support native histograms

[jan--f]

Fixes: #125

[jan--f]

Not sure if pulling in the pushgateway dependency is acceptable. should be easy enough the copy the code if that's preferable.

[beorn7]

Looks good. Thank you very much.

Just the dependency on the pushgateway seems really out of place.

Thinking about it, we cannot share code from prometheus/prometheus, because the latter is using gogo-protobuf, while we are using the official Go protobuf library via prometheus/client_model. Furthermore, prometheus/prometheus is using jsoniter for performance reason, while we are using just vanilla json marshaling here.

In the not too far future, we'll migrate prometheus/prometheus to a still maintained high-performance protobuf library. Maybe that would be a good time to also move all our other protobuf usage to that same, yet to be chosen library… From that perspective, the protobuf related code here is temporary, and it would maybe OK to just copy it for the time being.

Alternatively, maybe a histogram subdirectory in prometheus/common/model might be a good place to share the code.

My gut feeling is, let's copy for now.

[beorn7]

Is this update (to a specific hash) required?

[jan--f]

I didn't specifically update this. I'll copy the pushgateway for now, that should fix this dependency update too.

[jan--f]

This comes via the prometheus/prometheus dependency.

[beorn7]

OK, so not our fault… 🤷

[beorn7]

Another thing: Could you also update https://github.com/prometheus/prom2json?tab=readme-ov-file#json-format with a section that contains a native histogram?

[jan--f]

Thinking about it, we cannot share code from prometheus/prometheus, because the latter is using gogo-protobuf, while we are using the official Go protobuf library via prometheus/client_model. Furthermore, prometheus/prometheus is using jsoniter for performance reason, while we are using just vanilla json marshaling here.

Hmm not sure I understand how protobuf factors into this. The histogram_model code in pushgateway imports both github.com/prometheus/client_model/go and github.com/prometheus/prometheus/model/histogram specifically to go from the client model type to the prometheus model type. I wanted to avoid duplicating the Histogram type as defined in github.com/prometheus/prometheus/model/
Is this code different or should I not have done this in pushgatway either?

[beorn7]

You are doing the right thing WRT protobuf.

I was just hoping we could re-use even more code, but prometheus/prometheus is using https://github.com/prometheus/prometheus/blob/main/prompb/io/prometheus/client/ rather than github.com/prometheus/client_model/go when it uses the Go types autogenerated frem the proto spec.

[beorn7]

Thank you very much.