decodedBodySize, encodedBodySize and transferSize (tested only these) are not populated in PerformanceResourceTiming for cross origin requests with `Timing-Allow-Origin: *` http header set for both cached and non-cached resources. It works fine in Chrome and Firefox. See also https://w3c.github.io/resource-timing/#sec-cross-origin-resources.
<rdar://problem/127466015>
https://github.com/WebKit/WebKit/blob/main/Source/WebCore/page/PerformanceResourceTiming.cpp#L274 // This is intentionally stricter than a TAO check. // See https://github.com/w3c/server-timing/issues/89
Thank you for your response. Is there a plan to implement https://w3c.github.io/resource-timing/#dom-performanceresourcetiming-deliverytype? Otherwise, there is no way to find out whether a particular resource was loaded from the cache or not (without explicitly using Cache API or something similar).