aboutsummaryrefslogtreecommitdiff
path: root/tools/plink/telnet.c
blob: 8fbe886794053830b32c9142a0f68cf34a5ab9f9 (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
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
/*
 * Telnet backend.
 */

#include <stdio.h>
#include <stdlib.h>

#include "putty.h"

#ifndef FALSE
#define FALSE 0
#endif
#ifndef TRUE
#define TRUE 1
#endif

#define	IAC	255		       /* interpret as command: */
#define	DONT	254		       /* you are not to use option */
#define	DO	253		       /* please, you use option */
#define	WONT	252		       /* I won't use option */
#define	WILL	251		       /* I will use option */
#define	SB	250		       /* interpret as subnegotiation */
#define	SE	240		       /* end sub negotiation */

#define GA      249		       /* you may reverse the line */
#define EL      248		       /* erase the current line */
#define EC      247		       /* erase the current character */
#define	AYT	246		       /* are you there */
#define	AO	245		       /* abort output--but let prog finish */
#define	IP	244		       /* interrupt process--permanently */
#define	BREAK	243		       /* break */
#define DM      242		       /* data mark--for connect. cleaning */
#define NOP     241		       /* nop */
#define EOR     239		       /* end of record (transparent mode) */
#define ABORT   238		       /* Abort process */
#define SUSP    237		       /* Suspend process */
#define xEOF    236		       /* End of file: EOF is already used... */

#define TELOPTS(X) \
    X(BINARY, 0)                       /* 8-bit data path */ \
    X(ECHO, 1)                         /* echo */ \
    X(RCP, 2)                          /* prepare to reconnect */ \
    X(SGA, 3)                          /* suppress go ahead */ \
    X(NAMS, 4)                         /* approximate message size */ \
    X(STATUS, 5)                       /* give status */ \
    X(TM, 6)                           /* timing mark */ \
    X(RCTE, 7)                         /* remote controlled transmission and echo */ \
    X(NAOL, 8)                         /* negotiate about output line width */ \
    X(NAOP, 9)                         /* negotiate about output page size */ \
    X(NAOCRD, 10)                      /* negotiate about CR disposition */ \
    X(NAOHTS, 11)                      /* negotiate about horizontal tabstops */ \
    X(NAOHTD, 12)                      /* negotiate about horizontal tab disposition */ \
    X(NAOFFD, 13)                      /* negotiate about formfeed disposition */ \
    X(NAOVTS, 14)                      /* negotiate about vertical tab stops */ \
    X(NAOVTD, 15)                      /* negotiate about vertical tab disposition */ \
    X(NAOLFD, 16)                      /* negotiate about output LF disposition */ \
    X(XASCII, 17)                      /* extended ascic character set */ \
    X(LOGOUT, 18)                      /* force logout */ \
    X(BM, 19)                          /* byte macro */ \
    X(DET, 20)                         /* data entry terminal */ \
    X(SUPDUP, 21)                      /* supdup protocol */ \
    X(SUPDUPOUTPUT, 22)                /* supdup output */ \
    X(SNDLOC, 23)                      /* send location */ \
    X(TTYPE, 24)                       /* terminal type */ \
    X(EOR, 25)                         /* end or record */ \
    X(TUID, 26)                        /* TACACS user identification */ \
    X(OUTMRK, 27)                      /* output marking */ \
    X(TTYLOC, 28)                      /* terminal location number */ \
    X(3270REGIME, 29)                  /* 3270 regime */ \
    X(X3PAD, 30)                       /* X.3 PAD */ \
    X(NAWS, 31)                        /* window size */ \
    X(TSPEED, 32)                      /* terminal speed */ \
    X(LFLOW, 33)                       /* remote flow control */ \
    X(LINEMODE, 34)                    /* Linemode option */ \
    X(XDISPLOC, 35)                    /* X Display Location */ \
    X(OLD_ENVIRON, 36)                 /* Old - Environment variables */ \
    X(AUTHENTICATION, 37)              /* Authenticate */ \
    X(ENCRYPT, 38)                     /* Encryption option */ \
    X(NEW_ENVIRON, 39)                 /* New - Environment variables */ \
    X(TN3270E, 40)                     /* TN3270 enhancements */ \
    X(XAUTH, 41)                       \
    X(CHARSET, 42)                     /* Character set */ \
    X(RSP, 43)                         /* Remote serial port */ \
    X(COM_PORT_OPTION, 44)             /* Com port control */ \
    X(SLE, 45)                         /* Suppress local echo */ \
    X(STARTTLS, 46)                    /* Start TLS */ \
    X(KERMIT, 47)                      /* Automatic Kermit file transfer */ \
    X(SEND_URL, 48)                    \
    X(FORWARD_X, 49)                   \
    X(PRAGMA_LOGON, 138)               \
    X(SSPI_LOGON, 139)                 \
    X(PRAGMA_HEARTBEAT, 140)           \
    X(EXOPL, 255)                      /* extended-options-list */

