HTTP handler function

Question

I saw some http handler function declarations are varied. Two of them I found are the standard function and the one returning anonymous function inside the handler. For example:

Using standard way:

func helloworld(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintln(w, "Hello World")
}

This the most straight way to declare a handler for an http api.

Another way is using anonym/closure function inside the handler function:

func helloworld2() http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request){
        fmt.Fprintln(w, "Hello World")
    })
}

What are the differences and the benefit? When to use one of them? What's the best practice?

Answer 1

Pattern

func Middleware(next http.Handler) http.Handler{
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    // Do something
    next.ServeHTTP(w, r)
  })
}

often used to construct middleware chain like

http.Handle("/", middlewareOne(middlewareTwo(finalHandler)))

Answer 2

Returning an anonymous function is the only way to work with handlers that require additional arguments, by returning a closure. Example:

func fooHandler(db *someDatabase) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // do something with `db` variable
    }
}

Otherwise, there's typically no practical difference between the approaches. One may choose to use the anonymous function universally for consistency.