slhc.c

主要内容为linux内核代码

	if((deltaA = ntohl(th->ack_seq) - ntohl(oth->ack_seq)) != 0L){
		if(deltaA > 0x0000ffff)
			goto uncompressed;
		cp = encode(cp,deltaA);
		changes |= NEW_A;
	}
	if((deltaS = ntohl(th->seq) - ntohl(oth->seq)) != 0L){
		if(deltaS > 0x0000ffff)
			goto uncompressed;
		cp = encode(cp,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->tot_len != cs->cs_ip.tot_len && 
		   ntohs(cs->cs_ip.tot_len) == hlen)
			break;
		DPRINT(("comp: retrans\n"));
		goto uncompressed;
		break;
	case SPECIAL_I:
	case SPECIAL_D:
		/* actual changes match one of our special case encodings --
		 * send packet uncompressed.
		 */
		DPRINT(("comp: special\n"));
		goto uncompressed;
	case NEW_S|NEW_A:
		if(deltaS == deltaA &&
		    deltaS == ntohs(cs->cs_ip.tot_len) - hlen){
			/* special case for echoed terminal traffic */
			changes = SPECIAL_I;
			cp = new_seq;
		}
		break;
	case NEW_S:
		if(deltaS == ntohs(cs->cs_ip.tot_len) - hlen){
			/* special case for data xfer */
			changes = SPECIAL_D;
			cp = new_seq;
		}
		break;
	}
	deltaS = ntohs(ip->id) - ntohs(cs->cs_ip.id);
	if(deltaS != 1){
		cp = encode(cp,deltaS);
		changes |= NEW_I;
	}
	if(th->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->check);
	memcpy(&cs->cs_ip,ip,20);
	memcpy(&cs->cs_tcp,th,20);
	/* 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.
	 */
	deltaS = cp - new_seq;
	if(compress_cid == 0 || comp->xmit_current != cs->cs_this){
		cp = ocp;
		*cpp = ocp;
		*cp++ = changes | NEW_C;
		*cp++ = cs->cs_this;
		comp->xmit_current = cs->cs_this;
	} else {
		cp = ocp;
		*cpp = ocp;
		*cp++ = changes;
	}
	cp = put16(cp,(short)deltaA);	/* Write TCP checksum */
/* deltaS is now the size of the change section of the compressed header */
	DPRINT(("comp: %x %x %x %d %d\n", icp, cp, new_seq, hlen, deltaS));
	memcpy(cp,new_seq,deltaS);	/* Write list of deltas */
	memcpy(cp+deltaS,icp+hlen,isize-hlen);
	comp->sls_o_compressed++;
	ocp[0] |= SL_TYPE_COMPRESSED_TCP;
	return isize - hlen + deltaS + (cp - ocp);

	/* Update connection state cs & send uncompressed packet (i.e.,
	 * 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,20);
	memcpy(&cs->cs_tcp,th,20);
	if (ip->ihl > 5)
	  memcpy(cs->cs_ipopt, ip+1, ((ip->ihl) - 5) * 4);
	if (th->doff > 5)
	  memcpy(cs->cs_tcpopt, th+1, ((th->doff) - 5) * 4);
	comp->xmit_current = cs->cs_this;
	comp->sls_o_uncompressed++;
	memcpy(ocp, icp, isize);
	*cpp = ocp;
	ocp[9] = cs->cs_this;
	ocp[0] |= SL_TYPE_UNCOMPRESSED_TCP;
	return isize;
}


int
slhc_uncompress(struct slcompress *comp, unsigned char *icp, int isize)
{
	register int changes;
	long x;
	register struct tcphdr *thp;
	register struct iphdr *ip;
	register struct cstate *cs;
	int len, hdrlen;
	unsigned char *cp = icp;

	/* We've got a compressed packet; read the change byte */
	comp->sls_i_compressed++;
	if(isize < 3){
		comp->sls_i_error++;
		DPRINT(("uncomp: runt\n"));
		return 0;
	}
	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.
		 */
		x = *cp++;	/* Read conn index */
		if(x < 0 || x > comp->rslot_limit)
			goto bad;

		comp->flags &=~ SLF_TOSS;
		comp->recv_current = x;
	} 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){
			comp->sls_i_tossed++;
			DPRINT(("uncomp: toss\n"));
			return 0;
		}
	}
	cs = &comp->rstate[comp->recv_current];
	thp = &cs->cs_tcp;
	ip = &cs->cs_ip;

	if((x = pull16(&cp)) == -1) {	/* Read the TCP checksum */
		DPRINT(("uncomp: bad tcp chk\n"));
		goto bad;
        }
	thp->check = htons(x);

	thp->psh = (changes & TCP_PUSH_BIT) ? 1 : 0;
/* 
 * we can use the same number for the length of the saved header and
 * the current one, because the packet wouldn't have been sent
 * as compressed unless the options were the same as the previous one
 */

	hdrlen = ip->ihl * 4 + thp->doff * 4;

	switch(changes & SPECIALS_MASK){
	case SPECIAL_I:		/* Echoed terminal traffic */
		{
		register short i;
		i = ntohs(ip->tot_len) - hdrlen;
		thp->ack_seq = htonl( ntohl(thp->ack_seq) + i);
		thp->seq = htonl( ntohl(thp->seq) + i);
		}
		break;

	case SPECIAL_D:			/* Unidirectional data */
		thp->seq = htonl( ntohl(thp->seq) +
				  ntohs(ip->tot_len) - hdrlen);
		break;