#define telnet_enum(x,y) TELOPT_##x = y,
enum { TELOPTS(telnet_enum) dummy=0 };
#undef telnet_enum

#define	TELQUAL_IS	0	       /* option is... */
#define	TELQUAL_SEND	1	       /* send option */
#define	TELQUAL_INFO	2	       /* ENVIRON: informational version of IS */
#define BSD_VAR 1
#define BSD_VALUE 0
#define RFC_VAR 0
#define RFC_VALUE 1

#define CR 13
#define LF 10
#define NUL 0

#define iswritable(x) \
	( (x) != IAC && \
	      (telnet->opt_states[o_we_bin.index] == ACTIVE || (x) != CR))

static char *telopt(int opt)
{
#define telnet_str(x,y) case TELOPT_##x: return #x;
    switch (opt) {
	TELOPTS(telnet_str)
      default:
	return "<unknown>";
    }
#undef telnet_str
}

static void telnet_size(void *handle, int width, int height);

struct Opt {
    int send;			       /* what we initially send */
    int nsend;			       /* -ve send if requested to stop it */
    int ack, nak;		       /* +ve and -ve acknowledgements */
    int option;			       /* the option code */
    int index;			       /* index into telnet->opt_states[] */
    enum {
	REQUESTED, ACTIVE, INACTIVE, REALLY_INACTIVE
    } initial_state;
};

enum {
    OPTINDEX_NAWS,
    OPTINDEX_TSPEED,
    OPTINDEX_TTYPE,
    OPTINDEX_OENV,
    OPTINDEX_NENV,
    OPTINDEX_ECHO,
    OPTINDEX_WE_SGA,
    OPTINDEX_THEY_SGA,
    OPTINDEX_WE_BIN,
    OPTINDEX_THEY_BIN,
    NUM_OPTS
};

static const struct Opt o_naws =
    { WILL, WONT, DO, DONT, TELOPT_NAWS, OPTINDEX_NAWS, REQUESTED };
static const struct Opt o_tspeed =
    { WILL, WONT, DO, DONT, TELOPT_TSPEED, OPTINDEX_TSPEED, REQUESTED };
static const struct Opt o_ttype =
    { WILL, WONT, DO, DONT, TELOPT_TTYPE, OPTINDEX_TTYPE, REQUESTED };
static const struct Opt o_oenv =
    { WILL, WONT, DO, DONT, TELOPT_OLD_ENVIRON, OPTINDEX_OENV, INACTIVE };
static const struct Opt o_nenv =
    { WILL, WONT, DO, DONT, TELOPT_NEW_ENVIRON, OPTINDEX_NENV, REQUESTED };
static const struct Opt o_echo =
    { DO, DONT, WILL, WONT, TELOPT_ECHO, OPTINDEX_ECHO, REQUESTED };
static const struct Opt o_we_sga =
    { WILL, WONT, DO, DONT, TELOPT_SGA, OPTINDEX_WE_SGA, REQUESTED };
static const struct Opt o_they_sga =
    { DO, DONT, WILL, WONT, TELOPT_SGA, OPTINDEX_THEY_SGA, REQUESTED };
static const struct Opt o_we_bin =
    { WILL, WONT, DO, DONT, TELOPT_BINARY, OPTINDEX_WE_BIN, INACTIVE };
static const struct Opt o_they_bin =
    { DO, DONT, WILL, WONT, TELOPT_BINARY, OPTINDEX_THEY_BIN, INACTIVE };

static const struct Opt *const opts[] = {
    &o_naws, &o_tspeed, &o_ttype, &o_oenv, &o_nenv, &o_echo,
    &o_we_sga, &o_they_sga, &o_we_bin, &o_they_bin, NULL
};

typedef struct telnet_tag {
    const struct plug_function_table *fn;
    /* the above field _must_ be first in the structure */

    Socket s;

    void *frontend;
    void *ldisc;
    int term_width, term_height;

    int opt_states[NUM_OPTS];

    int echoing, editing;
    int activated;
    int bufsize;
    int in_synch;
    int sb_opt, sb_len;
    unsigned char *sb_buf;
    int sb_size;

    enum {
	TOP_LEVEL, SEENIAC, SEENWILL, SEENWONT, SEENDO, SEENDONT,
	    SEENSB, SUBNEGOT, SUBNEG_IAC, SEENCR
    } state;

    Config cfg;

    Pinger pinger;
} *Telnet;

