How to use expvar.Func to expose dynamic runtime information in Go?

To use expvar.Func to expose dynamic runtime information in Go, you need to follow these steps:

Step 1: Import the required packages.

import (
	"expvar"
	"net/http"
)

Step 2: Define a function that returns a value you want to expose.

func info() interface{} {
	// return dynamic runtime information here
}

Step 3: Register the function as a variable.

func main() {
	// ...

	expvar.Publish("runtime_info", expvar.Func(info))

	// ...
}

Note: In this example, "runtime_info" is the name of the variable that will be used to access the dynamic information.

Step 4: Serve the expvar variables via an HTTP handler.

func main() {
	// ...

	http.Handle("/debug/vars", expvar.Handler())

	// ...
}

Step 5: Start the HTTP server.

func main() {
	// ...

	http.ListenAndServe(":8080", nil)

	// ...
}

Note: Ensure that you adjust the port number according to your requirements.

Step 6: Run the program and access the dynamic information. Once you have your program running, you can access the runtime information by making an HTTP GET request to http://localhost:8080/debug/vars. You will get a JSON response containing the exposed variables, including the one registered with expvar.Func.

That's it! You have successfully used expvar.Func to expose dynamic runtime information in Go.