Modify 'render_to_file' function to make it operate on unicode objects

If we have non-ascii chars in rendered template we might end up with
UnicodeDecodeError exception when writing the content to a file. To
eliminate this issue io.open is used with additional 'encoding'
parameter

Change-Id: I73ee352a439d7a9d5c71033f31530a0ced68324c
Closes-Bug: #1475234

fuel_plugin_builder/fuel_plugin_builder/tests/test_utils.py

@@ -15,7 +15,9 @@
 #    under the License.
 
 import os
+import shutil
 import subprocess
+import tempfile
 
 import mock
 from mock import patch
@@ -241,6 +243,26 @@ class TestUtils(BaseTestCase):
         open_mock.assert_called_once_with(path)
         yaml_mock.load.assert_called_once_with(file_mock)
 
+    def test_render_to_file_unicode_handling(self):
+        expected = u'тест'
+        params = {'vendors': expected}
+        template_content = "${vendors}"
+
+        temp_dir = tempfile.mkdtemp()
+        self.addCleanup(shutil.rmtree, temp_dir)
+
+        src_file = os.path.join(temp_dir, 'test_template')
+        dst_file = os.path.join(temp_dir, 'test_rendered')
+
+        with open(src_file, 'w') as f:
+            f.write(template_content)
+
+        utils.render_to_file(src=src_file, dst=dst_file, params=params)
+
+        with open(dst_file, 'rb') as f:
+            actual = f.read()
+            self.assertEqual(expected, actual.decode('utf-8'))
+
     @mock.patch('fuel_plugin_builder.utils.copy_file_permissions')
     @mock.patch('fuel_plugin_builder.utils.render_to_file')
     @mock.patch('fuel_plugin_builder.utils.remove')

fuel_plugin_builder/fuel_plugin_builder/utils.py

@@ -16,6 +16,7 @@
 
 import datetime
 import hashlib
+import io
 import logging
 import os
 import shutil
@@ -172,10 +173,16 @@ def render_to_file(src, dst, params):
     logger.debug(u'Render template from {0} to {1} with params: {2}'.format(
         src, dst, params))
 
-    with open(src, 'r') as f:
+    # NOTE(aroma): we use io.open because sometimes we ended up with
+    # non-ascii chars in rendered template so must explicitly
+    # converse content to 'utf-8' encoding before writing
+
+    with io.open(src, 'r', encoding='utf-8') as f:
         template_file = f.read()
 
-    with open(dst, 'w') as f:
+    with io.open(dst, 'w', encoding='utf-8') as f:
+        # NOTE(aroma): 'render' in such configuration always
+        # return unicode object as the result
         rendered_file = Template(template_file).render(**params)
         f.write(rendered_file)