My source links are something linke this :

I cache content form links.I personally use wordpress_place_publish to publish cached content from source site to wordpress:

     $my_post = array(
    'post_title' => "$title",
    'post_content' => "$content",
    'post_status' => 'draft',
    'post_author' => 1,
    'post_category' => array(1),
     wp_insert_post( $my_post );

I wish to put each link in custom fields and within the next cache , before publish to Wordpress , check new links with links in custom fields. If link is repeated , prevent place content.

Sorry for my bad description.

I recieve my answer here