#define TELNET_MAX_BACKLOG 4096

#define SB_DELTA 1024

static void c_write(Telnet telnet, char *buf, int len)
{
    int backlog;
    backlog = from_backend(telnet->frontend, 0, buf, len);
    sk_set_frozen(telnet->s, backlog > TELNET_MAX_BACKLOG);
}

static void log_option(Telnet telnet, char *sender, int cmd, int option)
{
    char *buf;
    /*
     * The strange-looking "<?""?>" below is there to avoid a
     * trigraph - a double question mark followed by > maps to a
     * closing brace character!
     */
    buf = dupprintf("%s:\t%s %s", sender,
		    (cmd == WILL ? "WILL" : cmd == WONT ? "WONT" :
		     cmd == DO ? "DO" : cmd == DONT ? "DONT" : "<?""?>"),
		    telopt(option));
    logevent(telnet->frontend, buf);
    sfree(buf);
}

static void send_opt(Telnet telnet, int cmd, int option)
{
    unsigned char b[3];

    b[0] = IAC;
    b[1] = cmd;
    b[2] = option;
    telnet->bufsize = sk_write(telnet->s, (char *)b, 3);
    log_option(telnet, "client", cmd, option);
}

static void deactivate_option(Telnet telnet, const struct Opt *o)
{
    if (telnet->opt_states[o->index] == REQUESTED ||
	telnet->opt_states[o->index] == ACTIVE)
	send_opt(telnet, o->nsend, o->option);
    telnet->opt_states[o->index] = REALLY_INACTIVE;
}

/*
 * Generate side effects of enabling or disabling an option.
 */
static void option_side_effects(Telnet telnet, const struct Opt *o, int enabled)
{
    if (o->option == TELOPT_ECHO && o->send == DO)
	telnet->echoing = !enabled;
    else if (o->option == TELOPT_SGA && o->send == DO)
	telnet->editing = !enabled;
    if (telnet->ldisc)		       /* cause ldisc to notice the change */
	ldisc_send(telnet->ldisc, NULL, 0, 0);

    /* Ensure we get the minimum options */
    if (!telnet->activated) {
	if (telnet->opt_states[o_echo.index] == INACTIVE) {
	    telnet->opt_states[o_echo.index] = REQUESTED;
	    send_opt(telnet, o_echo.send, o_echo.option);
	}
	if (telnet->opt_states[o_we_sga.index] == INACTIVE) {
	    telnet->opt_states[o_we_sga.index] = REQUESTED;
	    send_opt(telnet, o_we_sga.send, o_we_sga.option);
	}
	if (telnet->opt_states[o_they_sga.index] == INACTIVE) {
	    telnet->opt_states[o_they_sga.index] = REQUESTED;
	    send_opt(telnet, o_they_sga.send, o_they_sga.option);
	}
	telnet->activated = TRUE;
    }
}

static void activate_option(Telnet telnet, const struct Opt *o)
{
    if (o->send == WILL && o->option == TELOPT_NAWS)
	telnet_size(telnet, telnet->term_width, telnet->term_height);
    if (o->send == WILL &&
	(o->option == TELOPT_NEW_ENVIRON ||
	 o->option == TELOPT_OLD_ENVIRON)) {
	/*
	 * We may only have one kind of ENVIRON going at a time.
	 * This is a hack, but who cares.
	 */
	deactivate_option(telnet, o->option ==
			  TELOPT_NEW_ENVIRON ? &o_oenv : &o_nenv);
    }
    option_side_effects(telnet, o, 1);
}

static void refused_option(Telnet telnet, const struct Opt *o)
{
    if (o->send == WILL && o->option == TELOPT_NEW_ENVIRON &&
	telnet->opt_states[o_oenv.index] == INACTIVE) {
	send_opt(telnet, WILL, TELOPT_OLD_ENVIRON);
	telnet->opt_states[o_oenv.index] = REQUESTED;
    }
    option_side_effects(telnet, o, 0);
}

static void proc_rec_opt(Telnet telnet, int cmd, int option)
{
    const struct Opt *const *o;

