How to make WordPress use protocol indepentent upload files?

Question

I am using FORCE_SSL_ADMIN in wp-config.php so everytime I upload a new image and inserted into the post, it is using SSL version

e.g.

<img src="https://www.example.com/wp-content/uploads/2013/01/test.png" ..

My blog is using HTTP in the public side, so how to make the upload path as rotocol independent, e.g.

<img src="//www.example.com/wp-content/uploads/2013/01/test.png" ..

Answer 1

You can define a function to remove the protocol and hook it to the attachment URL:

function wpse_79958_remove_protocol_from_attachment($url) {
    $url = str_replace(array('http:', 'https:'), '', $url);
    return $url;
}
add_filter( 'attachment_link', 'wpse_79958_remove_protocol_from_attachment' );

Also consider to use relative URLs for attachments by using WordPress builtin function wp_make_link_relative:

add_filter( 'attachment_link', 'wp_make_link_relative' );

Place this code to your functions.php. Not tested though.

Update: already tested