networking/telnet.c - codeaurora/busybox - Gitiles

 /* vi: set sw=4 ts=4: */
 /*
  * telnet implementation for busybox
  *
  * Author: Tomi Ollila <too@iki.fi>
  * Copyright (C) 1994-2000 by Tomi Ollila
  *
  * Created: Thu Apr  7 13:29:41 1994 too
  * Last modified: Fri Jun  9 14:34:24 2000 too
  *
  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  *
  * HISTORY
  * Revision 3.1  1994/04/17  11:31:54  too
  * initial revision
  * Modified 2000/06/13 for inclusion into BusyBox by Erik Andersen <andersen@codepoet.org>
  * Modified 2001/05/07 to add ability to pass TTYPE to remote host by Jim McQuillan
  * <jam@ltsp.org>
  * Modified 2004/02/11 to add ability to pass the USER variable to remote host
  * by Fernando Silveira <swrh@gmx.net>
  *
  */

 //usage:#if ENABLE_FEATURE_TELNET_AUTOLOGIN
 //usage:#define telnet_trivial_usage
 //usage:       "[-a] [-l USER] HOST [PORT]"
 //usage:#define telnet_full_usage "\n\n"
 //usage:       "Connect to telnet server\n"
 //usage:     "\n	-a	Automatic login with $USER variable"
 //usage:     "\n	-l USER	Automatic login as USER"
 //usage:
 //usage:#else
 //usage:#define telnet_trivial_usage
 //usage:       "HOST [PORT]"
 //usage:#define telnet_full_usage "\n\n"
 //usage:       "Connect to telnet server"
 //usage:#endif

 #include <arpa/telnet.h>
 #include <netinet/in.h>
 #include "libbb.h"

 #ifdef __BIONIC__
 /* should be in arpa/telnet.h */
 # 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 TELOPT_ECHO   1  /* echo */
 # define TELOPT_SGA    3  /* suppress go ahead */
 # define TELOPT_TTYPE 24  /* terminal type */
 # define TELOPT_NAWS  31  /* window size */
 #endif

 #ifdef DOTRACE
 # define TRACE(x, y) do { if (x) printf y; } while (0)
 #else
 # define TRACE(x, y)
 #endif

 enum {
 	DATABUFSIZE = 128,
 	IACBUFSIZE  = 128,

 	CHM_TRY = 0,
 	CHM_ON = 1,
 	CHM_OFF = 2,

 	UF_ECHO = 0x01,
 	UF_SGA = 0x02,

 	TS_NORMAL = 0,
 	TS_COPY = 1,
 	TS_IAC = 2,
 	TS_OPT = 3,
 	TS_SUB1 = 4,
 	TS_SUB2 = 5,
 	TS_CR = 6,
 };

 typedef unsigned char byte;

 enum { netfd = 3 };

 struct globals {
 	int	iaclen; /* could even use byte, but it's a loss on x86 */
 	byte	telstate; /* telnet negotiation state from network input */
 	byte	telwish;  /* DO, DONT, WILL, WONT */
 	byte    charmode;
 	byte    telflags;
 	byte	do_termios;
 #if ENABLE_FEATURE_TELNET_TTYPE
 	char	*ttype;
 #endif
 #if ENABLE_FEATURE_TELNET_AUTOLOGIN
 	const char *autologin;
 #endif
 #if ENABLE_FEATURE_AUTOWIDTH
 	unsigned win_width, win_height;
 #endif
 	/* same buffer used both for network and console read/write */
 	char    buf[DATABUFSIZE];
 	/* buffer to handle telnet negotiations */
 	char    iacbuf[IACBUFSIZE];
 	struct termios termios_def;
 	struct termios termios_raw;
 } FIX_ALIASING;
 #define G (*(struct globals*)&bb_common_bufsiz1)
 #define INIT_G() do { \
 	struct G_sizecheck { \
 		char G_sizecheck[sizeof(G) > COMMON_BUFSIZE ? -1 : 1]; \
 	}; \
 } while (0)


 static void rawmode(void);
 static void cookmode(void);
 static void do_linemode(void);
 static void will_charmode(void);
 static void telopt(byte c);
 static void subneg(byte c);

 static void iac_flush(void)
 {
 	full_write(netfd, G.iacbuf, G.iaclen);
 	G.iaclen = 0;
 }

 static void doexit(int ev) NORETURN;
 static void doexit(int ev)
 {
 	cookmode();
 	exit(ev);
 }

 static void con_escape(void)
 {
 	char b;

 	if (bb_got_signal) /* came from line mode... go raw */
 		rawmode();

 	full_write1_str("\r\nConsole escape. Commands are:\r\n\n"
 			" l	go to line mode\r\n"
 			" c	go to character mode\r\n"
 			" z	suspend telnet\r\n"
 			" e	exit telnet\r\n");

