I need to catch some warnings being thrown from some php native functions and then handle them.
Specifically:
array dns_get_record ( string $hostname [, int $type= DNS_ANY [, array &$authns [, array &$addtl ]]] )
It throws a warning when the DNS query fails.
try/catch doesn't work because a warning is not an exception.
I now have 2 options:
set_error_handler seems like overkill because I have to use it to filter every warning in the page (is this true?);
Adjust error reporting/display so these warnings don't get echoed to screen, then check the return value; if it's false, no records is found for hostname.
What's the best practice here?
Set and restore error handler
One possibility is to set your own error handler before the call and restore the previous error handler later with restore_error_handler().
set_error_handler(function() { /* ignore errors */ });
dns_get_record();
restore_error_handler();
You could build on this idea and write a re-usable error handler that logs the errors for you.
set_error_handler([$logger, 'onSilencedError']);
dns_get_record();
restore_error_handler();
Turning errors into exceptions
You can use set_error_handler() and the ErrorException class to turn all php errors into exceptions.
set_error_handler(function($errno, $errstr, $errfile, $errline) {
// error was suppressed with the #-operator
if (0 === error_reporting()) {
return false;
}
throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
});
try {
dns_get_record();
} catch (ErrorException $e) {
// ...
}
The important thing to note when using your own error handler is that it will bypass the error_reporting setting and pass all errors (notices, warnings, etc.) to your error handler. You can set a second argument on set_error_handler() to define which error types you want to receive, or access the current setting using ... = error_reporting() inside the error handler.
Suppressing the warning
Another possibility is to suppress the call with the # operator and check the return value of dns_get_record() afterwards. But I'd advise against this as errors/warnings are triggered to be handled, not to be suppressed.
The solution that really works turned out to be setting simple error handler with E_WARNING parameter, like so:
set_error_handler("warning_handler", E_WARNING);
dns_get_record(...)
restore_error_handler();
function warning_handler($errno, $errstr) {
// do something
}
Be careful with the # operator - while it suppresses warnings it also suppresses fatal errors. I spent a lot of time debugging a problem in a system where someone had written #mysql_query( '...' ) and the problem was that mysql support was not loaded into PHP and it threw a silent fatal error. It will be safe for those things that are part of the PHP core but please use it with care.
bob#mypc:~$ php -a
Interactive shell
php > echo #something(); // this will just silently die...
No further output - good luck debugging this!
bob#mypc:~$ php -a
Interactive shell
php > echo something(); // lets try it again but don't suppress the error
PHP Fatal error: Call to undefined function something() in php shell code on line 1
PHP Stack trace:
PHP 1. {main}() php shell code:0
bob#mypc:~$
This time we can see why it failed.
I wanted to try/catch a warning, but at the same time keep the usual warning/error logging (e.g. in /var/log/apache2/error.log); for which the handler has to return false. However, since the "throw new..." statement basically interrupts the execution, one then has to do the "wrap in function" trick, also discussed in:
Is there a static way to throw exception in php
Or, in brief:
function throwErrorException($errstr = null,$code = null, $errno = null, $errfile = null, $errline = null) {
throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
}
function warning_handler($errno, $errstr, $errfile, $errline, array $errcontext) {
return false && throwErrorException($errstr, 0, $errno, $errfile, $errline);
# error_log("AAA"); # will never run after throw
/* Do execute PHP internal error handler */
# return false; # will never run after throw
}
...
set_error_handler('warning_handler', E_WARNING);
...
try {
mkdir($path, 0777, true);
} catch (Exception $e) {
echo $e->getMessage();
// ...
}
EDIT: after closer inspection, it turns out it doesn't work: the "return false && throwErrorException ..." will, basically, not throw the exception, and just log in the error log; removing the "false &&" part, as in "return throwErrorException ...", will make the exception throwing work, but will then not log in the error_log... I'd still keep this posted, though, as I haven't seen this behavior documented elsewhere.
