auto import from //depot/cupcake/@135843

1 files changed, 1714 insertions, 0 deletions

diff --git a/slirp2/tcp_input.c b/slirp2/tcp_input.c
new file mode 100644
index 0000000..c3196d3
--- /dev/null
+++ b/slirp2/tcp_input.c
@@ -0,0 +1,1714 @@
+/*
+ * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994
+ *	The Regents of the University of California.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *	This product includes software developed by the University of
+ *	California, Berkeley and its contributors.
+ * 4. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ *	@(#)tcp_input.c	8.5 (Berkeley) 4/10/94
+ * tcp_input.c,v 1.10 1994/10/13 18:36:32 wollman Exp
+ */
+
+/*
+ * Changes and additions relating to SLiRP
+ * Copyright (c) 1995 Danny Gasparovski.
+ *
+ * Please read the file COPYRIGHT for the
+ * terms and conditions of the copyright.
+ */
+
+#include <slirp.h>
+#include "ip_icmp.h"
+
+struct socket tcb;
+
+int	tcprexmtthresh = 3;
+struct	socket *tcp_last_so = &tcb;
+
+tcp_seq tcp_iss;                /* tcp initial send seq # */
+
+#define TCP_PAWS_IDLE	(24 * 24 * 60 * 60 * PR_SLOWHZ)
+
+/* for modulo comparisons of timestamps */
+#define TSTMP_LT(a,b)	((int)((a)-(b)) < 0)
+#define TSTMP_GEQ(a,b)	((int)((a)-(b)) >= 0)
+
+/*
+ * Insert segment ti into reassembly queue of tcp with
+ * control block tp.  Return TH_FIN if reassembly now includes
+ * a segment with FIN.  The macro form does the common case inline
+ * (segment is the next to be received on an established connection,
+ * and the queue is empty), avoiding linkage into and removal
+ * from the queue and repetition of various conversions.
+ * Set DELACK for segments received in order, but ack immediately
+ * when segments are out of order (so fast retransmit can work).
+ */
+#ifdef TCP_ACK_HACK
+#define TCP_REASS(tp, ti, m, so, flags) {\
+       if ((ti)->ti_seq == (tp)->rcv_nxt && \
+           tcpfrag_list_empty(tp) && \
+           (tp)->t_state == TCPS_ESTABLISHED) {\
+               if (ti->ti_flags & TH_PUSH) \
+                       tp->t_flags |= TF_ACKNOW; \
+               else \
+                       tp->t_flags |= TF_DELACK; \
+               (tp)->rcv_nxt += (ti)->ti_len; \
+               flags = (ti)->ti_flags & TH_FIN; \
+               tcpstat.tcps_rcvpack++;\
+               tcpstat.tcps_rcvbyte += (ti)->ti_len;\
+               if (so->so_emu) { \
+		       if (tcp_emu((so),(m))) sbuf_append((so), (m)); \
+	       } else \
+	       	       sbuf_append((so), (m)); \
+/*               sorwakeup(so); */ \
+	} else {\
+               (flags) = tcp_reass((tp), (ti), (m)); \
+               tp->t_flags |= TF_ACKNOW; \
+       } \
+}
+#else
+#define	TCP_REASS(tp, ti, m, so, flags) { \
+	if ((ti)->ti_seq == (tp)->rcv_nxt && \
+	    tcpfrag_list_empty(tp) && \
+	    (tp)->t_state == TCPS_ESTABLISHED) { \
+		tp->t_flags |= TF_DELACK; \
+		(tp)->rcv_nxt += (ti)->ti_len; \
+		flags = (ti)->ti_flags & TH_FIN; \
+		tcpstat.tcps_rcvpack++;\
+		tcpstat.tcps_rcvbyte += (ti)->ti_len;\
+		if (so->so_emu) { \
+			if (tcp_emu((so),(m))) sbuf_append(so, (m)); \
+		} else \
+			sbuf_append((so), (m)); \
+/*		sorwakeup(so); */ \
+	} else { \
+		(flags) = tcp_reass((tp), (ti), (m)); \
+		tp->t_flags |= TF_ACKNOW; \
+	} \
+}
+#endif
+
+int
+tcp_reass(tp, ti, m)
+	register struct tcpcb *tp;
+	register struct tcpiphdr *ti;
+	MBuf m;
+{
+	register struct tcpiphdr *q;
+	struct socket *so = tp->t_socket;
+	int flags;
+
+	/*
+	 * Call with ti==0 after become established to
+	 * force pre-ESTABLISHED data up to user socket.
+	 */
+	if (ti == 0)
+		goto present;
+
+	/*
+	 * Find a segment which begins after this one does.
+	 */
+	for (q = tcpfrag_list_first(tp); !tcpfrag_list_end(q, tp);
+	     q = tcpiphdr_next(q))
+		if (SEQ_GT(q->ti_seq, ti->ti_seq))
+			break;
+
+	/*
+	 * If there is a preceding segment, it may provide some of
+	 * our data already.  If so, drop the data from the incoming
+	 * segment.  If it provides all of our data, drop us.
+	 */
+	if (!tcpfrag_list_end(tcpiphdr_prev(q), tp)) {
+		register int i;
+		q = tcpiphdr_prev(q);
+		/* conversion to int (in i) handles seq wraparound */
+		i = q->ti_seq + q->ti_len - ti->ti_seq;
+		if (i > 0) {
+			if (i >= ti->ti_len) {
+				tcpstat.tcps_rcvduppack++;
+				tcpstat.tcps_rcvdupbyte += ti->ti_len;
+				mbuf_free(m);
+				/*
+				 * Try to present any queued data
+				 * at the left window edge to the user.
+				 * This is needed after the 3-WHS
+				 * completes.
+				 */
+				goto present;   /* ??? */
+			}
+			mbuf_trim(m, i);
+			ti->ti_len -= i;
+			ti->ti_seq += i;
+		}
+		q = tcpiphdr_next(q);
+	}
+	tcpstat.tcps_rcvoopack++;
+	tcpstat.tcps_rcvoobyte += ti->ti_len;
+	ti->ti_mbuf = m;
+
+	/*
+	 * While we overlap succeeding segments trim them or,
+	 * if they are completely covered, dequeue them.
+	 */
+	while (!tcpfrag_list_end(q, tp)) {
+		register int i = (ti->ti_seq + ti->ti_len) - q->ti_seq;
+		if (i <= 0)
+			break;
+		if (i < q->ti_len) {
+			q->ti_seq += i;
+			q->ti_len -= i;
+			mbuf_trim(q->ti_mbuf, i);
+			break;
+		}
+		q = tcpiphdr_next(q);
+		m = tcpiphdr_prev(q)->ti_mbuf;
+		remque(tcpiphdr2qlink(tcpiphdr_prev(q)));
+		mbuf_free(m);
+	}
+
+	/*
+	 * Stick new segment in its place.
+	 */
+	insque(tcpiphdr2qlink(ti), tcpiphdr2qlink(tcpiphdr_prev(q)));
+
+present:
+	/*
+	 * Present data to user, advancing rcv_nxt through
+	 * completed sequence space.
+	 */
+	if (!TCPS_HAVEESTABLISHED(tp->t_state))
+		return (0);
+        ti = tcpfrag_list_first(tp);
+        if (tcpfrag_list_end(ti, tp) || ti->ti_seq != tp->rcv_nxt)
+		return (0);
+	if (tp->t_state == TCPS_SYN_RECEIVED && ti->ti_len)
+		return (0);
+	do {
+		tp->rcv_nxt += ti->ti_len;
+		flags = ti->ti_flags & TH_FIN;
+		remque(tcpiphdr2qlink(ti));
+		m = ti->ti_mbuf;
+		ti = tcpiphdr_next(ti);
+/*		if (so->so_state & SS_FCANTRCVMORE) */
+		if (so->so_state & SS_FCANTSENDMORE)
+			mbuf_free(m);
+		else {
+			if (so->so_emu) {
+				if (tcp_emu(so,m)) sbuf_append(so, m);
+			} else
+				sbuf_append(so, m);
+		}
+	} while (!tcpfrag_list_end(ti, tp) && ti->ti_seq == tp->rcv_nxt);
+/*	sorwakeup(so); */
+	return (flags);
+}
+
+/*
+ * TCP input routine, follows pages 65-76 of the
+ * protocol specification dated September, 1981 very closely.
