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 /* don't build if not configured for use in lwipopts.h */
  
  #include "ppp_impl.h"
  #include "pppdebug.h"
  
  #include "vj.h"
  
  #include <string.h>
  
  #if VJ_SUPPORT
  
  #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;
      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;
              }
  
          /* (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;
      }
  
      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);
      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 = (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;
      BCOPY(new_seq, cp, 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:
      BCOPY(ip, &cs->cs_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);
      BCOPY(ip, &cs->cs_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;
  
          np = pbuf_alloc(PBUF_RAW, n0->len + cs->cs_hlen, PBUF_POOL);
          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 = 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 /* VJ_SUPPORT */
  
  #endif /* PPP_SUPPORT */
  