Add response handlers to support different response types

Problem description
===================
The dynamic pollsters only support APIs that produce
JSON responses. Therefore the dynamic pollsters do not
support APIs where the response is an XML or not Restful
compliant APIs with HTTP 200 within a plain text message
on errors.

Proposal
========
To allow the dynamic pollsters to support other APIs
response formats, we propose to add a response handling
that supports multiple response types. It must be
configurable in the dynamic pollsters YAML. The default
continues to be JSON.

Change-Id: I4886cefe06eccac2dc24adbc2fad2166bcbfdd2c

1 files changed, 112 insertions, 1 deletions

diff --git a/doc/source/admin/telemetry-dynamic-pollster.rst b/doc/source/admin/telemetry-dynamic-pollster.rst
index d861c07f..f9118792 100644
--- a/doc/source/admin/telemetry-dynamic-pollster.rst
+++ b/doc/source/admin/telemetry-dynamic-pollster.rst
@@ -45,7 +45,7 @@ attributes to define a dynamic pollster:
    the unit or some other meaningful String value;
 
 *  ``value_attribute``: mandatory attribute; defines the attribute in the
-   JSON response from the URL of the component being polled. We also accept
+   response from the URL of the component being polled. We also accept
    nested values dictionaries. To use a nested value one can simply use
    ``attribute1.attribute2.<asMuchAsNeeded>.lastattribute``. It is also
    possible to reference the sample itself using ``"." (dot)``; the self
@@ -281,6 +281,117 @@ desires):
         name: "display_name"
     default_value: 0
 
+*  ``response_handlers``: optional parameter. Defines the response
+   handlers used to handle the response. For now, the supported values
+   are:
+
+   ``json``: This handler will interpret the response as a `JSON` and will
+   convert it to a `dictionary` which can be manipulated using the
+   operations options when mapping the attributes:
+
+   .. code-block:: yaml
+
+     ---
+
+     - name: "dynamic.json.response"
+       sample_type: "gauge"
+       [...]
+       response_handlers:
+          - json
+
+   Response to handle:
+
+   .. code-block:: json
+
+     {
+        "test": {
+          "list": [1, 2, 3]
+        }
+     }
+
+   Response handled:
+
+   .. code-block:: python
+
+     {
+        'test': {
+          'list': [1, 2, 3]
+        }
+     }
+
+
+   ``xml``: This handler will interpret the response as an `XML` and will
+   convert it to a `dictionary` which can be manipulated using the
+   operations options when mapping the attributes:
+
+   .. code-block:: yaml
+
+     ---
+
+     - name: "dynamic.json.response"
+       sample_type: "gauge"
+       [...]
+       response_handlers:
+          - xml
+
+   Response to handle:
+
+   .. code-block:: xml
+
+     <test>
+       <list>1</list>
+       <list>2</list>
+       <list>3</list>
+     </test>
+
+   Response handled:
+
+   .. code-block:: python
+
+     {
+        'test': {
+          'list': [1, 2, 3]
+        }
+     }
+
+   ``text``: This handler will interpret the response as a `PlainText` and
+   will convert it to a `dictionary` which can be manipulated using the
+   operations options when mapping the attributes:
+
+   .. code-block:: yaml
+
+     ---
+
+     - name: "dynamic.json.response"
+       sample_type: "gauge"
+       [...]
+       response_handlers:
+          - text
+
+   Response to handle:
+
+   .. code-block:: text
+
+     Plain text response
+
+   Response handled:
+
+   .. code-block:: python
+
+     {
+        'out': "Plain text response"
+     }
+
+   They can be used together or individually. If not defined, the
+   `default` value will be `json`. If you set 2 or more response
+   handlers, the first configured handler will be used to try to
+   handle the response, if it is not possible, a `DEBUG` log
+   message will be displayed, then the next will be used
+   and so on. If no configured handler was able to handle
+   the response, an empty dict will be returned and a `WARNING`
+   log will be displayed to warn operators that the response was
+   not able to be handled by any configured handler.
+
 The dynamic pollsters system configuration (for non-OpenStack APIs)
 -------------------------------------------------------------------