 	if (read(STDIN_FILENO, &b, 1) <= 0)
 		doexit(EXIT_FAILURE);

 	switch (b) {
 	case 'l':
 		if (!bb_got_signal) {
 			do_linemode();
 			goto ret;
 		}
 		break;
 	case 'c':
 		if (bb_got_signal) {
 			will_charmode();
 			goto ret;
 		}
 		break;
 	case 'z':
 		cookmode();
 		kill(0, SIGTSTP);
 		rawmode();
 		break;
 	case 'e':
 		doexit(EXIT_SUCCESS);
 	}

 	full_write1_str("continuing...\r\n");

 	if (bb_got_signal)
 		cookmode();
  ret:
 	bb_got_signal = 0;
 }

 static void handle_net_output(int len)
 {
 	byte outbuf[2 * DATABUFSIZE];
 	byte *dst = outbuf;
 	byte *src = (byte*)G.buf;
 	byte *end = src + len;

 	while (src < end) {
 		byte c = *src++;
 		if (c == 0x1d) {
 			con_escape();
 			return;
 		}
 		*dst = c;
 		if (c == IAC)
 			*++dst = c; /* IAC -> IAC IAC */
 		else
 		if (c == '\r' || c == '\n') {
 			/* Enter key sends '\r' in raw mode and '\n' in cooked one.
 			 *
 			 * See RFC 1123 3.3.1 Telnet End-of-Line Convention.
 			 * Using CR LF instead of other allowed possibilities
 			 * like CR NUL - easier to talk to HTTP/SMTP servers.
 			 */
 			*dst = '\r'; /* Enter -> CR LF */
 			*++dst = '\n';
 		}
 		dst++;
 	}
 	if (dst - outbuf != 0)
 		full_write(netfd, outbuf, dst - outbuf);
 }

 static void handle_net_input(int len)
 {
 	int i;
 	int cstart = 0;

 	for (i = 0; i < len; i++) {
 		byte c = G.buf[i];

 		if (G.telstate == TS_NORMAL) { /* most typical state */
 			if (c == IAC) {
 				cstart = i;
 				G.telstate = TS_IAC;
 			}
 			else if (c == '\r') {
 				cstart = i + 1;
 				G.telstate = TS_CR;
 			}
 			/* No IACs were seen so far, no need to copy
 			 * bytes within G.buf: */
 			continue;
 		}

 		switch (G.telstate) {
 		case TS_CR:
 			/* Prev char was CR. If cur one is NUL, ignore it.
 			 * See RFC 1123 section 3.3.1 for discussion of telnet EOL handling.
 			 */
 			G.telstate = TS_COPY;
 			if (c == '\0')
 				break;
 			/* else: fall through - need to handle CR IAC ... properly */

 		case TS_COPY: /* Prev char was ordinary */
 			/* Similar to NORMAL, but in TS_COPY we need to copy bytes */
 			if (c == IAC)
 				G.telstate = TS_IAC;
 			else
 				G.buf[cstart++] = c;
 			if (c == '\r')
 				G.telstate = TS_CR;
 			break;

 		case TS_IAC: /* Prev char was IAC */
 			if (c == IAC) { /* IAC IAC -> one IAC */
 				G.buf[cstart++] = c;
 				G.telstate = TS_COPY;
 				break;
 			}
 			/* else */
 			switch (c) {
 			case SB:
 				G.telstate = TS_SUB1;
 				break;
 			case DO:
 			case DONT:
 			case WILL:
 			case WONT:
 				G.telwish = c;
 				G.telstate = TS_OPT;
 				break;
 			/* DATA MARK must be added later */
 			default:
 				G.telstate = TS_COPY;
 			}
 			break;

 		case TS_OPT: /* Prev chars were IAC WILL/WONT/DO/DONT */
 			telopt(c);
 			G.telstate = TS_COPY;
 			break;

 		case TS_SUB1: /* Subnegotiation */
 		case TS_SUB2: /* Subnegotiation */
 			subneg(c); /* can change G.telstate */
 			break;
 		}
 	}

 	if (G.telstate != TS_NORMAL) {
 		/* We had some IACs, or CR */
 		if (G.iaclen)
 			iac_flush();
 		if (G.telstate == TS_COPY) /* we aren't in the middle of IAC */
 			G.telstate = TS_NORMAL;
 		len = cstart;
 	}

 	if (len)
 		full_write(STDOUT_FILENO, G.buf, len);
 }

 static void put_iac(int c)
 {
 	G.iacbuf[G.iaclen++] = c;
 }

 static void put_iac2(byte wwdd, byte c)
 {
 	if (G.iaclen + 3 > IACBUFSIZE)
 		iac_flush();