    log_option(telnet, "server", cmd, option);
    for (o = opts; *o; o++) {
	if ((*o)->option == option && (*o)->ack == cmd) {
	    switch (telnet->opt_states[(*o)->index]) {
	      case REQUESTED:
		telnet->opt_states[(*o)->index] = ACTIVE;
		activate_option(telnet, *o);
		break;
	      case ACTIVE:
		break;
	      case INACTIVE:
		telnet->opt_states[(*o)->index] = ACTIVE;
		send_opt(telnet, (*o)->send, option);
		activate_option(telnet, *o);
		break;
	      case REALLY_INACTIVE:
		send_opt(telnet, (*o)->nsend, option);
		break;
	    }
	    return;
	} else if ((*o)->option == option && (*o)->nak == cmd) {
	    switch (telnet->opt_states[(*o)->index]) {
	      case REQUESTED:
		telnet->opt_states[(*o)->index] = INACTIVE;
		refused_option(telnet, *o);
		break;
	      case ACTIVE:
		telnet->opt_states[(*o)->index] = INACTIVE;
		send_opt(telnet, (*o)->nsend, option);
		option_side_effects(telnet, *o, 0);
		break;
	      case INACTIVE:
	      case REALLY_INACTIVE:
		break;
	    }
	    return;
	}
    }
    /*
     * If we reach here, the option was one we weren't prepared to
     * cope with. If the request was positive (WILL or DO), we send
     * a negative ack to indicate refusal. If the request was
     * negative (WONT / DONT), we must do nothing.
     */
    if (cmd == WILL || cmd == DO)
        send_opt(telnet, (cmd == WILL ? DONT : WONT), option);
}

static void process_subneg(Telnet telnet)
{
    unsigned char b[2048], *p, *q;
    int var, value, n;
    char *e;

    switch (telnet->sb_opt) {
      case TELOPT_TSPEED:
	if (telnet->sb_len == 1 && telnet->sb_buf[0] == TELQUAL_SEND) {
	    char *logbuf;
	    b[0] = IAC;
	    b[1] = SB;
	    b[2] = TELOPT_TSPEED;
	    b[3] = TELQUAL_IS;
	    strcpy((char *)(b + 4), telnet->cfg.termspeed);
	    n = 4 + strlen(telnet->cfg.termspeed);
	    b[n] = IAC;
	    b[n + 1] = SE;
	    telnet->bufsize = sk_write(telnet->s, (char *)b, n + 2);
	    logevent(telnet->frontend, "server:\tSB TSPEED SEND");
	    logbuf = dupprintf("client:\tSB TSPEED IS %s", telnet->cfg.termspeed);
	    logevent(telnet->frontend, logbuf);
	    sfree(logbuf);
	} else
	    logevent(telnet->frontend, "server:\tSB TSPEED <something weird>");
	break;
      case TELOPT_TTYPE:
	if (telnet->sb_len == 1 && telnet->sb_buf[0] == TELQUAL_SEND) {
	    char *logbuf;
	    b[0] = IAC;
	    b[1] = SB;
	    b[2] = TELOPT_TTYPE;
	    b[3] = TELQUAL_IS;
	    for (n = 0; telnet->cfg.termtype[n]; n++)
		b[n + 4] = (telnet->cfg.termtype[n] >= 'a'
			    && telnet->cfg.termtype[n] <=
			    'z' ? telnet->cfg.termtype[n] + 'A' -
			    'a' : telnet->cfg.termtype[n]);
	    b[n + 4] = IAC;
	    b[n + 5] = SE;
	    telnet->bufsize = sk_write(telnet->s, (char *)b, n + 6);
	    b[n + 4] = 0;
	    logevent(telnet->frontend, "server:\tSB TTYPE SEND");
	    logbuf = dupprintf("client:\tSB TTYPE IS %s", b + 4);
	    logevent(telnet->frontend, logbuf);
	    sfree(logbuf);
	} else
	    logevent(telnet->frontend, "server:\tSB TTYPE <something weird>\r\n");
	break;
      case TELOPT_OLD_ENVIRON:
      case TELOPT_NEW_ENVIRON:
	p = telnet->sb_buf;
	q = p + telnet->sb_len;
	if (p < q && *p == TELQUAL_SEND) {
	    char *logbuf;
	    p++;
	    logbuf = dupprintf("server:\tSB %s SEND", telopt(telnet->sb_opt));
	    logevent(telnet->frontend, logbuf);
	    sfree(logbuf);
	    if (telnet->sb_opt == TELOPT_OLD_ENVIRON) {
		if (telnet->cfg.rfc_environ) {
		    value = RFC_VALUE;
		    var = RFC_VAR;
		} else {
		    value = BSD_VALUE;
		    var = BSD_VAR;
		}
		/*
		 * Try to guess the sense of VAR and VALUE.
		 */
		while (p < q) {
		    if (*p == RFC_VAR) {
			value = RFC_VALUE;
			var = RFC_VAR;
		    } else if (*p == BSD_VAR) {
			value = BSD_VALUE;
			var = BSD_VAR;
		    }
		    p++;
		}
	    } else {
		/*
		 * With NEW_ENVIRON, the sense of VAR and VALUE
		 * isn't in doubt.
		 */
		value = RFC_VALUE;
		var = RFC_VAR;
	    }
	    b[0] = IAC;
	    b[1] = SB;
	    b[2] = telnet->sb_opt;
	    b[3] = TELQUAL_IS;
	    n = 4;
	    e = telnet->cfg.environmt;
	    while (*e) {
		b[n++] = var;
		while (*e && *e != '\t')
		    b[n++] = *e++;
		if (*e == '\t')
		    e++;
		b[n++] = value;
		while (*e)
		    b[n++] = *e++;
		e++;
	    }
	    {
		char user[sizeof(telnet->cfg.username)];
		(void) get_remote_username(&telnet->cfg, user, sizeof(user));
		if (*user) {
		    b[n++] = var;
		    b[n++] = 'U';
		    b[n++] = 'S';
		    b[n++] = 'E';
		    b[n++] = 'R';
		    b[n++] = value;
		    e = user;
		    while (*e)
			b[n++] = *e++;
		}
		b[n++] = IAC;
		b[n++] = SE;
		telnet->bufsize = sk_write(telnet->s, (char *)b, n);
		logbuf = dupprintf("client:\tSB %s IS %s%s%s%s",
				   telopt(telnet->sb_opt),
				   *user ? "USER=" : "",
				   user,
				   *user ? " " : "",
				   n == 6 ? "<nothing>" :
				   (*telnet->cfg.environmt ? "<stuff>" : ""));
		logevent(telnet->frontend, logbuf);
		sfree(logbuf);
	    }
	}
	break;
    }
}

