pppcompress.c

unix and linux net driver

	}

	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
vj_uncompress_tcp(bufp, len, type, comp)
	u_char **bufp;
	int len;
	u_int type;
	struct vjcompress *comp;
{
	u_char *hdr, *cp;
	int hlen, vjlen;

	cp = bufp? *bufp: NULL;
	vjlen = vj_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 ((int)cp & 3) {
		if (len > 0)
			(void) ovbcopy(cp, (caddr_t)((int)cp &~ 3), len);
		cp = (u_char *)((int)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
vj_uncompress_tcp_core(buf, buflen, total_len, type, comp, hdrp, hlenp)
	u_char *buf;
	int buflen, total_len;
	u_int type;
	struct vjcompress *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_short *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_short *) &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);
}