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.

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h2. Plugin Initialization

The initialization process can be thought of as consisting of two phases: loading and validation of settings and runtime initialization -- selection of classes, their parameters, and how they will be instantiated.

During the first phase of the process, all modules are gathered into groups consisting of the main plugin and one or more providers. If any of the members of the group fail at any time during initialization, the rest of the modules in the group will be failed as well. Initialization starts with all loaded and enabled plugin (main modules) classes being collected, then for each:

* configuration file is loaded

* dependencies are loaded (also see load_classes)

* configuration-related code executed, and configuration updated (also see load_runtime_configuration)

* validators executed (also see load_validators)

* provider names resolved to provider classes

At this point the steps above are repeated for all providers, one module group at a time. During the second phase, for each of the modules:

* dependency injection wirings are resolved (also see load_dependency_injection_wirings)

* services started (also see start_services)

* module's versions are checked against other modules stated requirements (also see)

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.

We have some templates for creating your plugin:

* "smart_proxy_example plugin":https://github.com/theforeman/smart_proxy_example is a minimal example plugin that can be used as a skeleton

* "smart_proxy_dns_plugin_template":https://github.com/theforeman/smart_proxy_dns_plugin_template is a template for creating new DNS provider plugins

Also, "smart_proxy_pulp plugin":https://github.com/theforeman/smart-proxy-pulp is an example for a fully functional, yet easy to understand Smart-Proxy plugin.

h2. Making your plugin official

Once you're ready to release the first version, please see [[How_to_Create_a_Plugin#Making-your-plugin-official]] for info on making your plugin part of the Foreman project.

h2. Plugin definition

A 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'>

module Proxy::Example

  class Plugin < ::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!', :important_path => '/must/exist'

    load_classes ::Proxy::Example::ClassLoader

    load_programmable_settings "::Proxy::Example::ProgrammableSettings"

    load_dependency_injection_wirings "::Proxy::Example::DIConfiguration"

    load_validators "Proxy::Example::CustomValidators"

    validate_readable :optional_path, :important_path

    validate :a_setting, :my_validator => true, :if => lambda {|settings| !settings[:a_setting].nil?}

    validate :another_setting, :my_other_validator => true

    start_services :service_a, :service_b

  end

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. Setting any of the parameters in default_settings to nil will trigger a validation error.

 * validate_readable :optional_path, :important_path: *optional*. Verifies that settings listed here contain paths to files that exist and are readable. Optional settings (not listed under default_settings) will be skipped if left uninitialized. 

 * 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.

 * load_classes: must be a class or a block. Specified class must implement "load_classes" instance method that loads module's dependencies.

 * load_programmable_settings: can be a class or a class name. Specified class must implement load_programmable_settings(settings_hash) instance method that returns new or updated settings.

 * load_validators: can be a class or a class name. Specified class must implement load_validators instance method that returns a hash of validator name to validator class mappings.

 * load_dependency_injection_wirings: can be a class or a class name. The class must implement load_dependency_injection_wirings(di_container, settings_hash) instance method.

 * start_services: list of dependency injection wiring labels. Services that perform work independently (asynchroniously) of http requests should implement #start method.

 * validate: validate :setting_one, :setting_two, ..., :setting_n, :validator_name => { :validator_param_one => 'value one', ...,}, :if => lambda {|settings| ... }, alternatively use :validator_name => true if validator has no parameters. If predicate is specified, the validator will be called only if the lambda evaluates to true. Predicate's lambda expects module's settings passed as a parameter.

h3. Provider definition

Some plugins are *providers* for an existing plugin or module in the Smart Proxy, e.g. a DNS provider.

These are registered almost identically, but use Proxy::Provider instead of Proxy::Plugin. No rackup_paths are used for providers, since they don't add any new REST API, they only add functionality to an existing module.

<pre>

module Proxy::Dns::PluginTemplate

  class Plugin < ::Proxy::Provider

    plugin :dns_plugin_template, ::Proxy::Dns::PluginTemplate::VERSION

    requires :dns, '>= 1.11'

    after_activation do

      require 'smart_proxy_dns_plugin_template/dns_plugin_template_main'

      require 'smart_proxy_dns_plugin_template/dns_plugin_template_dependencies'

    end

  end

end

</pre>

Additionally, each provider must specify which class implements interface expected by the main plugin. This is done by declaring an association for module's dependency injection container.

