error handling in PHP

Hello


Motivation
The default error handling in PHP is very simple. An error message with filename, line number and a message describing the error is sent to the browser. 
What if you want to save this error also to a log file ? or catch warning\error\exception ?

Creating Custom Error Handler

Creating a custom error handler is quite simple. We simply create a special function that can be called when an error occurs in PHP.

This function must be able to handle a minimum of two parameters (error level and error message) but can accept up to five parameters (optionally: file, line-number, and the error context):

Syntax

error_function(error_level,error_message,
error_file,error_line,error_context)

Parameter	Description
error_level	Required. Specifies the error report level for the user-defined error. Must be a value number. See table below for possible error report levels
error_message	Required. Specifies the error message for the user-defined error
error_file	Optional. Specifies the filename in which the error occurred
error_line	Optional. Specifies the line number in which the error occurred
error_context	Optional. Specifies an array containing every variable, and their values, in use when the error occurred

Error Report levels

These error report levels are the different types of error the user-defined error handler can be used for:

Value	Constant	Description
2	E_WARNING	Non-fatal run-time errors. Execution of the script is not halted
8	E_NOTICE	Run-time notices. The script found something that might be an error, but could also happen when running a script normally
256	E_USER_ERROR	Fatal user-generated error. This is like an E_ERROR set by the programmer using the PHP function trigger_error()
512	E_USER_WARNING	Non-fatal user-generated warning. This is like an E_WARNING set by the programmer using the PHP function trigger_error()
1024	E_USER_NOTICE	User-generated notice. This is like an E_NOTICE set by the programmer using the PHP function trigger_error()
4096	E_RECOVERABLE_ERROR	Catchable fatal error. This is like an E_ERROR but can be caught by a user defined handle (see also set_error_handler())
8191	E_ALL	All errors and warnings (E_STRICT became a part of E_ALL in PHP 5.4)

Now lets create a function to handle errors: 

function customError($errno, $errstr) {
  echo "<b>Error:</b> [$errno] $errstr<br>";
  echo "Ending Script";
  die();
}

The code above is a simple error handling function. When it is triggered, it gets the error level and an error message. It then outputs the error level and message and terminates the script.

Now that we have created an error handling function we need to decide when it should be triggered.

Set Error Handler

function customError($errno, $errstr,$error_file,$error_line) 

{

    echo "<b>Error:</b> $error_file $error_line  [$errno] $errstr";

}

//set error handler

set_error_handler("customError");

//trigger error

echo($test);

this output :

Error: E:\nathan\PHP\VS\PHPWebProject2\PHPWebProject2\index.php 17 [8] Undefined variable: test

Using log file \ Email

you can send the error to a log_file using error_log

The error_log() function sends an error message to a log, to a file, or to a mail account.

---

error_log(message,type,destination,headers);

Parameter	Description
message	Required. Specifies the error message to log
type	Optional. Specifies where the error message should go. Possible values: 0 - Default. Message is sent to PHP's system logger, using the OS' system logging mechanism or a file, depending on what the error_log configuration is set to in php.ini 1 - Message is sent by email to the address in the destination parameter 2 - No longer in use (only available in PHP 3) 3 - Message is appended to the file specified in destination 4 - Message is sent directly to the SAPI logging handler
destination	Optional. Specifies the destination of the error message. This value depends on the value of thetype parameter
headers	Optional. Only used if the type parameter is set to 1. Specifies additional headers, like From, Cc, and Bcc. Multiple headers should be separated with a CRLF (\r\n)

function customError($errno, $errstr,$error_file,$error_line) 

{

    // --- error to display

    echo "<b>Error:</b>  [$errno] $errstr";

    // --- error to PHP system log

    $error = $error_file." ".$error_line." [".$errno."] ". $errstr;

    error_log($error,0); // send to php error file

   error_log($error,1,"natankrasney@gmail.com","From: webmaster@example.com");

}

//set error handler

set_error_handler("customError");

//trigger error

echo($test);

this will output to the browser :

and to the php error file (pending php.ini)

Exception Handling

the set_exception_handler() function sets a user-defined function to handle all uncaught exceptions.

<?php
function myException($exception) {
  echo "<b>Exception:</b> " . $exception->getMessage();
}

set_exception_handler('myException');

throw new Exception('Uncaught Exception occurred');
?>

The output of the code above should be something like this:

Exception: Uncaught Exception occurred

it is possible to log the exception as follows :

function customError($errno, $errstr,$error_file,$error_line)
{
    // --- error to display
    echo "<b>Error:</b>  [$errno] $errstr";
    // --- error to PHP system log
    $error = $error_file." ".$error_line." [".$errno."] ". $errstr;
    // send to php error file
    error_log($error,0); // send to php error file
    // send to php error to e-mail but need configuration
    //error_log($error,1,"natankrasney@gmail.com","From: webmaster@example.com");
}


function exception_handler($exception) {
    trigger_error( "Uncaught exception: ".$exception->getMessage()."\n");
}

set_exception_handler('exception_handler');


//set error handler
set_error_handler("customError");

$error = 'Always throw this error';
throw new Exception($error);

//trigger error
echo($test);



References

• http://www.w3schools.com/php/php_error.asp

Nathan