summaryrefslogtreecommitdiff
path: root/slirp/tcp_subr.c
blob: 143a2383c8570b9d6f971629a098eec917366ab0 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
/*
 * 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.
 *
 * Please read the file COPYRIGHT for the
 * terms and conditions of the copyright.
 */

#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;
}

/*
 * 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;
	n->ti_x1 = 0;
	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(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 == NULL) {
		if ((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 *);
		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, uint32_t);
		xchg(ti->ti_dport, ti->ti_sport, uint16_t);
#undef xchg
	}
	ti->ti_len = htons((u_short)(sizeof (struct tcphdr) + tlen));
	tlen += sizeof (struct tcpiphdr);
	m->m_len = tlen;

        ti->ti_mbuf = NULL;
	ti->ti_x1 = 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 ip *)ti)->ip_len = tlen;

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

	(void) ip_output((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(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 = TCP_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 = %lx", (long)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 = %lx", (long )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;
	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 = %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(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;
	}
	if (tp)
		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)
{
  Slirp *slirp = so->slirp;
  int ret=0;

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

  if( (ret = so->s = qemu_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 & slirp->vnetwork_mask.s_addr) ==
        slirp->vnetwork_addr.s_addr) {
      /* It's an alias */
      if (so->so_faddr.s_addr == slirp->vnameserver_addr.s_addr) {
	if (get_dns_addr(&addr.sin_addr) < 0)
	  addr.sin_addr = loopback_addr;
      } else {
	addr.sin_addr = loopback_addr;
      }
    } 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(struct socket *inso)
{
	Slirp *slirp = inso->slirp;
	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(slirp)) == NULL) {
			/* If it failed, get rid of the pending connection */
			closesocket(accept(inso->s,(struct sockaddr *)&addr,&addrlen));
			return;
		}
		if (tcp_attach(so) < 0) {
			free(so); /* NOT sofree */
			return;
		}
		so->so_laddr = inso->so_laddr;
		so->so_lport = inso->so_lport;
	}

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

	if ((s = accept(inso->s,(struct sockaddr *)&addr,&addrlen)) < 0) {
		tcp_close(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 = slirp->vhost_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_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, 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}
};

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;
	u_int n1, n2, n3, n4, n5, n6;
        char buff[257];
	uint32_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 = 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 = ntohs(addr.sin_port);
							break;
						}
					}
				}
                                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_hdr.mh_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_hdr.mh_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_hdr.mh_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_hdr.mh_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_hdr.mh_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_hdr.mh_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) {
			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(slirp, INADDR_ANY,
						       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;

	 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 ex_list *ex_ptr;
    int do_pty;

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

    if (so->so_faddr.s_addr != slirp->vhost_addr.s_addr) {
        /* Check if it's pty_exec */
        for (ex_ptr = slirp->exec_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->ex_pty == 3) {
                    so->s = -1;
                    so->extra = (void *)ex_ptr->ex_exec;
                    return 1;
                }
                do_pty = ex_ptr->ex_pty;
                DEBUG_MISC((dfd, " executing %s\n", ex_ptr->ex_exec));
                return fork_exec(so, ex_ptr->ex_exec, do_pty);
            }
        }
    }
    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;
}