+ */
+void
+tcp_input(m, iphlen, inso)
+	register MBuf m;
+	int iphlen;
+	struct socket *inso;
+{
+  	struct ip save_ip, *ip;
+	register struct tcpiphdr *ti;
+	caddr_t optp = NULL;
+	int optlen = 0;
+	int len, tlen, off;
+	register struct tcpcb *tp = 0;
+	register int tiflags;
+	struct socket *so = 0;
+	int todrop, acked, ourfinisacked, needoutput = 0;
+/*	int dropsocket = 0; */
+	int iss = 0;
+	u_long tiwin;
+	int ret;
+/*	int ts_present = 0; */
+
+	DEBUG_CALL("tcp_input");
+	DEBUG_ARGS((dfd," m = %8lx  iphlen = %2d  inso = %lx\n",
+		    (long )m, iphlen, (long )inso ));
+
+	/*
+	 * If called with m == 0, then we're continuing the connect
+	 */
+	if (m == NULL) {
+		so = inso;
+
+		/* Re-set a few variables */
+		tp = sototcpcb(so);
+		m = so->so_m;
+		so->so_m = 0;
+		ti = so->so_ti;
+		tiwin = ti->ti_win;
+		tiflags = ti->ti_flags;
+
+		goto cont_conn;
+	}
+
+
+	tcpstat.tcps_rcvtotal++;
+	/*
+	 * Get IP and TCP header together in first mbuf.
+	 * Note: IP leaves IP header in first mbuf.
+	 */
+	ti = MBUF_TO(m, struct tcpiphdr *);
+	if (iphlen > sizeof(struct ip )) {
+	  ip_stripoptions(m, (MBuf )0);
+	  iphlen=sizeof(struct ip );
+	}
+	/* XXX Check if too short */
+
+
+	/*
+	 * Save a copy of the IP header in case we want restore it
+	 * for sending an ICMP error message in response.
+	 */
+	ip=MBUF_TO(m, struct ip *);
+	save_ip = *ip;
+	save_ip.ip_len+= iphlen;
+
+	/*
+	 * Checksum extended TCP header and data.
+	 */
+	tlen = ((struct ip *)ti)->ip_len;
+	tcpiphdr2qlink(ti)->next = tcpiphdr2qlink(ti)->prev = 0;
+	memset(&ti->ti_i.ih_mbuf, 0, sizeof(struct mbuf_ptr));
+	ti->ti_x1 = 0;
+	ti->ti_len = htons((u_int16_t)tlen);
+	len = sizeof(struct ip ) + tlen;
+	/* keep checksum for ICMP reply
+	 * ti->ti_sum = cksum(m, len);
+	 * if (ti->ti_sum) { */
+	if(cksum(m, len)) {
+	  tcpstat.tcps_rcvbadsum++;
+	  goto drop;
+	}
+
+	/*
+	 * Check that TCP offset makes sense,
+	 * pull out TCP options and adjust length.		XXX
+	 */
+	off = ti->ti_off << 2;
+	if (off < sizeof (struct tcphdr) || off > tlen) {
+	  tcpstat.tcps_rcvbadoff++;
+	  goto drop;
+	}
+	tlen -= off;
+	ti->ti_len = tlen;
+	if (off > sizeof (struct tcphdr)) {
+	  optlen = off - sizeof (struct tcphdr);
+	  optp = MBUF_TO(m, caddr_t) + sizeof (struct tcpiphdr);
+
+		/*
+		 * Do quick retrieval of timestamp options ("options
+		 * prediction?").  If timestamp is the only option and it's
+		 * formatted as recommended in RFC 1323 appendix A, we
+		 * quickly get the values now and not bother calling
+		 * tcp_dooptions(), etc.
+		 */
+/*		if ((optlen == TCPOLEN_TSTAMP_APPA ||
+ *		     (optlen > TCPOLEN_TSTAMP_APPA &&
+ *			optp[TCPOLEN_TSTAMP_APPA] == TCPOPT_EOL)) &&
+ *		     *(u_int32_t *)optp == htonl(TCPOPT_TSTAMP_HDR) &&
+ *		     (ti->ti_flags & TH_SYN) == 0) {
+ *			ts_present = 1;
+ *			ts_val = ntohl(*(u_int32_t *)(optp + 4));
+ *			ts_ecr = ntohl(*(u_int32_t *)(optp + 8));
+ *			optp = NULL;   / * we've parsed the options * /
+ *		}
+ */
+	}
+	tiflags = ti->ti_flags;
+
+	/*
+	 * Convert TCP protocol specific fields to host format.
+	 */
+	NTOHL(ti->ti_seq);
+	NTOHL(ti->ti_ack);
+	NTOHS(ti->ti_win);
+	NTOHS(ti->ti_urp);
+
+	/*
+	 * Drop TCP, IP headers and TCP options.
+	 */
+	m->m_data += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
+	m->m_len  -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
+
+	/*
+	 * Locate pcb for segment.
+	 */
+findso:
+	so = tcp_last_so;
+        {
+            uint32_t  srcip   = ip_geth(ti->ti_src);
+            uint32_t  dstip   = ip_geth(ti->ti_dst);
+            uint16_t  dstport = port_geth(ti->ti_dport);
+            uint16_t  srcport = port_geth(ti->ti_sport);
+ 
+	if (so->so_faddr_port != dstport ||
+	    so->so_laddr_port != srcport ||
+	    so->so_laddr_ip   != srcip ||
+	    so->so_faddr_ip   != dstip) {
+		so = solookup(&tcb, srcip, srcport, dstip, dstport);
+		if (so)
+			tcp_last_so = so;
+		++tcpstat.tcps_socachemiss;
+	}
+        }
+
+	/*
+	 * If the state is CLOSED (i.e., TCB does not exist) then
+	 * all data in the incoming segment is discarded.
+	 * If the TCB exists but is in CLOSED state, it is embryonic,
+	 * but should either do a listen or a connect soon.
+	 *
+	 * state == CLOSED means we've done socreate() but haven't
+	 * attached it to a protocol yet...
+	 *
+	 * XXX If a TCB does not exist, and the TH_SYN flag is
+	 * the only flag set, then create a session, mark it
+	 * as if it was LISTENING, and continue...
+	 */
+	if (so == 0) {
+	  if ((tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) != TH_SYN)
+	    goto dropwithreset;
+
+	  if ((so = socreate()) == NULL)
+	    goto dropwithreset;
+	  if (tcp_attach(so) < 0) {
+	    free(so); /* Not sofree (if it failed, it's not insqued) */
+	    goto dropwithreset;
+	  }
+
+	  sbuf_reserve(&so->so_snd, tcp_sndspace);
+	  sbuf_reserve(&so->so_rcv, tcp_rcvspace);
+
+	  /*		tcp_last_so = so; */  /* XXX ? */
+	  /*		tp = sototcpcb(so);    */
+
+	  so->so_laddr_ip   = ip_geth(ti->ti_src);
+	  so->so_laddr_port = port_geth(ti->ti_sport);
+	  so->so_faddr_ip   = ip_geth(ti->ti_dst);
+	  so->so_faddr_port = port_geth(ti->ti_dport);
+
+	  if ((so->so_iptos = tcp_tos(so)) == 0)
+	    so->so_iptos = ((struct ip *)ti)->ip_tos;
+
+	  tp = sototcpcb(so);
+	  tp->t_state = TCPS_LISTEN;
+	}
+
+        /*
+         * If this is a still-connecting socket, this probably
+         * a retransmit of the SYN.  Whether it's a retransmit SYN
+	 * or something else, we nuke it.
+         */
+        if (so->so_state & SS_ISFCONNECTING)
+                goto drop;
+
+	tp = sototcpcb(so);
+
+	/* XXX Should never fail */
+	if (tp == 0)
+		goto dropwithreset;
+	if (tp->t_state == TCPS_CLOSED)
+		goto drop;
+
+	/* Unscale the window into a 32-bit value. */
+/*	if ((tiflags & TH_SYN) == 0)
+ *		tiwin = ti->ti_win << tp->snd_scale;
+ *	else
+ */
+		tiwin = ti->ti_win;
+
+	/*
+	 * Segment received on connection.
