git.distorted.org.uk Git - u/mdw/putty/blob - telnet.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3
   4 #include "putty.h"
   5
   6 #ifndef FALSE
   7 #define FALSE 0
   8 #endif
   9 #ifndef TRUE
  10 #define TRUE 1
  11 #endif
  12
  13 #define IAC     255                    /* interpret as command: */
  14 #define DONT    254                    /* you are not to use option */
  15 #define DO      253                    /* please, you use option */
  16 #define WONT    252                    /* I won't use option */
  17 #define WILL    251                    /* I will use option */
  18 #define SB      250                    /* interpret as subnegotiation */
  19 #define SE      240                    /* end sub negotiation */
  20
  21 #define GA      249                    /* you may reverse the line */
  22 #define EL      248                    /* erase the current line */
  23 #define EC      247                    /* erase the current character */
  24 #define AYT     246                    /* are you there */
  25 #define AO      245                    /* abort output--but let prog finish */
  26 #define IP      244                    /* interrupt process--permanently */
  27 #define BREAK   243                    /* break */
  28 #define DM      242                    /* data mark--for connect. cleaning */
  29 #define NOP     241                    /* nop */
  30 #define EOR     239                    /* end of record (transparent mode) */
  31 #define ABORT   238                    /* Abort process */
  32 #define SUSP    237                    /* Suspend process */
  33 #define xEOF    236                    /* End of file: EOF is already used... */
  34
  35 #define TELOPT_BINARY   0              /* 8-bit data path */
  36 #define TELOPT_ECHO     1              /* echo */
  37 #define TELOPT_RCP      2              /* prepare to reconnect */
  38 #define TELOPT_SGA      3              /* suppress go ahead */
  39 #define TELOPT_NAMS     4              /* approximate message size */
  40 #define TELOPT_STATUS   5              /* give status */
  41 #define TELOPT_TM       6              /* timing mark */
  42 #define TELOPT_RCTE     7              /* remote controlled transmission and echo */
  43 #define TELOPT_NAOL     8              /* negotiate about output line width */
  44 #define TELOPT_NAOP     9              /* negotiate about output page size */
  45 #define TELOPT_NAOCRD   10             /* negotiate about CR disposition */
  46 #define TELOPT_NAOHTS   11             /* negotiate about horizontal tabstops */
  47 #define TELOPT_NAOHTD   12             /* negotiate about horizontal tab disposition */
  48 #define TELOPT_NAOFFD   13             /* negotiate about formfeed disposition */
  49 #define TELOPT_NAOVTS   14             /* negotiate about vertical tab stops */
  50 #define TELOPT_NAOVTD   15             /* negotiate about vertical tab disposition */
  51 #define TELOPT_NAOLFD   16             /* negotiate about output LF disposition */
  52 #define TELOPT_XASCII   17             /* extended ascic character set */
  53 #define TELOPT_LOGOUT   18             /* force logout */
  54 #define TELOPT_BM       19             /* byte macro */
  55 #define TELOPT_DET      20             /* data entry terminal */
  56 #define TELOPT_SUPDUP   21             /* supdup protocol */
  57 #define TELOPT_SUPDUPOUTPUT 22         /* supdup output */
  58 #define TELOPT_SNDLOC   23             /* send location */
  59 #define TELOPT_TTYPE    24             /* terminal type */
  60 #define TELOPT_EOR      25             /* end or record */
  61 #define TELOPT_TUID     26             /* TACACS user identification */
  62 #define TELOPT_OUTMRK   27             /* output marking */
  63 #define TELOPT_TTYLOC   28             /* terminal location number */
  64 #define TELOPT_3270REGIME 29           /* 3270 regime */
  65 #define TELOPT_X3PAD    30             /* X.3 PAD */
  66 #define TELOPT_NAWS     31             /* window size */
  67 #define TELOPT_TSPEED   32             /* terminal speed */
  68 #define TELOPT_LFLOW    33             /* remote flow control */
  69 #define TELOPT_LINEMODE 34             /* Linemode option */
  70 #define TELOPT_XDISPLOC 35             /* X Display Location */
  71 #define TELOPT_OLD_ENVIRON 36          /* Old - Environment variables */
  72 #define TELOPT_AUTHENTICATION 37       /* Authenticate */
  73 #define TELOPT_ENCRYPT  38             /* Encryption option */
  74 #define TELOPT_NEW_ENVIRON 39          /* New - Environment variables */
  75 #define TELOPT_EXOPL    255            /* extended-options-list */
