module ActionController # Handles implicit rendering for a controller action that does not # explicitly respond with +render+, +respond_to+, +redirect+, or +head+. # # For API controllers, the implicit response is always 204 No Content. # # For all other controllers, we use these heuristics to decide whether to # render a template, raise an error for a missing template, or respond with # 204 No Content: # # First, if we DO find a template, it's rendered. Template lookup accounts # for the action name, locales, format, variant, template handlers, and more # (see +render+ for details). # # Second, if we DON'T find a template but the controller action does have # templates for other formats, variants, etc., then we trust that you meant # to provide a template for this response, too, and we raise # ActionController::UnknownFormat with an explanation. # # Third, if we DON'T find a template AND the request is a page load in a web # browser (technically, a non-XHR GET request for an HTML response) where # you reasonably expect to have rendered a template, then we raise # ActionView::UnknownFormat with an explanation. # # Finally, if we DON'T find a template AND the request isn't a browser page # load, then we implicitly respond with 204 No Content. module ImplicitRender # :stopdoc: include BasicImplicitRender def default_render(*args) if template_exists?(action_name.to_s, _prefixes, variants: request.variant) render(*args) elsif any_templates?(action_name.to_s, _prefixes) message = "#{self.class.name}\##{action_name} is missing a template " \ "for this request format and variant.\n" \ "\nrequest.formats: #{request.formats.map(&:to_s).inspect}" \ "\nrequest.variant: #{request.variant.inspect}" raise ActionController::UnknownFormat, message elsif interactive_browser_request? message = "#{self.class.name}\##{action_name} is missing a template " \ "for this request format and variant.\n\n" \ "request.formats: #{request.formats.map(&:to_s).inspect}\n" \ "request.variant: #{request.variant.inspect}\n\n" \ "NOTE! For XHR/Ajax or API requests, this action would normally " \ "respond with 204 No Content: an empty white screen. Since you're " \ "loading it in a web browser, we assume that you expected to " \ "actually render a template, not nothing, so we're showing an " \ "error to be extra-clear. If you expect 204 No Content, carry on. " \ "That's what you'll get from an XHR or API request. Give it a shot." raise ActionController::UnknownFormat, message else logger.info "No template found for #{self.class.name}\##{action_name}, rendering head :no_content" if logger super end end def method_for_action(action_name) super || if template_exists?(action_name.to_s, _prefixes) "default_render" end end private def interactive_browser_request? request.get? && request.format == Mime[:html] && !request.xhr? end end end