path: root/slirp/src/tcp_subr.c

/* SPDX-License-Identifier: BSD-3-Clause */
/*
 * 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_subr.c	8.1 (Berkeley) 6/10/93
 * tcp_subr.c,v 1.5 1994/10/08 22:39:58 phk Exp
 */

/*
 * Changes and additions relating to SLiRP
 * Copyright (c) 1995 Danny Gasparovski.
 */

#include "slirp.h"

/* patchable/settable parameters for tcp */
/* Don't do rfc1323 performance enhancements */
#define TCP_DO_RFC1323 0

/*
 * Tcp initialization
 */
void
tcp_init(Slirp *slirp)
{
    slirp->tcp_iss = 1;		/* wrong */
    slirp->tcb.so_next = slirp->tcb.so_prev = &slirp->tcb;
    slirp->tcp_last_so = &slirp->tcb;
}

void tcp_cleanup(Slirp *slirp)
{
    while (slirp->tcb.so_next != &slirp->tcb) {
        tcp_close(sototcpcb(slirp->tcb.so_next));
    }
}

/*
 * Create template to be used to send tcp packets on a connection.
 * Call after host entry created, fills
 * in a skeletal tcp/ip header, minimizing the amount of work
 * necessary when the connection is used.
 */
void
tcp_template(struct tcpcb *tp)
{
	struct socket *so = tp->t_socket;
	register struct tcpiphdr *n = &tp->t_template;

	n->ti_mbuf = NULL;
	memset(&n->ti, 0, sizeof(n->ti));
	n->ti_x0 = 0;
	switch (so->so_ffamily) {
	case AF_INET:
	    n->ti_pr = IPPROTO_TCP;
	    n->ti_len = htons(sizeof(struct tcphdr));
	    n->ti_src = so->so_faddr;
	    n->ti_dst = so->so_laddr;
	    n->ti_sport = so->so_fport;
	    n->ti_dport = so->so_lport;
	    break;

	case AF_INET6:
	    n->ti_nh6 = IPPROTO_TCP;
	    n->ti_len = htons(sizeof(struct tcphdr));
	    n->ti_src6 = so->so_faddr6;
	    n->ti_dst6 = so->so_laddr6;
	    n->ti_sport = so->so_fport6;
	    n->ti_dport = so->so_lport6;
	    break;

	default:
	    g_assert_not_reached();
	}

	n->ti_seq = 0;
	n->ti_ack = 0;
	n->ti_x2 = 0;
	n->ti_off = 5;
	n->ti_flags = 0;
	n->ti_win = 0;
	n->ti_sum = 0;
	n->ti_urp = 0;
}

/*
 * Send a single message to the TCP at address specified by
 * the given TCP/IP header.  If m == 0, then we make a copy
 * of the tcpiphdr at ti and send directly to the addressed host.
 * This is used to force keep alive messages out using the TCP
 * template for a connection tp->t_template.  If flags are given
 * then we send a message back to the TCP which originated the
 * segment ti, and discard the mbuf containing it and any other
 * attached mbufs.
 *
 * In any case the ack and sequence number of the transmitted
 * segment are as specified by the parameters.
 */
void
tcp_respond(struct tcpcb *tp, struct tcpiphdr *ti, struct mbuf *m,
            tcp_seq ack, tcp_seq seq, int flags, unsigned short af)
{
	register int tlen;
	int win = 0;

	DEBUG_CALL("tcp_respond");
	DEBUG_ARG("tp = %p", tp);
	DEBUG_ARG("ti = %p", ti);
	DEBUG_ARG("m = %p", m);
	DEBUG_ARG("ack = %u", ack);
	DEBUG_ARG("seq = %u", seq);
	DEBUG_ARG("flags = %x", flags);

	if (tp)
		win = sbspace(&tp->t_socket->so_rcv);
        if (m == NULL) {
		if (!tp || (m = m_get(tp->t_socket->slirp)) == NULL)
			return;
		tlen = 0;
		m->m_data += IF_MAXLINKHDR;
		*mtod(m, struct tcpiphdr *) = *ti;
		ti = mtod(m, struct tcpiphdr *);
		switch (af) {
		case AF_INET:
		    ti->ti.ti_i4.ih_x1 = 0;
		    break;
		case AF_INET6:
		    ti->ti.ti_i6.ih_x1 = 0;
		    break;
		default:
		    g_assert_not_reached();
		}
		flags = TH_ACK;
	} else {
		/*
		 * ti points into m so the next line is just making
		 * the mbuf point to ti
		 */
		m->m_data = (char *)ti;

