text: /*
   * 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).
   *
   * Modified March 1998 by Guy Lancaster, glanca@gesn.com,
   * for a 16 bit processor.
   */
  
  #include "lwip/opt.h"
  #if PPP_SUPPORT && VJ_SUPPORT /* don't build if not configured for use in lwipopts.h */
  
  #include "netif/ppp/ppp_impl.h"
  #include "netif/ppp/pppdebug.h"
  
  #include "netif/ppp/vj.h"
  
  #include <string.h>
  
  #if LINK_STATS
  #define INCR(counter) ++comp->stats.counter
  #else
  #define INCR(counter)
  #endif
  
  void
  vj_compress_init(struct vjcompress *comp)
  {
    register u_char i;
    register struct cstate *tstate = comp->tstate;
    
  #if MAX_SLOTS == 0
    memset((char *)comp, 0, sizeof(*comp));
  #endif
    comp->maxSlotIndex = MAX_SLOTS - 1;
    comp->compressSlot = 0;    /* Disable slot ID compression by default. */
    for (i = MAX_SLOTS - 1; i > 0; --i) {
      tstate[i].cs_id = i;
      tstate[i].cs_next = &tstate[i - 1];
    }
    tstate[0].cs_next = &tstate[MAX_SLOTS - 1];
    tstate[0].cs_id = 0;
    comp->last_cs = &tstate[0];
    comp->last_recv = 255;
    comp->last_xmit = 255;
    comp->flags = VJF_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] = (u_char)(n); \
      cp[0] = (u_char)((n) >> 8); \
      cp += 2; \
    } else { \
      *cp++ = (u_char)(n); \
    } \
  }
  #define ENCODEZ(n) { \
    if ((u_short)(n) >= 256 || (u_short)(n) == 0) { \
      *cp++ = 0; \
      cp[1] = (u_char)(n); \
      cp[0] = (u_char)((n) >> 8); \
      cp += 2; \
    } else { \
      *cp++ = (u_char)(n); \
    } \
  }
  
  #define DECODEL(f) { \
    if (*cp == 0) {\
      u32_t tmp_ = ntohl(f) + ((cp[1] << 8) | cp[2]); \
      (f) = htonl(tmp_); \
      cp += 3; \
    } else { \
      u32_t tmp_ = ntohl(f) + (u32_t)*cp++; \
      (f) = htonl(tmp_); \
    } \
  }
  
  #define DECODES(f) { \
    if (*cp == 0) {\
      u_short tmp_ = ntohs(f) + (((u_short)cp[1] << 8) | cp[2]); \
      (f) = htons(tmp_); \
      cp += 3; \
    } else { \
      u_short tmp_ = ntohs(f) + (u_short)*cp++; \
      (f) = htons(tmp_); \
    } \
  }
  
  #define DECODEU(f) { \
    if (*cp == 0) {\
      (f) = htons(((u_short)cp[1] << 8) | cp[2]); \
      cp += 3; \
    } else { \
      (f) = htons((u_short)*cp++); \
    } \
  }
  
  /*
   * vj_compress_tcp - Attempt to do Van Jacobson header compression on a
   * packet.  This assumes that nb and comp are not null and that the first
   * buffer of the chain contains a valid IP header.
   * Return the VJ type code indicating whether or not the packet was
   * compressed.
   */
  u_int
  vj_compress_tcp(struct vjcompress *comp, struct pbuf *pb)
  {
    register struct ip_hdr *ip = (struct ip_hdr *)pb->payload;
    register struct cstate *cs = comp->last_cs->cs_next;
    register u_short hlen = IPH_HL(ip);
    register struct tcp_hdr *oth;
    register struct tcp_hdr *th;
    register u_short deltaS, deltaA = 0;
    register u_long deltaL;
    register u_int changes = 0;
    u_char new_seq[16];
    register u_char *cp = new_seq;
  
    /*  
     * Check that the packet is IP proto TCP.
     */
    if (IPH_PROTO(ip) != IP_PROTO_TCP) {
      return (TYPE_IP);
    }
  
