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  <sect1 id="zend.controller.exceptions">
      <title>MVC Exceptions</title>
  
      <sect2 id="zend.controller.exceptions.introduction">
          <title>Introduction</title>
  
          <para>
              The <acronym>MVC</acronym> components in Zend Framework utilize a Front Controller,
              which means that all requests to a given site will go through a
              single entry point. As a result, all exceptions bubble up to the
              Front Controller eventually, allowing the developer to handle them
              in a single location.
          </para>
  
          <para>
              However, exception messages and backtrace information often contain
              sensitive system information, such as <acronym>SQL</acronym> statements, file
              locations, and more. To help protect your site, by default
              <classname>Zend_Controller_Front</classname> catches all exceptions and
              registers them with the response object; in turn, by default, the
              response object does not display exception messages.
          </para>
      </sect2>
  
      <sect2 id="zend.controller.exceptions.handling">
          <title>Handling Exceptions</title>
  
          <para>
              Several mechanisms are built in to the <acronym>MVC</acronym> components already to
              allow you to handle exceptions.
          </para>
  
          <itemizedlist>
              <listitem>
                  <para>
                      By default, the <link
                          linkend="zend.controller.plugins.standard.errorhandler">error
                      handler plugin</link> is registered and active. This plugin
                      was designed to handle:
                  </para>
  
                  <itemizedlist>
                      <listitem><para>Errors due to missing controllers or actions</para></listitem>
                      <listitem><para>Errors occurring within action controllers</para></listitem>
                  </itemizedlist>
  
                  <para>
                      It operates as a <methodname>postDispatch()</methodname> plugin, and
                      checks to see if a dispatcher, action controller, or
                      other exception has occurred. If so, it forwards to an error
                      handler controller.
                  </para>
  
                  <para>
                      This handler will cover most exceptional situations, and
                      handle missing controllers and actions gracefully.
                  </para>
              </listitem>
  
              <listitem>
                  <para><methodname>Zend_Controller_Front::throwExceptions()</methodname></para>
  
                  <para>
                      By passing a boolean <constant>TRUE</constant> value to this method, you can
                      tell the front controller that instead of aggregating exceptions
                      in the response object or using the error handler plugin,
                      you'd rather handle them yourself. As an example:
                  </para>
  
                  <programlisting language="php"><![CDATA[
  $front->throwExceptions(true);
  try {
      $front->dispatch();
  } catch (Exception $e) {
      // handle exceptions yourself
  }
  ]]></programlisting>
  
                  <para>
                      This method is probably the easiest way to add custom
                      exception handling covering the full range of possible
                      exceptions to your front controller application.
                  </para>
              </listitem>
  
              <listitem>
                  <para>
                      <methodname>Zend_Controller_Response_Abstract::renderExceptions()</methodname>
                  </para>
  
                  <para>
                      By passing a boolean <constant>TRUE</constant> value to this method, you tell
                      the response object that it should render an exception message
                      and backtrace when rendering itself. In this scenario, any
                      exception raised by your application will be displayed. This
                      is only recommended for non-production environments.
                  </para>
              </listitem>
  
              <listitem>
                  <para>
                      <methodname>Zend_Controller_Front::returnResponse()</methodname> and
                      <methodname>Zend_Controller_Response_Abstract::isException()</methodname>.
                  </para>
  
                  <para>
                      By passing a boolean <constant>TRUE</constant> to
                      <methodname>Zend_Controller_Front::returnResponse()</methodname>,
                      <methodname>Zend_Controller_Front::dispatch()</methodname> will not render the
                      response, but instead return it. Once you have the response,
                      you may then test to see if any exceptions were trapped using
                      its <methodname>isException()</methodname> method, and retrieving the
                      exceptions via the <methodname>getException()</methodname> method. As an
                      example:
                  </para>
  
                  <programlisting language="php"><![CDATA[
  $front->returnResponse(true);
  $response = $front->dispatch();
  if ($response->isException()) {
      $exceptions = $response->getException();
      // handle exceptions ...
  } else {
      $response->sendHeaders();
      $response->outputBody();
  }
  ]]></programlisting>
  
                  <para>
                      The primary advantage this method offers over
                      <methodname>Zend_Controller_Front::throwExceptions()</methodname> is to
                      allow you to conditionally render the response after
                      handling the exception. This will catch any exception in the
                      controller chain, unlike the error handler plugin.
                  </para>
              </listitem>
          </itemizedlist>
      </sect2>
  
      <sect2 id="zend.controller.exceptions.internal">
          <title>MVC Exceptions You May Encounter</title>
  
          <para>
              The various <acronym>MVC</acronym> components -- request, router, dispatcher, action
              controller, and response objects -- may each throw exceptions on
              occasion. Some exceptions may be conditionally overridden, and
              others are used to indicate the developer may need to consider
              their application structure.
          </para>
  
          <para>As some examples:</para>
  
          <itemizedlist>
              <listitem>
                  <para>
                      <methodname>Zend_Controller_Dispatcher::dispatch()</methodname> will,
                      by default, throw an exception if an invalid controller is
                      requested. There are two recommended ways to deal with
                      this.
                  </para>
  
                  <itemizedlist>
                      <listitem>
                          <para>
                              Set the <property>useDefaultControllerAlways</property> parameter.
                          </para>
  
                          <para>
                              In your front controller, or your dispatcher, add
                              the following directive:
                          </para>
  
                          <programlisting language="php"><![CDATA[
  $front->setParam('useDefaultControllerAlways', true);
  