 	put_iac(IAC);
 	put_iac(wwdd);
 	put_iac(c);
 }

 #if ENABLE_FEATURE_TELNET_TTYPE
 static void put_iac_subopt(byte c, char *str)
 {
 	int len = strlen(str) + 6;   // ( 2 + 1 + 1 + strlen + 2 )

 	if (G.iaclen + len > IACBUFSIZE)
 		iac_flush();

 	put_iac(IAC);
 	put_iac(SB);
 	put_iac(c);
 	put_iac(0);

 	while (*str)
 		put_iac(*str++);

 	put_iac(IAC);
 	put_iac(SE);
 }
 #endif

 #if ENABLE_FEATURE_TELNET_AUTOLOGIN
 static void put_iac_subopt_autologin(void)
 {
 	int len = strlen(G.autologin) + 6;	// (2 + 1 + 1 + strlen + 2)
 	const char *p = "USER";

 	if (G.iaclen + len > IACBUFSIZE)
 		iac_flush();

 	put_iac(IAC);
 	put_iac(SB);
 	put_iac(TELOPT_NEW_ENVIRON);
 	put_iac(TELQUAL_IS);
 	put_iac(NEW_ENV_VAR);

 	while (*p)
 		put_iac(*p++);

 	put_iac(NEW_ENV_VALUE);

 	p = G.autologin;
 	while (*p)
 		put_iac(*p++);

 	put_iac(IAC);
 	put_iac(SE);
 }
 #endif

 #if ENABLE_FEATURE_AUTOWIDTH
 static void put_iac_naws(byte c, int x, int y)
 {
 	if (G.iaclen + 9 > IACBUFSIZE)
 		iac_flush();

 	put_iac(IAC);
 	put_iac(SB);
 	put_iac(c);

 	/* "... & 0xff" implicitly done below */
 	put_iac(x >> 8);
 	put_iac(x);
 	put_iac(y >> 8);
 	put_iac(y);

 	put_iac(IAC);
 	put_iac(SE);
 }
 #endif

 static void setConMode(void)
 {
 	if (G.telflags & UF_ECHO) {
 		if (G.charmode == CHM_TRY) {
 			G.charmode = CHM_ON;
 			printf("\r\nEntering %s mode"
 				"\r\nEscape character is '^%c'.\r\n", "character", ']');
 			rawmode();
 		}
 	} else {
 		if (G.charmode != CHM_OFF) {
 			G.charmode = CHM_OFF;
 			printf("\r\nEntering %s mode"
 				"\r\nEscape character is '^%c'.\r\n", "line", 'C');
 			cookmode();
 		}
 	}
 }

 static void will_charmode(void)
 {
 	G.charmode = CHM_TRY;
 	G.telflags |= (UF_ECHO | UF_SGA);
 	setConMode();

 	put_iac2(DO, TELOPT_ECHO);
 	put_iac2(DO, TELOPT_SGA);
 	iac_flush();
 }

 static void do_linemode(void)
 {
 	G.charmode = CHM_TRY;
 	G.telflags &= ~(UF_ECHO | UF_SGA);
 	setConMode();

 	put_iac2(DONT, TELOPT_ECHO);
 	put_iac2(DONT, TELOPT_SGA);
 	iac_flush();
 }

 static void to_notsup(char c)
 {
 	if (G.telwish == WILL)
 		put_iac2(DONT, c);
 	else if (G.telwish == DO)
 		put_iac2(WONT, c);
 }

 static void to_echo(void)
 {
 	/* if server requests ECHO, don't agree */
 	if (G.telwish == DO) {
 		put_iac2(WONT, TELOPT_ECHO);
 		return;
 	}
 	if (G.telwish == DONT)
 		return;

 	if (G.telflags & UF_ECHO) {
 		if (G.telwish == WILL)
 			return;
 	} else if (G.telwish == WONT)
 		return;

 	if (G.charmode != CHM_OFF)
 		G.telflags ^= UF_ECHO;

 	if (G.telflags & UF_ECHO)
 		put_iac2(DO, TELOPT_ECHO);
 	else
 		put_iac2(DONT, TELOPT_ECHO);

 	setConMode();
 	full_write1_str("\r\n");  /* sudden modec */
 }

 static void to_sga(void)
 {
 	/* daemon always sends will/wont, client do/dont */

 	if (G.telflags & UF_SGA) {
 		if (G.telwish == WILL)
 			return;
 	} else if (G.telwish == WONT)
 		return;

 	G.telflags ^= UF_SGA; /* toggle */
 	if (G.telflags & UF_SGA)
 		put_iac2(DO, TELOPT_SGA);
 	else
 		put_iac2(DONT, TELOPT_SGA);
 }

