[golang] get specific network interface's IPv4 address

util.go

package util

import (
    "errors"
    "fmt"
    "net"
)

// useful links:
// https://stackoverflow.com/questions/27410764/dial-with-a-specific-address-interface-golang
// https://stackoverflow.com/questions/22751035/golang-distinguish-ipv4-ipv6
func GetInterfaceIpv4Addr(interfaceName string) (addr string, err error) {
    var (
        ief      *net.Interface
        addrs    []net.Addr
        ipv4Addr net.IP
    )
    if ief, err = net.InterfaceByName(interfaceName); err != nil { // get interface
        return
    }
    if addrs, err = ief.Addrs(); err != nil { // get addresses
        return
    }
    for _, addr := range addrs { // get ipv4 address
        if ipv4Addr = addr.(*net.IPNet).IP.To4(); ipv4Addr != nil {
            break
        }
    }
    if ipv4Addr == nil {
        return "", errors.New(fmt.Sprintf("interface %s don't have an ipv4 address\n", interfaceName))
    }
    return ipv4Addr.String(), nil
}