From 4369d5b66f89fb26520f3ed20c9d7ee250d10259 Mon Sep 17 00:00:00 2001
From: Martin Lund <martin.lund@keep-it-simple.com>
Date: Fri, 5 Apr 2024 13:46:12 +0200
Subject: [PATCH] Add ONULBRK mapping flag

Add ONULBRK mapping to map nul (zero) to send break signal on output.

This is useful if one needs to e.g. send the break signal to the tty
device when connected via socket.
---
 man/tio.1.in |  2 ++
 src/tty.c    | 14 +++++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/man/tio.1.in b/man/tio.1.in
index 501a260..d36c56a 100644
--- a/man/tio.1.in
+++ b/man/tio.1.in
@@ -182,6 +182,8 @@ Map DEL to BS on output
 Map NL to CR-NL on output
 .IP "\fBOLTU"
 Map lowercase characters to uppercase on output
+.IP "\fBONULBRK"
+Map nul (zero) to send break signal on output
 .IP "\fBMSB2LSB"
 Map MSB bit order to LSB on output
 .P
diff --git a/src/tty.c b/src/tty.c
index 6921d04..38bf1ef 100644
--- a/src/tty.c
+++ b/src/tty.c
@@ -153,6 +153,7 @@ static bool map_o_cr_nl = false;
 static bool map_o_nl_crnl = false;
 static bool map_o_del_bs = false;
 static bool map_o_ltu = false;
+static bool map_o_nulbrk = false;
 static bool map_o_msblsb = false;
 static char hex_chars[2];
 static unsigned char hex_char_index = 0;
@@ -1115,6 +1116,10 @@ void tty_configure(void)
             {
                 map_o_ltu = true;
             }
+            else if (strcmp(token, "ONULBRK") == 0)
+            {
+                map_o_nulbrk = true;
+            }
             else if (strcmp(token, "MSB2LSB") == 0)
             {
                 map_o_msblsb = true;
@@ -1289,7 +1294,14 @@ void forward_to_tty(int fd, char output_char)
         {
             /* Send output to tty device */
             optional_local_echo(output_char);
-            status = tty_write(fd, &output_char, 1);
+            if ((output_char == 0) && (map_o_nulbrk))
+            {
+                status = tcsendbreak(fd, 0);
+            }
+            else
+            {
+                status = tty_write(fd, &output_char, 1);
+            }
             if (status < 0)
             {
                 tio_warning_printf("Could not write to tty device");