Select correct self link when parsing Webfinger response (#31110)

app/lib/webfinger.rb

@@ -6,6 +6,8 @@ class Webfinger
   class RedirectError < Error; end
 
   class Response
+    ACTIVITYPUB_READY_TYPE = ['application/activity+json', 'application/ld+json; profile="https://www.w3.org/ns/activitystreams"'].freeze
+
     attr_reader :uri
 
     def initialize(uri, body)
@@ -20,17 +22,28 @@ class Webfinger
     end
 
     def link(rel, attribute)
-      links.dig(rel, attribute)
+      links.dig(rel, 0, attribute)
+    end
+
+    def self_link_href
+      self_link.fetch('href')
     end
 
     private
 
     def links
-      @links ||= @json['links'].index_by { |link| link['rel'] }
+      @links ||= @json.fetch('links', []).group_by { |link| link['rel'] }
+    end
+
+    def self_link
+      links.fetch('self', []).find do |link|
+        ACTIVITYPUB_READY_TYPE.include?(link['type'])
+      end
     end
 
     def validate_response!
       raise Webfinger::Error, "Missing subject in response for #{@uri}" if subject.blank?
+      raise Webfinger::Error, "Missing self link in response for #{@uri}" if self_link.blank?
     end
   end
 

app/services/activitypub/fetch_remote_actor_service.rb

@@ -49,7 +49,7 @@ class ActivityPub::FetchRemoteActorService < BaseService
     confirmed_username, confirmed_domain = split_acct(webfinger.subject)
 
     if @username.casecmp(confirmed_username).zero? && @domain.casecmp(confirmed_domain).zero?
-      raise Error, "Webfinger response for #{@username}@#{@domain} does not loop back to #{@uri}" if webfinger.link('self', 'href') != @uri
+      raise Error, "Webfinger response for #{@username}@#{@domain} does not loop back to #{@uri}" if webfinger.self_link_href != @uri
 
       return
     end
@@ -58,8 +58,7 @@ class ActivityPub::FetchRemoteActorService < BaseService
     @username, @domain                   = split_acct(webfinger.subject)
 
     raise Webfinger::RedirectError, "Too many webfinger redirects for URI #{@uri} (stopped at #{@username}@#{@domain})" unless confirmed_username.casecmp(@username).zero? && confirmed_domain.casecmp(@domain).zero?
-
-    raise Error, "Webfinger response for #{@username}@#{@domain} does not loop back to #{@uri}" if webfinger.link('self', 'href') != @uri
+    raise Error, "Webfinger response for #{@username}@#{@domain} does not loop back to #{@uri}" if webfinger.self_link_href != @uri
   rescue Webfinger::RedirectError => e
     raise Error, e.message
   rescue Webfinger::Error => e

app/services/resolve_account_service.rb

@@ -104,8 +104,6 @@ class ResolveAccountService < BaseService
   end
 
   def fetch_account!
-    return unless activitypub_ready?
-
     with_redis_lock("resolve:#{@username}@#{@domain}") do
       @account = ActivityPub::FetchRemoteAccountService.new.call(actor_url, suppress_errors: @options[:suppress_errors])
     end
@@ -120,12 +118,8 @@ class ResolveAccountService < BaseService
     @options[:skip_cache] || @account.nil? || @account.possibly_stale?
   end
 
-  def activitypub_ready?
-    ['application/activity+json', 'application/ld+json; profile="https://www.w3.org/ns/activitystreams"'].include?(@webfinger.link('self', 'type'))
-  end
-
   def actor_url
-    @actor_url ||= @webfinger.link('self', 'href')
+    @actor_url ||= @webfinger.self_link_href
   end
 
   def gone_from_origin?