[FEATURE] Use exception event for exception response

This is fantastic! I like where this is going, we should explore more.

1. +++ b/src/EventSubscriber/ExceptionSubscriber.php
   @@ -0,0 +1,102 @@
   +    $headers = $exception->getHeaders() + array('Content-Type' => $this->currentRequest->getMimeType($format));
   

   Please use the shorthand syntax []

2. +++ b/src/EventSubscriber/ExceptionSubscriber.php
   @@ -0,0 +1,102 @@
   +    return $this->currentRequest->query->get('_format') == 'api_json';
   

   All JSONAPI routes have an option flag called _is_jsonapi that we may want to check as well.

Also, there are some tests failing (uninitialized container?).

We will also need testing for the new subscriber. We already have test coverage for the exception serialization somewhere else, but we'll need to test the other stuff as well. Hopefully a unit test that checks the expected output for:

• onException
• applies

Thanks @Sutharsan. It seems that the actual patch is missing, there is only the interdiff :-P

+1 for the changes to RequestHandler.

-1 for the addition of that new exception event subscriber. \Drupal\serialization\EventSubscriber\DefaultExceptionSubscriber already does that, in a more generic way.

Taking this into an slightly different direction.

Fixed and merged. I decided to grant authorship to Sutharsan, because he is awesome and did a great job reporting this and taking it to near completion.

Thanks all!

1. +++ b/src/EventSubscriber/DefaultExceptionSubscriber.php
   @@ -0,0 +1,34 @@
   +class DefaultExceptionSubscriber extends SerializationDefaultExceptionSubscriber {
   

   Why do you need this class?

2. +++ b/src/EventSubscriber/DefaultExceptionSubscriber.php
   @@ -0,0 +1,34 @@
   +  protected static function getPriority() {
   +    return parent::getPriority() + 25;
   +  }
   

   Why does it need to run so early?

Thanks for the review Wim. I should've mentioned you in the commit credits as well. Shame on me.

Why do you need this class?

Because the \Drupal\serialization\EventSubscriber\DefaultExceptionSubscriber is opinionated on how I have to normalize my exceptions in the setEventResponse. Serializing an array ['message' => $exception->getMessage()] is not good enough for jsonapi.

I think that core should ship with HttpException normalizers that do the ['message' => $exception->getMessage()], if that is the desired format, in the normalizer instead of the event subscriber.

Why does it need to run so early?

No reason, it needs to take precedence over the parent. Since the parent is at -75 and the grandparent at 0 I thought that -50 could be a sensible number. Do you think it's too early?

I think that core should ship with HttpException normalizers that do the ['message' => $exception->getMessage()], if that is the desired format, in the normalizer instead of the event subscriber.

That makes sense! Can you open a new issue for that? We still have to clean up the current HTTP exception mess for non-HTML formats. So we might as well fix that at the same time.

Thanks for the clarifications!

Added a reference to the core issue.