Open Stack

Hi Devs,

We are adding support for returning 'x-openstack-request-id'  to the caller as per the design proposed in cross-project specs:
http://specs.openstack.org/openstack/openstack-specs/specs/return-request-id.html

Problem Description:
Cannot add a new property of list type to the warlock.model object.

How is a model object created:
Let's take an example of glanceclient.api.v2.images.get() call [1]:

Here after getting the response we call model() method. This model() does the job of creating a warlock.model object(essentially a dict) based on the schema given as argument (image schema retrieved from glance in this case). Inside model() the raw() method simply return the image schema as JSON object. The advantage of this warlock.model object over a simple dict is that it validates any changes to object based on the rules specified in the reference schema.  The keys of this  model object are available as object properties to the caller.

Underlying reason:
The schema for different sub APIs is returned a bit differently. For images, metadef APIs glance.schema.Schema.raw() is used which returns a schema containing "additionalProperties": {"type": "string"}. Whereas for members and tasks APIs glance.schema.Schema.minimal() is used to return schema object which does not contain "additionalProperties".

So we can add extra properties of any type to the model object returned from members or tasks API but for images and metadef APIs we can only add properties which can be of type string. Also for the latter case we depend on the glance configuration to allow additional properties.

As per our analysis we have come up with two approaches for resolving this issue:

Approach #1:  Inject request_ids property in the warlock model object in glance client
Here we do the following:
1. Inject the 'request_ids' as additional property into the model object(returned from model())
2. Return the model object which now contains request_ids property

Limitations:
1. Because the glance schemas for images and metadef only allows additional properties of type string, so even though natural type of request_ids should be list we have to make it as a comma separated 'string' of request ids as a compromise.
2. Lot of extra code is needed to wrap objects returned from the client API so that the caller can get request ids. For example we need to write wrapper classes for dict, list, str, tuple, generator.
3. Not a good design as we are adding a property which should actually be a base property but added as additional property as a compromise.
4. There is a dependency on glance whether to allow custom/additional properties or not. [2]

Approach #2:  Add 'request_ids' property to all schema definitions in glance

Here we add  'request_ids' property as follows to the various APIs (schema):

"request_ids": {
  "type": "array",
  "items": {
    "type": "string"
  }
}

Doing this will make changes in glance client very simple as compared to approach#1.
This also looks a better design as it will be consistent.
We simply need to modify the request_ids property in  various API calls for example glanceclient.v2.images.get().

Please let us know which approach is better or any suggestions for the same.

[1] https://github.com/openstack/python-glanceclient/blob/master/glanceclient/v2/images.py#L179
[2] https://github.com/openstack/glance/blob/master/glance/api/v2/images.py#L944

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