h1. How to Create a Smart-Proxy Plugin

This guide outlines main components of a plugin, but assumes some degree of familiarity with ruby gems, bundler, rack, and Sinatra. You'll find links to useful documentation in each of the sections below.

h2. Plugin Organization

Smart-Proxy plugins are normal ruby gems, please follow documentation at http://guides.rubygems.org/make-your-own-gem/ for guidance on gem creation and packaging. It is strongly recommended to follow smart_proxy_<your plugin name here> naming convention for your plugin. You can use "smart_proxy_pulp plugin":https://github.com/theforeman/smart-proxy-pulp as an example -- a fully functional, yet easy to understand Smart-Proxy plugin.

h2. Plugin Definition

Plugin Definition is used to define plugin's name, version, location of rackup configuration, and other parameters. At a minimum, Plugin Descriptor must define plugin name and version. Note the base class of the descriptor is ::Proxy::Plugin:

<pre><code class='ruby'>

class ExamplePlugin < ::Proxy::Plugin

  plugin :example, "0.0.1"

  http_rackup_path File.expand_path("http_config.ru", File.expand_path("../", __FILE__))

  https_rackup_path File.expand_path("https_config.ru", File.expand_path("../", __FILE__))

  default_settings :hello_greeting => 'Hello there!'

end

</code></pre>

Here we defined a plugin called "example", with version "0.0.1", that is going to listen on both http and https ports. Following is the full list of parameters that can be defined by the Plugin Descriptor.

 * plugin :example, "1.2.3": *required*. Sets plugin name to "example" and version to "0.0.1".

 * http_rackup_path "path/to/http_config.ru": *optional*. Sets path to http rackup configuration. If omitted, the plugin is not going to listen on the http port. Please see below for information on rackup configuration.

 * https_rackup_path "path/to/https_config.ru": *optional*. Sets path to https rackup configuration. If omitted, the plugin is not going to listen on the https port. Please see below for information on rackup configuration.

 * requires :another_plugin, '~> 1.2.0': *optional*. Specifies plugin dependencies, where ":another_plugin" is another plugin name, and '~> 1.2.0' is version specification (pls. see http://guides.rubygems.org/patterns/#pessimistic_version_constraint for details on version specification).

 * default_settings :first => 'my first setting', :another => 'my other setting': *optional*. Defines default values for plugin parameters. These parameters can be overridden in plugin settings file.

 * after_activation { do_something }: *optional*. Supplied block is going to be executed after the plugin has been loaded and enabled. Note that the block is going to be executed in the context of the Plugin Descriptor class.

 * bundler_group :my_plugin_group: *optional*.  Sets the name of the bundler group for plugin dependencies. If omitted the plugin name is used. 

h2. API

Modular Sinatra app is used to define plugin API. Note the base class Sinatra::Base and inclusion of ::Proxy::Helpers:

<pre><code class='ruby'>

 class ExampleApi < Sinatra::Base

  helpers ::Proxy::Helpers

  get "/hello" do

    ExamplePlugin.settings.hello_greeting

  end

end

</code></pre>

Here we return a string defined in 'hello_greeting' parameter (see Plugin Descriptor above and settings file below) when a client performs a GET /hello. Please refer to "Sinatra documentation":http://www.sinatrarb.com/intro.html on details about routing, template rendering, available helpers, etc.

h2. Rackup Configuration

During startup Smart-Proxy assembles web applications listening on http and https ports using rackup files of enabled plugins. Plugin rackup files define mounting points of plugin API:

<pre><code class="ruby">

require 'example_plugin/example_api'

map "/example" do

  run ExampleApi

end

</code></pre>

The example above should be sufficient for the majority of plugins. Please refer to "Sinatra+Rack":http://www.sinatrarb.com/intro.html documentation for additional information. 

h2. Plugin Settings

On startup Smart-Proxy will load and parse plugin configuration files located in its settings.d/ directory. Each plugin config file is named after the plugin and is a yaml-encoded collection of key-value pairs and used to override default values of plugin parameters. 

<pre>

---

:enabled: true

:hello_greeting: "O hai!"

</pre>

This settings file enables the plugin (by default all plugins are disabled), and overrides :hello_greeting parameter. Plugin settings can be accessed through .settings method of the Plugin class, for example: ExamplePlugin.settings.hello_greeting. Global Smart-Proxy parameters are accessible through Proxy::SETTINGS, for example Proxy::SETTINGS.foreman_url returns Foreman url configured for this Smart-Proxy. 

h2. Bundler Configuration

Smart-Proxy relies on bundler to load its dependencies and plugins. We recommend to create a dedicated bundler config file for your plugin, and name it after the plugin. For example:

<pre><code class="ruby">

  gem 'smart_proxy_example'

  group :example do

    gem 'json'

  end

</code></pre>

You'll need to create a dedicated bundler group for additional dependencies of your plugin. By default the group shares the name with the plugin, but you can override it using bundler_group parameter in Plugin Descriptor. Please refer to [[How_to_Install_a_Smart-Proxy_Plugin]] for additional details on "from source" plugin installations.