/*

 * Copyright (c) 1982, 1986, 1988, 1990, 1993

 *	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_timer.c	8.1 (Berkeley) 6/10/93

 * tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp

 */

#include <slirp.h>

#ifdef LOG_ENABLED

struct   tcpstat tcpstat;        /* tcp statistics */

#endif

u_int32_t        tcp_now;                /* for RFC 1323 timestamps */

static struct tcpcb *tcp_timers(register struct tcpcb *tp, int timer);

/*

 * Fast timeout routine for processing delayed acks

 */

void

tcp_fasttimo()

{

	register struct socket *so;

	register struct tcpcb *tp;

	DEBUG_CALL("tcp_fasttimo");

	so = tcb.so_next;

	if (so)

	for (; so != &tcb; so = so->so_next)

		if ((tp = (struct tcpcb *)so->so_tcpcb) &&

		    (tp->t_flags & TF_DELACK)) {

			tp->t_flags &= ~TF_DELACK;

			tp->t_flags |= TF_ACKNOW;

			STAT(tcpstat.tcps_delack++);

			(void) tcp_output(tp);

		}

}

/*

 * Tcp protocol timeout routine called every 500 ms.

 * Updates the timers in all active tcb's and

 * causes finite state machine actions if timers expire.

 */

void

tcp_slowtimo()

{

	register struct socket *ip, *ipnxt;

	register struct tcpcb *tp;

	register int i;

	DEBUG_CALL("tcp_slowtimo");

	/*

	 * Search through tcb's and update active timers.

	 */

	ip = tcb.so_next;

	if (ip == 0)

	   return;

	for (; ip != &tcb; ip = ipnxt) {

		ipnxt = ip->so_next;

		tp = sototcpcb(ip);

		if (tp == 0)

			continue;

		for (i = 0; i < TCPT_NTIMERS; i++) {

			if (tp->t_timer[i] && --tp->t_timer[i] == 0) {

				tcp_timers(tp,i);

				if (ipnxt->so_prev != ip)

					goto tpgone;

			}

		}

		tp->t_idle++;

		if (tp->t_rtt)

		   tp->t_rtt++;

tpgone:

		;

	}

	tcp_iss += TCP_ISSINCR/PR_SLOWHZ;		/* increment iss */

#ifdef TCP_COMPAT_42

	if ((int)tcp_iss < 0)

		tcp_iss = 0;				/* XXX */

#endif

	tcp_now++;					/* for timestamps */

}

/*

 * Cancel all timers for TCP tp.

 */

void

tcp_canceltimers(tp)

	struct tcpcb *tp;

{

	register int i;

	for (i = 0; i < TCPT_NTIMERS; i++)

		tp->t_timer[i] = 0;

}

const int tcp_backoff[TCP_MAXRXTSHIFT + 1] =

   { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };

/*

 * TCP timer processing.

 */

static struct tcpcb *

tcp_timers(register struct tcpcb *tp, int timer)

{

	register int rexmt;

	DEBUG_CALL("tcp_timers");

	switch (timer) {

	/*

	 * 2 MSL timeout in shutdown went off.  If we're closed but

	 * still waiting for peer to close and connection has been idle

	 * too long, or if 2MSL time is up from TIME_WAIT, delete connection

	 * control block.  Otherwise, check again in a bit.

	 */

	case TCPT_2MSL:

		if (tp->t_state != TCPS_TIME_WAIT &&

		    tp->t_idle <= TCP_MAXIDLE)

			tp->t_timer[TCPT_2MSL] = TCPTV_KEEPINTVL;

		else

			tp = tcp_close(tp);

		break;

	/*

	 * Retransmission timer went off.  Message has not

	 * been acked within retransmit interval.  Back off

	 * to a longer retransmit interval and retransmit one segment.

	 */

	case TCPT_REXMT:

		/*

		 * XXXXX If a packet has timed out, then remove all the queued

		 * packets for that session.

		 */

		if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {

			/*

			 * This is a hack to suit our terminal server here at the uni of canberra

			 * since they have trouble with zeroes... It usually lets them through

			 * unharmed, but under some conditions, it'll eat the zeros.  If we

			 * keep retransmitting it, it'll keep eating the zeroes, so we keep

			 * retransmitting, and eventually the connection dies...

			 * (this only happens on incoming data)

			 *

			 * So, if we were gonna drop the connection from too many retransmits,

			 * don't... instead halve the t_maxseg, which might break up the NULLs and

			 * let them through

			 *

			 * *sigh*

			 */

			tp->t_maxseg >>= 1;

			if (tp->t_maxseg < 32) {

				/*

				 * We tried our best, now the connection must die!

