Federated "featureable in collections" preference (#37298)

app/lib/activitypub/parser/interaction_policy_parser.rb

@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+class ActivityPub::Parser::InteractionPolicyParser
+  def initialize(json, account)
+    @json = json
+    @account = account
+  end
+
+  def bitmap
+    flags = 0
+    return flags if @json.blank?
+
+    flags |= subpolicy(@json['automaticApproval'])
+    flags <<= 16
+    flags |= subpolicy(@json['manualApproval'])
+
+    flags
+  end
+
+  private
+
+  def subpolicy(partial_json)
+    flags = 0
+
+    allowed_actors = Array(partial_json).dup
+    allowed_actors.uniq!
+
+    flags |= InteractionPolicy::POLICY_FLAGS[:public] if allowed_actors.delete('as:Public') || allowed_actors.delete('Public') || allowed_actors.delete('https://www.w3.org/ns/activitystreams#Public')
+    flags |= InteractionPolicy::POLICY_FLAGS[:followers] if allowed_actors.delete(@account.followers_url)
+    flags |= InteractionPolicy::POLICY_FLAGS[:following] if allowed_actors.delete(@account.following_url)
+
+    includes_target_actor = allowed_actors.delete(ActivityPub::TagManager.instance.uri_for(@account)).present?
+
+    # Any unrecognized actor is marked as unsupported
+    flags |= InteractionPolicy::POLICY_FLAGS[:unsupported_policy] unless allowed_actors.empty?
+
+    flags |= InteractionPolicy::POLICY_FLAGS[:disabled] if flags.zero? && includes_target_actor
+
+    flags
+  end
+end

app/models/account.rb

@@ -5,54 +5,55 @@
 # Table name: accounts
 #
 #  id                            :bigint(8)        not null, primary key
-#  username                      :string           default(""), not null
+#  actor_type                    :string
-#  domain                        :string
+#  also_known_as                 :string           is an Array
-#  private_key                   :text
+#  attribution_domains           :string           default([]), is an Array
-#  public_key                    :text             default(""), not null
-#  created_at                    :datetime         not null
-#  updated_at                    :datetime         not null
-#  note                          :text             default(""), not null
-#  display_name                  :string           default(""), not null
-#  uri                           :string           default(""), not null
-#  url                           :string
-#  avatar_file_name              :string
 #  avatar_content_type           :string
+#  avatar_file_name              :string
 #  avatar_file_size              :integer
-#  avatar_updated_at             :datetime
-#  header_file_name              :string
-#  header_content_type           :string
-#  header_file_size              :integer
-#  header_updated_at             :datetime
 #  avatar_remote_url             :string
-#  locked                        :boolean          default(FALSE), not null
+#  avatar_storage_schema_version :integer
-#  header_remote_url             :string           default(""), not null
+#  avatar_updated_at             :datetime
-#  last_webfingered_at           :datetime
+#  discoverable                  :boolean
-#  inbox_url                     :string           default(""), not null
+#  display_name                  :string           default(""), not null
-#  outbox_url                    :string           default(""), not null
+#  domain                        :string
-#  shared_inbox_url              :string           default(""), not null
+#  feature_approval_policy       :integer          default(0), not null
-#  followers_url                 :string           default(""), not null
-#  following_url                 :string           default(""), not null
-#  protocol                      :integer          default("ostatus"), not null
-#  memorial                      :boolean          default(FALSE), not null
-#  moved_to_account_id           :bigint(8)
 #  featured_collection_url       :string
 #  fields                        :jsonb
-#  actor_type                    :string
+#  followers_url                 :string           default(""), not null
-#  discoverable                  :boolean
+#  following_url                 :string           default(""), not null
-#  also_known_as                 :string           is an Array
+#  header_content_type           :string
+#  header_file_name              :string
+#  header_file_size              :integer
+#  header_remote_url             :string           default(""), not null
+#  header_storage_schema_version :integer
+#  header_updated_at             :datetime
+#  hide_collections              :boolean
+#  id_scheme                     :integer          default("numeric_ap_id")
+#  inbox_url                     :string           default(""), not null
+#  indexable                     :boolean          default(FALSE), not null
+#  last_webfingered_at           :datetime
+#  locked                        :boolean          default(FALSE), not null
+#  memorial                      :boolean          default(FALSE), not null
+#  note                          :text             default(""), not null
+#  outbox_url                    :string           default(""), not null
+#  private_key                   :text
+#  protocol                      :integer          default("ostatus"), not null
+#  public_key                    :text             default(""), not null
+#  requested_review_at           :datetime
+#  reviewed_at                   :datetime
+#  sensitized_at                 :datetime
+#  shared_inbox_url              :string           default(""), not null
 #  silenced_at                   :datetime
 #  suspended_at                  :datetime
-#  hide_collections              :boolean
-#  avatar_storage_schema_version :integer
-#  header_storage_schema_version :integer
 #  suspension_origin             :integer
-#  sensitized_at                 :datetime
 #  trendable                     :boolean
-#  reviewed_at                   :datetime
+#  uri                           :string           default(""), not null
-#  requested_review_at           :datetime
+#  url                           :string
-#  indexable                     :boolean          default(FALSE), not null
+#  username                      :string           default(""), not null
-#  attribution_domains           :string           default([]), is an Array
+#  created_at                    :datetime         not null
-#  id_scheme                     :integer          default("numeric_ap_id")
+#  updated_at                    :datetime         not null
+#  moved_to_account_id           :bigint(8)
 #
 
