Bring abstract_controller up to date with rails/master

Resolved all the conflicts since 2.3.0 -> HEAD. Following is a list
of commits that could not be applied cleanly or are obviated with the
abstract_controller refactor. They all need to be revisited to ensure
that fixes made in 2.3 do not reappear in 3.0:

2259ecf368e6a6715966f69216e3ee86bf1a82a7
AR not available
  * This will be reimplemented with ActionORM or equivalent

06182ea02e92afad579998aa80144588e8865ac3
implicitly rendering a js response should not use the default layout
[#1844 state:resolved]
  * This will be handled generically

893e9eb99504705419ad6edac14d00e71cef5f12
Improve view rendering performance in development mode and reinstate
template recompiling in production [#1909 state:resolved]
  * We will need to reimplement rails-dev-boost on top of the refactor;
    the changes here are very implementation specific and cannot be
    cleanly applied. The following commits are implicated:

      199e750d46c04970b5e7684998d09405648ecbd4
      3942cb406e1d5db0ac00e03153809cc8dc4cc4db
      f8ea9f85d4f1e3e6f3b5d895bef6b013aa4b0690
      e3b166aab37ddc2fbab030b146eb61713b91bf55
      ae9f258e03c9fd5088da12c1c6cd216cc89a01f7
      44423126c6f6133a1d9cf1d0832b527e8711d40f

0cb020b4d6d838025859bd60fb8151c8e21b8e84
workaround for picking layouts based on wrong view_paths
[#1974 state:resolved]
  * The specifics of this commit no longer apply. Since it is a two-line
    commit, we will reimplement this change.

8c5cc66a831aadb159f3daaffa4208064c30af0e
make action_controller/layouts pick templates from the current instance's
view_paths instead of the class view_paths [#1974 state:resolved]
  * This does not apply at all. It should be trivial to apply the feature
    to the reimplemented ActionController::Base.

87e8b162463f13bd50d27398f020769460a770e3
fix HTML fallback for explicit templates [#2052 state:resolved]
  * There were a number of patches related to this that simply compounded
    each other. Basically none of them apply cleanly, and the underlying
    issue needs to be revisited. After discussing the underlying problem
    with Koz, we will defer these fixes for further discussion.

