Add RequestResult.first_byte field for measuring first body byte latency

[jonilaitinen]

This adds an optional first_byte field which is set when the first byte of the response body is received. This enables collecting data for first byte latency during the tests.

There is also a new first-byte field added into the CSV output for each request.

[Copilot]

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

[hatoo]

Adding a field to RequestResult increases overhead to the entire system.
I don't think the first_byte field is useful enough.

[jonilaitinen]

Adding a field to RequestResult increases overhead to the entire system. I don't think the first_byte field is useful enough.

Is your concern that the RequestResult struct becomes too big (size of the struct in bytes is big)?

I've used the Response-delay (= first byte) and Response-read (= last byte) values in hey (see: https://github.com/rakyll/hey/blob/898582754e00405372f0686641441168f4e2f489/requester/print.go#L30-L31) because those values describe the viewer experience well (users care how fast they get the content). So I was hoping to get similar data with oha.

[hatoo]

Is your concern that the RequestResult struct becomes too big (size of the struct in bytes is big)?

Yes

I've used the Response-delay (= first byte) and Response-read (= last byte) values in hey (see: https://github.com/rakyll/hey/blob/898582754e00405372f0686641441168f4e2f489/requester/print.go#L30-L31) because those values describe the viewer experience well (users care how fast they get the content). So I was hoping to get similar data with oha.

Gotcha. I agree that collecting first_byte is good.
So, could you change the CSV column order and name to the same as hey?

[jonilaitinen]

I've renamed the new field to be Response-delay in the CSV (same as hey).
For the column ordering, the current order is request-start,DNS,DNS+dialup,Response-delay,request-duration,bytes,status which seems logical to me as the events are in the order in which they happen (first request-start, then resolve DNS, connect to the server, and so on) or what do you think?

[hatoo]

For the column ordering, the current order is request-start,DNS,DNS+dialup,Response-delay,request-duration,bytes,status which seems logical to me as the events are in the order in which they happen (first request-start, then resolve DNS, connect to the server, and so on) or what do you think?

Looks good. Thank you!