Wordpress Warning: call_user_func_array() expects parameter 1 to be a valid callback, array must have exactly two members

Question

I am trying to add a custom function that will add the Access-Control-Allow-Origin Header since I cannot access the .conf files on the server.

Below is my code;

add_filter( 'wp_headers', array( 'eg_send_cors_headers' ), 10, 1 );

function eg_send_cors_headers( $headers ) {

    $headers['Access-Control-Allow-Origin']      = get_http_origin();
    $headers['Access-Control-Allow-Credentials'] = 'true';

    if ( 'OPTIONS' == $_SERVER['REQUEST_METHOD'] ) {
        if ( isset( $_SERVER['HTTP_ACCESS_CONTROL_REQUEST_METHOD'] ) ) {
                $headers['Access-Control-Allow-Methods'] = 'GET, POST, OPTIONS';
        }

        if ( isset( $_SERVER['HTTP_ACCESS_CONTROL_REQUEST_HEADERS'] ) ) {
            $headers['Access-Control-Allow-Headers'] = $_SERVER['HTTP_ACCESS_CONTROL_REQUEST_HEADERS'];
        }
    }

    return $headers;
}

I then get this error when I save:

Notice: Undefined offset: 1 in /example/wp-includes/plugin.php on line 873 Warning: call_user_func_array() expects parameter 1 to be a valid callback, array must have exactly two members in /example/wp-includes/plugin.php on line 192

Answer 1

Since I am only calling a function without a method, I just removed the array () around my function name in the add_filter function. As you can see in Example #1 here, if you are only calling a function with arguments you only need to wrap your function name in single quotes.

fixed code looks like:

add_filter( 'wp_headers', 'eg_send_cors_headers', 10, 1 );
function eg_send_cors_headers( $headers ) {

        $headers['Access-Control-Allow-Origin']= get_http_origin(); 
        $headers['Access-Control-Allow-Credentials'] = 'true';


        if ( 'OPTIONS' == $_SERVER['REQUEST_METHOD'] ) {

            if ( isset( $_SERVER['HTTP_ACCESS_CONTROL_REQUEST_METHOD'] ) ) {
                $headers['Access-Control-Allow-Methods'] = 'GET, POST, OPTIONS';
            }

            if ( isset( $_SERVER['HTTP_ACCESS_CONTROL_REQUEST_HEADERS'] ) ) {
                $headers['Access-Control-Allow-Headers'] = $_SERVER['HTTP_ACCESS_CONTROL_REQUEST_HEADERS'];
            }

        }

    return $headers;
}