ldisc.c

/*
 * ldisc.c: PuTTY line discipline. Sits between the input coming
 * from keypresses in the window, and the output channel leading to
 * the back end. Implements echo and/or local line editing,
 * depending on what's currently configured.
 */

#include <stdio.h>
#include <ctype.h>
#include <assert.h>

#include "putty.h"
#include "terminal.h"
#include "ldisc.h"

#define ECHOING                                                                \
  (ldisc->localecho == FORCE_ON ||                                             \
   (ldisc->localecho == AUTO &&                                                \
    (ldisc->back->ldisc(ldisc->backhandle, LD_ECHO) ||                         \
     term_ldisc(ldisc->term, LD_ECHO))))
#define EDITING                                                                \
  (ldisc->localedit == FORCE_ON ||                                             \
   (ldisc->localedit == AUTO &&                                                \
    (ldisc->back->ldisc(ldisc->backhandle, LD_EDIT) ||                         \
     term_ldisc(ldisc->term, LD_EDIT))))

static void c_write(Ldisc ldisc, const char *buf, int len)
{
  from_backend(ldisc->frontend, 0, buf, len);
}

static int plen(Ldisc ldisc, unsigned char c)
{
  if ((c >= 32 && c <= 126) || (c >= 160 && !in_utf(ldisc->term)))
    return 1;
  else if (c < 128)
    return 2; /* ^x for some x */
  else if (in_utf(ldisc->term) && c >= 0xC0)
    return 1; /* UTF-8 introducer character
               * (FIXME: combining / wide chars) */
  else if (in_utf(ldisc->term) && c >= 0x80 && c < 0xC0)
    return 0; /* UTF-8 followup character */
  else
    return 4; /* <XY> hex representation */
}

static void pwrite(Ldisc ldisc, unsigned char c)
{
  if ((c >= 32 && c <= 126) || (!in_utf(ldisc->term) && c >= 0xA0) ||
      (in_utf(ldisc->term) && c >= 0x80)) {
    c_write(ldisc, (char *)&c, 1);
  } else if (c < 128) {
    char cc[2];
    cc[1] = (c == 127 ? '?' : c + 0x40);
    cc[0] = '^';
    c_write(ldisc, cc, 2);
  } else {
    char cc[5];
    sprintf(cc, "<%02X>", c);
    c_write(ldisc, cc, 4);
  }
}

static int char_start(Ldisc ldisc, unsigned char c)
{
  if (in_utf(ldisc->term))
    return (c < 0x80 || c >= 0xC0);
  else
    return 1;
}

static void bsb(Ldisc ldisc, int n)
{
  while (n--)
    c_write(ldisc, "\010 \010", 3);
}

#define CTRL(x) (x ^ '@')
#define KCTRL(x) ((x ^ '@') | 0x100)

void *ldisc_create(
    Conf *conf, Terminal *term, Backend *back, void *backhandle, void *frontend)
{
  Ldisc ldisc = snew(struct ldisc_tag);

  ldisc->buf = NULL;
  ldisc->buflen = 0;
  ldisc->bufsiz = 0;
  ldisc->quotenext = 0;

  ldisc->back = back;
  ldisc->backhandle = backhandle;
  ldisc->term = term;
  ldisc->frontend = frontend;

  ldisc_configure(ldisc, conf);

  /* Link ourselves into the backend and the terminal */
  if (term)
    term->ldisc = ldisc;
  if (back)
    back->provide_ldisc(backhandle, ldisc);

  return ldisc;
}

void ldisc_configure(void *handle, Conf *conf)
{
  Ldisc ldisc = (Ldisc)handle;

  ldisc->telnet_keyboard = conf_get_int(conf, CONF_telnet_keyboard);
  ldisc->telnet_newline = conf_get_int(conf, CONF_telnet_newline);
  ldisc->protocol = conf_get_int(conf, CONF_protocol);
  ldisc->localecho = conf_get_int(conf, CONF_localecho);
  ldisc->localedit = conf_get_int(conf, CONF_localedit);
}

void ldisc_free(void *handle)
{
  Ldisc ldisc = (Ldisc)handle;

  if (ldisc->term)
    ldisc->term->ldisc = NULL;
  if (ldisc->back)
    ldisc->back->provide_ldisc(ldisc->backhandle, NULL);
  if (ldisc->buf)
    sfree(ldisc->buf);
  sfree(ldisc);
}

void ldisc_echoedit_update(void *handle)
{
  Ldisc ldisc = (Ldisc)handle;
  frontend_echoedit_update(ldisc->frontend, ECHOING, EDITING);
}

void ldisc_send(void *handle, const char *buf, int len, int interactive)
{
  Ldisc ldisc = (Ldisc)handle;
  int keyflag = 0;

  assert(ldisc->term);
  assert(len);

