Anything that is close to fetchStart in resource timing API?

Resource Timing API defines this:

“If there are no HTTP redirects or equivalent, this attribute must return the time immediately before the user agent starts to fetch the resource.”

What could be a corresponding field in the WPT HAR file? This event definitely happens before the dns lookup starts. But, the lowest start value in WPT for a given resource is _all_start which, I think, cannot be less than _dns_start and so I am not sure if WPT provides this metric at all.

The resource timing definition is defining fetchStart as when the UA actually puts the request on the wire so my view it’s the earliest of _dns_start, _connect_start, and _ttfb_start in WPT terms.

If you want to verify you can use a WPT custom metric to dump the resource timing entries into a JSON string:

return JSON.stringify(window.performance.getEntriesByType("resource"));