+	 * Reset idle time and keep-alive timer.
+	 */
+	tp->t_idle = 0;
+	if (so_options)
+	   tp->t_timer[TCPT_KEEP] = tcp_keepintvl;
+	else
+	   tp->t_timer[TCPT_KEEP] = tcp_keepidle;
+
+	/*
+	 * Process options if not in LISTEN state,
+	 * else do it below (after getting remote address).
+	 */
+	if (optp && tp->t_state != TCPS_LISTEN)
+		tcp_dooptions(tp, (u_char *)optp, optlen, ti);
+/* , */
+/*			&ts_present, &ts_val, &ts_ecr); */
+
+	/*
+	 * Header prediction: check for the two common cases
+	 * of a uni-directional data xfer.  If the packet has
+	 * no control flags, is in-sequence, the window didn't
+	 * change and we're not retransmitting, it's a
+	 * candidate.  If the length is zero and the ack moved
+	 * forward, we're the sender side of the xfer.  Just
+	 * free the data acked & wake any higher level process
+	 * that was blocked waiting for space.  If the length
+	 * is non-zero and the ack didn't move, we're the
+	 * receiver side.  If we're getting packets in-order
+	 * (the reassembly queue is empty), add the data to
+	 * the socket buffer and note that we need a delayed ack.
+	 *
+	 * XXX Some of these tests are not needed
+	 * eg: the tiwin == tp->snd_wnd prevents many more
+	 * predictions.. with no *real* advantage..
+	 */
+	if (tp->t_state == TCPS_ESTABLISHED &&
+	    (tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
+/*	    (!ts_present || TSTMP_GEQ(ts_val, tp->ts_recent)) && */
+	    ti->ti_seq == tp->rcv_nxt &&
+	    tiwin && tiwin == tp->snd_wnd &&
+	    tp->snd_nxt == tp->snd_max) {
+		/*
+		 * If last ACK falls within this segment's sequence numbers,
+		 *  record the timestamp.
+		 */
+/*		if (ts_present && SEQ_LEQ(ti->ti_seq, tp->last_ack_sent) &&
+ *		   SEQ_LT(tp->last_ack_sent, ti->ti_seq + ti->ti_len)) {
+ *			tp->ts_recent_age = tcp_now;
+ *			tp->ts_recent = ts_val;
+ *		}
+ */
+		if (ti->ti_len == 0) {
+			if (SEQ_GT(ti->ti_ack, tp->snd_una) &&
+			    SEQ_LEQ(ti->ti_ack, tp->snd_max) &&
+			    tp->snd_cwnd >= tp->snd_wnd) {
+				/*
+				 * this is a pure ack for outstanding data.
+				 */
+				++tcpstat.tcps_predack;
+/*				if (ts_present)
+ *					tcp_xmit_timer(tp, tcp_now-ts_ecr+1);
+ *				else
+ */				     if (tp->t_rtt &&
+					    SEQ_GT(ti->ti_ack, tp->t_rtseq))
+					tcp_xmit_timer(tp, tp->t_rtt);
+				acked = ti->ti_ack - tp->snd_una;
+				tcpstat.tcps_rcvackpack++;
+				tcpstat.tcps_rcvackbyte += acked;
+				sbuf_drop(&so->so_snd, acked);
+				tp->snd_una = ti->ti_ack;
+				mbuf_free(m);
+
+				/*
+				 * If all outstanding data are acked, stop
+				 * retransmit timer, otherwise restart timer
+				 * using current (possibly backed-off) value.
+				 * If process is waiting for space,
+				 * wakeup/selwakeup/signal.  If data
+				 * are ready to send, let tcp_output
+				 * decide between more output or persist.
+				 */
+				if (tp->snd_una == tp->snd_max)
+					tp->t_timer[TCPT_REXMT] = 0;
+				else if (tp->t_timer[TCPT_PERSIST] == 0)
+					tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
+
+				/*
+				 * There's room in so_snd, sowwakup will read()
+				 * from the socket if we can
+				 */
+/*				if (so->so_snd.sb_flags & SB_NOTIFY)
+ *					sowwakeup(so);
+ */
+				/*
+				 * This is called because sowwakeup might have
+				 * put data into so_snd.  Since we don't so sowwakeup,
+				 * we don't need this.. XXX???
+				 */
+				if (so->so_snd.sb_cc)
+					(void) tcp_output(tp);
+
+				return;
+			}
+		} else if (ti->ti_ack == tp->snd_una &&
+		    tcpfrag_list_empty(tp) &&
+		    ti->ti_len <= sbuf_space(&so->so_rcv)) {
+			/*
+			 * this is a pure, in-sequence data packet
+			 * with nothing on the reassembly queue and
+			 * we have enough buffer space to take it.
+			 */
+			++tcpstat.tcps_preddat;
+			tp->rcv_nxt += ti->ti_len;
+			tcpstat.tcps_rcvpack++;
+			tcpstat.tcps_rcvbyte += ti->ti_len;
+			/*
+			 * Add data to socket buffer.
+			 */
+			if (so->so_emu) {
+				if (tcp_emu(so,m)) sbuf_append(so, m);
+			} else
+				sbuf_append(so, m);
+
+			/*
+			 * XXX This is called when data arrives.  Later, check
+			 * if we can actually write() to the socket
+			 * XXX Need to check? It's be NON_BLOCKING
+			 */
+/*			sorwakeup(so); */
+
+			/*
+			 * If this is a short packet, then ACK now - with Nagel
+			 *	congestion avoidance sender won't send more until
+			 *	he gets an ACK.
+			 *
+			 * It is better to not delay acks at all to maximize
+			 * TCP throughput.  See RFC 2581.
+			 */
+			tp->t_flags |= TF_ACKNOW;
+			tcp_output(tp);
+			return;
+		}
+	} /* header prediction */
+	/*
+	 * Calculate amount of space in receive window,
+	 * and then do TCP input processing.
+	 * Receive window is amount of space in rcv queue,
+	 * but not less than advertised window.
+	 */
+	{ int win;
+          win = sbuf_space(&so->so_rcv);
+	  if (win < 0)
+	    win = 0;
+	  tp->rcv_wnd = max(win, (int)(tp->rcv_adv - tp->rcv_nxt));
+	}
+
+	switch (tp->t_state) {
+
+	/*
+	 * If the state is LISTEN then ignore segment if it contains an RST.
+	 * If the segment contains an ACK then it is bad and send a RST.
+	 * If it does not contain a SYN then it is not interesting; drop it.
+	 * Don't bother responding if the destination was a broadcast.
+	 * Otherwise initialize tp->rcv_nxt, and tp->irs, select an initial
+	 * tp->iss, and send a segment:
+	 *     <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
+	 * Also initialize tp->snd_nxt to tp->iss+1 and tp->snd_una to tp->iss.
+	 * Fill in remote peer address fields if not previously specified.
+	 * Enter SYN_RECEIVED state, and process any other fields of this
+	 * segment in this state.
+	 */
+	case TCPS_LISTEN: {
+
+	  if (tiflags & TH_RST)
+	    goto drop;
+	  if (tiflags & TH_ACK)
+	    goto dropwithreset;
+	  if ((tiflags & TH_SYN) == 0)
+	    goto drop;
+
+	  /*
+	   * This has way too many gotos...
