I'd like to find out what error handler is currently, well, handling errors.
I know that set_error_handler() will return the previous error handler, but is there a way to find out what the current error handler is without setting a new one?
Despite the lack of a get_error_handler() function in PHP, you can use a little trickery with set_error_handler() to retrieve the current error handler, although you might not be able to do much with that information, depending on it's value. Nonetheless:
set_error_handler($handler = set_error_handler('var_dump'));
// Set the handler back to itself immediately after capturing it.
var_dump($handler); // NULL | string | array(2) | Closure
Look, ma, it's idempotent!
Yes, there is a way to find out the error handler without setting up new one. This is not the one step native php function. but its effects are exactly that what you need.
summarizing all suggestions of #aurbano, #AL the X, #Jesse and #Dominic108 replacement method can look like this
function get_error_handler(){
$handler = set_error_handler(function(){});
restore_error_handler();
return $handler;
}
You could use set_error_handler(). set_error_handler() returns the current error handler (though as 'mixed'). After you retrieved it, use restore_error_handler(), which will leave it as it was.
This isn't possible in PHP - as you said, you could retrive the current error handler when you call set_error_handler and restore it with restore_error_handler
<?php
class MyException extends Exception {}
set_exception_handler(function(Exception $e){
echo "Old handler:".$e->getMessage();
});
$lastHandler = set_exception_handler(function(Exception $e) use (&$lastHandler) {
if ($e instanceof MyException) {
echo "New handler:".$e->getMessage();
return;
}
if (is_callable($lastHandler)) {
return call_user_func_array($lastHandler, [$e]);
}
throw $e;
});
Trigger the exception handler:
throw new MyException("Exception one", 1);
Output: New handler:Exception one
throw new Exception("Exception two", 1);
Output: Old handler:Exception two
one can also use https://stackoverflow.com/a/43342227 for getting the last exception handler:
function get_exception_handler()
{
$handler = set_exception_handler(function () {});
restore_exception_handler();
return $handler;
}
this might be useful if you want - eg in a unit test - which exception handler has been registered.
I check the source and the answer is no.
Related
I need some function that will accept a function as the parameter and will run it in try {} catch (Exception $e) {}. If it runs successfully, do nothing, otherwise, throw new Exception. That's something like function-checker, which checks functions if they ran successfully. Anybody can help me or give advice?
Thanks for any replies.
The function should work like that:
function itwillfail () {
echo 10 / 0;
}
check("itwillfail");
Output: Caught exception: Custom exception text here, because it has been thrown as custom.
("check" is that function I need)
What I tried:
function check($func) {
try {
call_user_func($func);
} catch (Exception $e) {
throw new Exception("Custom text here.");
}
}
EDIT: More explained: I need to create function, which do the same as "try" and a lot of different "catch"es for different types of exceptions.
Summarizing your question:
You want a way to call a custom function from a string variable (which you have already figured out that would be via call_user_func($var);.
You then want that function to throw a custom exception error
Confused
What is not clear is the reason you would opt to not define your error handler using the set_error_handler function which would effectively do what your asking and set a switch statement to output different messages based on the error generated.
Example
The following example is not using a call_user_func but it effectively allows you to write how the error will be handled
<?php
function myerror($error_no, $error_msg) {
echo "Error: [$error_no] $error_msg ";
echo "\n Now Script will end";
die();
}
// Setting set_error_handler
set_error_handler("myerror");
$a = 10;
$b = 0;
// Force the error
echo($a / $b);
?>
Not every function throws an exception when they fail. Many functions, especially ones that have been around for a long time, simply trigger PHP errors rather than exceptions.
To handle those, you would use a custom error handler:
https://www.php.net/manual/en/function.set-error-handler.php
So you could set up a custom error handler that would intercept those kinds of failures and throw them as exceptions. The whole point of that function is to do what you're trying to do - handle errors in a custom way.
Consider the following code, where I want to throw a new exception to wrap "previous" exceptions that I just caught.
try {
doSomething();
}
catch (SomethingException $eSomething) {
try {
rollback();
}
catch (RollbackException $eRollback) {
throw new SomethingRollbackException('Copying failed, rollback failed.', null, $eSomething, $eRollback);
}
}
At some point I have two exceptions that I would want to pass in as "$previous", when constructing a new exception.
But natively, only one "previous exception" is supported.
Options I can think of so far:
Create my own exception class that accepts an additional "previous" exception. But then what? Store it as a private property? Or public? With an accessor? How would I make calling code to care about the extra information?
Of course I could just write to the log, and discard one or both of the exceptions. But this is not the point of this question.
Create my own exception class that accepts an additional "previous" exception. - Yes, let's say SomethingRollbackException
Store it as a private property? - Yes, but is matter of taste
With an accessor? - Yes, see above
How would I make calling code to care about the extra information? - something like this:
if ($exception instanceof SomethingRollbackException) {
// at this point you know $exception has 2 previous exceptions
}
or
try {
// ....
