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tcp_input.c

/*
 * 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;

#define     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 && \
           (tp)->seg_next == (tcpiphdrp_32)(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; \
               STAT(tcpstat.tcps_rcvpack++);         \
               STAT(tcpstat.tcps_rcvbyte += (ti)->ti_len);   \
               if (so->so_emu) { \
                   if (tcp_emu((so),(m))) sbappend((so), (m)); \
             } else \
                         sbappend((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 && \
          (tp)->seg_next == (tcpiphdrp_32)(tp) && \
          (tp)->t_state == TCPS_ESTABLISHED) { \
            tp->t_flags |= TF_DELACK; \
            (tp)->rcv_nxt += (ti)->ti_len; \
            flags = (ti)->ti_flags & TH_FIN; \
            STAT(tcpstat.tcps_rcvpack++);        \
            STAT(tcpstat.tcps_rcvbyte += (ti)->ti_len);  \
            if (so->so_emu) { \
                  if (tcp_emu((so),(m))) sbappend(so, (m)); \
            } else \
                  sbappend((so), (m)); \
/*          sorwakeup(so); */ \
      } else { \
            (flags) = tcp_reass((tp), (ti), (m)); \
            tp->t_flags |= TF_ACKNOW; \
      } \
}
#endif
static void tcp_dooptions(struct tcpcb *tp, u_char *cp, int cnt,
                          struct tcpiphdr *ti);
static void tcp_xmit_timer(register struct tcpcb *tp, int rtt);

static int
tcp_reass(register struct tcpcb *tp, register struct tcpiphdr *ti,
          struct 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 = (struct tcpiphdr *)tp->seg_next; q != (struct tcpiphdr *)tp;
          q = (struct tcpiphdr *)q->ti_next)
            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 ((struct tcpiphdr *)q->ti_prev != (struct tcpiphdr *)tp) {
            register int i;
            q = (struct tcpiphdr *)q->ti_prev;
            /* 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) {
                        STAT(tcpstat.tcps_rcvduppack++);
                        STAT(tcpstat.tcps_rcvdupbyte += ti->ti_len);
                        m_freem(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;   /* ??? */
                  }
                  m_adj(m, i);
                  ti->ti_len -= i;
                  ti->ti_seq += i;
            }
            q = (struct tcpiphdr *)(q->ti_next);
      }
      STAT(tcpstat.tcps_rcvoopack++);
      STAT(tcpstat.tcps_rcvoobyte += ti->ti_len);
      REASS_MBUF(ti) = (mbufp_32) m;            /* XXX */

      /*
       * While we overlap succeeding segments trim them or,
       * if they are completely covered, dequeue them.
       */
      while (q != (struct tcpiphdr *)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;
                  m_adj((struct mbuf *) REASS_MBUF(q), i);
                  break;
            }
            q = (struct tcpiphdr *)q->ti_next;
            m = (struct mbuf *) REASS_MBUF((struct tcpiphdr *)q->ti_prev);
            remque_32((void *)(q->ti_prev));
            m_freem(m);
      }

      /*
       * Stick new segment in its place.
       */
      insque_32(ti, (void *)(q->ti_prev));

present:
      /*
       * Present data to user, advancing rcv_nxt through
       * completed sequence space.
       */
      if (!TCPS_HAVEESTABLISHED(tp->t_state))
            return (0);
      ti = (struct tcpiphdr *) tp->seg_next;
      if (ti == (struct tcpiphdr *)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_32(ti);
            m = (struct mbuf *) REASS_MBUF(ti); /* XXX */
            ti = (struct tcpiphdr *)ti->ti_next;
/*          if (so->so_state & SS_FCANTRCVMORE) */
            if (so->so_state & SS_FCANTSENDMORE)
                  m_freem(m);
            else {
                  if (so->so_emu) {
                        if (tcp_emu(so,m)) sbappend(so, m);
                  } else
                        sbappend(so, m);
            }
      } while (ti != (struct tcpiphdr *)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 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 = 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;
      }


      STAT(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(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;
      ti->ti_next = ti->ti_prev = 0;
      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)) {
        STAT(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) {
        STAT(tcpstat.tcps_rcvbadoff++);
        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);

            /*
             * 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;
      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(&tcb, ti->ti_src, ti->ti_sport,
                         ti->ti_dst, ti->ti_dport);
            if (so)
                  tcp_last_so = so;
            STAT(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;
        }

