Redirect file-like object, don't use isinstance

This fixes aws/aws-cli#544 and aws/aws-cli#654

The issue here is that the CLI uses a file like object
that implements .read() and .seek(), but doesn't actually
inherit from the file/_IOBase.

botocore/awsrequest.py

@@ -82,10 +82,13 @@ def __init__(self, original_request):
 
     def reset_stream_on_redirect(self, response, **kwargs):
         if response.status_code in REDIRECT_STATI and \
-                isinstance(self.body, file_type):
+                self._looks_like_file(self.body):
             logger.debug("Redirect received, rewinding stream: %s", self.body)
             self.reset_stream()
 
+    def _looks_like_file(self, body):
+        return hasattr(body, 'read') and hasattr(body, 'seek')
+
     def reset_stream(self):
         # Trying to reset a stream when there is a no stream will
         # just immediately return.  It's not an error, it will produce

tests/unit/test_awsrequest.py

@@ -79,14 +79,42 @@ def test_cannot_reset_stream_raises_error(self):
             # This means that we read the body:
             body.read()
             # And create a response object that indicates
-            # a redirect.
+            # a redirect
             fake_response = Mock()
             fake_response.status_code = 307
 
             # Then requests calls our reset_stream hook.
             with self.assertRaises(UnseekableStreamError):
                 self.prepared_request.reset_stream_on_redirect(fake_response)
 
+    def test_duck_type_for_file_check(self):
+        # As part of determining whether or not we can rewind a stream
+        # we first need to determine if the thing is a file like object.
+        # We should not be using an isinstance check.  Instead, we should
+        # be using duck type checks.
+        class LooksLikeFile(object):
+            def __init__(self):
+                self.seek_called = False
+
+            def read(self, amount=None):
+                pass
+
+            def seek(self, where):
+                self.seek_called = True
+
+        looks_like_file = LooksLikeFile()
+        self.prepared_request.body = looks_like_file
+
+        fake_response = Mock()
+        fake_response.status_code = 307
+
+        # Then requests calls our reset_stream hook.
+        self.prepared_request.reset_stream_on_redirect(fake_response)
+
+        # The stream should now be reset.
+        self.assertTrue(looks_like_file.seek_called)
+
+
 
 if __name__ == "__main__":
     unittest.main()