text: /*
   * Rlogin backend.
   */
  
  #include <stdio.h>
  #include <stdlib.h>
  #include <limits.h>
  #include <ctype.h>
  
  #include "putty.h"
  
  #ifndef FALSE
  #define FALSE 0
  #endif
  #ifndef TRUE
  #define TRUE 1
  #endif
  
  #define RLOGIN_MAX_BACKLOG 4096
  
  typedef struct rlogin_tag {
      const struct plug_function_table *fn;
      /* the above field _must_ be first in the structure */
  
      Socket s;
      int closed_on_socket_error;
      int bufsize;
      int firstbyte;
      int cansize;
      int term_width, term_height;
      void *frontend;
  
      Conf *conf;
  
      /* In case we need to read a username from the terminal before starting */
      prompts_t *prompt;
  } *Rlogin;
  
  static void rlogin_size(void *handle, int width, int height);
  
  static void c_write(Rlogin rlogin, char *buf, int len)
  {
      int backlog = from_backend(rlogin->frontend, 0, buf, len);
      sk_set_frozen(rlogin->s, backlog > RLOGIN_MAX_BACKLOG);
  }
  
  static void rlogin_log(Plug plug, int type, SockAddr addr, int port,
  		       const char *error_msg, int error_code)
  {
      Rlogin rlogin = (Rlogin) plug;
      backend_socket_log(rlogin->frontend, type, addr, port,
                         error_msg, error_code,
                         rlogin->conf, !rlogin->firstbyte);
  }
  
  static int rlogin_closing(Plug plug, const char *error_msg, int error_code,
  			  int calling_back)
  {
      Rlogin rlogin = (Rlogin) plug;
  
      /*
       * We don't implement independent EOF in each direction for Telnet
       * connections; as soon as we get word that the remote side has
       * sent us EOF, we wind up the whole connection.
       */
  
      if (rlogin->s) {
          sk_close(rlogin->s);
          rlogin->s = NULL;
          if (error_msg)
              rlogin->closed_on_socket_error = TRUE;
  	notify_remote_exit(rlogin->frontend);
      }
      if (error_msg) {
  	/* A socket error has occurred. */
  	logevent(rlogin->frontend, error_msg);
  	connection_fatal(rlogin->frontend, "%s", error_msg);
      }				       /* Otherwise, the remote side closed the connection normally. */
      return 0;
  }
  
  static int rlogin_receive(Plug plug, int urgent, char *data, int len)
  {
      Rlogin rlogin = (Rlogin) plug;
      if (urgent == 2) {
  	char c;
  
  	c = *data++;
  	len--;
  	if (c == '\x80') {
  	    rlogin->cansize = 1;
  	    rlogin_size(rlogin, rlogin->term_width, rlogin->term_height);
          }
  	/*
  	 * We should flush everything (aka Telnet SYNCH) if we see
  	 * 0x02, and we should turn off and on _local_ flow control
  	 * on 0x10 and 0x20 respectively. I'm not convinced it's
  	 * worth it...
  	 */
      } else {
  	/*
  	 * Main rlogin protocol. This is really simple: the first
  	 * byte is expected to be NULL and is ignored, and the rest
  	 * is printed.
  	 */
  	if (rlogin->firstbyte) {
  	    if (data[0] == '\0') {
  		data++;
  		len--;
  	    }
  	    rlogin->firstbyte = 0;
  	}
  	if (len > 0)
              c_write(rlogin, data, len);
      }
      return 1;
  }
  
  static void rlogin_sent(Plug plug, int bufsize)
  {
      Rlogin rlogin = (Rlogin) plug;
      rlogin->bufsize = bufsize;
  }
  
  static void rlogin_startup(Rlogin rlogin, const char *ruser)
  {
      char z = 0;
      char *p;
  
      sk_write(rlogin->s, &z, 1);
      p = conf_get_str(rlogin->conf, CONF_localusername);
      sk_write(rlogin->s, p, strlen(p));
      sk_write(rlogin->s, &z, 1);
      sk_write(rlogin->s, ruser, strlen(ruser));
      sk_write(rlogin->s, &z, 1);
      p = conf_get_str(rlogin->conf, CONF_termtype);
      sk_write(rlogin->s, p, strlen(p));
      sk_write(rlogin->s, "/", 1);
      p = conf_get_str(rlogin->conf, CONF_termspeed);
      sk_write(rlogin->s, p, strspn(p, "0123456789"));
      rlogin->bufsize = sk_write(rlogin->s, &z, 1);
  
