Number of fixes in response to code review

This version cannot complete a handshake.
The program will panic upon receiving any message on the UDP socket.

src/tun.go

@@ -6,10 +6,19 @@ package main
 
 const DefaultMTU = 1420
 
+type TUNEvent int
+
+const (
+	TUNEventUp = 1 << iota
+	TUNEventDown
+	TUNEventMTUUpdate
+)
+
 type TUNDevice interface {
 	Read([]byte) (int, error)  // read a packet from the device (without any additional headers)
 	Write([]byte) (int, error) // writes a packet to the device (without any additional headers)
-	IsUp() (bool, error)       // is the interface up?
 	MTU() (int, error)         // returns the MTU of the device
 	Name() string              // returns the current name
+	Events() chan TUNEvent     // returns a constant channel of events related to the device
+	Close() error              // stops the device and closes the event channel
 }