ntpd: fix a case when discipline_jitter = 0 if we step
[oweals/busybox.git] / networking / telnet.c
index 86586600ba3b5b45d644cbc71bc895e3870617b1..e8e51dce4aaa7cc314155cf0bf2fd5eaa71731c5 100644 (file)
@@ -8,7 +8,7 @@
  * Created: Thu Apr  7 13:29:41 1994 too
  * Last modified: Fri Jun  9 14:34:24 2000 too
  *
- * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  *
  * HISTORY
  * Revision 3.1  1994/04/17  11:31:54  too
  *
  */
 
-#include <termios.h>
+//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 "busybox.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
-#include <arpa/inet.h> /* for inet_ntoa()... */
-#define TRACE(x, y) do { if (x) printf y; } while (0)
+# define TRACE(x, y) do { if (x) printf y; } while (0)
 #else
-#define TRACE(x, y)
+# define TRACE(x, y)
 #endif
 
-#define DATABUFSIZE  128
-#define IACBUFSIZE   128
-
 enum {
+       DATABUFSIZE = 128,
+       IACBUFSIZE  = 128,
+
        CHM_TRY = 0,
        CHM_ON = 1,
        CHM_OFF = 2,
@@ -44,107 +72,99 @@ enum {
        UF_ECHO = 0x01,
        UF_SGA = 0x02,
 
-       TS_0 = 1,
+       TS_NORMAL = 0,
+       TS_COPY = 1,
        TS_IAC = 2,
        TS_OPT = 3,
        TS_SUB1 = 4,
        TS_SUB2 = 5,
+       TS_CR = 6,
 };
 
-#define WriteCS(fd, str) write(fd, str, sizeof str -1)
-
 typedef unsigned char byte;
 
-/* use globals to reduce size ??? */ /* test this hypothesis later */
-static struct Globalvars {
-       int             netfd; /* console fd:s are 0 and 1 (and 2) */
-    /* same buffer used both for network and console read/write */
-       char    buf[DATABUFSIZE]; /* allocating so static size is smaller */
+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    gotsig;
        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];
-       short   iaclen; /* could even use byte */
        struct termios termios_def;
        struct termios termios_raw;
-} G;
+} 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)
 
-#define xUSE_GLOBALVAR_PTR /* xUSE... -> don't use :D (makes smaller code) */
-
-#ifdef USE_GLOBALVAR_PTR
-struct Globalvars * Gptr;
-#define G (*Gptr)
-#endif
-
-static void iacflush(void)
-{
-       write(G.netfd, G.iacbuf, G.iaclen);
-       G.iaclen = 0;
-}
 
-/* Function prototypes */
 static void rawmode(void);
 static void cookmode(void);
 static void do_linemode(void);
 static void will_charmode(void);
 static void telopt(byte c);
-static int subneg(byte c);
-
-/* Some globals */
-static const int one = 1;
-
-#ifdef CONFIG_FEATURE_TELNET_TTYPE
-static char *ttype;
-#endif
+static void subneg(byte c);
 
-#ifdef CONFIG_FEATURE_TELNET_AUTOLOGIN
-static const char *autologin;
-#endif
+static void iac_flush(void)
+{
+       write(netfd, G.iacbuf, G.iaclen);
+       G.iaclen = 0;
+}
 
-#ifdef CONFIG_FEATURE_AUTOWIDTH
-static int win_width, win_height;
-#endif
+#define write_str(fd, str) write(fd, str, sizeof(str) - 1)
 
+static void doexit(int ev) NORETURN;
 static void doexit(int ev)
 {
        cookmode();
        exit(ev);
 }
 
-static void conescape(void)
+static void con_escape(void)
 {
        char b;
 
-       if (G.gotsig)   /* came from line  mode... go raw */
+       if (bb_got_signal) /* came from line mode... go raw */
                rawmode();
 
-       WriteCS(1, "\r\nConsole escape. Commands are:\r\n\n"
+       write_str(1, "\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(0, &b, 1) <= 0)
-               doexit(1);
+       if (read(STDIN_FILENO, &b, 1) <= 0)
+               doexit(EXIT_FAILURE);
 
