source: vbox/trunk/src/VBox/Devices/Network/slirp/tcp_subr.c@ 15791

/*
 * 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_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.
 *
 * Please read the file COPYRIGHT for the
 * terms and conditions of the copyright.
 */

#define WANT_SYS_IOCTL_H
#include <slirp.h>


/*
 * Tcp initialization
 */
void
tcp_init(PNATState pData)
{
    tcp_iss = 1;            /* wrong */
    tcb.so_next = tcb.so_prev = &tcb;
    tcp_last_so = &tcb;
    tcp_reass_maxqlen = 48;
    tcp_reass_maxseg  = 256;
}

/*
 * 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.
 */
/* struct tcpiphdr * */
void
tcp_template(struct tcpcb *tp)
{
    struct socket *so = tp->t_socket;
    register struct tcpiphdr *n = &tp->t_template;

    memset(n->ti_x1, 0, 9);
    n->ti_pr = IPPROTO_TCP;
    n->ti_len = htons(sizeof (struct tcpiphdr) - sizeof (struct ip));
    n->ti_src = so->so_faddr;
    n->ti_dst = so->so_laddr;
    n->ti_sport = so->so_fport;
    n->ti_dport = so->so_lport;

    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(PNATState pData, struct tcpcb *tp, struct tcpiphdr *ti, struct mbuf *m, tcp_seq ack, tcp_seq seq, int flags)
{
    register int tlen;
    int win = 0;

    DEBUG_CALL("tcp_respond");
    DEBUG_ARG("tp = %lx", (long)tp);
    DEBUG_ARG("ti = %lx", (long)ti);
    DEBUG_ARG("m = %lx", (long)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 == 0)
    {
        if ((m = m_get(pData)) == NULL)
            return;
#ifdef TCP_COMPAT_42
        tlen = 1;
#else
        tlen = 0;
#endif
        m->m_data += if_maxlinkhdr;
        *mtod(m, struct tcpiphdr *) = *ti;
        ti = mtod(m, struct tcpiphdr *);
        flags = TH_ACK;
    }
    else
    {
        /*
         * ti points into m so the next line is just making
         * the mbuf point to ti
         */
        m->m_data = (caddr_t)ti;

        m->m_len = sizeof (struct tcpiphdr);
        tlen = 0;
#define xchg(a,b,type) { type t; t = a; a = b; b = t; }
        xchg(ti->ti_dst.s_addr, ti->ti_src.s_addr, u_int32_t);
        xchg(ti->ti_dport, ti->ti_sport, u_int16_t);
#undef xchg
    }
    ti->ti_len = htons((u_short)(sizeof (struct tcphdr) + tlen));
    tlen += sizeof (struct tcpiphdr);
    m->m_len = tlen;

    memset(ti->ti_x1, 0, 9);
    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((u_int16_t) (win >> tp->rcv_scale));
    else
        ti->ti_win = htons((u_int16_t)win);
    ti->ti_urp = 0;
    ti->ti_sum = 0;
    ti->ti_sum = cksum(m, tlen);
    ((struct ip *)ti)->ip_len = tlen;

    if(flags & TH_RST)
        ((struct ip *)ti)->ip_ttl = MAXTTL;
    else
        ((struct ip *)ti)->ip_ttl = ip_defttl;

    (void) ip_output(pData, (struct socket *)0, m);
}

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

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

    memset((char *) tp, 0, sizeof(struct tcpcb));
    tp->t_maxseg = tcp_mssdflt;

    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 = tcp_rttdflt * PR_SLOWHZ << 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(PNATState pData, struct tcpcb *tp, int err)
{
/* tcp_drop(tp, errno)
        register struct tcpcb *tp;
        int errno;
{
*/
    DEBUG_CALL("tcp_drop");
    DEBUG_ARG("tp = %lx", (long)tp);
    DEBUG_ARG("errno = %d", errno);

    if (TCPS_HAVERCVDSYN(tp->t_state))
    {
        tp->t_state = TCPS_CLOSED;
        (void) tcp_output(pData, tp);
        tcpstat.tcps_drops++;
    }
    else
        tcpstat.tcps_conndrops++;
#if 0
      if (errno == ETIMEDOUT && tp->t_softerror)
              errno = tp->t_softerror;

      so->so_error = errno;
#endif
      return (tcp_close(pData, 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(PNATState pData, register struct tcpcb *tp)
{
    register struct tcpiphdr *t;
    struct socket *so = tp->t_socket;
    register struct mbuf *m;

