Go服务器上的一页REST API返回系统MAC地址

I have a PHP based web application. On the login page, it makes an AJAX call to a Go server (located on the client machine) to get its MAC address. Below is the Go server code:

package main

import (
  "net"
  "net/http"
  "encoding/json"
)

//define struct for mac address json
type MacAddress struct {
    Id string
}

/**
 * Get device mac address
 */
func GetMacAddress(w http.ResponseWriter, r *http.Request) {

   w.Header().Set("Access-Control-Allow-Origin", "*")


   mac := &MacAddress{Id: ""}
   ifas, err := net.Interfaces()
   if err != nil {
       json.NewEncoder(w).Encode(mac)
       return
   }

   for _, ifa := range ifas {
       a := ifa.HardwareAddr.String()
       if a != "" {
           mac := &MacAddress{Id: a}
           json.NewEncoder(w).Encode(mac)
           break
       }
   }
   return
}

/**
 * Main function
 */
func main() {

  http.HandleFunc("/", GetMacAddress)
  if err := http.ListenAndServe(":8000", nil); err != nil {
    panic(err)
  }
}

Result:

{Id: "8c:16:45:5h:1e:0e"}

Here I have 2 questions.

Sometimes i get the error

panic: listen tcp :8000: bind: address already in use

and I manually kill the process. So, what can be improved in my code to avoid this error and close the previously running server?

Can a stand-alone, compiled Go file (created on ubuntu) be run on other systems like windows or linux or mac without having all Go libs and setup?

Information on how to cross-compile a Go program for different operation systems can be found here. Briefly, instead of running go build main.go, run:

env GOARCH=amd64 GOOS=<target_OS> CGO_ENABLED=1 go build -v main.go

I usually have a Makefile to simplify the process of cross-compiling for linux, windows, and macOS.

With regard to your second question, I can only reproduce your error on my machine when I try to ListenAndServe twice. I.e. I suspect that during your debugging cycles, you forgot to close a running server while trying to start a new instance in another terminal window. Make sure to abort your Go program with ctrl + c before running it again.