vjcompress.c

经典的ppp程序

/*
 * 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).
 */

/*
 * This version is used under SunOS 4.x, Digital UNIX, AIX 4.x,
 * and SVR4 systems including Solaris 2.
 *
 * $Id: vjcompress.c,v 1.10 1999/09/15 23:49:06 masputra Exp $
 */

#include <sys/types.h>
#include <sys/param.h>

#ifdef SVR4
#ifndef __GNUC__
#include <sys/byteorder.h>	/* for ntohl, etc. */
#else
/* make sure we don't get the gnu "fixed" one! */
#include "/usr/include/sys/byteorder.h"
#endif
#endif

#ifdef __osf__
#include <net/net_globals.h>
#endif
#include <netinet/in.h>

#ifdef AIX4
#define _NETINET_IN_SYSTM_H_
typedef u_long  n_long;
#else
#include <netinet/in_systm.h>
#endif

#include <netinet/ip.h>
#include <netinet/tcp.h>

#include <net/ppp_defs.h>
#include <net/vjcompress.h>

#ifndef VJ_NO_STATS
#define INCR(counter) ++comp->stats.counter
#else
#define INCR(counter)
#endif

#define BCMP(p1, p2, n) bcmp((char *)(p1), (char *)(p2), (int)(n))
#undef  BCOPY
#define BCOPY(p1, p2, n) bcopy((char *)(p1), (char *)(p2), (int)(n))
#ifndef KERNEL
#define ovbcopy bcopy
#endif

#ifdef __osf__
#define getip_hl(base)	(((base).ip_vhl)&0xf)
#define getth_off(base)	((((base).th_xoff)&0xf0)>>4)

#else
#define getip_hl(base)	((base).ip_hl)
#define getth_off(base)	((base).th_off)
#endif

void
vj_compress_init(comp, max_state)
    struct vjcompress *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));
    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 = 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) {\
		u_int32_t tmp = ntohl(f) + ((cp[1] << 8) | cp[2]); \
		(f) = htonl(tmp); \
		cp += 3; \
	} else { \
		u_int32_t tmp = ntohl(f) + (u_int32_t)*cp++; \
		(f) = htonl(tmp); \
	} \
}

#define DECODES(f) { \
	if (*cp == 0) {\
		u_short tmp = ntohs(f) + ((cp[1] << 8) | cp[2]); \
		(f) = htons(tmp); \
		cp += 3; \
	} else { \
		u_short tmp = ntohs(f) + (u_int32_t)*cp++; \
		(f) = htons(tmp); \
	} \
}

#define DECODEU(f) { \
	if (*cp == 0) {\
		(f) = htons((cp[1] << 8) | cp[2]); \
		cp += 3; \
	} else { \
		(f) = htons((u_int32_t)*cp++); \
	} \
}

u_int
vj_compress_tcp(ip, mlen, comp, compress_cid, vjhdrp)
    register struct ip *ip;
    u_int mlen;
    struct vjcompress *comp;
    int compress_cid;
    u_char **vjhdrp;
{
    register struct cstate *cs = comp->last_cs->cs_next;
    register u_int hlen = getip_hl(*ip);
    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)) || mlen < 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(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 ||
	*(int *)th != ((int *)&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
		&& *(int *)th == ((int *)&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;
	if (hlen > mlen)
	    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 *)&((int *)&cs->cs_ip)[hlen];
    deltaS = hlen;
    hlen += getth_off(*th);
    hlen <<= 2;
    if (hlen > mlen)
	return (TYPE_IP);

    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 & TH_URG) {
	deltaS = ntohs(th->th_urp);
	ENCODEZ(deltaS);