  76
  77 #define TELQUAL_IS      0              /* option is... */
  78 #define TELQUAL_SEND    1              /* send option */
  79 #define TELQUAL_INFO    2              /* ENVIRON: informational version of IS */
  80 #define BSD_VAR 1
  81 #define BSD_VALUE 0
  82 #define RFC_VAR 0
  83 #define RFC_VALUE 1
  84
  85 #define CR 13
  86 #define LF 10
  87 #define NUL 0
  88
  89 #define iswritable(x) ( (x) != IAC && (x) != CR )
  90
  91 static char *telopt(int opt)
  92 {
  93 #define i(x) if (opt == TELOPT_ ## x) return #x;
  94     i(BINARY);
  95     i(ECHO);
  96     i(RCP);
  97     i(SGA);
  98     i(NAMS);
  99     i(STATUS);
 100     i(TM);
 101     i(RCTE);
 102     i(NAOL);
 103     i(NAOP);
 104     i(NAOCRD);
 105     i(NAOHTS);
 106     i(NAOHTD);
 107     i(NAOFFD);
 108     i(NAOVTS);
 109     i(NAOVTD);
 110     i(NAOLFD);
 111     i(XASCII);
 112     i(LOGOUT);
 113     i(BM);
 114     i(DET);
 115     i(SUPDUP);
 116     i(SUPDUPOUTPUT);
 117     i(SNDLOC);
 118     i(TTYPE);
 119     i(EOR);
 120     i(TUID);
 121     i(OUTMRK);
 122     i(TTYLOC);
 123     i(X3PAD);
 124     i(NAWS);
 125     i(TSPEED);
 126     i(LFLOW);
 127     i(LINEMODE);
 128     i(XDISPLOC);
 129     i(OLD_ENVIRON);
 130     i(AUTHENTICATION);
 131     i(ENCRYPT);
 132     i(NEW_ENVIRON);
 133     i(EXOPL);
 134 #undef i
 135     return "<unknown>";
 136 }
 137
 138 static void telnet_size(void *handle, int width, int height);
 139
 140 struct Opt {
 141     int send;                          /* what we initially send */
 142     int nsend;                         /* -ve send if requested to stop it */
 143     int ack, nak;                      /* +ve and -ve acknowledgements */
 144     int option;                        /* the option code */
 145     int index;                         /* index into telnet->opt_states[] */
 146     enum {
 147         REQUESTED, ACTIVE, INACTIVE, REALLY_INACTIVE
 148     } initial_state;
 149 };
 150
 151 enum {
 152     OPTINDEX_NAWS,
 153     OPTINDEX_TSPEED,
 154     OPTINDEX_TTYPE,
 155     OPTINDEX_OENV,
 156     OPTINDEX_NENV,
 157     OPTINDEX_ECHO,
 158     OPTINDEX_WE_SGA,
 159     OPTINDEX_THEY_SGA,
 160     NUM_OPTS
 161 };
 162
 163 static const struct Opt o_naws =
 164     { WILL, WONT, DO, DONT, TELOPT_NAWS, OPTINDEX_NAWS, REQUESTED };
 165 static const struct Opt o_tspeed =
 166     { WILL, WONT, DO, DONT, TELOPT_TSPEED, OPTINDEX_TSPEED, REQUESTED };
 167 static const struct Opt o_ttype =
 168     { WILL, WONT, DO, DONT, TELOPT_TTYPE, OPTINDEX_TTYPE, REQUESTED };
 169 static const struct Opt o_oenv = { WILL, WONT, DO, DONT, TELOPT_OLD_ENVIRON,
 170     OPTINDEX_OENV, INACTIVE
 171 };
 172 static const struct Opt o_nenv = { WILL, WONT, DO, DONT, TELOPT_NEW_ENVIRON,
 173     OPTINDEX_NENV, REQUESTED
 174 };
 175 static const struct Opt o_echo =
 176     { DO, DONT, WILL, WONT, TELOPT_ECHO, OPTINDEX_ECHO, REQUESTED };
 177 static const struct Opt o_we_sga =
 178     { WILL, WONT, DO, DONT, TELOPT_SGA, OPTINDEX_WE_SGA, REQUESTED };
 179 static const struct Opt o_they_sga =
 180     { DO, DONT, WILL, WONT, TELOPT_SGA, OPTINDEX_THEY_SGA, REQUESTED };
 181
 182 static const struct Opt *const opts[] = {
 183     &o_naws, &o_tspeed, &o_ttype, &o_oenv, &o_nenv, &o_echo,
 184     &o_we_sga, &o_they_sga, NULL
 185 };
 186
 187 typedef struct telnet_tag {
 188     const struct plug_function_table *fn;
 189     /* the above field _must_ be first in the structure */
 190
 191     Socket s;
 192
 193     void *frontend;
 194     void *ldisc;
 195     int term_width, term_height;
 196
 197     int opt_states[NUM_OPTS];
 198
 199     int echoing, editing;
 200     int activated;
 201     int bufsize;
 202     int in_synch;
 203     int sb_opt, sb_len;
 204     char *sb_buf;
 205     int sb_size;
 206
 207     enum {
 208         TOP_LEVEL, SEENIAC, SEENWILL, SEENWONT, SEENDO, SEENDONT,
 209             SEENSB, SUBNEGOT, SUBNEG_IAC, SEENCR
 210     } state;
 211
 212 } *Telnet;
 213
 214 #define TELNET_MAX_BACKLOG 4096
 215
 216 #define SB_DELTA 1024
 217
 218 static void c_write1(Telnet telnet, int c)
 219 {
 220     int backlog;
 221     char cc = (char) c;
 222     backlog = from_backend(telnet->frontend, 0, &cc, 1);
 223     sk_set_frozen(telnet->s, backlog > TELNET_MAX_BACKLOG);
 224 }
 225
 226 static void log_option(Telnet telnet, char *sender, int cmd, int option)
 227 {
 228     char *buf;
 229     /*
 230      * The strange-looking "<?""?>" below is there to avoid a
 231      * trigraph - a double question mark followed by > maps to a
 232      * closing brace character!
