Example #1
0
/*
 * TCP input routine, follows pages 65-76 of the
 * protocol specification dated September, 1981 very closely.
 */
void
tcp_input(struct 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 = NULL;
	register int tiflags;
        struct socket *so = NULL;
	int todrop, acked, ourfinisacked, needoutput = 0;
	int iss = 0;
	u_long tiwin;
	int ret;
    struct ex_list *ex_ptr;
    Slirp *slirp;

	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;
		slirp = so->slirp;

		/* Re-set a few variables */
		tp = sototcpcb(so);
		m = so->so_m;
                so->so_m = NULL;
		ti = so->so_ti;
		tiwin = ti->ti_win;
		tiflags = ti->ti_flags;

		goto cont_conn;
	}
	slirp = m->slirp;

	/*
	 * Get IP and TCP header together in first mbuf.
	 * Note: IP leaves IP header in first mbuf.
	 */
	ti = mtod(m, struct tcpiphdr *);
	if (iphlen > sizeof(struct ip )) {
	  ip_stripoptions(m, (struct 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=mtod(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 = NULL;
        memset(&ti->ti_i.ih_mbuf, 0 , sizeof(struct mbuf_ptr));
	ti->ti_x1 = 0;
	ti->ti_len = htons((uint16_t)tlen);
	len = sizeof(struct ip ) + tlen;
	if(cksum(m, len)) {
	  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) {
	  goto drop;
	}
	tlen -= off;
	ti->ti_len = tlen;
	if (off > sizeof (struct tcphdr)) {
	  optlen = off - sizeof (struct tcphdr);
	  optp = mtod(m, caddr_t) + sizeof (struct tcpiphdr);
	}
	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 = slirp->tcp_last_so;
	if (so->so_fport != ti->ti_dport ||
	    so->so_lport != ti->ti_sport ||
	    so->so_laddr.s_addr != ti->ti_src.s_addr ||
	    so->so_faddr.s_addr != ti->ti_dst.s_addr) {
		so = solookup(&slirp->tcb, ti->ti_src, ti->ti_sport,
			       ti->ti_dst, ti->ti_dport);
		if (so)
			slirp->tcp_last_so = so;
	}

	/*
	 * 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 == NULL) {
          if (slirp->restricted) {
            /* Any hostfwds will have an existing socket, so we only get here
             * for non-hostfwd connections. These should be dropped, unless it
             * happens to be a guestfwd.
             */
            for (ex_ptr = slirp->exec_list; ex_ptr; ex_ptr = ex_ptr->ex_next) {
                if (ex_ptr->ex_fport == ti->ti_dport &&
                    ti->ti_dst.s_addr == ex_ptr->ex_addr.s_addr) {
                    break;
                }
            }
            if (!ex_ptr) {
                goto dropwithreset;
            }
          }

	  if ((tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) != TH_SYN)
	    goto dropwithreset;

	  if ((so = socreate(slirp)) == NULL)
	    goto dropwithreset;
	  if (tcp_attach(so) < 0) {
	    free(so); /* Not sofree (if it failed, it's not insqued) */
	    goto dropwithreset;
	  }

	  sbreserve(&so->so_snd, TCP_SNDSPACE);
	  sbreserve(&so->so_rcv, TCP_RCVSPACE);

	  so->so_laddr = ti->ti_src;
	  so->so_lport = ti->ti_sport;
	  so->so_faddr = ti->ti_dst;
	  so->so_fport = 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 == NULL)
		goto dropwithreset;
	if (tp->t_state == TCPS_CLOSED)
		goto drop;

	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] = TCPTV_KEEPINTVL;
	else
	   tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE;

	/*
	 * 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);

	/*
	 * 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 &&
	    ti->ti_seq == tp->rcv_nxt &&
	    tiwin && tiwin == tp->snd_wnd &&
	    tp->snd_nxt == tp->snd_max) {
		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.
				 */
				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;
				sbdrop(&so->so_snd, acked);
				tp->snd_una = ti->ti_ack;
				m_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;