  /*
   * Notify the front end that something was pressed, in case
   * it's depending on finding out (e.g. keypress termination for
   * Close On Exit).
   */
  frontend_keypress(ldisc->frontend);

  if (interactive) {
    /*
     * Interrupt a paste from the clipboard, if one was in
     * progress when the user pressed a key. This is easier than
     * buffering the current piece of data and saving it until the
     * terminal has finished pasting, and has the potential side
     * benefit of permitting a user to cancel an accidental huge
     * paste.
     */
    term_nopaste(ldisc->term);
  }

  /*
   * Less than zero means null terminated special string.
   */
  if (len < 0) {
    len = strlen(buf);
    keyflag = KCTRL('@');
  }
  /*
   * Either perform local editing, or just send characters.
   */
  if (EDITING) {
    while (len--) {
      int c;
      c = (unsigned char)(*buf++) + keyflag;
      if (!interactive && c == '\r')
        c += KCTRL('@');
      switch (ldisc->quotenext ? ' ' : c) {
        /*
         * ^h/^?: delete, and output BSBs, to return to
         * last character boundary (in UTF-8 mode this may
         * be more than one byte)
         * ^w: delete, and output BSBs, to return to last
         * space/nonspace boundary
         * ^u: delete, and output BSBs, to return to BOL
         * ^c: Do a ^u then send a telnet IP
         * ^z: Do a ^u then send a telnet SUSP
         * ^\: Do a ^u then send a telnet ABORT
         * ^r: echo "^R\n" and redraw line
         * ^v: quote next char
         * ^d: if at BOL, end of file and close connection,
         * else send line and reset to BOL
         * ^m: send line-plus-\r\n and reset to BOL
         */
      case KCTRL('H'):
      case KCTRL('?'): /* backspace/delete */
        if (ldisc->buflen > 0) {
          do {
            if (ECHOING)
              bsb(ldisc, plen(ldisc, ldisc->buf[ldisc->buflen - 1]));
            ldisc->buflen--;
          } while (!char_start(ldisc, ldisc->buf[ldisc->buflen]));
        }
        break;
      case CTRL('W'): /* delete word */
        while (ldisc->buflen > 0) {
          if (ECHOING)
            bsb(ldisc, plen(ldisc, ldisc->buf[ldisc->buflen - 1]));
          ldisc->buflen--;
          if (ldisc->buflen > 0 &&
              isspace((unsigned char)ldisc->buf[ldisc->buflen - 1]) &&
              !isspace((unsigned char)ldisc->buf[ldisc->buflen]))
            break;
        }
        break;
      case CTRL('U'):  /* delete line */
      case CTRL('C'):  /* Send IP */
      case CTRL('\\'): /* Quit */
      case CTRL('Z'):  /* Suspend */
        while (ldisc->buflen > 0) {
          if (ECHOING)
            bsb(ldisc, plen(ldisc, ldisc->buf[ldisc->buflen - 1]));
          ldisc->buflen--;
        }
        ldisc->back->special(ldisc->backhandle, TS_EL);
        /*
         * We don't send IP, SUSP or ABORT if the user has
         * configured telnet specials off! This breaks
         * talkers otherwise.
         */
        if (!ldisc->telnet_keyboard)
          goto default_case;
        if (c == CTRL('C'))
          ldisc->back->special(ldisc->backhandle, TS_IP);
        if (c == CTRL('Z'))
          ldisc->back->special(ldisc->backhandle, TS_SUSP);
        if (c == CTRL('\\'))
          ldisc->back->special(ldisc->backhandle, TS_ABORT);
        break;
      case CTRL('R'): /* redraw line */
        if (ECHOING) {
          int i;
          c_write(ldisc, "^R\r\n", 4);
          for (i = 0; i < ldisc->buflen; i++)
            pwrite(ldisc, ldisc->buf[i]);
        }
        break;
      case CTRL('V'): /* quote next char */
        ldisc->quotenext = TRUE;
        break;
      case CTRL('D'): /* logout or send */
        if (ldisc->buflen == 0) {
          ldisc->back->special(ldisc->backhandle, TS_EOF);
        } else {
          ldisc->back->send(ldisc->backhandle, ldisc->buf, ldisc->buflen);