 233      */
 234     buf = dupprintf("%s:\t%s %s", sender,
 235                     (cmd == WILL ? "WILL" : cmd == WONT ? "WONT" :
 236                      cmd == DO ? "DO" : cmd == DONT ? "DONT" : "<?""?>"),
 237                     telopt(option));
 238     logevent(telnet->frontend, buf);
 239     sfree(buf);
 240 }
 241
 242 static void send_opt(Telnet telnet, int cmd, int option)
 243 {
 244     unsigned char b[3];
 245
 246     b[0] = IAC;
 247     b[1] = cmd;
 248     b[2] = option;
 249     telnet->bufsize = sk_write(telnet->s, b, 3);
 250     log_option(telnet, "client", cmd, option);
 251 }
 252
 253 static void deactivate_option(Telnet telnet, const struct Opt *o)
 254 {
 255     if (telnet->opt_states[o->index] == REQUESTED ||
 256         telnet->opt_states[o->index] == ACTIVE)
 257         send_opt(telnet, o->nsend, o->option);
 258     telnet->opt_states[o->index] = REALLY_INACTIVE;
 259 }
 260
 261 /*
 262  * Generate side effects of enabling or disabling an option.
 263  */
 264 static void option_side_effects(Telnet telnet, const struct Opt *o, int enabled)
 265 {
 266     if (o->option == TELOPT_ECHO && o->send == DO)
 267         telnet->echoing = !enabled;
 268     else if (o->option == TELOPT_SGA && o->send == DO)
 269         telnet->editing = !enabled;
 270     if (telnet->ldisc)                 /* cause ldisc to notice the change */
 271         ldisc_send(telnet->ldisc, NULL, 0, 0);
 272
 273     /* Ensure we get the minimum options */
 274     if (!telnet->activated) {
 275         if (telnet->opt_states[o_echo.index] == INACTIVE) {
 276             telnet->opt_states[o_echo.index] = REQUESTED;
 277             send_opt(telnet, o_echo.send, o_echo.option);
 278         }
 279         if (telnet->opt_states[o_we_sga.index] == INACTIVE) {
 280             telnet->opt_states[o_we_sga.index] = REQUESTED;
 281             send_opt(telnet, o_we_sga.send, o_we_sga.option);
 282         }
 283         if (telnet->opt_states[o_they_sga.index] == INACTIVE) {
 284             telnet->opt_states[o_they_sga.index] = REQUESTED;
 285             send_opt(telnet, o_they_sga.send, o_they_sga.option);
 286         }
 287         telnet->activated = TRUE;
 288     }
 289 }
 290
 291 static void activate_option(Telnet telnet, const struct Opt *o)
 292 {
 293     if (o->send == WILL && o->option == TELOPT_NAWS)
 294         telnet_size(telnet, telnet->term_width, telnet->term_height);
 295     if (o->send == WILL &&
 296         (o->option == TELOPT_NEW_ENVIRON ||
 297          o->option == TELOPT_OLD_ENVIRON)) {
 298         /*
 299          * We may only have one kind of ENVIRON going at a time.
 300          * This is a hack, but who cares.
