utils: T9185: fix ask_yes_no() busy-looping forever on non-tty stdin

commit-confirm (and ~40 other call sites) hang and burn a full CPU core
indefinitely when invoked with stdin that isn't a TTY, e.g. a
non-interactive vbash session (vbash -c "... commit-confirm 10; exit").
input() raises EOFError immediately and repeatedly in that case, and the
except handler in ask_yes_no() looped straight back to input() with no
backoff or exit condition.

Check stdin.isatty() up front and return the default immediately when
it's not a TTY, matching what a user pressing Enter (accepting the
default) would already do interactively.

1 files changed, 46 insertions, 0 deletions

diff --git a/src/tests/test_utils_io.py b/src/tests/test_utils_io.py
new file mode 100644
index 000000000..7adb0dc61
--- /dev/null
+++ b/src/tests/test_utils_io.py
@@ -0,0 +1,46 @@
+# Copyright VyOS maintainers and contributors <maintainers@vyos.io>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 or later as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import unittest
+from unittest.mock import patch
+
+from vyos.utils.io import ask_yes_no
+
+
+class TestVyOSUtilsIO(unittest.TestCase):
+    def test_ask_yes_no_non_interactive_returns_default_without_reading_stdin(self):
+        # T9185: on a non-TTY stdin (e.g. a non-interactive vbash session),
+        # input() raises EOFError immediately and forever; ask_yes_no() must
+        # return the default straight away instead of ever looping on input().
+        with patch('sys.stdin') as mock_stdin:
+            mock_stdin.isatty.return_value = False
+            with patch('builtins.input') as mock_input:
+                self.assertTrue(ask_yes_no('Proceed?', default=True))
+                self.assertFalse(ask_yes_no('Proceed?', default=False))
+                mock_input.assert_not_called()
+
+    def test_ask_yes_no_interactive_reads_input(self):
+        with patch('sys.stdin') as mock_stdin:
+            mock_stdin.isatty.return_value = True
+            with patch('builtins.input', return_value='y'):
+                self.assertTrue(ask_yes_no('Proceed?', default=False))
+            with patch('builtins.input', return_value='n'):
+                self.assertFalse(ask_yes_no('Proceed?', default=True))
+            with patch('builtins.input', return_value=''):
+                self.assertTrue(ask_yes_no('Proceed?', default=True))
+                self.assertFalse(ask_yes_no('Proceed?', default=False))
+
+
+if __name__ == '__main__':
+    unittest.main()