		m->m_len = sizeof (struct tcpiphdr);
		tlen = 0;
#define xchg(a,b,type) { type t; t=a; a=b; b=t; }
		switch (af) {
		case AF_INET:
		    xchg(ti->ti_dst.s_addr, ti->ti_src.s_addr, uint32_t);
		    xchg(ti->ti_dport, ti->ti_sport, uint16_t);
		    break;
		case AF_INET6:
		    xchg(ti->ti_dst6, ti->ti_src6, struct in6_addr);
		    xchg(ti->ti_dport, ti->ti_sport, uint16_t);
		    break;
		default:
		    g_assert_not_reached();
		}
#undef xchg
	}
	ti->ti_len = htons((uint16_t)(sizeof (struct tcphdr) + tlen));
	tlen += sizeof (struct tcpiphdr);
	m->m_len = tlen;

	ti->ti_mbuf = NULL;
	ti->ti_x0 = 0;
	ti->ti_seq = htonl(seq);
	ti->ti_ack = htonl(ack);
	ti->ti_x2 = 0;
	ti->ti_off = sizeof (struct tcphdr) >> 2;
	ti->ti_flags = flags;
	if (tp)
		ti->ti_win = htons((uint16_t) (win >> tp->rcv_scale));
	else
		ti->ti_win = htons((uint16_t)win);
	ti->ti_urp = 0;
	ti->ti_sum = 0;
	ti->ti_sum = cksum(m, tlen);

	struct tcpiphdr tcpiph_save = *(mtod(m, struct tcpiphdr *));
	struct ip *ip;
	struct ip6 *ip6;

	switch (af) {
	case AF_INET:
	    m->m_data += sizeof(struct tcpiphdr) - sizeof(struct tcphdr)
	                                         - sizeof(struct ip);
	    m->m_len  -= sizeof(struct tcpiphdr) - sizeof(struct tcphdr)
	                                         - sizeof(struct ip);
	    ip = mtod(m, struct ip *);
	    ip->ip_len = m->m_len;
	    ip->ip_dst = tcpiph_save.ti_dst;
	    ip->ip_src = tcpiph_save.ti_src;
	    ip->ip_p = tcpiph_save.ti_pr;

	    if (flags & TH_RST) {
	        ip->ip_ttl = MAXTTL;
	    } else {
	        ip->ip_ttl = IPDEFTTL;
	    }

	    ip_output(NULL, m);
	    break;

	case AF_INET6:
	    m->m_data += sizeof(struct tcpiphdr) - sizeof(struct tcphdr)
	                                         - sizeof(struct ip6);
	    m->m_len  -= sizeof(struct tcpiphdr) - sizeof(struct tcphdr)
	                                         - sizeof(struct ip6);
	    ip6 = mtod(m, struct ip6 *);
	    ip6->ip_pl = tcpiph_save.ti_len;
	    ip6->ip_dst = tcpiph_save.ti_dst6;
	    ip6->ip_src = tcpiph_save.ti_src6;
	    ip6->ip_nh = tcpiph_save.ti_nh6;

	    ip6_output(NULL, m, 0);
	    break;

	default:
	    g_assert_not_reached();
	}
}

/*
 * Create a new TCP control block, making an
 * empty reassembly queue and hooking it to the argument
 * protocol control block.
 */
struct tcpcb *
tcp_newtcpcb(struct socket *so)
{
	register struct tcpcb *tp;

	tp = (struct tcpcb *)malloc(sizeof(*tp));
	if (tp == NULL)
		return ((struct tcpcb *)0);

	memset((char *) tp, 0, sizeof(struct tcpcb));
	tp->seg_next = tp->seg_prev = (struct tcpiphdr*)tp;
	tp->t_maxseg = (so->so_ffamily == AF_INET) ? TCP_MSS : TCP6_MSS;

	tp->t_flags = TCP_DO_RFC1323 ? (TF_REQ_SCALE|TF_REQ_TSTMP) : 0;
	tp->t_socket = so;

	/*
	 * Init srtt to TCPTV_SRTTBASE (0), so we can tell that we have no
	 * rtt estimate.  Set rttvar so that srtt + 2 * rttvar gives
	 * reasonable initial retransmit time.
	 */
	tp->t_srtt = TCPTV_SRTTBASE;
	tp->t_rttvar = TCPTV_SRTTDFLT << 2;
	tp->t_rttmin = TCPTV_MIN;