1 files changed, 516 insertions, 0 deletions

diff --git a/railties/guides/source/caching_with_rails.textile b/railties/guides/source/caching_with_rails.textile
new file mode 100644
index 0000000000..f1ad7b820d
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+++ b/railties/guides/source/caching_with_rails.textile
@@ -0,0 +1,516 @@
+h2. Caching with Rails: An overview
+
+Everyone caches. This guide will teach you what you need to know about
+avoiding that expensive round-trip to your database and returning what you
+need to return to those hungry web clients in the shortest time possible.
+
+After reading this guide, you should be able to use and configure:
+
+* Page, action, and fragment caching
+* Sweepers
+* Alternative cache stores
+* Conditional GET support
+
+endprologue.
+
+h3. Basic Caching
+
+This is an introduction to the three types of caching techniques that Rails
+provides by default without the use of any third party plugins.
+
+To start playing with testing you'll want to ensure that
++config.action_controller.perform_caching+ is set
+to +true+ if you're running in development mode. This flag is normally set in the
+corresponding config/environments/*.rb and caching is disabled by default
+ for development and test, and enabled for production.
+
+<ruby>
+config.action_controller.perform_caching = true
+</ruby>
+
+h4. Page Caching
+
+Page caching is a Rails mechanism which allows the request for a generated
+page to be fulfilled by the webserver (i.e. apache or nginx), without ever having to go through the
+Rails stack at all. Obviously, this is super-fast. Unfortunately, it can't be
+applied to every situation (such as pages that need authentication) and since
+the webserver is literally just serving a file from the filesystem, cache
+expiration is an issue that needs to be dealt with.
+
+So, how do you enable this super-fast cache behavior?  Simple, let's say you
+have a controller called +ProductsController+ and an +index+ action that lists all
+the products
+
+<ruby>
+class ProductsController < ActionController
+
+  caches_page :index
+
+  def index
+    @products = Products.all
+  end
+
+end
+</ruby>
+
+The first time anyone requests +/products+, Rails will generate a file
+called +products.html+ and the webserver will then look for that file before it
+passes the next request for +/products+ to your Rails application.
+
+By default, the page cache directory is set to +Rails.public_path+ (which is
+usually set to the +public+ folder) and this can be configured by
+changing the configuration setting +config.action_controller.page_cache_directory+.
+Changing the default from +public+ helps avoid naming conflicts, since you may
+want to put other static html in +public+, but changing this will require web
+server reconfiguration to let the web server know where to serve the cached
+files from.
+
+The Page Caching mechanism will automatically add a +.html+ extension to
+requests for pages that do not have an extension to make it easy for the
+webserver to find those pages and this can be configured by changing the
+configuration setting +config.action_controller.page_cache_extension+.
+
+In order to expire this page when a new product is added we could extend our
+example controller like this:
+
+<ruby>
+class ProductsController < ActionController
+
+  caches_page :index
+
+  def index
+    @products = Products.all
+  end
+
+  def create
+    expire_page :action => :index
+  end
+
+end
+</ruby>
+
+If you want a more complicated expiration scheme, you can use cache sweepers
+to expire cached objects when things change. This is covered in the section on Sweepers.
+
+Note: Page caching ignores all parameters. For example +/products?page=1+ will be written out to the filesystem as +products.html+ with no reference to the +page+ parameter. Thus, if someone requests +/products?page=2+ later, they will get the cached first page. Be careful when page caching GET parameters in the URL!
+
+h4. Action Caching
+
+One of the issues with Page Caching is that you cannot use it for pages that
+require to restrict access somehow. This is where Action Caching comes in.
+Action Caching works like Page Caching except for the fact that the incoming
+web request does go from the webserver to the Rails stack and Action Pack so
+that before filters can be run on it before the cache is served. This allows
+authentication and other restriction to be run while still serving the
+result of the output from a cached copy.
+
+Clearing the cache works in the exact same way as with Page Caching.
+
+Let's say you only wanted authenticated users to call actions on +ProductsController+.
+
+<ruby>
+class ProductsController < ActionController
+
+  before_filter :authenticate
+  caches_action :index
+
+  def index
+    @products = Product.all
+  end
+
+  def create
+    expire_action :action => :index
+  end
+
+end
+</ruby>
+
+You can also use +:if+ (or +:unless+) to pass a Proc that specifies when the
+action should be cached. Also, you can use +:layout => false+ to cache without
