/* 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>
 */
//config:config TELNET
//config:       bool "telnet (8.8 kb)"
//config:       default y
//config:       help
//config:       Telnet is an interface to the TELNET protocol, but is also commonly
//config:       used to test other simple protocols.
//config:
//config:config FEATURE_TELNET_TTYPE
//config:       bool "Pass TERM type to remote host"
//config:       default y
//config:       depends on TELNET
//config:       help
//config:       Setting this option will forward the TERM environment variable to the
//config:       remote host you are connecting to. This is useful to make sure that
//config:       things like ANSI colors and other control sequences behave.
//config:
//config:config FEATURE_TELNET_AUTOLOGIN
//config:       bool "Pass USER type to remote host"
//config:       default y
//config:       depends on TELNET
//config:       help
//config:       Setting this option will forward the USER environment variable to the
//config:       remote host you are connecting to. This is useful when you need to
//config:       log into a machine without telling the username (autologin). This
//config:       option enables '-a' and '-l USER' options.
//config:
//config:config FEATURE_TELNET_WIDTH
//config:       bool "Enable window size autodetection"
//config:       default y
//config:       depends on TELNET

//applet:IF_TELNET(APPLET(telnet, BB_DIR_USR_BIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_TELNET) += telnet.o

//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"
#include "common_bufsiz.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

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_TELNET_WIDTH
        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 { \
        setup_common_bufsiz(); \
        BUILD_BUG_ON(sizeof(G) > COMMON_BUFSIZE); \
} 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_merged(unsigned wwdd_and_c)
{
        if (G.iaclen + 3 > IACBUFSIZE)
                iac_flush();

        put_iac(IAC);
        put_iac(wwdd_and_c >> 8);
        put_iac(wwdd_and_c & 0xff);
}
#define put_iac2(wwdd,c) put_iac2_merged(((wwdd)<<8) + (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_TELNET_WIDTH
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_TELNET_WIDTH
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_TELNET_WIDTH
        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_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)) {
                /* Only -a without -l USER picks $USER from envvar */
                G.autologin = getenv("USER");
        }
        argv += optind;
#else
        argv++;
#endif
        if (!*argv)
                bb_show_usage();
        host = *argv++;
        port = *argv ? bb_lookup_port(*argv++, "tcp", 23)
                : bb_lookup_std_port("telnet", "tcp", 23);
        if (*argv) /* extra params?? */
                bb_show_usage();

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

        setsockopt_keepalive(netfd);

#if ENABLE_FEATURE_TELNET_WIDTH
        get_terminal_width_height(0, &G.win_width, &G.win_height);
//TODO: support dynamic resize?
#endif

        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);
                        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);
                        }
                        handle_net_input(len);
                }
        } /* while (1) */
}