-       switch (b)
-       {
+       switch (b) {
        case 'l':
-               if (!G.gotsig)
-               {
+               if (!bb_got_signal) {
                        do_linemode();
-                       goto rrturn;
+                       goto ret;
                }
                break;
        case 'c':
-               if (G.gotsig)
-               {
+               if (bb_got_signal) {
                        will_charmode();
-                       goto rrturn;
+                       goto ret;
                }
                break;
        case 'z':
@@ -153,239 +173,242 @@ static void conescape(void)
                rawmode();
                break;
        case 'e':
-               doexit(0);
+               doexit(EXIT_SUCCESS);
        }
 
-       WriteCS(1, "continuing...\r\n");
+       write_str(1, "continuing...\r\n");
 
-       if (G.gotsig)
+       if (bb_got_signal)
                cookmode();
-
- rrturn:
-       G.gotsig = 0;
-
+ ret:
+       bb_got_signal = 0;
 }
-static void handlenetoutput(int len)
+
+static void handle_net_output(int len)
 {
-       /*      here we could do smart tricks how to handle 0xFF:s in output
-        *      stream  like writing twice every sequence of FF:s (thus doing
-        *      many write()s. But I think interactive telnet application does
-        *      not need to be 100% 8-bit clean, so changing every 0xff:s to
-        *      0x7f:s
+       /* here we could do smart tricks how to handle 0xFF:s in output
+        * stream like writing twice every sequence of FF:s (thus doing
+        * many write()s. But I think interactive telnet application does
+        * not need to be 100% 8-bit clean, so changing every 0xff:s to
+        * 0x7f:s
         *
-        *      2002-mar-21, Przemyslaw Czerpak (druzus@polbox.com)
-        *      I don't agree.
-        *      first - I cannot use programs like sz/rz
-        *      second - the 0x0D is sent as one character and if the next
-        *               char is 0x0A then it's eaten by a server side.
-        *      third - whay doy you have to make 'many write()s'?
-        *              I don't understand.
-        *      So I implemented it. It's realy useful for me. I hope that
-        *      others people will find it interesting to.
+        * 2002-mar-21, Przemyslaw Czerpak (druzus@polbox.com)
+        * I don't agree.
+        * first - I cannot use programs like sz/rz
+        * second - the 0x0D is sent as one character and if the next
+        *      char is 0x0A then it's eaten by a server side.
+        * third - why do you have to make 'many write()s'?
+        *      I don't understand.
+        * So I implemented it. It's really useful for me. I hope that
+        * other people will find it interesting too.
         */
-
-       int i, j;
-       byte * p = (byte*)G.buf;
-       byte outbuf[4*DATABUFSIZE];
-
-       for (i = len, j = 0; i > 0; i--, p++)
-       {
-               if (*p == 0x1d)
-               {
-                       conescape();
+       byte outbuf[2 * DATABUFSIZE];
+       byte *p = (byte*)G.buf;
+       int j = 0;
+
+       for (; len > 0; len--, p++) {
+               byte c = *p;
+               if (c == 0x1d) {
+                       con_escape();
                        return;
                }
-               outbuf[j++] = *p;
-               if (*p == 0xff)
-                       outbuf[j++] = 0xff;
-               else if (*p == 0x0d)
-                       outbuf[j++] = 0x00;
+               outbuf[j++] = c;
+               if (c == IAC)
+                       outbuf[j++] = c; /* IAC -> IAC IAC */
+               else if (c == '\r')
+                       outbuf[j++] = '\0'; /* CR -> CR NUL */
        }
-       if (j > 0 )
-               write(G.netfd, outbuf, j);
+       if (j > 0)
+               full_write(netfd, outbuf, j);
 }
 
-
-static void handlenetinput(int len)
+static void handle_net_input(int len)
 {
        int i;
        int cstart = 0;
 
-       for (i = 0; i < len; i++)
-       {
+       for (i = 0; i < len; i++) {
                byte c = G.buf[i];
 
-               if (G.telstate == 0) /* most of the time state == 0 */
-               {
-                       if (c == IAC)
-                       {
+               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;
                }
-               else
-                       switch (G.telstate)
-                        {
-                        case TS_0:
-                                if (c == IAC)
-                                        G.telstate = TS_IAC;
-                                else
-                                        G.buf[cstart++] = c;
-                                break;
-
-                        case TS_IAC:
-                                if (c == IAC) /* IAC IAC -> 0xFF */
-                                {
-                                        G.buf[cstart++] = c;
-                                        G.telstate = TS_0;
-                                        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;
-                                default:
-                                        G.telstate = TS_0;     /* DATA MARK must be added later */
-                                }
-                                break;
-                        case TS_OPT: /* WILL, WONT, DO, DONT */
-                                telopt(c);
-                                G.telstate = TS_0;
-                                break;
-                        case TS_SUB1: /* Subnegotiation */
-                        case TS_SUB2: /* Subnegotiation */
-                                if (subneg(c))
-                                        G.telstate = TS_0;
-                                break;
-                        }
        }
-       if (G.telstate)
-       {
-               if (G.iaclen)                   iacflush();
-               if (G.telstate == TS_0) G.telstate = 0;
 
