telnet.c

   1 /*
   2  * Telnet backend.
   3  */
   4
   5 #include <stdio.h>
   6 #include <stdlib.h>
   7
   8 #include "putty.h"
   9
  10 #ifndef FALSE
  11 #define FALSE 0
  12 #endif
  13 #ifndef TRUE
  14 #define TRUE 1
  15 #endif
  16
  17 #define IAC     255                    /* interpret as command: */
  18 #define DONT    254                    /* you are not to use option */
  19 #define DO      253                    /* please, you use option */
  20 #define WONT    252                    /* I won't use option */
  21 #define WILL    251                    /* I will use option */
  22 #define SB      250                    /* interpret as subnegotiation */
  23 #define SE      240                    /* end sub negotiation */
  24
  25 #define GA      249                    /* you may reverse the line */
  26 #define EL      248                    /* erase the current line */
  27 #define EC      247                    /* erase the current character */
  28 #define AYT     246                    /* are you there */
  29 #define AO      245                    /* abort output--but let prog finish */
  30 #define IP      244                    /* interrupt process--permanently */
  31 #define BREAK   243                    /* break */
  32 #define DM      242                    /* data mark--for connect. cleaning */
  33 #define NOP     241                    /* nop */
  34 #define EOR     239                    /* end of record (transparent mode) */
  35 #define ABORT   238                    /* Abort process */
  36 #define SUSP    237                    /* Suspend process */
  37 #define xEOF    236                    /* End of file: EOF is already used... */
  38
  39 #define TELOPTS(X) \
  40     X(BINARY, 0)                       /* 8-bit data path */ \
  41     X(ECHO, 1)                         /* echo */ \
  42     X(RCP, 2)                          /* prepare to reconnect */ \
  43     X(SGA, 3)                          /* suppress go ahead */ \
  44     X(NAMS, 4)                         /* approximate message size */ \
  45     X(STATUS, 5)                       /* give status */ \
  46     X(TM, 6)                           /* timing mark */ \
  47     X(RCTE, 7)                         /* remote controlled transmission and echo */ \
  48     X(NAOL, 8)                         /* negotiate about output line width */ \
  49     X(NAOP, 9)                         /* negotiate about output page size */ \
  50     X(NAOCRD, 10)                      /* negotiate about CR disposition */ \
  51     X(NAOHTS, 11)                      /* negotiate about horizontal tabstops */ \
  52     X(NAOHTD, 12)                      /* negotiate about horizontal tab disposition */ \
  53     X(NAOFFD, 13)                      /* negotiate about formfeed disposition */ \
  54     X(NAOVTS, 14)                      /* negotiate about vertical tab stops */ \
  55     X(NAOVTD, 15)                      /* negotiate about vertical tab disposition */ \
  56     X(NAOLFD, 16)                      /* negotiate about output LF disposition */ \
  57     X(XASCII, 17)                      /* extended ascic character set */ \
  58     X(LOGOUT, 18)                      /* force logout */ \
  59     X(BM, 19)                          /* byte macro */ \
  60     X(DET, 20)                         /* data entry terminal */ \
  61     X(SUPDUP, 21)                      /* supdup protocol */ \
  62     X(SUPDUPOUTPUT, 22)                /* supdup output */ \
  63     X(SNDLOC, 23)                      /* send location */ \
  64     X(TTYPE, 24)                       /* terminal type */ \
  65     X(EOR, 25)                         /* end or record */ \
  66     X(TUID, 26)                        /* TACACS user identification */ \
  67     X(OUTMRK, 27)                      /* output marking */ \
  68     X(TTYLOC, 28)                      /* terminal location number */ \
  69     X(3270REGIME, 29)                  /* 3270 regime */ \
  70     X(X3PAD, 30)                       /* X.3 PAD */ \
  71     X(NAWS, 31)                        /* window size */ \
  72     X(TSPEED, 32)                      /* terminal speed */ \
  73     X(LFLOW, 33)                       /* remote flow control */ \
  74     X(LINEMODE, 34)                    /* Linemode option */ \
  75     X(XDISPLOC, 35)                    /* X Display Location */ \
  76     X(OLD_ENVIRON, 36)                 /* Old - Environment variables */ \
  77     X(AUTHENTICATION, 37)              /* Authenticate */ \
  78     X(ENCRYPT, 38)                     /* Encryption option */ \
  79     X(NEW_ENVIRON, 39)                 /* New - Environment variables */ \
  80     X(TN3270E, 40)                     /* TN3270 enhancements */ \
  81     X(XAUTH, 41)                       \
  82     X(CHARSET, 42)                     /* Character set */ \
  83     X(RSP, 43)                         /* Remote serial port */ \
  84     X(COM_PORT_OPTION, 44)             /* Com port control */ \