 #if ENABLE_FEATURE_TELNET_TTYPE
 static void to_ttype(void)
 {
 	/* Tell server we will (or won't) do TTYPE */
 	if (G.ttype)
 		put_iac2(WILL, TELOPT_TTYPE);
 	else
 		put_iac2(WONT, TELOPT_TTYPE);
 }
 #endif

 #if ENABLE_FEATURE_TELNET_AUTOLOGIN
 static void to_new_environ(void)
 {
 	/* Tell server we will (or will not) do AUTOLOGIN */
 	if (G.autologin)
 		put_iac2(WILL, TELOPT_NEW_ENVIRON);
 	else
 		put_iac2(WONT, TELOPT_NEW_ENVIRON);
 }
 #endif

 #if ENABLE_FEATURE_AUTOWIDTH
 static void to_naws(void)
 {
 	/* Tell server we will do NAWS */
 	put_iac2(WILL, TELOPT_NAWS);
 }
 #endif

 static void telopt(byte c)
 {
 	switch (c) {
 	case TELOPT_ECHO:
 		to_echo(); break;
 	case TELOPT_SGA:
 		to_sga(); break;
 #if ENABLE_FEATURE_TELNET_TTYPE
 	case TELOPT_TTYPE:
 		to_ttype(); break;
 #endif
 #if ENABLE_FEATURE_TELNET_AUTOLOGIN
 	case TELOPT_NEW_ENVIRON:
 		to_new_environ(); break;
 #endif
 #if ENABLE_FEATURE_AUTOWIDTH
 	case TELOPT_NAWS:
 		to_naws();
 		put_iac_naws(c, G.win_width, G.win_height);
 		break;
 #endif
 	default:
 		to_notsup(c);
 		break;
 	}
 }

 /* subnegotiation -- ignore all (except TTYPE,NAWS) */
 static void subneg(byte c)
 {
 	switch (G.telstate) {
 	case TS_SUB1:
 		if (c == IAC)
 			G.telstate = TS_SUB2;
 #if ENABLE_FEATURE_TELNET_TTYPE
 		else
 		if (c == TELOPT_TTYPE && G.ttype)
 			put_iac_subopt(TELOPT_TTYPE, G.ttype);
 #endif
 #if ENABLE_FEATURE_TELNET_AUTOLOGIN
 		else
 		if (c == TELOPT_NEW_ENVIRON && G.autologin)
 			put_iac_subopt_autologin();
 #endif
 		break;
 	case TS_SUB2:
 		if (c == SE) {
 			G.telstate = TS_COPY;
 			return;
 		}
 		G.telstate = TS_SUB1;
 		break;
 	}
 }

 static void rawmode(void)
 {
 	if (G.do_termios)
 		tcsetattr(0, TCSADRAIN, &G.termios_raw);
 }

 static void cookmode(void)
 {
 	if (G.do_termios)
 		tcsetattr(0, TCSADRAIN, &G.termios_def);
 }

 int telnet_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int telnet_main(int argc UNUSED_PARAM, char **argv)
 {
 	char *host;
 	int port;
 	int len;
 	struct pollfd ufds[2];

 	INIT_G();

 #if ENABLE_FEATURE_AUTOWIDTH
 	get_terminal_width_height(0, &G.win_width, &G.win_height);
 #endif

 #if ENABLE_FEATURE_TELNET_TTYPE
 	G.ttype = getenv("TERM");
 #endif

 	if (tcgetattr(0, &G.termios_def) >= 0) {
 		G.do_termios = 1;
 		G.termios_raw = G.termios_def;
 		cfmakeraw(&G.termios_raw);
 	}

 #if ENABLE_FEATURE_TELNET_AUTOLOGIN
 	if (1 & getopt32(argv, "al:", &G.autologin))
 		G.autologin = getenv("USER");
 	argv += optind;
 #else
 	argv++;
 #endif
 	if (!*argv)
 		bb_show_usage();
 	host = *argv++;
 	port = bb_lookup_port(*argv ? *argv++ : "telnet", "tcp", 23);
 	if (*argv) /* extra params?? */
 		bb_show_usage();

 	xmove_fd(create_and_connect_stream_or_die(host, port), netfd);

 	setsockopt_keepalive(netfd);

 	signal(SIGINT, record_signo);

 	ufds[0].fd = STDIN_FILENO;
 	ufds[0].events = POLLIN;
 	ufds[1].fd = netfd;
 	ufds[1].events = POLLIN;

 	while (1) {
 		if (poll(ufds, 2, -1) < 0) {
 			/* error, ignore and/or log something, bay go to loop */
 			if (bb_got_signal)
 				con_escape();
 			else
 				sleep(1);
 			continue;
 		}

 // FIXME: reads can block. Need full bidirectional buffering.