 301          */
 302         deactivate_option(telnet, o->option ==
 303                           TELOPT_NEW_ENVIRON ? &o_oenv : &o_nenv);
 304     }
 305     option_side_effects(telnet, o, 1);
 306 }
 307
 308 static void refused_option(Telnet telnet, const struct Opt *o)
 309 {
 310     if (o->send == WILL && o->option == TELOPT_NEW_ENVIRON &&
 311         telnet->opt_states[o_oenv.index] == INACTIVE) {
 312         send_opt(telnet, WILL, TELOPT_OLD_ENVIRON);
 313         telnet->opt_states[o_oenv.index] = REQUESTED;
 314     }
 315     option_side_effects(telnet, o, 0);
 316 }
 317
 318 static void proc_rec_opt(Telnet telnet, int cmd, int option)
 319 {
 320     const struct Opt *const *o;
 321
 322     log_option(telnet, "server", cmd, option);
 323     for (o = opts; *o; o++) {
 324         if ((*o)->option == option && (*o)->ack == cmd) {
 325             switch (telnet->opt_states[(*o)->index]) {
 326               case REQUESTED:
 327                 telnet->opt_states[(*o)->index] = ACTIVE;
 328                 activate_option(telnet, *o);
 329                 break;
 330               case ACTIVE:
 331                 break;
 332               case INACTIVE:
 333                 telnet->opt_states[(*o)->index] = ACTIVE;
 334                 send_opt(telnet, (*o)->send, option);
 335                 activate_option(telnet, *o);
 336                 break;
 337               case REALLY_INACTIVE:
 338                 send_opt(telnet, (*o)->nsend, option);
 339                 break;
 340             }
 341             return;
 342         } else if ((*o)->option == option && (*o)->nak == cmd) {
 343             switch (telnet->opt_states[(*o)->index]) {
 344               case REQUESTED:
 345                 telnet->opt_states[(*o)->index] = INACTIVE;
 346                 refused_option(telnet, *o);
 347                 break;
 348               case ACTIVE:
 349                 telnet->opt_states[(*o)->index] = INACTIVE;
 350                 send_opt(telnet, (*o)->nsend, option);
 351                 option_side_effects(telnet, *o, 0);
 352                 break;
 353               case INACTIVE:
 354               case REALLY_INACTIVE:
 355                 break;
 356             }
 357             return;
 358         }
 359     }
 360     /*
 361      * If we reach here, the option was one we weren't prepared to
 362      * cope with. So send a negative ack.
 363      */
 364     send_opt(telnet, (cmd == WILL ? DONT : WONT), option);
 365 }
 366
 367 static void process_subneg(Telnet telnet)
 368 {
 369     unsigned char b[2048], *p, *q;
 370     int var, value, n;
 371     char *e;
 372
 373     switch (telnet->sb_opt) {
 374       case TELOPT_TSPEED:
 375         if (telnet->sb_len == 1 && telnet->sb_buf[0] == TELQUAL_SEND) {
 376             char *logbuf;
 377             b[0] = IAC;
 378             b[1] = SB;
 379             b[2] = TELOPT_TSPEED;
 380             b[3] = TELQUAL_IS;
 381             strcpy(b + 4, cfg.termspeed);
 382             n = 4 + strlen(cfg.termspeed);
 383             b[n] = IAC;
 384             b[n + 1] = SE;
 385             telnet->bufsize = sk_write(telnet->s, b, n + 2);
 386             logevent(telnet->frontend, "server:\tSB TSPEED SEND");
 387             logbuf = dupprintf("client:\tSB TSPEED IS %s", cfg.termspeed);
 388             logevent(telnet->frontend, logbuf);
 389             sfree(logbuf);
 390         } else
 391             logevent(telnet->frontend, "server:\tSB TSPEED <something weird>");
 392         break;
 393       case TELOPT_TTYPE:
 394         if (telnet->sb_len == 1 && telnet->sb_buf[0] == TELQUAL_SEND) {
 395             char *logbuf;
 396             b[0] = IAC;
 397             b[1] = SB;
 398             b[2] = TELOPT_TTYPE;
 399             b[3] = TELQUAL_IS;
 400             for (n = 0; cfg.termtype[n]; n++)
 401                 b[n + 4] = (cfg.termtype[n] >= 'a'
 402                             && cfg.termtype[n] <=
 403                             'z' ? cfg.termtype[n] + 'A' -
 404                             'a' : cfg.termtype[n]);
 405             b[n + 4] = IAC;
 406             b[n + 5] = SE;
 407             telnet->bufsize = sk_write(telnet->s, b, n + 6);
 408             b[n + 4] = 0;
 409             logevent(telnet->frontend, "server:\tSB TTYPE SEND");
 410             logbuf = dupprintf("client:\tSB TTYPE IS %s", b + 4);
 411             logevent(telnet->frontend, logbuf);
 412             sfree(logbuf);
 413         } else
 414             logevent(telnet->frontend, "server:\tSB TTYPE <something weird>\r\n");
 415         break;
 416       case TELOPT_OLD_ENVIRON:
 417       case TELOPT_NEW_ENVIRON:
 418         p = telnet->sb_buf;
 419         q = p + telnet->sb_len;
 420         if (p < q && *p == TELQUAL_SEND) {
 421             char *logbuf;
 422             p++;
 423             logbuf = dupprintf("server:\tSB %s SEND", telopt(telnet->sb_opt));
 424             logevent(telnet->frontend, logbuf);
 425             sfree(logbuf);
 426             if (telnet->sb_opt == TELOPT_OLD_ENVIRON) {
 427                 if (cfg.rfc_environ) {
 428                     value = RFC_VALUE;
 429                     var = RFC_VAR;
 430                 } else {
 431                     value = BSD_VALUE;
 432                     var = BSD_VAR;
 433                 }
 434                 /*
 435                  * Try to guess the sense of VAR and VALUE.