  85     X(SLE, 45)                         /* Suppress local echo */ \
  86     X(STARTTLS, 46)                    /* Start TLS */ \
  87     X(KERMIT, 47)                      /* Automatic Kermit file transfer */ \
  88     X(SEND_URL, 48)                    \
  89     X(FORWARD_X, 49)                   \
  90     X(PRAGMA_LOGON, 138)               \
  91     X(SSPI_LOGON, 139)                 \
  92     X(PRAGMA_HEARTBEAT, 140)           \
  93     X(EXOPL, 255)                      /* extended-options-list */
  94
  95 #define telnet_enum(x,y) TELOPT_##x = y,
  96 enum { TELOPTS(telnet_enum) dummy=0 };
  97 #undef telnet_enum
  98
  99 #define TELQUAL_IS      0              /* option is... */
 100 #define TELQUAL_SEND    1              /* send option */
 101 #define TELQUAL_INFO    2              /* ENVIRON: informational version of IS */
 102 #define BSD_VAR 1
 103 #define BSD_VALUE 0
 104 #define RFC_VAR 0
 105 #define RFC_VALUE 1
 106
 107 #define CR 13
 108 #define LF 10
 109 #define NUL 0
 110
 111 #define iswritable(x) \
 112         ( (x) != IAC && \
 113               (telnet->opt_states[o_we_bin.index] == ACTIVE || (x) != CR))
 114
 115 static char *telopt(int opt)
 116 {
 117 #define telnet_str(x,y) case TELOPT_##x: return #x;
 118     switch (opt) {
 119         TELOPTS(telnet_str)
 120       default:
 121         return "<unknown>";
 122     }
 123 #undef telnet_str
 124 }
 125
 126 static void telnet_size(void *handle, int width, int height);
 127
 128 struct Opt {
 129     int send;                          /* what we initially send */
 130     int nsend;                         /* -ve send if requested to stop it */
 131     int ack, nak;                      /* +ve and -ve acknowledgements */
 132     int option;                        /* the option code */
 133     int index;                         /* index into telnet->opt_states[] */
 134     enum {
 135         REQUESTED, ACTIVE, INACTIVE, REALLY_INACTIVE
 136     } initial_state;
 137 };
 138
 139 enum {
 140     OPTINDEX_NAWS,
 141     OPTINDEX_TSPEED,
 142     OPTINDEX_TTYPE,
 143     OPTINDEX_OENV,
 144     OPTINDEX_NENV,
 145     OPTINDEX_ECHO,
 146     OPTINDEX_WE_SGA,
 147     OPTINDEX_THEY_SGA,
 148     OPTINDEX_WE_BIN,
 149     OPTINDEX_THEY_BIN,
 150     NUM_OPTS
 151 };
 152
 153 static const struct Opt o_naws =
 154     { WILL, WONT, DO, DONT, TELOPT_NAWS, OPTINDEX_NAWS, REQUESTED };
 155 static const struct Opt o_tspeed =
 156     { WILL, WONT, DO, DONT, TELOPT_TSPEED, OPTINDEX_TSPEED, REQUESTED };
 157 static const struct Opt o_ttype =
 158     { WILL, WONT, DO, DONT, TELOPT_TTYPE, OPTINDEX_TTYPE, REQUESTED };
 159 static const struct Opt o_oenv =
 160     { WILL, WONT, DO, DONT, TELOPT_OLD_ENVIRON, OPTINDEX_OENV, INACTIVE };
 161 static const struct Opt o_nenv =
 162     { WILL, WONT, DO, DONT, TELOPT_NEW_ENVIRON, OPTINDEX_NENV, REQUESTED };
 163 static const struct Opt o_echo =
 164     { DO, DONT, WILL, WONT, TELOPT_ECHO, OPTINDEX_ECHO, REQUESTED };
 165 static const struct Opt o_we_sga =
 166     { WILL, WONT, DO, DONT, TELOPT_SGA, OPTINDEX_WE_SGA, REQUESTED };
 167 static const struct Opt o_they_sga =
 168     { DO, DONT, WILL, WONT, TELOPT_SGA, OPTINDEX_THEY_SGA, REQUESTED };
 169 static const struct Opt o_we_bin =
 170     { WILL, WONT, DO, DONT, TELOPT_BINARY, OPTINDEX_WE_BIN, INACTIVE };
 171 static const struct Opt o_they_bin =
 172     { DO, DONT, WILL, WONT, TELOPT_BINARY, OPTINDEX_THEY_BIN, INACTIVE };
 173
 174 static const struct Opt *const opts[] = {
 175     &o_naws, &o_tspeed, &o_ttype, &o_oenv, &o_nenv, &o_echo,
 176     &o_we_sga, &o_they_sga, &o_we_bin, &o_they_bin, NULL
 177 };
 178
 179 typedef struct telnet_tag {
 180     const struct plug_function_table *fn;
 181     /* the above field _must_ be first in the structure */
 182
 183     Socket s;
 184
 185     void *frontend;
 186     void *ldisc;
 187     int term_width, term_height;
 188
 189     int opt_states[NUM_OPTS];
 190
 191     int echoing, editing;
 192     int activated;
 193     int bufsize;
 194     int in_synch;
 195     int sb_opt, sb_len;
 196     unsigned char *sb_buf;
 197     int sb_size;
 198
 199     enum {
 200         TOP_LEVEL, SEENIAC, SEENWILL, SEENWONT, SEENDO, SEENDONT,
 201             SEENSB, SUBNEGOT, SUBNEG_IAC, SEENCR
 202     } state;
 203
 204     Config cfg;
 205
 206     Pinger pinger;
 207 } *Telnet;
 208
 209 #define TELNET_MAX_BACKLOG 4096
 210
 211 #define SB_DELTA 1024
 212
 213 static void c_write(Telnet telnet, char *buf, int len)
 214 {
 215     int backlog;
 216     backlog = from_backend(telnet->frontend, 0, buf, len);
 217     sk_set_frozen(telnet->s, backlog > TELNET_MAX_BACKLOG);
 218 }
 219
 220 static void log_option(Telnet telnet, char *sender, int cmd, int option)
 221 {
 222     char *buf;
 223     /*
 224      * The strange-looking "<?""?>" below is there to avoid a
 225      * trigraph - a double question mark followed by > maps to a
 226      * closing brace character!
