Render complex sub-objects using json.dumps

Normally pystache will just use the python unicode representation of
objects. This is not very useful programatically. Rendering using json
makes these values more useful.

os_config_applier/os_config_applier.py

@@ -2,7 +2,6 @@
 import json
 import logging
 import os
-import pystache
 import sys
 from argparse import ArgumentParser
 from pystache.context import KeyNotFoundError
@@ -10,6 +9,7 @@ from subprocess import Popen, PIPE
 from tempfile import NamedTemporaryFile
 from value_types import ensure_type
 from config_exception import ConfigException
+from renderers import JsonRenderer
 
 TEMPLATES_DIR = os.environ.get('OS_CONFIG_APPLIER_TEMPLATES',
                                '/opt/stack/os-config-applier/templates')
@@ -76,7 +76,7 @@ def is_executable(path):
 
 
 def render_moustache(text, config):
-    r = pystache.Renderer(missing_tags='strict')
+    r = JsonRenderer(missing_tags='strict')
     return r.render(text, config)
 
 

os_config_applier/renderers.py

@@ -0,0 +1,26 @@
+import json
+
+from pystache import Renderer
+
+
+class JsonRenderer(Renderer):
+    def __init__(self,
+                 file_encoding=None,
+                 string_encoding=None,
+                 decode_errors=None,
+                 search_dirs=None,
+                 file_extension=None,
+                 escape=None,
+                 partials=None,
+                 missing_tags=None):
+        # json would be html escaped otherwise
+        if escape is None:
+            escape = lambda u: u
+        return super(JsonRenderer, self).__init__(file_encoding,
+                                                  string_encoding,
+                                                  decode_errors, search_dirs,
+                                                  file_extension, escape,
+                                                  partials, missing_tags)
+
+    def str_coerce(self, val):
+        return json.dumps(val)

tests/json_renderer_tests.py

@@ -0,0 +1,19 @@
+import json
+
+from nose.tools import assert_equals
+from os_config_applier.renderers import JsonRenderer
+
+TEST_JSON = '{"a":{"b":[1,2,3,"foo"],"c": "the quick brown fox"}}'
+
+
+def test_json_renderer():
+    context = json.loads(TEST_JSON)
+    x = JsonRenderer()
+    result = x.render('{{a.b}}', context)
+    print result
+    result_structure = json.loads(result)
+    desire_structure = json.loads('[1,2,3,"foo"]')
+    assert_equals(desire_structure, result_structure)
+    result = x.render('{{a.c}}', context)
+    print result
+    assert_equals(u'the quick brown fox', result)