[TYPO3-core] RFC: #15094: Refactor of content objects of tslib_content

[Ingo Renner]

Hi all,

as I found out this refactoring can cause major trouble when cloning 
tslib_cObj instance.

Bug tracker reference: http://bugs.typo3.org/view.php?id=16568

Thanks to Joey for pointing me to PHP's reference on cloning objects and 
having it read again I stumbled over the important points:

http://php.net/__clone :

"When an object is cloned, PHP 5 will perform a shallow copy of all of 
the object's properties. Any properties that are references to other 
variables, will remain references."

This means that, when cloning an instance of tslib_cObj, PHP (in the 
nature of a clone) copies all the properties of the original instance to 
the clone instance.

$original->contentObjects contains references to instances of 
tslib_content_*, these instances of tslib_content_* have back references 
to their parent tslib_cObj instance. Now when cloning, instead of 
pointing to the new $clone tslib_cObj instance, these tslib_content_* 
instances still point the $original tslib_cObj. This causes major 
problems resulting in rendering of the frontend hitting maximum 
execution time or memory limits and still not rendering the expected 
content.

1)
==============================================================================
$cObjA (tslib_cObj) <------------------------|
|                                            |
|$cObjA->contentObjects[]                    |
|--------------> CASE (tslib_content_Case) --|
|--------------> USER (tslib_content_User) --|
|--------------> HTML (tslib_content_Html) --|
|--------------> TEXT (tslib_content_Text) --|

2)
==============================================================================
$cObjB = clone $cObjA;

3)
==============================================================================
$cObjA (tslib_cObj) <------------------------|
|                                            | $cObjA->contentObjects[]!
|                                            |             ^
|--------------> CASE (tslib_content_Case) --|  XXX  <-----|
|--------------> USER (tslib_content_User) --|  XXX  <-----|
|--------------> HTML (tslib_content_Html) --|  XXX  <-----|
|--------------> TEXT (tslib_content_Text) --|  XXX  <-----|
                                                            |
$cObjB (tslib_cObj) ---------------------------------------|

I hope the sketch makes it a little easier to understand.

Notes:
You can test the issue with EXT:kb_nescefe v1.1.1 from TER f.e.
The attached patch solves the issue by introducing a __clone() helper 
method in tslib_cObj to reset $clone->contentObjects.

"Once the cloning is complete, if a __clone() method is defined, then 
the newly created object's __clone() method will be called, to allow any 
necessary properties that need to be changed."



best
Ingo

-- 
Ingo Renner
TYPO3 Core Developer, Release Manager TYPO3 4.2, Admin Google Summer of Code

TYPO3 - Open Source Enterprise Content Management System
http://typo3.org

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