Question

I have a Sinatra based REST service app and I would like to call one of the resources from within one of the routes, effectively composing one resource from another. E.g.

get '/someresource' do
  otherresource = get '/otherresource'
  # do something with otherresource, return a new resource
end

get '/otherresource' do
  # etc.
end

A redirect will not work since I need to do some processing on the second resource and create a new one from it. Obviously I could a) use RestClient or some other client framework or b) structure my code so all of the logic for otherresource is in a method and just call that, however, it feels like it would be much cleaner if I could just re-use my resources from within Sinatra using their DSL.

Answer 1

I was able to hack something up by making a quick and dirty rack request and calling the Sinatra (a rack app) application directly. It’s not pretty, but it works. Note that it would probably be better to extract the code that generates this resource into a helper method instead of doing something like this. But it is possible, and there might be better, cleaner ways of doing it than this.

#!/usr/bin/env ruby
require 'rubygems'
require 'stringio'
require 'sinatra'

get '/someresource' do
  resource = self.call(
    'REQUEST_METHOD' => 'GET',
    'PATH_INFO' => '/otherresource',
    'rack.input' => StringIO.new
  )[2].join('')

  resource.upcase
end

get '/otherresource' do
  "test"
end

If you want to know more about what’s going on behind the scenes, I’ve written a few articles on the basics of Rack you can read. There is What is Rack? and Using Rack.