2

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?

Daniel Schütte
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NkTheGame
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  • (1) Only have a single instance of your service running (on Windows, you can use [`golang.org/x/sys/windows/svc`](https://godoc.org/golang.org/x/sys/windows/svc)) (2) Yes, search for Go cross compiling. –  Jul 06 '18 at 11:50
  • Does this issue occur when you use some other arbitrary port like `:9382`? – Mihailo Jul 06 '18 at 12:08
  • @Mihailo I used port 8080 and issue occurred, then i am using 8000. Same thing for both. I think it occurred if i terminate running program incorrectly but don't know how to resolve it. – NkTheGame Jul 06 '18 at 12:26
  • @TimCooper Thanks for quick response. Unable to find when and how i used multiple instances of running server. For cross compiling, i m looking – NkTheGame Jul 06 '18 at 12:27
  • @TimCooper I created executable files as per link https://www.digitalocean.com/community/tutorials/how-to-build-go-executables-for-multiple-platforms-on-ubuntu-16-04. One of them file is for linux amd64. Its getting run on my machine but not on other linux amd64 machine. I am able to find 'Run' option when right click on compiled file but on other system 'Run' option not there. Did i miss anything ? Kindly help. – NkTheGame Jul 06 '18 at 14:07

1 Answers1

0

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.

Daniel Schütte
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