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| author | José Valim <jose.valim@gmail.com> | 2011-05-01 14:50:42 +0200 |
|---|---|---|
| committer | José Valim <jose.valim@gmail.com> | 2011-05-01 14:50:42 +0200 |
| commit | 8dbee3aba6920edcae20abf3af7f803e528f9ee0 (patch) | |
| tree | be75f9a64d6183f26b3bf752c4ba17533fa00e26 /actionpack/lib/action_controller/metal/streaming.rb | |
| parent | 46611a995d91abf7bb2a64c62af13b6449c75b07 (diff) | |
| download | rails-8dbee3aba6920edcae20abf3af7f803e528f9ee0.tar.gz rails-8dbee3aba6920edcae20abf3af7f803e528f9ee0.tar.bz2 rails-8dbee3aba6920edcae20abf3af7f803e528f9ee0.zip | |
Streaming docs.
Diffstat (limited to 'actionpack/lib/action_controller/metal/streaming.rb')
| -rw-r--r-- | actionpack/lib/action_controller/metal/streaming.rb | 202 |
1 files changed, 201 insertions, 1 deletions
diff --git a/actionpack/lib/action_controller/metal/streaming.rb b/actionpack/lib/action_controller/metal/streaming.rb index 5b8111f30d..0dd847f967 100644 --- a/actionpack/lib/action_controller/metal/streaming.rb +++ b/actionpack/lib/action_controller/metal/streaming.rb @@ -2,7 +2,207 @@ require 'active_support/core_ext/file/path' require 'rack/chunked' module ActionController #:nodoc: - # Methods for sending streaming templates back to the client. + # Allow views to be streamed back to the client as they are rendered. + # + # The default way Rails renders views is by first rendering the template + # and then the layout. The first chunk of response is sent to the client + # just after the whole template is rendered, all queries are made and the + # layout is processed. + # + # Streaming inverts the rendering flow by rendering the layout first and + # streaming each part of the layout as they are processed. This allows the + # header of the html (which is usually in the layout) to be streamed back + # to client very quickly, allowing javascripts and stylesheets to be loaded + # earlier than usual. + # + # This approach was introduced in Rails 3.1 and is still improving. Several + # Rack middlewares may not work and you need to be careful when streaming. + # Those points are going to be addressed soon. + # + # In order to use streaming, you will need to use a Ruby version that + # supports Fibers (Fibers are supported since version 1.9.2 of the main + # Ruby implementation). + # + # == Examples + # + # Streaming can be added to a controller easily, all you need to do is + # call stream at the controller class: + # + # class PostsController + # stream + # end + # + # The +stream+ method accepts the same options as +before_filter+ and friends: + # + # class PostsController + # stream :only => :index + # end + # + # You can also selectively turn on streaming for specific actions: + # + # class PostsController + # def index + # @post = Post.scoped + # render :stream => true + # end + # end + # + # == When to use streaming + # + # Streaming may be considering an overkill for common actions like + # new or edit. The real benefit of streaming is on expensive actions + # that, for example, does a lot of queries on the database. + # + # In such actions, you want to delay queries execution as much as you can. + # For example, imagine the following dashboard action: + # + # def dashboard + # @posts = Post.all + # @pages = Page.all + # @articles = Article.all + # end + # + # Most of the queries here are happening in the controller. In order to benefit + # most of streaming, you would want to rewrite it as: + # + # def dashboard + # # Allow lazily execution of the query + # @posts = Post.scoped + # @pages = Page.scoped + # @articles = Article.scoped + # render :stream => true + # end + # + # == Communication between layout and template + # + # When streaming, the layout is rendered first than the template. + # This means that, if your application currently rely on variables set + # in the template to be used in the layout, they won't work once you + # move to streaming. The proper way to communicate between layout and + # template, regardless if you use streaming or not, is by using + # +content_for+, +provide+ and +yield+. + # + # Take a simple example where the layout expects the template to tell + # which title to use: + # + # <html> + # <head><title><%= yield :title %></title></head> + # <body><%= yield %></body> + # </html> + # + # You would use +content_for+ in your template to specify the title: + # + # <%= content_for :title, "Main" %> + # Hello + # + # And the final result would be: + # + # <html> + # <head><title>Main</title></head> + # <body>Hello</body> + # </html> + # + # However, if +content_for+ is called several times, the final result + # would have all calls concatenated. For instance, if we have the following + # template: + # + # <%= content_for :title, "Main" %> + # Hello + # <%= content_for :title, " page" %> + # + # The final result would be: + # + # <html> + # <head><title>Main page</title></head> + # <body>Hello</body> + # </html> + # + # This means that, if you have <code>yield :title</code> in your layout + # and you want to use streaming, you would have to render the whole template + # (and eventually trigger all queries) before streaming the title and all + # assets, which kills the purpose of streaming. For this reason Rails 3.1 + # introduces a helper called +provide+ that does the same as +content_for+ + # but tells the layout to stop searching for other entries and continue rendering. + # + # For instance, the template below, using +provide+: + # + # <%= provide :title, "Main" %> + # Hello + # <%= content_for :title, " page" %> + # + # Has as final result: + # + # <html> + # <head><title>Main</title></head> + # <body>Hello</body> + # </html> + # + # That said, when streaming, you need to properly check your templates + # and chose when to use +provide+ and +content_for+. + # + # == Headers, cookies, session and flash + # + # When streaming, the HTTP headers are sent to the client right before + # it renders the first line. This means that, modifying headers, cookies, + # session or flash after the template start rendering will not propagate + # to the client. + # + # If you try to modify cookies, session or flash, a ClosedError will be + # raised, showing those objects are closed for modification. + # + # == Middlewares + # + # Middlewares that need to manipulate the body won't work with streaming. + # You should disable those middlewares whenever streaming in development + # or production. For instance, Rack::Bug won't work when streaming as it + # needs to inject contents in the HTML body. + # + # Also Rack::Cache won't work with streaming as it does not support + # streaming bodies yet. So, whenever streaming, Cache-Control is automatically + # set to "no-cache". + # + # == Errors + # + # When it comes to streaming, exceptions get a bit more complicated. This + # happens because part of the template was already rendered and streamed to + # the client, making it impossible to render a whole exception page. + # + # Currently, when an exception happens in development or production, Rails + # will automatically stream to the client: + # + # "><script type="text/javascript">window.location = "/500.html"</script></html> + # + # The first two characters (">) are required in case the exception happens + # while rendering attributes for a given tag. You can check the real cause + # for the exception in your logger. + # + # == Web server support + # + # Not all web servers support streaming out-of-the-box. You need to check + # the instructions for each of them. + # + # ==== Unicorn + # + # Unicorn supports streaming but it needs to be configured. For this, you + # need to create a config file as follow: + # + # # unicorn.config.rb + # listen 3000, :tcp_nopush => false + # + # And use it on initialization: + # + # unicorn_rails --config-file unicorn.config.rb + # + # You may also want to configure other parameters like :tcp_nodelay. Please + # check its documentation for more information: http://unicorn.bogomips.org/Unicorn/Configurator.html#method-i-listen + # + # If you are using unicorn with nginx, you may need to tweak nginx. + # Streaming should work out of the box on Rainbows. + # + # ==== Passenger + # + # To be described. + # module Streaming extend ActiveSupport::Concern |