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silverstripe-framework/docs/en/topics/error-handling.md

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Error Handling

SilverStripe has its own error trapping and handling support.

Error Levels

SilverStripe recognises two basic levels of error:

  • WARNING: Something strange has happened; the system has attempted to continue as best it can, but the developers need to look at this. This category also include areas where a newer version of SilverStripe requires changes to the site's customised code.

  • FATAL ERROR: There is no way that the system can attempt to continue with the particular operation; it would be dangerous to report success to the user.

You should use user_error to throw errors where appropriate. The more information we have about what's not right in the system, the better we can make the application.

  • E_USER_WARNING: Err on the side of over-reporting warnings. The more warnings we have, the less chance there is of a developer leaving a bug. Throwing warnings provides a means of ensuring that developers know whow

    • Deprecated functions / usage patterns
    • Strange data formats
    • Things that will prevent an internal function from continuing. Throw a warning and return null.

  • E_USER_ERROR: Throwing one of these errors is going to take down the production site. So you should only throw E_USER_ERROR if it's going to be dangerous or impossible to continue with the request.

Note that currently, the SilverStripe core doesn't follow these standards perfectly.

  • Right now, every failed SQL statement throws a fatal error. Many 'select' queries could probably be reduced to warnings.
  • A lot of assertion checking in the system that throws errors when it should throw warnings.

Friendly Website Errors

An HTTP 500 error will be sent when there has been a fatal error on either a test or production site. You can make this friendlier - much like the 404 page, the error content can be edited within the CMS.

  • Create a page of type [api:ErrorPage]
  • Set the error code to 500
  • Publish the page.

**HOW IT WORKS: **The publication script for ErrorPage will write the full HTML content, including the template styling, to assets/error-500.html. The fatal error handler looks for the presence of this file, and if it exists, dumps the content. This means that database access isn't required to provide a 500 error page.

Filesystem Logs

From SilverStripe

Requires SilverStripe 2.3 You can indicate a log file relative to the site root. The named file will have a terse log sent to it, and the full log (an encoded file containing backtraces and things) will go to a file of a similar name, but with the suffix ".full" added.

/_config.php:

:::php
// log errors and warnings
SS_Log::add_writer(new SS_LogFileWriter('/my/logfile/path'), SS_Log::WARN, '<=');
// or just errors
SS_Log::add_writer(new SS_LogFileWriter('/my/logfile/path'), SS_Log::ERR);

Deprecated method (SS 2.3 ?)

/_config.php:

:::php
Debug::log_errors_to("/my/logfile/path");

From PHP

In addition to SilverStripe-integrated logging, it is adviseable to fall back to PHPs native logging functionality. A script might terminate before it reaches the SilverStripe errorhandling, for example in the case of a fatal error.

/_config.php:

:::php
ini_set("log_errors", "On");
ini_set("error_log", "/my/logfile/path");

Email Logs

You can send both fatal errors and warnings in your code to a specified email-address. /_config.php:

:::php
// log errors and warnings
SS_Log::add_writer(new SS_LogEmailWriter('admin@domain.com'), SS_Log::WARN, '<=');
// or just errors
SS_Log::add_writer(new SS_LogEmailWriter('admin@domain.com'), SS_Log::ERR);

Deprecated method (SS 2.3 ?)

:::php
Debug::send_errors_to("developer@example.org");
Debug::send_warnings_to("developer@example.org"); // Optional, implied by send_errors_to()