 436                  */
 437                 while (p < q) {
 438                     if (*p == RFC_VAR) {
 439                         value = RFC_VALUE;
 440                         var = RFC_VAR;
 441                     } else if (*p == BSD_VAR) {
 442                         value = BSD_VALUE;
 443                         var = BSD_VAR;
 444                     }
 445                     p++;
 446                 }
 447             } else {
 448                 /*
 449                  * With NEW_ENVIRON, the sense of VAR and VALUE
 450                  * isn't in doubt.
 451                  */
 452                 value = RFC_VALUE;
 453                 var = RFC_VAR;
 454             }
 455             b[0] = IAC;
 456             b[1] = SB;
 457             b[2] = telnet->sb_opt;
 458             b[3] = TELQUAL_IS;
 459             n = 4;
 460             e = cfg.environmt;
 461             while (*e) {
 462                 b[n++] = var;
 463                 while (*e && *e != '\t')
 464                     b[n++] = *e++;
 465                 if (*e == '\t')
 466                     e++;
 467                 b[n++] = value;
 468                 while (*e)
 469                     b[n++] = *e++;
 470                 e++;
 471             }
 472             if (*cfg.username) {
 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 = cfg.username;
 480                 while (*e)
 481                     b[n++] = *e++;
 482             }
 483             b[n++] = IAC;
 484             b[n++] = SE;
 485             telnet->bufsize = sk_write(telnet->s, b, n);
 486             logbuf = dupprintf("client:\tSB %s IS %s", telopt(telnet->sb_opt),
 487                                n == 6 ? "<nothing>" : "<stuff>");
 488             logevent(telnet->frontend, logbuf);
 489             sfree(logbuf);
 490         }
 491         break;
 492     }
 493 }
 494
 495 static void do_telnet_read(Telnet telnet, char *buf, int len)
 496 {
 497
 498     while (len--) {
 499         int c = (unsigned char) *buf++;
 500
 501         switch (telnet->state) {
 502           case TOP_LEVEL:
 503           case SEENCR:
 504             if (c == NUL && telnet->state == SEENCR)
 505                 telnet->state = TOP_LEVEL;
 506             else if (c == IAC)
 507                 telnet->state = SEENIAC;
 508             else {
 509                 if (!telnet->in_synch)
 510                     c_write1(telnet, c);
 511
 512 #if 1
 513                 /* I can't get the F***ing winsock to insert the urgent IAC
 514                  * into the right position! Even with SO_OOBINLINE it gives
 515                  * it to recv too soon. And of course the DM byte (that
 516                  * arrives in the same packet!) appears several K later!!
 517                  *
 518                  * Oh well, we do get the DM in the right place so I'll
 519                  * just stop hiding on the next 0xf2 and hope for the best.
 520                  */
 521                 else if (c == DM)
 522                     telnet->in_synch = 0;
 523 #endif
 524                 if (c == CR)
 525                     telnet->state = SEENCR;
 526                 else
 527                     telnet->state = TOP_LEVEL;
 528             }
 529             break;
 530           case SEENIAC:
 531             if (c == DO)
 532                 telnet->state = SEENDO;
 533             else if (c == DONT)
 534                 telnet->state = SEENDONT;
 535             else if (c == WILL)
 536                 telnet->state = SEENWILL;
 537             else if (c == WONT)
 538                 telnet->state = SEENWONT;
 539             else if (c == SB)
 540                 telnet->state = SEENSB;
 541             else if (c == DM) {
 542                 telnet->in_synch = 0;
 543                 telnet->state = TOP_LEVEL;
 544             } else {
 545                 /* ignore everything else; print it if it's IAC */
 546                 if (c == IAC) {
 547                     c_write1(telnet, c);
 548                 }
 549                 telnet->state = TOP_LEVEL;
 550             }
 551             break;
 552           case SEENWILL:
 553             proc_rec_opt(telnet, WILL, c);
 554             telnet->state = TOP_LEVEL;
 555             break;
 556           case SEENWONT:
 557             proc_rec_opt(telnet, WONT, c);
 558             telnet->state = TOP_LEVEL;
 559             break;
 560           case SEENDO:
 561             proc_rec_opt(telnet, DO, c);
 562             telnet->state = TOP_LEVEL;
 563             break;
 564           case SEENDONT:
 565             proc_rec_opt(telnet, DONT, c);
 566             telnet->state = TOP_LEVEL;
 567             break;
 568           case SEENSB:
 569             telnet->sb_opt = c;
 570             telnet->sb_len = 0;
 571             telnet->state = SUBNEGOT;
 572             break;
 573           case SUBNEGOT:
 574             if (c == IAC)
 575                 telnet->state = SUBNEG_IAC;
 576             else {
 577               subneg_addchar:
 578                 if (telnet->sb_len >= telnet->sb_size) {
 579                     char *newbuf;
 580                     telnet->sb_size += SB_DELTA;
 581                     newbuf = (telnet->sb_buf ?