+       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)
-               write(1, G.buf, len);
+               full_write(STDOUT_FILENO, G.buf, len);
 }
 
-
-/* ******************************* */
-
-static void putiac(int c)
+static void put_iac(int c)
 {
        G.iacbuf[G.iaclen++] = c;
 }
 
-
-static void putiac2(byte wwdd, byte c)
+static void put_iac2(byte wwdd, byte c)
 {
        if (G.iaclen + 3 > IACBUFSIZE)
-               iacflush();
+               iac_flush();
 
-       putiac(IAC);
-       putiac(wwdd);
-       putiac(c);
+       put_iac(IAC);
+       put_iac(wwdd);
+       put_iac(c);
 }
 
-#ifdef CONFIG_FEATURE_TELNET_TTYPE
-static void putiac_subopt(byte c, char *str)
+#if ENABLE_FEATURE_TELNET_TTYPE
+static void put_iac_subopt(byte c, char *str)
 {
-       int     len = strlen(str) + 6;   // ( 2 + 1 + 1 + strlen + 2 )
+       int len = strlen(str) + 6;   // ( 2 + 1 + 1 + strlen + 2 )
 
        if (G.iaclen + len > IACBUFSIZE)
-               iacflush();
+               iac_flush();
 
-       putiac(IAC);
-       putiac(SB);
-       putiac(c);
-       putiac(0);
+       put_iac(IAC);
+       put_iac(SB);
+       put_iac(c);
+       put_iac(0);
 
        while (*str)
-               putiac(*str++);
+               put_iac(*str++);
 
-       putiac(IAC);
-       putiac(SE);
+       put_iac(IAC);
+       put_iac(SE);
 }
 #endif
 
-#ifdef CONFIG_FEATURE_TELNET_AUTOLOGIN
-static void putiac_subopt_autologin(void)
+#if ENABLE_FEATURE_TELNET_AUTOLOGIN
+static void put_iac_subopt_autologin(void)
 {
-       int len = strlen(autologin) + 6;        // (2 + 1 + 1 + strlen + 2)
-       char *user = "USER";
+       int len = strlen(G.autologin) + 6;      // (2 + 1 + 1 + strlen + 2)
+       const char *p = "USER";
 
        if (G.iaclen + len > IACBUFSIZE)
-               iacflush();
+               iac_flush();
 
-       putiac(IAC);
-       putiac(SB);
-       putiac(TELOPT_NEW_ENVIRON);
-       putiac(TELQUAL_IS);
-       putiac(NEW_ENV_VAR);
+       put_iac(IAC);
+       put_iac(SB);
+       put_iac(TELOPT_NEW_ENVIRON);
+       put_iac(TELQUAL_IS);
+       put_iac(NEW_ENV_VAR);
 
-       while (*user)
-               putiac(*user++);
+       while (*p)
+               put_iac(*p++);
 
-       putiac(NEW_ENV_VALUE);
+       put_iac(NEW_ENV_VALUE);
 
-       while (*autologin)
-               putiac(*autologin++);
+       p = G.autologin;
+       while (*p)
+               put_iac(*p++);
 
-       putiac(IAC);
-       putiac(SE);
+       put_iac(IAC);
+       put_iac(SE);
 }
 #endif
 
-#ifdef CONFIG_FEATURE_AUTOWIDTH
-static void putiac_naws(byte c, int x, int y)
+#if ENABLE_FEATURE_AUTOWIDTH
+static void put_iac_naws(byte c, int x, int y)
 {
        if (G.iaclen + 9 > IACBUFSIZE)
-               iacflush();
+               iac_flush();
 
-       putiac(IAC);
-       putiac(SB);
-       putiac(c);
+       put_iac(IAC);
+       put_iac(SB);
+       put_iac(c);
 
