/*

 * 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_output.c	8.3 (Berkeley) 12/30/93

 * tcp_output.c,v 1.3 1994/09/15 10:36:55 davidg 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>

/*

 * Since this is only used in "stats socket", we give meaning

 * names instead of the REAL names

 */

const char * const tcpstates[] = {

/*	"CLOSED",       "LISTEN",       "SYN_SENT",     "SYN_RCVD", */

	"REDIRECT",	"LISTEN",	"SYN_SENT",     "SYN_RCVD",

	"ESTABLISHED",  "CLOSE_WAIT",   "FIN_WAIT_1",   "CLOSING",

	"LAST_ACK",     "FIN_WAIT_2",   "TIME_WAIT",

};

static const u_char  tcp_outflags[TCP_NSTATES] = {

	TH_RST|TH_ACK, 0,      TH_SYN,        TH_SYN|TH_ACK,

	TH_ACK,        TH_ACK, TH_FIN|TH_ACK, TH_FIN|TH_ACK,

	TH_FIN|TH_ACK, TH_ACK, TH_ACK,

};

#define MAX_TCPOPTLEN	32	/* max # bytes that go in options */

/*

 * Tcp output routine: figure out what should be sent and send it.

 */

int

tcp_output(tp)

	register struct tcpcb *tp;

{

	register struct socket *so = tp->t_socket;

	register long len, win;

	int off, flags, error;

	register struct mbuf *m;

	register struct tcpiphdr *ti;

	u_char opt[MAX_TCPOPTLEN];

	unsigned optlen, hdrlen;

	int idle, sendalot;

	DEBUG_CALL("tcp_output");

	DEBUG_ARG("tp = %lx", (long )tp);

	/*

	 * Determine length of data that should be transmitted,

	 * and flags that will be used.

	 * If there is some data or critical controls (SYN, RST)

	 * to send, then transmit; otherwise, investigate further.

	 */

	idle = (tp->snd_max == tp->snd_una);

	if (idle && tp->t_idle >= tp->t_rxtcur)

		/*

		 * We have been idle for "a while" and no acks are

		 * expected to clock out any data we send --

		 * slow start to get ack "clock" running again.

		 */

		tp->snd_cwnd = tp->t_maxseg;

again:

	sendalot = 0;

	off = tp->snd_nxt - tp->snd_una;

	win = min(tp->snd_wnd, tp->snd_cwnd);

	flags = tcp_outflags[tp->t_state];

	DEBUG_MISC((dfd, " --- tcp_output flags = 0x%x\n",flags));

	/*

	 * If in persist timeout with window of 0, send 1 byte.

	 * Otherwise, if window is small but nonzero

	 * and timer expired, we will send what we can

	 * and go to transmit state.

	 */

	if (tp->t_force) {

		if (win == 0) {

			/*

			 * If we still have some data to send, then

			 * clear the FIN bit.  Usually this would

			 * happen below when it realizes that we

			 * aren't sending all the data.  However,

			 * if we have exactly 1 byte of unset data,

			 * then it won't clear the FIN bit below,

			 * and if we are in persist state, we wind

			 * up sending the packet without recording

			 * that we sent the FIN bit.

			 *

			 * We can't just blindly clear the FIN bit,

			 * because if we don't have any more data

			 * to send then the probe will be the FIN

			 * itself.

			 */

			if (off < so->so_snd.sb_cc)

				flags &= ~TH_FIN;

			win = 1;

		} else {

			tp->t_timer[TCPT_PERSIST] = 0;

			tp->t_rxtshift = 0;

		}

	}

	len = min(so->so_snd.sb_cc, win) - off;

	if (len < 0) {

		/*

		 * If FIN has been sent but not acked,

		 * but we haven't been called to retransmit,

		 * len will be -1.  Otherwise, window shrank

		 * after we sent into it.  If window shrank to 0,

		 * cancel pending retransmit and pull snd_nxt

		 * back to (closed) window.  We will enter persist

		 * state below.  If the window didn't close completely,

		 * just wait for an ACK.

