Yo dawg, I heard you like streaming. So I put a fiber, inside a block, inside a body, so you can stream.

1 files changed, 79 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..a8c6ecbde1
--- /dev/null
+++ b/actionpack/lib/action_view/renderer/streaming_template_renderer.rb
@@ -0,0 +1,79 @@
+require 'fiber'
+
+module ActionView
+  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 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._view_flow, 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