Joe Gordon a1e8fc6dd9 Update docs layout

* Explain these docs are for trunk (copied from ironic)
* All the docs in this repo are meant to be developer docs, so having a
  devref inside of the docs is redundant and just makes the docs more
  complicated to navigate. Move everything out of the devref folder and
  link to everything from main index.
* Move man pages into separate section. The man pages are pretty sparse
* right now, we should either make them useful or just delete them
* Remove dead docs from unused_docs list in doc/source/conf.py
* Shuffle docs landing page, move common referees to the top (API,
  hypervisor support matrix), Add a introduction section and more. The
  hope is the updated layout makes this document easier to navigate.
* Use maxdepth of 1
* Rename a few sections with what are hopefully better names

The next step is to prune out outdated documents and further cleanup
this page.

Change-Id: Iff453e47ccc902a0e72b1a5f6ce1ee939ff3a1a0

2015-05-15 10:47:18 -07:00

2.7 KiB

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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 nova/api/openstack/__init__/ApiRouter.__init__ .

See http://routes.groovie.org/manual.html 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 nova/api/openstack, and inherit from nova.wsgi.Controller.

See nova/api/openstack/compute/servers.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.

If you define a new controller, you'll need to define a _serialization_metadata attribute on the class, to tell wsgi.Controller how to convert your dictionary to XML. It needs to know the singular form of any list tag (e.g. <servers> list contains <server> tags) and which dictionary keys are to be XML attributes as opposed to subtags (e.g. <server id="4"/> instead of <server><id>4</id></server>).

See nova/api/openstack/compute/servers.py for an example.

Faults

If you need to return a non-200, you should return faults.Fault(webob.exc.HTTPNotFound()) replacing the exception as appropriate.

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