 227      */
 228     buf = dupprintf("%s:\t%s %s", sender,
 229                     (cmd == WILL ? "WILL" : cmd == WONT ? "WONT" :
 230                      cmd == DO ? "DO" : cmd == DONT ? "DONT" : "<?""?>"),
 231                     telopt(option));
 232     logevent(telnet->frontend, buf);
 233     sfree(buf);
 234 }
 235
 236 static void send_opt(Telnet telnet, int cmd, int option)
 237 {
 238     unsigned char b[3];
 239
 240     b[0] = IAC;
 241     b[1] = cmd;
 242     b[2] = option;
 243     telnet->bufsize = sk_write(telnet->s, (char *)b, 3);
 244     log_option(telnet, "client", cmd, option);
 245 }
 246
 247 static void deactivate_option(Telnet telnet, const struct Opt *o)
 248 {
 249     if (telnet->opt_states[o->index] == REQUESTED ||
 250         telnet->opt_states[o->index] == ACTIVE)
 251         send_opt(telnet, o->nsend, o->option);
 252     telnet->opt_states[o->index] = REALLY_INACTIVE;
 253 }
 254
 255 /*
 256  * Generate side effects of enabling or disabling an option.
 257  */
 258 static void option_side_effects(Telnet telnet, const struct Opt *o, int enabled)
 259 {
 260     if (o->option == TELOPT_ECHO && o->send == DO)
 261         telnet->echoing = !enabled;
 262     else if (o->option == TELOPT_SGA && o->send == DO)
 263         telnet->editing = !enabled;
 264     if (telnet->ldisc)                 /* cause ldisc to notice the change */
 265         ldisc_send(telnet->ldisc, NULL, 0, 0);
 266
 267     /* Ensure we get the minimum options */
 268     if (!telnet->activated) {
 269         if (telnet->opt_states[o_echo.index] == INACTIVE) {
 270             telnet->opt_states[o_echo.index] = REQUESTED;
 271             send_opt(telnet, o_echo.send, o_echo.option);
 272         }
 273         if (telnet->opt_states[o_we_sga.index] == INACTIVE) {
 274             telnet->opt_states[o_we_sga.index] = REQUESTED;
 275             send_opt(telnet, o_we_sga.send, o_we_sga.option);
 276         }
 277         if (telnet->opt_states[o_they_sga.index] == INACTIVE) {
 278             telnet->opt_states[o_they_sga.index] = REQUESTED;
 279             send_opt(telnet, o_they_sga.send, o_they_sga.option);
 280         }
 281         telnet->activated = TRUE;
 282     }
 283 }
 284
 285 static void activate_option(Telnet telnet, const struct Opt *o)
 286 {
 287     if (o->send == WILL && o->option == TELOPT_NAWS)
 288         telnet_size(telnet, telnet->term_width, telnet->term_height);
 289     if (o->send == WILL &&
 290         (o->option == TELOPT_NEW_ENVIRON ||
 291          o->option == TELOPT_OLD_ENVIRON)) {
 292         /*
 293          * We may only have one kind of ENVIRON going at a time.
 294          * This is a hack, but who cares.
 295          */
 296         deactivate_option(telnet, o->option ==
 297                           TELOPT_NEW_ENVIRON ? &o_oenv : &o_nenv);
 298     }
 299     option_side_effects(telnet, o, 1);
 300 }
 301
 302 static void refused_option(Telnet telnet, const struct Opt *o)
 303 {
 304     if (o->send == WILL && o->option == TELOPT_NEW_ENVIRON &&
 305         telnet->opt_states[o_oenv.index] == INACTIVE) {
 306         send_opt(telnet, WILL, TELOPT_OLD_ENVIRON);
 307         telnet->opt_states[o_oenv.index] = REQUESTED;
 308     }
 309     option_side_effects(telnet, o, 0);
 310 }
 311
 312 static void proc_rec_opt(Telnet telnet, int cmd, int option)
 313 {
 314     const struct Opt *const *o;
 315
 316     log_option(telnet, "server", cmd, option);
 317     for (o = opts; *o; o++) {
 318         if ((*o)->option == option && (*o)->ack == cmd) {
 319             switch (telnet->opt_states[(*o)->index]) {
 320               case REQUESTED:
 321                 telnet->opt_states[(*o)->index] = ACTIVE;
 322                 activate_option(telnet, *o);
 323                 break;
 324               case ACTIVE:
 325                 break;
 326               case INACTIVE:
 327                 telnet->opt_states[(*o)->index] = ACTIVE;
 328                 send_opt(telnet, (*o)->send, option);
 329                 activate_option(telnet, *o);
 330                 break;
 331               case REALLY_INACTIVE:
 332                 send_opt(telnet, (*o)->nsend, option);
 333                 break;
 334             }
 335             return;
 336         } else if ((*o)->option == option && (*o)->nak == cmd) {
 337             switch (telnet->opt_states[(*o)->index]) {
 338               case REQUESTED:
 339                 telnet->opt_states[(*o)->index] = INACTIVE;
 340                 refused_option(telnet, *o);
 341                 break;
 342               case ACTIVE:
 343                 telnet->opt_states[(*o)->index] = INACTIVE;
 344                 send_opt(telnet, (*o)->nsend, option);
 345                 option_side_effects(telnet, *o, 0);
 346                 break;
 347               case INACTIVE:
 348               case REALLY_INACTIVE:
 349                 break;
 350             }
 351             return;
 352         }
 353     }
 354     /*
 355      * If we reach here, the option was one we weren't prepared to
 356      * cope with. If the request was positive (WILL or DO), we send
 357      * a negative ack to indicate refusal. If the request was
 358      * negative (WONT / DONT), we must do nothing.
