bp++;

                changes = (changes & 0xffff) + (changes >> 16);

                changes = (changes & 0xffff) + (changes >> 16);

        cs->cs_ip.ip_sum = ~ changes;

        *hdrp = (u_char *) &cs->cs_ip;

        *hlenp = cs->cs_hlen;

        return vjlen;

bad:

        comp->flags |= SLF_TOSS;

        INCR(sls_errorin)

        return (-1);

}