    /*
     * 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).  
     */
    if ((IPH_OFFSET(ip) & PP_HTONS(0x3fff)) || pb->tot_len < 40) {
      return (TYPE_IP);
    }
    th = (struct tcp_hdr *)&((long *)ip)[hlen];
    if ((TCPH_FLAGS(th) & (TCP_SYN|TCP_FIN|TCP_RST|TCP_ACK)) != TCP_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(vjs_packets);
    if (!ip_addr_cmp(&ip->src, &cs->cs_ip.src)
        || !ip_addr_cmp(&ip->dest, &cs->cs_ip.dest)
        || *(long *)th != ((long *)&cs->cs_ip)[IPH_HL(&cs->cs_ip)]) {
      /*
       * 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(vjs_searches);
        if (ip_addr_cmp(&ip->src, &cs->cs_ip.src)
            && ip_addr_cmp(&ip->dest, &cs->cs_ip.dest)
            && *(long *)th == ((long *)&cs->cs_ip)[IPH_HL(&cs->cs_ip)]) {
          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(vjs_misses);
      comp->last_cs = lcs;
      hlen += TCPH_HDRLEN(th);
      hlen <<= 2;
      /* Check that the IP/TCP headers are contained in the first buffer. */
      if (hlen > pb->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;
      }
    }
  
    oth = (struct tcp_hdr *)&((long *)&cs->cs_ip)[hlen];
    deltaS = hlen;
    hlen += TCPH_HDRLEN(th);
    hlen <<= 2;
    /* Check that the IP/TCP headers are contained in the first buffer. */
    if (hlen > pb->len) {
      PPPDEBUG(LOG_INFO, ("vj_compress_tcp: header len %d spans buffers\n", hlen));
      return (TYPE_IP);
    }
  
    /*
     * 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'.
     */
    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] 
        || TCPH_HDRLEN(th) != TCPH_HDRLEN(oth) 
        || (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) 
        || (TCPH_HDRLEN(th) > 5 && BCMP(th + 1, oth + 1, (TCPH_HDRLEN(th) - 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 (TCPH_FLAGS(th) & TCP_URG) {
      deltaS = ntohs(th->urgp);
      ENCODEZ(deltaS);
      changes |= NEW_U;
    } else if (th->urgp != oth->urgp) {
      /* 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->wnd) - ntohs(oth->wnd))) != 0) {
      ENCODE(deltaS);
      changes |= NEW_W;
    }
  
    if ((deltaL = ntohl(th->ackno) - ntohl(oth->ackno)) != 0) {
      if (deltaL > 0xffff) {
        goto uncompressed;
      }
      deltaA = (u_short)deltaL;
      ENCODE(deltaA);
      changes |= NEW_A;
    }
  
    if ((deltaL = ntohl(th->seqno) - ntohl(oth->seqno)) != 0) {
      if (deltaL > 0xffff) {
        goto uncompressed;
      }
      deltaS = (u_short)deltaL;
      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 (IPH_LEN(ip) != IPH_LEN(&cs->cs_ip) &&
        ntohs(IPH_LEN(&cs->cs_ip)) == hlen) {
        break;
      }
      /* no 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(IPH_LEN(&cs->cs_ip)) - hlen) {
        /* special case for echoed terminal traffic */
        changes = SPECIAL_I;
        cp = new_seq;
      }
      break;
  
    case NEW_S:
      if (deltaS == ntohs(IPH_LEN(&cs->cs_ip)) - hlen) {
        /* special case for data xfer */
        changes = SPECIAL_D;
        cp = new_seq;
      }
      break;
    default:
       break;
    }
  
    deltaS = (u_short)(ntohs(IPH_ID(ip)) - ntohs(IPH_ID(&cs->cs_ip)));
    if (deltaS != 1) {
      ENCODEZ(deltaS);
      changes |= NEW_I;
    }
    if (TCPH_FLAGS(th) & TCP_PSH) {
      changes |= TCP_PUSH_BIT;
    }
    /*
     * Grab the cksum before we overwrite it below.  Then update our
     * state with this packet's header.
     */
    deltaA = ntohs(th->chksum);
    MEMCPY(&cs->cs_ip, 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 = (u_short)(cp - new_seq);
    if (!comp->compressSlot || comp->last_xmit != cs->cs_id) {
      comp->last_xmit = cs->cs_id;
      hlen -= deltaS + 4;
      if(pbuf_header(pb, -hlen)){
        /* Can we cope with this failing?  Just assert for now */
        LWIP_ASSERT("pbuf_header failed\n", 0);
      }
      cp = (u_char *)pb->payload;
      *cp++ = (u_char)(changes | NEW_C);
      *cp++ = cs->cs_id;
    } else {
      hlen -= deltaS + 3;
      if(pbuf_header(pb, -hlen)) {
        /* Can we cope with this failing?  Just assert for now */
        LWIP_ASSERT("pbuf_header failed\n", 0);
      }
      cp = (u_char *)pb->payload;
      *cp++ = (u_char)changes;
    }
    *cp++ = (u_char)(deltaA >> 8);
    *cp++ = (u_char)deltaA;
    MEMCPY(cp, new_seq, deltaS);
    INCR(vjs_compressed);
    return (TYPE_COMPRESSED_TCP);
  
