Resolve links to unknown remote objects when posting (#38711)

app/services/process_links_service.rb

@@ -23,12 +23,15 @@ class ProcessLinksService < BaseService
   def scan_text!
     urls = @status.text.scan(FetchLinkCardService::URL_PATTERN).map { |array| Addressable::URI.parse(array[1]).normalize }
 
+    domains = urls.map(&:domain).uniq
+    valid_domains = Instance.searchable.where(domain: domains).pluck(:domain)
+
     urls.each do |url|
       # We only support `FeaturedCollection` at this time
 
-      # TODO: We probably want to resolve unknown objects at authoring time
       object = ActivityPub::TagManager.instance.uri_to_resource(url.to_s, Collection)
-      next if object.nil?
+      object ||= ResolveURLService.new.call(url.to_s) if valid_domains.include?(url.domain)
+      next unless object.is_a?(Collection)
 
       tagged_object = @previous_objects.find { |x| x.object == object || x.uri == url }
       tagged_object ||= @current_objects.find { |x| x.object == object || x.uri == url }

spec/services/process_links_service_spec.rb

@@ -9,17 +9,34 @@ RSpec.describe ProcessLinksService do
 
   context 'when status mentions known collections' do
     let!(:collection) { Fabricate(:collection) }
-    let(:status) { Fabricate(:status, account: account, text: "Hello check out this collection! #{ActivityPub::TagManager.instance.uri_for(collection)}", visibility: :public) }
+    let(:status) { Fabricate(:status, account: account, text:, visibility: :public) }
 
-    it 'creates a tagged object' do
-      expect { subject.call(status) }
-        .to change { status.tagged_objects.count }.by(1)
+    context 'when the collection is mentioned by URI' do
+      let(:text) { "Hello check out this collection! #{ActivityPub::TagManager.instance.uri_for(collection)}" }
+
+      it 'creates a tagged object' do
+        expect { subject.call(status) }
+          .to change { status.tagged_objects.count }.by(1)
+      end
+    end
+
+    context 'when the collection is mentioned by URL' do
+      let(:text) { "Hello check out this collection! #{ActivityPub::TagManager.instance.url_for(collection)}" }
+
+      it 'creates a tagged object' do
+        expect { subject.call(status) }
+          .to change { status.tagged_objects.count }.by(1)
+      end
     end
   end
 
-  context 'when status has a generic link' do
+  context 'when status has a generic link to something that is not a collection' do
     let(:status) { Fabricate(:status, account: account, text: 'Hello check out my personal web page: https://example.com/test', visibility: :public) }
 
+    before do
+      stub_request(:get, 'https://example.com/test').to_return(status: 404)
+    end
+
     it 'skips the link and does not create a tagged object' do
       expect { expect { subject.call(status) }.to_not raise_error }
         .to not_change { status.tagged_objects.count }.from(0)