 class Account < ApplicationRecord

app/serializers/activitypub/actor_serializer.rb

@@ -10,12 +10,16 @@ class ActivityPub::ActorSerializer < ActivityPub::Serializer
                      :moved_to, :property_value, :discoverable, :suspended,
                      :memorial, :indexable, :attribution_domains
 
+  context_extensions :interaction_policies if Mastodon::Feature.collections_enabled?
+
   attributes :id, :type, :following, :followers,
              :inbox, :outbox, :featured, :featured_tags,
              :preferred_username, :name, :summary,
              :url, :manually_approves_followers,
              :discoverable, :indexable, :published, :memorial
 
+  attribute :interaction_policy, if: -> { Mastodon::Feature.collections_enabled? }
+
   has_one :public_key, serializer: ActivityPub::PublicKeySerializer
 
   has_many :virtual_tags, key: :tag
@@ -163,6 +167,16 @@ class ActivityPub::ActorSerializer < ActivityPub::Serializer
     object.created_at.midnight.iso8601
   end
 
+  def interaction_policy
+    uri = object.discoverable? ? ActivityPub::TagManager::COLLECTIONS[:public] : ActivityPub::TagManager.instance.uri_for(object)
+
+    {
+      canFeature: {
+        automaticApproval: [uri],
+      },
+    }
+  end
+
   class CustomEmojiSerializer < ActivityPub::EmojiSerializer
   end
 

app/services/activitypub/process_account_service.rb

@@ -107,6 +107,7 @@ class ActivityPub::ProcessAccountService < BaseService
     @account.uri                     = @uri
     @account.actor_type              = actor_type
     @account.created_at              = @json['published'] if @json['published'].present?
+    @account.feature_approval_policy = feature_approval_policy if Mastodon::Feature.collections_enabled?
   end
 
   def valid_collection_uri(uri)
@@ -360,4 +361,8 @@ class ActivityPub::ProcessAccountService < BaseService
     emoji.image_remote_url = image_url
     emoji.save
   end
+
+  def feature_approval_policy
+    ActivityPub::Parser::InteractionPolicyParser.new(@json.dig('interactionPolicy', 'canFeature'), @account).bitmap
+  end
 end

db/migrate/20251217091936_add_feature_approval_policy_to_accounts.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AddFeatureApprovalPolicyToAccounts < ActiveRecord::Migration[8.0]
+  def change
+    add_column :accounts, :feature_approval_policy, :integer, null: false, default: 0
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2025_12_09_093813) do
+ActiveRecord::Schema[8.0].define(version: 2025_12_17_091936) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_catalog.plpgsql"
 
@@ -200,6 +200,7 @@ ActiveRecord::Schema[8.0].define(version: 2025_12_09_093813) do
     t.string "attribution_domains", default: [], array: true
     t.string "following_url", default: "", null: false
     t.integer "id_scheme", default: 1
+    t.integer "feature_approval_policy", default: 0, null: false
     t.index "(((setweight(to_tsvector('simple'::regconfig, (display_name)::text), 'A'::\"char\") || setweight(to_tsvector('simple'::regconfig, (username)::text), 'B'::\"char\")) || setweight(to_tsvector('simple'::regconfig, (COALESCE(domain, ''::character varying))::text), 'C'::\"char\")))", name: "search_index", using: :gin
     t.index "lower((username)::text), COALESCE(lower((domain)::text), ''::text)", name: "index_accounts_on_username_and_domain_lower", unique: true
     t.index ["domain", "id"], name: "index_accounts_on_domain_and_id"