    /*
     * Update connection state cs & send uncompressed packet (that is,
     * a regular ip/tcp packet but with the 'conversation id' we hope
     * to use on future compressed packets in the protocol field).
     */
  uncompressed:
    MEMCPY(&cs->cs_ip, ip, hlen);
    IPH_PROTO_SET(ip, cs->cs_id);
    comp->last_xmit = cs->cs_id;
    return (TYPE_UNCOMPRESSED_TCP);
  }
  
  /*
   * Called when we may have missed a packet.
   */
  void
  vj_uncompress_err(struct vjcompress *comp)
  {
    comp->flags |= VJF_TOSS;
    INCR(vjs_errorin);
  }
  
  /*
   * "Uncompress" a packet of type TYPE_UNCOMPRESSED_TCP.
   * Return 0 on success, -1 on failure.
   */
  int
  vj_uncompress_uncomp(struct pbuf *nb, struct vjcompress *comp)
  {
    register u_int hlen;
    register struct cstate *cs;
    register struct ip_hdr *ip;
    
    ip = (struct ip_hdr *)nb->payload;
    hlen = IPH_HL(ip) << 2;
    if (IPH_PROTO(ip) >= MAX_SLOTS
        || hlen + sizeof(struct tcp_hdr) > nb->len
        || (hlen += TCPH_HDRLEN(((struct tcp_hdr *)&((char *)ip)[hlen])) << 2)
            > nb->len
        || hlen > MAX_HDR) {
      PPPDEBUG(LOG_INFO, ("vj_uncompress_uncomp: bad cid=%d, hlen=%d buflen=%d\n", 
        IPH_PROTO(ip), hlen, nb->len));
      comp->flags |= VJF_TOSS;
      INCR(vjs_errorin);
      return -1;
    }
    cs = &comp->rstate[comp->last_recv = IPH_PROTO(ip)];
    comp->flags &=~ VJF_TOSS;
    IPH_PROTO_SET(ip, IP_PROTO_TCP);
    MEMCPY(&cs->cs_ip, ip, hlen);
    cs->cs_hlen = (u_short)hlen;
    INCR(vjs_uncompressedin);
    return 0;
  }
  
  /*
   * Uncompress a packet of type TYPE_COMPRESSED_TCP.
   * The packet is composed of a buffer chain and the first buffer
   * must contain an accurate chain length.
   * The first buffer must include the entire compressed TCP/IP header. 
   * This procedure replaces the compressed header with the uncompressed
   * header and returns the length of the VJ header.
   */
  int
  vj_uncompress_tcp(struct pbuf **nb, struct vjcompress *comp)
  {
    u_char *cp;
    struct tcp_hdr *th;
    struct cstate *cs;
    u_short *bp;
    struct pbuf *n0 = *nb;
    u32_t tmp;
    u_int vjlen, hlen, changes;
  
    INCR(vjs_compressedin);
    cp = (u_char *)n0->payload;
    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_SLOTS) {
        PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: bad cid=%d\n", *cp));
        goto bad;
      }
  
      comp->flags &=~ VJF_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 & VJF_TOSS) {
        PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: tossing\n"));
        INCR(vjs_tossed);
        return (-1);
      }
    }
    cs = &comp->rstate[comp->last_recv];
    hlen = IPH_HL(&cs->cs_ip) << 2;
    th = (struct tcp_hdr *)&((u_char *)&cs->cs_ip)[hlen];
    th->chksum = htons((*cp << 8) | cp[1]);
    cp += 2;
    if (changes & TCP_PUSH_BIT) {
      TCPH_SET_FLAG(th, TCP_PSH);
    } else {
      TCPH_UNSET_FLAG(th, TCP_PSH);
    }
  
    switch (changes & SPECIALS_MASK) {
    case SPECIAL_I:
      {
        register u32_t i = ntohs(IPH_LEN(&cs->cs_ip)) - cs->cs_hlen;
        /* some compilers can't nest inline assembler.. */
        tmp = ntohl(th->ackno) + i;
        th->ackno = htonl(tmp);
        tmp = ntohl(th->seqno) + i;
        th->seqno = htonl(tmp);
      }
      break;
  
    case SPECIAL_D:
      /* some compilers can't nest inline assembler.. */
      tmp = ntohl(th->seqno) + ntohs(IPH_LEN(&cs->cs_ip)) - cs->cs_hlen;
      th->seqno = htonl(tmp);
      break;
  
    default:
      if (changes & NEW_U) {
        TCPH_SET_FLAG(th, TCP_URG);
        DECODEU(th->urgp);
      } else {
        TCPH_UNSET_FLAG(th, TCP_URG);
      }
      if (changes & NEW_W) {
        DECODES(th->wnd);
      }
      if (changes & NEW_A) {
        DECODEL(th->ackno);
      }
      if (changes & NEW_S) {
        DECODEL(th->seqno);
      }
      break;
    }
    if (changes & NEW_I) {
      DECODES(cs->cs_ip._id);
    } else {
      IPH_ID_SET(&cs->cs_ip, ntohs(IPH_ID(&cs->cs_ip)) + 1);
      IPH_ID_SET(&cs->cs_ip, htons(IPH_ID(&cs->cs_ip)));
    }
  