-       putiac((x >> 8) & 0xff);
-       putiac(x & 0xff);
-       putiac((y >> 8) & 0xff);
-       putiac(y & 0xff);
+       put_iac((x >> 8) & 0xff);
+       put_iac(x & 0xff);
+       put_iac((y >> 8) & 0xff);
+       put_iac(y & 0xff);
 
-       putiac(IAC);
-       putiac(SE);
+       put_iac(IAC);
+       put_iac(SE);
 }
 #endif
 
-/* void putiacstring (subneg strings) */
-
-/* ******************************* */
-
-static char const escapecharis[] = "\r\nEscape character is ";
+static char const escapecharis[] ALIGN1 = "\r\nEscape character is ";
 
 static void setConMode(void)
 {
-       if (G.telflags & UF_ECHO)
-       {
+       if (G.telflags & UF_ECHO) {
                if (G.charmode == CHM_TRY) {
                        G.charmode = CHM_ON;
                        printf("\r\nEntering character mode%s'^]'.\r\n", escapecharis);
                        rawmode();
                }
-       }
-       else
-       {
+       } else {
                if (G.charmode != CHM_OFF) {
                        G.charmode = CHM_OFF;
                        printf("\r\nEntering line mode%s'^C'.\r\n", escapecharis);
@@ -394,17 +417,15 @@ static void setConMode(void)
        }
 }
 
-/* ******************************* */
-
 static void will_charmode(void)
 {
        G.charmode = CHM_TRY;
        G.telflags |= (UF_ECHO | UF_SGA);
        setConMode();
 
-       putiac2(DO, TELOPT_ECHO);
-       putiac2(DO, TELOPT_SGA);
-       iacflush();
+       put_iac2(DO, TELOPT_ECHO);
+       put_iac2(DO, TELOPT_SGA);
+       iac_flush();
 }
 
 static void do_linemode(void)
@@ -413,197 +434,178 @@ static void do_linemode(void)
        G.telflags &= ~(UF_ECHO | UF_SGA);
        setConMode();
 
-       putiac2(DONT, TELOPT_ECHO);
-       putiac2(DONT, TELOPT_SGA);
-       iacflush();
+       put_iac2(DONT, TELOPT_ECHO);
+       put_iac2(DONT, TELOPT_SGA);
+       iac_flush();
 }
 
-/* ******************************* */
-
 static void to_notsup(char c)
 {
-       if      (G.telwish == WILL)     putiac2(DONT, c);
-       else if (G.telwish == DO)       putiac2(WONT, 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) {     putiac2(WONT, TELOPT_ECHO);     return; }
-       else if (G.telwish == DONT)     return;
+       if (G.telwish == DO) {
+               put_iac2(WONT, TELOPT_ECHO);
+               return;
+       }
+       if (G.telwish == DONT)
+               return;
 
-       if (G.telflags & UF_ECHO)
-       {
+       if (G.telflags & UF_ECHO) {
                if (G.telwish == WILL)
                        return;
-       }
-       else
-               if (G.telwish == WONT)
-                       return;
+       } else if (G.telwish == WONT)
+               return;
 
        if (G.charmode != CHM_OFF)
                G.telflags ^= UF_ECHO;
 
        if (G.telflags & UF_ECHO)
-               putiac2(DO, TELOPT_ECHO);
+               put_iac2(DO, TELOPT_ECHO);
        else
-               putiac2(DONT, TELOPT_ECHO);
+               put_iac2(DONT, TELOPT_ECHO);
 
        setConMode();
-       WriteCS(1, "\r\n");  /* sudden modec */
+       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.telflags & UF_SGA) {
                if (G.telwish == WILL)
                        return;
-       }
-       else
-               if (G.telwish == WONT)
-                       return;
+       } else if (G.telwish == WONT)
+               return;
 
-       if ((G.telflags ^= UF_SGA) & UF_SGA) /* toggle */
-               putiac2(DO, TELOPT_SGA);
+       G.telflags ^= UF_SGA; /* toggle */
+       if (G.telflags & UF_SGA)
+               put_iac2(DO, TELOPT_SGA);
        else
-               putiac2(DONT, TELOPT_SGA);
-
-       return;
+               put_iac2(DONT, TELOPT_SGA);
 }
 
