require "fiber" module ActionView # == TODO # # * Support streaming from child templates, partials and so on. # * Integrate exceptions with exceptron # * Rack::Cache needs to support streaming bodies class StreamingTemplateRenderer < TemplateRenderer #:nodoc: # A valid Rack::Body (i.e. it responds to each). # It is initialized with a block that, when called, starts # rendering the template. class Body #:nodoc: def initialize(&start) @start = start end def each(&block) begin @start.call(block) rescue Exception => exception log_error(exception) block.call ActionView::Base.streaming_completion_on_exception end self end private # This is the same logging logic as in ShowExceptions middleware. # TODO Once "exceptron" is in, refactor this piece to simply re-use exceptron. def log_error(exception) logger = ActionView::Base.logger return unless logger message = "\n#{exception.class} (#{exception.message}):\n" message << exception.annoted_source_code.to_s if exception.respond_to?(:annoted_source_code) message << " " << exception.backtrace.join("\n ") logger.fatal("#{message}\n\n") end end # For streaming, instead of rendering a given a template, we return a Body # object that responds to each. This object is initialized with a block # that knows how to render the template. def render_template(template, layout_name = nil, locals = {}) #:nodoc: return [super] unless layout_name && template.supports_streaming? locals ||= {} layout = layout_name && find_layout(layout_name, locals.keys, [formats.first]) Body.new do |buffer| delayed_render(buffer, template, layout, @view, locals) end end private def delayed_render(buffer, template, layout, view, locals) # Wrap the given buffer in the StreamingBuffer and pass it to the # underlying template handler. Now, every time something is concatenated # to the buffer, it is not appended to an array, but streamed straight # to the client. output = ActionView::StreamingBuffer.new(buffer) yielder = lambda { |*name| view._layout_for(*name) } instrument(:template, identifier: template.identifier, layout: layout.try(:virtual_path)) do fiber = Fiber.new do if layout layout.render(view, locals, output, &yielder) else # If you don't have a layout, just render the thing # and concatenate the final result. This is the same # as a layout with just <%= yield %> output.safe_concat view._layout_for end end # Set the view flow to support streaming. It will be aware # when to stop rendering the layout because it needs to search # something in the template and vice-versa. view.view_flow = StreamingFlow.new(view, fiber) # Yo! Start the fiber! fiber.resume # If the fiber is still alive, it means we need something # from the template, so start rendering it. If not, it means # the layout exited without requiring anything from the template. if fiber.alive? content = template.render(view, locals, &yielder) # Once rendering the template is done, sets its content in the :layout key. view.view_flow.set(:layout, content) # In case the layout continues yielding, we need to resume # the fiber until all yields are handled. fiber.resume while fiber.alive? end end end end end