Added the "addr" parameter

Added the "addr" parameter in order to choose where to bind
fixed format with go fmt

main.go

 package main
 
 import (
-  "log"
-  "net/http"
-  "strings"
-  "encoding/json"
+	"encoding/json"
+	"flag"
+	"log"
+	"net/http"
+	"strings"
 )
 
 type jsonOutput struct {
 	Ip string `json:"ip"`
 }
 
-func ipJsonOutput (w http.ResponseWriter, r *http.Request) {
+func ipJsonOutput(w http.ResponseWriter, r *http.Request) {
 	var ip jsonOutput
 	ip.Ip = remoteAddr(r)
 	output, err := json.Marshal(ip)
 	w.Write([]byte(output))
 }
 
-func ipOutput (w http.ResponseWriter, r *http.Request) {
+func ipOutput(w http.ResponseWriter, r *http.Request) {
 	ip := remoteAddr(r)
 	w.Write([]byte(ip))
 }
 
-func remoteAddr ( r *http.Request) string {
+func remoteAddr(r *http.Request) string {
 	var ip string
 	if r.RemoteAddr[0] == '[' {
-		ip = strings.Split(r.RemoteAddr,"]")[0][1:]
+		ip = strings.Split(r.RemoteAddr, "]")[0][1:]
 	} else {
-		ip = strings.Split(r.RemoteAddr,":")[0]
+		ip = strings.Split(r.RemoteAddr, ":")[0]
 	}
 	return ip
 }
 
 func main() {
-	http.HandleFunc("/",ipOutput)
-	http.HandleFunc("/json",ipJsonOutput)
-	log.Fatal(http.ListenAndServe(":8080", nil))
+	addr := flag.String("addr", ":8080", "local ip:port to bind")
+	flag.Parse()
+	http.HandleFunc("/", ipOutput)
+	http.HandleFunc("/json", ipJsonOutput)
+	log.Fatal(http.ListenAndServe(*addr, nil))
 }