diff options
Diffstat (limited to 'actionpack/lib/action_view/renderer/streaming_template_renderer.rb')
| -rw-r--r-- | actionpack/lib/action_view/renderer/streaming_template_renderer.rb | 129 |
1 files changed, 129 insertions, 0 deletions
diff --git a/actionpack/lib/action_view/renderer/streaming_template_renderer.rb b/actionpack/lib/action_view/renderer/streaming_template_renderer.rb new file mode 100644 index 0000000000..52f0e9f5bd --- /dev/null +++ b/actionpack/lib/action_view/renderer/streaming_template_renderer.rb @@ -0,0 +1,129 @@ +# 1.9 ships with Fibers but we need to require the extra +# methods explicitly. We only load those extra methods if +# Fiber is available in the first place. +require 'fiber' if defined?(Fiber) + +module ActionView + # Consider the following layout: + # + # <%= yield :header %> + # 2 + # <%= yield %> + # 5 + # <%= yield :footer %> + # + # And template: + # + # <%= provide :header, "1" %> + # 3 + # 4 + # <%= provide :footer, "6" %> + # + # It will stream: + # + # "1\n", "2\n", "3\n4\n", "5\n", "6\n" + # + # Notice that once you <%= yield %>, it will render the whole template + # before streaming again. In the future, we can also support streaming + # from the template and not only the layout. + # + # Also, notice we use +provide+ instead of +content_for+, as +provide+ + # gives the control back to the layout as soon as it is called. + # With +content_for+, it would render all the template to find all + # +content_for+ calls. For instance, consider this layout: + # + # <%= yield :header %> + # + # With this template: + # + # <%= content_for :header, "1" %> + # <%= provide :header, "2" %> + # <%= provide :header, "3" %> + # + # It will return "12\n" because +content_for+ continues rendering the + # template but it is returns back to the layout as soon as it sees the + # first +provide+. + # + # == TODO + # + # * Add streaming support in the controllers with no-cache settings + # * What should happen when an error happens? + # * Support streaming from child templates, partials and so on. + # * Support on sprockets async JS load? + # + 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) + @start.call(block) + self + 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) + + 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, everytime 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 |