+	   * But a bit of spaghetti code never hurt anybody :)
+	   */
+
+	  /*
+	   * If this is destined for the control address, then flag to
+	   * tcp_ctl once connected, otherwise connect
+	   */
+	  if ((so->so_faddr_ip & 0xffffff00) == special_addr_ip) {
+	    //int lastbyte=ntohl(so->so_faddr.s_addr) & 0xff;
+	    /* CTL_ALIAS: Do nothing, tcp_fconnect will be called on it */
+	  }
+
+	  if (so->so_emu & EMU_NOCONNECT) {
+	    so->so_emu &= ~EMU_NOCONNECT;
+	    goto cont_input;
+	  }
+
+	  if((tcp_fconnect(so) == -1) && (errno != EINPROGRESS) && (errno != EWOULDBLOCK)) {
+	    u_char code=ICMP_UNREACH_NET;
+	    DEBUG_MISC((dfd," tcp fconnect errno = %d-%s\n",
+			errno,errno_str));
+	    if(errno == ECONNREFUSED) {
+	      /* ACK the SYN, send RST to refuse the connection */
+	      tcp_respond(tp, ti, m, ti->ti_seq+1, (tcp_seq)0,
+			  TH_RST|TH_ACK);
+	    } else {
+	      if(errno == EHOSTUNREACH) code=ICMP_UNREACH_HOST;
+	      HTONL(ti->ti_seq);             /* restore tcp header */
+	      HTONL(ti->ti_ack);
+	      HTONS(ti->ti_win);
+	      HTONS(ti->ti_urp);
+	      m->m_data -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
+	      m->m_len  += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
+	      *ip=save_ip;
+	      icmp_error(m, ICMP_UNREACH,code, 0,errno_str);
+	    }
+	    tp = tcp_close(tp);
+	    mbuf_free(m);
+	  } else {
+	    /*
+	     * Haven't connected yet, save the current mbuf
+	     * and ti, and return
+	     * XXX Some OS's don't tell us whether the connect()
+	     * succeeded or not.  So we must time it out.
+	     */
+	    so->so_m = m;
+	    so->so_ti = ti;
+	    tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
+	    tp->t_state = TCPS_SYN_RECEIVED;
+	  }
+	  return;
+
+	cont_conn:
+	  /* m==NULL
+	   * Check if the connect succeeded
+	   */
+	  if (so->so_state & SS_NOFDREF) {
+            DEBUG_MISC((dfd, " tcp_input closing connecting socket %lx\n", (long)so));
+	    tp = tcp_close(tp);
+	    goto dropwithreset;
+	  }
+	cont_input:
+	  tcp_template(tp);
+
+	  if (optp)
+	    tcp_dooptions(tp, (u_char *)optp, optlen, ti);
+	  /* , */
+	  /*				&ts_present, &ts_val, &ts_ecr); */
+
+	  if (iss)
+	    tp->iss = iss;
+	  else
+	    tp->iss = tcp_iss;
+	  tcp_iss += TCP_ISSINCR/2;
+	  tp->irs = ti->ti_seq;
+	  tcp_sendseqinit(tp);
+	  tcp_rcvseqinit(tp);
+	  tp->t_flags |= TF_ACKNOW;
+	  tp->t_state = TCPS_SYN_RECEIVED;
+	  tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
+	  tcpstat.tcps_accepts++;
+          DEBUG_MISC((dfd, " tcp_input accept connected socket %lx\n", (long)so));
+	  goto trimthenstep6;
+	} /* case TCPS_LISTEN */
+
+	/*
+	 * If the state is SYN_SENT:
+	 *	if seg contains an ACK, but not for our SYN, drop the input.
+	 *	if seg contains a RST, then drop the connection.
+	 *	if seg does not contain SYN, then drop it.
+	 * Otherwise this is an acceptable SYN segment
+	 *	initialize tp->rcv_nxt and tp->irs
+	 *	if seg contains ack then advance tp->snd_una
+	 *	if SYN has been acked change to ESTABLISHED else SYN_RCVD state
+	 *	arrange for segment to be acked (eventually)
+	 *	continue processing rest of data/controls, beginning with URG
+	 */
+	case TCPS_SYN_SENT:
+		if ((tiflags & TH_ACK) &&
+		    (SEQ_LEQ(ti->ti_ack, tp->iss) ||
+		     SEQ_GT(ti->ti_ack, tp->snd_max)))
+			goto dropwithreset;
+
+		if (tiflags & TH_RST) {
+			if (tiflags & TH_ACK)
+				tp = tcp_drop(tp,0); /* XXX Check t_softerror! */
+			goto drop;
+		}
+
+		if ((tiflags & TH_SYN) == 0)
+			goto drop;
+		if (tiflags & TH_ACK) {
+			tp->snd_una = ti->ti_ack;
+			if (SEQ_LT(tp->snd_nxt, tp->snd_una))
+				tp->snd_nxt = tp->snd_una;
+		}
+
+		tp->t_timer[TCPT_REXMT] = 0;
+		tp->irs = ti->ti_seq;
+		tcp_rcvseqinit(tp);
+		tp->t_flags |= TF_ACKNOW;
+		if (tiflags & TH_ACK && SEQ_GT(tp->snd_una, tp->iss)) {
+			tcpstat.tcps_connects++;
+			soisfconnected(so);
+			tp->t_state = TCPS_ESTABLISHED;
+
+			/* Do window scaling on this connection? */
+/*			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
+ *				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
+ * 				tp->snd_scale = tp->requested_s_scale;
+ *				tp->rcv_scale = tp->request_r_scale;
+ *			}
+ */
+			(void) tcp_reass(tp, (struct tcpiphdr *)0,
+				(MBuf )0);
+			/*
+			 * if we didn't have to retransmit the SYN,
+			 * use its rtt as our initial srtt & rtt var.
+			 */
+			if (tp->t_rtt)
+				tcp_xmit_timer(tp, tp->t_rtt);
+		} else
+			tp->t_state = TCPS_SYN_RECEIVED;
+
+trimthenstep6:
+		/*
+		 * Advance ti->ti_seq to correspond to first data byte.
+		 * If data, trim to stay within window,
+		 * dropping FIN if necessary.
+		 */
+		ti->ti_seq++;
+		if (ti->ti_len > tp->rcv_wnd) {
+			todrop = ti->ti_len - tp->rcv_wnd;
+			mbuf_trim(m, -todrop);
+			ti->ti_len = tp->rcv_wnd;
+			tiflags &= ~TH_FIN;
+			tcpstat.tcps_rcvpackafterwin++;
+			tcpstat.tcps_rcvbyteafterwin += todrop;
+		}
+		tp->snd_wl1 = ti->ti_seq - 1;
+		tp->rcv_up = ti->ti_seq;
+		goto step6;
+	} /* switch tp->t_state */
+	/*
+	 * States other than LISTEN or SYN_SENT.
+	 * First check timestamp, if present.
+	 * Then check that at least some bytes of segment are within
+	 * receive window.  If segment begins before rcv_nxt,
+	 * drop leading data (and SYN); if nothing left, just ack.
+	 *
+	 * RFC 1323 PAWS: If we have a timestamp reply on this segment
+	 * and it's less than ts_recent, drop it.
+	 */
+/*	if (ts_present && (tiflags & TH_RST) == 0 && tp->ts_recent &&
+ *	    TSTMP_LT(ts_val, tp->ts_recent)) {
+ *
+ */		/* Check to see if ts_recent is over 24 days old.  */
+/*		if ((int)(tcp_now - tp->ts_recent_age) > TCP_PAWS_IDLE) {
+ */			/*
+ *			 * Invalidate ts_recent.  If this segment updates
+ *			 * ts_recent, the age will be reset later and ts_recent
+ *			 * will get a valid value.  If it does not, setting
+ *			 * ts_recent to zero will at least satisfy the
+ *			 * requirement that zero be placed in the timestamp
+ *			 * echo reply when ts_recent isn't valid.  The
+ *			 * age isn't reset until we get a valid ts_recent
+ *			 * because we don't want out-of-order segments to be
+ *			 * dropped when ts_recent is old.
+ *			 */
+/*			tp->ts_recent = 0;
+ *		} else {
+ *			tcpstat.tcps_rcvduppack++;
+ *			tcpstat.tcps_rcvdupbyte += ti->ti_len;
+ *			tcpstat.tcps_pawsdrop++;
+ *			goto dropafterack;
+ *		}
+ *	}
+ */
+
+	todrop = tp->rcv_nxt - ti->ti_seq;
+	if (todrop > 0) {
+		if (tiflags & TH_SYN) {
+			tiflags &= ~TH_SYN;
+			ti->ti_seq++;
+			if (ti->ti_urp > 1)
+				ti->ti_urp--;
+			else
+				tiflags &= ~TH_URG;
+			todrop--;
+		}
+		/*
+		 * Following if statement from Stevens, vol. 2, p. 960.
