Cannot save underscore custom fields in one wordpress installation using xmlrpc and underscores

Question

I have a local installation of wordpress for testing and a production server.

I use XMLRPC to create custom posts with custom fields and everything works flawlessly on my local installation BUT it doesn't work for the production server. Custom Fields are not saved, I checked the table and it doesn't store it.

Is related to the underscores present in the start of the custom fields, for example: _al_listing_price

I have tried to store a custom field al_listing_price and it was saved in the database.

Where I can disable that behavior so it allow to post prefixed underscore custom fields?

Answer 1

You have to unprotect meta to be able to access it with XML-RPC:

<?php

function my_unprotect_meta( $protected, $meta_key, $meta_type ) {

    if( '_al_listing_price' == $meta_key ) {
        return false;
    }

}

add_filter( 'is_protected_meta', 'my_unprotect_meta', 10, 3 );

The solution you've mentioned in the comment to the question is 'duct tape' though it works. It completely removes meta value sanitization, which is the bad idea.