+layout so that dynamic information in the layout such as logged in user info
+or the number of items in the cart can be left uncached. This feature is
+available as of Rails 2.2.
+
+You can modify the default action cache path by passing a +:cache_path+ option.
+This will be passed directly to +ActionCachePath.path_for+.  This is handy for
+actions with multiple possible routes that should be cached differently.  If
+a block is given, it is called with the current controller instance.  
+
+Finally, if you are using memcached, you can also pass +:expires_in+. In fact,
+all parameters not used by +caches_action+ are sent to the underlying cache
+store. 
+
+h4. Fragment Caching
+
+Life would be perfect if we could get away with caching the entire contents of
+a page or action and serving it out to the world. Unfortunately, dynamic web
+applications usually build pages with a variety of components not all of which
+have the same caching characteristics. In order to address such a dynamically
+created page where different parts of the page need to be cached and expired
+differently Rails provides a mechanism called Fragment Caching.
+
+Fragment Caching allows a fragment of view logic to be wrapped in a cache
+block and served out of the cache store when the next request comes in.
+
+As an example, if you wanted to show all the orders placed on your website
+in real time and didn't want to cache that part of the page, but did want
+to cache the part of the page which lists all products available, you
+could use this piece of code:
+
+<ruby>
+<% Order.find_recent.each do |o| %>
+  <%= o.buyer.name %> bought <% o.product.name %>
+<% end %>
+
+<% cache do %>
+  All available products:
+  <% Product.all.each do |p| %>
+    <%= link_to p.name, product_url(p) %>
+  <% end %>
+<% end %>
+</ruby>
+
+The cache block in our example will bind to the action that called it and is
+written out to the same place as the Action Cache, which means that if you
+want to cache multiple fragments per action, you should provide an +action_suffix+ to the cache call:
+
+<ruby>
+<% cache(:action => 'recent', :action_suffix => 'all_products') do %>
+  All available products:
+</ruby>
+
+and you can expire it using the +expire_fragment+ method, like so:
+
+<ruby>
+expire_fragment(:controller => 'products', :action => 'recent', :action_suffix => 'all_products')
+</ruby>
+
+If you don't want the cache block to bind to the action that called it, You can
+also use globally keyed fragments by calling the +cache+ method with a key, like
+so:
+
+<ruby>
+<% cache('all_available_products') do %>
+  All available products:
+<% end %>
+</ruby>
+
+This fragment is then available to all actions in the +ProductsController+ using
+the key and can be expired the same way:
+
+<ruby>
+expire_fragment('all_available_products')
+</ruby>
+
+h4. Sweepers
+
+Cache sweeping is a mechanism which allows you to get around having a ton of
++expire_{page,action,fragment}+ calls in your code.  It does this by moving all the work
+required to expire cached content into a +ActionController::Caching::Sweeper+
+class.  This class is an Observer and looks for changes to an object via callbacks,
+and when a change occurs it expires the caches associated with that object in
+an around or after filter.
+
+Continuing with our Product controller example, we could rewrite it with a
+sweeper like this:
+
+<ruby>
+class ProductSweeper < ActionController::Caching::Sweeper
+  observe Product # This sweeper is going to keep an eye on the Product model
+
+  # If our sweeper detects that a Product was created call this
+  def after_create(product)
+          expire_cache_for(product)
+  end
+
+  # If our sweeper detects that a Product was updated call this
+  def after_update(product)
+          expire_cache_for(product)
+  end
+
+  # If our sweeper detects that a Product was deleted call this
+  def after_destroy(product)
+          expire_cache_for(product)
+  end
+
+  private
+  def expire_cache_for(product)
+    # Expire the index page now that we added a new product
+    expire_page(:controller => 'products', :action => 'index')
+
+    # Expire a fragment
+    expire_fragment('all_available_products')
+  end
+end
+</ruby>
+
+You may notice that the actual product gets passed to the sweeper, so if we
+were caching the edit action for each product, we could add a expire method
+which specifies the page we want to expire:
+
+<ruby>
+  expire_action(:controller => 'products', :action => 'edit', :id => product)
+</ruby>
+
+Then we add it to our controller to tell it to call the sweeper when certain
+actions are called. So, if we wanted to expire the cached content for the
+list and edit actions when the create action was called, we could do the
+following:
+
+<ruby>
+class ProductsController < ActionController
+
+  before_filter :authenticate
+  caches_action :index
+  cache_sweeper :product_sweeper
+
+  def index
+    @products = Product.all
+  end
+
+end
+</ruby>
+
+h4. SQL Caching
+
+Query caching is a Rails feature that caches the result set returned by each
