We found that Chrome was caching a number of requests as these were being redirected with a 302 status code without headers to prevent caching. Specifically this occurred from the ‘Edit Order’ screen when creating a shipment in Australia Post – the page would often reload without creating the shipment.

The below code fixes this issue:

//Prevent caching of API requests to Australia Post
$is_api_call = false;
if( !empty($_GET) ){
	foreach($_GET as $get => $gval){
		if( false !== strstr($get, 'wf_australiapost_') ){
			$is_api_call = true;
		}
	}
}
if( $is_api_call ){
	header("Cache-Control: no-store, no-cache, must-revalidate, max-age=0");
	header("Cache-Control: post-check=0, pre-check=0", false);
	header("Pragma: no-cache");
}
add_filter( 'wp_redirect_status', 'rfg_change_redirect_status' );
function rfg_change_redirect_status( $status=302 ){
	if( 302 == $status ){
		$status = 307;
	}
	
	return $status;
}

This adds PHP headers to prevent caching of these pages where a $_GET variable starts with ‘wf_australiapost_’. It also changes the 302 redirects to 307 redirects which browsers are less likely to cache.