Question

I’m creating a Sinatra web application which I would like to serve mime type application/xhtml+xml for all web pages served. I am using Builder as template engine. Note that the application will also be serving application/xml for various AJAX api interfaces, also using the Builder template engine, as well as text/css using the scss template engine.

I notice that the webpages that get generated receive a text/html content type while the api interfaces get an application/xml content type instead. However, I don’t know how the mime type is decided; presence of the html tag? usage of a layout or not? Whichever the case, I would like the application to issue a application/xhtml+xml mimetype instead of the text/html mime type.

I know I can specify the mime type with the content_type call, but I’d like to refrain from needing this in every routing function. Is there any way I can set a default mime type for a given template engine? Or can the mime type be controlled by the view’s filename? Does Tilt provide any means to control mime type in a nice way?

Answer 1

Since your application is factored into separate objects, it should be straightforward to pull all of the AJAX routes into a separate Sinatra application. This will allow you to use Sinatra’s after hook. The only requirement is for your AJAX calls to have something that identifies them as AJAX; for example, by setting a request header to a special value, or by using a specially formatted route. Here is an example rackup file of the unique route method:

require 'sinatra/base'

class MainApp

  def get_info params
    # return some data structure
  end

end

class MainAppRoutes < Sinatra::Base

  def initialize mainapp
    super()
    @mainapp = mainapp
  end

  get '/' do # main page
    data = @mainapp.get_info(params)
    # render response from data
  end

end

class AjaxRoutes < Sinatra::Base

  def initialize mainapp
    super()
    @mainapp = mainapp
  end

  get '/getinfo' do # handler for /ajax/getinfo
    data = @mainapp.get_info(params)
    # generate XML response from data
  end

  after do
    content_type 'application/xml'
  end

end

mainapp = MainApp.new

map '/ajax' do
  run AjaxRoutes.new(mainapp)
end
run MainAppRoutes.new(mainapp)

In this example, all routes starting with /ajax are handled by instances of the AjaxRoutes class. The after hook ensures that the content type for those responses are ‘application/xml’. The non-ajax routes are not affected.

A few things to remember:

• Rack::Builder.map strips off the parts of the URL it matches. So a ‘/’ route in AjaxRoutes would actually answer a request for ‘/ajax/’.
• Always call super() in the initializers of your Sinatra-derived endpoint classes. For Sinatra middleware, pass the first argument up (Rack calls #new with the next rack app as the first parameter).
• Review the doc about Sinatra filters. There is a potentially frustrating quirk about modifying responses with the after hook.