Combining these lines of code around a file_get_contents() call to an external url helped me handle warnings like "failed to open stream: Connection timed out" much better:
set_error_handler(function ($err_severity, $err_msg, $err_file, $err_line, array $err_context)
{
throw new ErrorException( $err_msg, 0, $err_severity, $err_file, $err_line );
}, E_WARNING);
try {
$iResult = file_get_contents($sUrl);
} catch (Exception $e) {
$this->sErrorMsg = $e->getMessage();
}
restore_error_handler();
This solution works within object context, too. You could use it in a function:
public function myContentGetter($sUrl)
{
... code above ...
return $iResult;
}
Normaly you should never use # unless this is the only solution. In that specific case the function dns_check_record should be use first to know if the record exists.
If dns_get_record() fails, it should return FALSE, so you can suppress the warning with # and then check the return value.
You should probably try to get rid of the warning completely, but if that's not possible, you can prepend the call with # (i.e. #dns_get_record(...)) and then use any information you can get to figure out if the warning happened or not.
try checking whether it returns some boolean value then you can simply put it as a condition. I encountered this with the oci_execute(...) which was returning some violation with my unique keys.
ex.
oci_parse($res, "[oracle pl/sql]");
if(oci_execute){
...do something
}
As of PHP8, you can do the following instead of setting error handlers to catch Errors and Warnings. I Believe in PHP 7.something you could catch some Errors.
try {
call_user_func('sprintf', array_merge([$string], $args));
} catch (Throwable $e) {
$logger->info('mesage...');
}
You should generally be somewhere that you can pass or access a logger if you bulkhead in this way, as it can obfuscate coder errors, such as passing incorrectly typed parameters to a method, and mask a variety of other problems.
https://php.watch/versions/8.0/internal-function-exceptions
Not sure if notices are caught (likely not), but you can likely solve around examples like this one, by thinking a little more about what you are looking to do.
Both builder pattern, and options patterns provide solutions for this where prior to the site of call, which can be a private function or just after validity checks, you can throw a real custom exception that is attributable only to your code. That will make even built-in functions very safe to use.
One other nice practice is to use either debug_backtrace, with DEBUG_BACKTRACE_IGNORE_ARGS or use the getTrace or getTraceAsString methods on the Throwable so that some of the context is preseved.
FolderStructure
index.php //Script File
logs //Folder for log Every warning and Errors
CustomException.php //Custom exception File
CustomException.php
/**
* Custom error handler
*/
function handleError($code, $description, $file = null, $line = null, $context = null) {
$displayErrors = ini_get("display_errors");;
$displayErrors = strtolower($displayErrors);
if (error_reporting() === 0 || $displayErrors === "on") {
return false;
}
list($error, $log) = mapErrorCode($code);
$data = array(
'timestamp' => date("Y-m-d H:i:s:u", time()),
'level' => $log,
'code' => $code,
'type' => $error,
'description' => $description,
'file' => $file,
'line' => $line,
'context' => $context,
'path' => $file,
'message' => $error . ' (' . $code . '): ' . $description . ' in [' . $file . ', line ' . $line . ']'
);
$data = array_map('htmlentities',$data);
return fileLog(json_encode($data));
}
/**
* This method is used to write data in file
* #param mixed $logData
* #param string $fileName
* #return boolean
*/
function fileLog($logData, $fileName = ERROR_LOG_FILE) {
$fh = fopen($fileName, 'a+');
if (is_array($logData)) {
$logData = print_r($logData, 1);
}
$status = fwrite($fh, $logData . "\n");
fclose($fh);
// $file = file_get_contents($filename);
// $content = '[' . $file .']';
// file_put_contents($content);
return ($status) ? true : false;
}
/**
* Map an error code into an Error word, and log location.
*
* #param int $code Error code to map
* #return array Array of error word, and log location.