		 */

		len = 0;

		if (win == 0) {

			tp->t_timer[TCPT_REXMT] = 0;

			tp->snd_nxt = tp->snd_una;

		}

	}

	if (len > tp->t_maxseg) {

		len = tp->t_maxseg;

		sendalot = 1;

	}

	if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))

		flags &= ~TH_FIN;

	win = sbspace(&so->so_rcv);

	/*

	 * Sender silly window avoidance.  If connection is idle

	 * and can send all data, a maximum segment,

	 * at least a maximum default-size segment do it,

	 * or are forced, do it; otherwise don't bother.

	 * If peer's buffer is tiny, then send

	 * when window is at least half open.

	 * If retransmitting (possibly after persist timer forced us

	 * to send into a small window), then must resend.

	 */

	if (len) {

		if (len == tp->t_maxseg)

			goto send;

		if ((1 || idle || tp->t_flags & TF_NODELAY) &&

		    len + off >= so->so_snd.sb_cc)

			goto send;

		if (tp->t_force)

			goto send;

		if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)

			goto send;

		if (SEQ_LT(tp->snd_nxt, tp->snd_max))

			goto send;

	}

	/*

	 * Compare available window to amount of window

	 * known to peer (as advertised window less

	 * next expected input).  If the difference is at least two

	 * max size segments, or at least 50% of the maximum possible

	 * window, then want to send a window update to peer.

	 */

	if (win > 0) {

		/*

		 * "adv" is the amount we can increase the window,

		 * taking into account that we are limited by

		 * TCP_MAXWIN << tp->rcv_scale.

		 */

		long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) -

			(tp->rcv_adv - tp->rcv_nxt);

		if (adv >= (long) (2 * tp->t_maxseg))

			goto send;

		if (2 * adv >= (long) so->so_rcv.sb_datalen)

			goto send;

	}

	/*

	 * Send if we owe peer an ACK.

	 */

	if (tp->t_flags & TF_ACKNOW)

		goto send;

	if (flags & (TH_SYN|TH_RST))

		goto send;

	if (SEQ_GT(tp->snd_up, tp->snd_una))

		goto send;

	/*

	 * If our state indicates that FIN should be sent

	 * and we have not yet done so, or we're retransmitting the FIN,

	 * then we need to send.

	 */

	if (flags & TH_FIN &&

	    ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))

		goto send;

	/*

	 * TCP window updates are not reliable, rather a polling protocol

	 * using ``persist'' packets is used to insure receipt of window

	 * updates.  The three ``states'' for the output side are:

	 *	idle			not doing retransmits or persists

	 *	persisting		to move a small or zero window

	 *	(re)transmitting	and thereby not persisting

	 *

	 * tp->t_timer[TCPT_PERSIST]

	 *	is set when we are in persist state.

	 * tp->t_force

	 *	is set when we are called to send a persist packet.

	 * tp->t_timer[TCPT_REXMT]

	 *	is set when we are retransmitting

	 * The output side is idle when both timers are zero.

	 *

	 * If send window is too small, there is data to transmit, and no

	 * retransmit or persist is pending, then go to persist state.

	 * If nothing happens soon, send when timer expires:

	 * if window is nonzero, transmit what we can,

	 * otherwise force out a byte.

	 */

	if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 &&

	    tp->t_timer[TCPT_PERSIST] == 0) {

		tp->t_rxtshift = 0;

		tcp_setpersist(tp);

	}

	/*

	 * No reason to send a segment, just return.

	 */

	STAT(tcpstat.tcps_didnuttin++);

	return (0);

send:

	/*

	 * Before ESTABLISHED, force sending of initial options

	 * unless TCP set not to do any options.

	 * NOTE: we assume that the IP/TCP header plus TCP options

	 * always fit in a single mbuf, leaving room for a maximum

	 * link header, i.e.

	 *	max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MHLEN

	 */

	optlen = 0;

	hdrlen = sizeof (struct tcpiphdr);

	if (flags & TH_SYN) {

		tp->snd_nxt = tp->iss;

		if ((tp->t_flags & TF_NOOPT) == 0) {

			u_int16_t mss;

			opt[0] = TCPOPT_MAXSEG;

			opt[1] = 4;

			mss = htons((u_int16_t) tcp_mss(tp, 0));

			memcpy((caddr_t)(opt + 2), (caddr_t)&mss, sizeof(mss));

			optlen = 4;

/*			if ((tp->t_flags & TF_REQ_SCALE) &&

 *			    ((flags & TH_ACK) == 0 ||

 *			    (tp->t_flags & TF_RCVD_SCALE))) {

 *				*((u_int32_t *) (opt + optlen)) = htonl(

 *					TCPOPT_NOP << 24 |

 *					TCPOPT_WINDOW << 16 |

 *					TCPOLEN_WINDOW << 8 |

 *					tp->request_r_scale);

 *				optlen += 4;

 *			}

 */

		}

 	}

 	/*

	 * Send a timestamp and echo-reply if this is a SYN and our side

	 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side

	 * and our peer have sent timestamps in our SYN's.