<pre>

require 'dns_common/dependency_injection/dependencies'

class Proxy::Dns::DependencyInjection::Dependencies

  dependency :dns_provider, Proxy::Dns::PluginTemplate::Record

end

</pre>

h2. How to Load Dependencies

The class loader must implement load_classes instance method:

<pre>

class ::Proxy::Example::ClassLoader

  def load_classes

    require 'example/class_a'

    require 'example/class_b'

  end

end

</pre>

alternatively, a block can be used to load dependencies:

<pre>

module Proxy::Example

  class Plugin < ::Proxy::Plugin

    ...

    load_classes do

      require 'example/class_a'

      require 'example/class_b'

    end

    ...

  end

end

</pre>

h2. How to Programmatically Update Settings

The class must implement load_programmable_settings(settings_hash) instance method that returns new or updated settings:

<pre>

class ::Proxy::Example::RuntimeConfiguration

  def load_programmable_settings(settings_hash)

    settings_hash[:a_setting] = "Hello, world"

    settings_hash

  end

end

</pre>

h2. How to Define Dependency Injection Wirings

The class must implement load_dependency_injection_wirings instance method that has dependency injection container and settings hash as its parameters:

<pre>

class ::Proxy::Example::DIConfiguration

  def load_dependency_injection_wirings(container_instance, settings)

    container_instance.dependency :depedency_a, ::Proxy::Example::ClassA

    container_instance.dependency :dependency_b, ::Proxy::Example::ClassB

    container_instance.singleton_dependency :service_a, lambda {|container| ::Proxy::Example::ServiceA.new(settings[:example_setting], container_instance.get_dependency(:dependency_a))}

  end

end

</pre>

When Proxy::DependencyInjection::Container#dependency is used to define a dependency, a new instance of a class will be returned, or lambda executed every time the dependency is requested.

If only a single instance of a class is ever required, use Proxy::DependencyInjection::Container#singleton_dependency: the class will be instantiated first time the dependency is requested, and then reused on all subsequent requests. 

h2. How to Create and Load Custom Validators

The class used for loading of custom validators must implement load_validators that returns a hash of validator name to validator class mappings. A validator must use ::Proxy::PluginValidators::Base as its base class and implement validate!(settings) instance method that accepts a hash containing module settings. validate! should raise an exception if the check it's making fails.

<pre>

class Proxy::Example::CustomValidators

  class MyValidator < ::Proxy::PluginValidators::Base

    def validate!(settings)

      raise ::Proxy::Error::ConfigurationError("Unsupported greeting") if settings[@setting_name] != "Hello, world"

    end

  end

  def load_validators

    {:my_validator => MyValidator}

  end

end

</pre>

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'>

module Proxy::Example

 class Api < Sinatra::Base

  helpers ::Proxy::Helpers

  get "/hello" do

    Proxy::Example::Plugin.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 Proxy::Example::Api

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.

h2. Adding a DNS provider

*Requires Smart Proxy 1.11 or higher.*

When extending the 'dns' smart proxy module, the plugin needs to create a new Proxy::Dns::Record class with @create_a_record@, @create_ptr_record@, @remove_a_record@, and @remove_ptr_record@ methods for adding and removing of DNS records.

The easiest way to do this is using the "Smart Proxy DNS plugin template":https://github.com/theforeman/smart_proxy_dns_plugin_template which can get you up and running with a new DNS provider plugin in minutes.

DNS Provider classes are instantiated by DNS module's dependency injection container.