 359      */
 360     if (cmd == WILL || cmd == DO)
 361         send_opt(telnet, (cmd == WILL ? DONT : WONT), option);
 362 }
 363
 364 static void process_subneg(Telnet telnet)
 365 {
 366     unsigned char b[2048], *p, *q;
 367     int var, value, n;
 368     char *e;
 369
 370     switch (telnet->sb_opt) {
 371       case TELOPT_TSPEED:
 372         if (telnet->sb_len == 1 && telnet->sb_buf[0] == TELQUAL_SEND) {
 373             char *logbuf;
 374             b[0] = IAC;
 375             b[1] = SB;
 376             b[2] = TELOPT_TSPEED;
 377             b[3] = TELQUAL_IS;
 378             strcpy((char *)(b + 4), telnet->cfg.termspeed);
 379             n = 4 + strlen(telnet->cfg.termspeed);
 380             b[n] = IAC;
 381             b[n + 1] = SE;
 382             telnet->bufsize = sk_write(telnet->s, (char *)b, n + 2);
 383             logevent(telnet->frontend, "server:\tSB TSPEED SEND");
 384             logbuf = dupprintf("client:\tSB TSPEED IS %s", telnet->cfg.termspeed);
 385             logevent(telnet->frontend, logbuf);
 386             sfree(logbuf);
 387         } else
 388             logevent(telnet->frontend, "server:\tSB TSPEED <something weird>");
 389         break;
 390       case TELOPT_TTYPE:
 391         if (telnet->sb_len == 1 && telnet->sb_buf[0] == TELQUAL_SEND) {
 392             char *logbuf;
 393             b[0] = IAC;
 394             b[1] = SB;
 395             b[2] = TELOPT_TTYPE;
 396             b[3] = TELQUAL_IS;
 397             for (n = 0; telnet->cfg.termtype[n]; n++)
 398                 b[n + 4] = (telnet->cfg.termtype[n] >= 'a'
 399                             && telnet->cfg.termtype[n] <=
 400                             'z' ? telnet->cfg.termtype[n] + 'A' -
 401                             'a' : telnet->cfg.termtype[n]);
 402             b[n + 4] = IAC;
 403             b[n + 5] = SE;
 404             telnet->bufsize = sk_write(telnet->s, (char *)b, n + 6);
 405             b[n + 4] = 0;
 406             logevent(telnet->frontend, "server:\tSB TTYPE SEND");
 407             logbuf = dupprintf("client:\tSB TTYPE IS %s", b + 4);
 408             logevent(telnet->frontend, logbuf);
 409             sfree(logbuf);
 410         } else
 411             logevent(telnet->frontend, "server:\tSB TTYPE <something weird>\r\n");
 412         break;
 413       case TELOPT_OLD_ENVIRON:
 414       case TELOPT_NEW_ENVIRON:
 415         p = telnet->sb_buf;
 416         q = p + telnet->sb_len;
 417         if (p < q && *p == TELQUAL_SEND) {
 418             char *logbuf;
 419             p++;
 420             logbuf = dupprintf("server:\tSB %s SEND", telopt(telnet->sb_opt));
 421             logevent(telnet->frontend, logbuf);
 422             sfree(logbuf);
 423             if (telnet->sb_opt == TELOPT_OLD_ENVIRON) {
 424                 if (telnet->cfg.rfc_environ) {
 425                     value = RFC_VALUE;
 426                     var = RFC_VAR;
 427                 } else {
 428                     value = BSD_VALUE;
 429                     var = BSD_VAR;
 430                 }
 431                 /*
 432                  * Try to guess the sense of VAR and VALUE.
 433                  */
 434                 while (p < q) {
 435                     if (*p == RFC_VAR) {
 436                         value = RFC_VALUE;
 437                         var = RFC_VAR;
 438                     } else if (*p == BSD_VAR) {
 439                         value = BSD_VALUE;
 440                         var = BSD_VAR;
 441                     }
 442                     p++;
 443                 }
 444             } else {
 445                 /*
 446                  * With NEW_ENVIRON, the sense of VAR and VALUE
 447                  * isn't in doubt.