	TCPT_RANGESET(tp->t_rxtcur,
	    ((TCPTV_SRTTBASE >> 2) + (TCPTV_SRTTDFLT << 2)) >> 1,
	    TCPTV_MIN, TCPTV_REXMTMAX);

	tp->snd_cwnd = TCP_MAXWIN << TCP_MAX_WINSHIFT;
	tp->snd_ssthresh = TCP_MAXWIN << TCP_MAX_WINSHIFT;
	tp->t_state = TCPS_CLOSED;

	so->so_tcpcb = tp;

	return (tp);
}

/*
 * Drop a TCP connection, reporting
 * the specified error.  If connection is synchronized,
 * then send a RST to peer.
 */
struct tcpcb *tcp_drop(struct tcpcb *tp, int err)
{
	DEBUG_CALL("tcp_drop");
	DEBUG_ARG("tp = %p", tp);
	DEBUG_ARG("errno = %d", errno);

	if (TCPS_HAVERCVDSYN(tp->t_state)) {
		tp->t_state = TCPS_CLOSED;
		(void) tcp_output(tp);
	}
	return (tcp_close(tp));
}

/*
 * Close a TCP control block:
 *	discard all space held by the tcp
 *	discard internet protocol block
 *	wake up any sleepers
 */
struct tcpcb *
tcp_close(struct tcpcb *tp)
{
	register struct tcpiphdr *t;
	struct socket *so = tp->t_socket;
	Slirp *slirp = so->slirp;
	register struct mbuf *m;

	DEBUG_CALL("tcp_close");
	DEBUG_ARG("tp = %p", tp);

	/* free the reassembly queue, if any */
	t = tcpfrag_list_first(tp);
	while (!tcpfrag_list_end(t, tp)) {
		t = tcpiphdr_next(t);
		m = tcpiphdr_prev(t)->ti_mbuf;
		remque(tcpiphdr2qlink(tcpiphdr_prev(t)));
		m_free(m);
	}
	free(tp);
        so->so_tcpcb = NULL;
	/* clobber input socket cache if we're closing the cached connection */
	if (so == slirp->tcp_last_so)
		slirp->tcp_last_so = &slirp->tcb;
	so->slirp->cb->unregister_poll_fd(so->s, so->slirp->opaque);
	closesocket(so->s);
	sbfree(&so->so_rcv);
	sbfree(&so->so_snd);
	sofree(so);
	return ((struct tcpcb *)0);
}

/*
 * TCP protocol interface to socket abstraction.
 */

/*
 * User issued close, and wish to trail through shutdown states:
 * if never received SYN, just forget it.  If got a SYN from peer,
 * but haven't sent FIN, then go to FIN_WAIT_1 state to send peer a FIN.
 * If already got a FIN from peer, then almost done; go to LAST_ACK
 * state.  In all other cases, have already sent FIN to peer (e.g.
 * after PRU_SHUTDOWN), and just have to play tedious game waiting
 * for peer to send FIN or not respond to keep-alives, etc.
 * We can let the user exit from the close as soon as the FIN is acked.
 */
void
tcp_sockclosed(struct tcpcb *tp)
{

	DEBUG_CALL("tcp_sockclosed");
	DEBUG_ARG("tp = %p", tp);

	if (!tp) {
		return;
	}

	switch (tp->t_state) {

	case TCPS_CLOSED:
	case TCPS_LISTEN:
	case TCPS_SYN_SENT:
		tp->t_state = TCPS_CLOSED;
		tp = tcp_close(tp);
		break;

	case TCPS_SYN_RECEIVED:
	case TCPS_ESTABLISHED:
		tp->t_state = TCPS_FIN_WAIT_1;
		break;

	case TCPS_CLOSE_WAIT:
		tp->t_state = TCPS_LAST_ACK;
		break;
	}
	tcp_output(tp);
}

/*
 * Connect to a host on the Internet
 * Called by tcp_input
 * Only do a connect, the tcp fields will be set in tcp_input
 * return 0 if there's a result of the connect,
 * else return -1 means we're still connecting
 * The return value is almost always -1 since the socket is
 * nonblocking.  Connect returns after the SYN is sent, and does
 * not wait for ACK+SYN.
 */
int tcp_fconnect(struct socket *so, unsigned short af)
{
  int ret=0;