 		if (ufds[0].revents) {
 			len = safe_read(STDIN_FILENO, G.buf, DATABUFSIZE);
 			if (len <= 0)
 				doexit(EXIT_SUCCESS);
 			TRACE(0, ("Read con: %d\n", len));
 			handle_net_output(len);
 		}

 		if (ufds[1].revents) {
 			len = safe_read(netfd, G.buf, DATABUFSIZE);
 			if (len <= 0) {
 				full_write1_str("Connection closed by foreign host\r\n");
 				doexit(EXIT_FAILURE);
 			}
 			TRACE(0, ("Read netfd (%d): %d\n", netfd, len));
 			handle_net_input(len);
 		}
 	} /* while (1) */
 }
	/* vi: set sw=4 ts=4: */
	/*
	* telnet implementation for busybox
	*
	* Author: Tomi Ollila <too@iki.fi>
	* Copyright (C) 1994-2000 by Tomi Ollila
	*
	* Created: Thu Apr 7 13:29:41 1994 too
	* Last modified: Fri Jun 9 14:34:24 2000 too
	*
	* Licensed under GPLv2 or later, see file LICENSE in this source tree.
	*
	* HISTORY
	* Revision 3.1 1994/04/17 11:31:54 too
	* initial revision
	* Modified 2000/06/13 for inclusion into BusyBox by Erik Andersen <andersen@codepoet.org>
	* Modified 2001/05/07 to add ability to pass TTYPE to remote host by Jim McQuillan
	* <jam@ltsp.org>
	* Modified 2004/02/11 to add ability to pass the USER variable to remote host
	* by Fernando Silveira <swrh@gmx.net>
	*
	*/

	//usage:#if ENABLE_FEATURE_TELNET_AUTOLOGIN
	//usage:#define telnet_trivial_usage
	//usage: "[-a] [-l USER] HOST [PORT]"
	//usage:#define telnet_full_usage "\n\n"
	//usage: "Connect to telnet server\n"
	//usage: "\n -a Automatic login with $USER variable"
	//usage: "\n -l USER Automatic login as USER"
	//usage:
	//usage:#else
	//usage:#define telnet_trivial_usage
	//usage: "HOST [PORT]"
	//usage:#define telnet_full_usage "\n\n"
	//usage: "Connect to telnet server"
	//usage:#endif

	#include <arpa/telnet.h>
	#include <netinet/in.h>
	#include "libbb.h"

	#ifdef __BIONIC__
	/* should be in arpa/telnet.h */
	# 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 TELOPT_ECHO 1 /* echo */
	# define TELOPT_SGA 3 /* suppress go ahead */
	# define TELOPT_TTYPE 24 /* terminal type */
	# define TELOPT_NAWS 31 /* window size */
	#endif

	#ifdef DOTRACE
	# define TRACE(x, y) do { if (x) printf y; } while (0)
	#else
	# define TRACE(x, y)
	#endif

	enum {
	DATABUFSIZE = 128,
	IACBUFSIZE = 128,

	CHM_TRY = 0,
	CHM_ON = 1,
	CHM_OFF = 2,

	UF_ECHO = 0x01,
	UF_SGA = 0x02,

	TS_NORMAL = 0,
	TS_COPY = 1,
	TS_IAC = 2,
	TS_OPT = 3,
	TS_SUB1 = 4,
	TS_SUB2 = 5,
	TS_CR = 6,
	};

	typedef unsigned char byte;

	enum { netfd = 3 };

	struct globals {
	int iaclen; /* could even use byte, but it's a loss on x86 */
	byte telstate; /* telnet negotiation state from network input */
	byte telwish; /* DO, DONT, WILL, WONT */
	byte charmode;
	byte telflags;
	byte do_termios;
	#if ENABLE_FEATURE_TELNET_TTYPE
	char *ttype;
	#endif
	#if ENABLE_FEATURE_TELNET_AUTOLOGIN
	const char *autologin;
	#endif
	#if ENABLE_FEATURE_AUTOWIDTH
	unsigned win_width, win_height;
	#endif
	/* same buffer used both for network and console read/write */
	char buf[DATABUFSIZE];
	/* buffer to handle telnet negotiations */
	char iacbuf[IACBUFSIZE];
	struct termios termios_def;
	struct termios termios_raw;
	} FIX_ALIASING;
	#define G ((struct globals)&bb_common_bufsiz1)
	#define INIT_G() do { \
	struct G_sizecheck { \
	char G_sizecheck[sizeof(G) > COMMON_BUFSIZE ? -1 : 1]; \
	}; \
	} while (0)


	static void rawmode(void);
	static void cookmode(void);
	static void do_linemode(void);
	static void will_charmode(void);
	static void telopt(byte c);
	static void subneg(byte c);

	static void iac_flush(void)
	{
	full_write(netfd, G.iacbuf, G.iaclen);
	G.iaclen = 0;
	}

	static void doexit(int ev) NORETURN;
	static void doexit(int ev)
	{
	cookmode();
	exit(ev);
	}

