I have custom field data that I would like to modify on its way to the database.
wp_insert_post_data filter seems to be the closest thing I can find to achieving this. I dumped the $data and $postarr values but I don't see how I can access my custom field data as those fields aren't in the dump.
Can wp_insert_post_data be used to save custom field data, and if not, what is the preferred filter / practice?
EDIT: additional detail:
I have a front end form that asks for a user's company website address. If the user simply types in 'example.com' then the target for that website in his post defaults to mywebsite.com/example.com instead of opening up example.com.