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

1 files changed, 41 insertions, 30 deletions

diff --git a/networking/telnetd.c b/networking/telnetd.c
index efc2bf6..f60c420 100644
--- 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;