Add support for fetching Create and Announce activities by URI (#16383)

* Add support for fetching Create and Announce activities by URI

This should improve compatibility with ZAP and offer a way to fetch boosts,
which is currently not possible.

* Add tests

app/services/activitypub/fetch_remote_status_service.rb

@@ -13,7 +13,20 @@ class ActivityPub::FetchRemoteStatusService < BaseService
       end
     end
 
-    return if !(supported_context? && expected_type?) || actor_id.nil? || !trustworthy_attribution?(@json['id'], actor_id)
+    return unless supported_context?
+
+    actor_id = nil
+    activity_json = nil
+
+    if expected_object_type?
+      actor_id = value_or_id(first_of_value(@json['attributedTo']))
+      activity_json = { 'type' => 'Create', 'actor' => actor_id, 'object' => @json }
+    elsif expected_activity_type?
+      actor_id = value_or_id(first_of_value(@json['actor']))
+      activity_json = @json
+    end
+
+    return if activity_json.nil? || !trustworthy_attribution?(@json['id'], actor_id)
 
     actor = ActivityPub::TagManager.instance.uri_to_resource(actor_id, Account)
     actor = ActivityPub::FetchRemoteAccountService.new.call(actor_id, id: true) if actor.nil? || needs_update?(actor)
@@ -25,14 +38,6 @@ class ActivityPub::FetchRemoteStatusService < BaseService
 
   private
 
-  def activity_json
-    { 'type' => 'Create', 'actor' => actor_id, 'object' => @json }
-  end
-
-  def actor_id
-    value_or_id(first_of_value(@json['attributedTo']))
-  end
-
   def trustworthy_attribution?(uri, attributed_to)
     return false if uri.nil? || attributed_to.nil?
     Addressable::URI.parse(uri).normalized_host.casecmp(Addressable::URI.parse(attributed_to).normalized_host).zero?
@@ -42,7 +47,11 @@ class ActivityPub::FetchRemoteStatusService < BaseService
     super(@json)
   end
 
-  def expected_type?
+  def expected_activity_type?
+    equals_or_includes_any?(@json['type'], %w(Create Announce))
+  end
+
+  def expected_object_type?
     equals_or_includes_any?(@json['type'], ActivityPub::Activity::Create::SUPPORTED_TYPES + ActivityPub::Activity::Create::CONVERTED_TYPES)
   end
 

spec/services/activitypub/fetch_remote_status_service_spec.rb

@@ -145,5 +145,46 @@ RSpec.describe ActivityPub::FetchRemoteStatusService, type: :service do
         expect(sender.statuses.first).to be_nil
       end
     end
+
+    context 'with a valid Create activity' do
+      let(:object) do
+        {
+          '@context': 'https://www.w3.org/ns/activitystreams',
+          id: "https://#{valid_domain}/@foo/1234/create",
+          type: 'Create',
+          actor: ActivityPub::TagManager.instance.uri_for(sender),
+          object: note,
+        }
+      end
+
+      it 'creates status' do
+        status = sender.statuses.first
+
+        expect(status).to_not be_nil
+        expect(status.uri).to eq note[:id]
+        expect(status.text).to eq note[:content]
+      end
+    end
+
+    context 'with a Create activity with a mismatching id' do
+      let(:object) do
+        {
+          '@context': 'https://www.w3.org/ns/activitystreams',
+          id: "https://#{valid_domain}/@foo/1234/create",
+          type: 'Create',
+          actor: ActivityPub::TagManager.instance.uri_for(sender),
+          object: {
+            id: "https://real.address/@foo/1234",
+            type: 'Note',
+            content: 'Lorem ipsum',
+            attributedTo: ActivityPub::TagManager.instance.uri_for(sender),
+          },
+        }
+      end
+
+      it 'does not create status' do
+        expect(sender.statuses.first).to be_nil
+      end
+    end
   end
 end