} catch(SomethingRollbackException $e) {
// at this point you know $exception has 2 previous exceptions
}
When my Beanstalkd job has an error, like "exception 'ErrorException' with message 'Notice: Undefined index: id in /var/www/mysite/app/libraries/lib.php line 248' in /var/www/mysite/app/libraries/lib.php:248, how should Beanstalkd knows that an error has occured and mark it as failed so it can be retried again?
Install a monitor for beanstalkd which can be useful when developing/testing your app. Some alternatives that uses PHP: http://mnapoli.github.io/phpBeanstalkdAdmin/ and https://github.com/ptrofimov/beanstalk_console
As for handling the errors, you could define your own error handler for beanstalkd jobs and in that handler decide if you want to:
bury (put the job aside for later inspection)
kick (put it back into the queue)
delete (remove it, if this is safe for your application)
EDIT - Did you manage to solve your problem?
The best way might be to use a try/catch around your jobs to catch the exceptions, and then bury it if the exception is raised at the worker. If the exception is raised at the producer it is probably never added into the queue so no need to bury() then, but use a monitor to make sure.
If you want to try to define an own error handler for your object I´ve done something similar before by setting up a custom error handler for your class. It might be a ugly hack by trying to get the pheanstalk (job) object through $errcontext - but might be something to try.. Here is some pseudo-code I quickly put together if you want to try it out (created a subclass to avoid put code into pheanstalk class):
class MyPheanstalk extends Pheanstalk {
function __construct() {
//register your custom error_handler for objects of this class
set_error_handler(array($this, 'myPheanstalk_error_handler'));
//call parent constructor
parent::__construct();
}
function myPheanstalk_error_handler($errno, $errstr, $errfile, $errline, $errcontext) {
// get the current job that failed
foreach($errcontext as $val) //print_r($errcontext) to find info on the object(job) you are looking for
{
if(is_object($val)) {
if(get_class($val) == 'Pheanstalk') { //and replace with correct class here
//optionally check errstr to decide if you want to delete() or kick() instead of bury()
$this->bury($val);
}
}
}
}
}
Its your script that has the error, not beanstalkd.
try {
//your code from Line 248 here
} catch (ErrorException $e) { //this section catches the error.
//you can print the error
echo 'An error occurred'. $e->getMessage();
//or do something else like try reporting the ID is bad.
if (!isset($id)) {
echo 'The id was not set!';
}
} //end of try/catch
Can someone tell me the most common reasons to see this error in PHP:
Cannot destroy active lambda function in...
I'm guessing that somewhere there is code that's trying to destroy a closure that contains a reference to itself and the compiler is annoyed at this.
We get these more regularly than I'd like and I'm wondering what pattern we are using that's the likely culprit that's causing it.
I would attach a code snippet but the error typically points to a file not to a line in a file that might provide a hint.
There is similar bug posted in php.net regarding the same. Below is the link .
Hope it will be helpful to you.
https://bugs.php.net/bug.php?id=62452
Such a fatal error will result in code like this:
set_exception_handler(function ($e) {
echo "My exception handler";
restore_exception_handler();
throw new Exception("Throw this instead.");
});
throw new Exception("An exception");
Or like this:
function destroy_handler() {
restore_exception_handler();
}
function update_handler() {
destroy_handler();
}
set_exception_handler(function ($e) {
echo "My exception handler";
update_handler();
throw new Exception("Throw this instead.");
});
throw new Exception("An exception");
When an exception is thrown the callback given to set_exception_handler() is executed and as soon as the restore_exception_handler() is called, the fatal error occurs because the same reference to that closure is being destroyed (or reassigned) inside its own scope (the same goes in the example of hanskrentel at yahoo dot de in the link posted by Sameer K).
You can see from the second example that, even with nested scopes, the same occurs. This is because restore_exception_handler will destroy the last set exception handler, and not a copy of it (it's like re-assigning a variable or unset it while you are still evaluating the expression that will give the variable an initial value).
If you say that the error in your code points to another file, I suggest you to check all the calls in your lambda which execution "jumps" in functions and or methods in other files and check there if you are reassigning or destroying a reference to the lambda itself.
The set_exception_handler will return the previous exception handler:
Returns the name of the previously defined exception handler, or NULL on error. If no previous handler was defined, NULL is also returned.
php.net: set_exception_handler
<?php
class MyException extends Exception {}
set_exception_handler(function(Exception $e){
echo "Old handler:".$e->getMessage();
});
$lastHandler = set_exception_handler(function(Exception $e) use (&$lastHandler) {
if ($e instanceof MyException) {
echo "New handler:".$e->getMessage();
return;
}
if (is_callable($lastHandler)) {
return call_user_func_array($lastHandler, [$e]);
}
throw $e;
});
Trigger the exception handler:
throw new MyException("Exception one", 1);
Output: New handler:Exception one
throw new Exception("Exception two", 1);
Output: Old handler:Exception two
I've been wondering why would I use Exceptions in my PHP. Let's take a look at a simple example:
class Worker
{
public function goToWork()
{
return $isInThatMood ?
// Okay, I'll do it.
true :
// In your dreams...
false;
}
}
$worker = new Worker;
if (!$worker->goToWork())
{
if (date('l',time()) == 'Sunday')
echo "Fine, you don't have to work on Sundays...";
else
echo "Get your a** back to work!";
}
else
echo "Good.";
Is there a reason for me to use Exceptions for that kind of code? Why? How would the code be built?