 448                  */
 449                 value = RFC_VALUE;
 450                 var = RFC_VAR;
 451             }
 452             b[0] = IAC;
 453             b[1] = SB;
 454             b[2] = telnet->sb_opt;
 455             b[3] = TELQUAL_IS;
 456             n = 4;
 457             e = telnet->cfg.environmt;
 458             while (*e) {
 459                 b[n++] = var;
 460                 while (*e && *e != '\t')
 461                     b[n++] = *e++;
 462                 if (*e == '\t')
 463                     e++;
 464                 b[n++] = value;
 465                 while (*e)
 466                     b[n++] = *e++;
 467                 e++;
 468             }
 469             {
 470                 char user[sizeof(telnet->cfg.username)];
 471                 (void) get_remote_username(&telnet->cfg, user, sizeof(user));
 472                 if (*user) {
 473                     b[n++] = var;
 474                     b[n++] = 'U';
 475                     b[n++] = 'S';
 476                     b[n++] = 'E';
 477                     b[n++] = 'R';
 478                     b[n++] = value;
 479                     e = user;
 480                     while (*e)
 481                         b[n++] = *e++;
 482                 }
 483                 b[n++] = IAC;
 484                 b[n++] = SE;
 485                 telnet->bufsize = sk_write(telnet->s, (char *)b, n);
 486                 logbuf = dupprintf("client:\tSB %s IS %s%s%s%s",
 487                                    telopt(telnet->sb_opt),
 488                                    *user ? "USER=" : "",
 489                                    user,
 490                                    *user ? " " : "",
 491                                    n == 6 ? "<nothing>" :
 492                                    (*telnet->cfg.environmt ? "<stuff>" : ""));
 493                 logevent(telnet->frontend, logbuf);
 494                 sfree(logbuf);
 495             }
 496         }
 497         break;
 498     }
 499 }
 500
 501 static void do_telnet_read(Telnet telnet, char *buf, int len)
 502 {
 503     char *outbuf = NULL;
 504     int outbuflen = 0, outbufsize = 0;
 505
 506 #define ADDTOBUF(c) do { \
 507     if (outbuflen >= outbufsize) { \
 508         outbufsize = outbuflen + 256; \
 509         outbuf = sresize(outbuf, outbufsize, char); \
 510     } \
 511     outbuf[outbuflen++] = (c); \
 512 } while (0)
 513
 514     while (len--) {
 515         int c = (unsigned char) *buf++;
 516
 517         switch (telnet->state) {
 518           case TOP_LEVEL:
 519           case SEENCR:
 520             if (c == NUL && telnet->state == SEENCR)
 521                 telnet->state = TOP_LEVEL;
 522             else if (c == IAC)
 523                 telnet->state = SEENIAC;
 524             else {
 525                 if (!telnet->in_synch)
 526                     ADDTOBUF(c);
 527
 528 #if 1
 529                 /* I can't get the F***ing winsock to insert the urgent IAC
 530                  * into the right position! Even with SO_OOBINLINE it gives
 531                  * it to recv too soon. And of course the DM byte (that
 532                  * arrives in the same packet!) appears several K later!!
 533                  *
 534                  * Oh well, we do get the DM in the right place so I'll
 535                  * just stop hiding on the next 0xf2 and hope for the best.
 536                  */
 537                 else if (c == DM)
 538                     telnet->in_synch = 0;
 539 #endif
 540                 if (c == CR && telnet->opt_states[o_they_bin.index] != ACTIVE)
 541                     telnet->state = SEENCR;
 542                 else
 543                     telnet->state = TOP_LEVEL;
 544             }
 545             break;
 546           case SEENIAC:
 547             if (c == DO)
 548                 telnet->state = SEENDO;
 549             else if (c == DONT)
 550                 telnet->state = SEENDONT;
 551             else if (c == WILL)
 552                 telnet->state = SEENWILL;
 553             else if (c == WONT)
 554                 telnet->state = SEENWONT;
 555             else if (c == SB)
 556                 telnet->state = SEENSB;
 557             else if (c == DM) {
 558                 telnet->in_synch = 0;
 559                 telnet->state = TOP_LEVEL;
 560             } else {
 561                 /* ignore everything else; print it if it's IAC */
 562                 if (c == IAC) {
 563                     ADDTOBUF(c);
 564                 }
 565                 telnet->state = TOP_LEVEL;
 566             }
 567             break;
 568           case SEENWILL:
 569             proc_rec_opt(telnet, WILL, c);
 570             telnet->state = TOP_LEVEL;
 571             break;
 572           case SEENWONT:
 573             proc_rec_opt(telnet, WONT, c);
 574             telnet->state = TOP_LEVEL;
 575             break;
 576           case SEENDO:
 577             proc_rec_opt(telnet, DO, c);
 578             telnet->state = TOP_LEVEL;
 579             break;
 580           case SEENDONT:
 581             proc_rec_opt(telnet, DONT, c);
 582             telnet->state = TOP_LEVEL;
 583             break;
 584           case SEENSB:
 585             telnet->sb_opt = c;
 586             telnet->sb_len = 0;
 587             telnet->state = SUBNEGOT;
 588             break;
 589           case SUBNEGOT:
 590             if (c == IAC)
 591                 telnet->state = SUBNEG_IAC;
 592             else {
 593               subneg_addchar:
 594                 if (telnet->sb_len >= telnet->sb_size) {
 595                     telnet->sb_size += SB_DELTA;
 596                     telnet->sb_buf = sresize(telnet->sb_buf, telnet->sb_size,
