CValidationInterface, mempool: add new callback to `CValidationInterface`

This commit adds a new callback `MempoolTransactionsRemovedForBlock` which notify
its listeners of the transactions that are removed from the mempool because a new
block is connected, along with the block height the transactions were removed.
The transactions are in `RemovedMempoolTransactionInfo` format.

`CTransactionRef`, base fee, virtual size, and height which the transaction was added
to the mempool are all members of the struct called `RemovedMempoolTransactionInfo`.

A struct `NewMempoolTransactionInfo`, which has fields similar to `RemovedMempoolTransactionInfo`,
will be added in a later commit, create a struct `TransactionInfo` with all similar fields.
They can both have a member with type `TransactionInfo`.

1 files changed, 14 insertions, 3 deletions

diff --git a/src/validationinterface.h b/src/validationinterface.h
index eb15aa4d5f..ea49a45aa8 100644
--- a/src/validationinterface.h
+++ b/src/validationinterface.h
@@ -21,6 +21,7 @@ struct CBlockLocator;
 class CValidationInterface;
 class CScheduler;
 enum class MemPoolRemovalReason;
+struct RemovedMempoolTransactionInfo;
 
 /** Register subscriber */
 void RegisterValidationInterface(CValidationInterface* callbacks);
@@ -60,10 +61,10 @@ void CallFunctionInValidationInterfaceQueue(std::function<void ()> func);
 void SyncWithValidationInterfaceQueue() LOCKS_EXCLUDED(cs_main);
 
 /**
- * Implement this to subscribe to events generated in validation
+ * Implement this to subscribe to events generated in validation and mempool
  *
  * Each CValidationInterface() subscriber will receive event callbacks
- * in the order in which the events were generated by validation.
+ * in the order in which the events were generated by validation and mempool.
  * Furthermore, each ValidationInterface() subscriber may assume that
  * callbacks effectively run in a single thread with single-threaded
  * memory consistency. That is, for a given ValidationInterface()
@@ -113,7 +114,7 @@ protected:
      * This does not fire for transactions that are removed from the mempool
      * because they have been included in a block. Any client that is interested
      * in transactions removed from the mempool for inclusion in a block can learn
-     * about those transactions from the BlockConnected notification.
+     * about those transactions from the MempoolTransactionsRemovedForBlock notification.
      *
      * Transactions that are removed from the mempool because they conflict
      * with a transaction in the new block will have
@@ -131,6 +132,14 @@ protected:
      * Called on a background thread.
      */
     virtual void TransactionRemovedFromMempool(const CTransactionRef& tx, MemPoolRemovalReason reason, uint64_t mempool_sequence) {}
+    /*
+     * Notifies listeners of transactions removed from the mempool as
+     * as a result of new block being connected.
+     * MempoolTransactionsRemovedForBlock will be fired before BlockConnected.
+     *
+     * Called on a background thread.
+     */
+    virtual void MempoolTransactionsRemovedForBlock(const std::vector<RemovedMempoolTransactionInfo>& txs_removed_for_block, unsigned int nBlockHeight) {}
     /**
      * Notifies listeners of a block being connected.
      * Provides a vector of transactions evicted from the mempool as a result.
@@ -140,6 +149,7 @@ protected:
     virtual void BlockConnected(ChainstateRole role, const std::shared_ptr<const CBlock> &block, const CBlockIndex *pindex) {}
     /**
      * Notifies listeners of a block being disconnected
+     *  Provides the block that was connected.
      *
      * Called on a background thread. Only called for the active chainstate, since
      * background chainstates should never disconnect blocks.
@@ -202,6 +212,7 @@ public:
     void UpdatedBlockTip(const CBlockIndex *, const CBlockIndex *, bool fInitialDownload);
     void TransactionAddedToMempool(const CTransactionRef&, uint64_t mempool_sequence);
     void TransactionRemovedFromMempool(const CTransactionRef&, MemPoolRemovalReason, uint64_t mempool_sequence);
+    void MempoolTransactionsRemovedForBlock(const std::vector<RemovedMempoolTransactionInfo>&, unsigned int nBlockHeight);
     void BlockConnected(ChainstateRole, const std::shared_ptr<const CBlock> &, const CBlockIndex *pindex);
     void BlockDisconnected(const std::shared_ptr<const CBlock> &, const CBlockIndex* pindex);
     void ChainStateFlushed(ChainstateRole, const CBlockLocator &);