Handle SIGPIPE exit gracefully

If we are piping output to a command that exits before the entire
output is written (e.g. "head") then we will receive a BrokenPipeError.
This is expected and we should react by exiting gracefully, setting an
appropriate return code (128 + SIGPIPE).

Change-Id: I0d60e44450da1f48dbd8f459549da80fda69aad5

cliff/app.py

@@ -33,6 +33,7 @@ logging.getLogger('cliff').addHandler(logging.NullHandler())
 
 # Exit code for exiting due to a signal is 128 + the signal number
 _SIGINT_EXIT = 130
+_SIGPIPE_EXIT = 141
 
 
 class App(object):
@@ -256,6 +257,8 @@ class App(object):
                 remainder.insert(0, "help")
             self.initialize_app(remainder)
             self.print_help_if_requested()
+        except BrokenPipeError:
+            return _SIGPIPE_EXIT
         except Exception as err:
             if hasattr(self, 'options'):
                 debug = self.options.debug
@@ -275,6 +278,8 @@ class App(object):
         else:
             try:
                 result = self.run_subcommand(remainder)
+            except BrokenPipeError:
+                return _SIGPIPE_EXIT
             except KeyboardInterrupt:
                 return _SIGINT_EXIT
         return result
@@ -400,6 +405,10 @@ class App(object):
             except SystemExit as ex:
                 raise cmd2.exceptions.Cmd2ArgparseError from ex
             result = cmd.run(parsed_args)
+        except BrokenPipeError as err1:
+            result = _SIGPIPE_EXIT
+            err = err1
+            raise
         except help.HelpExit:
             result = 0
         except Exception as err1:

cliff/tests/test_app.py

@@ -54,6 +54,15 @@ def make_app(**kwargs):
     interrupt_command.return_value = interrupt_command_inst
     cmd_mgr.add_command('interrupt', interrupt_command)
 
+    # Register a command that is interrrupted by a broken pipe
+    pipeclose_command = mock.Mock(name='pipeclose_command', spec=c_cmd.Command)
+    pipeclose_command_inst = mock.Mock(spec=c_cmd.Command)
+    pipeclose_command_inst.run = mock.Mock(
+        side_effect=BrokenPipeError
+    )
+    pipeclose_command.return_value = pipeclose_command_inst
+    cmd_mgr.add_command('pipe-close', pipeclose_command)
+
     app = application.App('testing interactive mode',
                           '1',
                           cmd_mgr,
@@ -121,6 +130,11 @@ class TestInitAndCleanup(base.TestBase):
         result = app.run(['interrupt'])
         self.assertEqual(result, 130)
 
+    def test_pipeclose_command(self):
+        app, command = make_app()
+        result = app.run(['pipe-close'])
+        self.assertEqual(result, 141)
+
     def test_clean_up_success(self):
         app, command = make_app()
         app.clean_up = mock.MagicMock(name='clean_up')
@@ -169,6 +183,19 @@ class TestInitAndCleanup(base.TestBase):
         args, kwargs = call_args
         self.assertIsInstance(args[2], KeyboardInterrupt)
 
+    def test_clean_up_pipeclose(self):
+        app, command = make_app()
+
+        app.clean_up = mock.MagicMock(name='clean_up')
+        ret = app.run(['pipe-close'])
+        self.assertNotEqual(ret, 0)
+
+        app.clean_up.assert_called_once_with(mock.ANY, mock.ANY, mock.ANY)
+        call_args = app.clean_up.call_args_list[0]
+        self.assertEqual(mock.call(mock.ANY, 141, mock.ANY), call_args)
+        args, kwargs = call_args
+        self.assertIsInstance(args[2], BrokenPipeError)
+
     def test_error_handling_clean_up_raises_exception(self):
         app, command = make_app()
 
@@ -356,6 +383,18 @@ class TestHelpHandling(base.TestBase):
     def test_interrupted_deferred_help(self):
         self._test_interrupted_help(True)
 
+    def _test_pipeclose_help(self, deferred_help):
+        app, _ = make_app(deferred_help=deferred_help)
+        with mock.patch('cliff.help.HelpAction.__call__',
+                        side_effect=BrokenPipeError):
+            app.run(['--help'])
+
+    def test_pipeclose_help(self):
+        self._test_pipeclose_help(False)
+
+    def test_pipeclose_deferred_help(self):
+        self._test_pipeclose_help(True)
+
     def test_subcommand_help(self):
         app, _ = make_app(deferred_help=False)