 	 */

/* 	if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&

 *	     (flags & TH_RST) == 0 &&

 *	    ((flags & (TH_SYN|TH_ACK)) == TH_SYN ||

 *	     (tp->t_flags & TF_RCVD_TSTMP))) {

 *		u_int32_t *lp = (u_int32_t *)(opt + optlen);

 *

 *		/ * Form timestamp option as shown in appendix A of RFC 1323. *  /

 *		*lp++ = htonl(TCPOPT_TSTAMP_HDR);

 *		*lp++ = htonl(tcp_now);

 *		*lp   = htonl(tp->ts_recent);

 *		optlen += TCPOLEN_TSTAMP_APPA;

 *	}

 */

 	hdrlen += optlen;

	/*

	 * Adjust data length if insertion of options will

	 * bump the packet length beyond the t_maxseg length.

	 */

	 if (len > tp->t_maxseg - optlen) {

		len = tp->t_maxseg - optlen;

		sendalot = 1;

	 }

	/*

	 * Grab a header mbuf, attaching a copy of data to

	 * be transmitted, and initialize the header from

	 * the template for sends on this connection.

	 */

	if (len) {

		if (tp->t_force && len == 1)

			STAT(tcpstat.tcps_sndprobe++);

		else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {

			STAT(tcpstat.tcps_sndrexmitpack++);

			STAT(tcpstat.tcps_sndrexmitbyte += len);

		} else {

			STAT(tcpstat.tcps_sndpack++);

			STAT(tcpstat.tcps_sndbyte += len);

		}

		m = m_get();

		if (m == NULL) {

/*			error = ENOBUFS; */

			error = 1;

			goto out;

		}

		m->m_data += IF_MAXLINKHDR;

		m->m_len = hdrlen;

		/*

		 * This will always succeed, since we make sure our mbufs

		 * are big enough to hold one MSS packet + header + ... etc.

		 */

/*		if (len <= MHLEN - hdrlen - max_linkhdr) { */

			sbcopy(&so->so_snd, off, (int) len, mtod(m, caddr_t) + hdrlen);

			m->m_len += len;

/*		} else {

 *			m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);

 *			if (m->m_next == 0)

 *				len = 0;

 *		}

 */

		/*

		 * If we're sending everything we've got, set PUSH.

		 * (This will keep happy those implementations which only

		 * give data to the user when a buffer fills or

		 * a PUSH comes in.)

		 */

		if (off + len == so->so_snd.sb_cc)

			flags |= TH_PUSH;

	} else {

		if (tp->t_flags & TF_ACKNOW)

			STAT(tcpstat.tcps_sndacks++);

		else if (flags & (TH_SYN|TH_FIN|TH_RST))

			STAT(tcpstat.tcps_sndctrl++);

		else if (SEQ_GT(tp->snd_up, tp->snd_una))

			STAT(tcpstat.tcps_sndurg++);

		else

			STAT(tcpstat.tcps_sndwinup++);

		m = m_get();

		if (m == NULL) {

/*			error = ENOBUFS; */

			error = 1;

			goto out;

		}

		m->m_data += IF_MAXLINKHDR;

		m->m_len = hdrlen;

	}

	ti = mtod(m, struct tcpiphdr *);

	memcpy((caddr_t)ti, &tp->t_template, sizeof (struct tcpiphdr));

	/*

	 * Fill in fields, remembering maximum advertised

	 * window for use in delaying messages about window sizes.

	 * If resending a FIN, be sure not to use a new sequence number.

