package main

import "net"
import "os"
import "strings"
import "log"

// Get Fully Qualified Domain Name
// returns "unknown" or hostanme in case of error
func fqdnGet() string {
	log.Println("fqdnGet() START")
	hostname, err := os.Hostname()
	if err != nil {
		return "unknown"
	}

	log.Println("\tfqdnGet() net.LookupIP(hostname) hostname =", hostname)
	addrs, err := net.LookupIP(hostname)
	if err != nil {
		log.Println("\tfqdnGet() net.LookupIP(hostname) err =", err)
		return hostname
	}

	log.Println("\tfqdnGet() range addrs")
	for _, addr := range addrs {
		log.Println("\tfqdnGet() addr = ", addr)
		if ipv4 := addr.To4(); ipv4 != nil {
			ip, err := ipv4.MarshalText()
			log.Println("\tfqdnGet() ip = ", string(ip))
			if err != nil {
				return hostname
			}
			log.Println("\tfqdnGet() net.LookupAddr = ", string(ip))
			hosts, err := net.LookupAddr(string(ip))
			if err != nil || len(hosts) == 0 {
				return hostname
			}
			fqdn := hosts[0]
			return strings.TrimSuffix(fqdn, ".") // return fqdn without trailing dot
		}
	}
	return hostname
}