+		 */
+		if (todrop > ti->ti_len
+		    || (todrop == ti->ti_len && (tiflags & TH_FIN) == 0)) {
+			/*
+			 * Any valid FIN must be to the left of the window.
+			 * At this point the FIN must be a duplicate or out
+			 * of sequence; drop it.
+			 */
+			tiflags &= ~TH_FIN;
+
+			/*
+			 * Send an ACK to resynchronize and drop any data.
+			 * But keep on processing for RST or ACK.
+			 */
+			tp->t_flags |= TF_ACKNOW;
+			todrop = ti->ti_len;
+			tcpstat.tcps_rcvduppack++;
+			tcpstat.tcps_rcvdupbyte += todrop;
+		} else {
+			tcpstat.tcps_rcvpartduppack++;
+			tcpstat.tcps_rcvpartdupbyte += todrop;
+		}
+		mbuf_trim(m, todrop);
+		ti->ti_seq += todrop;
+		ti->ti_len -= todrop;
+		if (ti->ti_urp > todrop)
+			ti->ti_urp -= todrop;
+		else {
+			tiflags &= ~TH_URG;
+			ti->ti_urp = 0;
+		}
+	}
+	/*
+	 * If new data are received on a connection after the
+	 * user processes are gone, then RST the other end.
+	 */
+	if ((so->so_state & SS_NOFDREF) &&
+	    tp->t_state > TCPS_CLOSE_WAIT && ti->ti_len) {
+		tp = tcp_close(tp);
+		tcpstat.tcps_rcvafterclose++;
+		goto dropwithreset;
+	}
+
+	/*
+	 * If segment ends after window, drop trailing data
+	 * (and PUSH and FIN); if nothing left, just ACK.
+	 */
+	todrop = (ti->ti_seq+ti->ti_len) - (tp->rcv_nxt+tp->rcv_wnd);
+	if (todrop > 0) {
+		tcpstat.tcps_rcvpackafterwin++;
+		if (todrop >= ti->ti_len) {
+			tcpstat.tcps_rcvbyteafterwin += ti->ti_len;
+			/*
+			 * If a new connection request is received
+			 * while in TIME_WAIT, drop the old connection
+			 * and start over if the sequence numbers
+			 * are above the previous ones.
+			 */
+			if (tiflags & TH_SYN &&
+			    tp->t_state == TCPS_TIME_WAIT &&
+			    SEQ_GT(ti->ti_seq, tp->rcv_nxt)) {
+				iss = tp->rcv_nxt + TCP_ISSINCR;
+				tp = tcp_close(tp);
+				goto findso;
+			}
+			/*
+			 * If window is closed can only take segments at
+			 * window edge, and have to drop data and PUSH from
+			 * incoming segments.  Continue processing, but
+			 * remember to ack.  Otherwise, drop segment
+			 * and ack.
+			 */
+			if (tp->rcv_wnd == 0 && ti->ti_seq == tp->rcv_nxt) {
+				tp->t_flags |= TF_ACKNOW;
+				tcpstat.tcps_rcvwinprobe++;
+			} else
+				goto dropafterack;
+		} else
+			tcpstat.tcps_rcvbyteafterwin += todrop;
+		mbuf_trim(m, -todrop);
+		ti->ti_len -= todrop;
+		tiflags &= ~(TH_PUSH|TH_FIN);
+	}
+
+	/*
+	 * If last ACK falls within this segment's sequence numbers,
+	 * record its timestamp.
+	 */
+/*	if (ts_present && SEQ_LEQ(ti->ti_seq, tp->last_ack_sent) &&
+ *	    SEQ_LT(tp->last_ack_sent, ti->ti_seq + ti->ti_len +
+ *		   ((tiflags & (TH_SYN|TH_FIN)) != 0))) {
+ *		tp->ts_recent_age = tcp_now;
+ *		tp->ts_recent = ts_val;
+ *	}
+ */
+
+	/*
+	 * If the RST bit is set examine the state:
+	 *    SYN_RECEIVED STATE:
+	 *	If passive open, return to LISTEN state.
+	 *	If active open, inform user that connection was refused.
+	 *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT2, CLOSE_WAIT STATES:
+	 *	Inform user that connection was reset, and close tcb.
+	 *    CLOSING, LAST_ACK, TIME_WAIT STATES
+	 *	Close the tcb.
+	 */
+	if (tiflags&TH_RST) switch (tp->t_state) {
+
+	case TCPS_SYN_RECEIVED:
+/*		so->so_error = ECONNREFUSED; */
+		goto close;
+
+	case TCPS_ESTABLISHED:
+	case TCPS_FIN_WAIT_1:
+	case TCPS_FIN_WAIT_2:
+	case TCPS_CLOSE_WAIT:
+/*		so->so_error = ECONNRESET; */
+	close:
+		tp->t_state = TCPS_CLOSED;
+		tcpstat.tcps_drops++;
+		tp = tcp_close(tp);
+		goto drop;
+
+	case TCPS_CLOSING:
+	case TCPS_LAST_ACK:
+	case TCPS_TIME_WAIT:
+		tp = tcp_close(tp);
+		goto drop;
+	}
+
+	/*
+	 * If a SYN is in the window, then this is an
+	 * error and we send an RST and drop the connection.
+	 */
+	if (tiflags & TH_SYN) {
+		tp = tcp_drop(tp,0);
+		goto dropwithreset;
+	}
+
+	/*
+	 * If the ACK bit is off we drop the segment and return.
+	 */
+	if ((tiflags & TH_ACK) == 0) goto drop;
+
+	/*
+	 * Ack processing.
+	 */
+	switch (tp->t_state) {
+	/*
+	 * In SYN_RECEIVED state if the ack ACKs our SYN then enter
+	 * ESTABLISHED state and continue processing, otherwise
+	 * send an RST.  una<=ack<=max
+	 */
+	case TCPS_SYN_RECEIVED:
+
+		if (SEQ_GT(tp->snd_una, ti->ti_ack) ||
+		    SEQ_GT(ti->ti_ack, tp->snd_max))
+			goto dropwithreset;
+		tcpstat.tcps_connects++;
+		tp->t_state = TCPS_ESTABLISHED;
+		/*
+		 * The sent SYN is ack'ed with our sequence number +1
+		 * The first data byte already in the buffer will get
+		 * lost if no correction is made.  This is only needed for
+		 * SS_CTL since the buffer is empty otherwise.
+		 * tp->snd_una++; or:
+		 */
+		tp->snd_una=ti->ti_ack;
+		if (so->so_state & SS_CTL) {
+		  /* So tcp_ctl reports the right state */
+		  ret = tcp_ctl(so);
+		  if (ret == 1) {
+		    soisfconnected(so);
+		    so->so_state &= ~SS_CTL;   /* success XXX */
+		  } else if (ret == 2) {
+		    so->so_state = SS_NOFDREF; /* CTL_CMD */
+		  } else {
+		    needoutput = 1;
+		    tp->t_state = TCPS_FIN_WAIT_1;
+		  }
+		} else {
+		  soisfconnected(so);
+		}
+
+		/* Do window scaling? */
+/*		if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
+ *			(TF_RCVD_SCALE|TF_REQ_SCALE)) {
+ *			tp->snd_scale = tp->requested_s_scale;
+ *			tp->rcv_scale = tp->request_r_scale;
+ *		}
+ */
+		(void) tcp_reass(tp, (struct tcpiphdr *)0, (MBuf )0);
+		tp->snd_wl1 = ti->ti_seq - 1;
+		/* Avoid ack processing; snd_una==ti_ack  =>  dup ack */
+		goto synrx_to_est;
+		/* fall into ... */
+
+	/*
+	 * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
+	 * ACKs.  If the ack is in the range
+	 *	tp->snd_una < ti->ti_ack <= tp->snd_max
+	 * then advance tp->snd_una to ti->ti_ack and drop
+	 * data from the retransmission queue.  If this ACK reflects
+	 * more up to date window information we update our window information.
