Google sitemap files for Rails projects

Is there an easy way to create a sitemaps file for Rails projects? Especially for dynamic sites (such as Stack Overflow for example) there should be a way to dynamically create a sitemaps file. What is the way to go in Ruby and/or Rails?

What would you suggest? Is there any good gem out there?

Add this route towards the bottom of your config/routes.rb file (more specific routes should be listed above it):

map.sitemap '/sitemap.xml', :controller => 'sitemap'

Create the SitemapController (app/controllers/sitemap_controller):

class SitemapController < ApplicationController
  layout nil

  def index
    headers['Content-Type'] = 'application/xml'
    last_post = Post.last
    if stale?(:etag => last_post, :last_modified => last_post.updated_at.utc)
      respond_to do |format|
        format.xml { @posts = Post.sitemap } # sitemap is a named scope
      end
    end
  end
end

—As you can see, this is for a blog, so is using a Post model. This is the HAML view template (app/views/sitemap/index.xml.haml):

- base_url = "http://#{request.host_with_port}"
!!! XML
%urlset{:xmlns => "http://www.sitemaps.org/schemas/sitemap/0.9"}
  - for post in @posts
    %url
      %loc #{base_url}#{post.permalink}
      %lastmod=post.last_modified
      %changefreq monthly
      %priority 0.5

That's it! You can test it by bringing up http://localhost:3000/sitemap.xml (if using Mongrel) in a browser, or perhaps by using cURL.

Note that the controller uses the stale? method to issue a HTTP 304 Not Modified response if there are no new posts sinces the sitemap was last requested.

Now for rails3, it is better off using full-featured sitemap_generator gem.