Support for the OpenMetrics format

[atheriel]

Feature request

Currently the Pushgateway can only accept and emit metrics using Prometheus's original text format. There is no support for the new OpenMetrics format, even though Prometheus itself (and a growing number of clients) are moving to this format.

I don't have a strong argument for this feature, other than the merits of the OpenMetrics format itself -- in particular I'd love to have support for exemplars.

In addition, since Pushgateway uses Prometheus's own Golang libraries, this is probably not too hard to achieve -- it has been supported with an opt-in flag since 1.4.0, released more than a year ago.

[beorn7]

The feature request is legitimate, but it depends on support in https://github.com/prometheus/common . The latter already has https://github.com/prometheus/common/blob/main/expfmt/openmetrics_create.go , which is used by client_golang to expose OpenMetrics (if so requested, and within certain limitations). However, what's missing is https://github.com/prometheus/common/blob/main/expfmt/openmetrics_parse.go , i.e. parsing OpenMetrics text format into protobuf DTOs. (The OpenMetrics parser in Prometheus itself is different as it directly parses OpenMetrics into the form needed for ingestion into TSDB.)

[atheriel]

That makes sense.