Handle broken pipe errors

If stdout is being piped to another process and that process
closes stdin, then we get an IOError with a broken pipe message.
If the reading end of the pipe closes the pipe, we should just exit.
This is a normal (and common) case and we shouldn't be printing
an error message when this happens.

awscli/formatter.py

@@ -44,6 +44,12 @@ def _remove_request_id(self, response_data):
     def _get_default_stream(self):
         return compat.get_stdout_text_writer()
 
+    def _flush_stream(self, stream):
+        try:
+            stream.flush()
+        except IOError:
+            pass
+
 
 class FullyBufferedFormatter(Formatter):
     def __call__(self, operation, response, stream=None):
@@ -58,15 +64,19 @@ def __call__(self, operation, response, stream=None):
             response_data = response.build_full_result()
         else:
             response_data = response
+        self._remove_request_id(response_data)
+        if self._args.query is not None:
+            response_data = self._args.query.search(response_data)
         try:
-            self._remove_request_id(response_data)
-            if self._args.query is not None:
-                response_data = self._args.query.search(response_data)
             self._format_response(operation, response_data, stream)
+        except IOError as e:
+            # If the reading end of our stdout stream has closed the file
+            # we can just exit.
+            pass
         finally:
             # flush is needed to avoid the "close failed in file object
             # destructor" in python2.x (see http://bugs.python.org/issue11380).
-            stream.flush()
+            self._flush_stream(stream)
 
 
 class JSONFormatter(FullyBufferedFormatter):
@@ -238,7 +248,7 @@ def __call__(self, operation, response, stream=None):
         finally:
             # flush is needed to avoid the "close failed in file object
             # destructor" in python2.x (see http://bugs.python.org/issue11380).
-            stream.flush()
+            self._flush_stream(stream)
 
     def _format_response(self, response, stream):
         if self._args.query is not None:

tests/unit/output/test_json_output.py

@@ -15,6 +15,7 @@
 import platform
 import mock
 from awscli.compat import six
+from awscli.formatter import JSONFormatter
 
 from awscli.testutils import BaseAWSCommandParamsTest, unittest
 from awscli.compat import get_stdout_text_writer
@@ -95,3 +96,18 @@ def test_json_prints_unicode_chars(self):
         # It should be encoded into the default encoding.
         self.assertNotIn('\\u2713', output)
         self.assertIn(expected, output)
+
+
+class TestFormattersHandleClosedPipes(unittest.TestCase):
+    def test_fully_buffered_handles_io_error(self):
+        args = mock.Mock(query=None)
+        operation = mock.Mock(can_paginate=False)
+        response = '{"Foo": "Bar"}'
+        fake_closed_stream = mock.Mock(spec=six.StringIO)
+        fake_closed_stream.flush.side_effect = IOError
+        formatter = JSONFormatter(args)
+        formatter(operation, response, fake_closed_stream)
+        # We should not have let the IOError propogate, but
+        # we still should have called the flush() on the
+        # stream.
+        fake_closed_stream.flush.assert_called_with()