static void do_telnet_read(Telnet telnet, char *buf, int len)
{
    char *outbuf = NULL;
    int outbuflen = 0, outbufsize = 0;

#define ADDTOBUF(c) do { \
    if (outbuflen >= outbufsize) { \
	outbufsize = outbuflen + 256; \
        outbuf = sresize(outbuf, outbufsize, char); \
    } \
    outbuf[outbuflen++] = (c); \
} while (0)

    while (len--) {
	int c = (unsigned char) *buf++;

	switch (telnet->state) {
	  case TOP_LEVEL:
	  case SEENCR:
	    if (c == NUL && telnet->state == SEENCR)
		telnet->state = TOP_LEVEL;
	    else if (c == IAC)
		telnet->state = SEENIAC;
	    else {
		if (!telnet->in_synch)
		    ADDTOBUF(c);

#if 1
		/* I can't get the F***ing winsock to insert the urgent IAC
		 * into the right position! Even with SO_OOBINLINE it gives
		 * it to recv too soon. And of course the DM byte (that
		 * arrives in the same packet!) appears several K later!!
		 *
		 * Oh well, we do get the DM in the right place so I'll
		 * just stop hiding on the next 0xf2 and hope for the best.
		 */
		else if (c == DM)
		    telnet->in_synch = 0;
#endif
		if (c == CR && telnet->opt_states[o_they_bin.index] != ACTIVE)
		    telnet->state = SEENCR;
		else
		    telnet->state = TOP_LEVEL;
	    }
	    break;
	  case SEENIAC:
	    if (c == DO)
		telnet->state = SEENDO;
	    else if (c == DONT)
		telnet->state = SEENDONT;
	    else if (c == WILL)
		telnet->state = SEENWILL;
	    else if (c == WONT)
		telnet->state = SEENWONT;
	    else if (c == SB)
		telnet->state = SEENSB;
	    else if (c == DM) {
		telnet->in_synch = 0;
		telnet->state = TOP_LEVEL;
	    } else {
		/* ignore everything else; print it if it's IAC */
		if (c == IAC) {
		    ADDTOBUF(c);
		}
		telnet->state = TOP_LEVEL;
	    }
	    break;
	  case SEENWILL:
	    proc_rec_opt(telnet, WILL, c);
	    telnet->state = TOP_LEVEL;
	    break;
	  case SEENWONT:
	    proc_rec_opt(telnet, WONT, c);
	    telnet->state = TOP_LEVEL;
	    break;
	  case SEENDO:
	    proc_rec_opt(telnet, DO, c);
	    telnet->state = TOP_LEVEL;
	    break;
	  case SEENDONT:
	    proc_rec_opt(telnet, DONT, c);
	    telnet->state = TOP_LEVEL;
	    break;
	  case SEENSB:
	    telnet->sb_opt = c;
	    telnet->sb_len = 0;
	    telnet->state = SUBNEGOT;
	    break;
	  case SUBNEGOT:
	    if (c == IAC)
		telnet->state = SUBNEG_IAC;
	    else {
	      subneg_addchar:
		if (telnet->sb_len >= telnet->sb_size) {
		    telnet->sb_size += SB_DELTA;
		    telnet->sb_buf = sresize(telnet->sb_buf, telnet->sb_size,
					     unsigned char);
		}
		telnet->sb_buf[telnet->sb_len++] = c;
		telnet->state = SUBNEGOT;	/* in case we came here by goto */
	    }
	    break;
	  case SUBNEG_IAC:
	    if (c != SE)
		goto subneg_addchar;   /* yes, it's a hack, I know, but... */
	    else {
		process_subneg(telnet);
		telnet->state = TOP_LEVEL;
	    }
	    break;
	}
    }

