upnp protocol
====
A simple implements UPnP protocol for Golang library. Add port mapping for NAT devices.
在内网中搜索网关设备，检查网关是否支持upnp协议，若支持，添加端口映射。
====
example:
1. add a port mapping
mapping := new(upnp.Upnp)
if err := mapping.AddPortMapping(55789, 55789, "TCP"); err == nil {
fmt.Println("success !")
// remove port mapping in gatway
mapping.Reclaim()
} else {
fmt.Println("fail !")
}2. search gateway device.
upnpMan := new(upnp.Upnp)
err := upnpMan.SearchGateway()
if err != nil {
fmt.Println(err.Error())
} else {
fmt.Println("local ip address: ", upnpMan.LocalHost)
fmt.Println("gateway ip address: ", upnpMan.Gateway.Host)
}3. get an internet ip address in gatway.
upnpMan := new(upnp.Upnp)
err := upnpMan.ExternalIPAddr()
if err != nil {
fmt.Println(err.Error())
} else {
fmt.Println("internet ip address: ", upnpMan.GatewayOutsideIP)
}