Drupal - Error Handling

In this chapter, we will study about Drupal error handling for managing error messages on Drupal site.

Error Handling is a process of detection and finding the resolutions for the errors. It can be programming application errors or communicable errors.

The following steps describe how to manage error messages in Drupa −

Step 1 − Go to Configuration and click Logging and errors.

Step 2 − The Logging and errors page will get displayed as shown in the following screen.

Following are the details of the fields as seen in the preceding screen −

• Error messages to display − It specifies error messages to be displayed on the Drupal site.

• None − This option doesn't display any error message.

• Errors and warnings − This option displays only messages related to errors and warnings.

• All messages − This option specifies all types of error messages such as errors, warnings, etc. to be displayed on the site.

• Database log messages to keep − It indicates the maximum number of messages to be kept in the database log.

Drupal uses _drupal_exception_handler ($exception) function to handle the errors on the site. These errors will not be enclosed in a try/catch block. The script won't execute the function when an exception handler exits.

The code for _drupal_exception_handler is as follows −

function _drupal_exception_handler($exception) {
   require_once DRUPAL_ROOT . '/includes/errors.inc';
   try {
      // display the error message in the log and return the error messages to the user
      _drupal_log_error(_drupal_decode_exception($exception), TRUE);
   }
   catch (Exception $excp2) {
      // Another uncaught exception was thrown while handling the first one.
      // If we are displaying errors, then do so with no possibility of 
         a further uncaught exception being thrown.
         
      if (error_displayable()) {
         print '<h1>Additional uncaught exception thrown while handling exception.</h1>';
         print '<h2>Original</h2> <p>'. _drupal_render_exception_safe($exception).'</p>';
         print '<h2>Additional</h2> <p>'. _drupal_render_exception_safe($excp2).'</p><hr/>';
      }
   }
}

The function must be used on every Drupal request. This function is present at the line 2328 in the file includes/bootstrap.inc.

There are two string references to _drupal_exception_handler such as_drupal_bootstrap_configuration() present in the bootstrap.inc file and_drupal_get_last_caller present in the errors.inc file. Both these files are present in the ‘includes’ folder.