Add yaml and json parsing functions

Sometimes you'll get a string back from some action (like swift
get_object) and it will be in either a yaml or json format. These
functions will allow you to parse those into a useful object.

Change-Id: I375219f4b019319e1b3d756dca512f7f90cd097f

mistral/utils/expression_utils.py

@@ -17,6 +17,7 @@ from functools import partial
 
 from oslo_serialization import jsonutils
 from stevedore import extension
+import yaml
 import yaql
 
 from mistral.db.v2 import api as db_api
@@ -271,3 +272,11 @@ def global_(context, var_name):
     wf_ex = db_api.get_workflow_execution(context['__execution']['id'])
 
     return wf_ex.context.get(var_name)
+
+
+def json_parse_(context, data):
+    return jsonutils.loads(data)
+
+
+def yaml_parse_(context, data):
+    return yaml.safe_load(data)

releasenotes/notes/yaml-json-parse-53217627a647dc1d.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    Add yaml_parse and json_parse expression functions. Each accepts a string
+    and will parse as either json or yaml, and return an object.

setup.cfg

@@ -83,6 +83,8 @@ mistral.expression.functions =
     execution = mistral.utils.expression_utils:execution_
     env = mistral.utils.expression_utils:env_
     uuid = mistral.utils.expression_utils:uuid_
+    json_parse = mistral.utils.expression_utils:json_parse_
+    yaml_parse = mistral.utils.expression_utils:yaml_parse_
 
 mistral.expression.evaluators =
     yaql = mistral.expressions.yaql_expression:InlineYAQLEvaluator