    if (outbuflen)
	c_write(telnet, outbuf, outbuflen);
    sfree(outbuf);
}

static void telnet_log(Plug plug, int type, SockAddr addr, int port,
		       const char *error_msg, int error_code)
{
    Telnet telnet = (Telnet) plug;
    char addrbuf[256], *msg;

    sk_getaddr(addr, addrbuf, lenof(addrbuf));

    if (type == 0)
	msg = dupprintf("Connecting to %s port %d", addrbuf, port);
    else
	msg = dupprintf("Failed to connect to %s: %s", addrbuf, error_msg);

    logevent(telnet->frontend, msg);
}

static int telnet_closing(Plug plug, const char *error_msg, int error_code,
			  int calling_back)
{
    Telnet telnet = (Telnet) plug;

    if (telnet->s) {
        sk_close(telnet->s);
        telnet->s = NULL;
	notify_remote_exit(telnet->frontend);
    }
    if (error_msg) {
	logevent(telnet->frontend, error_msg);
	connection_fatal(telnet->frontend, "%s", error_msg);
    }
    /* Otherwise, the remote side closed the connection normally. */
    return 0;
}

static int telnet_receive(Plug plug, int urgent, char *data, int len)
{
    Telnet telnet = (Telnet) plug;
    if (urgent)
	telnet->in_synch = TRUE;
    do_telnet_read(telnet, data, len);
    return 1;
}

static void telnet_sent(Plug plug, int bufsize)
{
    Telnet telnet = (Telnet) plug;
    telnet->bufsize = bufsize;
}

/*
 * Called to set up the Telnet connection.
 *
 * Returns an error message, or NULL on success.
 *
 * Also places the canonical host name into `realhost'. It must be
 * freed by the caller.
 */
static const char *telnet_init(void *frontend_handle, void **backend_handle,
			       Config *cfg,
			       char *host, int port, char **realhost,
			       int nodelay, int keepalive)
{
    static const struct plug_function_table fn_table = {
	telnet_log,
	telnet_closing,
	telnet_receive,
	telnet_sent
    };
    SockAddr addr;
    const char *err;
    Telnet telnet;

    telnet = snew(struct telnet_tag);
    telnet->fn = &fn_table;
    telnet->cfg = *cfg;		       /* STRUCTURE COPY */
    telnet->s = NULL;
    telnet->echoing = TRUE;
    telnet->editing = TRUE;
    telnet->activated = FALSE;
    telnet->sb_buf = NULL;
    telnet->sb_size = 0;
    telnet->frontend = frontend_handle;
    telnet->term_width = telnet->cfg.width;
    telnet->term_height = telnet->cfg.height;
    telnet->state = TOP_LEVEL;
    telnet->ldisc = NULL;
    telnet->pinger = NULL;
    *backend_handle = telnet;

    /*
     * Try to find host.
     */
    {
	char *buf;
	buf = dupprintf("Looking up host \"%s\"%s", host,
			(cfg->addressfamily == ADDRTYPE_IPV4 ? " (IPv4)" :
			 (cfg->addressfamily == ADDRTYPE_IPV6 ? " (IPv6)" :
			  "")));
	logevent(telnet->frontend, buf);
	sfree(buf);
    }
    addr = name_lookup(host, port, realhost, &telnet->cfg, cfg->addressfamily);
    if ((err = sk_addr_error(addr)) != NULL) {
	sk_addr_free(addr);
	return err;
    }

    if (port < 0)
	port = 23;		       /* default telnet port */

    /*
     * Open socket.
     */
    telnet->s = new_connection(addr, *realhost, port, 0, 1,
			       nodelay, keepalive, (Plug) telnet, &telnet->cfg);
    if ((err = sk_socket_error(telnet->s)) != NULL)
	return err;

    telnet->pinger = pinger_new(&telnet->cfg, &telnet_backend, telnet);

    /*
     * Initialise option states.
     */
    if (telnet->cfg.passive_telnet) {
	const struct Opt *const *o;

	for (o = opts; *o; o++)
	    telnet->opt_states[(*o)->index] = INACTIVE;
    } else {
	const struct Opt *const *o;

	for (o = opts; *o; o++) {
	    telnet->opt_states[(*o)->index] = (*o)->initial_state;
	    if (telnet->opt_states[(*o)->index] == REQUESTED)
		send_opt(telnet, (*o)->send, (*o)->option);
	}
	telnet->activated = TRUE;
    }