 597                                              unsigned char);
 598                 }
 599                 telnet->sb_buf[telnet->sb_len++] = c;
 600                 telnet->state = SUBNEGOT;       /* in case we came here by goto */
 601             }
 602             break;
 603           case SUBNEG_IAC:
 604             if (c != SE)
 605                 goto subneg_addchar;   /* yes, it's a hack, I know, but... */
 606             else {
 607                 process_subneg(telnet);
 608                 telnet->state = TOP_LEVEL;
 609             }
 610             break;
 611         }
 612     }
 613
 614     if (outbuflen)
 615         c_write(telnet, outbuf, outbuflen);
 616     sfree(outbuf);
 617 }
 618
 619 static void telnet_log(Plug plug, int type, SockAddr addr, int port,
 620                        const char *error_msg, int error_code)
 621 {
 622     Telnet telnet = (Telnet) plug;
 623     char addrbuf[256], *msg;
 624
 625     sk_getaddr(addr, addrbuf, lenof(addrbuf));
 626
 627     if (type == 0)
 628         msg = dupprintf("Connecting to %s port %d", addrbuf, port);
 629     else
 630         msg = dupprintf("Failed to connect to %s: %s", addrbuf, error_msg);
 631
 632     logevent(telnet->frontend, msg);
 633 }
 634
 635 static int telnet_closing(Plug plug, const char *error_msg, int error_code,
 636                           int calling_back)
 637 {
 638     Telnet telnet = (Telnet) plug;
 639
 640     if (telnet->s) {
 641         sk_close(telnet->s);
 642         telnet->s = NULL;
 643         notify_remote_exit(telnet->frontend);
 644     }
 645     if (error_msg) {
 646         logevent(telnet->frontend, error_msg);
 647         connection_fatal(telnet->frontend, "%s", error_msg);
 648     }
 649     /* Otherwise, the remote side closed the connection normally. */
 650     return 0;
 651 }
 652
 653 static int telnet_receive(Plug plug, int urgent, char *data, int len)
 654 {
 655     Telnet telnet = (Telnet) plug;
 656     if (urgent)
 657         telnet->in_synch = TRUE;
 658     do_telnet_read(telnet, data, len);
 659     return 1;
 660 }
 661
 662 static void telnet_sent(Plug plug, int bufsize)
 663 {
 664     Telnet telnet = (Telnet) plug;
 665     telnet->bufsize = bufsize;
 666 }
 667
 668 /*
 669  * Called to set up the Telnet connection.
 670  *
 671  * Returns an error message, or NULL on success.
 672  *
 673  * Also places the canonical host name into `realhost'. It must be
 674  * freed by the caller.
 675  */
 676 static const char *telnet_init(void *frontend_handle, void **backend_handle,
 677                                Config *cfg,
 678                                char *host, int port, char **realhost,
 679                                int nodelay, int keepalive)
 680 {
 681     static const struct plug_function_table fn_table = {
 682         telnet_log,
 683         telnet_closing,
 684         telnet_receive,
 685         telnet_sent
 686     };
 687     SockAddr addr;
 688     const char *err;
 689     Telnet telnet;
 690
 691     telnet = snew(struct telnet_tag);
 692     telnet->fn = &fn_table;
 693     telnet->cfg = *cfg;                /* STRUCTURE COPY */
 694     telnet->s = NULL;
 695     telnet->echoing = TRUE;
 696     telnet->editing = TRUE;
 697     telnet->activated = FALSE;
 698     telnet->sb_buf = NULL;
 699     telnet->sb_size = 0;
 700     telnet->frontend = frontend_handle;
 701     telnet->term_width = telnet->cfg.width;
 702     telnet->term_height = telnet->cfg.height;
 703     telnet->state = TOP_LEVEL;
 704     telnet->ldisc = NULL;
 705     telnet->pinger = NULL;
 706     *backend_handle = telnet;
 707
 708     /*
 709      * Try to find host.
 710      */
 711     {
 712         char *buf;
 713         buf = dupprintf("Looking up host \"%s\"%s", host,
 714                         (cfg->addressfamily == ADDRTYPE_IPV4 ? " (IPv4)" :
 715                          (cfg->addressfamily == ADDRTYPE_IPV6 ? " (IPv6)" :
 716                           "")));
 717         logevent(telnet->frontend, buf);
 718         sfree(buf);
 719     }
 720     addr = name_lookup(host, port, realhost, &telnet->cfg, cfg->addressfamily);
 721     if ((err = sk_addr_error(addr)) != NULL) {
 722         sk_addr_free(addr);
 723         return err;
 724     }
 725
 726     if (port < 0)
 727         port = 23;                     /* default telnet port */
 728
 729     /*
 730      * Open socket.
 731      */
 732     telnet->s = new_connection(addr, *realhost, port, 0, 1,
 733                                nodelay, keepalive, (Plug) telnet, &telnet->cfg);
 734     if ((err = sk_socket_error(telnet->s)) != NULL)
 735         return err;
 736
 737     telnet->pinger = pinger_new(&telnet->cfg, &telnet_backend, telnet);
 738
 739     /*
 740      * Initialise option states.
 741      */
 742     if (telnet->cfg.passive_telnet) {
 743         const struct Opt *const *o;
 744
 745         for (o = opts; *o; o++)
 746             telnet->opt_states[(*o)->index] = INACTIVE;
 747     } else {
 748         const struct Opt *const *o;
 749
 750         for (o = opts; *o; o++) {
 751             telnet->opt_states[(*o)->index] = (*o)->initial_state;
 752             if (telnet->opt_states[(*o)->index] == REQUESTED)
 753                 send_opt(telnet, (*o)->send, (*o)->option);
 754         }
 755         telnet->activated = TRUE;
 756     }
 757
 758     /*
 759      * Set up SYNCH state.
 760      */
 761     telnet->in_synch = FALSE;
 762
 763     /*
 764      * We can send special commands from the start.
 765      */
 766     update_specials_menu(telnet->frontend);
 767
 768     /*
 769      * loghost overrides realhost, if specified.
