A golang web server on a randomly (os) chosen port.

server.go

package main

import (
	"fmt"
	"github.com/skratchdot/open-golang/open"
	"net"
	"net/http"
)

func main() {
	http.HandleFunc("/", helloWorld)

	listener, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		panic(err)
	}
	fmt.Println("listening on", listener.Addr().String())
	open.Run("http://" + listener.Addr().String())
	panic(http.Serve(listener, nil))
}

func helloWorld(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("hello world"))
}

You just answered my question, "how is the port being randomly assigned?", while debugging some other random project. Thanks!

https://daniel.haxx.se/blog/2014/10/25/pretending-port-zero-is-a-normal-one/

Thanks for sharing <3