allow duck-typing of source streams

CHANGELOG.rst

@@ -2,13 +2,15 @@
 Changelog
 *********
 
-1.3.6 -- 2018-08-29
+1.3.6 -- 2018-08-xx
 ===================
 
 Bugfixes
 --------
 * :class:`StreamEncryptor` and :class:`StreamDecryptor` should always report as readable if they are open.
   `#73 <https://github.com/aws/aws-encryption-sdk-python/issues/73>`_
+* Allow duck-typing of source streams.
+  `#75 <https://github.com/aws/aws-encryption-sdk-python/issues/75>`_
 
 1.3.5 -- 2018-08-01
 ===================

src/aws_encryption_sdk/internal/utils/__init__.py

@@ -127,24 +127,17 @@ def prepare_data_keys(primary_master_key, master_keys, algorithm, encryption_con
     return data_encryption_key, encrypted_data_keys
 
 
-try:
-    _FILE_TYPE = file  # Python 2
-except NameError:
-    _FILE_TYPE = io.IOBase  # Python 3 pylint: disable=invalid-name
-
-
 def prep_stream_data(data):
-    """Takes an input str, bytes, io.IOBase, or file object and returns an appropriate
-    stream for _EncryptionStream objects.
+    """Take an input and prepare it for use as a stream.
 
     :param data: Input data
-    :type data: str, bytes, io.IOBase, or file
     :returns: Prepared stream
     :rtype: io.BytesIO
     """
-    if isinstance(data, (_FILE_TYPE, io.IOBase, six.StringIO)):
-        return data
-    return io.BytesIO(to_bytes(data))
+    if isinstance(data, (six.string_types, six.binary_type)):
+        return io.BytesIO(to_bytes(data))
+
+    return data
 
 
 def source_data_key_length_check(source_data_key, algorithm):

test/unit/test_utils.py

@@ -1,3 +1,4 @@
+# coding: utf-8
 # Copyright 2017 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License"). You
@@ -11,6 +12,7 @@
 # ANY KIND, either express or implied. See the License for the specific
 # language governing permissions and limitations under the License.
 """Test suite for aws_encryption_sdk.internal.utils"""
+import io
 import unittest
 
 import pytest
@@ -28,6 +30,19 @@
 pytestmark = [pytest.mark.unit, pytest.mark.local]
 
 
+def test_prep_stream_data_passthrough():
+    test = aws_encryption_sdk.internal.utils.prep_stream_data(sentinel.not_a_string_or_bytes)
+
+    assert test is sentinel.not_a_string_or_bytes
+
+
+@pytest.mark.parametrize("source", (u"some unicode data ловие", b"\x00\x01\x02"))
+def test_prep_stream_data_wrap(source):
+    test = aws_encryption_sdk.internal.utils.prep_stream_data(source)
+
+    assert isinstance(test, io.BytesIO)
+
+
 class TestUtils(unittest.TestCase):
     def setUp(self):
         # Set up mock key provider and keys
@@ -235,14 +250,6 @@ def test_prepare_data_keys(self):
             [mock_encrypted_data_encryption_key, sentinel.encrypted_data_key_1, sentinel.encrypted_data_key_2]
         )
 
-    @patch("aws_encryption_sdk.internal.utils.to_bytes", return_value=sentinel.bytes)
-    @patch("aws_encryption_sdk.internal.utils.io.BytesIO", return_value=sentinel.bytesio)
-    def test_prep_stream_data(self, mock_bytesio, mock_to_bytes):
-        test = aws_encryption_sdk.internal.utils.prep_stream_data(sentinel.data)
-        mock_to_bytes.assert_called_once_with(sentinel.data)
-        mock_bytesio.assert_called_once_with(sentinel.bytes)
-        assert test is sentinel.bytesio
-
     def test_source_data_key_length_check_valid(self):
         mock_algorithm = MagicMock()
         mock_algorithm.kdf_input_len = 5