Wordpress Warning: call_user_func_array() expects parameter 1 to be a valid callback, array must have exactly two members
Well I figured it out. Hope this helps someone else.
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;}