Prometheus gauge for in-flight requests

[yabberyabber]

I would really like to be able to track the number of requests that are currently in flight for my application.

To do this, I could of course create my own middleware that wraps each request, but with this approach it would be difficult for my custom metric to match the naming convention and label-set as those metrics provided by the prometheus package in this repo.

Would the maintainers here be open to a PR from me where I add an requests_in_flight gauge to track the number of currently running packages?

[aldas]

closing, new middleware was added with #94

I think you can create custom gauge metric and use BeforeNext and AfterNext functions to inc/dec that gauge value

package main

import (
	"errors"
	"github.com/labstack/echo-contrib/echoprometheus"
	"github.com/labstack/echo/v4"
	"github.com/prometheus/client_golang/prometheus"
	"log"
	"net/http"
)

func main() {
	e := echo.New()

	customCounter := prometheus.NewGauge( // create new gauge metric.
		prometheus.GaugeOpts{
			Name: "requests_in_flight",
			Help: "How many HTTP requests are currently being served",
		},
	)
	if err := prometheus.Register(customCounter); err != nil { // register your new counter metric with default prometheus registry
		log.Fatal(err)
	}

	e.Use(echoprometheus.NewMiddlewareWithConfig(echoprometheus.MiddlewareConfig{
		BeforeNext: func(c echo.Context) {
			customCounter.Inc() // before every request increment the counter

		},
		AfterNext: func(c echo.Context, err error) {
			customCounter.Dec() // after every request decrements the counter
		},
	}))
	// register route for getting gathered metrics data
	e.GET("/metrics", echoprometheus.NewHandler())

	if err := e.Start(":8080"); err != nil && !errors.Is(err, http.ErrServerClosed) {
		log.Fatal(err)
	}
}