				/*
				 * 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 <= sbspace(&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.
			 */
			tp->rcv_nxt += ti->ti_len;
			/*
			 * Add data to socket buffer.
			 */
			if (so->so_emu) {
				if (tcp_emu(so,m)) sbappend(so, m);
			} else
				sbappend(so, m);

			/*
			 * 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 = sbspace(&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.s_addr & slirp->vnetwork_mask.s_addr) ==
	      slirp->vnetwork_addr.s_addr) {
	    if (so->so_faddr.s_addr != slirp->vhost_addr.s_addr &&
		so->so_faddr.s_addr != slirp->vnameserver_addr.s_addr) {
		/* May be an add exec */
		for (ex_ptr = slirp->exec_list; ex_ptr;
		     ex_ptr = ex_ptr->ex_next) {
		  if(ex_ptr->ex_fport == so->so_fport &&
		     so->so_faddr.s_addr == ex_ptr->ex_addr.s_addr) {
		    so->so_state |= SS_CTL;
		    break;
		  }
		}
		if (so->so_state & SS_CTL) {
		    goto cont_input;
		}
	    }
	    /* 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) &&
#if defined(_WIN32)
              socket_error() != WSAEWOULDBLOCK
#else
              (errno != EINPROGRESS) && (errno != EWOULDBLOCK)
#endif
          ) {
	    u_char code=ICMP_UNREACH_NET;
	    DEBUG_MISC((dfd, " tcp fconnect errno = %d-%s\n",
			errno,strerror(errno)));
	    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,strerror(errno));
	    }
            tcp_close(tp);
	    m_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;
	    tcp_template(tp);
	  }
	  return;

	cont_conn:
	  /* m==NULL
	   * Check if the connect succeeded
	   */
	  if (so->so_state & SS_NOFDREF) {
	    tp = tcp_close(tp);
	    goto dropwithreset;
	  }
	cont_input:
	  tcp_template(tp);

	  if (optp)
	    tcp_dooptions(tp, (u_char *)optp, optlen, ti);

	  if (iss)
	    tp->iss = iss;
	  else
	    tp->iss = slirp->tcp_iss;
	  slirp->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;
	  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) {
                                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)) {
			soisfconnected(so);
			tp->t_state = TCPS_ESTABLISHED;

			(void) tcp_reass(tp, (struct tcpiphdr *)0,
				(struct 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;
			m_adj(m, -todrop);
			ti->ti_len = tp->rcv_wnd;
			tiflags &= ~TH_FIN;
		}
		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.
	 * 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.
	 */
	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;
		}
		m_adj(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);
		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) {
		if (todrop >= 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;
			} else {
				goto dropafterack;
			}
		}
		m_adj(m, -todrop);
		ti->ti_len -= todrop;
		tiflags &= ~(TH_PUSH|TH_FIN);
	}

	/*
	 * 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:
	case TCPS_ESTABLISHED:
	case TCPS_FIN_WAIT_1:
	case TCPS_FIN_WAIT_2:
	case TCPS_CLOSE_WAIT:
		tp->t_state = TCPS_CLOSED;
                tcp_close(tp);
		goto drop;

	case TCPS_CLOSING:
	case TCPS_LAST_ACK:
	case TCPS_TIME_WAIT:
                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;
		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_PERSISTENT_MASK;
		    so->so_state |= SS_NOFDREF; /* CTL_CMD */
		  } else {
		    needoutput = 1;
		    tp->t_state = TCPS_FIN_WAIT_1;
		  }
		} else {
		  soisfconnected(so);
		}

		(void) tcp_reass(tp, (struct tcpiphdr *)0, (struct 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) {
			  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)) {
			goto dropafterack;
		}
		acked = ti->ti_ack - tp->snd_una;