spec/lib/activitypub/parser/interaction_policy_parser_spec.rb

@@ -0,0 +1,102 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe ActivityPub::Parser::InteractionPolicyParser do
+  subject { described_class.new(json_policy, account) }
+
+  let(:account) do
+    Fabricate(:account,
+              uri: 'https://foo.test',
+              domain: 'foo.test',
+              followers_url: 'https://foo.test/followers',
+              following_url: 'https://foo.test/following')
+  end
+
+  describe '#bitmap' do
+    context 'when no policy is given' do
+      let(:json_policy) { nil }
+
+      it 'returns zero' do
+        expect(subject.bitmap).to be_zero
+      end
+    end
+
+    context 'with special public URI' do
+      let(:json_policy) do
+        {
+          'manualApproval' => [public_uri],
+        }
+      end
+
+      shared_examples 'setting the public bit' do
+        it 'sets the public bit' do
+          expect(subject.bitmap).to eq 0b10
+        end
+      end
+
+      context 'when public URI is given in full' do
+        let(:public_uri) { 'https://www.w3.org/ns/activitystreams#Public' }
+
+        it_behaves_like 'setting the public bit'
+      end
+
+      context 'when public URI is abbreviated using namespace' do
+        let(:public_uri) { 'as:Public' }
+
+        it_behaves_like 'setting the public bit'
+      end
+
+      context 'when public URI is abbreviated without namespace' do
+        let(:public_uri) { 'Public' }
+
+        it_behaves_like 'setting the public bit'
+      end
+    end
+
+    context 'when mixing array and scalar values' do
+      let(:json_policy) do
+        {
+          'automaticApproval' => 'https://foo.test',
+          'manualApproval' => [
+            'https://foo.test/followers',
+            'https://foo.test/following',
+          ],
+        }
+      end
+
+      it 'sets the correct flags' do
+        expect(subject.bitmap).to eq 0b100000000000000001100
+      end
+    end
+
+    context 'when including individual actor URIs' do
+      let(:json_policy) do
+        {
+          'automaticApproval' => ['https://example.com/actor', 'https://masto.example.com/@user'],
+          'manualApproval' => ['https://masto.example.com/@other'],
+        }
+      end
+
+      it 'sets the unsupported bit' do
+        expect(subject.bitmap).to eq 0b10000000000000001
+      end
+    end
+
+    context "when giving the affected actor's URI in addition to other supported URIs" do
+      let(:json_policy) do
+        {
+          'manualApproval' => [
+            'https://foo.test/followers',
+            'https://foo.test/following',
+            'https://foo.test',
+          ],
+        }
+      end
+
+      it 'is being ignored' do
+        expect(subject.bitmap).to eq 0b1100
+      end
+    end
+  end
+end

spec/serializers/activitypub/actor_serializer_spec.rb

@@ -3,7 +3,7 @@
 require 'rails_helper'
 
 RSpec.describe ActivityPub::ActorSerializer do
-  subject { serialized_record_json(record, described_class) }
+  subject { serialized_record_json(record, described_class, adapter: ActivityPub::Adapter) }
 
   describe '#type' do
     context 'with the instance actor' do
@@ -36,4 +36,39 @@ RSpec.describe ActivityPub::ActorSerializer do
       it { is_expected.to include('type' => 'Person') }
     end
   end
+
+  describe '#interactionPolicy' do
+    let(:record) { Fabricate(:account) }
+
+    # TODO: Remove when feature flag is removed
+    context 'when collections feature is disabled?' do
+      it 'is not present' do
+        expect(subject).to_not have_key('interactionPolicy')
+      end
+    end
+
+    context 'when collections feature is enabled', feature: :collections do
+      context 'when actor is discoverable' do
+        it 'includes an automatic policy allowing everyone' do
+          expect(subject).to include('interactionPolicy' => {
+            'canFeature' => {
+              'automaticApproval' => ['https://www.w3.org/ns/activitystreams#Public'],
+            },
+          })
+        end
+      end
+
+      context 'when actor is not discoverable' do
+        let(:record) { Fabricate(:account, discoverable: false) }
+
+        it 'includes an automatic policy limited to the actor itself' do
+          expect(subject).to include('interactionPolicy' => {
+            'canFeature' => {
+              'automaticApproval' => [ActivityPub::TagManager.instance.uri_for(record)],
+            },
+          })
+        end
+      end
+    end
+  end
 end

spec/services/activitypub/process_account_service_spec.rb

@@ -272,6 +272,49 @@ RSpec.describe ActivityPub::ProcessAccountService do
     end
   end
 
+  context 'with interaction policy' do
+    let(:payload) do
+      {
+        id: 'https://foo.test',
+        type: 'Actor',
+        inbox: 'https://foo.test/inbox',
+        followers: 'https://foo.test/followers',
+        following: 'https://foo.test/following',
+        interactionPolicy: {
+          canFeature: {
+            automaticApproval: 'https://foo.test',
+            manualApproval: [
+              'https://foo.test/followers',
+              'https://foo.test/following',
+            ],
+          },
+        },
+      }.with_indifferent_access
+    end
+
+    before do
+      stub_request(:get, %r{^https://foo\.test/follow})
+        .to_return(status: 200, body: '', headers: {})
+    end
+
+    # TODO: Remove when feature flag is removed
+    context 'when collections feature is disabled' do
+      it 'does not set the interaction policy' do
+        account = subject.call('user1', 'foo.test', payload)
+
+        expect(account.feature_approval_policy).to be_zero
+      end
+    end
+
+    context 'when collections feature is enabled', feature: :collections do
+      it 'sets the interaction policy to the correct value' do
+        account = subject.call('user1', 'foo.test', payload)
+
+        expect(account.feature_approval_policy).to eq 0b100000000000000001100
+      end
+    end
+  end
+
   private
 
   def create_some_remote_accounts