1 files changed, 80 insertions, 0 deletions
diff --git a/app/services/activitypub/fetch_remote_actor_service.rb b/app/services/activitypub/fetch_remote_actor_service.rb
new file mode 100644
index 000000000..db09c38d8
--- /dev/null
+++ b/app/services/activitypub/fetch_remote_actor_service.rb
@@ -0,0 +1,80 @@
+# frozen_string_literal: true
+
+class ActivityPub::FetchRemoteActorService < BaseService
+  include JsonLdHelper
+  include DomainControlHelper
+  include WebfingerHelper
+
+  class Error < StandardError; end
+
+  SUPPORTED_TYPES = %w(Application Group Organization Person Service).freeze
+
+  # Does a WebFinger roundtrip on each call, unless `only_key` is true
+  def call(uri, id: true, prefetched_body: nil, break_on_redirect: false, only_key: false, suppress_errors: true)
+    return if domain_not_allowed?(uri)
+    return ActivityPub::TagManager.instance.uri_to_actor(uri) if ActivityPub::TagManager.instance.local_uri?(uri)
+
+    @json = begin
+      if prefetched_body.nil?
+        fetch_resource(uri, id)
+      else
+        body_to_json(prefetched_body, compare_id: id ? uri : nil)
+      end
+    rescue Oj::ParseError
+      raise Error, "Error parsing JSON-LD document #{uri}"
+    end
+
+    raise Error, "Error fetching actor JSON at #{uri}" if @json.nil?
+    raise Error, "Unsupported JSON-LD context for document #{uri}" unless supported_context?
+    raise Error, "Unexpected object type for actor #{uri} (expected any of: #{SUPPORTED_TYPES})" unless expected_type?
+    raise Error, "Actor #{uri} has moved to #{@json['movedTo']}" if break_on_redirect && @json['movedTo'].present?
+
+    @uri      = @json['id']
+    @username = @json['preferredUsername']
+    @domain   = Addressable::URI.parse(@uri).normalized_host
+
+    check_webfinger! unless only_key
+
+    ActivityPub::ProcessAccountService.new.call(@username, @domain, @json, only_key: only_key, verified_webfinger: !only_key)
+  rescue Error => e
+    Rails.logger.debug "Fetching actor #{uri} failed: #{e.message}"
+    raise unless suppress_errors
+  end
+
+  private
+
+  def check_webfinger!
+    webfinger                            = webfinger!("acct:#{@username}@#{@domain}")
+    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
+      return
+    end
+
+    webfinger                            = webfinger!("acct:#{confirmed_username}@#{confirmed_domain}")
+    @username, @domain                   = split_acct(webfinger.subject)
+
+    unless confirmed_username.casecmp(@username).zero? && confirmed_domain.casecmp(@domain).zero?
+      raise Webfinger::RedirectError, "Too many webfinger redirects for URI #{@uri} (stopped at #{@username}@#{@domain})"
+    end
+
+    raise Error, "Webfinger response for #{@username}@#{@domain} does not loop back to #{@uri}" if webfinger.link('self', 'href') != @uri
+  rescue Webfinger::RedirectError => e
+    raise Error, e.message
+  rescue Webfinger::Error => e
+    raise Error, "Webfinger error when resolving #{@username}@#{@domain}: #{e.message}"
+  end
+
+  def split_acct(acct)
+    acct.gsub(/\Aacct:/, '').split('@')
+  end
+
+  def supported_context?
+    super(@json)
+  end
+
+  def expected_type?
+    equals_or_includes_any?(@json['type'], SUPPORTED_TYPES)
+  end
+end