		/*
		 * If 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 (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;
			sbdrop(&so->so_snd, (int )so->so_snd.sb_cc);
			ourfinisacked = 1;
		} else {
			sbdrop(&so->so_snd, acked);
			tp->snd_wnd -= acked;
			ourfinisacked = 0;
		}
		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) {
					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;
			}
			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) {
                                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))))) {
		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:

	/*
	 * If this is a small packet, then ACK now - with Nagel
	 *      congestion avoidance sender won't send more until
	 *      he gets an ACK.
	 */
	if (ti->ti_len && (unsigned)ti->ti_len <= 5 &&
	    ((struct tcpiphdr_2 *)ti)->first_char == (char)27) {
		tp->t_flags |= TF_ACKNOW;
	}

	/*
	 * 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);
	} else {
		m_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.
			 */
			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;
			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;
		}
	}

	/*
	 * 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;
	m_free(m);
	tp->t_flags |= TF_ACKNOW;
	(void) tcp_output(tp);
	return;

dropwithreset:
	/* reuses m if m!=NULL, m_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.
	 */
	m_free(m);
}
Example #2
0
/*
 * TCP input routine, follows pages 65-76 of the
 * protocol specification dated September, 1981 very closely.
 */
void
tcp_input(usn_mbuf_t *m, int iphlen)
{
	struct tcpiphdr *ti;
	struct inpcb *inp;
	u_char *optp = NULL;
	int optlen;
	int len, tlen, off;
	struct tcpcb *tp = 0;
	int tiflags;
	struct usn_socket *so = 0;
	int todrop, acked, ourfinisacked;
   int needoutput = 0;
	short ostate;
	struct usn_in_addr laddr;
	int dropsocket = 0;
	int iss = 0;
	u_long tiwin, ts_val, ts_ecr;
	int ts_present = 0;

   (void)needoutput;
	g_tcpstat.tcps_rcvtotal++;
 
	// Get IP and TCP header together in first mbuf.
	// Note: IP leaves IP header in first mbuf.
	ti = mtod(m, struct tcpiphdr *);
	if (iphlen > sizeof (usn_ip_t))
		ip_stripoptions(m, (usn_mbuf_t *)0);
	if (m->mlen < sizeof (struct tcpiphdr)) {
		if ((m = m_pullup(m, sizeof (struct tcpiphdr))) == 0) {
			g_tcpstat.tcps_rcvshort++;
			return;
		}
		ti = mtod(m, struct tcpiphdr *);
	}

#ifdef DUMP_PAYLOAD
   dump_chain(m,"tcp");
#endif

   /*
	 * Checksum extended TCP header and data.
    */
	tlen = ntohs(((usn_ip_t *)ti)->ip_len);
	len = sizeof (usn_ip_t) + tlen;
	ti->ti_next = ti->ti_prev = 0;
	ti->ti_x1 = 0;
	ti->ti_len = (u_short)tlen;
	HTONS(ti->ti_len);
   ti->ti_sum = in_cksum(m, len);
	if (ti->ti_sum) {
		g_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) {
		g_tcpstat.tcps_rcvbadoff++;
		goto drop;
	}
	tlen -= off;
	ti->ti_len = tlen;
	if (off > sizeof (struct tcphdr)) {
		if (m->mlen < sizeof(usn_ip_t) + off) {
			if ((m = m_pullup(m, sizeof (usn_ip_t) + off)) == 0) {
				g_tcpstat.tcps_rcvshort++;
				return;
			}
			ti = mtod(m, struct tcpiphdr *);
		}
		optlen = off - sizeof (struct tcphdr);
		optp = mtod(m, u_char *) + 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_int *)optp == htonl(TCPOPT_TSTAMP_HDR) &&
		     (ti->ti_flags & TH_SYN) == 0) {
			ts_present = 1;
			ts_val = ntohl(*(u_long *)(optp + 4));
			ts_ecr = ntohl(*(u_long *)(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);

