GEOIP continent lookup

ipcontinent.go

package main

import (
	"flag"
	"fmt"
	"log"
	"math/rand"
	"net"
	"net/url"
	"os"
	"time"

	"github.com/fiorix/freegeoip"
)

var maxmindFile = "http://geolite.maxmind.com/download/geoip/database/GeoLite2-City.mmdb.gz"

func main() {
	ipdb := flag.String("db", maxmindFile, "IP database file or URL")
	flag.Usage = func() {
		fmt.Printf("usage: %s [-db file_or_url] hostname_or_ip\n", os.Args[0])
		os.Exit(1)
	}
	flag.Parse()
	args := flag.Args()
	if len(args) != 1 {
		flag.Usage()
	}
	addr, err := net.LookupHost(args[0])
	if err != nil {
		log.Fatal(err)
	}
	ip := net.ParseIP(addr[rand.Intn(len(addr))])
	if ip == nil {
		flag.Usage()
	}
	db, err := openDB(*ipdb, time.Hour, time.Minute)
	if err != nil {
		log.Fatal(err)
	}
	select {
	case <-db.NotifyOpen(): // Wait for db to be ready.
	case err = <-db.NotifyError():
		log.Fatal(err)
	}
	var resp maxmindQuery
	err = db.Lookup(ip, &resp)
	if err != nil {
		log.Fatal(err)
	}
	continent := resp.Continent.Names["en"]
	if len(continent) == 0 {
		fmt.Println(ip, "not found")
	} else {
		fmt.Println(ip, "is in", continent)
	}
}

// openDB opens and returns the IP database.
func openDB(dsn string, updateIntvl, maxRetryIntvl time.Duration) (db *freegeoip.DB, err error) {
	u, err := url.Parse(dsn)
	if err != nil || len(u.Scheme) == 0 {
		db, err = freegeoip.Open(dsn)
	} else {
		db, err = freegeoip.OpenURL(dsn, updateIntvl, maxRetryIntvl)
	}
	return
}

type maxmindQuery struct {
	Continent struct {
		Names map[string]string `maxminddb:"names"`
	} `maxminddb:"continent"`
}