+	 */
+	case TCPS_ESTABLISHED:
+	case TCPS_FIN_WAIT_1:
+	case TCPS_FIN_WAIT_2:
+	case TCPS_CLOSE_WAIT:
+	case TCPS_CLOSING:
+	case TCPS_LAST_ACK:
+	case TCPS_TIME_WAIT:
+
+		if (SEQ_LEQ(ti->ti_ack, tp->snd_una)) {
+			if (ti->ti_len == 0 && tiwin == tp->snd_wnd) {
+			  tcpstat.tcps_rcvdupack++;
+			  DEBUG_MISC((dfd," dup ack  m = %lx  so = %lx \n",
+				      (long )m, (long )so));
+				/*
+				 * If we have outstanding data (other than
+				 * a window probe), this is a completely
+				 * duplicate ack (ie, window info didn't
+				 * change), the ack is the biggest we've
+				 * seen and we've seen exactly our rexmt
+				 * threshold of them, assume a packet
+				 * has been dropped and retransmit it.
+				 * Kludge snd_nxt & the congestion
+				 * window so we send only this one
+				 * packet.
+				 *
+				 * We know we're losing at the current
+				 * window size so do congestion avoidance
+				 * (set ssthresh to half the current window
+				 * and pull our congestion window back to
+				 * the new ssthresh).
+				 *
+				 * Dup acks mean that packets have left the
+				 * network (they're now cached at the receiver)
+				 * so bump cwnd by the amount in the receiver
+				 * to keep a constant cwnd packets in the
+				 * network.
+				 */
+				if (tp->t_timer[TCPT_REXMT] == 0 ||
+				    ti->ti_ack != tp->snd_una)
+					tp->t_dupacks = 0;
+				else if (++tp->t_dupacks == tcprexmtthresh) {
+					tcp_seq onxt = tp->snd_nxt;
+					u_int win =
+					    min(tp->snd_wnd, tp->snd_cwnd) / 2 /
+						tp->t_maxseg;
+
+					if (win < 2)
+						win = 2;
+					tp->snd_ssthresh = win * tp->t_maxseg;
+					tp->t_timer[TCPT_REXMT] = 0;
+					tp->t_rtt = 0;
+					tp->snd_nxt = ti->ti_ack;
+					tp->snd_cwnd = tp->t_maxseg;
+					(void) tcp_output(tp);
+					tp->snd_cwnd = tp->snd_ssthresh +
+					       tp->t_maxseg * tp->t_dupacks;
+					if (SEQ_GT(onxt, tp->snd_nxt))
+						tp->snd_nxt = onxt;
+					goto drop;
+				} else if (tp->t_dupacks > tcprexmtthresh) {
+					tp->snd_cwnd += tp->t_maxseg;
+					(void) tcp_output(tp);
+					goto drop;
+				}
+			} else
+				tp->t_dupacks = 0;
+			break;
+		}
+	synrx_to_est:
+		/*
+		 * If the congestion window was inflated to account
+		 * for the other side's cached packets, retract it.
+		 */
+		if (tp->t_dupacks > tcprexmtthresh &&
+		    tp->snd_cwnd > tp->snd_ssthresh)
+			tp->snd_cwnd = tp->snd_ssthresh;
+		tp->t_dupacks = 0;
+		if (SEQ_GT(ti->ti_ack, tp->snd_max)) {
+			tcpstat.tcps_rcvacktoomuch++;
+			goto dropafterack;
+		}
+		acked = ti->ti_ack - tp->snd_una;
+		tcpstat.tcps_rcvackpack++;
+		tcpstat.tcps_rcvackbyte += acked;
+
+		/*
+		 * If we have a timestamp reply, update smoothed
+		 * round trip time.  If no timestamp is present but
+		 * transmit timer is running and timed sequence
+		 * number was acked, update smoothed round trip time.
+		 * Since we now have an rtt measurement, cancel the
+		 * timer backoff (cf., Phil Karn's retransmit alg.).
+		 * Recompute the initial retransmit timer.
+		 */
+/*		if (ts_present)
+ *			tcp_xmit_timer(tp, tcp_now-ts_ecr+1);
+ *		else
+ */
+		     if (tp->t_rtt && SEQ_GT(ti->ti_ack, tp->t_rtseq))
+			tcp_xmit_timer(tp,tp->t_rtt);
+
+		/*
+		 * If all outstanding data is acked, stop retransmit
+		 * timer and remember to restart (more output or persist).
+		 * If there is more data to be acked, restart retransmit
+		 * timer, using current (possibly backed-off) value.
+		 */
+		if (ti->ti_ack == tp->snd_max) {
+			tp->t_timer[TCPT_REXMT] = 0;
+			needoutput = 1;
+		} else if (tp->t_timer[TCPT_PERSIST] == 0)
+			tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
+		/*
+		 * When new data is acked, open the congestion window.
+		 * If the window gives us less than ssthresh packets
+		 * in flight, open exponentially (maxseg per packet).
+		 * Otherwise open linearly: maxseg per window
+		 * (maxseg^2 / cwnd per packet).
+		 */
+		{
+		  register u_int cw = tp->snd_cwnd;
+		  register u_int incr = tp->t_maxseg;
+
+		  if (cw > tp->snd_ssthresh)
+		    incr = incr * incr / cw;
+		  tp->snd_cwnd = min(cw + incr, TCP_MAXWIN<<tp->snd_scale);
+		}
+		if (acked > so->so_snd.sb_cc) {
+			tp->snd_wnd -= so->so_snd.sb_cc;
+			sbuf_drop(&so->so_snd, (int )so->so_snd.sb_cc);
+			ourfinisacked = 1;
+		} else {
+			sbuf_drop(&so->so_snd, acked);
+			tp->snd_wnd -= acked;
+			ourfinisacked = 0;
+		}
+		/*
+		 * XXX sowwakup is called when data is acked and there's room for
+		 * for more data... it should read() the socket
+		 */
+/*		if (so->so_snd.sb_flags & SB_NOTIFY)
+ *			sowwakeup(so);
+ */
+		tp->snd_una = ti->ti_ack;
+		if (SEQ_LT(tp->snd_nxt, tp->snd_una))
+			tp->snd_nxt = tp->snd_una;
+
+		switch (tp->t_state) {
+
+		/*
+		 * In FIN_WAIT_1 STATE in addition to the processing
+		 * for the ESTABLISHED state if our FIN is now acknowledged
+		 * then enter FIN_WAIT_2.
+		 */
+		case TCPS_FIN_WAIT_1:
+			if (ourfinisacked) {
+				/*
+				 * If we can't receive any more
+				 * data, then closing user can proceed.
+				 * Starting the timer is contrary to the
+				 * specification, but if we don't get a FIN
+				 * we'll hang forever.
+				 */
+				if (so->so_state & SS_FCANTRCVMORE) {
+					soisfdisconnected(so);
+					tp->t_timer[TCPT_2MSL] = tcp_maxidle;
+				}
+				tp->t_state = TCPS_FIN_WAIT_2;
+			}
+			break;
+
+	 	/*
+		 * In CLOSING STATE in addition to the processing for
+		 * the ESTABLISHED state if the ACK acknowledges our FIN
+		 * then enter the TIME-WAIT state, otherwise ignore
+		 * the segment.
+		 */
+		case TCPS_CLOSING:
+			if (ourfinisacked) {
+				tp->t_state = TCPS_TIME_WAIT;
+				tcp_canceltimers(tp);
+				tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
+				soisfdisconnected(so);
+			}
+			break;
+
+		/*
+		 * In LAST_ACK, we may still be waiting for data to drain
+		 * and/or to be acked, as well as for the ack of our FIN.
+		 * If our FIN is now acknowledged, delete the TCB,
+		 * enter the closed state and return.
+		 */
+		case TCPS_LAST_ACK:
+			if (ourfinisacked) {
+				tp = tcp_close(tp);
+				goto drop;
+			}
+			break;
+
+		/*
+		 * In TIME_WAIT state the only thing that should arrive
+		 * is a retransmission of the remote FIN.  Acknowledge
+		 * it and restart the finack timer.
+		 */
+		case TCPS_TIME_WAIT:
+			tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
+			goto dropafterack;
+		}
+	} /* switch(tp->t_state) */
+
+step6:
+	/*
+	 * Update window information.
+	 * Don't look at window if no ACK: TAC's send garbage on first SYN.
