system default nameserver in windows

pkg/config/config_unix.go

@@ -0,0 +1,19 @@
+// +build !windows
+
+package config
+
+import (
+	"github.com/miekg/dns"
+)
+
+//DefaultResolvConfPath specifies path to default resolv config file on UNIX.
+const DefaultResolvConfPath = "/etc/resolv.conf"
+
+func GetDefaultServers() ([]string, int, []string, error) {
+	// if no nameserver is provided, take it from `resolv.conf`
+	cfg, err := dns.ClientConfigFromFile(DefaultResolvConfPath)
+	if err != nil {
+		return nil, 0, nil, err
+	}
+	return cfg.Servers, cfg.Ndots, cfg.Search, nil
+}