Packet

- Added `setTokenLength(ulong)` which returns `false` if the token length is above 15, else sets the token length (<=15) and returns `true`
- Added `setToken(ubyte[])` which sets the token (and length) and checks that the length is fine

Exceptions

- Added new exception time `CoapException`

source/doap/exceptions.d

@@ -0,0 +1,9 @@
+module doap.exceptions;
+
+public class CoapException : Exception
+{
+    this(string msg)
+    {
+        super(msg);
+    }
+}

source/doap/packet.d

@@ -2,6 +2,7 @@ module doap.packet;
 
 import doap.types : MessageType;
 import doap.codes : Code;
+import doap.exceptions : CoapException;
 
 /** 
  * Represents a CoAP packet
@@ -47,6 +48,31 @@ public class CoapPacket
         this.type = type;
     }
 
+    public void setToken(ubyte[] token)
+    {
+        if(setTokenLength(token.length))
+        {
+            this.token = token;
+        }
+        else
+        {
+            throw new CoapException("Token length above 15 bytes not allowed");
+        }
+    }
+
+    private bool setTokenLength(ulong tkl)
+    {
+        if(tkl > 15)
+        {
+            return false;
+        }
+        else
+        {
+            this.tokenLen = cast(ubyte)tkl;
+            return true;    
+        }
+    }
+
     // public ubyte getVersion()
     // {