What is an http request multiplexer? - http

Question

I've been studying golang and I noticed a lot of people create servers by using the http.NewServeMux() function and I don't really understand what it does.
I read this:
In go ServeMux is an HTTP request multiplexer. It matches the URL of
each incoming request against a list of registered patterns and calls
the handler for the pattern that most closely matches the URL.
How is that different than just doing something like:
http.ListenAndServe(addr, nil)
http.Handle("/home", home)
http.Handle("/login", login)
What is the purpose of using multiplexing?

Answer 1

From net/http GoDoc and Source.
ListenAndServe starts an HTTP server with a given address and handler. The handler is usually nil, which means to use DefaultServeMux. Handle and HandleFunc add handlers to DefaultServeMux
DefaultServeMux is just a predefined http.ServeMux
var DefaultServeMux = &defaultServeMux
var defaultServeMux ServeMux
As you can see http.Handle calls DefaultServeMux internally.
func Handle(pattern string, handler Handler) { DefaultServeMux.Handle(pattern, handler) }
The purpose of http.NewServeMux() is to have your own instance of http.ServerMux for instances like when you require two http.ListenAndServe functions listening to different ports with different routes.

Answer 2

the multiplexer in Golang is some things like multiplexer in hardware which multiply some inputs into some outputs
i gave you a simple exampe
type CustomMultiplexer struct {
}
the given multiplexer have to implement the ServeHTTP method to be registered int http to server inputs
func (mux CustomMultiplexer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
if r.URL.Path == "/" {
SimpleRequestHandler(w, r)
return
}
http.NotFound(w, r)
return
}
my SimpleRequestHandler is a method as follow
func SimpleRequestHandler(w http.ResponseWriter, r *http.Request) {
switch r.Method {
case http.MethodGet:
mySimpleGetRequestHandler(w, r)
break
default:
http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
break
}
}
now i can use my CustomMultiplxere to do multiplexing between incoming requested
func main() {
customServer := CustomServer{}
err := http.ListenAndServe(":9001", &customServer)
if err != nil {
panic(err)
}
}
the http.HandleFunc method works as my given simple multiplexer.