  DEBUG_CALL("tcp_fconnect");
  DEBUG_ARG("so = %p", so);

  ret = so->s = slirp_socket(af, SOCK_STREAM, 0);
  if (ret >= 0) {
    int opt, s=so->s;
    struct sockaddr_storage addr;

    slirp_set_nonblock(s);
    so->slirp->cb->register_poll_fd(so->s, so->slirp->opaque);
    slirp_socket_set_fast_reuse(s);
    opt = 1;
    setsockopt(s, SOL_SOCKET, SO_OOBINLINE, &opt, sizeof(opt));
    opt = 1;
    setsockopt(s, IPPROTO_TCP, TCP_NODELAY, &opt, sizeof(opt));

    addr = so->fhost.ss;
    DEBUG_CALL(" connect()ing");
    sotranslate_out(so, &addr);

    /* We don't care what port we get */
    ret = connect(s, (struct sockaddr *)&addr, sockaddr_size(&addr));

    /*
     * If it's not in progress, it failed, so we just return 0,
     * without clearing SS_NOFDREF
     */
    soisfconnecting(so);
  }

  return(ret);
}

/*
 * Accept the socket and connect to the local-host
 *
 * We have a problem. The correct thing to do would be
 * to first connect to the local-host, and only if the
 * connection is accepted, then do an accept() here.
 * But, a) we need to know who's trying to connect
 * to the socket to be able to SYN the local-host, and
 * b) we are already connected to the foreign host by
 * the time it gets to accept(), so... We simply accept
 * here and SYN the local-host.
 */
void tcp_connect(struct socket *inso)
{
    Slirp *slirp = inso->slirp;
    struct socket *so;
    struct sockaddr_storage addr;
    socklen_t addrlen = sizeof(struct sockaddr_storage);
    struct tcpcb *tp;
    int s, opt;

    DEBUG_CALL("tcp_connect");
    DEBUG_ARG("inso = %p", inso);

    /*
     * If it's an SS_ACCEPTONCE socket, no need to socreate()
     * another socket, just use the accept() socket.
     */
    if (inso->so_state & SS_FACCEPTONCE) {
        /* FACCEPTONCE already have a tcpcb */
        so = inso;
    } else {
        so = socreate(slirp);
        if (tcp_attach(so) < 0) {
            g_free(so); /* NOT sofree */
            return;
        }
        so->lhost = inso->lhost;
        so->so_ffamily = inso->so_ffamily;
    }

    tcp_mss(sototcpcb(so), 0);

    s = accept(inso->s, (struct sockaddr *)&addr, &addrlen);
    if (s < 0) {
        tcp_close(sototcpcb(so)); /* This will sofree() as well */
        return;
    }
    slirp_set_nonblock(s);
    so->slirp->cb->register_poll_fd(so->s, so->slirp->opaque);
    slirp_socket_set_fast_reuse(s);
    opt = 1;
    setsockopt(s, SOL_SOCKET, SO_OOBINLINE, &opt, sizeof(int));
    slirp_socket_set_nodelay(s);

    so->fhost.ss = addr;
    sotranslate_accept(so);

    /* Close the accept() socket, set right state */
    if (inso->so_state & SS_FACCEPTONCE) {
        /* If we only accept once, close the accept() socket */
        so->slirp->cb->unregister_poll_fd(so->s, so->slirp->opaque);
        closesocket(so->s);

        /* Don't select it yet, even though we have an FD */
        /* if it's not FACCEPTONCE, it's already NOFDREF */
        so->so_state = SS_NOFDREF;
    }
    so->s = s;
    so->so_state |= SS_INCOMING;

    so->so_iptos = tcp_tos(so);
    tp = sototcpcb(so);

    tcp_template(tp);

    tp->t_state = TCPS_SYN_SENT;
    tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
    tp->iss = slirp->tcp_iss;
    slirp->tcp_iss += TCP_ISSINCR/2;
    tcp_sendseqinit(tp);
    tcp_output(tp);
}