*/
function mapErrorCode($code) {
$error = $log = null;
switch ($code) {
case E_PARSE:
case E_ERROR:
case E_CORE_ERROR:
case E_COMPILE_ERROR:
case E_USER_ERROR:
$error = 'Fatal Error';
$log = LOG_ERR;
break;
case E_WARNING:
case E_USER_WARNING:
case E_COMPILE_WARNING:
case E_RECOVERABLE_ERROR:
$error = 'Warning';
$log = LOG_WARNING;
break;
case E_NOTICE:
case E_USER_NOTICE:
$error = 'Notice';
$log = LOG_NOTICE;
break;
case E_STRICT:
$error = 'Strict';
$log = LOG_NOTICE;
break;
case E_DEPRECATED:
case E_USER_DEPRECATED:
$error = 'Deprecated';
$log = LOG_NOTICE;
break;
default :
break;
}
return array($error, $log);
}
//calling custom error handler
set_error_handler("handleError");
just include above file into your script file like this
index.php
error_reporting(E_ALL);
ini_set('display_errors', 'off');
define('ERROR_LOG_FILE', 'logs/app_errors.log');
include_once 'CustomException.php';
echo $a; // here undefined variable warning will be logged into logs/app_errors.log
Since PHP7 you can catch most errors and warnings like so:
try {
whatever();
} catch (Throwable $e) {
}
More: https://www.php.net/manual/en/language.errors.php7.php
I would only recommend using # to suppress warnings when it's a straight forward operation (e.g. $prop = #($high/($width - $depth)); to skip division by zero warnings). However in most cases it's better to handle.
Since a short period of time I'm working with Try Catch in PHP. Now, every time a new error is thrown you get a fatal error on the screen, this isn't really user friendly so I was wondering if there's a way to give the user a nice message like an echo instead of a fatal error.
This is the code I have now:
public static function forceNumber($int){
if(is_numeric($int)){
return $int;
} else {
throw new TypeEnforcerException($int.' must be a number');
}
}
public function setStatus($status) {
try {
$this->status = TypeEnforcer::forceInt($status);
} catch (TypeEnforcerException $e) {
throw new Exception($e->getMessage());
} catch (Exception $e) {
throw new Exception($e->getMessage());
}
}
This is best solved with a frontend controller that is able to catch all uncatched exceptions:
<?php
require('bootstrap.php');
try {
$controllerService->execute($request);
} catch (Exception $e) {
$controllerService->handleControllerException($e);
}
You can then write code to return the internal server error because an exception signals an exceptional case so it normally is an 500 internal server error. The user must not be interested what went wrong other than it just didn't work out and your program crashed.
If you throw exceptions to give validation notices you need to catch those in a different layer (and you're probably doing it wrong if you use exceptions for that).
Edit: For low-level functions, because PHP is loosely typed, if a function expects and int, cast to intDocs:
public static function forceNumber($int){
$int = (int) $int;
return $int;
}
this will actually force the integer. In case the cast is not possible to do (e.g. $int it totally incompatible) PHP will throw the exception for you.
The example is a bit akward because by the method's name you use it to validate some number and provide an error if not (here wrongly with an exception). Instead you should do some validation. If you expect wrong input, it's not an exceptional case when wrong input is provided, so I would not use exceptions for that.
PHPs token_get_all function (which allows converting a PHP source code into tokens) can throw two errors: One if an unterminated multiline comment is encountered, the other if an unexpected char is found.
I would like to catch those errors and throw them as Exceptions.
Problem is: As those errors are parse errors they cannot be handled with an error handling function you would normally specify using set_error_handler.
What I have currently implemented is the following:
// Reset the error message in error_get_last()
#$errorGetLastResetUndefinedVariable;
$this->tokens = #token_get_all($code);
$error = error_get_last();
if (preg_match(
'~^(Unterminated comment) starting line ([0-9]+)$~',
$error['message'],
$matches
)
) {
throw new ParseErrorException($matches[1], $matches[2]);
}
if (preg_match(
'~^(Unexpected character in input:\s+\'(.)\' \(ASCII=[0-9]+\))~s',
$error['message'],
$matches
)
) {
throw new ParseErrorException($matches[1]);
}
It should be obvious that I'm not really excited to use that solution. Especially the fact that I reset the error message in error_get_last by accessing an undefined variable seems pretty unsatisfactory.
So: Is there a better solution to this problem?
Set a custom errorhandler using set_error_handler.
Call token_get_all.
Then unset the error handler by calling restore_error_handler.
This will allow you to catch warnings. Make sure you remove the # suppressor.
You can for instance register an error handler that is in a class that will just record any warnings for inspection later on.