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

        /*        tcp_last_so = so; */  /* XXX ? */
        /*        tp = sototcpcb(so);    */

        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 == 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] = 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);
/* , */
/*                &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.
                         */
                        STAT(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;
                        STAT(tcpstat.tcps_rcvackpack++);
                        STAT(tcpstat.tcps_rcvackbyte += acked);
                        sbdrop(&so->so_snd, acked);
                        tp->snd_una = ti->ti_ack;
                        m_freem(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 &&
                tp->seg_next == (tcpiphdrp_32)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.
                   */
                  STAT(tcpstat.tcps_preddat++);
                  tp->rcv_nxt += ti->ti_len;
                  STAT(tcpstat.tcps_rcvpack++);
                  STAT(tcpstat.tcps_rcvbyte += ti->ti_len);
                  /*
                   * Add data to socket buffer.
                   */
                  if (so->so_emu) {
                        if (tcp_emu(so,m)) sbappend(so, m);
                  } else
                        sbappend(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 = 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&htonl(0xffffff00)) == special_addr.s_addr) {
          int lastbyte=ntohl(so->so_faddr.s_addr) & 0xff;
          if (lastbyte!=CTL_ALIAS && lastbyte!=CTL_DNS) {
#if 0
            if(lastbyte==CTL_CMD || lastbyte==CTL_EXEC) {
            /* Command or exec adress */
            so->so_state |= SS_CTL;
            } else
#endif
              {
            /* May be an add exec */
            struct ex_list *ex_ptr;
            for(ex_ptr = exec_list; ex_ptr; ex_ptr = ex_ptr->ex_next) {
              if(ex_ptr->ex_fport == so->so_fport &&
                 lastbyte == ex_ptr->ex_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) && (errno != EINPROGRESS) && (errno != EWOULDBLOCK)) {
          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));
          }
          tp = 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;
        }
        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);
        /* , */
        /*                    &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;
        STAT(tcpstat.tcps_accepts++);
        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)) {
                  STAT(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,
                        (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;
                  STAT(tcpstat.tcps_rcvpackafterwin++);
                  STAT(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;
                  STAT(tcpstat.tcps_rcvduppack++);
                  STAT(tcpstat.tcps_rcvdupbyte += todrop);
            } else {
                  STAT(tcpstat.tcps_rcvpartduppack++);
                  STAT(tcpstat.tcps_rcvpartdupbyte += todrop);
            }
            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);
            STAT(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) {
            STAT(tcpstat.tcps_rcvpackafterwin++);
            if (todrop >= ti->ti_len) {
                  STAT(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;
                        STAT(tcpstat.tcps_rcvwinprobe++);
                  } else
                        goto dropafterack;
            } else
                  STAT(tcpstat.tcps_rcvbyteafterwin += todrop);
            m_adj(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;
            STAT(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;
            STAT(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, (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) {
                    STAT(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)) {
                  STAT(tcpstat.tcps_rcvacktoomuch++);
                  goto dropafterack;
            }
            acked = ti->ti_ack - tp->snd_una;
            STAT(tcpstat.tcps_rcvackpack++);
            STAT(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;
                  sbdrop(&so->so_snd, (int )so->so_snd.sb_cc);
                  ourfinisacked = 1;
            } else {
                  sbdrop(&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)
                  STAT(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 {
            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.
                   */
/*                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;
      m_freem(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);

      return;
}

 /* , ts_present, ts_val, ts_ecr) */
/*    int *ts_present;
 *    u_int32_t *ts_val, *ts_ecr;
 */
static void
tcp_dooptions(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 struct mbuf *m;
{
      int cnt = ti->ti_urp - 1;

      while (cnt >= 0) {
            if (m->m_len > cnt) {
                  char *cp = mtod(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.
 */

static void
tcp_xmit_timer(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);

      STAT(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;

      sbreserve(&so->so_snd, TCP_SNDSPACE + ((TCP_SNDSPACE % mss) ?
                                               (mss - (TCP_SNDSPACE % mss)) :
                                               0));
      sbreserve(&so->so_rcv, TCP_RCVSPACE + ((TCP_RCVSPACE % mss) ?
                                               (mss - (TCP_RCVSPACE % mss)) :
                                               0));

      DEBUG_MISC((dfd, " returning mss = %d\n", mss));

      return mss;
}

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