    struct tseg_qent *te;
    DEBUG_CALL("tcp_close");
    DEBUG_ARG("tp = %lx", (long )tp);
    /*XXX: freeing the reassembly queue */
    LIST_FOREACH(te, &tp->t_segq, tqe_q)
    {
        LIST_REMOVE(te, tqe_q);
        m_freem(pData, te->tqe_m);
        free(te);
        tcp_reass_qsize--;
    }
    free(tp);
    so->so_tcpcb = 0;
    soisfdisconnected(so);
    /* clobber input socket cache if we're closing the cached connection */
    if (so == tcp_last_so)
        tcp_last_so = &tcb;
    closesocket(so->s);
    sbfree(&so->so_rcv);
    sbfree(&so->so_snd);
    sofree(pData, so);
    tcpstat.tcps_closed++;
    return ((struct tcpcb *)0);
}

void
tcp_drain()
{
    /* XXX */
}

/*
 * When a source quench is received, close congestion window
 * to one segment.  We will gradually open it again as we proceed.
 */

#if 0

void
tcp_quench(i, int errno)
{
    struct tcpcb *tp = intotcpcb(inp);

    if (tp)
        tp->snd_cwnd = tp->t_maxseg;
}

#endif

/*
 * 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(PNATState pData, struct tcpcb *tp)
{
    DEBUG_CALL("tcp_sockclosed");
    DEBUG_ARG("tp = %lx", (long)tp);

    switch (tp->t_state)
    {
        case TCPS_CLOSED:
        case TCPS_LISTEN:
        case TCPS_SYN_SENT:
            tp->t_state = TCPS_CLOSED;
            tp = tcp_close(pData, 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;
    }
/*  soisfdisconnecting(tp->t_socket); */
    if (   tp 
        && tp->t_state >= TCPS_FIN_WAIT_2)
        soisfdisconnected(tp->t_socket);
    if (tp)
        tcp_output(pData, 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(PNATState pData, struct socket *so)
{
    int ret = 0;

    DEBUG_CALL("tcp_fconnect");
    DEBUG_ARG("so = %lx", (long )so);

    if ((ret = so->s = socket(AF_INET,SOCK_STREAM,0)) >= 0)
    {
        int opt, s = so->s;
        struct sockaddr_in addr;

        fd_nonblock(s);
        opt = 1;
        setsockopt(s,SOL_SOCKET,SO_REUSEADDR,(char *)&opt, sizeof(opt));
        opt = 1;
        setsockopt(s,SOL_SOCKET,SO_OOBINLINE,(char *)&opt, sizeof(opt));

        addr.sin_family = AF_INET;
        if ((so->so_faddr.s_addr & htonl(pData->netmask)) == special_addr.s_addr)
        {
            /* It's an alias */
            switch(ntohl(so->so_faddr.s_addr) & ~pData->netmask)
            {
                case CTL_DNS:
                    if (!get_dns_addr(pData, &dns_addr))
                        addr.sin_addr = dns_addr;
                    else
                        addr.sin_addr = loopback_addr;
                    break;
                case CTL_ALIAS:
                default:
                    addr.sin_addr = loopback_addr;
                    break;
            }
        }
        else
            addr.sin_addr = so->so_faddr;
        addr.sin_port = so->so_fport;

        DEBUG_MISC((dfd, " connect()ing, addr.sin_port=%d, "
                         "addr.sin_addr.s_addr=%.16s\n",
                         ntohs(addr.sin_port), inet_ntoa(addr.sin_addr)));
        /* We don't care what port we get */
        ret = connect(s,(struct sockaddr *)&addr,sizeof (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(PNATState pData, struct socket *inso)
{
    struct socket *so;
    struct sockaddr_in addr;
    socklen_t addrlen = sizeof(struct sockaddr_in);
    struct tcpcb *tp;
    int s, opt;

    DEBUG_CALL("tcp_connect");
    DEBUG_ARG("inso = %lx", (long)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
    {
        if ((so = socreate()) == NULL)
        {
            /* If it failed, get rid of the pending connection */
            closesocket(accept(inso->s,(struct sockaddr *)&addr,&addrlen));
            return;
        }
        if (tcp_attach(pData, so) < 0)
        {
            free(so); /* NOT sofree */
            return;
        }
        so->so_laddr = inso->so_laddr;
        so->so_lport = inso->so_lport;
    }

