Fix processing of compacted single-item JSON-LD collections (#28816)

app/services/activitypub/fetch_featured_collection_service.rb

@@ -23,9 +23,9 @@ class ActivityPub::FetchFeaturedCollectionService < BaseService
 
     case collection['type']
     when 'Collection', 'CollectionPage'
-      collection['items']
+      as_array(collection['items'])
     when 'OrderedCollection', 'OrderedCollectionPage'
-      collection['orderedItems']
+      as_array(collection['orderedItems'])
     end
   end
 

app/services/activitypub/fetch_replies_service.rb

@@ -26,9 +26,9 @@ class ActivityPub::FetchRepliesService < BaseService
 
     case collection['type']
     when 'Collection', 'CollectionPage'
-      collection['items']
+      as_array(collection['items'])
     when 'OrderedCollection', 'OrderedCollectionPage'
-      collection['orderedItems']
+      as_array(collection['orderedItems'])
     end
   end
 

app/services/activitypub/synchronize_followers_service.rb

@@ -59,9 +59,9 @@ class ActivityPub::SynchronizeFollowersService < BaseService
 
     case collection['type']
     when 'Collection', 'CollectionPage'
-      collection['items']
+      as_array(collection['items'])
     when 'OrderedCollection', 'OrderedCollectionPage'
-      collection['orderedItems']
+      as_array(collection['orderedItems'])
     end
   end
 

app/services/keys/query_service.rb

@@ -69,7 +69,7 @@ class Keys::QueryService < BaseService
 
     return if json['items'].blank?
 
-    @devices = json['items'].map do |device|
+    @devices = as_array(json['items']).map do |device|
       Device.new(device_id: device['id'], name: device['name'], identity_key: device.dig('identityKey', 'publicKeyBase64'), fingerprint_key: device.dig('fingerprintKey', 'publicKeyBase64'), claim_url: device['claim'])
     end
   rescue HTTP::Error, OpenSSL::SSL::SSLError, Mastodon::Error => e

spec/services/activitypub/fetch_featured_collection_service_spec.rb

@@ -97,6 +97,21 @@ RSpec.describe ActivityPub::FetchFeaturedCollectionService, type: :service do
       end
 
       it_behaves_like 'sets pinned posts'
+
+      context 'when there is a single item, with the array compacted away' do
+        let(:items) { 'https://example.com/account/pinned/4' }
+
+        before do
+          stub_request(:get, 'https://example.com/account/pinned/4').to_return(status: 200, body: Oj.dump(status_json_4))
+          subject.call(actor, note: true, hashtag: false)
+        end
+
+        it 'sets expected posts as pinned posts' do
+          expect(actor.pinned_statuses.pluck(:uri)).to contain_exactly(
+            'https://example.com/account/pinned/4'
+          )
+        end
+      end
     end
 
     context 'when the endpoint is a paginated Collection' do
@@ -118,6 +133,21 @@ RSpec.describe ActivityPub::FetchFeaturedCollectionService, type: :service do
       end
 
       it_behaves_like 'sets pinned posts'
+
+      context 'when there is a single item, with the array compacted away' do
+        let(:items) { 'https://example.com/account/pinned/4' }
+
+        before do
+          stub_request(:get, 'https://example.com/account/pinned/4').to_return(status: 200, body: Oj.dump(status_json_4))
+          subject.call(actor, note: true, hashtag: false)
+        end
+
+        it 'sets expected posts as pinned posts' do
+          expect(actor.pinned_statuses.pluck(:uri)).to contain_exactly(
+            'https://example.com/account/pinned/4'
+          )
+        end
+      end
     end
   end
 end

spec/services/activitypub/fetch_replies_service_spec.rb

@@ -32,6 +32,18 @@ RSpec.describe ActivityPub::FetchRepliesService, type: :service do
 
   describe '#call' do
     context 'when the payload is a Collection with inlined replies' do
+      context 'when there is a single reply, with the array compacted away' do
+        let(:items) { 'http://example.com/self-reply-1' }
+
+        it 'queues the expected worker' do
+          allow(FetchReplyWorker).to receive(:push_bulk)
+
+          subject.call(status, payload)
+
+          expect(FetchReplyWorker).to have_received(:push_bulk).with(['http://example.com/self-reply-1'])
+        end
+      end
+
       context 'when passing the collection itself' do
         it 'spawns workers for up to 5 replies on the same server' do
           expect(FetchReplyWorker).to receive(:push_bulk).with(['http://example.com/self-reply-1', 'http://example.com/self-reply-2', 'http://example.com/self-reply-3', 'http://example.com/self-reply-4', 'http://example.com/self-reply-5'])