Dynamic pollsters: enable operation on attributes

This PR enables the use of python operation to transform the attributes that
 are extracted in the JSON response that the Dynamic pollster handle. By
 enabling operators to define transformations on the fly, we can provide even
 more flexibility for the dynamic pollsters' system.

One example of use case is the RadosGW that uses <project_id$project_id> as the
 username. With this implementation, one can create configurations in the
 dynamic pollster to clean that variable. It is as simple as defining
 `resource_id_attribute: "user | value.split('$')[0].strip()"`

The operations are separated by `|` symbol. The first element of the expression
 is the key to be retrieved from the JSON object. The other elements are
 operations that can be applied to the `value` variable. The value variable is
 the variable we use to hold the data.

Depends-On: https://review.opendev.org/#/c/693088/
Change-Id: I9ee209410491b3f04259e1a5c62ac20461070ae1
Signed-off-by: Rafael Weingärtner <rafael@apache.org>

1 files changed, 24 insertions, 1 deletions

diff --git a/ceilometer/polling/dynamic_pollster.py b/ceilometer/polling/dynamic_pollster.py
index f501c1b5..6d4662a6 100644
--- a/ceilometer/polling/dynamic_pollster.py
+++ b/ceilometer/polling/dynamic_pollster.py
@@ -264,5 +264,28 @@ class DynamicPollster(plugin_base.PollsterBase):
     def retrieve_attribute_nested_value(self, json_object, attribute_key):
         LOG.debug("Retrieving the nested keys [%s] from [%s].",
                   attribute_key, json_object)
+
+        keys_and_operations = attribute_key.split("|")
+        attribute_key = keys_and_operations[0].strip()
+
         nested_keys = attribute_key.split(".")
-        return reduce(operator.getitem, nested_keys, json_object)
+        value = reduce(operator.getitem, nested_keys, json_object)
+
+        # We have operations to be executed against the value extracted
+        if len(keys_and_operations) > 1:
+            for operation in keys_and_operations[1::]:
+                # The operation must be performed onto the 'value' variable
+                if 'value' not in operation:
+                    raise declarative.DynamicPollsterDefinitionException(
+                        "The attribute field operation [%s] must use the ["
+                        "value] variable." % operation,
+                        self.pollster_definitions)
+
+                LOG.debug("Executing operation [%s] against value[%s].",
+                          operation, value)
+
+                value = eval(operation.strip())
+
+                LOG.debug("Result [%s] of operation [%s] against value [%s].",
+                          value, operation)
+        return value