Add flags to specify server bind

main.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"flag"
 	"fmt"
+	"log"
 	"net"
 	"net/http"
 	_ "net/http/pprof"
@@ -23,6 +24,10 @@ type errorMessage struct {
 	Error string `json:error`
 }
 
+var (
+	listen_spec = flag.String("bind", "127.0.0.1:8086", "http server bind spec")
+)
+
 func responseWithError(resp http.ResponseWriter, statusCode int, message string) {
 	resp.Header().Set("Content-Type", "text/plain")
 	resp.WriteHeader(statusCode)
@@ -34,11 +39,11 @@ func responseWithJsonError(resp http.ResponseWriter, statusCode int, message str
 	body, err := json.Marshal(&errorMessage{
 		Error: message,
 	})
-	resp.Header().Set("Content-Length", strconv.Itoa(len(body)))
 	if err != nil {
 		// This should never happen
 		panic("json marshal failed, check code")
 	}
+	resp.Header().Set("Content-Length", strconv.Itoa(len(body)))
 	resp.WriteHeader(statusCode)
 	resp.Write(body)
 }
@@ -132,8 +137,10 @@ func main() {
 		resp.Header().Set("Content-Type", "text/plain")
 		resp.WriteHeader(http.StatusOK)
 		server := mapping.Get(ip)
+		log.Printf("%s => %s\n", ip, server)
 		fmt.Fprint(resp, server)
 	})
 	ipgeo.Init()
-	http.ListenAndServe("0.0.0.0:8086", nil)
+	log.Println("HTTP server is running on", *listen_spec)
+	http.ListenAndServe(*listen_spec, nil)
 }