	// Locate pcb for segment.
findpcb:
	inp = g_tcp_last_inpcb;
	if (inp->inp_lport != ti->ti_dport ||
	    inp->inp_fport != ti->ti_sport ||
	    inp->inp_faddr.s_addr != ti->ti_src.s_addr ||
	    inp->inp_laddr.s_addr != ti->ti_dst.s_addr) {
		inp = in_pcblookup(&g_tcb, ti->ti_src, ti->ti_sport,
		    ti->ti_dst, ti->ti_dport, INPLOOKUP_WILDCARD);
		if (inp)
			g_tcp_last_inpcb = inp;
		++g_tcpstat.tcps_pcbcachemiss;
	}

	// 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.
	if (inp == 0)
		goto dropwithreset;

	tp = intotcpcb(inp);

   DEBUG("found inp cb, laddr=%x, lport=%d, faddr=%x,"
         " fport=%d, tp_state=%d, tp_flags=%d",
         inp->inp_laddr.s_addr,
         inp->inp_lport,
         inp->inp_faddr.s_addr,
         inp->inp_fport, tp->t_state, tp->t_flags);

	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;

	so = inp->inp_socket;
   DEBUG("socket info, options=%x", so->so_options);

	if (so->so_options & (SO_DEBUG|SO_ACCEPTCONN)) {
		if (so->so_options & SO_DEBUG) {
			ostate = tp->t_state;
			g_tcp_saveti = *ti;
		}
		if (so->so_options & SO_ACCEPTCONN) {
			if ((tiflags & (TH_RST|TH_ACK|TH_SYN)) != TH_SYN) {
				// Note: dropwithreset makes sure we don't
				// send a reset in response to a RST.
				if (tiflags & TH_ACK) {
					g_tcpstat.tcps_badsyn++;
					goto dropwithreset;
				}
            DEBUG("SYN is expected, tiflags=%d", tiflags);
				goto drop;
			}
			so = sonewconn(so, 0);
			if (so == 0) {
            DEBUG("failed to create new connection, tiflags=%d", tiflags);
				goto drop;
         }

			// Mark socket as temporary until we're
			// committed to keeping it.  The code at
			// ``drop'' and ``dropwithreset'' check the
			// flag dropsocket to see if the temporary
			// socket created here should be discarded.
			// We mark the socket as discardable until
			// we're committed to it below in TCPS_LISTEN.
			dropsocket++;
			inp = (struct inpcb *)so->so_pcb;
			inp->inp_laddr = ti->ti_dst;
			inp->inp_lport = ti->ti_dport;

         // BSD >= 4.3
			inp->inp_options = ip_srcroute();

			tp = intotcpcb(inp);
			tp->t_state = TCPS_LISTEN;

			// Compute proper scaling value from buffer space
			while (tp->request_r_scale < TCP_MAX_WINSHIFT &&
			   TCP_MAXWIN << tp->request_r_scale < so->so_rcv->sb_hiwat)
				tp->request_r_scale++;
		}
	}

	// Segment received on connection.
	// Reset idle time and keep-alive timer.
	tp->t_idle = 0;
	tp->t_timer[TCPT_KEEP] = g_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, 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.
	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 && TSTMP_GEQ(ts_val, tp->ts_recent) &&
            SEQ_LEQ(ti->ti_seq, tp->last_ack_sent) ){
			tp->ts_recent_age = g_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.
				++g_tcpstat.tcps_predack;
				if (ts_present)
					tcp_xmit_timer(tp, g_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;
				g_tcpstat.tcps_rcvackpack++;
				g_tcpstat.tcps_rcvackbyte += acked;
            TRACE("drop so_snd buffer, drop_bytes=%d, len=%d", 
                  acked, so->so_snd.sb_cc);

				sbdrop(so->so_snd, acked);
				tp->snd_una = ti->ti_ack;
				usn_free_cmbuf(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;

	         if (so->so_options & SO_DEBUG)
             	tcp_trace(TA_INPUT, ostate, tp, &g_tcp_saveti, 0);