  // or
  
  $dispatcher->setParam('useDefaultControllerAlways', true);
  ]]></programlisting>
  
                          <para>
                              When this flag is set, the dispatcher will use the
                              default controller and action instead of throwing an
                              exception. The disadvantage to this method is that
                              any typos a user makes when accessing your site will
                              still resolve and display your home page, which can
                              wreak havoc with search engine optimization.
                          </para>
                      </listitem>
  
                      <listitem>
                          <para>
                              The exception thrown by <methodname>dispatch()</methodname> is
                              a <classname>Zend_Controller_Dispatcher_Exception</classname>
                              containing the text 'Invalid controller specified'.
                              Use one of the methods outlined in <link
                                  linkend="zend.controller.exceptions.handling">the
                                  previous section</link> to catch the exception,
                              and then redirect to a generic error page or the
                              home page.
                          </para>
                      </listitem>
                  </itemizedlist>
              </listitem>
  
              <listitem>
                  <para>
                      <methodname>Zend_Controller_Action::__call()</methodname> will throw a
                      <classname>Zend_Controller_Action_Exception</classname> if it cannot
                      dispatch a non-existent action to a method. Most likely,
                      you will want to use some default action in the controller
                      in cases like this. Ways to achieve this include:
                  </para>
  
                  <itemizedlist>
                      <listitem>
                          <para>
                              Subclass <classname>Zend_Controller_Action</classname> and
                              override the <methodname>__call()</methodname> method. As an
                              example:
                          </para>
  
                          <programlisting language="php"><![CDATA[
  class My_Controller_Action extends Zend_Controller_Action
  {
      public function __call($method, $args)
      {
          if ('Action' == substr($method, -6)) {
              $controller = $this->getRequest()->getControllerName();
              $url = '/' . $controller . '/index';
              return $this->_redirect($url);
          }
  
          throw new Exception('Invalid method');
      }
  }
  ]]></programlisting>
  
                          <para>
                              The example above intercepts any undefined action
                              method called and redirects it to the default action
                              in the controller.
                          </para>
                      </listitem>
  
                      <listitem>
                          <para>
                              Subclass <classname>Zend_Controller_Dispatcher</classname>
                              and override the <methodname>getAction()</methodname> method to
                              verify the action exists. As an example:
                          </para>
  
                          <programlisting language="php"><![CDATA[
  class My_Controller_Dispatcher extends Zend_Controller_Dispatcher
  {
      public function getAction($request)
      {
          $action = $request->getActionName();
          if (empty($action)) {
              $action = $this->getDefaultAction();
              $request->setActionName($action);
              $action = $this->formatActionName($action);
          } else {
              $controller = $this->getController();
              $action     = $this->formatActionName($action);
              if (!method_exists($controller, $action)) {
                  $action = $this->getDefaultAction();
                  $request->setActionName($action);
                  $action = $this->formatActionName($action);
              }
          }
  
          return $action;
      }
  }
  ]]></programlisting>
  
                          <para>
                              The above code checks to see that the requested
                              action exists in the controller class; if not, it
                              resets the action to the default action.
                          </para>
  
                          <para>
                              This method is nice because you can transparently
                              alter the action prior to final dispatch. However,
                              it also means that typos in the <acronym>URL</acronym> may still
                              dispatch correctly, which is not great for search
                              engine optimization.
                          </para>
                      </listitem>
  
                      <listitem>
                          <para>
                              Use
                              <methodname>Zend_Controller_Action::preDispatch()</methodname>
                              or
                              <methodname>Zend_Controller_Plugin_Abstract::preDispatch()</methodname>
                              to identify invalid actions.
                          </para>
  
                          <para>
                              By subclassing <classname>Zend_Controller_Action</classname>
                              and modifying <methodname>preDispatch()</methodname>, you can
                              modify all of your controllers to forward to
                              another action or redirect prior to actually
                              dispatching the action. The code for this will look
                              similar to the code for overriding
                              <methodname>__call()</methodname>, above.
                          </para>
  
                          <para>
                              Alternatively, you can check this information in a
                              global plugin. This has the advantage of being
                              action controller independent; if your application
                              consists of a variety of action controllers, and not
                              all of them inherit from the same class, this method
                              can add consistency in handling your various
                              classes.
                          </para>
  
                          <para>
                              As an example:
                          </para>
  
                          <programlisting language="php"><![CDATA[
  class My_Controller_PreDispatchPlugin extends Zend_Controller_Plugin_Abstract
  {
      public function preDispatch(Zend_Controller_Request_Abstract $request)
      {
          $front      = Zend_Controller_Front::getInstance();
          $dispatcher = $front->getDispatcher();
          $class      = $dispatcher->getControllerClass($request);
          if (!$class) {
              $class = $dispatcher->getDefaultControllerClass($request);
          }
  
          $r      = new ReflectionClass($class);
          $action = $dispatcher->getActionMethod($request);
  
          if (!$r->hasMethod($action)) {
              $defaultAction  = $dispatcher->getDefaultAction();
              $controllerName = $request->getControllerName();
              $response       = $front->getResponse();
              $response->setRedirect('/' . $controllerName
                                    . '/' . $defaultAction);
              $response->sendHeaders();
              exit;
          }
      }
  }
  ]]></programlisting>
  
                          <para>
                              In this example, we check to see if the action
                              requested is available in the controller. If not, we
                              redirect to the default action in the controller,
                              and exit script execution immediately.
                          </para>
                      </listitem>
                  </itemizedlist>
              </listitem>
          </itemizedlist>
      </sect2>
  </sect1>
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