How to implement custom HTTP middleware for request and response processing in Go?

To implement custom HTTP middleware for request and response processing in Go, you can use the net/http package. Middleware functions are essentially wrappers around the http.Handler type, allowing you to modify incoming requests and outgoing responses.

Here's an example of how to implement a custom HTTP middleware in Go:

Define a new type for your middleware handler that implements the http.Handler interface:

type MiddlewareHandler struct {
    next http.Handler
}

Implement the ServeHTTP method for your middleware handler. This method will be called for each incoming request:

func (m *MiddlewareHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    // Pre-processing logic before passing the request to the next handler
    // e.g., Logging, Authentication, etc.

    // Pass the request to the next handler in the chain
    m.next.ServeHTTP(w, r)

    // Post-processing logic after the response has been generated
    // e.g., Adding headers, modifying response body, etc.
}

Create a new instance of your middleware handler and chain it with your existing handlers. You can do this using the http.Handle or http.HandleFunc function:

func main() {
    // Create a new instance of your middleware handler
    middleware := &MiddlewareHandler{
        // Set the next handler in the chain
        next: http.HandlerFunc(handlerFunc),
    }

    // Chain the middleware with your existing handlers
    http.Handle("/", middleware)

    // Start the server
    http.ListenAndServe(":8080", nil)
}

func handlerFunc(w http.ResponseWriter, r *http.Request) {
    // Your existing handler logic goes here
    w.Write([]byte("Hello, world!"))
}

In this example, the MiddlewareHandler middleware is created and set as the root handler using http.Handle("/", middleware). It wraps the existing handlerFunc and adds pre-processing and post-processing logic.

Note that the order of middleware matters. If you need to apply multiple middleware functions, you can chain them by setting the next field of each middleware handler to the next handler in the chain.

That's it! Now you have a basic example of how to implement custom HTTP middleware for request and response processing in Go. Feel free to modify the MiddlewareHandler to fit your specific use case.