feat: support arbitrary query params in request

[alecmerdler]

Adds WithCustomOption() func which allows
setting arbitrary key/value pairs to the URL
query parameters of the request.

The primary use case for this is to work with
https://github.com/prometheus-community/prom-label-proxy.

[alecmerdler]

This is a naive approach, I will be happy to update the pull request with any feedback. But as it stands today, the official Prometheus client cannot be used with prom-label-proxy.

[kakkoyun]

@alecmerdler Let's open an issue and discuss this further before jumping into any conclusions.

I would love to learn more about your use cases, especially.

[bwplotka]

Thanks!

But as it stands today, the official Prometheus client cannot be used with prom-label-proxy.

Are we sure? Would custom roundtripper be possible for those use cases? We could add example how to write one - should be trivial to write one that appends parameters to the query for all requests. Similar to

client_golang/api/prometheus/v1/example_test.go

Line 90 in 93a67cb

func (u userAgentRoundTripper) RoundTrip(r *http.Request) (*http.Response, error) {

Perhaps hacky, but for advanced use cases should be enough.

Otherwise adding WithCustomOption would mean:

• There are many ways of doing the same thing (WithStats vs WithCustomOptions("stats", ...) vs roundtripper )
• In the next PR someone proposes WithCustomOptions to every other method.. which is not simple (Option has other stuff).

Generally as we repeat on every API contribution.. it's NOT a perfect API interface. We learned a lot. It's time for a new one, ideally auto-generated (prometheus/prometheus#2392 (comment)). Given that, I would say roundtripper should suffice, WDYT?