      rlogin->prompt = NULL;
  }
  
  /*
   * Called to set up the rlogin connection.
   * 
   * Returns an error message, or NULL on success.
   *
   * Also places the canonical host name into `realhost'. It must be
   * freed by the caller.
   */
  static const char *rlogin_init(void *frontend_handle, void **backend_handle,
  			       Conf *conf,
  			       const char *host, int port, char **realhost,
  			       int nodelay, int keepalive)
  {
      static const struct plug_function_table fn_table = {
  	rlogin_log,
  	rlogin_closing,
  	rlogin_receive,
  	rlogin_sent
      };
      SockAddr addr;
      const char *err;
      Rlogin rlogin;
      char *ruser;
      int addressfamily;
      char *loghost;
  
      rlogin = snew(struct rlogin_tag);
      rlogin->fn = &fn_table;
      rlogin->s = NULL;
      rlogin->closed_on_socket_error = FALSE;
      rlogin->frontend = frontend_handle;
      rlogin->term_width = conf_get_int(conf, CONF_width);
      rlogin->term_height = conf_get_int(conf, CONF_height);
      rlogin->firstbyte = 1;
      rlogin->cansize = 0;
      rlogin->prompt = NULL;
      rlogin->conf = conf_copy(conf);
      *backend_handle = rlogin;
  
      addressfamily = conf_get_int(conf, CONF_addressfamily);
      /*
       * Try to find host.
       */
      addr = name_lookup(host, port, realhost, conf, addressfamily,
                         rlogin->frontend, "rlogin connection");
      if ((err = sk_addr_error(addr)) != NULL) {
  	sk_addr_free(addr);
  	return err;
      }
  
      if (port < 0)
  	port = 513;		       /* default rlogin port */
  
      /*
       * Open socket.
       */
      rlogin->s = new_connection(addr, *realhost, port, 1, 0,
  			       nodelay, keepalive, (Plug) rlogin, conf);
      if ((err = sk_socket_error(rlogin->s)) != NULL)
  	return err;
  
      loghost = conf_get_str(conf, CONF_loghost);
      if (*loghost) {
  	char *colon;
  
  	sfree(*realhost);
  	*realhost = dupstr(loghost);
  
  	colon = host_strrchr(*realhost, ':');
  	if (colon)
  	    *colon++ = '\0';
      }
  
      /*
       * Send local username, remote username, terminal type and
       * terminal speed - unless we don't have the remote username yet,
       * in which case we prompt for it and may end up deferring doing
       * anything else until the local prompt mechanism returns.
       */
      if ((ruser = get_remote_username(conf)) != NULL) {
          rlogin_startup(rlogin, ruser);
          sfree(ruser);
      } else {
          int ret;
  
          rlogin->prompt = new_prompts(rlogin->frontend);
          rlogin->prompt->to_server = TRUE;
          rlogin->prompt->name = dupstr("Rlogin login name");
          add_prompt(rlogin->prompt, dupstr("rlogin username: "), TRUE); 
          ret = get_userpass_input(rlogin->prompt, NULL, 0);
          if (ret >= 0) {
              rlogin_startup(rlogin, rlogin->prompt->prompts[0]->result);
          }
      }
  
      return NULL;
  }
  
  static void rlogin_free(void *handle)
  {
      Rlogin rlogin = (Rlogin) handle;
  
      if (rlogin->prompt)
          free_prompts(rlogin->prompt);
      if (rlogin->s)
  	sk_close(rlogin->s);
      conf_free(rlogin->conf);
      sfree(rlogin);
  }
  
  /*
   * Stub routine (we don't have any need to reconfigure this backend).
   */
  static void rlogin_reconfig(void *handle, Conf *conf)
  {
  }
  
