Fork'd to follow

format_accepts.rb

module Rack
  #
  # A Rack middleware for automatically removing the format token at the end
  # of a request path and adding its media type to the HTTP_ACCEPT header.
  # 
  # MIT-License - Rein Henrichs
  # 
  class FormatAccepts
    def initialize(app)
      @app = app
    end
    
    def call(env)
      req = Rack::Request.new(env)
      
      if req.path_info =~ /(.*)(\..+)$/
        env["PATH_INFO"] = $1
        ext = $2
        accept = env['HTTP_ACCEPT'].split(',') rescue []
        media_type = Rack::Mime::MIME_TYPES[ext]
        accept.unshift(media_type) if media_type
        env['HTTP_ACCEPT'] = accept.join(',')
      end
      @app.call(env)
    end
  end
end