	static void con_escape(void)
	{
	char b;

	if (bb_got_signal) /* came from line mode... go raw */
	rawmode();

	full_write1_str("\r\nConsole escape. Commands are:\r\n\n"
	" l go to line mode\r\n"
	" c go to character mode\r\n"
	" z suspend telnet\r\n"
	" e exit telnet\r\n");

	if (read(STDIN_FILENO, &b, 1) <= 0)
	doexit(EXIT_FAILURE);

	switch (b) {
	case 'l':
	if (!bb_got_signal) {
	do_linemode();
	goto ret;
	}
	break;
	case 'c':
	if (bb_got_signal) {
	will_charmode();
	goto ret;
	}
	break;
	case 'z':
	cookmode();
	kill(0, SIGTSTP);
	rawmode();
	break;
	case 'e':
	doexit(EXIT_SUCCESS);
	}

	full_write1_str("continuing...\r\n");

	if (bb_got_signal)
	cookmode();
	ret:
	bb_got_signal = 0;
	}

	static void handle_net_output(int len)
	{
	byte outbuf[2 * DATABUFSIZE];
	byte *dst = outbuf;
	byte src = (byte)G.buf;
	byte *end = src + len;

	while (src < end) {
	byte c = *src++;
	if (c == 0x1d) {
	con_escape();
	return;
	}
	*dst = c;
	if (c == IAC)
	++dst = c; / IAC -> IAC IAC */
	else
	if (c == '\r' \|\| c == '\n') {
	/* Enter key sends '\r' in raw mode and '\n' in cooked one.
	*
	* See RFC 1123 3.3.1 Telnet End-of-Line Convention.
	* Using CR LF instead of other allowed possibilities
	* like CR NUL - easier to talk to HTTP/SMTP servers.
	*/
	dst = '\r'; / Enter -> CR LF */
	*++dst = '\n';
	}
	dst++;
	}
	if (dst - outbuf != 0)
	full_write(netfd, outbuf, dst - outbuf);
	}

	static void handle_net_input(int len)
	{
	int i;
	int cstart = 0;

	for (i = 0; i < len; i++) {
	byte c = G.buf[i];

	if (G.telstate == TS_NORMAL) { /* most typical state */
	if (c == IAC) {
	cstart = i;
	G.telstate = TS_IAC;
	}
	else if (c == '\r') {
	cstart = i + 1;
	G.telstate = TS_CR;
	}
	/* No IACs were seen so far, no need to copy
	* bytes within G.buf: */
	continue;
	}

	switch (G.telstate) {
	case TS_CR:
	/* Prev char was CR. If cur one is NUL, ignore it.
	* See RFC 1123 section 3.3.1 for discussion of telnet EOL handling.
	*/
	G.telstate = TS_COPY;
	if (c == '\0')
	break;
	/* else: fall through - need to handle CR IAC ... properly */

	case TS_COPY: /* Prev char was ordinary */
	/* Similar to NORMAL, but in TS_COPY we need to copy bytes */
	if (c == IAC)
	G.telstate = TS_IAC;
	else
	G.buf[cstart++] = c;
	if (c == '\r')
	G.telstate = TS_CR;
	break;

	case TS_IAC: /* Prev char was IAC */
	if (c == IAC) { /* IAC IAC -> one IAC */
	G.buf[cstart++] = c;
	G.telstate = TS_COPY;
	break;
	}
	/* else */
	switch (c) {
	case SB:
	G.telstate = TS_SUB1;
	break;
	case DO:
	case DONT:
	case WILL:
	case WONT:
	G.telwish = c;
	G.telstate = TS_OPT;
	break;
	/* DATA MARK must be added later */
	default:
	G.telstate = TS_COPY;
	}
	break;

	case TS_OPT: /* Prev chars were IAC WILL/WONT/DO/DONT */
	telopt(c);
	G.telstate = TS_COPY;
	break;

	case TS_SUB1: /* Subnegotiation */
	case TS_SUB2: /* Subnegotiation */
	subneg(c); /* can change G.telstate */
	break;
	}
	}

	if (G.telstate != TS_NORMAL) {
	/* We had some IACs, or CR */
	if (G.iaclen)
	iac_flush();
	if (G.telstate == TS_COPY) /* we aren't in the middle of IAC */
	G.telstate = TS_NORMAL;
	len = cstart;
	}

	if (len)
	full_write(STDOUT_FILENO, G.buf, len);
	}

	static void put_iac(int c)
	{
	G.iacbuf[G.iaclen++] = c;
	}

	static void put_iac2(byte wwdd, byte c)
	{
	if (G.iaclen + 3 > IACBUFSIZE)
	iac_flush();