+	 */
+	if ((tiflags & TH_ACK) &&
+	    (SEQ_LT(tp->snd_wl1, ti->ti_seq) ||
+	    (tp->snd_wl1 == ti->ti_seq && (SEQ_LT(tp->snd_wl2, ti->ti_ack) ||
+	    (tp->snd_wl2 == ti->ti_ack && tiwin > tp->snd_wnd))))) {
+		/* keep track of pure window updates */
+		if (ti->ti_len == 0 &&
+		    tp->snd_wl2 == ti->ti_ack && tiwin > tp->snd_wnd)
+			tcpstat.tcps_rcvwinupd++;
+		tp->snd_wnd = tiwin;
+		tp->snd_wl1 = ti->ti_seq;
+		tp->snd_wl2 = ti->ti_ack;
+		if (tp->snd_wnd > tp->max_sndwnd)
+			tp->max_sndwnd = tp->snd_wnd;
+		needoutput = 1;
+	}
+
+	/*
+	 * Process segments with URG.
+	 */
+	if ((tiflags & TH_URG) && ti->ti_urp &&
+	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
+		/*
+		 * This is a kludge, but if we receive and accept
+		 * random urgent pointers, we'll crash in
+		 * soreceive.  It's hard to imagine someone
+		 * actually wanting to send this much urgent data.
+		 */
+		if (ti->ti_urp + so->so_rcv.sb_cc > so->so_rcv.sb_datalen) {
+			ti->ti_urp = 0;
+			tiflags &= ~TH_URG;
+			goto dodata;
+		}
+		/*
+		 * If this segment advances the known urgent pointer,
+		 * then mark the data stream.  This should not happen
+		 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
+		 * a FIN has been received from the remote side.
+		 * In these states we ignore the URG.
+		 *
+		 * According to RFC961 (Assigned Protocols),
+		 * the urgent pointer points to the last octet
+		 * of urgent data.  We continue, however,
+		 * to consider it to indicate the first octet
+		 * of data past the urgent section as the original
+		 * spec states (in one of two places).
+		 */
+		if (SEQ_GT(ti->ti_seq+ti->ti_urp, tp->rcv_up)) {
+			tp->rcv_up = ti->ti_seq + ti->ti_urp;
+			so->so_urgc =  so->so_rcv.sb_cc +
+				(tp->rcv_up - tp->rcv_nxt); /* -1; */
+			tp->rcv_up = ti->ti_seq + ti->ti_urp;
+
+		}
+	} else
+		/*
+		 * If no out of band data is expected,
+		 * pull receive urgent pointer along
+		 * with the receive window.
+		 */
+		if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
+			tp->rcv_up = tp->rcv_nxt;
+dodata:
+
+	/*
+	 * Process the segment text, merging it into the TCP sequencing queue,
+	 * and arranging for acknowledgment of receipt if necessary.
+	 * This process logically involves adjusting tp->rcv_wnd as data
+	 * is presented to the user (this happens in tcp_usrreq.c,
+	 * case PRU_RCVD).  If a FIN has already been received on this
+	 * connection then we just ignore the text.
+	 */
+	if ((ti->ti_len || (tiflags&TH_FIN)) &&
+	    TCPS_HAVERCVDFIN(tp->t_state) == 0) {
+		TCP_REASS(tp, ti, m, so, tiflags);
+		/*
+		 * Note the amount of data that peer has sent into
+		 * our window, in order to estimate the sender's
+		 * buffer size.
+		 */
+		len = so->so_rcv.sb_datalen - (tp->rcv_adv - tp->rcv_nxt);
+	} else {
+		mbuf_free(m);
+		tiflags &= ~TH_FIN;
+	}
+
+	/*
+	 * If FIN is received ACK the FIN and let the user know
+	 * that the connection is closing.
+	 */
+	if (tiflags & TH_FIN) {
+		if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
+			/*
+			 * If we receive a FIN we can't send more data,
+			 * set it SS_FDRAIN
+                         * Shutdown the socket if there is no rx data in the
+			 * buffer.
+			 * soread() is called on completion of shutdown() and
+			 * will got to TCPS_LAST_ACK, and use tcp_output()
+			 * to send the FIN.
+			 */
+/*			sofcantrcvmore(so); */
+			sofwdrain(so);
+
+			tp->t_flags |= TF_ACKNOW;
+			tp->rcv_nxt++;
+		}
+		switch (tp->t_state) {
+
+	 	/*
+		 * In SYN_RECEIVED and ESTABLISHED STATES
+		 * enter the CLOSE_WAIT state.
+		 */
+		case TCPS_SYN_RECEIVED:
+		case TCPS_ESTABLISHED:
+		  if(so->so_emu == EMU_CTL)        /* no shutdown on socket */
+		    tp->t_state = TCPS_LAST_ACK;
+		  else
+		    tp->t_state = TCPS_CLOSE_WAIT;
+		  break;
+
+	 	/*
+		 * If still in FIN_WAIT_1 STATE FIN has not been acked so
+		 * enter the CLOSING state.
+		 */
+		case TCPS_FIN_WAIT_1:
+			tp->t_state = TCPS_CLOSING;
+			break;
+
+	 	/*
+		 * In FIN_WAIT_2 state enter the TIME_WAIT state,
+		 * starting the time-wait timer, turning off the other
+		 * standard timers.
+		 */
+		case TCPS_FIN_WAIT_2:
+			tp->t_state = TCPS_TIME_WAIT;
+			tcp_canceltimers(tp);
+			tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
+			soisfdisconnected(so);
+			break;
+
+		/*
+		 * In TIME_WAIT state restart the 2 MSL time_wait timer.
+		 */
+		case TCPS_TIME_WAIT:
+			tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
+			break;
+		}
+	}
+
+	/*
+	 * If this is a small packet, then ACK now - with Nagel
+	 *      congestion avoidance sender won't send more until
+	 *      he gets an ACK.
+	 *
+	 * See above.
+	 */
+/*	if (ti->ti_len && (unsigned)ti->ti_len < tp->t_maxseg) {
+ */
+/*	if ((ti->ti_len && (unsigned)ti->ti_len < tp->t_maxseg &&
+ *		(so->so_iptos & IPTOS_LOWDELAY) == 0) ||
+ *	       ((so->so_iptos & IPTOS_LOWDELAY) &&
+ *	       ((struct tcpiphdr_2 *)ti)->first_char == (char)27)) {
+ */
+	if (ti->ti_len && (unsigned)ti->ti_len <= 5 &&
+	    ((struct tcpiphdr_2 *)ti)->first_char == (char)27) {
+		tp->t_flags |= TF_ACKNOW;
+	}
+
+	/*
+	 * Return any desired output.
+	 */
+	if (needoutput || (tp->t_flags & TF_ACKNOW)) {
+		(void) tcp_output(tp);
+	}
+	return;
+
+dropafterack:
+	/*
+	 * Generate an ACK dropping incoming segment if it occupies
+	 * sequence space, where the ACK reflects our state.
+	 */
+	if (tiflags & TH_RST)
+		goto drop;
+	mbuf_free(m);
+	tp->t_flags |= TF_ACKNOW;
+	(void) tcp_output(tp);
+	return;
+
+dropwithreset:
+	/* reuses m if m!=NULL, mbuf_free() unnecessary */
+	if (tiflags & TH_ACK)
+		tcp_respond(tp, ti, m, (tcp_seq)0, ti->ti_ack, TH_RST);
+	else {
+		if (tiflags & TH_SYN) ti->ti_len++;
+		tcp_respond(tp, ti, m, ti->ti_seq+ti->ti_len, (tcp_seq)0,
+		    TH_RST|TH_ACK);
+	}
+
+	return;
+
+drop:
+	/*
+	 * Drop space held by incoming segment and return.
