vj.c

最新的lwip 1.3.0版本在ucos平台上的移植

/*
 * 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 ([e-mail]), Dec 31, 1989:
 *   Initial distribution.
 *
 * Modified June 1993 by Paul Mackerras, [e-mail],
 * 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, [e-mail],
 * 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.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

#if defined(NO_CHAR_BITFIELDS)
#define getip_hl(base)  ((base).ip_hl_v&0xf)
#define getth_off(base) (((base).th_x2_off&0xf0)>>4)
#else
#define getip_hl(base)  ((base).ip_hl)
#define getth_off(base) ((base).th_off)
#endif

void
vj_compress_init(struct vjcompress *comp)
{
  register u_int 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] = (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) {\
    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 Jacobsen 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 *ip = (struct ip *)pb->payload;
  register struct cstate *cs = comp->last_cs->cs_next;
  register u_short hlen = getip_hl(*ip);
  register struct tcphdr *oth;
  register struct tcphdr *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 (ip->ip_p != IPPROTO_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 ((ip->ip_off & htons(0x3fff)) || pb->tot_len < 40) {
    return (TYPE_IP);
  }
  th = (struct tcphdr *)&((long *)ip)[hlen];
  if ((th->th_flags & (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->ip_src.s_addr != cs->cs_ip.ip_src.s_addr 
      || ip->ip_dst.s_addr != cs->cs_ip.ip_dst.s_addr 
      || *(long *)th != ((long *)&cs->cs_ip)[getip_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->ip_src.s_addr == cs->cs_ip.ip_src.s_addr
          && ip->ip_dst.s_addr == cs->cs_ip.ip_dst.s_addr
          && *(long *)th == ((long *)&cs->cs_ip)[getip_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 += getth_off(*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 tcphdr *)&((long *)&cs->cs_ip)[hlen];
  deltaS = hlen;
  hlen += getth_off(*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] 
      || getth_off(*th) != getth_off(*oth) 
      || (deltaS > 5 && BCMP(ip + 1, &cs->cs_ip + 1, (deltaS - 5) << 2)) 
      || (getth_off(*th) > 5 && BCMP(th + 1, oth + 1, (getth_off(*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 (th->th_flags & TCP_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))) != 0) {
    ENCODE(deltaS);
    changes |= NEW_W;
  }

  if ((deltaL = ntohl(th->th_ack) - ntohl(oth->th_ack)) != 0) {
    if (deltaL > 0xffff) {
      goto uncompressed;
    }
    deltaA = (u_short)deltaL;
    ENCODE(deltaA);
    changes |= NEW_A;
  }

  if ((deltaL = ntohl(th->th_seq) - ntohl(oth->th_seq)) != 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 (ip->ip_len != cs->cs_ip.ip_len &&
      ntohs(cs->cs_ip.ip_len) == hlen) {
      break;
    }

  /* (fall through) */