	put_iac(IAC);
	put_iac(wwdd);
	put_iac(c);
	}

	#if ENABLE_FEATURE_TELNET_TTYPE
	static void put_iac_subopt(byte c, char *str)
	{
	int len = strlen(str) + 6; // ( 2 + 1 + 1 + strlen + 2 )

	if (G.iaclen + len > IACBUFSIZE)
	iac_flush();

	put_iac(IAC);
	put_iac(SB);
	put_iac(c);
	put_iac(0);

	while (*str)
	put_iac(*str++);

	put_iac(IAC);
	put_iac(SE);
	}
	#endif

	#if ENABLE_FEATURE_TELNET_AUTOLOGIN
	static void put_iac_subopt_autologin(void)
	{
	int len = strlen(G.autologin) + 6; // (2 + 1 + 1 + strlen + 2)
	const char *p = "USER";

	if (G.iaclen + len > IACBUFSIZE)
	iac_flush();

	put_iac(IAC);
	put_iac(SB);
	put_iac(TELOPT_NEW_ENVIRON);
	put_iac(TELQUAL_IS);
	put_iac(NEW_ENV_VAR);

	while (*p)
	put_iac(*p++);

	put_iac(NEW_ENV_VALUE);

	p = G.autologin;
	while (*p)
	put_iac(*p++);

	put_iac(IAC);
	put_iac(SE);
	}
	#endif

	#if ENABLE_FEATURE_AUTOWIDTH
	static void put_iac_naws(byte c, int x, int y)
	{
	if (G.iaclen + 9 > IACBUFSIZE)
	iac_flush();

	put_iac(IAC);
	put_iac(SB);
	put_iac(c);

	/* "... & 0xff" implicitly done below */
	put_iac(x >> 8);
	put_iac(x);
	put_iac(y >> 8);
	put_iac(y);

	put_iac(IAC);
	put_iac(SE);
	}
	#endif

	static void setConMode(void)
	{
	if (G.telflags & UF_ECHO) {
	if (G.charmode == CHM_TRY) {
	G.charmode = CHM_ON;
	printf("\r\nEntering %s mode"
	"\r\nEscape character is '^%c'.\r\n", "character", ']');
	rawmode();
	}
	} else {
	if (G.charmode != CHM_OFF) {
	G.charmode = CHM_OFF;
	printf("\r\nEntering %s mode"
	"\r\nEscape character is '^%c'.\r\n", "line", 'C');
	cookmode();
	}
	}
	}

	static void will_charmode(void)
	{
	G.charmode = CHM_TRY;
	G.telflags \|= (UF_ECHO \| UF_SGA);
	setConMode();

	put_iac2(DO, TELOPT_ECHO);
	put_iac2(DO, TELOPT_SGA);
	iac_flush();
	}

	static void do_linemode(void)
	{
	G.charmode = CHM_TRY;
	G.telflags &= ~(UF_ECHO \| UF_SGA);
	setConMode();

	put_iac2(DONT, TELOPT_ECHO);
	put_iac2(DONT, TELOPT_SGA);
	iac_flush();
	}

	static void to_notsup(char c)
	{
	if (G.telwish == WILL)
	put_iac2(DONT, c);
	else if (G.telwish == DO)
	put_iac2(WONT, c);
	}

	static void to_echo(void)
	{
	/* if server requests ECHO, don't agree */
	if (G.telwish == DO) {
	put_iac2(WONT, TELOPT_ECHO);
	return;
	}
	if (G.telwish == DONT)
	return;

	if (G.telflags & UF_ECHO) {
	if (G.telwish == WILL)
	return;
	} else if (G.telwish == WONT)
	return;

	if (G.charmode != CHM_OFF)
	G.telflags ^= UF_ECHO;

	if (G.telflags & UF_ECHO)
	put_iac2(DO, TELOPT_ECHO);
	else
	put_iac2(DONT, TELOPT_ECHO);

	setConMode();
	full_write1_str("\r\n"); /* sudden modec */
	}

	static void to_sga(void)
	{
	/* daemon always sends will/wont, client do/dont */

	if (G.telflags & UF_SGA) {
	if (G.telwish == WILL)
	return;
	} else if (G.telwish == WONT)
	return;

	G.telflags ^= UF_SGA; /* toggle */
	if (G.telflags & UF_SGA)
	put_iac2(DO, TELOPT_SGA);
	else
	put_iac2(DONT, TELOPT_SGA);
	}

	#if ENABLE_FEATURE_TELNET_TTYPE
	static void to_ttype(void)
	{
	/* Tell server we will (or won't) do TTYPE */
	if (G.ttype)
	put_iac2(WILL, TELOPT_TTYPE);
	else
	put_iac2(WONT, TELOPT_TTYPE);
	}
	#endif

