Setting a value in structure fails - http

Question

I set the value in the structure, but it is not set. The methods are called consequently, not in parallel. How can that be? This is golang, forgot to say.
If I change the code to set value in the "start" method (instead of "init" method), it works; but setting value in "init" method fails. Looks very strange to me.
package main
import (
"log"
"net/http"
"time"
)
type tServer struct {
ipAddress string
port string
server http.Server
}
var server tServer
func main() {
server.ipAddress = "0.0.0.0"
server.port = "12345"
server.init()
server.start()
time.Sleep(time.Second * 5)
}
func (srv tServer) init() {
srv.server.Addr = srv.ipAddress + ":" + srv.port
log.Println("srv.server.Addr=", srv.server.Addr) ////////////////////
}
func (srv tServer) start() {
log.Println("srv.server.Addr=", srv.server.Addr) ////////////////////
go srv.startServerRoutine()
}
func (srv tServer) startServerRoutine() {
log.Println("Server started at", srv.server.Addr) //
err := srv.server.ListenAndServe()
if err != nil {
log.Println("Server Error:", err) //
return
}
}
Here is the console:
2017/04/18 19:43:07 srv.server.Addr= 0.0.0.0:12345
2017/04/18 19:43:07 srv.server.Addr=
2017/04/18 19:43:07 Server started at
2017/04/18 19:43:07 Server Error: listen tcp :80: bind: permission denied

Answer 1

This is due to prototype of methods:
func (srv tServer) init()
// ^^^ copies values
so:
server.init() // updates its own copy of server,
// copy gets disposed after init() returns
server.start() // uses its own copy of server
You need to pass srv by pointer to methods:
func (srv *tServer) init()
in that case both init() and start() calls will work on the same copy of tServer structure and will share values in its fields.

Answer 2

If you look at the docs for http.Server you will see that a blank value is possible, and means ":http":
type Server struct {
Addr string // TCP address to listen on, ":http" if empty
You set srv.server.Addr directly in init(), but this is not the proper way to use the http.Server type.
Perhaps you meant to do this:
func (srv tServer) startServerRoutine() {
log.Println("Server started at", srv.ipAddress + ":" + srv.port) //
err := srv.server.ListenAndServe(srv.ipAddress + ":" + srv.port)
if err != nil {
log.Println("Server Error:", err) //
return
}
}