-#ifdef CONFIG_FEATURE_TELNET_TTYPE
+#if ENABLE_FEATURE_TELNET_TTYPE
 static void to_ttype(void)
 {
        /* Tell server we will (or won't) do TTYPE */
-
-       if(ttype)
-               putiac2(WILL, TELOPT_TTYPE);
+       if (G.ttype)
+               put_iac2(WILL, TELOPT_TTYPE);
        else
-               putiac2(WONT, TELOPT_TTYPE);
-
-       return;
+               put_iac2(WONT, TELOPT_TTYPE);
 }
 #endif
 
-#ifdef CONFIG_FEATURE_TELNET_AUTOLOGIN
+#if ENABLE_FEATURE_TELNET_AUTOLOGIN
 static void to_new_environ(void)
 {
        /* Tell server we will (or will not) do AUTOLOGIN */
-
-       if (autologin)
-               putiac2(WILL, TELOPT_NEW_ENVIRON);
+       if (G.autologin)
+               put_iac2(WILL, TELOPT_NEW_ENVIRON);
        else
-               putiac2(WONT, TELOPT_NEW_ENVIRON);
-
-       return;
+               put_iac2(WONT, TELOPT_NEW_ENVIRON);
 }
 #endif
 
-#ifdef CONFIG_FEATURE_AUTOWIDTH
+#if ENABLE_FEATURE_AUTOWIDTH
 static void to_naws(void)
 {
        /* Tell server we will do NAWS */
-       putiac2(WILL, TELOPT_NAWS);
-       return;
+       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;
-#ifdef CONFIG_FEATURE_TELNET_TTYPE
-               case TELOPT_TTYPE:              to_ttype();break;
+       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
-#ifdef CONFIG_FEATURE_TELNET_AUTOLOGIN
-               case TELOPT_NEW_ENVIRON:        to_new_environ();       break;
+#if ENABLE_FEATURE_TELNET_AUTOLOGIN
+       case TELOPT_NEW_ENVIRON:
+               to_new_environ(); break;
 #endif
-#ifdef CONFIG_FEATURE_AUTOWIDTH
-               case TELOPT_NAWS:               to_naws();
-                                                               putiac_naws(c, win_width, win_height);
-                                                               break;
+#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;
+       default:
+               to_notsup(c);
+               break;
        }
 }
 
-
-/* ******************************* */
-
 /* subnegotiation -- ignore all (except TTYPE,NAWS) */
-
-static int subneg(byte c)
+static void subneg(byte c)
 {
-       switch (G.telstate)
-       {
+       switch (G.telstate) {
        case TS_SUB1:
                if (c == IAC)
                        G.telstate = TS_SUB2;
-#ifdef CONFIG_FEATURE_TELNET_TTYPE
+#if ENABLE_FEATURE_TELNET_TTYPE
                else
-               if (c == TELOPT_TTYPE)
-                       putiac_subopt(TELOPT_TTYPE,ttype);
+               if (c == TELOPT_TTYPE && G.ttype)
+                       put_iac_subopt(TELOPT_TTYPE, G.ttype);
 #endif
-#ifdef CONFIG_FEATURE_TELNET_AUTOLOGIN
+#if ENABLE_FEATURE_TELNET_AUTOLOGIN
                else
-               if (c == TELOPT_NEW_ENVIRON)
-                       putiac_subopt_autologin();
+               if (c == TELOPT_NEW_ENVIRON && G.autologin)
+                       put_iac_subopt_autologin();
 #endif
                break;
        case TS_SUB2:
-               if (c == SE)
-                       return TRUE;
+               if (c == SE) {
+                       G.telstate = TS_COPY;
+                       return;
+               }
                G.telstate = TS_SUB1;
-               /* break; */
+               break;
        }
-       return FALSE;
-}
-
-/* ******************************* */
-
-static void fgotsig(int sig)
-{
-       G.gotsig = sig;
 }
 
-
 static void rawmode(void)
 {
-       if (G.do_termios) tcsetattr(0, TCSADRAIN, &G.termios_raw);
+       if (G.do_termios)
+               tcsetattr(0, TCSADRAIN, &G.termios_raw);
 }
 
 static void cookmode(void)
 {
-       if (G.do_termios) tcsetattr(0, TCSADRAIN, &G.termios_def);
+       if (G.do_termios)
+               tcsetattr(0, TCSADRAIN, &G.termios_def);
 }
 
-int telnet_main(int argc, char** argv)
+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;
-#ifdef USE_POLL
        struct pollfd ufds[2];
-#else
-       fd_set readfds;
-       int maxfd;
-#endif
 
