fix PING attack [CVE-2019-17048]

src/txmempool.h

@@ -148,6 +148,10 @@ private:
     uint64_t totalTxSize = 0; //! sum of all mempool tx' byte sizes
     uint64_t cachedInnerUsage; //! sum of dynamic memory usage of all the map elements (NOT the maps themselves)
 
+    std::map<uint256, const CTransaction*> mapRecentlyAddedTx;
+    uint64_t nRecentlyAddedSequence = 0;
+    uint64_t nNotifiedSequence = 0;
+
     std::map<uint256, const CTransaction*> mapSproutNullifiers;
     std::map<uint256, const CTransaction*> mapSaplingNullifiers;
 
@@ -234,6 +238,9 @@ public:
 
     bool nullifierExists(const uint256& nullifier, ShieldedType type) const;
 
+    void NotifyRecentlyAdded();
+    bool IsFullyNotified();
+    
     unsigned long size()
     {
         LOCK(cs);