no_www.rb

class NoWWW

  STARTS_WITH_WWW = /^www\./i
  
  def initialize(app)
    @app = app
  end
  
  def call(env)
    if env['HTTP_HOST'] =~ STARTS_WITH_WWW
      [301, { 'Location' => Rack::Request.new(env).url.sub(/www\./i, '') }, ['Redirecting...']]
    else
      @app.call(env)
    end
  end
  
end

no_www_test.rb

require 'rubygems'
require '../no_www'
require 'test/unit'
require 'rack/test'

class NoWWWTest < Test::Unit::TestCase
  include Rack::Test::Methods

  def app
    Rack::Builder.new do
      use NoWWW
      run Proc.new {|env| [200, {"Content-Type" => "text/html"}, "the body"] }
    end  
  end

  def test_for_redirect
    get '/', { }, { 'HTTP_HOST' => 'www.test.host'}
    assert_equal 301, last_response.status
    assert_equal last_response['Location'].to_s, 'http://test.host/' 
  end

  def test_for_keeping_path
    get '/wowza', { }, { 'HTTP_HOST' => 'www.test.host'}
    assert_equal 301, last_response.status
    assert_equal last_response['Location'].to_s, 'http://test.host/wowza' 
  end  

  def test_for_pass_through
    get '/', { }, { 'HTTP_HOST' => 'test.host'}
    assert_equal 200, last_response.status
    get '/wowza', { }, { 'HTTP_HOST' => 'test.host'}
    assert_equal 200, last_response.status    
  end

end