 582                               srealloc(telnet->sb_buf, telnet->sb_size) :
 583                               smalloc(telnet->sb_size));
 584                     if (newbuf)
 585                         telnet->sb_buf = newbuf;
 586                     else
 587                         telnet->sb_size -= SB_DELTA;
 588                 }
 589                 if (telnet->sb_len < telnet->sb_size)
 590                     telnet->sb_buf[telnet->sb_len++] = c;
 591                 telnet->state = SUBNEGOT;       /* in case we came here by goto */
 592             }
 593             break;
 594           case SUBNEG_IAC:
 595             if (c != SE)
 596                 goto subneg_addchar;   /* yes, it's a hack, I know, but... */
 597             else {
 598                 process_subneg(telnet);
 599                 telnet->state = TOP_LEVEL;
 600             }
 601             break;
 602         }
 603     }
 604 }
 605
 606 static int telnet_closing(Plug plug, char *error_msg, int error_code,
 607                           int calling_back)
 608 {
 609     Telnet telnet = (Telnet) plug;
 610
 611     if (telnet->s) {
 612         sk_close(telnet->s);
 613         telnet->s = NULL;
 614     }
 615     if (error_msg) {
 616         /* A socket error has occurred. */
 617         logevent(telnet->frontend, error_msg);
 618         connection_fatal("%s", error_msg);
 619     }                                  /* Otherwise, the remote side closed the connection normally. */
 620     return 0;
 621 }
 622
 623 static int telnet_receive(Plug plug, int urgent, char *data, int len)
 624 {
 625     Telnet telnet = (Telnet) plug;
 626     if (urgent)
 627         telnet->in_synch = TRUE;
 628     do_telnet_read(telnet, data, len);
 629     return 1;
 630 }
 631
 632 static void telnet_sent(Plug plug, int bufsize)
 633 {
 634     Telnet telnet = (Telnet) plug;
 635     telnet->bufsize = bufsize;
 636 }
 637
 638 /*
 639  * Called to set up the Telnet connection.
 640  *
 641  * Returns an error message, or NULL on success.
 642  *
 643  * Also places the canonical host name into `realhost'. It must be
 644  * freed by the caller.
 645  */
 646 static char *telnet_init(void *frontend_handle, void **backend_handle,
 647                          char *host, int port, char **realhost, int nodelay)
 648 {
 649     static const struct plug_function_table fn_table = {
 650         telnet_closing,
 651         telnet_receive,
 652         telnet_sent
 653     };
 654     SockAddr addr;
 655     char *err;
 656     Telnet telnet;
 657
 658     telnet = smalloc(sizeof(*telnet));
 659     telnet->fn = &fn_table;
 660     telnet->s = NULL;
 661     telnet->echoing = TRUE;
 662     telnet->editing = TRUE;
 663     telnet->activated = FALSE;
 664     telnet->sb_buf = NULL;
 665     telnet->sb_size = 0;
 666     telnet->frontend = frontend_handle;
 667     telnet->term_width = cfg.width;
 668     telnet->term_height = cfg.height;
 669     telnet->state = TOP_LEVEL;
 670     *backend_handle = telnet;
 671
 672     /*
 673      * Try to find host.
 674      */
 675     {
 676         char *buf;
 677         buf = dupprintf("Looking up host \"%s\"", host);
 678         logevent(telnet->frontend, buf);
 679         sfree(buf);
 680     }
 681     addr = name_lookup(host, port, realhost);
 682     if ((err = sk_addr_error(addr)))
 683         return err;
 684
 685     if (port < 0)
 686         port = 23;                     /* default telnet port */
 687
 688     /*
 689      * Open socket.
