Add a new method to queue class for checking if a packet is going to be dropped

diff -r 31da0db925b6 src/node/drop-tail-queue.cc
--- a/src/node/drop-tail-queue.cc	Wed Jul 08 23:00:49 2009 +0800
+++ b/src/node/drop-tail-queue.cc	Thu Jul 09 21:25:49 2009 +0800
@@ -78,25 +78,38 @@
   NS_LOG_FUNCTION_NOARGS ();
   return m_mode;
 }
+
+bool 
+DropTailQueue::WillDrop (Ptr<Packet> p) const
+{
+  NS_LOG_FUNCTION (p);
+
+  if (m_mode == PACKETS && (m_packets.size () >= m_maxPackets))
+  {
+    NS_LOG_LOGIC ("Queue full (at max packets) -- droppping pkt");
+    return true;
+  }
+
+  if (m_mode == BYTES && (m_bytesInQueue + p->GetSize () >= m_maxBytes))
+  {
+    NS_LOG_LOGIC ("Queue full (packet would exceed max bytes) -- droppping pkt");
+    return true;
+  }
+
+  // the packet is not going to be dropped
+  return false;
+}
   
 bool 
 DropTailQueue::DoEnqueue (Ptr<Packet> p)
 {
   NS_LOG_FUNCTION (this << p);
 
-  if (m_mode == PACKETS && (m_packets.size () >= m_maxPackets))
-    {
-      NS_LOG_LOGIC ("Queue full (at max packets) -- droppping pkt");
-      Drop (p);
-      return false;
-    }
-
-  if (m_mode == BYTES && (m_bytesInQueue + p->GetSize () >= m_maxBytes))
-    {
-      NS_LOG_LOGIC ("Queue full (packet would exceed max bytes) -- droppping pkt");
-      Drop (p);
-      return false;
-    }
+  if (WillDrop (p)) 
+  {
+    Drop (p);
+    return false;
+  }
 
   m_bytesInQueue += p->GetSize ();
   m_packets.push(p);
diff -r 31da0db925b6 src/node/drop-tail-queue.h
--- a/src/node/drop-tail-queue.h	Wed Jul 08 23:00:49 2009 +0800
+++ b/src/node/drop-tail-queue.h	Thu Jul 09 21:25:49 2009 +0800
@@ -68,6 +68,10 @@
    * \returns The encapsulation mode of this device.
    */
   DropTailQueue::Mode  GetMode (void);
+  /**
+   * \see Queue::WillDrop ()
+   */
+  bool WillDrop (Ptr<Packet> p) const;
 
 private:
   virtual bool DoEnqueue (Ptr<Packet> p);
diff -r 31da0db925b6 src/node/queue.h
--- a/src/node/queue.h	Wed Jul 08 23:00:49 2009 +0800
+++ b/src/node/queue.h	Thu Jul 09 21:25:49 2009 +0800
@@ -60,6 +60,12 @@
    */
   bool Enqueue (Ptr<Packet> p);
   /**
+   * \brief Check if the packet is going to be dropped
+   * \param p The packet that is going to enqueue into a net device
+   * \return True of the packet is decided to be dropped, false otherwise
+   */
+  virtual bool WillDrop (Ptr<Packet> p) const = 0;
+  /**
    * Remove a packet from the front of the Queue
    * \return 0 if the operation was not successful; the packet otherwise.
    */