Golang types in net package

I'm coding in golang some tools to make my life easier and I'm not understanding at all how the types in the net package works. This is part of my code:

import (
    "bufio"
    "fmt"
    "log"
    "net"
    "os"
)
type configFile struct {
	gateway, net             net.IP
	mask, port               int
	telnetUser, telnetPasswd string
}
var dataConfig configFile
func createConfigFile() {
	reader := bufio.NewReader(os.Stdin)    
	fmt.Println("Let's fill te config file for the application.")
	fmt.Println("Which is your gateway IP?")
	readGateway, err := reader.ReadString('\n')
	if err != nil {
		log.Fatal(err)
	}
	dataConfig.gateway = net.ParseIP(readGateway)
	if dataConfig.gateway == nil {
		log.Fatal("Problem here")
	} else {
		fmt.Println("Your gateway is: ", dataConfig.gateway.String())
	}
}

My problem is the next:

I want to read an IP address from the command line and storage it in the configFile object, which I will user later to create a .json file with all the configuration of my program.

When I read from the command line the IP address the readGateway variable storages it ok, that's expected, but when I try to make
dataConfig.gateway = net.ParseIP(readGateway)
and I try to cast the string object to a net.IP object I'm always getting a nill in the dataConfig.gateway field, so I'm not able to work with that parameter neither convert it to a string.

Could somebody help me?
Thanks in advance.

The documentation of net.ParseIP(s string) states that if the string s provided is not a valid textual representation of an IP address the function will return a nil value, so that must be the case.

Please log the string s before calling net.ParseIP so you can check if you are passing and reading it properly in the program.

bufio.Reader.ReadString's docs explain (emphasis mine)

> ReadString reads until the first occurrence of delim in the input,
> returning a string containing the data up to and including the
> delimiter

So readGateway ends up looking like "192.168.1.1\n". Your newline delimiter would not exist in a properly formatted IP address, which means when you parse it with net.ParseIP it's kicking it out as nil.

You can use strings.TrimRight to trim out the newline:

readGateway, err := reader.ReadString('\n')
if err != nil {
    log.Fatal(err)
}
readGateway = strings.TrimRight(readGateway, "\n")