Untested example code:
class CatchWarnings {
private $warnings = array();
public function handler($errno, $errstr, $errfile, $errline) {
switch ($errno) {
case E_USER_WARNING:
$this->warnings[] = $errstr;
return true; // cancel error handling bubble
}
return false; // error handling as usual
}
public function has_warnings() {
return count($this->warnings) > 0;
}
}
$cw = new CatchWarnings();
set_error_handler(array($cw, "handler"));
token_get_all();
restore_error_handler();
Usually validation and execution are two separate things, but it seems like there is no way to validate/lint a piece of PHP code (not since 5.x anyway).
basically i have a custom exception handler. When i handle an exception, i just want it to echo the message and continue the script. But after my method handles the exception, the script doesnt continue.
Is this a behaviour of php or is my exception handler doing something wrong?
This is a behavior of php. This differs from set_error_handler() in that, according to the manual on set_exception_handler(), Execution will stop after the exception_handler is called. Therefore, ensure you catch all exceptions, letting only those you want to kill your script through.
This is actually why set_error_handler() doesn't pair well with exceptions and set_exception_handler() when converting all errors to exceptions... unless you actually mean your application to be so strictly coded that any notice or warning halts the script. But at least it gives you a trace on that call involving an unset array key.
With a custom exception handler, you'll want to catch the exception in a try/catch block and do whatever handling you want in there.
The following is the example from The CodeUnit of Craig
try {
$error = 'Throw this error';
throw new Exception($error);
echo 'Never get here';
}
catch (Exception $e)
{
echo 'Exception caught: ', $e->getMessage(), "\n";
}
If you want to catch and print any unhandled exception, you can set a top level exception handler like this example from w3schools(near the bottom of the page)
<?php
function myException($exception){
echo "<b>Exception:</b> " , $exception->getMessage();
}
set_exception_handler('myException');
throw new Exception('Uncaught Exception occurred');
?>
should print: "Exception: Uncaught Exception occurred"
Look at the following code. it worked for me:
define(BR, "<br/>");
try {
echo "throwing exception" . BR;
throw new Exception("This is exception");
}
catch(Exception $ex) {
echo "caught exception: " . BR . $ex->getMessage() . BR;
}
echo "Keep on going!. ..." . BR;
it prints the following:
throwing exception
caught exception:
This is exception
Keep on going!. ...
What do you say ?
Can you show the code of your code handler ?
You could do this :
function handleError($errno, $errstring, $errfile, $errline, $errcontext) {
if (error_reporting() & $errno) {
// only process when included in error_reporting
return processError($errno, $errstring);
}
return true;
}
function handleException($exception){
// Here, you do whatever you want with the generated
// exceptions. You can store them in a file or database,
// output them in a debug section of your page or do
// pretty much anything else with it, as if it's a
// normal variable
}
function processError($code, $message){
switch ($code) {
case E_ERROR:
case E_CORE_ERROR:
case E_USER_ERROR:
// Throw exception and stop execution of script
throw new Exception($message, $code);
default:
// Execute exception handler and continue execution afterwards
return handleException(new Exception($message, $code));
}
}
// Set error handler to your custom handler
set_error_handler('handleError');
// Set exception handler to your custom handler
set_exception_handler('handleException');
// ---------------------------------- //
// Generate warning
processError(E_USER_WARNING, 'This went wrong, but we can continue');
// Generate fatal error :
processError(E_USER_ERROR, 'This went horrible wrong');
Alternate approach :
function handleError($errno, $errstring, $errfile, $errline, $errcontext) {
if (error_reporting() & $errno) {
// only process when included in error_reporting
return handleException(new \Exception($errstring, $errno));
}
return true;
}
function handleException($exception){
// Here, you do whatever you want with the generated
// exceptions. You can store them in a file or database,
// output them in a debug section of your page or do
// pretty much anything else with it, as if it's a
// normal variable
switch ($code) {
case E_ERROR:
case E_CORE_ERROR:
case E_USER_ERROR:
// Make sure script exits here
exit(1);
default:
// Let script continue
return true;
}
}
// Set error handler to your custom handler
set_error_handler('handleError');
// Set exception handler to your custom handler
set_exception_handler('handleException');
// ---------------------------------- //
// Generate warning
trigger_error('This went wrong, but we can continue', E_USER_WARNING);
// Generate fatal error :
trigger_error('This went horrible wrong', E_USER_ERROR);
An advantage of the latter strategy, is that you get the $errcontext parameter if you do $exception->getTrace() within the function handleException.
