gistfile1.txt

ObserveHistogram - Name: http_request_duration_seconds, Value: 0.000007, Labels: [handler:HelloWorldHandler code:200]
ObserveHistogram - Name: http_request_duration_seconds, Value: 0.000006, Labels: [handler:HelloWorldHandler code:200]
ObserveHistogram - Name: http_request_duration_seconds, Value: 0.000003, Labels: [handler:HelloWorldHandler code:200]

metrics.go

package main

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"time"
)

type MetricCollector interface {
	ObserveHistogram(ctx context.Context, name string, value float64, labels ...string)
	SetGauge(ctx context.Context, name string, value float64, labels ...string)
	IncrementCounter(ctx context.Context, name string, value int, labels ...string)
}

type ContextKey string

const MetricCollectorKey ContextKey = "metricCollector"

func WithMetricCollector(ctx context.Context, collector MetricCollector) context.Context {
	return context.WithValue(ctx, MetricCollectorKey, collector)
}

func GetMetricCollector(ctx context.Context) MetricCollector {
	collector, ok := ctx.Value(MetricCollectorKey).(MetricCollector)
	if !ok {
		return nil
	}
	return collector
}

type DemoMetricCollector struct {
	counter int// You can add any necessary fields or dependencies here.
}

func NewDemoMetricCollector() MetricCollector {
	// Initialize and return an instance of your metric collector.
	return &DemoMetricCollector{}
}

func (c *DemoMetricCollector) ObserveHistogram(ctx context.Context, name string, value float64, labels ...string) {
	// Implement the ObserveHistogram method to log metrics for demonstration purposes.
	fmt.Printf("ObserveHistogram - Name: %s, Value: %f, Labels: %v\n", name, value, labels)
}

func (c *DemoMetricCollector) SetGauge(ctx context.Context, name string, value float64, labels ...string) {
	// Implement the SetGauge method to log metrics for demonstration purposes.
	fmt.Printf("SetGauge - Name: %s, Value: %f, Labels: %v\n", name, value, labels)
}

func (c *DemoMetricCollector) IncrementCounter(ctx context.Context, name string, value int, labels ...string) {
	c.counter += value
	// Implement the IncrementCounter method to log metrics for demonstration purposes.
	fmt.Println("IncrementCounter")
	fmt.Printf("IncrementCounter - Name: %s, Value: %f, Labels: %v\n", name, c.counter, labels)
}

func HelloWorldHandler(w http.ResponseWriter, r *http.Request) {
	// Get the metric collector from the context.
	ctx := r.Context()
	metricCollector := GetMetricCollector(ctx)
	defer func(startTime time.Time) {
		if metricCollector != nil {
			metricCollector.ObserveHistogram(ctx, "http_request_duration_seconds", time.Since(startTime).Seconds(), "handler:HelloWorldHandler", "code:200")
		}
	}(time.Now())

	// Your application logic here.
	w.Write([]byte("Hello, World!"))
}

func main() {
	// Create a context with a metric collector.
	metricCollector := NewDemoMetricCollector()
	ctx := WithMetricCollector(context.Background(), metricCollector)

	// Create an HTTP server and handle requests.
	server := &http.Server{
		Addr:    ":8080",
		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			// Pass the context with the metric collector to the handler.
			HelloWorldHandler(w, r.WithContext(ctx))
		}),
	}

	// Start the HTTP server.
	if err := server.ListenAndServe(); err != nil {
		log.Fatal(err)
	}
}