Repository: rails/rails
File: activerecord/lib/active_record/signed_id.rb (Ruby)

Code before:
      #   signed_id = User.first.signed_id
      #   User.first.destroy
      #   User.find_signed! signed_id # => ActiveRecord::RecordNotFound
      def find_signed!(signed_id, purpose: nil, on_rotation: nil)
        options = { on_rotation: on_rotation }.compact
        if id = signed_id_verifier.verify(signed_id, purpose: combine_signed_id_purposes(purpose), **options)
          find(id)
        end
      end

      def signed_id_verifier
        return self._signed_id_verifier if self._signed_id_verifier

        if signed_id_verifier_secret != ActiveRecord::Base.signed_id_verifier_secret
          secret = signed_id_verifier_secret
          secret = secret.call if secret.respond_to?(:call)

          if secret.nil?
            raise ArgumentError, "You must set ActiveRecord::Base.signed_id_verifier_secret to use signed ids"
          else
            self._signed_id_verifier = ActiveSupport::MessageVerifier.new secret, digest: "SHA256", serializer: JSON, url_safe: true
          end
        elsif ActiveRecord::Base.message_verifiers
          ActiveRecord::Base.message_verifiers["active_record/signed_id"]
        else
          nil
        end
      end

      # Allows you to pass in a custom verifier used for the signed ids. This also allows you to use different
      # verifiers for different classes. This is also helpful if you need to rotate keys, as you can prepare
      # your custom verifier for that in advance. See ActiveSupport::MessageVerifier for details.
      def signed_id_verifier=(verifier)
        self._signed_id_verifier = verifier
      end

      # :nodoc:
      def combine_signed_id_purposes(purpose)
        [ base_class.name.underscore, purpose.to_s ].compact_blank.join("/")
      end
    end


    # Returns a signed id that's generated using a preconfigured +ActiveSupport::MessageVerifier+ instance.
    #
    # This signed id is tamper proof, so it's safe to send in an email or otherwise share with the outside world.
    # However, as with any message signed with a +ActiveSupport::MessageVerifier+,
    # {the signed id is not encrypted}[link:classes/ActiveSupport/MessageVerifier.html#class-ActiveSupport::MessageVerifier-label-Signing+is+not+encryption].
    # It's just encoded and protected against tampering.
    #
    # This means that the ID can be decoded by anyone; however, if tampered with (so to point to a different ID),

Review comment (suggestion):
If `message_verifiers` is nil, we should raise an error instead of returning nil for `signed_id_verifier`.

Code after:
      #
      #   signed_id = User.first.signed_id
      #   User.first.destroy
      #   User.find_signed! signed_id # => ActiveRecord::RecordNotFound
      def find_signed!(signed_id, purpose: nil, on_rotation: nil)
        options = { on_rotation: on_rotation }.compact
        if id = signed_id_verifier.verify(signed_id, purpose: combine_signed_id_purposes(purpose), **options)
          find(id)
        end
      end

      def signed_id_verifier
        if signed_id_verifier_secret
          @signed_id_verifier ||= begin
            secret = signed_id_verifier_secret
            secret = secret.call if secret.respond_to?(:call)

            if secret.nil?
              raise ArgumentError, "You must set ActiveRecord::Base.signed_id_verifier_secret to use signed IDs"
            end

            ActiveSupport::MessageVerifier.new secret, digest: "SHA256", serializer: JSON, url_safe: true
          end
        else
          return _signed_id_verifier if _signed_id_verifier

          if ActiveRecord.message_verifiers.nil?
            raise "You must set ActiveRecord.message_verifiers to use signed IDs"
          end

          ActiveRecord.message_verifiers["active_record/signed_id"]
        end
      end

      # Allows you to pass in a custom verifier used for the signed ids. This also allows you to use different
      # verifiers for different classes. This is also helpful if you need to rotate keys, as you can prepare
      # your custom verifier for that in advance. See ActiveSupport::MessageVerifier for details.
      def signed_id_verifier=(verifier)
        if signed_id_verifier_secret
          @signed_id_verifier = verifier
        else
          self._signed_id_verifier = verifier
        end
      end

      # :nodoc:
      def combine_signed_id_purposes(purpose)
        [ base_class.name.underscore, purpose.to_s ].compact_blank.join("/")
      end
    end