 690      */
 691     {
 692         char *buf, addrbuf[100];
 693         sk_getaddr(addr, addrbuf, 100);
 694         buf = dupprintf("Connecting to %s port %d", addrbuf, port);
 695         logevent(telnet->frontend, buf);
 696         sfree(buf);
 697     }
 698     telnet->s = new_connection(addr, *realhost, port, 0, 1,
 699                                nodelay, (Plug) telnet);
 700     if ((err = sk_socket_error(telnet->s)))
 701         return err;
 702
 703     sk_addr_free(addr);
 704
 705     /*
 706      * Initialise option states.
 707      */
 708     if (cfg.passive_telnet) {
 709         const struct Opt *const *o;
 710
 711         for (o = opts; *o; o++)
 712             telnet->opt_states[(*o)->index] = INACTIVE;
 713     } else {
 714         const struct Opt *const *o;
 715
 716         for (o = opts; *o; o++) {
 717             telnet->opt_states[(*o)->index] = (*o)->initial_state;
 718             if (telnet->opt_states[(*o)->index] == REQUESTED)
 719                 send_opt(telnet, (*o)->send, (*o)->option);
 720         }
 721         telnet->activated = TRUE;
 722     }
 723
 724     /*
 725      * Set up SYNCH state.
 726      */
 727     telnet->in_synch = FALSE;
 728
 729     return NULL;
 730 }
 731
 732 /*
 733  * Called to send data down the Telnet connection.
 734  */
 735 static int telnet_send(void *handle, char *buf, int len)
 736 {
 737     Telnet telnet = (Telnet) handle;
 738     char *p;
 739     static unsigned char iac[2] = { IAC, IAC };
 740     static unsigned char cr[2] = { CR, NUL };
 741 #if 0
 742     static unsigned char nl[2] = { CR, LF };
 743 #endif
 744
 745     if (telnet->s == NULL)
 746         return 0;
 747
 748     p = buf;
 749     while (p < buf + len) {
 750         char *q = p;
 751
 752         while (p < buf + len && iswritable((unsigned char) *p))
 753             p++;
 754         telnet->bufsize = sk_write(telnet->s, q, p - q);
 755
 756         while (p < buf + len && !iswritable((unsigned char) *p)) {
 757             telnet->bufsize =
 758                 sk_write(telnet->s, (unsigned char) *p == IAC ? iac : cr, 2);
 759             p++;
 760         }
 761     }
 762
 763     return telnet->bufsize;
 764 }
 765
 766 /*
 767  * Called to query the current socket sendability status.
 768  */
 769 static int telnet_sendbuffer(void *handle)
 770 {
 771     Telnet telnet = (Telnet) handle;
 772     return telnet->bufsize;
 773 }
 774
 775 /*
 776  * Called to set the size of the window from Telnet's POV.
 777  */
 778 static void telnet_size(void *handle, int width, int height)
 779 {
 780     Telnet telnet = (Telnet) handle;
 781     unsigned char b[16];
 782     char *logbuf;
 783
 784     telnet->term_width = width;
 785     telnet->term_height = height;
 786
 787     if (telnet->s == NULL || telnet->opt_states[o_naws.index] != ACTIVE)
 788         return;
 789     b[0] = IAC;
 790     b[1] = SB;
 791     b[2] = TELOPT_NAWS;
 792     b[3] = telnet->term_width >> 8;
 793     b[4] = telnet->term_width & 0xFF;
 794     b[5] = telnet->term_height >> 8;
 795     b[6] = telnet->term_height & 0xFF;
 796     b[7] = IAC;
 797     b[8] = SE;
 798     telnet->bufsize = sk_write(telnet->s, b, 9);
 799     logbuf = dupprintf("client:\tSB NAWS %d,%d",
 800                        ((unsigned char) b[3] << 8) + (unsigned char) b[4],
 801                        ((unsigned char) b[5] << 8) + (unsigned char) b[6]);
 802     logevent(telnet->frontend, logbuf);
 803     sfree(logbuf);
 804 }
 805
 806 /*
 807  * Send Telnet special codes.