 770      */
 771     if (*telnet->cfg.loghost) {
 772         char *colon;
 773
 774         sfree(*realhost);
 775         *realhost = dupstr(telnet->cfg.loghost);
 776         colon = strrchr(*realhost, ':');
 777         if (colon) {
 778             /*
 779              * FIXME: if we ever update this aspect of ssh.c for
 780              * IPv6 literal management, this should change in line
 781              * with it.
 782              */
 783             *colon++ = '\0';
 784         }
 785     }
 786
 787     return NULL;
 788 }
 789
 790 static void telnet_free(void *handle)
 791 {
 792     Telnet telnet = (Telnet) handle;
 793
 794     sfree(telnet->sb_buf);
 795     if (telnet->s)
 796         sk_close(telnet->s);
 797     if (telnet->pinger)
 798         pinger_free(telnet->pinger);
 799     sfree(telnet);
 800 }
 801 /*
 802  * Reconfigure the Telnet backend. There's no immediate action
 803  * necessary, in this backend: we just save the fresh config for
 804  * any subsequent negotiations.
 805  */
 806 static void telnet_reconfig(void *handle, Config *cfg)
 807 {
 808     Telnet telnet = (Telnet) handle;
 809     pinger_reconfig(telnet->pinger, &telnet->cfg, cfg);
 810     telnet->cfg = *cfg;                /* STRUCTURE COPY */
 811 }
 812
 813 /*
 814  * Called to send data down the Telnet connection.
 815  */
 816 static int telnet_send(void *handle, char *buf, int len)
 817 {
 818     Telnet telnet = (Telnet) handle;
 819     unsigned char *p, *end;
 820     static const unsigned char iac[2] = { IAC, IAC };
 821     static const unsigned char cr[2] = { CR, NUL };
 822 #if 0
 823     static const unsigned char nl[2] = { CR, LF };
 824 #endif
 825
 826     if (telnet->s == NULL)
 827         return 0;
 828
 829     p = (unsigned char *)buf;
 830     end = (unsigned char *)(buf + len);
 831     while (p < end) {
 832         unsigned char *q = p;
 833
 834         while (p < end && iswritable(*p))
 835             p++;
 836         telnet->bufsize = sk_write(telnet->s, (char *)q, p - q);
 837
 838         while (p < end && !iswritable(*p)) {
 839             telnet->bufsize =
 840                 sk_write(telnet->s, (char *)(*p == IAC ? iac : cr), 2);
 841             p++;
 842         }
 843     }
 844
 845     return telnet->bufsize;
 846 }
 847
 848 /*
 849  * Called to query the current socket sendability status.
 850  */
 851 static int telnet_sendbuffer(void *handle)
 852 {
 853     Telnet telnet = (Telnet) handle;
 854     return telnet->bufsize;
 855 }
 856
 857 /*
 858  * Called to set the size of the window from Telnet's POV.
 859  */
 860 static void telnet_size(void *handle, int width, int height)
 861 {
 862     Telnet telnet = (Telnet) handle;
 863     unsigned char b[24];
 864     int n;
 865     char *logbuf;
 866
 867     telnet->term_width = width;
 868     telnet->term_height = height;
 869
 870     if (telnet->s == NULL || telnet->opt_states[o_naws.index] != ACTIVE)
 871         return;
 872     n = 0;
 873     b[n++] = IAC;
 874     b[n++] = SB;
 875     b[n++] = TELOPT_NAWS;
 876     b[n++] = telnet->term_width >> 8;
 877     if (b[n-1] == IAC) b[n++] = IAC;   /* duplicate any IAC byte occurs */
 878     b[n++] = telnet->term_width & 0xFF;
 879     if (b[n-1] == IAC) b[n++] = IAC;   /* duplicate any IAC byte occurs */
 880     b[n++] = telnet->term_height >> 8;
 881     if (b[n-1] == IAC) b[n++] = IAC;   /* duplicate any IAC byte occurs */
 882     b[n++] = telnet->term_height & 0xFF;
 883     if (b[n-1] == IAC) b[n++] = IAC;   /* duplicate any IAC byte occurs */
 884     b[n++] = IAC;
 885     b[n++] = SE;
 886     telnet->bufsize = sk_write(telnet->s, (char *)b, n);
 887     logbuf = dupprintf("client:\tSB NAWS %d,%d",
 888                        telnet->term_width, telnet->term_height);
 889     logevent(telnet->frontend, logbuf);
 890     sfree(logbuf);
 891 }
 892
 893 /*
 894  * Send Telnet special codes.
