LAYING OUT THE FOUNDATIONS in C#

Generation Code-39 in C# LAYING OUT THE FOUNDATIONS

The method that intercepts web site errors and deals with them is ErrorHandler::Handler (located in error_handler.php). The code that registers the ErrorHandler::Handler function to be the one that handles errors in your site is in the ErrorHandler::SetHandler method that is invoked in app_top.php: /* Set user error handler method to ErrorHandler::Handler method */ public static function SetHandler($errTypes = ERROR_TYPES) { return set_error_handler(array ('ErrorHandler', 'Handler'), $errTypes); }

Note The second parameter of set_error_handler specifies the range of errors that should be intercepted. E_ALL specifies all types of errors, including E_NOTICE errors, which should be reported during web site development.

When called, ErrorHandler::Handler constructs the error message with the help of a method named ErrorHandler::GetBacktrace, and forwards the error message to the client s browser, a log file, the administrator (by email), or a combination of these, which can be configured by editing config.php. GetBacktrace gets the backtrace information from the debug_backtrace function (which was introduced in PHP 4.3.0) and changes its output format to generate an HTML error message similar to a Java error. It isn t important to understand every line in GetBacktrace unless you want to personalize the backtrace displayed in case of an error. The 2 parameter sent to GetBacktrace specifies that the backtrace results should omit the first two entries (the calls to ErrorHandler::Handler and ErrorHandler::GetBacktrace). You build the detailed error string in ErrorHandler::Handler, including the backtrace information: $backtrace = ErrorHandler::GetBacktrace(2); // Error message to be displayed, logged or mailed $error_message = "\nERRNO: $errNo\nTEXT: $errStr" . "\nLOCATION: $errFile, line " . "$errLine, at " . date('F j, Y, g:i a') . "\nShowing backtrace:\n$backtrace\n\n"; Depending on the configuration options from the config.php file, you decide whether to display, log, and/or email the error. Here we use PHP s error_log method, which knows how to email or write the error s details to a log file: // Email the error details, in case SEND_ERROR_MAIL is true if (SEND_ERROR_MAIL == true) error_log($error_message, 1, ADMIN_ERROR_MAIL, "From: " . SENDMAIL_FROM . "\r\nTo: " . ADMIN_ERROR_MAIL); // Log the error, in case LOG_ERRORS is true if (LOG_ERRORS == true) error_log($error_message, 3, LOG_ERRORS_FILE);

Note If you want to be able to send an error email to a localhost mail account (your_name@ locahost), then you should have an SMTP (Simple Mail Transfer Protocol) server started on your machine.

On a Red Hat (or Fedora) Linux distribution, you can start an SMTP server with the following command:

Note On Windows systems, you should check in IIS (Internet Information Services) Manager for Default

While you are developing the site, the DEBUGGING constant should be set to true, but after launching the site in the wild, you should make it false, causing a user-friendly error message to be displayed instead of the debugging information in case of serious errors, and no message shown at all in case of nonfatal errors. The errors of type E_WARNING are pretty tricky because you don't know which of them should stop the execution of the request. The IS_WARNING_FATAL constant set in config.php decides whether this type of error should be considered fatal for the project. Also, errors of type E_NOTICE and E_USER_NOTICE are not considered fatal: /* Warnings don't abort execution if IS_WARNING_FATAL is false E_NOTICE and E_USER_NOTICE errors don't abort execution */ if (($errNo == E_WARNING && IS_WARNING_FATAL == false) || ($errNo == E_NOTICE || $errNo == E_USER_NOTICE)) // If the error is nonfatal ... { // Show message only if DEBUGGING is true if (DEBUGGING == true) echo '<pre>' . $error_message . '</pre>'; } else // If error is fatal ... { // Show error message if (DEBUGGING == true) echo '<pre>' . $error_message . '</pre>'; else echo SITE_GENERIC_ERROR_MESSAGE; // Stop processing the request exit; } In the following chapters, you ll need to manually trigger errors using the trigger_error PHP function, which lets you specify the kind of error to generate. By default, it generates E_USER_NOTICE errors, which are not considered fatal but are logged and reported by ErrorHandler::Handler code.