/*
 * 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. 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/slirp.h"

/*
 * Since this is only used in "stats socket", we give meaning
 * names instead of the REAL names
 */
char *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",
};

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) struct tcpcb *tp;
{
        struct SLIRPsocket *so = tp->t_socket;
        register long len, win;
        int off, flags, error;
        struct SLIRPmbuf *m;
        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.
         */
        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 SLIRPmbuf, 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((SLIRPcaddr_t)(opt + 2), (SLIRPcaddr_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 SLIRPmbuf, 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)
                        tcpstat.tcps_sndprobe++;
                else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
                        tcpstat.tcps_sndrexmitpack++;
                        tcpstat.tcps_sndrexmitbyte += len;
                } else {
                        tcpstat.tcps_sndpack++;
                        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 SLIRPmbufs
                 * 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, SLIRPcaddr_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)
                        tcpstat.tcps_sndacks++;
                else if (flags & (TH_SYN | TH_FIN | TH_RST))
                        tcpstat.tcps_sndctrl++;
                else if (SEQ_GT(tp->snd_up, tp->snd_una))
                        tcpstat.tcps_sndurg++;
                else
                        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((SLIRPcaddr_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((SLIRPcaddr_t)(ti + 1), (SLIRPcaddr_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;
                                        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
                 * send to IP level.  There should be a better way
                 * to handle ttl and tos; we could keep them in
                 * the template, but need a way to checksum without them.
                 */
                m->m_len = hdrlen + len; /* XXX Needed? m_len should be correct */

                {

                        ((struct ip *)ti)->ip_len = m->m_len;

                        ((struct ip *)ti)->ip_ttl = ip_defttl;
                        ((struct ip *)ti)->ip_tos = so->so_iptos;

                        /* #if BSD >= 43 */
                        /* Don't do IP options... */
                        /*	error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
                         *	    so->so_options & SO_DONTROUTE, 0);
                         */
                        error = ip_output(so, m);

                        /* #else
                         *	error = ip_output(m, (struct SLIRPmbuf *)0, &tp->t_inpcb->inp_route,
                         *	    so->so_options & SO_DONTROUTE);
                         * #endif
                         */
                }
                if (error) {
                out:
                        /*		if (error == ENOBUFS) {
                         *			tcp_quench(tp->t_inpcb, 0);
                         *			return (0);
                         *		}
                         */
                        /*		if ((error == EHOSTUNREACH || error == ENETDOWN)
                         *		    && TCPS_HAVERCVDSYN(tp->t_state)) {
                         *			tp->t_softerror = error;
                         *			return (0);
                         *		}
                         */
                        return (error);
                }
                tcpstat.tcps_sndtotal++;

                /*
                 * Data sent (as far as we can tell).
                 * If this advertises a larger window than any other segment,
                 * then remember the size of the advertised window.
                 * Any pending ACK has now been sent.
                 */
                if (win > 0 && SEQ_GT(tp->rcv_nxt + win, tp->rcv_adv))
                        tp->rcv_adv = tp->rcv_nxt + win;
                tp->last_ack_sent = tp->rcv_nxt;
                tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
                if (sendalot)
                        goto again;

                return (0);
        }

        void tcp_setpersist(tp) struct tcpcb *tp;
        {
                int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;

                /*	if (tp->t_timer[TCPT_REXMT])
                 *		panic("tcp_output REXMT");
                 */
                /*
                 * Start/restart persistence timer.
                 */
                TCPT_RANGESET(tp->t_timer[TCPT_PERSIST], t * tcp_backoff[tp->t_rxtshift], TCPTV_PERSMIN, TCPTV_PERSMAX);
                if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
                        tp->t_rxtshift++;
        }
