cmd/cli: ignore un-usable interfaces on darwin

So multi interfaces config won't emit un-necessary errors if the network
cable adapters are not being used on MacOS.

cmd/cli/os_darwin.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"net"
 	"os/exec"
+	"strings"
 
 	"github.com/Control-D-Inc/ctrld/internal/resolvconffile"
 )
@@ -30,6 +31,18 @@ func deAllocateIP(ip string) error {
 	return nil
 }
 
+// setDnsIgnoreUnusableInterface likes setDNS, but return a nil error if the interface is not usable.
+func setDnsIgnoreUnusableInterface(iface *net.Interface, nameservers []string) error {
+	if err := setDNS(iface, nameservers); err != nil {
+		// TODO: investiate whether we can detect this without relying on error message.
+		if strings.Contains(err.Error(), " is not a recognized network service") {
+			return nil
+		}
+		return err
+	}
+	return nil
+}
+
 // set the dns server for the provided network interface
 // networksetup -setdnsservers Wi-Fi 8.8.8.8 1.1.1.1
 // TODO(cuonglm): use system API

cmd/cli/os_freebsd.go

@@ -29,6 +29,11 @@ func deAllocateIP(ip string) error {
 	return nil
 }
 
+// setDnsIgnoreUnusableInterface likes setDNS, but return a nil error if the interface is not usable.
+func setDnsIgnoreUnusableInterface(iface *net.Interface, nameservers []string) error {
+	return setDNS(iface, nameservers)
+}
+
 // set the dns server for the provided network interface
 func setDNS(iface *net.Interface, nameservers []string) error {
 	r, err := dns.NewOSConfigurator(logf, iface.Name)

cmd/cli/os_linux.go

@@ -45,7 +45,11 @@ func deAllocateIP(ip string) error {
 
 const maxSetDNSAttempts = 5
 
-// set the dns server for the provided network interface
+// setDnsIgnoreUnusableInterface likes setDNS, but return a nil error if the interface is not usable.
+func setDnsIgnoreUnusableInterface(iface *net.Interface, nameservers []string) error {
+	return setDNS(iface, nameservers)
+}
+
 func setDNS(iface *net.Interface, nameservers []string) error {
 	r, err := dns.NewOSConfigurator(logf, iface.Name)
 	if err != nil {

cmd/cli/os_windows.go

@@ -26,6 +26,12 @@ var (
 	resetDNSOnce sync.Once
 )
 
+// setDnsIgnoreUnusableInterface likes setDNS, but return a nil error if the interface is not usable.
+func setDnsIgnoreUnusableInterface(iface *net.Interface, nameservers []string) error {
+	return setDNS(iface, nameservers)
+}
+
+// setDNS sets the dns server for the provided network interface
 func setDNS(iface *net.Interface, nameservers []string) error {
 	if len(nameservers) == 0 {
 		return errors.New("empty DNS nameservers")

cmd/cli/prog.go

@@ -477,7 +477,7 @@ func (p *prog) setDNS() {
 	}
 	if allIfaces {
 		withEachPhysicalInterfaces(netIface.Name, "set DNS", func(i *net.Interface) error {
-			return setDNS(i, nameservers)
+			return setDnsIgnoreUnusableInterface(i, nameservers)
 		})
 	}
 }