RESOLVED FIXED304235
[Resource Timing] Add finalResponseHeadersStart and firstInterimResponseStart attributes 
https://bugs.webkit.org/show_bug.cgi?id=304235
Summary [Resource Timing] Add finalResponseHeadersStart and firstInterimResponseStart...
Helmut Januschka
Reported 2025-12-16 00:54:49 PST
Implement W3C Resource Timing Level 3 PR #408: https://github.com/w3c/resource-timing/pull/408 Adds two new timing attributes to PerformanceResourceTiming: - finalResponseHeadersStart: Timestamp when final (2xx/3xx/4xx/5xx) response headers arrive - firstInterimResponseStart: Timestamp when first 1xx (informational) response arrives Updates responseStart behavior to return interim timing if present, otherwise final timing. Use case: Enables proper measurement of HTTP 103 Early Hints performance impact. Implementation uses standard NSURLSession delegate APIs (no CFNetwork changes required). Browser compatibility: - Chrome 133+: Shipped - Firefox: Positive feedback at W3C TPAC 2024 - Safari: This implementation Test coverage: 25/25 WPT subtests passing - resource-timing/interim-response-times.html - resource-timing/interim-response-times.h2.html - loading/early-hints/early-hints-response-time.h2.html PR: https://github.com/WebKit/WebKit/pull/55464
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Radar WebKit Bug Importer
Comment 1 2025-12-23 00:55:11 PST
<rdar://problem/167073003>
EWS
Comment 2 2025-12-23 09:28:05 PST
Committed 304905@main (68d1bafc0c13): <https://commits.webkit.org/304905@main> Reviewed commits have been landed. Closing PR #55467 and removing active labels.
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