How to aggregate and expose multiple expvar variables in a single JSON endpoint in Go?

To aggregate and expose multiple expvar variables in a single JSON endpoint in Go, you can use the expvar package along with the net/http package. Here's an example of how you can achieve this:

Import the required packages:

import (
	"encoding/json"
	"expvar"
	"net/http"
)

Define your custom expvar variables:

var (
	counter1 = expvar.NewInt("counter1")
	counter2 = expvar.NewInt("counter2")
)

Create a handler function that returns the aggregated expvar variables as JSON:

func expvarHandler(w http.ResponseWriter, r *http.Request) {
	// Aggregate the expvar variables into a map
	expvars := map[string]interface{}{
		"counter1": counter1.Value(),
		"counter2": counter2.Value(),
	}

	// Convert the map to JSON
	jsonData, err := json.Marshal(expvars)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	// Set the appropriate headers and write the JSON response
	w.Header().Set("Content-Type", "application/json")
	w.Write(jsonData)
}

func main() {
	http.HandleFunc("/expvar", expvarHandler)
	http.ListenAndServe(":8080", nil)
}

Now, when you access /expvar on your Go server, it will return a JSON response containing the aggregated values of counter1 and counter2 expvar variables:

{
  "counter1": 10,
  "counter2": 5
}

Additionally, you can continue using the expvar variables in your code, for example, by incrementing them:

counter1.Add(1)
counter2.Add(1)

Note: Make sure to update the code to match your specific implementation and add any additional error handling or customization as needed.