Actual time to first byte metric for HTTP tests?

[alexeyr-ci]

Feature Description

https://grafana.com/docs/k6/latest/using-k6/metrics/reference/ and #190 (comment) describe http_req_waiting as

Time spent waiting for response from remote host (a.k.a. “time to first byte”, or “TTFB”).

However, when experimenting with a request where response is intentionally delivered in multiple chunks with a delay between them, it looks like http_req_waiting includes all the time waiting between chunks as well, because http_req_receiving is much smaller than the delays.

I'd like to know the time to the first byte as a proxy for time to the first chunk; currently I have to switch to browser tests for this, and TTFB there ends up being greater than the total http_req_duration for the HTTP test.

This information doesn't seem to be available in Response.timings either.

Suggested Solution (optional)

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Already existing or connected issues / PRs (optional)

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[mstoykov]

Hi @alexeyr-ci, sorry for the slow reply, the action assigning issues doesn't take github status into account :(

Looking at the code

https://github.com/grafana/k6/blob/master/lib/netext/httpext/tracer.go#L367

It seems like what you report should not happen. Do you have a reproducible example I can run.

Also the way receiving is calculated

k6/lib/netext/httpext/tracer.go

Line 375 in ec1f601

trail.Receiving = done.Sub(time.Unix(0, gotFirstResponseByte))

I will expect either something is terribly wrong with our code or something with your code isn't working quite right.

[alexeyr-ci]

I have a reproducible example but it's in our private repository and probably too complicated, with both a JS server and a Rails server involved. I'll try to minimize it first, though it isn't a high priority for us, or just to get a permission to share the private repo.

[mstoykov]

It definitely will be nicer for the reproducible example to be smaller and simpler :)

just to get a permission to share the private repo.

That probably will slow us down considerably if whoever has to look into this has to figure out all the things required to get it going.

[alexeyr-ci]

It definitely would include the full instructions to reproduce, but let's hope minimizing it works first.