+query so that if Rails encounters the same query again for that request, it
+will used the cached result set as opposed to running the query against the
+database again.
+
+For example:
+
+<ruby>
+class ProductsController < ActionController
+
+  def index
+    # Run a find query
+    @products = Product.all
+
+    ...
+
+    # Run the same query again
+    @products = Product.all
+  end
+
+end
+</ruby>
+
+The second time the same query is run against the database, it's not actually
+going to hit the database.  The first time the result is returned from the query
+it is stored in the query cache (in memory) and the second time it's pulled from memory.
+
+However, it's important to note that query caches are created at the start of an action and destroyed at the end of
+that action and thus persist only for the duration of the action.  If you'd like to store query results in a more
+persistent fashion, you can in Rails by using low level caching.
+
+h4. Cache stores
+
+Rails (as of 2.1) provides different stores for the cached data created by action and
+fragment caches. Page caches are always stored on disk.
+
+Rails 2.1 and above provide +ActiveSupport::Cache::Store+ which can be used to
+cache strings. Some cache store implementations, like MemoryStore, are able to
+cache arbitrary Ruby objects, but don't count on every cache store to be able
+to do that.
+
+The default cache stores provided with Rails include:
+
+1) ActiveSupport::Cache::MemoryStore: A cache store implementation which stores
+everything into memory in the same process. If you're running multiple Ruby on
+Rails server processes (which is the case if you're using mongrel_cluster or
+Phusion Passenger), then this means that your Rails server process instances
+won't be able to share cache data with each other. If your application never
+performs manual cache item expiry (e.g. when you‘re using generational cache
+keys), then using +MemoryStore+ is ok. Otherwise, consider carefully whether you
+should be using this cache store.  
+
++MemoryStore+ is not only able to store strings, but also arbitrary Ruby objects.
+
++MemoryStore+ is not thread-safe. Use +SynchronizedMemoryStore+ instead if you
+need thread-safety.
+                                      
+
+<ruby>
+ActionController::Base.cache_store = :memory_store
+</ruby>
+
+2) ActiveSupport::Cache::FileStore: Cached data is stored on the disk, this is
+the default store and the default path for this store is: /tmp/cache. Works
+well for all types of environments and allows all processes running from the
+same application directory to access the cached content. If /tmp/cache does not
+exist, the default store becomes MemoryStore.
+
+
+<ruby>
+ActionController::Base.cache_store = :file_store, "/path/to/cache/directory"
+</ruby>
+
+3) ActiveSupport::Cache::DRbStore: Cached data is stored in a separate shared
+DRb process that all servers communicate with. This works for all environments
+and only keeps one cache around for all processes, but requires that you run
+and manage a separate DRb process.
+
+
+<ruby>
+ActionController::Base.cache_store = :drb_store, "druby://localhost:9192"
+</ruby>
+
+4) MemCached store: Works like DRbStore, but uses Danga's MemCache instead.
+Rails uses the bundled memcached-client gem by default. This is currently the
+most popular cache store for production websites.
+
+Special features:
+ * Clustering and load balancing. One can specify multiple memcached servers,
+   and MemCacheStore will load balance between all available servers. If a
+   server goes down, then MemCacheStore will ignore it until it goes back
+   online.
+ * Time-based expiry support. See +write+ and the +:expires_in+ option.
+ * Per-request in memory cache for all communication with the MemCache server(s).
+
+It also accepts a hash of additional options:
+
+ * +:namespace+- specifies a string that will automatically be prepended to keys when accessing the memcached store.
+ * +:readonly+- a boolean value that when set to true will make the store read-only, with an error raised on any attempt to write.
+ * +:multithread+ - a boolean value that adds thread safety to read/write operations - it is unlikely you'll need to use this option as the Rails threadsafe! method offers the same functionality.
+
+The read and write methods of the MemCacheStore accept an options hash too.
+When reading you can specify +:raw => true+ to prevent the object being marshaled
+(by default this is false which means the raw value in the cache is passed to
++Marshal.load+ before being returned to you.)
+
+When writing to the cache it is also possible to specify +:raw => true+ means
+the value is not passed to +Marshal.dump+ before being stored in the cache (by
+default this is false). 
+
+The write method also accepts an +:unless_exist+ flag which determines whether
+the memcached add (when true) or set (when false) method is used to store the
+item in the cache and an +:expires_in+ option that specifies the time-to-live
+for the cached item in seconds.
+
+
+<ruby>
+ActionController::Base.cache_store = :mem_cache_store, "localhost"