    /*
     * Set up SYNCH state.
     */
    telnet->in_synch = FALSE;

    /*
     * We can send special commands from the start.
     */
    update_specials_menu(telnet->frontend);

    /*
     * loghost overrides realhost, if specified.
     */
    if (*telnet->cfg.loghost) {
	char *colon;

	sfree(*realhost);
	*realhost = dupstr(telnet->cfg.loghost);
	colon = strrchr(*realhost, ':');
	if (colon) {
	    /*
	     * FIXME: if we ever update this aspect of ssh.c for
	     * IPv6 literal management, this should change in line
	     * with it.
	     */
	    *colon++ = '\0';
	}
    }

    return NULL;
}

static void telnet_free(void *handle)
{
    Telnet telnet = (Telnet) handle;

    sfree(telnet->sb_buf);
    if (telnet->s)
	sk_close(telnet->s);
    if (telnet->pinger)
	pinger_free(telnet->pinger);
    sfree(telnet);
}
/*
 * Reconfigure the Telnet backend. There's no immediate action
 * necessary, in this backend: we just save the fresh config for
 * any subsequent negotiations.
 */
static void telnet_reconfig(void *handle, Config *cfg)
{
    Telnet telnet = (Telnet) handle;
    pinger_reconfig(telnet->pinger, &telnet->cfg, cfg);
    telnet->cfg = *cfg;		       /* STRUCTURE COPY */
}

/*
 * Called to send data down the Telnet connection.
 */
static int telnet_send(void *handle, char *buf, int len)
{
    Telnet telnet = (Telnet) handle;
    unsigned char *p, *end;
    static const unsigned char iac[2] = { IAC, IAC };
    static const unsigned char cr[2] = { CR, NUL };
#if 0
    static const unsigned char nl[2] = { CR, LF };
#endif

    if (telnet->s == NULL)
	return 0;

    p = (unsigned char *)buf;
    end = (unsigned char *)(buf + len);
    while (p < end) {
	unsigned char *q = p;

	while (p < end && iswritable(*p))
	    p++;
	telnet->bufsize = sk_write(telnet->s, (char *)q, p - q);

	while (p < end && !iswritable(*p)) {
	    telnet->bufsize = 
		sk_write(telnet->s, (char *)(*p == IAC ? iac : cr), 2);
	    p++;
	}
    }

    return telnet->bufsize;
}

/*
 * Called to query the current socket sendability status.
 */
static int telnet_sendbuffer(void *handle)
{
    Telnet telnet = (Telnet) handle;
    return telnet->bufsize;
}

/*
 * Called to set the size of the window from Telnet's POV.
 */
static void telnet_size(void *handle, int width, int height)
{
    Telnet telnet = (Telnet) handle;
    unsigned char b[24];
    int n;
    char *logbuf;

    telnet->term_width = width;
    telnet->term_height = height;

    if (telnet->s == NULL || telnet->opt_states[o_naws.index] != ACTIVE)
	return;
    n = 0;
    b[n++] = IAC;
    b[n++] = SB;
    b[n++] = TELOPT_NAWS;
    b[n++] = telnet->term_width >> 8;
    if (b[n-1] == IAC) b[n++] = IAC;   /* duplicate any IAC byte occurs */
    b[n++] = telnet->term_width & 0xFF;
    if (b[n-1] == IAC) b[n++] = IAC;   /* duplicate any IAC byte occurs */
    b[n++] = telnet->term_height >> 8;
    if (b[n-1] == IAC) b[n++] = IAC;   /* duplicate any IAC byte occurs */
    b[n++] = telnet->term_height & 0xFF;
    if (b[n-1] == IAC) b[n++] = IAC;   /* duplicate any IAC byte occurs */
    b[n++] = IAC;
    b[n++] = SE;
    telnet->bufsize = sk_write(telnet->s, (char *)b, n);
    logbuf = dupprintf("client:\tSB NAWS %d,%d",
		       telnet->term_width, telnet->term_height);
    logevent(telnet->frontend, logbuf);
    sfree(logbuf);
}

