Added method to close tun device

Throw error when trying to operate on closed tun device

source/app.d

@@ -11,6 +11,9 @@ void main()
 	while(true)
 	{
 		adapter.send([1,1,2,2,2,2]);
+		byte[] buffer;
+		adapter.receive(buffer);
+		writeln(buffer);
 		Thread.sleep(dur!("msecs")(500));
 	}
 	

source/libtun/adapter.d

@@ -7,18 +7,20 @@ import core.stdc.stdio;
 
 
 /**
-* TUN maintenance routines in `test.c`
+* TUN maintenance routines in `tunctl.c`
 */
 extern (C) int createTun(char* interfaceName, int iffFlags);
 extern (C) int destroyTun(int fd);
 extern (C) int tunWrite(int fd, char* data, int length);
+extern (C) int tunRead(int fd, char* data);
 
 public class TUNAdapter
 {
     /* Tunnel device descriptor */
     private int tunFD;
+    private bool isClosed;
 
-    this(string interfaceName)
+    this(string interfaceName, AdapterType adapterType = AdapterType.TAP)
     {
         init(interfaceName);
     }
@@ -32,13 +34,36 @@ public class TUNAdapter
         }
     }
 
-    public void receive(byte[] buffer)
+    private void sanityCheck()
     {
+        if(isClosed)
+        {
+            throw new TUNException("Cannot operate on closed tunnel device");
+        }
+    }
 
+    public void close()
+    {
+        sanityCheck();
+
+        isClosed = true;
+        destroyTun(tunFD);
+    }
+
+    public void receive(ref byte[] buffer)
+    {
+        sanityCheck();
+
+        /* TODO: Get amount read */
+        /* FIXME: For now set it length to 20 */
+        buffer.length = 400;
+        tunRead(tunFD, cast(char*)buffer.ptr);
     }
 
     public void send(byte[] buffer)
     {
+        sanityCheck();
+
         tunWrite(tunFD, cast(char*)buffer.ptr, cast(int)buffer.length);
     }
 }
@@ -49,4 +74,10 @@ public final class TUNException : Exception
     {
         super(msg);
     }
+}
+
+public enum AdapterType
+{
+    TUN,
+    TAP
 }

source/libtun/tunctl.c

@@ -54,3 +54,14 @@ int tunWrite(int fd, char* data, int length)
 {
     write(fd, data, length);
 }
+
+/**
+* TODO: Depending on mode we need to read a certain amount
+* to get the length and then from there move onwards
+*
+* (FIXME: For now we just read 20 bytes)
+*/
+int tunRead(int fd, char* data)
+{
+    read(fd, data, 400);
+}