Introduce header and Rails caching for schemas

This commit introduces cached project-scoped work packages schema.
Their caches are expired on a key based on

- the Project ID
- the Type ID
- the allowed custom fields for the given project

This commit only caches schema, not form endpoints.

Gemfile

@@ -200,6 +200,8 @@ end
 
 # API gems
 gem 'grape', '~> 0.10.1'
+gem 'grape-cache_control', '~> 1.0.1'
+
 gem 'roar',   '~> 1.0.0'
 gem 'reform', '~> 1.2.6', require: false
 

Gemfile.lock

@@ -286,6 +286,8 @@ GEM
       rack-accept
       rack-mount
       virtus (>= 1.0.0)
+    grape-cache_control (1.0.1)
+      grape (~> 0.3)
     gravatar_image_tag (1.2.0)
     hashie (3.4.1)
     health_check (1.5.1)
@@ -595,6 +597,7 @@ DEPENDENCIES
   globalize (~> 5.0.1)
   gon (~> 4.0)
   grape (~> 0.10.1)
+  grape-cache_control (~> 1.0.1)
   gravatar_image_tag (~> 1.2.0)
   health_check
   htmldiff

lib/api/caching/helpers.rb

@@ -0,0 +1,26 @@
+module API
+  module Caching
+    module Helpers
+      def with_etag!(key)
+        etag = %(W/"#{::Digest::SHA1.hexdigest(key.to_s)}")
+        error!('Not Modified'.freeze, 304) if headers['If-None-Match'.freeze] == etag
+
+        header 'ETag'.freeze, etag
+      end
+
+      ##
+      # Store a represented object in its JSON representation
+      def cache(key, args = {})
+        # Save serialization since we're only dealing with strings here
+        args[:raw] = true
+
+        json = Rails.cache.fetch(key, args) {
+          result = yield
+          result.to_json
+        }
+
+        ::API::Caching::StoredRepresenter.new json
+      end
+    end
+  end
+end

lib/api/caching/stored_representer.rb

@@ -0,0 +1,13 @@
+module API
+  module Caching
+    class StoredRepresenter
+      def initialize(json)
+        @json = json
+      end
+
+      def to_json
+        @json
+      end
+    end
+  end
+end

lib/api/root.rb

@@ -66,6 +66,7 @@ module API
 
     use OpenProject::Authentication::Manager
 
+    helpers API::Caching::Helpers
     helpers do
       def current_user
         User.current

lib/api/v3/work_packages/schema/work_package_schema_representer.rb

@@ -126,9 +126,6 @@ module API
 
           schema :spent_time,
                  type: 'Duration',
-                 show_if: -> (_) do
-                   current_user_allowed_to(:view_time_entries, context: represented.project)
-                 end,
                  required: false
 
           schema :percentage_done,

lib/api/v3/work_packages/schema/work_package_schemas_api.rb

@@ -46,6 +46,10 @@ module API
               def raise404
                 raise ::API::Errors::NotFound.new
               end
+
+              def cache_key(project_id, type_id)
+                "api/v3/work_packages/schema/#{project_id}-#{type_id}"
+              end
             end
 
             # The schema identifier is an artificial identifier that is composed of a work packages
@@ -56,25 +60,30 @@ module API
             namespace ':project-:type' do
               before do
                 begin
-                  project = Project.find(params[:project])
-                  type = Type.find(params[:type])
+                  @project = Project.find(params[:project])
+                  @type = Type.find(params[:type])
                 rescue ActiveRecord::RecordNotFound
                   raise404
                 end
 
-                authorize(:view_work_packages, context: project) do
+                authorize(:view_work_packages, context: @project) do
                   raise404
                 end
 
-                schema = TypedWorkPackageSchema.new(project: project, type: type)
-                self_link = api_v3_paths.work_package_schema(project.id, type.id)
-                @representer = WorkPackageSchemaRepresenter.create(schema,
-                                                                   self_link: self_link,
-                                                                   current_user: current_user)
+                # Compare with ETag composed of project and customizations
+                # to avoid evaluating the server request
+                @custom_fields = @project.all_work_package_custom_fields
+                with_etag! "#{@project.id}/#{@custom_fields.count}/#{@custom_fields.to_param}"
               end
 
               get do
-                @representer
+                cache(key: [cache_key(@project.id, @type.id), @custom_fields]) do
+                  schema = TypedWorkPackageSchema.new(project: @project, type: @type)
+                  self_link = api_v3_paths.work_package_schema(@project.id, @type.id)
+                  WorkPackageSchemaRepresenter.create(schema,
+                                                      self_link: self_link,
+                                                      current_user: nil)
+                end
               end
             end
 

spec/lib/api/v3/work_packages/schema/work_package_schema_representer_spec.rb

@@ -280,18 +280,6 @@ describe ::API::V3::WorkPackages::Schema::WorkPackageSchemaRepresenter do
         let(:required) { false }
         let(:writable) { false }
       end
-
-      context 'not allowed to view time entries' do
-        before do
-          allow(current_user).to receive(:allowed_to?).with(:view_time_entries,
-                                                            work_package.project)
-            .and_return false
-        end
-
-        it 'does not show spentTime' do
-          is_expected.not_to have_json_path('spentTime')
-        end
-      end
     end
 
     describe 'percentageDone' do

spec/requests/api/v3/work_packages/work_packages_schemas_resource_spec.rb

@@ -50,6 +50,10 @@ describe API::V3::WorkPackages::Schema::WorkPackageSchemasAPI, type: :request do
         it 'should return HTTP 200' do
           expect(last_response.status).to eql(200)
         end
+
+        it 'should set a weak ETag' do
+          expect(last_response.headers['ETag']).to match(/W\/\"\w+\"/)
+        end
       end
 
       context 'id is too long' do