    /*
     * 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 = (u_short)(cp - (u_char*)n0->payload);
    if (n0->len < vjlen) {
      /* 
       * We must have dropped some characters (crc should detect
       * this but the old slip framing won't) 
       */
      PPPDEBUG(LOG_INFO, ("vj_uncompress_tcp: head buffer %d too short %d\n", 
            n0->len, vjlen));
      goto bad;
    }
  
  #if BYTE_ORDER == LITTLE_ENDIAN
    tmp = n0->tot_len - vjlen + cs->cs_hlen;
    IPH_LEN_SET(&cs->cs_ip, htons((u_short)tmp));
  #else
    IPH_LEN_SET(&cs->cs_ip, htons(n0->tot_len - vjlen + cs->cs_hlen));
  #endif
  
    /* recompute the ip header checksum */
    bp = (u_short *) &cs->cs_ip;
    IPH_CHKSUM_SET(&cs->cs_ip, 0);
    for (tmp = 0; hlen > 0; hlen -= 2) {
      tmp += *bp++;
    }
    tmp = (tmp & 0xffff) + (tmp >> 16);
    tmp = (tmp & 0xffff) + (tmp >> 16);
    IPH_CHKSUM_SET(&cs->cs_ip,  (u_short)(~tmp));
    
    /* Remove the compressed header and prepend the uncompressed header. */
    if(pbuf_header(n0, -((s16_t)(vjlen)))) {
      /* Can we cope with this failing?  Just assert for now */
      LWIP_ASSERT("pbuf_header failed\n", 0);
      goto bad;
    }
  
    if(LWIP_MEM_ALIGN(n0->payload) != n0->payload) {
      struct pbuf *np, *q;
      u8_t *bufptr;
  
  #if IP_FORWARD
      /* If IP forwarding is enabled we are using a PBUF_LINK packet type so
       * the packet is being allocated with enough header space to be
       * forwarded (to Ethernet for example).
       */
      np = pbuf_alloc(PBUF_LINK, n0->len + cs->cs_hlen, PBUF_POOL);
  #else /* IP_FORWARD */
      np = pbuf_alloc(PBUF_RAW, n0->len + cs->cs_hlen, PBUF_POOL);
  #endif /* IP_FORWARD */
      if(!np) {
        PPPDEBUG(LOG_WARNING, ("vj_uncompress_tcp: realign failed\n"));
        goto bad;
      }
  
      if(pbuf_header(np, -cs->cs_hlen)) {
        /* Can we cope with this failing?  Just assert for now */
        LWIP_ASSERT("pbuf_header failed\n", 0);
        goto bad;
      }
  
      bufptr = (u8_t*)n0->payload;
      for(q = np; q != NULL; q = q->next) {
        MEMCPY(q->payload, bufptr, q->len);
        bufptr += q->len;
      }
  
      if(n0->next) {
        pbuf_chain(np, n0->next);
        pbuf_dechain(n0);
      }
      pbuf_free(n0);
      n0 = np;
    }
  
    if(pbuf_header(n0, cs->cs_hlen)) {
      struct pbuf *np;
  
      LWIP_ASSERT("vj_uncompress_tcp: cs->cs_hlen <= PBUF_POOL_BUFSIZE", cs->cs_hlen <= PBUF_POOL_BUFSIZE);
      np = pbuf_alloc(PBUF_RAW, cs->cs_hlen, PBUF_POOL);
      if(!np) {
        PPPDEBUG(LOG_WARNING, ("vj_uncompress_tcp: prepend failed\n"));
        goto bad;
      }
      pbuf_cat(np, n0);
      n0 = np;
    }
    LWIP_ASSERT("n0->len >= cs->cs_hlen", n0->len >= cs->cs_hlen);
    MEMCPY(n0->payload, &cs->cs_ip, cs->cs_hlen);
  
    *nb = n0;
  
    return vjlen;
  
  bad:
    comp->flags |= VJF_TOSS;
    INCR(vjs_errorin);
    return (-1);
  }
  
  #endif /* PPP_SUPPORT && VJ_SUPPORT */
  