Extensions

Overview

The simplest way to describe the pieces of the client is to start with an example:

$ pulp-admin rpm repo list --details

In the above command:

• pulp-admin is the name of the client script itself.

• rpm and repo are sections. A section is used for organization and may contain one or more subsections and/or commands.

• list is the actual command that is being invoked.

• --details is a flag that is used to drive the command’s behavior. Commands can accept flags or options, the difference being that the latter requires a value to be specified (e.g. --repo-id demo-1).

Extensions can add both sections and commands to the client. Commands can be added to existing sections, however it is typically preferred that commands be added to a section created by the extension itself (see Conventions for more information).

Framework Hook

The starting point for an extension is a single method with the following signature:

def initialize(context):
  """
  Entry point into the extension, called when the extension is loaded. This
  call should make any additions or changes to the CLI required by the
  extension. The supplied context provides the necessary hooks to access the
  CLI instance as well as functionality for accessing the Pulp server and
  utilities for displaying information to the user.

  :param context: client context in which the extension is being loaded
  :type  context: pulp.client.extensions.core.ClientContext
  """

The sole argument is the client context in which the extension will run (more information can be found in Client Context. This method may then delegate to whatever other modules are necessary.

Client Context

The client context is passed into the extension by the framework when the extension is initialized. The context is meant to provide all of the functionality necessary for the extension to interact with both the client framework and the server itself. The context contains the following pieces:

• cli - The cli attribute is the instance of the actual client framework itself. This object is used to add new sections to the client or retrieve existing ones.

• prompt - The prompt is a utility for writing output to the screen as well as for reading user input for interactive commands. A number of formatting methods are provided to provide a consistent look and feel for the client, such as methods to display a header or print an error message.

• server - The client framework creates and initializes an instance of the server bindings to connect to the configured Pulp server. Extensions should use these bindings when making calls against the server.

• config - The client framework will load all of the configuration files and make them accessible to the extension. A separate copy of the configuration is supplied to each extension, so changes may be made to this object without affecting other extensions.

Note

Currently, the API for the client context is not published. The code can be found at ClientContext in client_lib/pulp/client/extensions/core.py.

Conventions

In order to prevent collisions among section names, it is suggested that each type support bundle create a section at the root of the CLI to contain its extensions. For example, when installed, the RPM support bundle adds a section called rpm in the root of the CLI. Commands within apply only to the plugins and consumers revolving around the RPM-related content types. The Puppet support bundle provides a similar structure under the root-level section puppet.

Naturally, there will be similarities between different support commands. Each support bundle will likely have commands to create a repository, customized with the configuration options relevant to that bundle’s server plugins. Similarly, the command to sync a repository will be present in each bundle’s section, with specific handling to render the progress report.

To facilitate those similarities, the pulp.client.commands package provides a number of reusable commands for common tasks, such as displaying a list of repositories or adding schedules for an operation. It is preferred that an extension subclass these reusable commands and use their integration points to customize them to your needs.

Note

Again, the API for these reusable commands is not yet published. The code can be found under client_lib/pulp/client/commands.

Installation

Entry Points

Your extension should define a method that will be an entry point. It should accept one argument and return None. The convention is to use this definition:

from pulp.client.extensions.decorator import priority

@priority()
def initialize(context):
    """
    :type context: pulp.client.extensions.core.ClientContext
    """
    pass

The ClientContext instance includes a reference to everything you need to add new commands and sections to the CLI. Look at the Puppet Extensions for an example of how to add features to the CLI.

The @priority() decorator controls the order in which this extension will be loaded relative to other extensions. By not passing a value, this example accepts the default priority level. The default is found in pulp.client.extensions.loader.DEFAULT_PRIORITY, and its value is 5 as of this writing.

Python entry points are advertised within the package’s setup.py file. As an example, here is that file from the Pulp Puppet Extensions Admin package.

from setuptools import setup, find_packages

setup(
    name='pulp_puppet_extensions_admin',
    version='2.0.0',
    license='GPLv2+',
    packages=find_packages(exclude=['test', 'test.*']),
    author='Pulp Team',
    author_email='pulp-list@redhat.com',
    entry_points = {
        'pulp.extensions.admin': [
            'repo_admin = pulp_puppet.extensions.admin.repo.pulp_cli:initialize',
        ]
    }
)

Notice that the entry point name is pulp.extensions.admin. That distinguishes it as an extension for the admin client. A consumer extension would use the name pulp.extensions.consumer. Technically these names could be changed, or new ones could be used if new CLI tools are developed. The “admin” and “consumer” portions of these names come from config files /etc/pulp/admin/admin.conf and /etc/pulp/consumer/consumer.conf. Each has a “[client]” section with a “role” setting. That said, the intent is for these to stay the same, and it is sufficient to assume that they will.

Directory Loading

For one-off testing purposes, the code for an extension can be placed directly in a specific directory without the need to install to site-packages. The entry point method described above is the preferred way to integrate new extensions:

• Create directory in /usr/lib/pulp/admin/extensions/ or /usr/lib/pulp/consumer/extensions/

• Add __init__.py to created directory.

• Add pulp_cli.py or pulp_shell.py as appropriate.

• In the above module, add a def initialize(context) method.

• The context object contains the CLI or shell instance that can be manipulated to add the extension’s functionality.