Add Dispatcher.to_prepare and config.to_prepare to provide a pre-request hook.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4686 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

4 files changed, 102 insertions, 3 deletions

diff --git a/railties/CHANGELOG b/railties/CHANGELOG
index 63f3197fcd..74ce8c0a3a 100644
--- a/railties/CHANGELOG
+++ b/railties/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Add Dispatcher.to_prepare and config.to_prepare to provide a pre-request hook. [Nicholas Seckar]
+
 * Tweak the Rails load order so observers are loaded after plugins, and reloaded in development mode. Closed #5279.  [Rick Olson]
 
 * Added that you can change the web server port in config/lighttpd.conf from script/server --port/-p #5465 [mats@imediatec.co.uk]
diff --git a/railties/lib/dispatcher.rb b/railties/lib/dispatcher.rb
index 32f286434f..a125018446 100644
--- a/railties/lib/dispatcher.rb
+++ b/railties/lib/dispatcher.rb
@@ -25,6 +25,7 @@
 # to the appropriate controller and action. It also takes care of resetting
 # the environment (when Dependencies.load? is true) after each request.
 class Dispatcher
+  
   class << self
 
     # Dispatch the given CGI request, using the given session options, and
@@ -54,11 +55,36 @@ class Dispatcher
     # to restart the server (WEBrick, FastCGI, etc.).
     def reset_application!
       Dependencies.clear
-      ActiveRecord::Base.reset
+      ActiveRecord::Base.reset if defined?(ActiveRecord)
       Class.remove_class(*Reloadable.reloadable_classes)
     end
+    
+    
+    # Add a preparation callback. Preparation callbacks are run before every
+    # request in development mode, and before the first request in production
+    # mode.
+    # 
+    # An optional identifier may be supplied for the callback. If provided,
+    # to_prepare may be called again with the same identifier to replace the
+    # existing callback. Passing an identifier is a suggested practice if the
+    # code adding a preparation block may be reloaded.
+    def to_prepare(identifier = nil, &block)
+      unless identifier.nil?
+        callback = preparation_callbacks.detect { |ident, _| ident == identifier }
+        if callback # Already registered: update the existing callback
+          callback[-1] = block
+          return
+        end
+      end
+      preparation_callbacks << [identifier, block]
+      nil
+    end
 
     private
+
+      attr_accessor :preparation_callbacks, :preparation_callbacks_run
+      alias_method :preparation_callbacks_run?, :preparation_callbacks_run
+      
       # CGI.new plus exception handling.  CGI#read_multipart raises EOFError
       # if body.empty? or body.size != Content-Length and raises ArgumentError
       # if Content-Length is non-integer.
@@ -67,10 +93,15 @@ class Dispatcher
       end
 
       def prepare_application
-        ActionController::Routing::Routes.reload if Dependencies.load?
+        if Dependencies.load?
+          ActionController::Routing::Routes.reload
+          self.preparation_callbacks_run = false
+        end
+
         prepare_breakpoint
         require_dependency('application.rb') unless Object.const_defined?(:ApplicationController)
-        ActiveRecord::Base.verify_active_connections!
+        ActiveRecord::Base.verify_active_connections! if defined?(ActiveRecord)
+        run_preparation_callbacks
       end
 
       def reset_after_dispatch
@@ -87,6 +118,12 @@ class Dispatcher
         nil
       end
 
+      def run_preparation_callbacks
+        return if preparation_callbacks_run?
+        preparation_callbacks.each { |_, callback| callback.call }
+        self.preparation_callbacks_run = true
+      end
+
       # If the block raises, send status code as a last-ditch response.
       def failsafe_response(output, status, exception = nil)
         yield
@@ -117,4 +154,8 @@ class Dispatcher
         end
       end
   end
+  
+  self.preparation_callbacks = []
+  self.preparation_callbacks_run = false
+  
 end
diff --git a/railties/lib/initializer.rb b/railties/lib/initializer.rb
index de58051f97..d18a5ecc4d 100644
--- a/railties/lib/initializer.rb
+++ b/railties/lib/initializer.rb
@@ -294,6 +294,13 @@ module Rails
       configuration.after_initialize_block.call if configuration.after_initialize_block
     end
     
+    # Add a preparation callback that will run before every request in development
+    # mode, or before the first request in production.
+    # 
+    # See Dispatcher#to_prepare.
+    def to_prepare(&callback)
+      Dispatcher.to_prepare(&callback)
+    end
 
     protected
       # Return a list of plugin paths within base_path.  A plugin path is
diff --git a/railties/test/dispatcher_test.rb b/railties/test/dispatcher_test.rb
index 41d08e224e..8fb19b173a 100644
--- a/railties/test/dispatcher_test.rb
+++ b/railties/test/dispatcher_test.rb
@@ -24,6 +24,8 @@ class DispatcherTest < Test::Unit::TestCase
   def setup
     @output = StringIO.new
     ENV['REQUEST_METHOD'] = "GET"
+    Dispatcher.send(:preparation_callbacks).clear
+    Dispatcher.send(:preparation_callbacks_run=, false)
   end
 
   def teardown
@@ -84,6 +86,53 @@ class DispatcherTest < Test::Unit::TestCase
   ensure
     $stdin = old_stdin
   end
+  
+  def test_preparation_callbacks
+    Object.const_set :ApplicationController, nil
+    old_mechanism = Dependencies.mechanism
+    
+    a = b = c = nil
+    Dispatcher.to_prepare { a = b = c = 1 }
+    Dispatcher.to_prepare { b = c = 2 }
+    Dispatcher.to_prepare { c = 3 }
+    
+    Dispatcher.send :prepare_application
+    
+    assert_equal 1, a
+    assert_equal 2, b
+    assert_equal 3, c
+    
+    # When mechanism is :load, perform the callbacks each request:
+    Dependencies.mechanism = :load
+    a = b = c = nil
+    Dispatcher.send :prepare_application
+    assert_equal 1, a
+    assert_equal 2, b
+    assert_equal 3, c
+    
+    # But when not :load, make sure they are only run once
+    a = b = c = nil
+    Dependencies.mechanism = :not_load
+    Dispatcher.send :prepare_application
+    assert_equal nil, a || b || c
+  ensure
+    Dependencies.mechanism = old_mechanism
+    Object.send :remove_const, :ApplicationController
+  end
+  
+  def test_to_prepare_with_identifier_replaces
+    Object.const_set :ApplicationController, nil
+    
+    a = b = nil
+    Dispatcher.to_prepare(:unique_id) { a = b = 1 }
+    Dispatcher.to_prepare(:unique_id) { a = 2 }
+    
+    Dispatcher.send :prepare_application
+    assert_equal 2, a
+    assert_equal nil, b
+  ensure
+    Object.send :remove_const, :ApplicationController
+  end
 
   private
     def dispatch