How to create and use middleware in a Go web application?

To create and use middleware in a Go web application, you can follow these steps:

Import the required packages:

import (
	"net/http"
	"log"
)

Define a middleware function:

func middleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Code for middleware logic goes here
		log.Println("Executing middleware")
		
		// Call the next handler
		next.ServeHTTP(w, r)
	})
}

Create a handler function that will be executed after the middleware:

func handler(w http.ResponseWriter, r *http.Request) {
	// Code for handling the request goes here
	log.Println("Executing handler")
}

Create a new ServeMux and register the middleware and handler functions:

func main() {
	mux := http.NewServeMux()

	// Use the middleware for all requests
	mux.Handle("/", middleware(http.HandlerFunc(handler)))

	// Start the server
	log.Println("Starting server on port 8080")
	http.ListenAndServe(":8080", mux)
}

Run the application and visit http://localhost:8080 to see the logs for the middleware and handler functions.

Note: The middleware function can be used for any custom logic that needs to be executed before or after handling a request, such as authentication, logging, error handling, etc. You can add additional middleware functions by chaining them in the ServeMux registration.