running ip4 server on a Mac - go

Question

I'm using some code from Jan Newmarch's book on Go to run a daytime server on my mac. It uses this code
func main() {
service := ":1200"
tcpAddr, err := net.ResolveTCPAddr("ip4", service)
checkError(err)
listener, err := net.ListenTCP("tcp", tcpAddr)
checkError(err)
however, when I run it (on a Mac), I get this error
Fatal error: unknown network ip4
Is there anything other than ip4 that I can include in this code to avoid that error?
tcpAddr, err := net.ResolveTCPAddr("ip4", service)
Note, I also tried ip6 and got the same error.

Answer 1

According to the documentation for ResolveTCPAddr the only valid values for the net arg are "tcp", "tcp4" and "tcp6"
I suspect you're getting mixed up between ResolveTCPAddr and ResolveIPAddr

Answer 2

"ip4" isn't a valid network for ResolveTCPAddr (source).
Use ResolveIPAddr for resolving a general IP address.

Answer 3

"ip4" is not a valid string
See the Documentation for ResolveTCPAddr
ResolveTCPAddr parses addr as a TCP address of the form "host:port" or
"[ipv6-host%zone]:port" and resolves a pair of domain name and port
name on the network net, which must be "tcp", "tcp4" or "tcp6". A
literal address or host name for IPv6 must be enclosed in square
brackets, as in "[::1]:80", "[ipv6-host]:http" or
"[ipv6-host%zone]:80".
And the code:
func ResolveTCPAddr(net, addr string) (*TCPAddr, error) {
switch net {
case "tcp", "tcp4", "tcp6":
case "": // a hint wildcard for Go 1.0 undocumented behavior
net = "tcp"
default:
return nil, UnknownNetworkError(net)
}
a, err := resolveInternetAddr(net, addr, noDeadline)
if err != nil {
return nil, err
}
return a.toAddr().(*TCPAddr), nil
}