Show purl endpoint

This will allow purl to know whether an item should be crawlable or not

README.md

@@ -95,7 +95,37 @@ rake rubocop
 
 ### Purls
 
-#### `/purls/:druid`
+#### GET `/purls/:druid`
+
+`GET /purls/:druid`
+
+##### Summary
+
+Display a single purl
+
+##### Description
+
+The GET `/purls/:druid` endpoint provides the ability to display a PURL document. This endpoint is used by [purl](https://github.com/sul-dlss/purl/) to know if an item should be in the sitemap
+
+##### Parameters
+
+| Name      | Located In | Description                                | Required | Schema                          | Default |
+| --------- | ---------- | ------------------------------------------ | -------- | ------------------------------- | ------- |
+| `druid`   | url        | Druid of a specific PURL                   | Yes      | string eg(`druid:cc1111dd2222`) | null    |
+| `version` | header     | Version of the API request eg(`version=1`) | No       | integer                         | 1       |
+
+##### Example Response
+
+```json
+{
+  "druid": "druid:dd111ee2222",
+  "latest_change": "2014-01-01T00:00:00Z",
+  "true_targets": ["PURL sitemap"],
+  "collections": ["druid:oo000oo0001"]
+}
+```
+
+#### POST `/purls/:druid`
 
 `POST /purls/:druid`
 

app/controllers/application_controller.rb

@@ -16,7 +16,7 @@ def per_page_params
 
     def druid_param
       druid = params.require(:druid)
-      druid = "druid:#{druid}" unless druid.include?('druid:')
+      druid = "druid:#{druid}" unless druid.start_with?('druid:')
       druid
     end
 end

app/controllers/v1/purls_controller.rb

@@ -1,5 +1,11 @@
 module V1
   class PurlsController < ApplicationController
+    # Show the public json for the object. Used by purl to know if this object should be indexed by crawlers.
+    def show
+      purl = Purl.find_by(druid: druid_param)
+      render json: purl.as_public_json
+    end
+
     ##
     # Update the database purl record from the passed in cocina
     def update

config/routes.rb

@@ -9,7 +9,7 @@
 
     resources :released, only: :show
 
-    resources :purls, only: [:destroy], param: :druid do
+    resources :purls, only: [:destroy, :show], param: :druid do
       member do
         post '/', action: 'update'
       end

spec/factories/purl.rb

@@ -1,7 +1,7 @@
 FactoryBot.define do
   factory :purl do
     sequence :druid do |n|
-      "druid:zz#{n.to_s * 3}yy#{n.to_s * 4}"
+      "druid:zz#{format('%03d', n)}yy0000"
     end
     published_at { 1.day.ago }
   end

spec/factories/release_tag.rb

@@ -3,5 +3,9 @@
     purl
     name { 'Searchworks' }
     release_type { true }
+
+    trait :sitemap do
+      name { 'PURL sitemap' }
+    end
   end
 end

spec/rails_helper.rb

@@ -45,7 +45,7 @@
   # https://relishapp.com/rspec/rspec-rails/docs
   config.infer_spec_type_from_file_location!
 
-  config.fixture_paths = ["#{::Rails.root}/test/fixtures"]
+  config.fixture_paths = [Rails.root.join('test/fixtures')]
 
   config.use_transactional_fixtures = true
 

spec/requests/v1/purls_controller_spec.rb

@@ -1,6 +1,19 @@
 require 'rails_helper'
 
 RSpec.describe V1::PurlsController do
+  describe 'GET show' do
+    let!(:release_tag) { create(:release_tag, :sitemap) }
+    let(:purl_object) { release_tag.purl }
+    let(:druid) { purl_object.druid }
+
+    it 'displays the purl data' do
+      get "/purls/#{druid}"
+
+      expect(response).to have_http_status(:ok)
+      expect(response.parsed_body).to include("true_targets" => ["PURL sitemap", "SearchWorksPreview", "ContentSearch"])
+    end
+  end
+
   describe 'POST update' do
     context 'with cocina json' do
       before do

spec/requests/v1/released_controller_spec.rb

@@ -2,7 +2,7 @@
 
 RSpec.describe V1::ReleasedController do
   describe '#show' do
-    let!(:release_tag) { create(:release_tag, name: "PURL sitemap") }
+    let!(:release_tag) { create(:release_tag, :sitemap) }
     let(:purl) { release_tag.purl }
 
     it 'returns list of druids' do