				//if (so->so_snd->sb_flags & SB_NOTIFY) {
            //   usnet_tcpin_wwakeup(so, USN_TCP_IN, usn_tcpev_sbnotify, 0);
				//	sowwakeup(so);
            //}

            // send buffer is available for app thread. 
            usnet_tcpin_wwakeup(so, USN_TCP_IN, USN_TCPEV_WRITE, 0);

				if (so->so_snd->sb_cc)
					tcp_output(tp);
				return;
			}
		} else if (ti->ti_ack == tp->snd_una &&
		    tp->seg_next == (struct tcpiphdr *)tp &&
		    ti->ti_len <= sbspace(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.
			++g_tcpstat.tcps_preddat;
			tp->rcv_nxt += ti->ti_len;
			g_tcpstat.tcps_rcvpack++;
			g_tcpstat.tcps_rcvbyte += ti->ti_len;

			// Drop TCP, IP headers and TCP options then add data
			// to socket buffer.
			m->head += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
			m->mlen -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);

         TRACE("add data to rcv buf");
			sbappend(so->so_rcv, m);
			sorwakeup(so);

         // new data is available for app threads.
         usnet_tcpin_rwakeup(so, USN_TCP_IN, USN_TCPEV_READ, m);

	      if (so->so_options & SO_DEBUG) {
            TRACE("tcp trace, so_options=%d", so->so_options);
          	tcp_trace(TA_INPUT, ostate, tp, &g_tcp_saveti, 0);
         }

			tp->t_flags |= TF_DELACK;
			return;
		}
	}

	// Drop TCP, IP headers and TCP options.
	m->head += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
	m->mlen -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);

	// 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 = sbspace(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: {
		usn_mbuf_t *am;
		struct usn_sockaddr_in *sin;

		if (tiflags & TH_RST)
			goto drop;
		if (tiflags & TH_ACK)
			goto dropwithreset;
		if ((tiflags & TH_SYN) == 0)
			goto drop;

		// RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
		// in_broadcast() should never return true on a received
		// packet with M_BCAST not set.

		//if (m->m_flags & (M_BCAST|M_MCAST) ||
		//    IN_MULTICAST(ntohl(ti->ti_dst.s_addr)))
		//	goto drop;

		am = usn_get_mbuf(0, BUF_MSIZE, 0);	// XXX: the size!
		if (am == NULL)
			goto drop;
		am->mlen = sizeof (struct usn_sockaddr_in);
		sin = mtod(am, struct usn_sockaddr_in *);
		sin->sin_family = AF_INET;
		sin->sin_len = sizeof(*sin);
		sin->sin_addr = ti->ti_src;
		sin->sin_port = ti->ti_sport;
		bzero((caddr_t)sin->sin_zero, sizeof(sin->sin_zero));

		laddr = inp->inp_laddr;
		if (inp->inp_laddr.s_addr == USN_INADDR_ANY)
			inp->inp_laddr = ti->ti_dst;

		if (in_pcbconnect(inp, am)) {
			inp->inp_laddr = laddr;
			usn_free_mbuf(am);
			goto drop;
		}
		usn_free_mbuf(am);
		tp->t_template = tcp_template(tp);
		if (tp->t_template == 0) {
			tp = tcp_drop(tp, ENOBUFS);
			dropsocket = 0;		// socket is already gone
			goto drop;
		}
		if (optp)
			tcp_dooptions(tp, optp, optlen, ti,
				&ts_present, &ts_val, &ts_ecr);
		if (iss)
			tp->iss = iss;
		else
			tp->iss = g_tcp_iss;
		g_tcp_iss += TCP_ISSINCR/4;
		tp->irs = ti->ti_seq;
		tcp_sendseqinit(tp);
		tcp_rcvseqinit(tp);
		tp->t_flags |= TF_ACKNOW;
      TRACE("change tcp state to TCPS_SYN_RECEIVED, state=%d, tp_flags=%d",
            tp->t_state, tp->t_flags);
		tp->t_state = TCPS_SYN_RECEIVED;

