tcp: Added callbacks for timings in TcpTxBuffer

When a SACK is received or when an item is discarded (the segment was fully
acked) then fire a callback with the modified item. This will help when we will
have some mechanism that will look for the timing of these actions.

src/internet/model/tcp-tx-buffer.cc

@@ -34,6 +34,7 @@ namespace ns3 {
 NS_LOG_COMPONENT_DEFINE ("TcpTxBuffer");
 NS_OBJECT_ENSURE_REGISTERED (TcpTxBuffer);
 
+Callback<void, TcpTxItem *> TcpTxBuffer::m_nullCb = MakeNullCallback<void, TcpTxItem*> ();
 TypeId
 TcpTxBuffer::GetTypeId (void)
 {
@@ -587,7 +588,7 @@ TcpTxBuffer::MergeItems (TcpTxItem *t1, TcpTxItem *t2) const
 
   // If one is retrans and the other is not, cancel the retransmitted flag.
   // We are merging this segment for the retransmit, so the count will
-  // be updated in GetTransmittedSegment.
+  // be updated in MarkTransmittedSegment.
   if (! AreEquals (t1->m_retrans, t2->m_retrans))
     {
       if (t1->m_retrans)
@@ -637,7 +638,8 @@ TcpTxBuffer::RemoveFromCounts (TcpTxItem *item, uint32_t size)
     }
 }
 void
-TcpTxBuffer::DiscardUpTo (const SequenceNumber32& seq)
+TcpTxBuffer::DiscardUpTo (const SequenceNumber32& seq,
+                          const Callback<void, TcpTxItem *> &beforeDelCb)
 {
   NS_LOG_FUNCTION (this << seq);
 
@@ -685,6 +687,13 @@ TcpTxBuffer::DiscardUpTo (const SequenceNumber32& seq)
           NS_LOG_INFO ("Removed " << *item << " lost: " << m_lostOut <<
                        " retrans: " << m_retrans << " sacked: " << m_sackedOut <<
                        ". Remaining data " << m_size);
+
+          if (!beforeDelCb.IsNull ())
+            {
+              // Inform Rate algorithms only when a full packet is ACKed
+              beforeDelCb (item);
+            }
+
           delete item;
         }
       else if (offset > 0)
@@ -747,7 +756,8 @@ TcpTxBuffer::DiscardUpTo (const SequenceNumber32& seq)
 }
 
 uint32_t
-TcpTxBuffer::Update (const TcpOptionSack::SackList &list)
+TcpTxBuffer::Update (const TcpOptionSack::SackList &list,
+                     const Callback<void, TcpTxItem *> &sackedCb)
 {
   NS_LOG_FUNCTION (this);
   NS_LOG_INFO ("Updating scoreboard, got " << list.size () << " blocks to analyze");
@@ -806,6 +816,11 @@ TcpTxBuffer::Update (const TcpOptionSack::SackList &list)
                                ", checking sentList for block " << *(*item_it) <<
                                ", found in the sackboard, sacking, current highSack: " <<
                                m_highestSack.second);
+
+                  if (!sackedCb.IsNull ())
+                    {
+                      sackedCb (*item_it);
+                    }
                 }
             }
           else if (beginOfCurrentPacket + pktSize > (*option_it).second)

src/internet/model/tcp-tx-buffer.h

@@ -261,15 +261,21 @@ public:
    *
    * \param seq The first sequence number to maintain after discarding all the
    * previous sequences.
+   * \param beforeDelCb Callback invoked, if it is not null, before the deletion
+   * of an Item (because it was, probably, ACKed)
    */
-  void DiscardUpTo (const SequenceNumber32& seq);
+  void DiscardUpTo (const SequenceNumber32& seq,
+                    const Callback<void, TcpTxItem *> &beforeDelCb = m_nullCb);
 
   /**
    * \brief Update the scoreboard
    * \param list list of SACKed blocks
+   * \param sackedCb Callback invoked, if it is not null, when a segment has been
+   * SACKed by the receiver.
    * \returns the number of bytes newly sacked by the list of blocks
    */
-  uint32_t Update (const TcpOptionSack::SackList &list);
+  uint32_t Update (const TcpOptionSack::SackList &list,
+                   const Callback<void, TcpTxItem *> &sackedCb = m_nullCb);
 
   /**
    * \brief Check if a segment is lost
@@ -585,6 +591,7 @@ private:
   uint32_t m_segmentSize {0}; //!< Segment size from TcpSocketBase
   bool     m_renoSack {false}; //!< Indicates if AddRenoSack was called
 
+  static Callback<void, TcpTxItem *> m_nullCb; //!< Null callback for an item
 };
 
 /**