Check for write access on attributes

Hi,

when i'm trying to modify an attribute of an entry, i am not allow to
modify, the update method gives me of course an "Insufficent Access Error".

I want to prevent that, so my question is: How can i check _before_
doing the modify, if i am allowed to do it?

Or an other way: Is there a possibility, that the search method returns
only those attributes, i am allowed to modify?

Thank you for your help!
Kilian