Expedite removal of tx requests that are no longer needed

Whenever a transaction is added to the mempool or orphan pool, both
its txid and wtxid are considered AlreadyHave, and thus will eventually
be removed from m_txrequest.

The same is true for hashes added to the reject filter, but note that sometimes
only the wtxid is added (in which case only the wtxid can be removed from
m_txrequest).

Author: sipa

src/net_processing.cpp

@@ -1185,7 +1185,8 @@ PeerManager::PeerManager(const CChainParams& chainparams, CConnman& connman, Ban
 
 /**
  * Evict orphan txn pool entries (EraseOrphanTx) based on a newly connected
- * block. Also save the time of the last tip update.
+ * block, remember the recently confirmed transactions, and delete tracked
+ * announcements for them. Also save the time of the last tip update.
  */
 void PeerManager::BlockConnected(const std::shared_ptr<const CBlock>& pblock, const CBlockIndex* pindex)
 {
@@ -1229,6 +1230,13 @@ void PeerManager::BlockConnected(const std::shared_ptr<const CBlock>& pblock, co
             }
         }
     }
+    {
+        LOCK(cs_main);
+        for (const auto& ptx : pblock->vtx) {
+            m_txrequest.ForgetTxHash(ptx->GetHash());
+            m_txrequest.ForgetTxHash(ptx->GetWitnessHash());
+        }
+    }
 }
 
 void PeerManager::BlockDisconnected(const std::shared_ptr<const CBlock> &block, const CBlockIndex* pindex)
@@ -2942,6 +2950,10 @@ void PeerManager::ProcessMessage(CNode& pfrom, const std::string& msg_type, CDat
         if (!AlreadyHaveTx(GenTxid(/* is_wtxid=*/true, wtxid), m_mempool) &&
             AcceptToMemoryPool(m_mempool, state, ptx, &lRemovedTxn, false /* bypass_limits */)) {
             m_mempool.check(&::ChainstateActive().CoinsTip());
+            // As this version of the transaction was acceptable, we can forget about any
+            // requests for it.
+            m_txrequest.ForgetTxHash(tx.GetHash());
+            m_txrequest.ForgetTxHash(tx.GetWitnessHash());
             RelayTransaction(tx.GetHash(), tx.GetWitnessHash(), m_connman);
             for (unsigned int i = 0; i < tx.vout.size(); i++) {
                 auto it_by_prev = mapOrphanTransactionsByPrev.find(COutPoint(txid, i));
@@ -3001,6 +3013,10 @@ void PeerManager::ProcessMessage(CNode& pfrom, const std::string& msg_type, CDat
                 }
                 AddOrphanTx(ptx, pfrom.GetId());
 
+                // Once added to the orphan pool, a tx is considered AlreadyHave, and we shouldn't request it anymore.
+                m_txrequest.ForgetTxHash(tx.GetHash());
+                m_txrequest.ForgetTxHash(tx.GetWitnessHash());
+
                 // DoS prevention: do not allow mapOrphanTransactions to grow unbounded (see CVE-2012-3789)
                 unsigned int nMaxOrphanTx = (unsigned int)std::max((int64_t)0, gArgs.GetArg("-maxorphantx", DEFAULT_MAX_ORPHAN_TRANSACTIONS));
                 unsigned int nEvicted = LimitOrphanTxSize(nMaxOrphanTx);
@@ -3017,6 +3033,8 @@ void PeerManager::ProcessMessage(CNode& pfrom, const std::string& msg_type, CDat
                 // from any of our non-wtxidrelay peers.
                 recentRejects->insert(tx.GetHash());
                 recentRejects->insert(tx.GetWitnessHash());
+                m_txrequest.ForgetTxHash(tx.GetHash());
+                m_txrequest.ForgetTxHash(tx.GetWitnessHash());
             }
         } else {
             if (state.GetResult() != TxValidationResult::TX_WITNESS_STRIPPED) {
@@ -3035,6 +3053,7 @@ void PeerManager::ProcessMessage(CNode& pfrom, const std::string& msg_type, CDat
                 // if we start doing this too early.
                 assert(recentRejects);
                 recentRejects->insert(tx.GetWitnessHash());
+                m_txrequest.ForgetTxHash(tx.GetWitnessHash());
                 // If the transaction failed for TX_INPUTS_NOT_STANDARD,
                 // then we know that the witness was irrelevant to the policy
                 // failure, since this check depends only on the txid
@@ -3045,6 +3064,7 @@ void PeerManager::ProcessMessage(CNode& pfrom, const std::string& msg_type, CDat
                 // parent-fetching by txid via the orphan-handling logic).
                 if (state.GetResult() == TxValidationResult::TX_INPUTS_NOT_STANDARD && tx.GetWitnessHash() != tx.GetHash()) {
                     recentRejects->insert(tx.GetHash());
+                    m_txrequest.ForgetTxHash(tx.GetHash());
                 }
                 if (RecursiveDynamicUsage(*ptx) < 100000) {
                     AddToCompactExtraTransactions(ptx);
@@ -4479,7 +4499,8 @@ bool PeerManager::SendMessages(CNode* pto)
                 }
                 m_txrequest.RequestedTx(pto->GetId(), gtxid.GetHash(), current_time + GETDATA_TX_INTERVAL);
             } else {
-                // We have already seen this transaction, no need to download.
+                // We have already seen this transaction, no need to download. This is just a belt-and-suspenders, as
+                // this should already be called whenever a transaction becomes AlreadyHaveTx().
                 m_txrequest.ForgetTxHash(gtxid.GetHash());
             }
         }