fix: Concurrency issues with Global Registry, issues with incorrect Path in Metrics

[gaby]

• Fixed concurrency issues related to using the Prometheus Global Registry. Each instance now uses it's own registry
• Fixed issue with Path in metrics, it now uses the Path from the Request ctx.Request().RequestURI().
• Added benchmarks
• Added unit-tests for group handlers
• Replaced deprecated adaptor middleware with the one in https://github.com/gofiber/fiber

Fixes #187 #191
Closes #195 #196

@ansrivas I figured fixing these issues here first before migrating the middleware would make more sense. That way anyone using this repo will still get them.

[sashayakovtseva]

Seems like this PR broke existing code and http metrics will not be collected for users who used default registry and not used RegisterAt (for instance, one could have a separate metrics server, created elsewhere apart from fiberprometheus.New)

[gaby]

@sashayakovtseva That was a bug, the middleware was sharing a global variable. It was exposed when running test in parallel.

You can pass your current registry to the middleware and they both will use the same using NewWithRegistry()

[gaby]

Another option would be adding a config boolean to allow New use default registry or not. We are moving this middleware to https://github.com/gofiber/contrib I will implement that change there

[sashayakovtseva]

You can pass your current registry to the middleware and they both will use the same using NewWithRegistry()

Yeah, I found that out already when metrics disappeared :)

the middleware was sharing a global variable

I guess that is an issue if one has multiple fiberprometheus.New calls concurrently, correct?

[gaby]

You can pass your current registry to the middleware and they both will use the same using NewWithRegistry()

Yeah, I found that out already when metrics disappeared :)

the middleware was sharing a global variable

I guess that is an issue if one has multiple fiberprometheus.New calls concurrently, correct?

Yes, if you have multiple prometheus-go clients they all use the same defaultRegistry. So one solution is to create a Registry a pass it to all your clients.