How to read virtual IP in linux using golang/net package - linux

Question

I am trying to read a particular interface and all the virtual IP in that interface.
Here is and example of the linux ifconfig -a | grep -A eth0
ifconfig -a | grep -A2 eth0
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 100.180.89.148 netmask 255.255.255.224 broadcast 100.180.89.140
inct6 fe80::ac16:2dff:fead:a321 prefixlen 64 scopeid 0x20<link>
--
eth0:1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 100.180.89.150 netmask 255.255.255.255 broadcast 100.180.89.150
ether cc:16:2d:ad:a3:20 txqueuelen 1000 (Ethernet)
--
eth0:2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 100.180.89.151 netmask 255.255.255.255 broadcast 100.180.89.151
ether ac:16:2d:ad:a3:20 txqueuelen 1000 (Ethernet)
--
eth0:3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 100.180.89.152 netmask 255.255.255.255 broadcast 100.180.89.152
ether ac:16:2d:ad:a3:20 txqueuelen 1000 (Ethernet)
I tried like this in go code:
// nwkIfName = eth0
func networkInterfaces(nwkIfName string) ([]Interfaces, error) {
ifaces, err := net.Interfaces()
if err != nil {
return nil, fmt.Errorf("failed to get network interfaces: %w", err)
}
for _, nwIf := range ifaces {
fmt.Println(nwIf.Name)
if nwIf.Name == nwkIfName {
fmt.Println(nwIf.Addrs())
}
}
return nil, nil
}
Output:
[100.180.89.148/27 100.180.89.150/32 100.180.89.151/32 100.180.89.152/32 fe80::ae16:2dff:fead:a320/64] <nil>
How can I read the IP address of eth0:2 ?
Thanks James

Answer 1

Call Interface.Addrs() to get the interface's addresses, and type-assert *net.IPNet from the addresses.
Use its IPNet.IP field to get just the IP address (of type net.IP), and its IP.To4() method if you need an IPv4 address.
for _, nwIf := range ifaces {
fmt.Println(nwIf.Name)
if nwIf.Name == nwkIfName {
fmt.Println(nwIf.Addrs())
addrs, err := nwIf.Addrs()
if err != nil {
return nil, fmt.Errorf(
"failed to get addresses of interface: %s, err: %w",
nwIf.Name, err,
)
}
for _, addr := range addrs {
if ipNet, ok := addr.(*net.IPNet); ok {
fmt.Println("\tIP:", ipNet.IP)
} else {
fmt.Println("\tnot IPNet:", addr)
}
}
}
}