2011-04-16 04:28:47 -04:00
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require 'fiber'
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module ActionView
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2011-04-16 06:13:29 -04:00
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# Consider the following layout:
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#
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# <%= yield :header %>
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# 2
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# <%= yield %>
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# 5
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# <%= yield :footer %>
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#
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# And template:
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#
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# <%= provide :header, "1" %>
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# 3
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# 4
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# <%= provide :footer, "6" %>
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#
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# It will stream:
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#
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# "1\n", "2\n", "3\n4\n", "5\n", "6\n"
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#
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# Notice that once you <%= yield %>, it will render the whole template
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# before streaming again. In the future, we can also support streaming
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# from the template and not only the layout.
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#
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# Also, notice we use +provide+ instead of +content_for+, as +provide+
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# gives the control back to the layout as soon as it is called.
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# With +content_for+, it would render all the template to find all
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# +content_for+ calls. For instance, consider this layout:
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#
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# <%= yield :header %>
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#
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# With this template:
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#
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# <%= content_for :header, "1" %>
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# <%= provide :header, "2" %>
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# <%= provide :header, "3" %>
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#
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# It will return "12\n" because +content_for+ continues rendering the
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# template but it is returns back to the layout as soon as it sees the
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# first +provide+.
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#
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# == TODO
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#
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# * Add streaming support in the controllers with no-cache settings
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# * What should happen when an error happens?
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# * Support streaming from child templates, partials and so on.
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# * Support on sprockets async JS load?
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#
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2011-04-16 04:28:47 -04:00
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class StreamingTemplateRenderer < TemplateRenderer #:nodoc:
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# A valid Rack::Body (i.e. it responds to each).
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# It is initialized with a block that, when called, starts
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# rendering the template.
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class Body #:nodoc:
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def initialize(&start)
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@start = start
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end
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def each(&block)
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@start.call(block)
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self
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end
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end
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# For streaming, instead of rendering a given a template, we return a Body
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# object that responds to each. This object is initialized with a block
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# that knows how to render the template.
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def render_template(template, layout_name = nil, locals = {}) #:nodoc:
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2011-04-16 04:50:33 -04:00
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return [super] unless layout_name && template.supports_streaming?
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2011-04-16 04:28:47 -04:00
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locals ||= {}
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layout = layout_name && find_layout(layout_name, locals.keys)
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Body.new do |buffer|
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delayed_render(buffer, template, layout, @view, locals)
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end
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end
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private
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def delayed_render(buffer, template, layout, view, locals)
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# Wrap the given buffer in the StreamingBuffer and pass it to the
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# underlying template handler. Now, everytime something is concatenated
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# to the buffer, it is not appended to an array, but streamed straight
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# to the client.
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output = ActionView::StreamingBuffer.new(buffer)
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yielder = lambda { |*name| view._layout_for(*name) }
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instrument(:template, :identifier => template.identifier, :layout => layout.try(:virtual_path)) do
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fiber = Fiber.new do
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if layout
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layout.render(view, locals, output, &yielder)
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else
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# If you don't have a layout, just render the thing
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# and concatenate the final result. This is the same
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# as a layout with just <%= yield %>
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output.safe_concat view._layout_for
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end
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end
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# Set the view flow to support streaming. It will be aware
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# when to stop rendering the layout because it needs to search
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# something in the template and vice-versa.
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2011-04-16 05:22:36 -04:00
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view._view_flow = StreamingFlow.new(view, fiber)
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2011-04-16 04:28:47 -04:00
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# Yo! Start the fiber!
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fiber.resume
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# If the fiber is still alive, it means we need something
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# from the template, so start rendering it. If not, it means
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# the layout exited without requiring anything from the template.
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if fiber.alive?
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content = template.render(view, locals, &yielder)
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# Once rendering the template is done, sets its content in the :layout key.
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view._view_flow.set(:layout, content)
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# In case the layout continues yielding, we need to resume
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# the fiber until all yields are handled.
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fiber.resume while fiber.alive?
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end
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end
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end
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end
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end
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