Use json equality rather than raw text

It turns out sometimes json will serialize differently given the same
python structure. A check of the two parsed data structures will detect
changes more reliably.

Change-Id: Id165b36c0fa0fa89730c3507444a41c68bd70fb3
Closes-Bug: #1320262

os_collect_config/cache.py

@@ -57,16 +57,13 @@ def store(name, content):
         os.rename(new.name, dest_path)
 
     if not changed:
-        with open(dest_path) as now:
-            if os.path.exists(last_path):
-                with open(last_path) as then:
-                    for now_line in now:
-                        then_line = then.next()
-                        if then_line != now_line:
-                            changed = True
-                            break
-            else:
-                changed = True
+        if os.path.exists(last_path):
+            with open(last_path) as then:
+                then_value = json.load(then)
+                if then_value != content:
+                    changed = True
+        else:
+            changed = True
     return (changed, dest_path)
 
 

os_collect_config/tests/test_cache.py

@@ -83,5 +83,19 @@ class TestCache(testtools.TestCase):
         self.assertThat(list_list, matchers.IsInstance(list))
         self.assertIn(path, list_list)
 
+    def test_cache_ignores_json_inequality(self):
+        content1 = u'{"a": "value-a", "b": "value-b"}'
+        content2 = u'{"b": "value-b", "a": "value-a"}'
+        value1 = json.loads(content1)
+        value2 = json.loads(content2)
+        self.assertEqual(value1, value2)
+        (changed, path) = cache.store('content', value1)
+        self.assertTrue(changed)
+        cache.commit('content')
+        (changed, path) = cache.store('content', value1)
+        self.assertFalse(changed)
+        (changed, path) = cache.store('content', value2)
+        self.assertFalse(changed)
+
     def test_commit_no_cache(self):
         self.assertEqual(None, cache.commit('neversaved'))