Plugman

Plugman is a plugin manager that supports event driven communication with plugins. It handles the loading, initialization and all communications with the plugins.

Plugman's event driven approach lets you completely decouple the application from the plugins. This is in my opinion a major advantage because it lets you factor out functionality into plugins without much added complexity.

There are several plugin managers available from RubyGems.org, but none seems to let you use events as the means of communication. (The ones that I have looked at are: plugin, gem_plugin, little_plugger, plugin_manager, and plugin-loader)

The easiest way to get plugman is through rubygems

gem install plugman

or you can get it from https://github.com/kjellm/plugman.

require 'plugman'

class APlugin
 
  def hello_world
    puts "Hello World!"
  end
      
end

class TheApp

  def initialize
    @plugman = Plugman.new(plugins: [APlugin.new])
  end
  
  def main
    @plugman.notify :hello_world
  end

end

Note: Plugins that are to be loaded by plugman need to extend Plugman::PluginBase.

In the minimal example, the application did all the loading and initialization of the plugins. This is not very flexible. What you usually would rather do is to initialize Plugman with a Loader to handle all this.

Here's an example using the provided ConfigLoader:

# $HOME/.app.yml
---
:plugins : ['app/plugin/logger']

# app/lib/app.rb
require 'plugman'
require 'yaml'

class App

  def initialize
    rc = YAML.load_file("#{ENV['HOME']}/.app.yml")
    @plugman = Plugman.new(loader: Plugman::ConfigLoader.new(rc[:plugins]))
    @plugman.load_plugins
  end
  
  def main
    @plugman.notify :system_launched
    # ...
  end
  
end

# app-plugin-logger/lib/app/plugin/logger.rb
require 'logger'

class App
  module Plugin
    class Logger < Plugman::PluginBase
    
      def initialize
        @logger = ::Logger.new(STDERR)
      end
    
      def system_launched
        @logger.info "The system has launched!"
      end
        
    end
  end
end

Plugman lets you send arguments and/or blocks to plugins when calling #notify. Here is how it works:

# In a plugin:
def hello(world="")
    str = "Hello" << world
    str << yield if block_given?
    puts str
end

# Somewhere in the app:
@plugman.notify(:hello)                    # => "Hello"
@plugman.notify(:hello, " world")          # => "Hello world"
@plugman.notify(:hello, " world") { "!" }  # => "Hello world!"
@plugman.notify(:hello) { "!" }            # => "Hello!"

You can easily create your own loader as a Loader is nothing but an callable object (it responds to #call.)

Here is one that loads all ruby files in a directory:

->(a) { Dir.glob('/plugins/are/here/*.rb').each {|f| require f}}

And here is one that uses Gem.find_files

->(a) do
  seen = {}
  Gem.find_files('the_app/plugin/*', true).each do |f|
    name = File.basename(f)
    require name unless seen[f]
    seen[f] = true
  end
end

Report bugs to https://github.com/kjellm/plugman/issues.

Kjell-Magne Øierud <kjellm AT oierud DOT net>

(The MIT License)

Copyright © 2011-2012 Kjell-Magne Øierud

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the ‘Software’), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED ‘AS IS’, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.