What could cause a failure in PHP serialize function?

Question

I have some serverside PHP code that attempts persist a data object (essentially an multi-dimensional array) to a backend database. This data object originally comes in as AMF actionscript object sent from a flex application. I want persist the object in whole for later use so I have used the php serialize function and encode the object down a simple string that can go into a database field. The code looks like this:

$serializedDataObject = base64_encode(serialize($objectInstance->myDataObject));

When I want to revivify this object and bring it back I simply run the reverse

$unserializedDatanObject = unserialize(base64_decode($serializedDataObject));

So far this seems to work well. But sometimes my php script fails. I think it is failing at the serialization step. My question is theoretically speaking what could cause a php serialization and encoding process to fail? Are there certain characters or kinds of data in the data object array that could cause the serialization to bork?

Do I need to do some massaging of the data object before I try to serialize it?

Edit:

To clarify the process works like this

I have a Flex/Actionscript client app that sends AMF based actionscript objects to the server. On the PHP side I am using the Zend AMF library to read the AMF data. The object can be inspected in PHP and basically looks like an associative multi-dimensional array. It is at this point that I attempt to serialize and base 64 encode the object so that I can persist the object to the database as a encoded string.

Hopefully this makes sense. The problem is intermittent and not so easy to reproduce consistently. If I can get some specific error messages I will post them here for further clarification. But for now I was just wondering what are the limits of serialization to help me further debug.

Answer 1

Resources can't be serialized which might be the problem. A way to avoid this problem is to use the magic methods: __sleep and __wakeup.

Basically, your __sleep function is called when you call serialize, and __wakeup is for when you unserialize, so say it's a database connection: in sleep() close the connection and store the connection string somewhere (perhaps), and in wakeup, reconnect.