From 319b403916158fbde498b6bd5e494ad91a122c22 Mon Sep 17 00:00:00 2001
From: ache <ache@FreeBSD.org>
Date: Fri, 30 Dec 1994 16:09:31 +0000
Subject: [PATCH] Add check for writeable terminal Submitted by:
 mark@grondar.za (and slightly modified)

---
 usr.bin/talk/init_disp.c | 19 +++++++++++++++++++
 usr.bin/talk/talk.c      |  2 ++
 2 files changed, 21 insertions(+)

diff --git a/usr.bin/talk/init_disp.c b/usr.bin/talk/init_disp.c
index 5bebcd8bbef4..ee9955600e28 100644
--- a/usr.bin/talk/init_disp.c
+++ b/usr.bin/talk/init_disp.c
@@ -42,11 +42,30 @@ static char sccsid[] = "@(#)init_disp.c	8.2 (Berkeley) 2/16/94";
 
 #include <sys/ioctl.h>
 #include <sys/ioctl_compat.h>
+#include <sys/types.h>
+#include <sys/stat.h>
 
+#include <unistd.h>
 #include <signal.h>
 #include <err.h>
 #include "talk.h"
 
+/* 
+ * Make sure the callee can write to the screen
+ */
+void check_writeable()
+{
+	char *tty;
+	struct stat sb;
+
+	if ((tty = ttyname(STDERR_FILENO)) == NULL)
+		err(1, "ttyname");
+	if (stat(tty, &sb) < 0)
+		err(1, "%s", tty);
+	if (!(sb.st_mode & S_IWGRP))
+		errx(1, "The callee cannot write to this terminal, use \"mesg y\".");
+}
+
 /* 
  * Set up curses, catch the appropriate signals,
  * and build the various windows.
diff --git a/usr.bin/talk/talk.c b/usr.bin/talk/talk.c
index 702df162c134..8873e26afffe 100644
--- a/usr.bin/talk/talk.c
+++ b/usr.bin/talk/talk.c
@@ -55,6 +55,7 @@ static char sccsid[] = "@(#)talk.c	8.1 (Berkeley) 6/6/93";
  *		Modified to run under 4.1a by Clem Cole and Peter Moore
  *		Modified to run between hosts by Peter Moore, 8/19/82
  *		Modified to run under 4.1c by Peter Moore 3/17/83
+ *		Fixed to not run with unwriteable terminals MRVM 28/12/94
  */
 
 main(argc, argv)
@@ -62,6 +63,7 @@ main(argc, argv)
 	char *argv[];
 {
 	get_names(argc, argv);
+	check_writeable();
 	init_display();
 	open_ctl();
 	open_sockt();