      // tcp event
      usnet_tcpin_ewakeup(so, USN_TCP_IN, USN_TCPST_SYN_RECEIVED, 0);

		tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
		dropsocket = 0;		// committed to socket
		g_tcpstat.tcps_accepts++;
		goto trimthenstep6;
	}


	// 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, ECONNREFUSED);
			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;
      TRACE("ack now, tp flags=%d", tp->t_flags);

      // XXX: remove second test.
		if (tiflags & TH_ACK /*&& SEQ_GT(tp->snd_una, tp->iss)*/) {
			g_tcpstat.tcps_connects++;
			soisconnected(so);
         TRACE("change tcp state to TCPS_ESTABLISHED,"
               " state=%d, tp_flags=%d", tp->t_state, tp->t_flags);
			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;
			}
			tcp_reass(tp, (struct tcpiphdr *)0, (usn_mbuf_t *)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 {
         TRACE("change tcp state to TCPS_SYN_RECEIVED, state=%d, tp_flags=%d", 
               tp->t_state, tp->t_flags);
			tp->t_state = TCPS_SYN_RECEIVED;
         // tcp event
         usnet_tcpin_ewakeup(so, USN_TCP_IN, USN_TCPST_SYN_RECEIVED, 0);
      }

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;
			m_adj(m, -todrop);
			ti->ti_len = tp->rcv_wnd;
			tiflags &= ~TH_FIN;
			g_tcpstat.tcps_rcvpackafterwin++;
			g_tcpstat.tcps_rcvbyteafterwin += todrop;
		}
		tp->snd_wl1 = ti->ti_seq - 1;
		tp->rcv_up = ti->ti_seq;
		goto step6;
	}

	// 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)(g_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 {
			g_tcpstat.tcps_rcvduppack++;
			g_tcpstat.tcps_rcvdupbyte += ti->ti_len;
			g_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--;
		}
      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;
         TRACE("send ack now to resync, tp_flags=%d", tp->t_flags);
         todrop = ti->ti_len;
         g_tcpstat.tcps_rcvdupbyte += ti->ti_len;
         g_tcpstat.tcps_rcvduppack++;
      } else {
         g_tcpstat.tcps_rcvpartduppack++;
         g_tcpstat.tcps_rcvpartdupbyte += ti->ti_len;
      }

		m_adj(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 & USN_NOFDREF) && 
	    tp->t_state > TCPS_CLOSE_WAIT && ti->ti_len) {
		tp = tcp_close(tp);
		g_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) {
		g_tcpstat.tcps_rcvpackafterwin++;
		if (todrop >= ti->ti_len) {
			g_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->snd_nxt + TCP_ISSINCR;
				tp = tcp_close(tp);
				goto findpcb;
			}

			// 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;
				g_tcpstat.tcps_rcvwinprobe++;
			} else
				goto dropafterack;
		} else
			g_tcpstat.tcps_rcvbyteafterwin += todrop;
		m_adj(m, -todrop);
		ti->ti_len -= todrop;
		tiflags &= ~(TH_PUSH|TH_FIN);
	}

   // check valid timestamp. Replace code above.
   if (ts_present && TSTMP_GEQ(ts_val, tp->ts_recent) &&
         SEQ_LEQ(ti->ti_seq, tp->last_ack_sent) ) {
		tp->ts_recent_age = g_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:
      DEBUG("change tcp state to TCPS_CLOSED, state=%d", tp->t_state);
		tp->t_state = TCPS_CLOSED;
      // tcp event
      usnet_tcpin_ewakeup(so, USN_TCP_IN, USN_TCPST_CLOSED, 0);
		g_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, ECONNRESET);
		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.
	case TCPS_SYN_RECEIVED:
		if (SEQ_GT(tp->snd_una, ti->ti_ack) ||
		    SEQ_GT(ti->ti_ack, tp->snd_max))
			goto dropwithreset;
		g_tcpstat.tcps_connects++;

