Daily Archives: April 27, 2018

PHP

User Defined Errors

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• Userland code may trigger custom errors

trigger_error(
 "something went wrong",
 E_USER_WARNING);

• These errors may be handled with a custom error handler function

function myHandler($code, $text, $file, $line) {
 
 if ($code == E_USER_WARNING) {
 echo 'WARNING: ' .
 htmlspecialchars($text);
 return true;
 }
 
 return false;
}

• If the custom error handler function returns true, php´s error handling does not kick in

• Custom error handler function needs to be registered using set_error_handler(“myHandler”).

Example

<?php
 function myErrorHandler($errno, $errstr, $errfile, $errline) {
 echo "<b>Custom error:</b> [$errno] $errstr<br>";
 echo " Error on line $errline in $errfile<br>";
 }

set_error_handler("myErrorHandler");
 
 $test=2;

if ($test>1) {
 trigger_error("A custom error has been triggered");
 }
?>
PHP

Error Display

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• By default, all errors included in error_reporting are reported in php´s output

• This behavior can – and should – be deactivated on production systems using the display_errors = off php.ini setting

• Errors should still be logged, using the log_errors = on php.ini setting

• The error log is a file set in the error_log php configuration setting. if set to syslog, errors are logged in the system log independent on the operating system used.

PHP

Error Levels

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• PHP supports several types of errors

o notices at runtime
o errors during parsing (prevents code execution)
o warnings at runtime
o fatal errors at runtime (stop code execution)
o Core errors and warnings
o user-defined notices, warnings, and errors

• php configuration setting error_reporting, or php’s error_reporting() function may be used to define which kinds of errors shall be reported

• Value is an integer, or – much more convenient – a bitmask based on pre-defined constants

o E_NOTICE, E_PARSE, E_WARNING, E_ERROR

o E_CORE_WARNING, E_CORE_ERROR

o E_USER_NOTICE, E_USER_WARNING ,E_USER_ERROR

o E_STRICT(„best practices“ notices)

o E_DEPRECATED (features that might disappear in future php versions)

o E_ALL(everything) o and some more

• Typical production setting: E_ALL & ~E_DEPRECATED & ~E_STRICT

PHP

Exception Handling

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Exception handling is used to change the normal flow of the code execution if a specified error (exceptional) condition occurs. This condition is called an exception.

Exceptions or errors (more on that see below) end code execution, unless they are handled with try-catch.

try {
// code that throws an Exception
} catch (Exception $ex) {
// Exception is handled, code
continues
}

Several catch statements may be used to differentiate between several kinds of exceptions and errors.

try {
// code that throws an Exception
} catch (CustomExceptionClass $ex) {
// custom Exception is handled
} catch (Exception $ex) {
// Exception is handled
} catch (Error $err) {
// Error is handled
}

Several errors may be handled with the same code.

try {
// code that throws an Exception
} catch (Exception | CustomException $ex)
{
// custom Exception and Exception
}

Optional finally block contains code that runs after the trycatch block, no matter whether an error was caught or not

This is what normally happens when an exception is triggered:

  • The current code state is saved
  • The code execution will switch to a predefined (custom) exception handler function
  • Depending on the situation, the handler may then resume the execution from the saved code state, terminate the script execution or continue the script from a different location in the code
PHP

Error Class

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• Since php 7, many errors php reports now throw an error exception, not a fatal error as before.

• Subclasses of error exist for the specific type of error, such as parseerror or typeerror.

• To facilitate backwards compatibility, error is not derived from exception.

• Both error and exception implement the throwable interface