From 1531652e02d856c1b8c3ba6f6e51e1983ac0540c Mon Sep 17 00:00:00 2001
From: Matt Corallo <git@bluematt.me>
Date: Mon, 9 Jan 2017 14:38:06 -0500
Subject: [PATCH] Keep shared_ptrs to recently-replaced txn for compact blocks

---
 src/init.cpp           |  1 +
 src/net_processing.cpp | 24 ++++++++++++++++++++++--
 src/net_processing.h   |  2 ++
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/init.cpp b/src/init.cpp
index 992ce8ebd..7a89fb887 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -346,6 +346,7 @@ std::string HelpMessage(HelpMessageMode mode)
     strUsage += HelpMessageOpt("-maxorphantx=<n>", strprintf(_("Keep at most <n> unconnectable transactions in memory (default: %u)"), DEFAULT_MAX_ORPHAN_TRANSACTIONS));
     strUsage += HelpMessageOpt("-maxmempool=<n>", strprintf(_("Keep the transaction memory pool below <n> megabytes (default: %u)"), DEFAULT_MAX_MEMPOOL_SIZE));
     strUsage += HelpMessageOpt("-mempoolexpiry=<n>", strprintf(_("Do not keep transactions in the mempool longer than <n> hours (default: %u)"), DEFAULT_MEMPOOL_EXPIRY));
+    strUsage += HelpMessageOpt("-blockreconstructionextratxn=<n>", strprintf(_("Extra transactions to keep in memory for compact block reconstructions (default: %u)"), DEFAULT_BLOCK_RECONSTRUCTION_EXTRA_TXN));
     strUsage += HelpMessageOpt("-par=<n>", strprintf(_("Set the number of script verification threads (%u to %d, 0 = auto, <0 = leave that many cores free, default: %d)"),
         -GetNumCores(), MAX_SCRIPTCHECK_THREADS, DEFAULT_SCRIPTCHECK_THREADS));
 #ifndef WIN32
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 3a956e89e..c549b9eb9 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -59,6 +59,9 @@ map<uint256, COrphanTx> mapOrphanTransactions GUARDED_BY(cs_main);
 map<COutPoint, set<map<uint256, COrphanTx>::iterator, IteratorComparator>> mapOrphanTransactionsByPrev GUARDED_BY(cs_main);
 void EraseOrphansFor(NodeId peer) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
+static size_t vExtraTxnForCompactIt = 0;
+static std::vector<std::pair<uint256, CTransactionRef>> vExtraTxnForCompact GUARDED_BY(cs_main);
+
 static const uint64_t RANDOMIZER_ID_ADDRESS_RELAY = 0x3cac0035b5866b90ULL; // SHA256("main address relay")[0:8]
 
 // Internal stuff
@@ -586,6 +589,17 @@ void UnregisterNodeSignals(CNodeSignals& nodeSignals)
 // mapOrphanTransactions
 //
 
+void AddToCompactExtraTransactions(const CTransactionRef& tx)
+{
+    size_t max_extra_txn = GetArg("-blockreconstructionextratxn", DEFAULT_BLOCK_RECONSTRUCTION_EXTRA_TXN);
+    if (max_extra_txn <= 0)
+        return;
+    if (!vExtraTxnForCompact.size())
+        vExtraTxnForCompact.resize(max_extra_txn);
+    vExtraTxnForCompact[vExtraTxnForCompactIt] = std::make_pair(tx->GetWitnessHash(), tx);
+    vExtraTxnForCompactIt = (vExtraTxnForCompactIt + 1) % max_extra_txn;
+}
+
 bool AddOrphanTx(const CTransactionRef& tx, NodeId peer) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 {
     const uint256& hash = tx->GetHash();
@@ -1615,7 +1629,9 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         pfrom->setAskFor.erase(inv.hash);
         mapAlreadyAskedFor.erase(inv.hash);
 
-        if (!AlreadyHave(inv) && AcceptToMemoryPool(mempool, state, ptx, true, &fMissingInputs)) {
+        std::list<CTransactionRef> lRemovedTxn;
+
+        if (!AlreadyHave(inv) && AcceptToMemoryPool(mempool, state, ptx, true, &fMissingInputs, &lRemovedTxn)) {
             mempool.check(pcoinsTip);
             RelayTransaction(tx, connman);
             for (unsigned int i = 0; i < tx.vout.size(); i++) {
@@ -1653,7 +1669,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
 
                     if (setMisbehaving.count(fromPeer))
                         continue;
-                    if (AcceptToMemoryPool(mempool, stateDummy, porphanTx, true, &fMissingInputs2)) {
+                    if (AcceptToMemoryPool(mempool, stateDummy, porphanTx, true, &fMissingInputs2, &lRemovedTxn)) {
                         LogPrint("mempool", "   accepted orphan tx %s\n", orphanHash.ToString());
                         RelayTransaction(orphanTx, connman);
                         for (unsigned int i = 0; i < orphanTx.vout.size(); i++) {
@@ -1743,6 +1759,10 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                 }
             }
         }
+
+        for (const CTransactionRef& tx : lRemovedTxn)
+            AddToCompactExtraTransactions(tx);
+
         int nDoS = 0;
         if (state.IsInvalid(nDoS))
         {
diff --git a/src/net_processing.h b/src/net_processing.h
index 92ea21df7..a338e14a9 100644
--- a/src/net_processing.h
+++ b/src/net_processing.h
@@ -15,6 +15,8 @@ static const unsigned int DEFAULT_MAX_ORPHAN_TRANSACTIONS = 100;
 static const int64_t ORPHAN_TX_EXPIRE_TIME = 20 * 60;
 /** Minimum time between orphan transactions expire time checks in seconds */
 static const int64_t ORPHAN_TX_EXPIRE_INTERVAL = 5 * 60;
+/** Default number of orphan+recently-replaced txn to keep around for block reconstruction */
+static const unsigned int DEFAULT_BLOCK_RECONSTRUCTION_EXTRA_TXN = 100;
 
 /** Register with a network node to receive its signals */
 void RegisterNodeSignals(CNodeSignals& nodeSignals);