Fix handling of malformed ActivityPub payloads when URIs are nil (#7370)

* Fix handling of malformed ActivityPub payloads when URIs are nil

* Gracefully handle JSON-LD canonicalization failures

app/lib/activitypub/tag_manager.rb

@@ -86,6 +86,8 @@ class ActivityPub::TagManager
   end
 
   def local_uri?(uri)
+    return false if uri.nil?
+
     uri  = Addressable::URI.parse(uri)
     host = uri.normalized_host
     host = "#{host}:#{uri.port}" if uri.port
@@ -99,6 +101,8 @@ class ActivityPub::TagManager
   end
 
   def uri_to_resource(uri, klass)
+    return if uri.nil?
+
     if local_uri?(uri)
       case klass.name
       when 'Account'

app/services/activitypub/fetch_remote_status_service.rb

@@ -34,6 +34,7 @@ class ActivityPub::FetchRemoteStatusService < BaseService
   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?
   end
 

app/services/activitypub/process_collection_service.rb

@@ -45,5 +45,8 @@ class ActivityPub::ProcessCollectionService < BaseService
 
   def verify_account!
     @account = ActivityPub::LinkedDataSignature.new(@json).verify_account!
+  rescue JSON::LD::JsonLdError => e
+    Rails.logger.debug "Could not verify LD-Signature for #{value_or_id(@json['actor'])}: #{e.message}"
+    nil
   end
 end