Export interaction policies for local posts over ActivityPub (#35697)

app/serializers/activitypub/note_serializer.rb

@@ -3,7 +3,7 @@
 class ActivityPub::NoteSerializer < ActivityPub::Serializer
   include FormattingHelper
 
-  context_extensions :atom_uri, :conversation, :sensitive, :voters_count, :quotes
+  context_extensions :atom_uri, :conversation, :sensitive, :voters_count, :quotes, :interaction_policies
 
   attributes :id, :type, :summary,
              :in_reply_to, :published, :url,
@@ -35,6 +35,8 @@ class ActivityPub::NoteSerializer < ActivityPub::Serializer
   attribute :quote, key: :quote_uri, if: :quote?
   attribute :quote_authorization, if: :quote_authorization?
 
+  attribute :interaction_policy, if: -> { Mastodon::Feature.outgoing_quotes_enabled? }
+
   def id
     ActivityPub::TagManager.instance.uri_for(object)
   end
@@ -216,6 +218,23 @@ class ActivityPub::NoteSerializer < ActivityPub::Serializer
     ActivityPub::TagManager.instance.approval_uri_for(object.quote)
   end
 
+  def interaction_policy
+    approved_uris = []
+
+    # On outgoing posts, only automatic approval is supported
+    policy = object.quote_approval_policy >> 16
+    approved_uris << ActivityPub::TagManager::COLLECTIONS[:public] if policy.anybits?(Status::QUOTE_APPROVAL_POLICY_FLAGS[:public])
+    approved_uris << ActivityPub::TagManager.instance.followers_uri_for(object.account) if policy.anybits?(Status::QUOTE_APPROVAL_POLICY_FLAGS[:followers])
+    approved_uris << ActivityPub::TagManager.instance.following_uri_for(object.account) if policy.anybits?(Status::QUOTE_APPROVAL_POLICY_FLAGS[:followed])
+    approved_uris << ActivityPub::TagManager.instance.uri_for(object.account) if approved_uris.empty?
+
+    {
+      canQuote: {
+        automaticApproval: approved_uris,
+      },
+    }
+  end
+
   class MediaAttachmentSerializer < ActivityPub::Serializer
     context_extensions :blurhash, :focal_point
 

spec/serializers/activitypub/note_serializer_spec.rb

@@ -56,4 +56,19 @@ RSpec.describe ActivityPub::NoteSerializer do
       })
     end
   end
+
+  context 'with a quote policy', feature: :outgoing_quotes do
+    let(:parent) { Fabricate(:status, quote_approval_policy: Status::QUOTE_APPROVAL_POLICY_FLAGS[:followers] << 16) }
+
+    it 'has the expected shape' do
+      expect(subject).to include({
+        'type' => 'Note',
+        'interactionPolicy' => a_hash_including(
+          'canQuote' => a_hash_including(
+            'automaticApproval' => [ActivityPub::TagManager.instance.followers_uri_for(parent.account)]
+          )
+        ),
+      })
+    end
+  end
 end