/*
 * Attach a TCPCB to a socket.
 */
int
tcp_attach(struct socket *so)
{
	if ((so->so_tcpcb = tcp_newtcpcb(so)) == NULL)
	   return -1;

	insque(so, &so->slirp->tcb);

	return 0;
}

/*
 * Set the socket's type of service field
 */
static const struct tos_t tcptos[] = {
	  {0, 20, IPTOS_THROUGHPUT, 0},	/* ftp data */
	  {21, 21, IPTOS_LOWDELAY,  EMU_FTP},	/* ftp control */
	  {0, 23, IPTOS_LOWDELAY, 0},	/* telnet */
	  {0, 80, IPTOS_THROUGHPUT, 0},	/* WWW */
	  {0, 513, IPTOS_LOWDELAY, EMU_RLOGIN|EMU_NOCONNECT},	/* rlogin */
	  {0, 544, IPTOS_LOWDELAY, EMU_KSH},		/* kshell */
	  {0, 543, IPTOS_LOWDELAY, 0},	/* klogin */
	  {0, 6667, IPTOS_THROUGHPUT, EMU_IRC},	/* IRC */
	  {0, 6668, IPTOS_THROUGHPUT, EMU_IRC},	/* IRC undernet */
	  {0, 7070, IPTOS_LOWDELAY, EMU_REALAUDIO }, /* RealAudio control */
	  {0, 113, IPTOS_LOWDELAY, EMU_IDENT }, /* identd protocol */
	  {0, 0, 0, 0}
};

static struct emu_t *tcpemu = NULL;

/*
 * Return TOS according to the above table
 */
uint8_t
tcp_tos(struct socket *so)
{
	int i = 0;
	struct emu_t *emup;

	while(tcptos[i].tos) {
		if ((tcptos[i].fport && (ntohs(so->so_fport) == tcptos[i].fport)) ||
		    (tcptos[i].lport && (ntohs(so->so_lport) == tcptos[i].lport))) {
			so->so_emu = tcptos[i].emu;
			return tcptos[i].tos;
		}
		i++;
	}

	/* Nope, lets see if there's a user-added one */
	for (emup = tcpemu; emup; emup = emup->next) {
		if ((emup->fport && (ntohs(so->so_fport) == emup->fport)) ||
		    (emup->lport && (ntohs(so->so_lport) == emup->lport))) {
			so->so_emu = emup->emu;
			return emup->tos;
		}
	}

	return 0;
}

/*
 * Emulate programs that try and connect to us
 * This includes ftp (the data connection is
 * initiated by the server) and IRC (DCC CHAT and
 * DCC SEND) for now
 *
 * NOTE: It's possible to crash SLiRP by sending it
 * unstandard strings to emulate... if this is a problem,
 * more checks are needed here
 *
 * XXX Assumes the whole command came in one packet
 *
 * XXX Some ftp clients will have their TOS set to
 * LOWDELAY and so Nagel will kick in.  Because of this,
 * we'll get the first letter, followed by the rest, so
 * we simply scan for ORT instead of PORT...
 * DCC doesn't have this problem because there's other stuff
 * in the packet before the DCC command.
 *
 * Return 1 if the mbuf m is still valid and should be
 * sbappend()ed
 *
 * NOTE: if you return 0 you MUST m_free() the mbuf!
 */
int
tcp_emu(struct socket *so, struct mbuf *m)
{
	Slirp *slirp = so->slirp;
	unsigned n1, n2, n3, n4, n5, n6;
        char buff[257];
	uint32_t laddr;
	unsigned lport;
	char *bptr;

	DEBUG_CALL("tcp_emu");
	DEBUG_ARG("so = %p", so);
	DEBUG_ARG("m = %p", m);

	switch(so->so_emu) {
		int x, i;

        /* TODO: IPv6 */
	 case EMU_IDENT:
		/*
		 * Identification protocol as per rfc-1413
		 */

		{
			struct socket *tmpso;
			struct sockaddr_in addr;
			socklen_t addrlen = sizeof(struct sockaddr_in);
			struct sbuf *so_rcv = &so->so_rcv;

			if (m->m_len > so_rcv->sb_datalen
					- (so_rcv->sb_wptr - so_rcv->sb_data)) {
			    return 1;
			}