	#if ENABLE_FEATURE_TELNET_AUTOLOGIN
	static void to_new_environ(void)
	{
	/* Tell server we will (or will not) do AUTOLOGIN */
	if (G.autologin)
	put_iac2(WILL, TELOPT_NEW_ENVIRON);
	else
	put_iac2(WONT, TELOPT_NEW_ENVIRON);
	}
	#endif

	#if ENABLE_FEATURE_AUTOWIDTH
	static void to_naws(void)
	{
	/* Tell server we will do NAWS */
	put_iac2(WILL, TELOPT_NAWS);
	}
	#endif

	static void telopt(byte c)
	{
	switch (c) {
	case TELOPT_ECHO:
	to_echo(); break;
	case TELOPT_SGA:
	to_sga(); break;
	#if ENABLE_FEATURE_TELNET_TTYPE
	case TELOPT_TTYPE:
	to_ttype(); break;
	#endif
	#if ENABLE_FEATURE_TELNET_AUTOLOGIN
	case TELOPT_NEW_ENVIRON:
	to_new_environ(); break;
	#endif
	#if ENABLE_FEATURE_AUTOWIDTH
	case TELOPT_NAWS:
	to_naws();
	put_iac_naws(c, G.win_width, G.win_height);
	break;
	#endif
	default:
	to_notsup(c);
	break;
	}
	}

	/* subnegotiation -- ignore all (except TTYPE,NAWS) */
	static void subneg(byte c)
	{
	switch (G.telstate) {
	case TS_SUB1:
	if (c == IAC)
	G.telstate = TS_SUB2;
	#if ENABLE_FEATURE_TELNET_TTYPE
	else
	if (c == TELOPT_TTYPE && G.ttype)
	put_iac_subopt(TELOPT_TTYPE, G.ttype);
	#endif
	#if ENABLE_FEATURE_TELNET_AUTOLOGIN
	else
	if (c == TELOPT_NEW_ENVIRON && G.autologin)
	put_iac_subopt_autologin();
	#endif
	break;
	case TS_SUB2:
	if (c == SE) {
	G.telstate = TS_COPY;
	return;
	}
	G.telstate = TS_SUB1;
	break;
	}
	}

	static void rawmode(void)
	{
	if (G.do_termios)
	tcsetattr(0, TCSADRAIN, &G.termios_raw);
	}

	static void cookmode(void)
	{
	if (G.do_termios)
	tcsetattr(0, TCSADRAIN, &G.termios_def);
	}

	int telnet_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
	int telnet_main(int argc UNUSED_PARAM, char **argv)
	{
	char *host;
	int port;
	int len;
	struct pollfd ufds[2];

	INIT_G();

	#if ENABLE_FEATURE_AUTOWIDTH
	get_terminal_width_height(0, &G.win_width, &G.win_height);
	#endif

	#if ENABLE_FEATURE_TELNET_TTYPE
	G.ttype = getenv("TERM");
	#endif

	if (tcgetattr(0, &G.termios_def) >= 0) {
	G.do_termios = 1;
	G.termios_raw = G.termios_def;
	cfmakeraw(&G.termios_raw);
	}

	#if ENABLE_FEATURE_TELNET_AUTOLOGIN
	if (1 & getopt32(argv, "al:", &G.autologin))
	G.autologin = getenv("USER");
	argv += optind;
	#else
	argv++;
	#endif
	if (!*argv)
	bb_show_usage();
	host = *argv++;
	port = bb_lookup_port(argv ? argv++ : "telnet", "tcp", 23);
	if (argv) / extra params?? */
	bb_show_usage();

	xmove_fd(create_and_connect_stream_or_die(host, port), netfd);

	setsockopt_keepalive(netfd);

	signal(SIGINT, record_signo);

	ufds[0].fd = STDIN_FILENO;
	ufds[0].events = POLLIN;
	ufds[1].fd = netfd;
	ufds[1].events = POLLIN;

	while (1) {
	if (poll(ufds, 2, -1) < 0) {
	/* error, ignore and/or log something, bay go to loop */
	if (bb_got_signal)
	con_escape();
	else
	sleep(1);
	continue;
	}

	// FIXME: reads can block. Need full bidirectional buffering.

	if (ufds[0].revents) {
	len = safe_read(STDIN_FILENO, G.buf, DATABUFSIZE);
	if (len <= 0)
	doexit(EXIT_SUCCESS);
	TRACE(0, ("Read con: %d\n", len));
	handle_net_output(len);
	}

	if (ufds[1].revents) {
	len = safe_read(netfd, G.buf, DATABUFSIZE);
	if (len <= 0) {
	full_write1_str("Connection closed by foreign host\r\n");
	doexit(EXIT_FAILURE);
	}
	TRACE(0, ("Read netfd (%d): %d\n", netfd, len));
	handle_net_input(len);
	}
	} /* while (1) */
	}