And what about code that may produce errors:
class FileOutputter
{
public function outputFile($file)
{
if (!file_exists($file))
return false;
return file_get_contents($file);
}
}
Why would I use Exceptions in the above case? I have a feeling that Exceptions help you to recognize the type of the problem, which occured, true?
So, am I using Exceptions appropriately in this code:
class FileOutputter
{
public function outputFile($file)
{
if (!file_exists($file))
return throw new Exception("File not found.",123);
try
{
$contents = file_get_contents($file);
}
catch (Exception $e)
{
return $e;
}
return $contents;
}
}
Or is that poor? Now the underlying code can do this:
$fo = new FileOutputter;
try
{
$fo->outputFile("File.extension");
}
catch (Exception $e)
{
// Something happened, we could either display the error/problem directly
echo $e->getMessage();
// Or use the info to make alternative execution flows
if ($e->getCode() == 123) // The one we specified earlier
// Do something else now, create "an exception"
}
Or am I completely lost here?
When should I use an exception?
You use an exception to indicate an exceptional condition; that is, something which prevents a method from fulfilling its contract, and which shouldn't have occurred at that level.
For example, you might have a method, Record::save(), which saves changes to a record into a database. If, for some reason, this can't be done (e.g. a database error occurs, or a data constraint is broken), then you could throw an exception to indicate failure.
How do I create custom exceptions?
Exceptions are usually named such that they indicate the nature of the error, for example, DatabaseException. You can subclass Exception to create custom-named exceptions in this manner, e.g.
class DatabaseException extends Exception {}
(Of course, you could take advantage of inheritance to give this exception some additional diagnostic information, such as connection details or a database error code, for example.)
When shouldn't I use an exception?
Consider a further example; a method which checks for file existence. This should probably not throw an exception if the file doesn't exist, since the purpose of the method was to perform said check. However, a method which opens a file and performs some processing could throw an exception, since the file was expected to exist, etc.
Initially, it's not always clear when something is and isn't exceptional. Like most things, experience will teach you, over time, when you should and shouldn't throw an exception.
Why use exceptions instead of returning special error codes, etc?
The useful thing about exceptions is that they immediately leap out of the current method and head up the call stack until they're caught and handled, which means you can move error-handling logic higher up, although ideally, not too high.
By using a clear mechanism to deal with failure cases, you automatically kick off the error handling code when something bad happens, which means you can avoid dealing with all sorts of magic sentinel values which have to be checked, or worse, a global error flag to distinguish between a bunch of different possibilities.
I'm not a PHP programmer, but this looks similar to C#.
Typically you'd want to throw errors if it is a point of no return. Then you would be able to log something to show that the impossible happened.
If you can tell that the file doesn't exist then you could just say that. No real need in my mind to also throw an exception.
Now if the file was found and you are processing it, and say only half the file was uploaded and you had no way of telling that without an exception, then it'd be nice to have around.
I would say it's a good design practice to avoid the catch all exceptions "catch (Exception $e)" and design by contract instead, just like you seem to be doing in the prior example. I would at first be more specific with the type of exception being thrown and then work from there if needed. Otherwise, stay away from the try->catch and exceptions.
In no way can you assume that a file exists just because you called file_exists()! The function file_exists doesn't open the file, so the file can potentially be deleted or renamed or moved at any time!
class FileOutputter
{
public function outputFile($file)
{
if (!file_exists($file))
return false;
///<--- file may be deleted right here without you knowing it
return file_get_contents($file);//<-- then this will throw an error
//if you don't catch it, you're program may halt.
}
}
I believe this it better:
class FileOutputter
{
public function outputFile($file)
{
try{
if (!file_exists($file))
return false;
return file_get_contents($file);
}catch(Exception e){
check_what_went_wrong_and_go_to_plan_B();
}
}
}
(Edit: And it's probably even better to actually try to open the file from the beginning. If you succeed then you have a 'lock' on the file and it won't just disappear. If not, then catch the exception and see what went wrong.
Then again, you might feel that this level of reduncancy is just silly. In that case I don't think you need to worry about try/catch at all :)
Just a note really, your code for file outputter is invalid, since file_get_contents($file)
does not throw an exception. It will however raise a warning if the file doesn't exist, or can't be accessed for some reason. Additionally, you are returning an exception from outputFile, when you should probably be just letting the error propagate up the call stack.
However, you can register the error handler in php to throw exceptions when an error occurs:
function exception_error_handler($errno, $errstr, $errfile, $errline ) {
throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
}
set_error_handler("exception_error_handler");
That way, any standard function calls that cause an error will throw an exception.
So, I would change FileOutputter to this (with that snippet above added):
class FileOutputter
{
public function outputFile($file)
{
if (!file_exists($file))
throw new Exception("File not found.",123);
return file_get_contents($file);
}
}
The calling code is then basically the same.
Basically rule is not to return an Exception when an error occurs - you can catch it if you want, and throw a custom exception, but let the exception go up the call stack until you want to use it.