				 */

				tp->t_rxtshift = TCP_MAXRXTSHIFT;

				STAT(tcpstat.tcps_timeoutdrop++);

				tp = tcp_drop(tp, tp->t_softerror);

				/* tp->t_softerror : ETIMEDOUT); */ /* XXX */

				return (tp); /* XXX */

			}

			/*

			 * Set rxtshift to 6, which is still at the maximum

			 * backoff time

			 */

			tp->t_rxtshift = 6;

		}

		STAT(tcpstat.tcps_rexmttimeo++);

		rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];

		TCPT_RANGESET(tp->t_rxtcur, rexmt,

		    (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */

		tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;

		/*

		 * If losing, let the lower level know and try for

		 * a better route.  Also, if we backed off this far,

		 * our srtt estimate is probably bogus.  Clobber it

		 * so we'll take the next rtt measurement as our srtt;

		 * move the current srtt into rttvar to keep the current

		 * retransmit times until then.

		 */

		if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {

/*			in_losing(tp->t_inpcb); */

			tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);

			tp->t_srtt = 0;

		}

		tp->snd_nxt = tp->snd_una;

		/*

		 * If timing a segment in this window, stop the timer.

		 */

		tp->t_rtt = 0;

		/*

		 * Close the congestion window down to one segment

		 * (we'll open it by one segment for each ack we get).

		 * Since we probably have a window's worth of unacked

		 * data accumulated, this "slow start" keeps us from

		 * dumping all that data as back-to-back packets (which

		 * might overwhelm an intermediate gateway).

		 *

		 * There are two phases to the opening: Initially we

		 * open by one mss on each ack.  This makes the window

		 * size increase exponentially with time.  If the

		 * window is larger than the path can handle, this

		 * exponential growth results in dropped packet(s)

		 * almost immediately.  To get more time between

		 * drops but still "push" the network to take advantage

		 * of improving conditions, we switch from exponential

		 * to linear window opening at some threshold size.

		 * For a threshold, we use half the current window

		 * size, truncated to a multiple of the mss.

		 *

		 * (the minimum cwnd that will give us exponential

		 * growth is 2 mss.  We don't allow the threshold

		 * to go below this.)

		 */

		{

		u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;

		if (win < 2)

			win = 2;

		tp->snd_cwnd = tp->t_maxseg;

		tp->snd_ssthresh = win * tp->t_maxseg;

		tp->t_dupacks = 0;

		}

		(void) tcp_output(tp);

		break;

	/*

	 * Persistence timer into zero window.

	 * Force a byte to be output, if possible.

	 */

	case TCPT_PERSIST:

		STAT(tcpstat.tcps_persisttimeo++);

		tcp_setpersist(tp);

		tp->t_force = 1;

		(void) tcp_output(tp);

		tp->t_force = 0;

		break;

	/*

	 * Keep-alive timer went off; send something

	 * or drop connection if idle for too long.

	 */

	case TCPT_KEEP:

		STAT(tcpstat.tcps_keeptimeo++);

		if (tp->t_state < TCPS_ESTABLISHED)

			goto dropit;

/*		if (tp->t_socket->so_options & SO_KEEPALIVE && */

		if ((SO_OPTIONS) && tp->t_state <= TCPS_CLOSE_WAIT) {

		    	if (tp->t_idle >= TCPTV_KEEP_IDLE + TCP_MAXIDLE)

				goto dropit;

			/*

			 * Send a packet designed to force a response

			 * if the peer is up and reachable:

			 * either an ACK if the connection is still alive,

			 * or an RST if the peer has closed the connection

			 * due to timeout or reboot.

			 * Using sequence number tp->snd_una-1

			 * causes the transmitted zero-length segment

			 * to lie outside the receive window;

			 * by the protocol spec, this requires the

			 * correspondent TCP to respond.

			 */

			STAT(tcpstat.tcps_keepprobe++);

#ifdef TCP_COMPAT_42

			/*

			 * The keepalive packet must have nonzero length

			 * to get a 4.2 host to respond.

			 */

			tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,

			    tp->rcv_nxt - 1, tp->snd_una - 1, 0);

#else

			tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,

			    tp->rcv_nxt, tp->snd_una - 1, 0);

#endif

			tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL;

		} else

			tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE;

		break;

	dropit:

		STAT(tcpstat.tcps_keepdrops++);

		tp = tcp_drop(tp, 0); /* ETIMEDOUT); */

		break;

	}

	return (tp);

}