          ldisc->buflen = 0;
        }
        break;
        /*
         * This particularly hideous bit of code from RDB
         * allows ordinary ^M^J to do the same thing as
         * magic-^M when in Raw protocol. The line `case
         * KCTRL('M'):' is _inside_ the if block. Thus:
         *
         *  - receiving regular ^M goes straight to the
         *    default clause and inserts as a literal ^M.
         *  - receiving regular ^J _not_ directly after a
         *    literal ^M (or not in Raw protocol) fails the
         *    if condition, leaps to the bottom of the if,
         *    and falls through into the default clause
         *    again.
         *  - receiving regular ^J just after a literal ^M
         *    in Raw protocol passes the if condition,
         *    deletes the literal ^M, and falls through
         *    into the magic-^M code
         *  - receiving a magic-^M empties the line buffer,
         *    signals end-of-line in one of the various
         *    entertaining ways, and _doesn't_ fall out of
         *    the bottom of the if and through to the
         *    default clause because of the break.
         */
      case CTRL('J'):
        if (ldisc->protocol == PROT_RAW && ldisc->buflen > 0 &&
            ldisc->buf[ldisc->buflen - 1] == '\r') {
          if (ECHOING)
            bsb(ldisc, plen(ldisc, ldisc->buf[ldisc->buflen - 1]));
          ldisc->buflen--;
          /* FALLTHROUGH */
        case KCTRL('M'): /* send with newline */
          if (ldisc->buflen > 0)
            ldisc->back->send(ldisc->backhandle, ldisc->buf, ldisc->buflen);
          if (ldisc->protocol == PROT_RAW)
            ldisc->back->send(ldisc->backhandle, "\r\n", 2);
          else if (ldisc->protocol == PROT_TELNET && ldisc->telnet_newline)
            ldisc->back->special(ldisc->backhandle, TS_EOL);
          else
            ldisc->back->send(ldisc->backhandle, "\r", 1);
          if (ECHOING)
            c_write(ldisc, "\r\n", 2);
          ldisc->buflen = 0;
          break;
        }
        /* FALLTHROUGH */
      default: /* get to this label from ^V handler */
      default_case:
        if (ldisc->buflen >= ldisc->bufsiz) {
          ldisc->bufsiz = ldisc->buflen + 256;
          ldisc->buf = sresize(ldisc->buf, ldisc->bufsiz, char);
        }
        ldisc->buf[ldisc->buflen++] = c;
        if (ECHOING)
          pwrite(ldisc, (unsigned char)c);
        ldisc->quotenext = FALSE;
        break;
      }
    }
  } else {
    if (ldisc->buflen != 0) {
      ldisc->back->send(ldisc->backhandle, ldisc->buf, ldisc->buflen);
      while (ldisc->buflen > 0) {
        bsb(ldisc, plen(ldisc, ldisc->buf[ldisc->buflen - 1]));
        ldisc->buflen--;
      }
    }
    if (len > 0) {
      if (ECHOING)
        c_write(ldisc, buf, len);
      if (keyflag && ldisc->protocol == PROT_TELNET && len == 1) {
        switch (buf[0]) {
        case CTRL('M'):
          if (ldisc->protocol == PROT_TELNET && ldisc->telnet_newline)
            ldisc->back->special(ldisc->backhandle, TS_EOL);
          else
            ldisc->back->send(ldisc->backhandle, "\r", 1);
          break;
        case CTRL('?'):
        case CTRL('H'):
          if (ldisc->telnet_keyboard) {
            ldisc->back->special(ldisc->backhandle, TS_EC);
            break;
          }
        case CTRL('C'):
          if (ldisc->telnet_keyboard) {
            ldisc->back->special(ldisc->backhandle, TS_IP);
            break;
          }
        case CTRL('Z'):
          if (ldisc->telnet_keyboard) {
            ldisc->back->special(ldisc->backhandle, TS_SUSP);
            break;
          }

        default:
          ldisc->back->send(ldisc->backhandle, buf, len);
          break;
        }
      } else
        ldisc->back->send(ldisc->backhandle, buf, len);
    }
  }
}