 808  */
 809 static void telnet_special(void *handle, Telnet_Special code)
 810 {
 811     Telnet telnet = (Telnet) handle;
 812     unsigned char b[2];
 813
 814     if (telnet->s == NULL)
 815         return;
 816
 817     b[0] = IAC;
 818     switch (code) {
 819       case TS_AYT:
 820         b[1] = AYT;
 821         telnet->bufsize = sk_write(telnet->s, b, 2);
 822         break;
 823       case TS_BRK:
 824         b[1] = BREAK;
 825         telnet->bufsize = sk_write(telnet->s, b, 2);
 826         break;
 827       case TS_EC:
 828         b[1] = EC;
 829         telnet->bufsize = sk_write(telnet->s, b, 2);
 830         break;
 831       case TS_EL:
 832         b[1] = EL;
 833         telnet->bufsize = sk_write(telnet->s, b, 2);
 834         break;
 835       case TS_GA:
 836         b[1] = GA;
 837         telnet->bufsize = sk_write(telnet->s, b, 2);
 838         break;
 839       case TS_NOP:
 840         b[1] = NOP;
 841         telnet->bufsize = sk_write(telnet->s, b, 2);
 842         break;
 843       case TS_ABORT:
 844         b[1] = ABORT;
 845         telnet->bufsize = sk_write(telnet->s, b, 2);
 846         break;
 847       case TS_AO:
 848         b[1] = AO;
 849         telnet->bufsize = sk_write(telnet->s, b, 2);
 850         break;
 851       case TS_IP:
 852         b[1] = IP;
 853         telnet->bufsize = sk_write(telnet->s, b, 2);
 854         break;
 855       case TS_SUSP:
 856         b[1] = SUSP;
 857         telnet->bufsize = sk_write(telnet->s, b, 2);
 858         break;
 859       case TS_EOR:
 860         b[1] = EOR;
 861         telnet->bufsize = sk_write(telnet->s, b, 2);
 862         break;
 863       case TS_EOF:
 864         b[1] = xEOF;
 865         telnet->bufsize = sk_write(telnet->s, b, 2);
 866         break;
 867       case TS_EOL:
 868         telnet->bufsize = sk_write(telnet->s, "\r\n", 2);
 869         break;
 870       case TS_SYNCH:
 871         b[1] = DM;
 872         telnet->bufsize = sk_write(telnet->s, b, 1);
 873         telnet->bufsize = sk_write_oob(telnet->s, b + 1, 1);
 874         break;
 875       case TS_RECHO:
 876         if (telnet->opt_states[o_echo.index] == INACTIVE ||
 877             telnet->opt_states[o_echo.index] == REALLY_INACTIVE) {
 878             telnet->opt_states[o_echo.index] = REQUESTED;
 879             send_opt(telnet, o_echo.send, o_echo.option);
 880         }
 881         break;
 882       case TS_LECHO:
 883         if (telnet->opt_states[o_echo.index] == ACTIVE) {
 884             telnet->opt_states[o_echo.index] = REQUESTED;
 885             send_opt(telnet, o_echo.nsend, o_echo.option);
 886         }
 887         break;
 888       case TS_PING:
 889         if (telnet->opt_states[o_they_sga.index] == ACTIVE) {
 890             b[1] = NOP;
 891             telnet->bufsize = sk_write(telnet->s, b, 2);
 892         }
 893         break;
 894     }
 895 }
 896
 897 static Socket telnet_socket(void *handle)
 898 {
 899     Telnet telnet = (Telnet) handle;
 900     return telnet->s;
 901 }
 902
 903 static int telnet_sendok(void *handle)
 904 {
 905     /* Telnet telnet = (Telnet) handle; */
 906     return 1;
 907 }
 908
 909 static void telnet_unthrottle(void *handle, int backlog)
 910 {
 911     Telnet telnet = (Telnet) handle;
 912     sk_set_frozen(telnet->s, backlog > TELNET_MAX_BACKLOG);
 913 }
 914
 915 static int telnet_ldisc(void *handle, int option)
 916 {
 917     Telnet telnet = (Telnet) handle;
 918     if (option == LD_ECHO)
 919         return telnet->echoing;
 920     if (option == LD_EDIT)
 921         return telnet->editing;
 922     return FALSE;
 923 }
 924
 925 static void telnet_provide_ldisc(void *handle, void *ldisc)
 926 {
 927     Telnet telnet = (Telnet) handle;
 928     telnet->ldisc = ldisc;
 929 }
 930
 931 static void telnet_provide_logctx(void *handle, void *logctx)
 932 {
 933     /* This is a stub. */
 934 }
 935
 936 static int telnet_exitcode(void *handle)
 937 {
 938     /* Telnet telnet = (Telnet) handle; */
 939     /* Telnet doesn't transmit exit codes back to the client */
 940     return 0;
 941 }
 942
 943 Backend telnet_backend = {
 944     telnet_init,
 945     telnet_send,
 946     telnet_sendbuffer,
 947     telnet_size,
 948     telnet_special,
 949     telnet_socket,
 950     telnet_exitcode,
 951     telnet_sendok,
 952     telnet_ldisc,
 953     telnet_provide_ldisc,
 954     telnet_provide_logctx,
 955     telnet_unthrottle,
 956     23
 957 };