AP/AS serialization of Collections (#37434)

app/lib/activitypub/tag_manager.rb

@@ -62,6 +62,8 @@ class ActivityPub::TagManager
       emoji_url(target)
     when :flag
       target.uri
+    when :featured_collection
+      ap_account_featured_collection_url(target.account.id, target)
     end
   end
 

app/models/collection.rb

@@ -60,6 +60,10 @@ class Collection < ApplicationRecord
     self.tag = Tag.find_or_create_by_names(new_name).first
   end
 
+  def object_type
+    :featured_collection
+  end
+
   private
 
   def tag_is_usable

app/serializers/activitypub/featured_collection_serializer.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+class ActivityPub::FeaturedCollectionSerializer < ActivityPub::Serializer
+  class FeaturedItemSerializer < ActivityPub::Serializer
+    attributes :type, :featured_object, :featured_object_type
+
+    def type
+      'FeaturedItem'
+    end
+
+    def featured_object
+      ActivityPub::TagManager.instance.uri_for(object.account)
+    end
+
+    def featured_object_type
+      object.account.actor_type || 'Person'
+    end
+  end
+
+  attributes :id, :type, :total_items, :name, :summary, :attributed_to,
+             :sensitive, :discoverable, :published, :updated
+
+  has_one :tag, key: :topic, serializer: ActivityPub::NoteSerializer::TagSerializer
+
+  has_many :collection_items, key: :ordered_items, serializer: FeaturedItemSerializer
+
+  def id
+    ActivityPub::TagManager.instance.uri_for(object)
+  end
+
+  def type
+    'FeaturedCollection'
+  end
+
+  def summary
+    object.description
+  end
+
+  def attributed_to
+    ActivityPub::TagManager.instance.uri_for(object.account)
+  end
+
+  def total_items
+    object.collection_items.size
+  end
+
+  def published
+    object.created_at.iso8601
+  end
+
+  def updated
+    object.updated_at.iso8601
+  end
+end

config/routes.rb

@@ -96,6 +96,7 @@ Rails.application.routes.draw do
   get '/authorize_follow', to: redirect { |_, request| "/authorize_interaction?#{request.params.to_query}" }
 
   concern :account_resources do
+    resources :featured_collections, only: [:show]
     resources :followers, only: [:index], controller: :follower_accounts
     resources :following, only: [:index], controller: :following_accounts
 

spec/fabricators/collection_fabricator.rb

@@ -8,3 +8,10 @@ Fabricator(:collection) do
   sensitive    false
   discoverable true
 end
+
+Fabricator(:remote_collection, from: :collection) do
+  account { Fabricate.build(:remote_account) }
+  local false
+  uri { sequence(:uri) { |i| "https://example.com/collections/#{i}" } }
+  original_number_of_items 0
+end

spec/lib/activitypub/tag_manager_spec.rb

@@ -192,6 +192,23 @@ RSpec.describe ActivityPub::TagManager do
         expect(subject.uri_for(status.conversation)).to eq status.conversation.uri
       end
     end
+
+    context 'with a local collection' do
+      let(:collection) { Fabricate(:collection) }
+
+      it 'returns a string starting with web domain and with the expected path' do
+        expect(subject.uri_for(collection))
+          .to eq("#{host_prefix}/ap/users/#{collection.account.id}/featured_collections/#{collection.id}")
+      end
+    end
+
+    context 'with a remote collection' do
+      let(:collection) { Fabricate(:remote_collection) }
+
+      it 'returns the expected URL' do
+        expect(subject.uri_for(collection)).to eq collection.uri
+      end
+    end
   end
 
   describe '#key_uri_for' do

spec/models/collection_spec.rb

@@ -126,4 +126,10 @@ RSpec.describe Collection do
       end
     end
   end
+
+  describe '#object_type' do
+    it 'returns `:featured_collection`' do
+      expect(subject.object_type).to eq :featured_collection
+    end
+  end
 end

spec/serializers/activitypub/featured_collection_serializer_spec.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe ActivityPub::FeaturedCollectionSerializer do
+  subject { serialized_record_json(collection, described_class, adapter: ActivityPub::Adapter) }
+
+  let(:collection) do
+    Fabricate(:collection,
+              name: 'Incredible people',
+              description: 'These are really amazing',
+              tag_name: '#people',
+              discoverable: false)
+  end
+  let!(:collection_items) { Fabricate.times(2, :collection_item, collection:) }
+
+  it 'serializes to the expected structure' do
+    expect(subject).to include({
+      'type' => 'FeaturedCollection',
+      'id' => ActivityPub::TagManager.instance.uri_for(collection),
+      'name' => 'Incredible people',
+      'summary' => 'These are really amazing',
+      'attributedTo' => ActivityPub::TagManager.instance.uri_for(collection.account),
+      'sensitive' => false,
+      'discoverable' => false,
+      'topic' => {
+        'href' => match(%r{/tags/people$}),
+        'type' => 'Hashtag',
+        'name' => '#people',
+      },
+      'totalItems' => 2,
+      'orderedItems' => [
+        {
+          'type' => 'FeaturedItem',
+          'featuredObject' => ActivityPub::TagManager.instance.uri_for(collection_items.first.account),
+          'featuredObjectType' => 'Person',
+        },
+        {
+          'type' => 'FeaturedItem',
+          'featuredObject' => ActivityPub::TagManager.instance.uri_for(collection_items.last.account),
+          'featuredObjectType' => 'Person',
+        },
+      ],
+      'published' => match_api_datetime_format,
+      'updated' => match_api_datetime_format,
+    })
+  end
+end