			memcpy(so_rcv->sb_wptr, m->m_data, m->m_len);
			so_rcv->sb_wptr += m->m_len;
			so_rcv->sb_rptr += m->m_len;
			m->m_data[m->m_len] = 0; /* NULL terminate */
			if (strchr(m->m_data, '\r') || strchr(m->m_data, '\n')) {
				if (sscanf(so_rcv->sb_data, "%u%*[ ,]%u", &n1, &n2) == 2) {
					HTONS(n1);
					HTONS(n2);
					/* n2 is the one on our host */
					for (tmpso = slirp->tcb.so_next;
					     tmpso != &slirp->tcb;
					     tmpso = tmpso->so_next) {
						if (tmpso->so_laddr.s_addr == so->so_laddr.s_addr &&
						    tmpso->so_lport == n2 &&
						    tmpso->so_faddr.s_addr == so->so_faddr.s_addr &&
						    tmpso->so_fport == n1) {
							if (getsockname(tmpso->s,
								(struct sockaddr *)&addr, &addrlen) == 0)
							   n2 = addr.sin_port;
							break;
						}
					}
					NTOHS(n1);
					NTOHS(n2);
					so_rcv->sb_cc = snprintf(so_rcv->sb_data,
								 so_rcv->sb_datalen,
								 "%d,%d\r\n", n1, n2);
					so_rcv->sb_rptr = so_rcv->sb_data;
					so_rcv->sb_wptr = so_rcv->sb_data + so_rcv->sb_cc;
				}
			}
			m_free(m);
			return 0;
		}

        case EMU_FTP: /* ftp */
                *(m->m_data+m->m_len) = 0; /* NUL terminate for strstr */
		if ((bptr = (char *)strstr(m->m_data, "ORT")) != NULL) {
			/*
			 * Need to emulate the PORT command
			 */
			x = sscanf(bptr, "ORT %u,%u,%u,%u,%u,%u\r\n%256[^\177]",
				   &n1, &n2, &n3, &n4, &n5, &n6, buff);
			if (x < 6)
			   return 1;

			laddr = htonl((n1 << 24) | (n2 << 16) | (n3 << 8) | (n4));
			lport = htons((n5 << 8) | (n6));

			if ((so = tcp_listen(slirp, INADDR_ANY, 0, laddr,
			                     lport, SS_FACCEPTONCE)) == NULL) {
			   return 1;
			}
			n6 = ntohs(so->so_fport);

			n5 = (n6 >> 8) & 0xff;
			n6 &= 0xff;

			laddr = ntohl(so->so_faddr.s_addr);

			n1 = ((laddr >> 24) & 0xff);
			n2 = ((laddr >> 16) & 0xff);
			n3 = ((laddr >> 8)  & 0xff);
			n4 =  (laddr & 0xff);

			m->m_len = bptr - m->m_data; /* Adjust length */
                        m->m_len += snprintf(bptr, m->m_size - m->m_len,
                                             "ORT %d,%d,%d,%d,%d,%d\r\n%s",
                                             n1, n2, n3, n4, n5, n6, x==7?buff:"");
			return 1;
		} else if ((bptr = (char *)strstr(m->m_data, "27 Entering")) != NULL) {
			/*
			 * Need to emulate the PASV response
			 */
			x = sscanf(bptr, "27 Entering Passive Mode (%u,%u,%u,%u,%u,%u)\r\n%256[^\177]",
				   &n1, &n2, &n3, &n4, &n5, &n6, buff);
			if (x < 6)
			   return 1;

			laddr = htonl((n1 << 24) | (n2 << 16) | (n3 << 8) | (n4));
			lport = htons((n5 << 8) | (n6));

			if ((so = tcp_listen(slirp, INADDR_ANY, 0, laddr,
			                     lport, SS_FACCEPTONCE)) == NULL) {
			   return 1;
			}
			n6 = ntohs(so->so_fport);

			n5 = (n6 >> 8) & 0xff;
			n6 &= 0xff;

			laddr = ntohl(so->so_faddr.s_addr);

			n1 = ((laddr >> 24) & 0xff);
			n2 = ((laddr >> 16) & 0xff);
			n3 = ((laddr >> 8)  & 0xff);
			n4 =  (laddr & 0xff);

			m->m_len = bptr - m->m_data; /* Adjust length */
			m->m_len += snprintf(bptr, m->m_size - m->m_len,
                                             "27 Entering Passive Mode (%d,%d,%d,%d,%d,%d)\r\n%s",
                                             n1, n2, n3, n4, n5, n6, x==7?buff:"");

			return 1;
		}

		return 1;

