feat(http): Add http.request.time_to_first_byte attribute
#131
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AbhiPrasad
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Sep 9, 2025
Lms24
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Sep 12, 2025
…17562) Adds a few attributes to `resource.*` spans for request timing and status information. Most importantly: - `http.request.time_to_first_byte` [from `responseStart`](https://developer.mozilla.org/en-US/docs/Web/API/PerformanceResourceTiming/responseStart) which can be [interpreted as TTFB](https://web.dev/articles/ttfb#measure-resource-requests) for resource requests. This was requested via via getsentry/sentry#63739. - `http.response.status_code` the status code of the resource request. Requested in #16805 and #10995 To get these attributes, I adjusted the already existing `resourceTimingToSpanAttributes` a bit: - Moved it from browser to browser-utils because resource spans logic is located in browser-utils (this is safe, it never was exported from browser) - Changed the signature to return an object instead of an array of attributes. This is more ergonomical to use in both callsites and should reduce bundle size slightly - Added `http.request.redirect_end`, `http.request.worker_start` attributes which are stable timing values available on `PerformanceResourceTiming` but were previously missing - Also added to conventions: getsentry/sentry-conventions#130 - Added `http.request.time_to_first_byte`. Decided to add this attribute because `http.request.response_start` cannot be directly used as TTFB as its value is an absolute time stamp of `responseStart`. Instead the TTFB attribute is the relative response start attribute converted to seconds (happy to change to ms if reviewers prefer). - Also added to conventions: getsentry/sentry-conventions#131 Other consequences: - `http.client` spans now also have the three additional attributes Remarks: - Not super happy about us always defaulting to `0` in case a value is not present. But decided to leave this as-is to avoid any behaviour change for http.client spans.
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This PR adds the
http.request.time_to_first_byteattribute.This attribute is derived from the browser'S
PerformanceResourceTiming.responseStartattribute. In contrast to the thehttp.request.response_startattribute, which also usesresponseStartbut converts the value to an absolute time stamp, this attribute keeps the time stamp relative but only converts it to seconds. The relative timestamp can be interpreted as TTFB for resource requests.This attribute will be collected from to the browser JS SDK once getsentry/sentry-javascript#17562 is merged.
(decided to keep this separate from #130 since we might still change the value of this attribute)