	 */

	if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&

	    tp->snd_nxt == tp->snd_max)

		tp->snd_nxt--;

	/*

	 * If we are doing retransmissions, then snd_nxt will

	 * not reflect the first unsent octet.  For ACK only

	 * packets, we do not want the sequence number of the

	 * retransmitted packet, we want the sequence number

	 * of the next unsent octet.  So, if there is no data

	 * (and no SYN or FIN), use snd_max instead of snd_nxt

	 * when filling in ti_seq.  But if we are in persist

	 * state, snd_max might reflect one byte beyond the

	 * right edge of the window, so use snd_nxt in that

	 * case, since we know we aren't doing a retransmission.

	 * (retransmit and persist are mutually exclusive...)

	 */

	if (len || (flags & (TH_SYN|TH_FIN)) || tp->t_timer[TCPT_PERSIST])

		ti->ti_seq = htonl(tp->snd_nxt);

	else

		ti->ti_seq = htonl(tp->snd_max);

	ti->ti_ack = htonl(tp->rcv_nxt);

	if (optlen) {

		memcpy((caddr_t)(ti + 1), (caddr_t)opt, optlen);

		ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;

	}

	ti->ti_flags = flags;

	/*

	 * Calculate receive window.  Don't shrink window,

	 * but avoid silly window syndrome.

	 */

	if (win < (long)(so->so_rcv.sb_datalen / 4) && win < (long)tp->t_maxseg)

		win = 0;

	if (win > (long)TCP_MAXWIN << tp->rcv_scale)

		win = (long)TCP_MAXWIN << tp->rcv_scale;

	if (win < (long)(tp->rcv_adv - tp->rcv_nxt))

		win = (long)(tp->rcv_adv - tp->rcv_nxt);

	ti->ti_win = htons((u_int16_t) (win>>tp->rcv_scale));

	if (SEQ_GT(tp->snd_up, tp->snd_una)) {

		ti->ti_urp = htons((u_int16_t)(tp->snd_up - ntohl(ti->ti_seq)));

#ifdef notdef

	if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {

		ti->ti_urp = htons((u_int16_t)(tp->snd_up - tp->snd_nxt));

#endif

		ti->ti_flags |= TH_URG;

	} else

		/*

		 * If no urgent pointer to send, then we pull

		 * the urgent pointer to the left edge of the send window

		 * so that it doesn't drift into the send window on sequence

		 * number wraparound.

		 */

		tp->snd_up = tp->snd_una;		/* drag it along */

	/*

	 * Put TCP length in extended header, and then

	 * checksum extended header and data.

	 */

	if (len + optlen)

		ti->ti_len = htons((u_int16_t)(sizeof (struct tcphdr) +

		    optlen + len));

	ti->ti_sum = cksum(m, (int)(hdrlen + len));

	/*

	 * In transmit state, time the transmission and arrange for

	 * the retransmit.  In persist state, just set snd_max.

	 */

	if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) {

		tcp_seq startseq = tp->snd_nxt;

		/*

		 * Advance snd_nxt over sequence space of this segment.

		 */

		if (flags & (TH_SYN|TH_FIN)) {

			if (flags & TH_SYN)

				tp->snd_nxt++;

			if (flags & TH_FIN) {

				tp->snd_nxt++;

				tp->t_flags |= TF_SENTFIN;

			}

		}

		tp->snd_nxt += len;

		if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {

			tp->snd_max = tp->snd_nxt;

			/*

			 * Time this transmission if not a retransmission and

			 * not currently timing anything.

			 */

			if (tp->t_rtt == 0) {

				tp->t_rtt = 1;

				tp->t_rtseq = startseq;

				STAT(tcpstat.tcps_segstimed++);

			}

		}

		/*

		 * Set retransmit timer if not currently set,

		 * and not doing an ack or a keep-alive probe.

		 * Initial value for retransmit timer is smoothed

		 * round-trip time + 2 * round-trip time variance.

		 * Initialize shift counter which is used for backoff

		 * of retransmit time.

		 */

		if (tp->t_timer[TCPT_REXMT] == 0 &&

		    tp->snd_nxt != tp->snd_una) {

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

			if (tp->t_timer[TCPT_PERSIST]) {

				tp->t_timer[TCPT_PERSIST] = 0;

				tp->t_rxtshift = 0;

			}

		}

	} else

		if (SEQ_GT(tp->snd_nxt + len, tp->snd_max))

			tp->snd_max = tp->snd_nxt + len;

	/*

	 * Fill in IP length and desired time to live and