	 case EMU_KSH:
		/*
		 * The kshell (Kerberos rsh) and shell services both pass
		 * a local port port number to carry signals to the server
		 * and stderr to the client.  It is passed at the beginning
		 * of the connection as a NUL-terminated decimal ASCII string.
		 */
		so->so_emu = 0;
		for (lport = 0, i = 0; i < m->m_len-1; ++i) {
			if (m->m_data[i] < '0' || m->m_data[i] > '9')
				return 1;       /* invalid number */
			lport *= 10;
			lport += m->m_data[i] - '0';
		}
		if (m->m_data[m->m_len-1] == '\0' && lport != 0 &&
		    (so = tcp_listen(slirp, INADDR_ANY, 0, so->so_laddr.s_addr,
		                     htons(lport), SS_FACCEPTONCE)) != NULL)
                    m->m_len = snprintf(m->m_data, m->m_size, "%d",
                                        ntohs(so->so_fport)) + 1;
		return 1;

	 case EMU_IRC:
		/*
		 * Need to emulate DCC CHAT, DCC SEND and DCC MOVE
		 */
		*(m->m_data+m->m_len) = 0; /* NULL terminate the string for strstr */
		if ((bptr = (char *)strstr(m->m_data, "DCC")) == NULL)
			 return 1;

		/* The %256s is for the broken mIRC */
		if (sscanf(bptr, "DCC CHAT %256s %u %u", buff, &laddr, &lport) == 3) {
			if ((so = tcp_listen(slirp, INADDR_ANY, 0,
			                     htonl(laddr), htons(lport),
			                     SS_FACCEPTONCE)) == NULL) {
				return 1;
			}
			m->m_len = bptr - m->m_data; /* Adjust length */
                        m->m_len += snprintf(bptr, m->m_size,
                                             "DCC CHAT chat %lu %u%c\n",
                                             (unsigned long)ntohl(so->so_faddr.s_addr),
                                             ntohs(so->so_fport), 1);
		} else if (sscanf(bptr, "DCC SEND %256s %u %u %u", buff, &laddr, &lport, &n1) == 4) {
			if ((so = tcp_listen(slirp, INADDR_ANY, 0,
			                     htonl(laddr), htons(lport),
			                     SS_FACCEPTONCE)) == NULL) {
				return 1;
			}
			m->m_len = bptr - m->m_data; /* Adjust length */
                        m->m_len += snprintf(bptr, m->m_size,
                                             "DCC SEND %s %lu %u %u%c\n", buff,
                                             (unsigned long)ntohl(so->so_faddr.s_addr),
                                             ntohs(so->so_fport), n1, 1);
		} else if (sscanf(bptr, "DCC MOVE %256s %u %u %u", buff, &laddr, &lport, &n1) == 4) {
			if ((so = tcp_listen(slirp, INADDR_ANY, 0,
			                     htonl(laddr), htons(lport),
			                     SS_FACCEPTONCE)) == NULL) {
				return 1;
			}
			m->m_len = bptr - m->m_data; /* Adjust length */
                        m->m_len += snprintf(bptr, m->m_size,
                                             "DCC MOVE %s %lu %u %u%c\n", buff,
                                             (unsigned long)ntohl(so->so_faddr.s_addr),
                                             ntohs(so->so_fport), n1, 1);
		}
		return 1;

	 case EMU_REALAUDIO:
                /*
		 * RealAudio emulation - JP. We must try to parse the incoming
		 * data and try to find the two characters that contain the
		 * port number. Then we redirect an udp port and replace the
		 * number with the real port we got.
		 *
		 * The 1.0 beta versions of the player are not supported
		 * any more.
		 *
		 * A typical packet for player version 1.0 (release version):
		 *
		 * 0000:50 4E 41 00 05
		 * 0000:00 01 00 02 1B D7 00 00 67 E6 6C DC 63 00 12 50 ........g.l.c..P
		 * 0010:4E 43 4C 49 45 4E 54 20 31 30 31 20 41 4C 50 48 NCLIENT 101 ALPH
		 * 0020:41 6C 00 00 52 00 17 72 61 66 69 6C 65 73 2F 76 Al..R..rafiles/v
		 * 0030:6F 61 2F 65 6E 67 6C 69 73 68 5F 2E 72 61 79 42 oa/english_.rayB
		 *
		 * Now the port number 0x1BD7 is found at offset 0x04 of the
		 * Now the port number 0x1BD7 is found at offset 0x04 of the
		 * second packet. This time we received five bytes first and
		 * then the rest. You never know how many bytes you get.
		 *
		 * A typical packet for player version 2.0 (beta):
		 *
		 * 0000:50 4E 41 00 06 00 02 00 00 00 01 00 02 1B C1 00 PNA.............
		 * 0010:00 67 75 78 F5 63 00 0A 57 69 6E 32 2E 30 2E 30 .gux.c..Win2.0.0
		 * 0020:2E 35 6C 00 00 52 00 1C 72 61 66 69 6C 65 73 2F .5l..R..rafiles/
		 * 0030:77 65 62 73 69 74 65 2F 32 30 72 65 6C 65 61 73 website/20releas
		 * 0040:65 2E 72 61 79 53 00 00 06 36 42                e.rayS...6B
		 *
		 * Port number 0x1BC1 is found at offset 0x0d.
		 *
		 * This is just a horrible switch statement. Variable ra tells
		 * us where we're going.
		 */

