How can I use Sinatra to simulate a remote server in RSpec / VCR?

The VCR Cucumber documents show many examples using a tiny Sinatra app to simulate a remote server, using a function called start_sinatra_app loaded from vcr_cucumber_helpers.rb.

I'd like use something like that for my Rails / RSpec / VCR testing, but haven't figured out how to get start_sinatra_app (or equivalent) into my testing framework. My naive approach doesn't work since -- not surprisingly -- it can't find vcr_cucumber_helpers.rb.

What do I need to add to the following to make it work under RSpec? Or am I off in the weeds and doing this all wrong?

# file: spec/app/models/sinatra_test_spec.rb
require 'spec_helper'

start_sinatra_app(:port => 7777) do
  get("/") { "Hello" }
end

describe "sinatra rspec test" do
  it 'calls the sinatra app' do
    VCR.use_cassette("sinatra_rspec_test") do
      res = Net::HTTP.get_response('localhost', "/", 7777)
      res.body.should == 'Hello'
    end
  end
end

Here's the code you're looking for:

def start_sinatra_app(options, &block)
  raise ArgumentError.new("You must pass a port") unless options[:port]

  require 'sinatra'
  require 'support/vcr_localhost_server'
  klass = Class.new(Sinatra::Base)
  klass.disable :protection
  klass.class_eval(&block)

  VCR::LocalhostServer.new(klass.new, options[:port])
end

That in turn uses VCR::LocalhostServer:

require 'rack'
require 'rack/handler/webrick'
require 'net/http'

# The code for this is inspired by Capybara's server:
#   http://github.com/jnicklas/capybara/blob/0.3.9/lib/capybara/server.rb
module VCR
  class LocalhostServer
    READY_MESSAGE = "VCR server ready"

    class Identify
      def initialize(app)
        @app = app
      end

      def call(env)
        if env["PATH_INFO"] == "/__identify__"
          [200, {}, [VCR::LocalhostServer::READY_MESSAGE]]
        else
          @app.call(env)
        end
      end
    end

    attr_reader :port

    def initialize(rack_app, port = nil)
      @port = port || find_available_port
      @rack_app = rack_app
      concurrently { boot }
      wait_until(10, "Boot failed.") { booted? }
    end

    private

    def find_available_port
      server = TCPServer.new('127.0.0.1', 0)
      server.addr[1]
    ensure
      server.close if server
    end

    def boot
      # Use WEBrick since it's part of the ruby standard library and is available on all ruby interpreters.
      options = { :Port => port }
      options.merge!(:AccessLog => [], :Logger => WEBrick::BasicLog.new(StringIO.new)) unless ENV['VERBOSE_SERVER']
      Rack::Handler::WEBrick.run(Identify.new(@rack_app), options)
    end

    def booted?
      res = ::Net::HTTP.get_response("localhost", '/__identify__', port)
      if res.is_a?(::Net::HTTPSuccess) or res.is_a?(::Net::HTTPRedirection)
        return res.body == READY_MESSAGE
      end
    rescue Errno::ECONNREFUSED, Errno::EBADF
      return false
    end

    def concurrently
      # JRuby doesn't support forking.
      # Rubinius does, but there's a weird issue with the booted? check not working,
      # so we're just using a thread for now.
      Thread.new { yield }
    end

    def wait_until(timeout, error_message, &block)
      start_time = Time.now

      while true
        return if yield
        raise TimeoutError.new(error_message) if (Time.now - start_time) > timeout
        sleep(0.05)
      end
    end
  end
end