Rack middleware to help avoid SEO duplicate content issues. Removes www and trailing slash and performs a permanent redirect.

rails

config.middleware.insert_before(0, 'Rack::SeoRedirect')

seo_redirect.rb

# Avoid SEO duplicate content issues
# - Remove www from domain
# - Remove trailing slash

module Rack
  class SeoRedirect
    def initialize(app)
      @app = app
    end

    def call(env)
      request = Rack::Request.new env
      url = request.url
      url.sub!('//www.', '//') if request.host =~ /^www\./
      url.chomp!('/') if request.path_info =~ %r{^/(.*)/$}

      if url != request.url
        [301, { 'Location' => url, 'Content-Type' => 'text/html' }, []]
      else
        @app.call env
      end
    end
  end
end

sinatra

require 'seo_redirect'
use Rack::SeoRedirect 

Associated blog post --> http://quickleft.com/blog/avoiding-seo-duplicate-content-issues-with-ruby-and-rack-middleware--2