-#ifdef CONFIG_FEATURE_AUTOWIDTH
-       get_terminal_width_height(0, &win_width, &win_height);
-#endif
+       INIT_G();
 
-#ifdef CONFIG_FEATURE_TELNET_TTYPE
-       ttype = getenv("TERM");
+#if ENABLE_FEATURE_AUTOWIDTH
+       get_terminal_width_height(0, &G.win_width, &G.win_height);
 #endif
 
-       /* memset(&G, 0, sizeof G); - already is */
+#if ENABLE_FEATURE_TELNET_TTYPE
+       G.ttype = getenv("TERM");
+#endif
 
        if (tcgetattr(0, &G.termios_def) >= 0) {
                G.do_termios = 1;
@@ -611,12 +613,9 @@ int telnet_main(int argc, char** argv)
                cfmakeraw(&G.termios_raw);
        }
 
-       if (argc < 2)
-               bb_show_usage();
-
-#ifdef CONFIG_FEATURE_TELNET_AUTOLOGIN
-       if (1 & getopt32(argc, argv, "al:", &autologin))
-               autologin = getenv("USER");
+#if ENABLE_FEATURE_TELNET_AUTOLOGIN
+       if (1 & getopt32(argv, "al:", &G.autologin))
+               G.autologin = getenv("USER");
        argv += optind;
 #else
        argv++;
@@ -628,74 +627,45 @@ int telnet_main(int argc, char** argv)
        if (*argv) /* extra params?? */
                bb_show_usage();
 
-       G.netfd = create_and_connect_stream_or_die(host, port);
+       xmove_fd(create_and_connect_stream_or_die(host, port), netfd);
 
-       setsockopt(G.netfd, SOL_SOCKET, SO_KEEPALIVE, &one, sizeof one);
+       setsockopt(netfd, SOL_SOCKET, SO_KEEPALIVE, &const_int_1, sizeof(const_int_1));
 
-       signal(SIGINT, fgotsig);
+       signal(SIGINT, record_signo);
 
-#ifdef USE_POLL
-       ufds[0].fd = 0; ufds[1].fd = G.netfd;
-       ufds[0].events = ufds[1].events = POLLIN;
-#else
-       FD_ZERO(&readfds);
-       FD_SET(0, &readfds);
-       FD_SET(G.netfd, &readfds);
-       maxfd = G.netfd + 1;
-#endif
+       ufds[0].fd = STDIN_FILENO;
+       ufds[0].events = POLLIN;
+       ufds[1].fd = netfd;
+       ufds[1].events = POLLIN;
 
        while (1) {
-#ifndef USE_POLL
-               fd_set rfds = readfds;
-
-               switch (select(maxfd, &rfds, NULL, NULL, NULL))
-#else
-               switch (poll(ufds, 2, -1))
-#endif
-               {
-               case 0:
-                       /* timeout */
-               case -1:
+               if (poll(ufds, 2, -1) < 0) {
                        /* error, ignore and/or log something, bay go to loop */
-                       if (G.gotsig)
-                               conescape();
+                       if (bb_got_signal)
+                               con_escape();
                        else
                                sleep(1);
-                       break;
-               default:
-
-#ifdef USE_POLL
-                       if (ufds[0].revents) /* well, should check POLLIN, but ... */
-#else
-                       if (FD_ISSET(0, &rfds))
-#endif
-                       {
-                               len = read(0, G.buf, DATABUFSIZE);
-
-                               if (len <= 0)
-                                       doexit(0);
-
-                               TRACE(0, ("Read con: %d\n", len));
-
-                               handlenetoutput(len);
-                       }
+                       continue;
+               }
 
-#ifdef USE_POLL
-                       if (ufds[1].revents) /* well, should check POLLIN, but ... */
-#else
-                       if (FD_ISSET(G.netfd, &rfds))
-#endif
-                       {
-                               len = read(G.netfd, G.buf, DATABUFSIZE);
+// FIXME: reads can block. Need full bidirectional buffering.
 
-                               if (len <= 0) {
-                                       WriteCS(1, "Connection closed by foreign host.\r\n");
-                                       doexit(1);
-                               }
-                               TRACE(0, ("Read netfd (%d): %d\n", G.netfd, len));
+               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);
+               }
 
-                               handlenetinput(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) */
 }