 895  */
 896 static void telnet_special(void *handle, Telnet_Special code)
 897 {
 898     Telnet telnet = (Telnet) handle;
 899     unsigned char b[2];
 900
 901     if (telnet->s == NULL)
 902         return;
 903
 904     b[0] = IAC;
 905     switch (code) {
 906       case TS_AYT:
 907         b[1] = AYT;
 908         telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
 909         break;
 910       case TS_BRK:
 911         b[1] = BREAK;
 912         telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
 913         break;
 914       case TS_EC:
 915         b[1] = EC;
 916         telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
 917         break;
 918       case TS_EL:
 919         b[1] = EL;
 920         telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
 921         break;
 922       case TS_GA:
 923         b[1] = GA;
 924         telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
 925         break;
 926       case TS_NOP:
 927         b[1] = NOP;
 928         telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
 929         break;
 930       case TS_ABORT:
 931         b[1] = ABORT;
 932         telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
 933         break;
 934       case TS_AO:
 935         b[1] = AO;
 936         telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
 937         break;
 938       case TS_IP:
 939         b[1] = IP;
 940         telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
 941         break;
 942       case TS_SUSP:
 943         b[1] = SUSP;
 944         telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
 945         break;
 946       case TS_EOR:
 947         b[1] = EOR;
 948         telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
 949         break;
 950       case TS_EOF:
 951         b[1] = xEOF;
 952         telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
 953         break;
 954       case TS_EOL:
 955         /* In BINARY mode, CR-LF becomes just CR -
 956          * and without the NUL suffix too. */
 957         if (telnet->opt_states[o_we_bin.index] == ACTIVE)
 958             telnet->bufsize = sk_write(telnet->s, "\r", 1);
 959         else
 960             telnet->bufsize = sk_write(telnet->s, "\r\n", 2);
 961         break;
 962       case TS_SYNCH:
 963         b[1] = DM;
 964         telnet->bufsize = sk_write(telnet->s, (char *)b, 1);
 965         telnet->bufsize = sk_write_oob(telnet->s, (char *)(b + 1), 1);
 966         break;
 967       case TS_RECHO:
 968         if (telnet->opt_states[o_echo.index] == INACTIVE ||
 969             telnet->opt_states[o_echo.index] == REALLY_INACTIVE) {
 970             telnet->opt_states[o_echo.index] = REQUESTED;
 971             send_opt(telnet, o_echo.send, o_echo.option);
 972         }
 973         break;
 974       case TS_LECHO:
 975         if (telnet->opt_states[o_echo.index] == ACTIVE) {
 976             telnet->opt_states[o_echo.index] = REQUESTED;
 977             send_opt(telnet, o_echo.nsend, o_echo.option);
 978         }
 979         break;
 980       case TS_PING:
 981         if (telnet->opt_states[o_they_sga.index] == ACTIVE) {
 982             b[1] = NOP;
 983             telnet->bufsize = sk_write(telnet->s, (char *)b, 2);
 984         }
 985         break;
 986       default:
 987         break;  /* never heard of it */
 988     }
 989 }
 990
 991 static const struct telnet_special *telnet_get_specials(void *handle)
 992 {
 993     static const struct telnet_special specials[] = {
 994         {"Are You There", TS_AYT},
 995         {"Break", TS_BRK},
 996         {"Synch", TS_SYNCH},
 997         {"Erase Character", TS_EC},
 998         {"Erase Line", TS_EL},
 999         {"Go Ahead", TS_GA},
1000         {"No Operation", TS_NOP},
1001         {NULL, TS_SEP},
1002         {"Abort Process", TS_ABORT},
1003         {"Abort Output", TS_AO},
1004         {"Interrupt Process", TS_IP},
1005         {"Suspend Process", TS_SUSP},
1006         {NULL, TS_SEP},
1007         {"End Of Record", TS_EOR},
1008         {"End Of File", TS_EOF},
1009         {NULL, TS_EXITMENU}
1010     };
1011     return specials;
1012 }
1013
1014 static int telnet_connected(void *handle)
1015 {
1016     Telnet telnet = (Telnet) handle;
1017     return telnet->s != NULL;
1018 }
1019
1020 static int telnet_sendok(void *handle)
1021 {
1022     /* Telnet telnet = (Telnet) handle; */
1023     return 1;
1024 }
1025
1026 static void telnet_unthrottle(void *handle, int backlog)
1027 {
1028     Telnet telnet = (Telnet) handle;
1029     sk_set_frozen(telnet->s, backlog > TELNET_MAX_BACKLOG);
1030 }
1031
1032 static int telnet_ldisc(void *handle, int option)
1033 {
1034     Telnet telnet = (Telnet) handle;
1035     if (option == LD_ECHO)
1036         return telnet->echoing;
1037     if (option == LD_EDIT)
1038         return telnet->editing;
1039     return FALSE;
1040 }
1041
1042 static void telnet_provide_ldisc(void *handle, void *ldisc)
1043 {
1044     Telnet telnet = (Telnet) handle;
1045     telnet->ldisc = ldisc;
1046 }
1047
1048 static void telnet_provide_logctx(void *handle, void *logctx)
1049 {
1050     /* This is a stub. */
1051 }
1052
1053 static int telnet_exitcode(void *handle)
1054 {
1055     Telnet telnet = (Telnet) handle;
1056     if (telnet->s != NULL)
1057         return -1;                     /* still connected */
1058     else
1059         /* Telnet doesn't transmit exit codes back to the client */
1060         return 0;
1061 }
1062
1063 /*
1064  * cfg_info for Telnet does nothing at all.
1065  */
1066 static int telnet_cfg_info(void *handle)
1067 {
1068     return 0;
1069 }
1070
1071 Backend telnet_backend = {
1072     telnet_init,
1073     telnet_free,
1074     telnet_reconfig,
1075     telnet_send,
1076     telnet_sendbuffer,
1077     telnet_size,
1078     telnet_special,
1079     telnet_get_specials,
1080     telnet_connected,
1081     telnet_exitcode,
1082     telnet_sendok,
1083     telnet_ldisc,
1084     telnet_provide_ldisc,
1085     telnet_provide_logctx,
1086     telnet_unthrottle,
1087     telnet_cfg_info,
1088     "telnet",
1089     PROT_TELNET,
1090     23
1091 };