      DEBUG("change tcp state to TCPS_ESTABLISHED, state=%d", tp->t_state);
		tp->t_state = TCPS_ESTABLISHED;
		soisconnected(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;
		}
		tcp_reass(tp, (struct tcpiphdr *)0, (usn_mbuf_t *)0);
		tp->snd_wl1 = ti->ti_seq - 1;
		// 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) {
				g_tcpstat.tcps_rcvdupack++;
				// 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
				// threshhold 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 == g_tcprexmtthresh) {
               // congestion avoidance
					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;
					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 > g_tcprexmtthresh) {
					tp->snd_cwnd += tp->t_maxseg;
					tcp_output(tp);
					goto drop;
				}
			} else
				tp->t_dupacks = 0;
			break;
		}

		// If the congestion window was inflated to account
		// for the other side's cached packets, retract it.
		if (tp->t_dupacks > g_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)) {
			g_tcpstat.tcps_rcvacktoomuch++;
			goto dropafterack;
		}
		acked = ti->ti_ack - tp->snd_una;
		g_tcpstat.tcps_rcvackpack++;
		g_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, g_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;
         DEBUG("change needoutput to 1");
			needoutput = 1;
         tp->t_flags |= TF_NEEDOUTPUT;
		} 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 * (maxseg / cwnd) per packet).
		{
		   u_int cw = tp->snd_cwnd;
	   	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;
         DEBUG("drop all so_snd buffer, drop_bytes=%d, acked=%d", 
               so->so_snd->sb_cc, acked);
			sbdrop(so->so_snd, (int)so->so_snd->sb_cc);
			ourfinisacked = 1;
		} else {
         DEBUG("drop so_snd buffer, drop_bytes=%d, len=%d", acked, so->so_snd->sb_cc);
			sbdrop(so->so_snd, acked);
			tp->snd_wnd -= acked;
			ourfinisacked = 0;
		}
		//if (so->so_snd->sb_flags & SB_NOTIFY) {
			sowwakeup(so);
         usnet_tcpin_wwakeup(so, USN_TCP_IN, USN_TCPEV_WRITE, 0);
      //}

		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 & USN_CANTRCVMORE) {
					soisdisconnected(so);
					tp->t_timer[TCPT_2MSL] = g_tcp_maxidle;
				}
            DEBUG("change tcp state to TCPS_FIN_WAIT_2, state=%d", tp->t_state);
				tp->t_state = TCPS_FIN_WAIT_2;
            usnet_tcpin_ewakeup(so, USN_TCP_IN, USN_TCPST_FIN_WAIT2, 0);
			}
			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) {
            DEBUG("change tcp state to TCPS_TIME_WAIT, state=%d", tp->t_state);
				tp->t_state = TCPS_TIME_WAIT;
            usnet_tcpin_ewakeup(so, USN_TCP_IN, USN_TCPST_TIME_WAIT, 0);
				tcp_canceltimers(tp);
				tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
				soisdisconnected(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;
		}
	}

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)
			g_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;
      DEBUG("change needoutput to 1");
      tp->t_flags |= TF_NEEDOUTPUT;
		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 > g_sb_max) {
			ti->ti_urp = 0;			// XXX
			tiflags &= ~TH_URG;		// XXX
			goto dodata;			// XXX
		}

		// 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_oobmark = so->so_rcv->sb_cc +
			    (tp->rcv_up - tp->rcv_nxt) - 1;
			if (so->so_oobmark == 0)
				so->so_state |= USN_RCVATMARK;
			sohasoutofband(so);
         // send async event to app threads.
         usnet_tcpin_ewakeup(so, USN_TCP_IN, USN_TCPEV_OUTOFBOUND, 0);
			tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
		}