	default:
		if(changes & NEW_U){
			thp->urg = 1;
			if((x = decode(&cp)) == -1) {
				DPRINT(("uncomp: bad U\n"));
				goto bad;
			}
			thp->urg_ptr = htons(x);
		} else
			thp->urg = 0;
		if(changes & NEW_W){
			if((x = decode(&cp)) == -1) {
				DPRINT(("uncomp: bad W\n"));
				goto bad;
			}	
			thp->window = htons( ntohs(thp->window) + x);
		}
		if(changes & NEW_A){
			if((x = decode(&cp)) == -1) {
				DPRINT(("uncomp: bad A\n"));
				goto bad;
			}
			thp->ack_seq = htonl( ntohl(thp->ack_seq) + x);
		}
		if(changes & NEW_S){
			if((x = decode(&cp)) == -1) {
				DPRINT(("uncomp: bad S\n"));
				goto bad;
			}
			thp->seq = htonl( ntohl(thp->seq) + x);
		}
		break;
	}
	if(changes & NEW_I){
		if((x = decode(&cp)) == -1) {
			DPRINT(("uncomp: bad I\n"));
			goto bad;
		}
		ip->id = htons (ntohs (ip->id) + x);
	} else
		ip->id = htons (ntohs (ip->id) + 1);

	/*
	 * At this point, cp points to the first byte of data in the
	 * packet.  Put the reconstructed TCP and IP headers back on the
	 * packet.  Recalculate IP checksum (but not TCP checksum).
	 */

	len = isize - (cp - icp);
	if (len < 0)
		goto bad;
	len += hdrlen;
	ip->tot_len = htons(len);
	ip->check = 0;

	DPRINT(("uncomp: %d %d %d %d\n", cp - icp, hdrlen, isize, len));

	memmove(icp + hdrlen, cp, len - hdrlen);

	cp = icp;
	memcpy(cp, ip, 20);
	cp += 20;

	if (ip->ihl > 5) {
	  memcpy(cp, cs->cs_ipopt, ((ip->ihl) - 5) * 4);
	  cp += ((ip->ihl) - 5) * 4;
	}

	((struct iphdr *)icp)->check = ip_csum((struct iphdr*)icp);

	memcpy(cp, thp, 20);
	cp += 20;

	if (thp->doff > 5) {
	  memcpy(cp, cs->cs_tcpopt, ((thp->doff) - 5) * 4);
	  cp += ((thp->doff) - 5) * 4;
	}

if (inet_debug == DBG_SLIP) printk("\runcomp: change %x len %d\n", changes, len);
	return len;
bad:
	comp->sls_i_error++;
	return slhc_toss( comp );
}


int
slhc_remember(struct slcompress *comp, unsigned char *icp, int isize)
{
	register struct cstate *cs;
	short ip_len;
	struct iphdr *ip;
	struct tcphdr *thp;

	unsigned char index;

	if(isize < 20) {
		/* The packet is shorter than a legal IP header */
		comp->sls_i_runt++;
		return slhc_toss( comp );
	}
	/* Sneak a peek at the IP header's IHL field to find its length */
	ip_len = (icp[0] & 0xf) << 2;
	if(ip_len < 20){
		/* The IP header length field is too small */
		comp->sls_i_runt++;
		return slhc_toss( comp );
	}
	index = icp[9];
	icp[9] = IPPROTO_TCP;
	ip = (struct iphdr *) icp;

	if (ip_csum(ip)) {
		/* Bad IP header checksum; discard */
		comp->sls_i_badcheck++;
		return slhc_toss( comp );
	}
	thp = (struct tcphdr *)(((unsigned char *)ip) + ip->ihl*4);
	if(index > comp->rslot_limit) {
		comp->sls_i_error++;
		return slhc_toss(comp);
	}

	/* Update local state */
	cs = &comp->rstate[comp->recv_current = index];
	comp->flags &=~ SLF_TOSS;
	memcpy(&cs->cs_ip,ip,20);
	memcpy(&cs->cs_tcp,thp,20);
	if (ip->ihl > 5)
	  memcpy(cs->cs_ipopt, ip+1, ((ip->ihl) - 5) * 4);
	if (thp->doff > 5)
	  memcpy(cs->cs_tcpopt, thp+1, ((thp->doff) - 5) * 4);
	cs->cs_hsize = ip->ihl*2 + thp->doff*2;
	/* Put headers back on packet
	 * Neither header checksum is recalculated
	 */
	comp->sls_i_uncompressed++;
	return isize;
}


int
slhc_toss(struct slcompress *comp)
{
	if ( comp == NULLSLCOMPR )
		return 0;

	comp->flags |= SLF_TOSS;
	return 0;
}


void slhc_i_status(struct slcompress *comp)
{
	if (comp != NULLSLCOMPR) {
		printk("\t%ld Cmp, %ld Uncmp, %ld Bad, %ld Tossed\n",
			comp->sls_i_compressed,
			comp->sls_i_uncompressed,
			comp->sls_i_error,
			comp->sls_i_tossed);
	}
}


void slhc_o_status(struct slcompress *comp)
{
	if (comp != NULLSLCOMPR) {
		printk("\t%ld Cmp, %ld Uncmp, %ld AsIs, %ld NotTCP\n",
			comp->sls_o_compressed,
			comp->sls_o_uncompressed,
			comp->sls_o_tcp,
			comp->sls_o_nontcp);
		printk("\t%10ld Searches, %10ld Misses\n",
			comp->sls_o_searches,
			comp->sls_o_misses);
	}
}