This cleans up the cases where we had D001 violations so we can stop skipping that check in doc8 runs. Change-Id: Ie52f6ecac1a645fcbcc643b9ca63e033b622d830 Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>
3.4 KiB
Adding a Method to the OpenStack API
The interface is a mostly RESTful API. REST stands for Representational State Transfer and provides an architecture "style" for distributed systems using HTTP for transport. Figure out a way to express your request and response in terms of resources that are being created, modified, read, or destroyed.
Routing
To map URLs to controllers+actions, OpenStack uses the Routes package, a clone of Rails routes for Python implementations. See http://routes.groovie.org/ for more information.
URLs are mapped to "action" methods on "controller" classes in
cinder/api/openstack/__init__/ApiRouter.__init__
.
See http://routes.readthedocs.io/en/latest/ for all syntax, but you'll probably just need these two:
- mapper.connect() lets you map a single URL to a single action on a controller.
- mapper.resource() connects many standard URLs to actions on a controller.
Controllers and actions
Controllers live in cinder/api/openstack
, and inherit
from cinder.wsgi.Controller.
See cinder/api/v2/volumes.py
for an example.
Action methods take parameters that are sucked out of the URL by mapper.connect() or .resource(). The first two parameters are self and the WebOb request, from which you can get the req.environ, req.body, req.headers, etc.
Serialization
Actions return a dictionary, and wsgi.Controller serializes that to JSON or XML based on the request's content-type.
Errors
There will be occasions when you will want to return a REST error response to the caller and there are multiple valid ways to do this:
- If you are at the controller level you can use a
faults.Fault
instance to indicate the error. You can either return theFault
instance as the result of the action, or raise it, depending on what's more convenient:raise faults.Fault(webob.exc.HTTPBadRequest(explanation=msg))
. - If you are raising an exception our WSGI middleware exception
handler is smart enough to recognize webob exceptions as well, so you
don't really need to wrap the exceptions in a
Fault
class and you can just let the middleware add it for you:raise webob.exc.HTTPBadRequest(explanation=msg)
. - While most errors require an explicit webob exception there are some
Cinder exceptions (
NotFound
andInvalid
) that are so common that they are directly handled by the middleware and don't need us to convert them, we can just raise them at any point in the API service and they will return the appropriate REST error to the caller. So anyNotFound
exception, or child class, will return a 404 error, and anyInvalid
exception, or child class, will return a 400 error.