<pre>

plugin :dns_plugin_template, ::Proxy::Dns::PluginTemplate::VERSION

</pre>

And then in the main file of the plugin:

<pre>

require 'dns_common/dns_common'

module Proxy::Dns::PluginTemplate

  class Record < ::Proxy::Dns::Record

    include Proxy::Log

    include Proxy::Util

    def initialize

      super('localhost', ::Proxy::Dns::Plugin.settings.dns_ttl)

    end

    def create_a_record(fqdn, ip)

      # adds a forward 'A' record with fqdn, ip

    end

    def create_ptr_record(fqdn, ip)

      # adds a reverse 'PTR' record with ip, fqdn

    end

    def remove_a_record(fqdn)

      # removes the forward 'A' record with fqdn

    end

    def remove_ptr_record(ip)

      # removes the reverse 'PTR' record with ip

    end

  end

end

</pre>

DNS provider support was first added in version 1.10, but the interface was updated between 1.10 and 1.11.  Please see the history of this page for 1.10-compatible recommendations and the 1.10-stable branch of the example DNS plugin instead of master.

h2. Adding a DHCP provider

*Requires Smart Proxy 1.11 or higher.*

When creating a new 'dhcp' provider smart proxy module, the plugin needs to create a new Proxy::DHCP::Server class that implements @load_subnets@, @load_subnet_data@, @find_subnet@, @subnets@, @all_hosts@, @unused_ip@, @find_record@, @add_record@, and @del_record@ methods.

Provider classes are instantiated by DHCP module's dependency injection container.

<pre>

plugin :example_dhcp_provider, ::ExampleDhcpPlugin::Provider::VERSION

</pre>

And then in the main file of the plugin:

<pre>

require 'dhcp_common/server'

module ::ExampleDhcpPlugin

  class Provider < ::Proxy::DHCP::Server

    include Proxy::Log

    include Proxy::Util

    def initialize

      super('localhost')

    end

    def load_subnets

      # loads subnet data into memory

    end

    def find_subnet(network_address)

      # returns Proxy::DHCP::Subnet that has network_address or nil if none was found

    end

    def load_subnet_data(a_subnet)

      # loads lease- and host-records for a Proxy::DHCP::Subnet

    end

    def subnets

      # returns all available subnets (instances of Proxy::DHCP::Subnet)

    end

    def all_hosts(network_address)

      # returns all reservations in a subnet with network_address

    end

    def unused_ip(network_address, mac_address, from_ip_address, to_ip_address)

      # returns first available ip address in a subnet with network_address, for a host with mac_address, in the range of ip addresses: from_ip_address, to_ip_address

    end

    def find_record(network_address, ip_or_mac_address)

      # returns a Proxy::DHCP::Record from a subnet with network_address that has ip- or mac-address specified in ip_or_mac_address, or nil of none was found 

    end

    def add_record(params)

      # creates a record

    end

    def del_record(network_address,a_record)

      # removes a Proxy::DHCP::Record from a subnet with network_address

    end

  end

end

</pre>

DHCP provider support was first added in version 1.11.

h2. Testing

Make sure that Gemfile includes "smart-proxy" gem as a development dependency:

<pre><code class="ruby">

group :development do

  gem 'smart_proxy', :git => "https://github.com/theforeman/smart-proxy.git"

end

</code></pre>

Load 'smart_proxy_for_testing' in your tests:

<pre><code>

$: << File.join(File.dirname(__FILE__), '..', 'lib')

require 'smart_proxy_for_testing'

require 'test/unit'

require 'webmock/test_unit'

require 'mocha/test_unit'

require "rack/test"

require 'smart_proxy_pulp_plugin/pulp_plugin'

require 'smart_proxy_pulp_plugin/pulp_api'

class PulpApiTest < Test::Unit::TestCase

  include Rack::Test::Methods

  def app

    PulpProxy::Api.new

  end

  def test_returns_pulp_status_on_200

    stub_request(:get, "#{::PulpProxy::Plugin.settings.pulp_url.to_s}/api/v2/status/").to_return(:body => "{\"api_version\":\"2\"}")

    get '/status'

    assert last_response.ok?, "Last response was not ok: #{last_response.body}"

    assert_equal("{\"api_version\":\"2\"}", last_response.body)

  end

end

</code></pre>

To execute all tests <code><pre>bundle exec rake test</code></pre>.  To save time during development it is possible to execute tests in a single file: <code><pre>bundle exec rake test TEST=path/to/test/file</pre></code>

Please refer to "Sinatra documention":http://www.sinatrarb.com/testing.html for detailed information on testing of Sinatra applications.

Once you have tests, see "Jenkins":http://projects.theforeman.org/projects/foreman/wiki/Jenkins#Smart-proxy-plugin-testing for info on setting up tests under Jenkins.