		// Remove out of band data so doesn't get presented to user.
		// This can happen independent of advancing the URG pointer,
		// but if two URG's are pending at once, some out-of-band
		// data may creep in... ick.
		if (ti->ti_urp <= ti->ti_len
#ifdef SO_OOBINLINE
		     && (so->so_options & SO_OOBINLINE) == 0
#endif
		     )
			tcp_pulloutofband(so, ti, m);
	} 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:							// XXX
#ifdef DUMP_PAYLOAD
   DEBUG("Handle data");
   dump_chain(m,"tcp");
#endif

	// 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_hiwat - (tp->rcv_adv - tp->rcv_nxt);
	} else {
		usn_free_cmbuf(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) {
			socantrcvmore(so);
			tp->t_flags |= TF_ACKNOW;
         TRACE("ack FIN now, tp flags=%d", tp->t_flags);
			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:
         TRACE("change tcp state to TCPS_CLOSE_WAIT, state=%d", tp->t_state);
			tp->t_state = TCPS_CLOSE_WAIT;
         soewakeup(so, 0);
         usnet_tcpin_ewakeup(so, USN_TCP_IN, USN_TCPST_CLOSE_WAIT, 0);
			break;

		// If still in FIN_WAIT_1 STATE FIN has not been acked so
		// enter the CLOSING state.
		case TCPS_FIN_WAIT_1:
         TRACE("change tcp state to TCPS_CLOSING, state=%d", tp->t_state);
			tp->t_state = TCPS_CLOSING;
         usnet_tcpin_ewakeup(so, USN_TCP_IN, USN_TCPST_CLOSING, 0);
			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:
         TRACE("change tcp state to TCPS_TIME_WAIT, state=%d", tp->t_state);
			tp->t_state = TCPS_TIME_WAIT;
			tcp_canceltimers(tp);
			tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
			soisdisconnected(so);
         usnet_tcpin_ewakeup(so, USN_TCP_IN, USN_TCPST_TIME_WAIT, 0);
			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 (so->so_options & SO_DEBUG) {
      TRACE("tcp trace, so_options=%d", so->so_options);
		tcp_trace(TA_INPUT, ostate, tp, &g_tcp_saveti, 0);
   }

	// Return any desired output.
	//if (needoutput || (tp->t_flags & TF_ACKNOW)){
	if (tp->t_flags & TF_NEEDOUTPUT || (tp->t_flags & TF_ACKNOW)){
      TRACE("ack now or need to ouput, tp->t_flags=%d", tp->t_flags);
		tcp_output(tp);
   }
	return;

dropafterack:
   TRACE("dropafterack");
	// Generate an ACK dropping incoming segment if it occupies
	// sequence space, where the ACK reflects our state.
	if (tiflags & TH_RST)
		goto drop;
	usn_free_cmbuf(m);
	tp->t_flags |= TF_ACKNOW;
   TRACE("ack now, tp flags=%d", tp->t_flags);
	tcp_output(tp);
	return;

dropwithreset:
   TRACE("dropwithreset");
	// Generate a RST, dropping incoming segment.
	// Make ACK acceptable to originator of segment.
	// Don't bother to respond if destination was broadcast/multicast.
#define USN_MULTICAST(i) (((u_int)(i) & 0xf0000000) == 0xe0000000)
	if ((tiflags & TH_RST) || m->flags & (BUF_BCAST|BUF_MCAST) ||
	    USN_MULTICAST(ntohl(ti->ti_dst.s_addr)))
		goto drop;
   
	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);
	}
	// destroy temporarily created socket
	if (dropsocket)
		soabort(so);
	return;

drop:
   TRACE("drop");
	// Drop space held by incoming segment and return.
	if (tp && (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) {
      TRACE("tcp trace: drop a socket");
		tcp_trace(TA_DROP, ostate, tp, &g_tcp_saveti, 0);
   }
	usn_free_cmbuf(m);
	// destroy temporarily created socket
	if (dropsocket)
		soabort(so);
	return;
}