Preserve SIGINT handler after external paging

fire/console/console_io.py

@@ -96,13 +96,14 @@ def More(contents, out, prompt=None, check_pager=True):
       encoding.SetEncodedValue(os.environ, 'LESS', less)
       # Ignore SIGINT while the pager is running.
       # We don't want to terminate the parent while the child is still alive.
-      signal.signal(signal.SIGINT, signal.SIG_IGN)
-      p = subprocess.Popen(pager, stdin=subprocess.PIPE, shell=True)
-      enc = console_attr.GetConsoleAttr().GetEncoding()
-      p.communicate(input=contents.encode(enc))
-      p.wait()
-      # Start using default signal handling for SIGINT again.
-      signal.signal(signal.SIGINT, signal.SIG_DFL)
+      original_sigint = signal.signal(signal.SIGINT, signal.SIG_IGN)
+      try:
+        p = subprocess.Popen(pager, stdin=subprocess.PIPE, shell=True)
+        enc = console_attr.GetConsoleAttr().GetEncoding()
+        p.communicate(input=contents.encode(enc))
+        p.wait()
+      finally:
+        signal.signal(signal.SIGINT, original_sigint)
       if less_orig is None:
         encoding.SetEncodedValue(os.environ, 'LESS', None)
       return

fire/console/console_io_test.py

@@ -0,0 +1,132 @@
+# Copyright 2026 Google LLC. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tests for console_io.py."""
+
+import io
+import os
+import signal
+from unittest import mock
+
+from fire import core
+from fire import testutils
+from fire.console import console_io
+
+
+class MoreTest(testutils.BaseTestCase):
+
+  def setUp(self):
+    super().setUp()
+    original_handler = signal.getsignal(signal.SIGINT)
+    self.addCleanup(signal.signal, signal.SIGINT, original_handler)
+    self.handler = mock.Mock()
+    signal.signal(signal.SIGINT, self.handler)
+    self.out = io.StringIO()
+    self.process = mock.Mock()
+    self.process.communicate.side_effect = self.AssertSigintIgnored
+    self.process.wait.side_effect = self.AssertSigintIgnored
+    self.StartPatch(mock.patch.dict(os.environ, {'PAGER': 'test-pager'}))
+    self.interactive = self.StartPatch(
+        mock.patch.object(console_io, 'IsInteractive', return_value=True))
+    self.popen = self.StartPatch(mock.patch.object(
+        console_io.subprocess, 'Popen', side_effect=self.StartPager))
+    self.attr = self.StartPatch(
+        mock.patch.object(console_io.console_attr, 'GetConsoleAttr'))
+    self.attr.return_value.GetEncoding.return_value = 'utf-8'
+    self.find = self.StartPatch(
+        mock.patch.object(console_io.files, 'FindExecutableOnPath'))
+    self.internal = self.StartPatch(
+        mock.patch.object(console_io.console_pager, 'Pager'))
+
+  def StartPatch(self, patcher):
+    self.addCleanup(patcher.stop)
+    return patcher.start()
+
+  def AssertSigintIgnored(self, **_kwargs):
+    self.assertEqual(signal.getsignal(signal.SIGINT), signal.SIG_IGN)
+
+  def StartPager(self, *_args, **_kwargs):
+    self.AssertSigintIgnored()
+    return self.process
+
+  def testRestoresSigintAfterExternalPager(self):
+    for handler in (self.handler, signal.default_int_handler,
+                    signal.SIG_DFL, signal.SIG_IGN):
+      for pager in ('test-pager', 'less', 'pager'):
+        with self.subTest(handler=handler, pager=pager):
+          signal.signal(signal.SIGINT, handler)
+          os.environ['PAGER'] = pager if pager == 'test-pager' else ''
+          self.find.side_effect = lambda command, selected=pager: (
+              command == selected)
+          console_io.More('example', self.out)
+          self.assertEqual(signal.getsignal(signal.SIGINT), handler)
+          self.popen.assert_called_with(
+              pager, stdin=console_io.subprocess.PIPE, shell=True)
+          self.process.communicate.assert_called_with(input=b'example')
+          self.internal.assert_not_called()
+
+  def testRestoresSigintOnPagerError(self):
+    for target, error in (
+        (self.popen, OSError('spawn')),
+        (self.attr, ValueError('encoding lookup')),
+        (self.process.communicate, OSError('communicate')),
+        (self.process.wait, OSError('wait')),
+        (self.process.communicate, KeyboardInterrupt())):
+      with self.subTest(error=error):
+        signal.signal(signal.SIGINT, self.handler)
+        original_effect = target.side_effect
+        target.side_effect = error
+        try:
+          with self.assertRaises(type(error)) as caught:
+            console_io.More('example', self.out)
+        finally:
+          target.side_effect = original_effect
+        self.assertIs(caught.exception, error)
+        self.assertEqual(signal.getsignal(signal.SIGINT), self.handler)
+        self.internal.assert_not_called()
+
+  def testRestoresSigintOnEncodingError(self):
+    self.attr.return_value.GetEncoding.return_value = 'ascii'
+    with self.assertRaises(UnicodeEncodeError):
+      console_io.More('\u00e9', self.out)
+    self.assertEqual(signal.getsignal(signal.SIGINT), self.handler)
+    self.process.communicate.assert_not_called()
+
+  def testNoninteractivePreservesSigint(self):
+    self.interactive.return_value = False
+    console_io.More('example', self.out)
+    self.assertEqual(self.out.getvalue(), 'example')
+    self.assertEqual(signal.getsignal(signal.SIGINT), self.handler)
+    self.popen.assert_not_called()
+    self.internal.assert_not_called()
+
+  def testInternalPagerPreservesSigint(self):
+    for check_pager, pager in ((False, 'test-pager'), (True, '-'), (True, '')):
+      with self.subTest(check_pager=check_pager, pager=pager):
+        os.environ['PAGER'] = pager
+        self.find.return_value = None
+        console_io.More('example', self.out, check_pager=check_pager)
+        self.assertEqual(signal.getsignal(signal.SIGINT), self.handler)
+        self.popen.assert_not_called()
+        self.internal.assert_called_with('example', self.out, None)
+        self.internal.return_value.Run.assert_called_with()
+
+  def testDisplayPreservesSigint(self):
+    core.Display(['first', 'second'], self.out)
+    self.assertEqual(signal.getsignal(signal.SIGINT), self.handler)
+    self.process.communicate.assert_called_once_with(input=b'first\nsecond\n')
+
+
+if __name__ == '__main__':
+  testutils.main()