		bptr = m->m_data;
		while (bptr < m->m_data + m->m_len) {
			uint16_t p;
			static int ra = 0;
			char ra_tbl[4];

			ra_tbl[0] = 0x50;
			ra_tbl[1] = 0x4e;
			ra_tbl[2] = 0x41;
			ra_tbl[3] = 0;

			switch (ra) {
			 case 0:
			 case 2:
			 case 3:
				if (*bptr++ != ra_tbl[ra]) {
					ra = 0;
					continue;
				}
				break;

			 case 1:
				/*
				 * We may get 0x50 several times, ignore them
				 */
				if (*bptr == 0x50) {
					ra = 1;
					bptr++;
					continue;
				} else if (*bptr++ != ra_tbl[ra]) {
					ra = 0;
					continue;
				}
				break;

			 case 4:
				/*
				 * skip version number
				 */
				bptr++;
				break;

			 case 5:
				/*
				 * The difference between versions 1.0 and
				 * 2.0 is here. For future versions of
				 * the player this may need to be modified.
				 */
				if (*(bptr + 1) == 0x02)
				   bptr += 8;
				else
				   bptr += 4;
				break;

			 case 6:
				/* This is the field containing the port
				 * number that RA-player is listening to.
				 */
				lport = (((uint8_t*)bptr)[0] << 8)
				+ ((uint8_t *)bptr)[1];
				if (lport < 6970)
				   lport += 256;   /* don't know why */
				if (lport < 6970 || lport > 7170)
				   return 1;       /* failed */

				/* try to get udp port between 6970 - 7170 */
				for (p = 6970; p < 7071; p++) {
					if (udp_listen(slirp, INADDR_ANY,
						       htons(p),
						       so->so_laddr.s_addr,
						       htons(lport),
						       SS_FACCEPTONCE)) {
						break;
					}
				}
				if (p == 7071)
				   p = 0;
				*(uint8_t *)bptr++ = (p >> 8) & 0xff;
                                *(uint8_t *)bptr = p & 0xff;
				ra = 0;
				return 1;   /* port redirected, we're done */
				break;

			 default:
				ra = 0;
			}
			ra++;
		}
		return 1;

	 default:
		/* Ooops, not emulated, won't call tcp_emu again */
		so->so_emu = 0;
		return 1;
	}
}

/*
 * Do misc. config of SLiRP while its running.
 * Return 0 if this connections is to be closed, 1 otherwise,
 * return 2 if this is a command-line connection
 */
int tcp_ctl(struct socket *so)
{
    Slirp *slirp = so->slirp;
    struct sbuf *sb = &so->so_snd;
    struct gfwd_list *ex_ptr;

    DEBUG_CALL("tcp_ctl");
    DEBUG_ARG("so = %p", so);

    /* TODO: IPv6 */
    if (so->so_faddr.s_addr != slirp->vhost_addr.s_addr) {
        /* Check if it's pty_exec */
        for (ex_ptr = slirp->guestfwd_list; ex_ptr; ex_ptr = ex_ptr->ex_next) {
            if (ex_ptr->ex_fport == so->so_fport &&
                so->so_faddr.s_addr == ex_ptr->ex_addr.s_addr) {
                if (ex_ptr->write_cb) {
                    so->s = -1;
                    so->guestfwd = ex_ptr;
                    return 1;
                }
                DEBUG_MISC(" executing %s", ex_ptr->ex_exec);
                return fork_exec(so, ex_ptr->ex_exec);
            }
        }
    }
    sb->sb_cc =
        snprintf(sb->sb_wptr, sb->sb_datalen - (sb->sb_wptr - sb->sb_data),
                 "Error: No application configured.\r\n");
    sb->sb_wptr += sb->sb_cc;
    return 0;
}