How to require a login on a wordpress page with a shortcode

Question

When I attempt the following I get Warning: Cannot modify header information - headers already sent by......

I'm trying to require a user to be logged in before they access my page with the shortcode on it.

What am I missing? Thanks a million for any help you can offer.

add_shortcode( 'guest-posts', 'guestposts_shortcode' );

function guestposts_shortcode( $atts ) {
    auth_redirect();
}

Answer 1

It may work if you parse the post content before to render it. Then you should check if you find the shortcode inside the content.

Here is a small generic function to check it :

function has_shortcode($shortcode = '') {
    global $post;

    if (!$shortcode || $post == null) {  
        return false;  
    }

    if ( stripos($post->post_content, '[' . $shortcode) !== false ) {   
        return true;
    }

    return false;
}

Now we have to create a function that will check for our specific shortcode :

function unlogged_guest_posts_redirect() {
    if(has_shortcode('guest-posts') && !is_user_logged_in()) {
        auth_redirect();
    }
}

Then we have to hook our function (I think this can work in "wp" hook, but you can try anohter if it does not) :

add_action('wp', 'unlogged_guest_posts_redirect');

To finish, we have to ensure that the shortcode won't echo anything :

add_shortcode( 'guest-posts', 'guestposts_shortcode' );

function guestposts_shortcode( $atts ) {
    return false;
}

Actually we are dealing with shortcodes but we're not using the WordPress shortcode API. This functionnality should be done using a custom field, it would be simpler !