telnetd: handle emacs M-DEL and IAC-NOP (putty keepalive)

 by Jim Cathey (jcathey AT ciena.com)

function                                             old     new   delta
telnetd_main                                        1314    1364     +50

diff --git a/networking/telnetd.c b/networking/telnetd.c
index efc2bf60740f1ec3aebf2698f2491898c80ba246..f60c4205609a1781ab9c8efd85d0a919384c27f2 100644 (file)
--- a/networking/telnetd.c
+++ b/networking/telnetd.c
@@ -96,44 +96,55 @@ remove_iacs(struct tsession *ts, int *pnum_totty)
 
                        *totty++ = c;
                        ptr++;
-                       /* We now map \r\n ==> \r for pragmatic reasons.
+                       /* We map \r\n ==> \r for pragmatic reasons.
                         * Many client implementations send \r\n when
                         * the user hits the CarriageReturn key.
                         */
                        if (c == '\r' && ptr < end && (*ptr == '\n' || *ptr == '\0'))
                                ptr++;
-               } else {
-                       /*
-                        * TELOPT_NAWS support!
-                        */
-                       if ((ptr+2) >= end) {
-                               /* only the beginning of the IAC is in the
-                               buffer we were asked to process, we can't
-                               process this char. */
-                               break;
-                       }
+                       continue;
+               }
 
-                       /*
-                        * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE
-                        */
-                       else if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) {
-                               struct winsize ws;
-
-                               if ((ptr+8) >= end)
-                                       break;  /* incomplete, can't process */
-                               ws.ws_col = (ptr[3] << 8) | ptr[4];
-                               ws.ws_row = (ptr[5] << 8) | ptr[6];
-                               ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
-                               ptr += 9;
-                       } else {
-                               /* skip 3-byte IAC non-SB cmd */
+               if ((ptr+1) >= end)
+                       break;
+               if (ptr[1] == NOP) { /* Ignore? (putty keepalive, etc.) */
+                       ptr += 2;
+                       continue;
+               }
+               if (ptr[1] == IAC) { /* Literal IAC? (emacs M-DEL) */
+                       *totty++ = ptr[1];
+                       ptr += 2;
+                       continue;
+               }
+
+               /*
+                * TELOPT_NAWS support!
+                */
+               if ((ptr+2) >= end) {
+                       /* only the beginning of the IAC is in the
+                       buffer we were asked to process, we can't
+                       process this char. */
+                       break;
+               }
+               /*
+                * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE
+                */
+               if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) {
+                       struct winsize ws;
+                       if ((ptr+8) >= end)
+                               break;  /* incomplete, can't process */
+                       ws.ws_col = (ptr[3] << 8) | ptr[4];
+                       ws.ws_row = (ptr[5] << 8) | ptr[6];
+                       ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
+                       ptr += 9;
+                       continue;
+               }
+               /* skip 3-byte IAC non-SB cmd */
 #if DEBUG
-                               fprintf(stderr, "Ignoring IAC %s,%s\n",
-                                       TELCMD(ptr[1]), TELOPT(ptr[2]));
+               fprintf(stderr, "Ignoring IAC %s,%s\n",
+                               TELCMD(ptr[1]), TELOPT(ptr[2]));
 #endif
-                               ptr += 3;
-                       }
-               }
+               ptr += 3;
        }
 
        num_totty = totty - ptr0;