+</ruby>
+
+5) ActiveSupport::Cache::SynchronizedMemoryStore: Like ActiveSupport::Cache::MemoryStore but thread-safe.
+
+
+<ruby>
+ActionController::Base.cache_store = :synchronized_memory_store
+</ruby>
+
+6) ActiveSupport::Cache::CompressedMemCacheStore: Works just like the regular
+MemCacheStore but uses GZip to decompress/compress on read/write.
+
+
+<ruby>
+ActionController::Base.cache_store = :compressed_mem_cache_store, "localhost"
+</ruby>
+
+7) Custom store: You can define your own cache store (new in Rails 2.1)
+
+
+<ruby>
+ActionController::Base.cache_store = MyOwnStore.new("parameter")
+</ruby>
+
++Note: +config.cache_store+ can be used in place of
++ActionController::Base.cache_store+ in your +Rails::Initializer.run+ block in
++environment.rb+
+
+In addition to all of this, Rails also adds the +ActiveRecord::Base#cache_key+
+method that generates a key using the class name, +id+ and +updated_at+ timestamp (if available).
+
+You can access these cache stores at a low level for storing queries and other objects. Here's an example:
+
+<ruby>
+Rails.cache.read("city")   # => nil
+Rails.cache.write("city", "Duckburgh")
+Rails.cache.read("city")   # => "Duckburgh"
+</ruby>
+
+h3. Conditional GET support
+
+Conditional GETs are a feature of the HTTP specification that provide a way for web
+servers to tell browsers that the response to a GET request hasn't changed
+since the last request and can be safely pulled from the browser cache.
+
+They work by using the +HTTP_IF_NONE_MATCH+ and +HTTP_IF_MODIFIED_SINCE+ headers
+to pass back and forth both a unique content identifier and the timestamp of
+when the content was last changed. If the browser makes a request where the
+content identifier (etag) or last modified since timestamp matches the server’s
+version then the server only needs to send back an empty response with a not
+modified status.
+
+It is the server's (i.e. our) responsibility to look for a last modified
+timestamp and the if-none-match header and determine whether or not to send
+back the full response. With conditional-get support in rails this is a pretty
+easy task:
+
+<ruby>
+class ProductsController < ApplicationController
+
+  def show
+    @product = Product.find(params[:id])
+
+    # If the request is stale according to the given timestamp and etag value
+    # (i.e. it needs to be processed again) then execute this block
+    if stale?(:last_modified => @product.updated_at.utc, :etag => @product)
+      respond_to do |wants|
+        # ... normal response processing
+      end
+    end
+
+    # If the request is fresh (i.e. it's not modified) then you don't need to do
+    # anything. The default render checks for this using the parameters
+    # used in the previous call to stale? and will automatically send a
+    # :not_modified.  So that's it, you're done.
+end
+</ruby>
+
+If you don't have any special response processing and are using the default
+rendering mechanism (i.e. you're not using respond_to or calling render
+yourself) then you’ve got an easy helper in fresh_when:
+
+<ruby>
+class ProductsController < ApplicationController
+
+  # This will automatically send back a :not_modified if the request is fresh,
+  # and will render the default template (product.*) if it's stale.
+
+  def show
+    @product = Product.find(params[:id])
+    fresh_when :last_modified => @product.published_at.utc, :etag => @article
+  end
+end
+</ruby>
+
+h3. Advanced Caching
+
+Along with the built-in mechanisms outlined above, a number of excellent
+plugins exist to help with finer grained control over caching. These include
+Chris Wanstrath's excellent cache_fu plugin (more info "here": http://errtheblog.com/posts/57-kickin-ass-w-cachefu) and Evan Weaver's
+interlock plugin (more info "here": http://blog.evanweaver.com/articles/2007/12/13/better-rails-caching/). Both
+of these plugins play nice with memcached and are a must-see for anyone
+seriously considering optimizing their caching needs.
+
+Also the new "Cache money":http://github.com/nkallen/cache-money/tree/master plugin is supposed to be mad cool. 
+
+h3. References
+
+* "Scaling Rails Screencasts":http://railslab.newrelic.com/scaling-rails
+* "RailsEnvy, Rails Caching Tutorial, Part 1":http://www.railsenvy.com/2007/2/28/rails-caching-tutorial
+* "RailsEnvy, Rails Caching Tutorial, Part 1":http://www.railsenvy.com/2007/3/20/ruby-on-rails-caching-tutorial-part-2
+* "ActiveSupport::Cache documentation":http://api.rubyonrails.org/classes/ActiveSupport/Cache.html
+* "Rails 2.1 integrated caching tutorial":http://thewebfellas.com/blog/2008/6/9/rails-2-1-now-with-better-integrated-caching
+
+
+h3. Changelog
+"Lighthouse ticket":http://rails.lighthouseapp.com/projects/16213-rails-guides/tickets/10-guide-to-caching
+
+April      1, 2009: Made a bunch of small fixes
+February  22, 2009: Beefed up the section on cache_stores
+December  27, 2008: Typo fixes
+November  23, 2008: Incremental updates with various suggested changes and formatting cleanup
+September 15, 2008: Initial version by Aditya Chadha