Only handle IAC for telnet connections

This is a bit ugly because the muxer should not be aware of telnet protocol
specifics but it is aware already anyhow, so we can just as well expand it
a bit.

Fixes: #4
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Author: Uwe Kleine-König

microcom.h

@@ -26,6 +26,7 @@
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdbool.h>
 #include <signal.h>
 #include <string.h>
 #include <termios.h>
@@ -48,6 +49,7 @@ struct ios_ops {
 	int (*set_handshake_line)(struct ios_ops *, int pin, int enable);
 	int (*send_break)(struct ios_ops *);
 	void (*exit)(struct ios_ops *);
+	bool istelnet;
 	int fd;
 };
 

mux.c

@@ -308,17 +308,6 @@ static int handle_receive_buf(struct ios_ops *ios, unsigned char *buf, int len)
 
 	while (len) {
 		switch (*buf) {
-		case IAC:
-			/* BUG: this is telnet specific */
-			write_receive_buf(sendbuf, buf - sendbuf);
-			i = handle_command(ios, buf, len);
-			if (i < 0)
-				return i;
-
-			buf += i;
-			len -= i;
-			sendbuf = buf;
-			break;
 		case 5:
 			write_receive_buf(sendbuf, buf - sendbuf);
 			if (answerback)
@@ -330,6 +319,19 @@ static int handle_receive_buf(struct ios_ops *ios, unsigned char *buf, int len)
 			len -= 1;
 			sendbuf = buf;
 			break;
+		case IAC:
+			if (ios->istelnet) {
+				write_receive_buf(sendbuf, buf - sendbuf);
+				i = handle_command(ios, buf, len);
+				if (i < 0)
+					return i;
+
+				buf += i;
+				len -= i;
+				sendbuf = buf;
+				break;
+			}
+			/* fall through */
 		default:
 			buf += 1;
 			len -= 1;

telnet.c

@@ -95,6 +95,7 @@ struct ios_ops *telnet_init(char *hostport)
 	ios->set_speed = telnet_set_speed;
 	ios->set_flow = telnet_set_flow;
 	ios->send_break = telnet_send_break;
+	ios->istelnet = true;
 	ios->exit = telnet_exit;
 
 	memset(&hints, '\0', sizeof(hints));