This is very useful for certain debugging purposes. Unfortunately, this works only if you use trigger_error directly from your context, which means you can't use a wrapper function/method to alias the trigger_error function (so you can't do something like function debug($code, $message) { return trigger_error($message, $code); } if you want the context data in your trace).
EDIT
I've found one dirty workaround for the trigger_error problem.
Consider the following code :
define("__DEBUG__", "Use of undefined constant DEBUG - assumed 'DEBUG'");
public static function handleError($code, $message, $file, $line, $context = false) {
if ($message == __DEBUG__) {
return static::exception(new \Exception(__DEBUG__, E_USER_WARNING));
} else {
if (error_reporting() & $code) {
return static::exception(new \Exception($message, $code));
}
return true;
}
}
public static function handleException($e) {
global $debug;
$code = $e->getCode();
$trace = $e->getTrace();
if ($e->getMessage() == __DEBUG__) {
// DEBUG
array_push($debug, array(
'__TIME__' => microtime(),
'__CONTEXT__' => array(
'file' => $trace[0]['file'],
'line' => $trace[0]['line'],
'function' => $trace[1]['function'],
'class' => $trace[1]['class'],
'type' => $trace[1]['type'],
'args' => $trace[0]['args'][4]
)
));
} else {
// NORMAL ERROR HANDLING
}
return true;
}
With this code, you can use the statement DEBUG; to generate a list of all available variables and a stack trace for any specific context. This list is stored in the global variable $debug. You can add it to a log file, add it to a database or print it out.
This is a VERY, VERY dirty hack, though, so use it at your own discretion. However, it can make debugging a lot easier and allows you to create a clean UI for your debug code.
Which would you recommend?
Return an error code, such as E_USER_ERROR from a function, and determine proper message higher up:
function currentScriptFilename()
{
if(!isset($_SERVER['SCRIPT_FILENAME']))
{
//This?
return E_USER_ERROR;
}
else
{
$url = $_SERVER['SCRIPT_FILENAME'];
$exploded = explode('/', $url);
return end($exploded);
}
}
Execute trigger_error() from the function, with a specific error message:
function currentScriptFilename()
{
if(!isset($_SERVER['SCRIPT_FILENAME']))
{
//Or this?
trigger_error('$_SERVER[\'SCRIPT_FILENAME\'] is not set.', E_USER_ERROR);
}
else
{
$url = $_SERVER['SCRIPT_FILENAME'];
$exploded = explode('/', $url);
return end($exploded);
}
}
I am not sure if I will regret having put a bunch of error messages in my functions further down the line, since I would like to use them for other projects.
Or, would you recommend something totally different?
Do not mix the matters.
Error notification and error handling are different tasks.
You have to use both methods simultaneously.
If you think that $_SERVER['SCRIPT_FILENAME'] availability is worth an error message, you can use trigger error. However PHP itself will throw a notice if you won't check it.
If you want to handle this error, just check this function's return value.
But I would not create a special function for this task.
So,
if (!$filename = basename($_SERVER['SCRIPT_FILENAME']) {
// do whatever you want to handle this error.
}
would be enough
Exceptions could be useful to handle errors, to know if we had any errors occurred.
A simple example:
try {
$filename = basename($_SERVER['SCRIPT_FILENAME'])
if (!$filename) throw new Exception("no filename");
$data = get_some_data_from_db() or throw new Exception("no data");
$template = new Template();
//Exception could be thrown inside of Template class as well.
}
catch (Exception $e) {
//if we had any errors
show_error_page();
}
$template->show();
3.Use exceptions.
If this is the route you are going, I'd rather recommend throwing Exceptions rather then returing an E_ERROR (E_USER_ERROR should be used), as this is just an integer, and possibly a totally valid return for your function.
Advantages:
- Throwing of an Exception cannot be interpreted as anything else then an error by mistake.
- You keep the possibility to add a descriptive error message, even though you don't handle the error at that point/
- You keep a backtrace in your Exception.
- You can catch specific exceptions at specific points, making the decision where in your project a specific type of error should be handled a lot easier.
If not using exceptions which you should be, use trigger_error().
If it is an error you'd like to deal with, try returning FALSE like a lot of the in built functions do.
If you do use exceptions, catch them like this
try {
whatever()
} catch (Exception $e) {
// handle however
}