/*
 * Send Telnet special codes.
 */
static void telnet_special(void *handle, Telnet_Special code)
{
    Telnet telnet = (Telnet) handle;
    unsigned char b[2];

    if (telnet->s == NULL)
	return;

    b[0] = IAC;
    switch (code) {
      case TS_AYT:
	b[1] = AYT;
	telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
	break;
      case TS_BRK:
	b[1] = BREAK;
	telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
	break;
      case TS_EC:
	b[1] = EC;
	telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
	break;
      case TS_EL:
	b[1] = EL;
	telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
	break;
      case TS_GA:
	b[1] = GA;
	telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
	break;
      case TS_NOP:
	b[1] = NOP;
	telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
	break;
      case TS_ABORT:
	b[1] = ABORT;
	telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
	break;
      case TS_AO:
	b[1] = AO;
	telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
	break;
      case TS_IP:
	b[1] = IP;
	telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
	break;
      case TS_SUSP:
	b[1] = SUSP;
	telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
	break;
      case TS_EOR:
	b[1] = EOR;
	telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
	break;
      case TS_EOF:
	b[1] = xEOF;
	telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
	break;
      case TS_EOL:
	/* In BINARY mode, CR-LF becomes just CR -
	 * and without the NUL suffix too. */
	if (telnet->opt_states[o_we_bin.index] == ACTIVE)
	    telnet->bufsize = sk_write(telnet->s, "\r", 1);
	else
	    telnet->bufsize = sk_write(telnet->s, "\r\n", 2);
	break;
      case TS_SYNCH:
	b[1] = DM;
	telnet->bufsize = sk_write(telnet->s, (char *)b, 1);
	telnet->bufsize = sk_write_oob(telnet->s, (char *)(b + 1), 1);
	break;
      case TS_RECHO:
	if (telnet->opt_states[o_echo.index] == INACTIVE ||
	    telnet->opt_states[o_echo.index] == REALLY_INACTIVE) {
	    telnet->opt_states[o_echo.index] = REQUESTED;
	    send_opt(telnet, o_echo.send, o_echo.option);
	}
	break;
      case TS_LECHO:
	if (telnet->opt_states[o_echo.index] == ACTIVE) {
	    telnet->opt_states[o_echo.index] = REQUESTED;
	    send_opt(telnet, o_echo.nsend, o_echo.option);
	}
	break;
      case TS_PING:
	if (telnet->opt_states[o_they_sga.index] == ACTIVE) {
	    b[1] = NOP;
	    telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
	}
	break;
      default:
	break;	/* never heard of it */
    }
}

static const struct telnet_special *telnet_get_specials(void *handle)
{
    static const struct telnet_special specials[] = {
	{"Are You There", TS_AYT},
	{"Break", TS_BRK},
	{"Synch", TS_SYNCH},
	{"Erase Character", TS_EC},
	{"Erase Line", TS_EL},
	{"Go Ahead", TS_GA},
	{"No Operation", TS_NOP},
	{NULL, TS_SEP},
	{"Abort Process", TS_ABORT},
	{"Abort Output", TS_AO},
	{"Interrupt Process", TS_IP},
	{"Suspend Process", TS_SUSP},
	{NULL, TS_SEP},
	{"End Of Record", TS_EOR},
	{"End Of File", TS_EOF},
	{NULL, TS_EXITMENU}
    };
    return specials;
}

static int telnet_connected(void *handle)
{
    Telnet telnet = (Telnet) handle;
    return telnet->s != NULL;
}

static int telnet_sendok(void *handle)
{
    /* Telnet telnet = (Telnet) handle; */
    return 1;
}

static void telnet_unthrottle(void *handle, int backlog)
{
    Telnet telnet = (Telnet) handle;
    sk_set_frozen(telnet->s, backlog > TELNET_MAX_BACKLOG);
}

static int telnet_ldisc(void *handle, int option)
{
    Telnet telnet = (Telnet) handle;
    if (option == LD_ECHO)
	return telnet->echoing;
    if (option == LD_EDIT)
	return telnet->editing;
    return FALSE;
}

static void telnet_provide_ldisc(void *handle, void *ldisc)
{
    Telnet telnet = (Telnet) handle;
    telnet->ldisc = ldisc;
}

static void telnet_provide_logctx(void *handle, void *logctx)
{
    /* This is a stub. */
}

static int telnet_exitcode(void *handle)
{
    Telnet telnet = (Telnet) handle;
    if (telnet->s != NULL)
        return -1;                     /* still connected */
    else
        /* Telnet doesn't transmit exit codes back to the client */
        return 0;
}

/*
 * cfg_info for Telnet does nothing at all.
 */
static int telnet_cfg_info(void *handle)
{
    return 0;
}

Backend telnet_backend = {
    telnet_init,
    telnet_free,
    telnet_reconfig,
    telnet_send,
    telnet_sendbuffer,
    telnet_size,
    telnet_special,
    telnet_get_specials,
    telnet_connected,
    telnet_exitcode,
    telnet_sendok,
    telnet_ldisc,
    telnet_provide_ldisc,
    telnet_provide_logctx,
    telnet_unthrottle,
    telnet_cfg_info,
    "telnet",
    PROT_TELNET,
    23
};