+	 */
+	mbuf_free(m);
+
+	return;
+}
+
+ /* , ts_present, ts_val, ts_ecr) */
+/*	int *ts_present;
+ *	u_int32_t *ts_val, *ts_ecr;
+ */
+void
+tcp_dooptions(tp, cp, cnt, ti)
+	struct tcpcb *tp;
+	u_char *cp;
+	int cnt;
+	struct tcpiphdr *ti;
+{
+	u_int16_t mss;
+	int opt, optlen;
+
+	DEBUG_CALL("tcp_dooptions");
+	DEBUG_ARGS((dfd," tp = %lx  cnt=%i \n", (long )tp, cnt));
+
+	for (; cnt > 0; cnt -= optlen, cp += optlen) {
+		opt = cp[0];
+		if (opt == TCPOPT_EOL)
+			break;
+		if (opt == TCPOPT_NOP)
+			optlen = 1;
+		else {
+			optlen = cp[1];
+			if (optlen <= 0)
+				break;
+		}
+		switch (opt) {
+
+		default:
+			continue;
+
+		case TCPOPT_MAXSEG:
+			if (optlen != TCPOLEN_MAXSEG)
+				continue;
+			if (!(ti->ti_flags & TH_SYN))
+				continue;
+			memcpy((char *) &mss, (char *) cp + 2, sizeof(mss));
+			NTOHS(mss);
+			(void) tcp_mss(tp, mss);	/* sets t_maxseg */
+			break;
+
+/*		case TCPOPT_WINDOW:
+ *			if (optlen != TCPOLEN_WINDOW)
+ *				continue;
+ *			if (!(ti->ti_flags & TH_SYN))
+ *				continue;
+ *			tp->t_flags |= TF_RCVD_SCALE;
+ *			tp->requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
+ *			break;
+ */
+/*		case TCPOPT_TIMESTAMP:
+ *			if (optlen != TCPOLEN_TIMESTAMP)
+ *				continue;
+ *			*ts_present = 1;
+ *			memcpy((char *) ts_val, (char *)cp + 2, sizeof(*ts_val));
+ *			NTOHL(*ts_val);
+ *			memcpy((char *) ts_ecr, (char *)cp + 6, sizeof(*ts_ecr));
+ *			NTOHL(*ts_ecr);
+ *
+ */			/*
+ *			 * A timestamp received in a SYN makes
+ *			 * it ok to send timestamp requests and replies.
+ *			 */
+/*			if (ti->ti_flags & TH_SYN) {
+ *				tp->t_flags |= TF_RCVD_TSTMP;
+ *				tp->ts_recent = *ts_val;
+ *				tp->ts_recent_age = tcp_now;
+ *			}
+ */			break;
+		}
+	}
+}
+
+
+/*
+ * Pull out of band byte out of a segment so
+ * it doesn't appear in the user's data queue.
+ * It is still reflected in the segment length for
+ * sequencing purposes.
+ */
+
+#ifdef notdef
+
+void
+tcp_pulloutofband(so, ti, m)
+	struct socket *so;
+	struct tcpiphdr *ti;
+	register MBuf m;
+{
+	int cnt = ti->ti_urp - 1;
+
+	while (cnt >= 0) {
+		if (m->m_len > cnt) {
+			char *cp = MBUF_TO(m, caddr_t) + cnt;
+			struct tcpcb *tp = sototcpcb(so);
+
+			tp->t_iobc = *cp;
+			tp->t_oobflags |= TCPOOB_HAVEDATA;
+			memcpy(sp, cp+1, (unsigned)(m->m_len - cnt - 1));
+			m->m_len--;
+			return;
+		}
+		cnt -= m->m_len;
+		m = m->m_next; /* XXX WRONG! Fix it! */
+		if (m == 0)
+			break;
+	}
+	panic("tcp_pulloutofband");
+}
+
+#endif /* notdef */
+
+/*
+ * Collect new round-trip time estimate
+ * and update averages and current timeout.
+ */
+
+void
+tcp_xmit_timer(tp, rtt)
+	register struct tcpcb *tp;
+	int rtt;
+{
+	register short delta;
+
+	DEBUG_CALL("tcp_xmit_timer");
+	DEBUG_ARG("tp = %lx", (long)tp);
+	DEBUG_ARG("rtt = %d", rtt);
+
+	tcpstat.tcps_rttupdated++;
+	if (tp->t_srtt != 0) {
+		/*
+		 * srtt is stored as fixed point with 3 bits after the
+		 * binary point (i.e., scaled by 8).  The following magic
+		 * is equivalent to the smoothing algorithm in rfc793 with
+		 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
+		 * point).  Adjust rtt to origin 0.
+		 */
+		delta = rtt - 1 - (tp->t_srtt >> TCP_RTT_SHIFT);
+		if ((tp->t_srtt += delta) <= 0)
+			tp->t_srtt = 1;
+		/*
+		 * We accumulate a smoothed rtt variance (actually, a
+		 * smoothed mean difference), then set the retransmit
+		 * timer to smoothed rtt + 4 times the smoothed variance.
+		 * rttvar is stored as fixed point with 2 bits after the
+		 * binary point (scaled by 4).  The following is
+		 * equivalent to rfc793 smoothing with an alpha of .75
+		 * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
+		 * rfc793's wired-in beta.
+		 */
+		if (delta < 0)
+			delta = -delta;
+		delta -= (tp->t_rttvar >> TCP_RTTVAR_SHIFT);
+		if ((tp->t_rttvar += delta) <= 0)
+			tp->t_rttvar = 1;
+	} else {
+		/*
+		 * No rtt measurement yet - use the unsmoothed rtt.
+		 * Set the variance to half the rtt (so our first
+		 * retransmit happens at 3*rtt).
+		 */
+		tp->t_srtt = rtt << TCP_RTT_SHIFT;
+		tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
+	}
+	tp->t_rtt = 0;
+	tp->t_rxtshift = 0;
+
+	/*
+	 * the retransmit should happen at rtt + 4 * rttvar.
+	 * Because of the way we do the smoothing, srtt and rttvar
+	 * will each average +1/2 tick of bias.  When we compute
+	 * the retransmit timer, we want 1/2 tick of rounding and
+	 * 1 extra tick because of +-1/2 tick uncertainty in the
+	 * firing of the timer.  The bias will give us exactly the
+	 * 1.5 tick we need.  But, because the bias is
+	 * statistical, we have to test that we don't drop below
+	 * the minimum feasible timer (which is 2 ticks).
+	 */
+	TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
+	    (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
+
+	/*
+	 * We received an ack for a packet that wasn't retransmitted;
+	 * it is probably safe to discard any error indications we've
+	 * received recently.  This isn't quite right, but close enough
+	 * for now (a route might have failed after we sent a segment,
+	 * and the return path might not be symmetrical).
+	 */
+	tp->t_softerror = 0;
+}
+
+/*
+ * Determine a reasonable value for maxseg size.
+ * If the route is known, check route for mtu.
+ * If none, use an mss that can be handled on the outgoing
+ * interface without forcing IP to fragment; if bigger than
+ * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
+ * to utilize large mbufs.  If no route is found, route has no mtu,
+ * or the destination isn't local, use a default, hopefully conservative
+ * size (usually 512 or the default IP max size, but no more than the mtu
+ * of the interface), as we can't discover anything about intervening
+ * gateways or networks.  We also initialize the congestion/slow start
+ * window to be a single segment if the destination isn't local.
+ * While looking at the routing entry, we also initialize other path-dependent
+ * parameters from pre-set or cached values in the routing entry.
+ */
+
+int
+tcp_mss(tp, offer)
+        register struct tcpcb *tp;
+        u_int offer;
+{
+	struct socket *so = tp->t_socket;
+	int mss;
+
+	DEBUG_CALL("tcp_mss");
+	DEBUG_ARG("tp = %lx", (long)tp);
+	DEBUG_ARG("offer = %d", offer);
+
+	mss = min(if_mtu, if_mru) - sizeof(struct tcpiphdr);
+	if (offer)
+		mss = min(mss, offer);
+	mss = max(mss, 32);
+	if (mss < tp->t_maxseg || offer != 0)
+	   tp->t_maxseg = mss;
+
+	tp->snd_cwnd = mss;
+
+	sbuf_reserve(&so->so_snd, tcp_sndspace+((tcp_sndspace%mss)?(mss-(tcp_sndspace%mss)):0));
+	sbuf_reserve(&so->so_rcv, tcp_rcvspace+((tcp_rcvspace%mss)?(mss-(tcp_rcvspace%mss)):0));
+
+	DEBUG_MISC((dfd, " returning mss = %d\n", mss));
+
+	return mss;
+}