    (void) tcp_mss(pData, sototcpcb(so), 0);

    if ((s = accept(inso->s,(struct sockaddr *)&addr,&addrlen)) < 0)
    {
        tcp_close(pData, sototcpcb(so)); /* This will sofree() as well */
        return;
    }
    fd_nonblock(s);
    opt = 1;
    setsockopt(s,SOL_SOCKET,SO_REUSEADDR,(char *)&opt,sizeof(int));
    opt = 1;
    setsockopt(s,SOL_SOCKET,SO_OOBINLINE,(char *)&opt,sizeof(int));
    opt = 1;
    setsockopt(s,IPPROTO_TCP,TCP_NODELAY,(char *)&opt,sizeof(int));

    so->so_fport = addr.sin_port;
    so->so_faddr = addr.sin_addr;
    /* Translate connections from localhost to the real hostname */
    if (so->so_faddr.s_addr == 0 || so->so_faddr.s_addr == loopback_addr.s_addr)
        so->so_faddr = alias_addr;

    /* Close the accept() socket, set right state */
    if (inso->so_state & SS_FACCEPTONCE)
    {
        closesocket(so->s);        /* If we only accept once, close the accept() socket */
        so->so_state = SS_NOFDREF; /* Don't select it yet, even though we have an FD */
                                   /* if it's not FACCEPTONCE, it's already NOFDREF */
    }
    so->s = s;

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

    tcp_template(tp);

    /* Compute window scaling to request.  */
/*  while (tp->request_r_scale < TCP_MAX_WINSHIFT
 *         && (TCP_MAXWIN << tp->request_r_scale) < so->so_rcv.sb_hiwat)
 *      tp->request_r_scale++;
 */

/*  soisconnecting(so); */ /* NOFDREF used instead */
    tcpstat.tcps_connattempt++;

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

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

    insque(pData, so, &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, 514, IPTOS_LOWDELAY, EMU_RSH|EMU_NOCONNECT},    /* shell */
    {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}
};

/*
 * Return TOS according to the above table
 */
u_int8_t
tcp_tos(struct socket *so)
{
    int i = 0;

    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++;
    }

    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 cames 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(PNATState pData, struct socket *so, struct mbuf *m)
{
    u_int n1, n2, n3, n4, n5, n6;
    char buff[256];
    u_int32_t laddr;
    u_int lport;
    char *bptr;

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

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

        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;

            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 = tcb.so_next; tmpso != &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 = ntohs(addr.sin_port);
                            break;
                        }
                    }
                }
                so_rcv->sb_cc = sprintf(so_rcv->sb_data, "%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(pData, m);
            return 0;
        }

        case EMU_FTP:
            *(m->m_data+m->m_len) = 0; /* NULL 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 = solisten(pData, 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 += sprintf(bptr, "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 = solisten(pData, 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 += sprintf(bptr, "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 = solisten(pData, 0, so->so_laddr.s_addr, 
                                  htons(lport), SS_FACCEPTONCE)) != NULL)
                m->m_len = sprintf(m->m_data, "%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 = solisten(pData, 0, htonl(laddr), 
                                   htons(lport), SS_FACCEPTONCE)) == NULL)
                    return 1;

                m->m_len = bptr - m->m_data; /* Adjust length */
                m->m_len += sprintf(bptr, "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 = solisten(pData, 0, htonl(laddr), htons(lport), SS_FACCEPTONCE)) == NULL)
                    return 1;

                m->m_len = bptr - m->m_data; /* Adjust length */
                m->m_len += sprintf(bptr, "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 = solisten(pData, 0, htonl(laddr), htons(lport), SS_FACCEPTONCE)) == NULL)
                    return 1;

                m->m_len = bptr - m->m_data; /* Adjust length */
                m->m_len += sprintf(bptr, "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;

#ifdef VBOX
            /** @todo Disabled EMU_REALAUDIO, because it uses a static variable.
             * This is not legal when more than one slirp instance is active. */
#else /* !VBOX */
        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 .....×..gælÜc..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...........Á.
             * 0010:00 67 75 78 F5 63 00 0A 57 69 6E 32 2E 30 2E 30 .guxõc..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)
            {
                u_short 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 = (((u_char*)bptr)[0] << 8)
                              + ((u_char *)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(htons(p),
                                           so->so_laddr.s_addr,
                                           htons(lport),
                                           SS_FACCEPTONCE))
                            {
                                break;
                            }
                        }
                        if (p == 7071)
                            p = 0;
                        *(u_char *)bptr++ = (p >> 8) & 0xff;
                        *(u_char *)bptr++ = p & 0xff;
                        ra = 0;
                        return 1;   /* port redirected, we're done */
                        break;

                    default:
                        ra = 0;
                }
                ra++;
            }
            return 1;
#endif /* !VBOX */

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