Symfony：不能总是捕获异常

Question

Sorry for this vague title, I didn't know how to title my question.

I'm listening on kernel.exception via the kernel.event_listener service. I use it in my API to catch all exceptions and serialize them in JSON for a clean error handling for the API customers. I have to adapt the serialization depending on the exception types (my HTTP exceptions, Symfony HTTP exceptions, and others).

When a user is not authenticated when accessing a section restricted by access_control in security.yml, Symfony throws a non-HTTP Symfony\\Component\\Security\\Core\\Exception\\InsufficientAuthenticationException . In my serializer, a non-HTTP exception is converted in a 500 error. Since an InsufficientAuthenticationException is rather a 401 Unauthorized error, I have to catch this exception separately and convert it in my app-specific exception type.

Example:

# Find appropriate serialization
if($ex instanceof HttpErr\HttpErrorInterface) {
    # AppBundle\Exceptions\Http\*
    # A displayable error thrown intentionally by our controllers
    $status  = $ex->getStatusCode();
    $message = $ex->getMessage();
    $other   = $ex->getAdditionalDatas();
} elseif($ex instanceof InsufficientAuthenticationException) {
    throw new HttpErr\EUnauthorized; # look a this line
}
# more elseifs...

That works. The Symfony authentication exception is catched, then converted in EUnauthorized, and then EUnauthorized is serialized into JSON. But you can see that I throw the exception without message or previous exception. Because I want to do this:

elseif($ex instanceof InsufficientAuthenticationException) {
    # the standard argument $previous is in 2nd position in my exceptions instead of being 3rd.
    # the previous argument is important for me since it will keep context in error propagation.
    throw new HttpErr\EUnauthorized($ex->getMessage(), $ex);
}

When I do this (so, just adding two arguments), the serialization stops working, my event listener is not called and the app crashes (in prod, this will turn into a friendly WSoD):

Why?

Answer 1

In the first "if" you extract data for serialization, in the second you are just rethrowing a new exception.

This new exception does not go the kernel.exception flow anymore. It is correctly just thrown: as you can see you have the full stack of exceptions shown.

Ideally, you should end your onKernelException with some kind of Response.

EDIT

I'll expand a bit my previous answer with references to the Symfony documentation and code.

The HttpKernel docs say

If an exception is thrown at any point inside HttpKernel::handle, another event - kernel.exception is thrown. Internally, the body of the handle function is wrapped in a try-catch block. When any exception is thrown, the kernel.exception event is dispatched so that your system can somehow respond to the exception.

So, your listener is called after an exception in the handle function, but, as you can see in source no try/catch is provided by the handleException function. This basically means that an Exception thrown in your listener should not be caught.

In your listener you could swap the current exception with a new one with $event->setException(...) or just try to build a Response yourself.

In any case, throwing a new Exception does not seem the proper way here. I sadly don't know why you code works with or without parameters without all the code involved.

Answer 2

I don't know if it helps here, but I had similar problem my event listener is not called and the app crashes . So i worked around that and overrided one method in Kernel.php file like that:

protected function initializeContainer() {

    try {
        $container = parent::initializeContainer();
    } catch (\Throwable $throwable){
        // MY CATCH CODE GOES HERE
    }
    return $container;
}

You can also hook up to other Kernel methods and override them.
Notice: I'm using Symfony 4.2.*