Parse text openmetrics format to MetricFamilies

[ide-rea]

This PR is for prometheus/prometheus#8932. My solution about this issue is divided into two steps.

1. Use the openMetricsParser located in https://github.com/prometheus/prometheus/tree/main/pkg/textparse to parse the text exchange format into the MetricFamily map . this step is implemented in this PR.
2. Use https://github.com/prometheus/client_golang/blob/master/prometheus/testutil/promlint/promlint.go promlint to check the metric foramt. If the first step is correct, i'll fastly plan to implement this.

My concern is that, firstly as the openMetricsParser is located in github.com/prometheus/prometheus/ , there may be some hidden circular import problem, although i have tested it works. Secondly, I may be totally wrong about the right direction for solving this issue. i'm very happy to hear from any advices:)!

Signed-off-by: Xiaoyu Zhang [email protected]

[roidelapluie]

The two parsers should not be identical. The one in prometheus is a very optimized parser, made for scrape. It does not collect all the edge cases.

The parser in this repo is for validation and should be less permissive and catch all the issues.

[ide-rea]

Firstly, thanks @roidelapluie , but I have one more questions to ask. Does the parser may only supported limited openmetrics feature like https://github.com/prometheus/common/blob/main/expfmt/openmetrics_create.go right now, how do you think that?

[roidelapluie]

the parser should support: https://github.com/prometheus/client_python/blob/master/tests/openmetrics/test_parser.py