  /*
   * Called to send data down the rlogin connection.
   */
  static int rlogin_send(void *handle, const char *buf, int len)
  {
      Rlogin rlogin = (Rlogin) handle;
  
      if (rlogin->s == NULL)
  	return 0;
  
      if (rlogin->prompt) {
          /*
           * We're still prompting for a username, and aren't talking
           * directly to the network connection yet.
           */
          int ret = get_userpass_input(rlogin->prompt,
                                       (unsigned char *)buf, len);
          if (ret >= 0) {
              rlogin_startup(rlogin, rlogin->prompt->prompts[0]->result);
              /* that nulls out rlogin->prompt, so then we'll start sending
               * data down the wire in the obvious way */
          }
      } else {
          rlogin->bufsize = sk_write(rlogin->s, buf, len);
      }
  
      return rlogin->bufsize;
  }
  
  /*
   * Called to query the current socket sendability status.
   */
  static int rlogin_sendbuffer(void *handle)
  {
      Rlogin rlogin = (Rlogin) handle;
      return rlogin->bufsize;
  }
  
  /*
   * Called to set the size of the window
   */
  static void rlogin_size(void *handle, int width, int height)
  {
      Rlogin rlogin = (Rlogin) handle;
      char b[12] = { '\xFF', '\xFF', 0x73, 0x73, 0, 0, 0, 0, 0, 0, 0, 0 };
  
      rlogin->term_width = width;
      rlogin->term_height = height;
  
      if (rlogin->s == NULL || !rlogin->cansize)
  	return;
  
      b[6] = rlogin->term_width >> 8;
      b[7] = rlogin->term_width & 0xFF;
      b[4] = rlogin->term_height >> 8;
      b[5] = rlogin->term_height & 0xFF;
      rlogin->bufsize = sk_write(rlogin->s, b, 12);
      return;
  }
  
  /*
   * Send rlogin special codes.
   */
  static void rlogin_special(void *handle, Telnet_Special code)
  {
      /* Do nothing! */
      return;
  }
  
  /*
   * Return a list of the special codes that make sense in this
   * protocol.
   */
  static const struct telnet_special *rlogin_get_specials(void *handle)
  {
      return NULL;
  }
  
  static int rlogin_connected(void *handle)
  {
      Rlogin rlogin = (Rlogin) handle;
      return rlogin->s != NULL;
  }
  
  static int rlogin_sendok(void *handle)
  {
      /* Rlogin rlogin = (Rlogin) handle; */
      return 1;
  }
  
  static void rlogin_unthrottle(void *handle, int backlog)
  {
      Rlogin rlogin = (Rlogin) handle;
      sk_set_frozen(rlogin->s, backlog > RLOGIN_MAX_BACKLOG);
  }
  
  static int rlogin_ldisc(void *handle, int option)
  {
      /* Rlogin rlogin = (Rlogin) handle; */
      return 0;
  }
  
  static void rlogin_provide_ldisc(void *handle, void *ldisc)
  {
      /* This is a stub. */
  }
  
  static void rlogin_provide_logctx(void *handle, void *logctx)
  {
      /* This is a stub. */
  }
  
  static int rlogin_exitcode(void *handle)
  {
      Rlogin rlogin = (Rlogin) handle;
      if (rlogin->s != NULL)
          return -1;                     /* still connected */
      else if (rlogin->closed_on_socket_error)
          return INT_MAX;     /* a socket error counts as an unclean exit */
      else
          /* If we ever implement RSH, we'll probably need to do this properly */
          return 0;
  }
  
  /*
   * cfg_info for rlogin does nothing at all.
   */
  static int rlogin_cfg_info(void *handle)
  {
      return 0;
  }
  
  Backend rlogin_backend = {
      rlogin_init,
      rlogin_free,
      rlogin_reconfig,
      rlogin_send,
      rlogin_sendbuffer,
      rlogin_size,
      rlogin_special,
      rlogin_get_specials,
      rlogin_connected,
      rlogin_exitcode,
      rlogin_sendok,
      rlogin_ldisc,
      rlogin_provide_ldisc,
      rlogin_provide_logctx,
      rlogin_unthrottle,
      rlogin_cfg_info,
      NULL /* test_for_upstream */,
      "rlogin",
      PROT_RLOGIN,
      513
  };
  