addressing comments

Author: Yifan Gu

params_darwin.go

@@ -1,11 +1,14 @@
 package water
 
+// MacOSDriverProvider enumerates possible MacOS TUN/TAP implementations
+type MacOSDriverProvider int
+
 const (
-	// SystemDriver refers to the default P2P driver
-	SystemDriver = 0
-	// TunTapOSXDriver refers to the third-party tuntaposx driver
+	// MacOSDriverSystem refers to the default P2P driver
+	MacOSDriverSystem MacOSDriverProvider = 0
+	// MacOSDriverTunTapOSX refers to the third-party tuntaposx driver
 	// see https://sourceforge.net/p/tuntaposx
-	TunTapOSXDriver = 1
+	MacOSDriverTunTapOSX MacOSDriverProvider = 1
 )
 
 // PlatformSpecificParams defines parameters in Config that are specific to
@@ -19,7 +22,7 @@ type PlatformSpecificParams struct {
 	Name string
 	// Driver should be set if an alternative driver is desired
 	// e.g. TunTapOSXDriver
-	Driver int
+	Driver MacOSDriverProvider
 }
 
 func defaultPlatformSpecificParams() PlatformSpecificParams {

syscalls_darwin.go

@@ -61,11 +61,17 @@ type sockaddrCtl struct {
 var sockaddrCtlSize uintptr = 32
 
 func openDev(config Config) (ifce *Interface, err error) {
-	if config.Driver == TunTapOSXDriver {
+	if config.Driver == MacOSDriverTunTapOSX {
 		return openDevTunTapOSX(config)
-	} else if config.Driver != SystemDriver {
-		return nil, errors.New("unrecognized driver")
 	}
+	if config.Driver == MacOSDriverSystem {
+		return openDevSystem(config)
+	}
+	return nil, errors.New("unrecognized driver")
+}
+
+// openDevSystem opens tun device on system
+func openDevSystem(config Config) (ifce *Interface, err error) {
 	if config.DeviceType != TUN {
 		return nil, errors.New("only tun is implemented for SystemDriver, use TunTapOSXDriver for tap")
 	}
@@ -140,9 +146,11 @@ func openDevTunTapOSX(config Config) (ifce *Interface, err error) {
 
 	if config.DeviceType == TAP && !strings.HasPrefix(config.Name, "tap") {
 		return nil, errors.New("device name does not start with tap when creating a tap device")
-	} else if config.DeviceType == TUN && !strings.HasPrefix(config.Name, "tun") {
+	}
+	if config.DeviceType == TUN && !strings.HasPrefix(config.Name, "tun") {
 		return nil, errors.New("device name does not start with tun when creating a tun device")
-	} else if config.DeviceType != TAP && config.DeviceType != TUN {
+	}
+	if config.DeviceType != TAP && config.DeviceType != TUN {
 		return nil, errors.New("unsupported DeviceType")
 	}
 	if len(config.Name) >= 15 {