Optimization: Minimize the number of times it is checked that no money is created

by individual transactions to 2 places (but call only once in each):

- ConnectBlock ( before calculated fees per txs twice )
- AcceptToMemoryPoolWorker ( before called CheckTxInputs 4 times and calculated
   fees per tx one extra time )

Also call tx.GetValueOut() only once per call of CheckTxInputs (instead of 2)

src/consensus/tx_verify.cpp

@@ -205,16 +205,15 @@ bool CheckTransaction(const CTransaction& tx, CValidationState &state, bool fChe
     return true;
 }
 
-bool Consensus::CheckTxInputs(const CTransaction& tx, CValidationState& state, const CCoinsViewCache& inputs, int nSpendHeight)
+bool Consensus::CheckTxInputs(const CTransaction& tx, CValidationState& state, const CCoinsViewCache& inputs, int nSpendHeight, CAmount& txfee)
 {
-    // This doesn't trigger the DoS code on purpose; if it did, it would make it easier
-    // for an attacker to attempt to split the network.
+    // are the actual inputs available?
     if (!inputs.HaveInputs(tx)) {
-        return state.Invalid(false, 0, "", "Inputs unavailable");
+        return state.DoS(100, false, REJECT_INVALID, "bad-txns-inputs-missingorspent", false,
+                         strprintf("%s: inputs missing/spent", __func__));
     }
 
     CAmount nValueIn = 0;
-    CAmount nFees = 0;
     for (unsigned int i = 0; i < tx.vin.size(); ++i) {
         const COutPoint &prevout = tx.vin[i].prevout;
         const Coin& coin = inputs.AccessCoin(prevout);
@@ -234,19 +233,18 @@ bool Consensus::CheckTxInputs(const CTransaction& tx, CValidationState& state, c
         }
     }
 
-    if (nValueIn < tx.GetValueOut()) {
+    const CAmount value_out = tx.GetValueOut();
+    if (nValueIn < value_out) {
         return state.DoS(100, false, REJECT_INVALID, "bad-txns-in-belowout", false,
-            strprintf("value in (%s) < value out (%s)", FormatMoney(nValueIn), FormatMoney(tx.GetValueOut())));
+            strprintf("value in (%s) < value out (%s)", FormatMoney(nValueIn), FormatMoney(value_out)));
     }
 
     // Tally transaction fees
-    CAmount nTxFee = nValueIn - tx.GetValueOut();
-    if (nTxFee < 0) {
-        return state.DoS(100, false, REJECT_INVALID, "bad-txns-fee-negative");
-    }
-    nFees += nTxFee;
-    if (!MoneyRange(nFees)) {
+    const CAmount txfee_aux = nValueIn - value_out;
+    if (!MoneyRange(txfee_aux)) {
         return state.DoS(100, false, REJECT_INVALID, "bad-txns-fee-outofrange");
     }
+
+    txfee = txfee_aux;
     return true;
 }

src/consensus/tx_verify.h

@@ -5,6 +5,8 @@
 #ifndef BITCOIN_CONSENSUS_TX_VERIFY_H
 #define BITCOIN_CONSENSUS_TX_VERIFY_H
 
+#include "amount.h"
+
 #include <stdint.h>
 #include <vector>
 
@@ -22,9 +24,10 @@ namespace Consensus {
 /**
  * Check whether all inputs of this transaction are valid (no double spends and amounts)
  * This does not modify the UTXO set. This does not check scripts and sigs.
+ * @param[out] txfee Set to the transaction fee if successful.
  * Preconditions: tx.IsCoinBase() is false.
  */
-bool CheckTxInputs(const CTransaction& tx, CValidationState& state, const CCoinsViewCache& inputs, int nSpendHeight);
+bool CheckTxInputs(const CTransaction& tx, CValidationState& state, const CCoinsViewCache& inputs, int nSpendHeight, CAmount& txfee);
 } // namespace Consensus
 
 /** Auxiliary functions for transaction validation (ideally should not be exposed) */

src/txmempool.cpp

@@ -625,7 +625,7 @@ void CTxMemPool::check(const CCoinsViewCache *pcoins) const
     uint64_t innerUsage = 0;
 
     CCoinsViewCache mempoolDuplicate(const_cast<CCoinsViewCache*>(pcoins));
-    const int64_t nSpendHeight = GetSpendHeight(mempoolDuplicate);
+    const int64_t spendheight = GetSpendHeight(mempoolDuplicate);
 
     LOCK(cs);
     std::list<const CTxMemPoolEntry*> waitingOnDependants;
@@ -705,8 +705,9 @@ void CTxMemPool::check(const CCoinsViewCache *pcoins) const
             waitingOnDependants.push_back(&(*it));
         else {
             CValidationState state;
+            CAmount txfee = 0;
             bool fCheckResult = tx.IsCoinBase() ||
-                Consensus::CheckTxInputs(tx, state, mempoolDuplicate, nSpendHeight);
+                Consensus::CheckTxInputs(tx, state, mempoolDuplicate, spendheight, txfee);
             assert(fCheckResult);
             UpdateCoins(tx, mempoolDuplicate, 1000000);
         }
@@ -721,8 +722,9 @@ void CTxMemPool::check(const CCoinsViewCache *pcoins) const
             stepsSinceLastRemove++;
             assert(stepsSinceLastRemove < waitingOnDependants.size());
         } else {
+            CAmount txfee = 0;
             bool fCheckResult = entry->GetTx().IsCoinBase() ||
-                Consensus::CheckTxInputs(entry->GetTx(), state, mempoolDuplicate, nSpendHeight);
+                Consensus::CheckTxInputs(entry->GetTx(), state, mempoolDuplicate, spendheight, txfee);
             assert(fCheckResult);
             UpdateCoins(entry->GetTx(), mempoolDuplicate, 1000000);
             stepsSinceLastRemove = 0;

src/validation.cpp

@@ -484,7 +484,6 @@ static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool
         CCoinsView dummy;
         CCoinsViewCache view(&dummy);
 
-        CAmount nValueIn = 0;
         LockPoints lp;
         {
         LOCK(pool.cs);
@@ -519,8 +518,6 @@ static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool
         // Bring the best block into scope
         view.GetBestBlock();
 
-        nValueIn = view.GetValueIn(tx);
-
         // we have all inputs cached now, so switch back to dummy, so we don't need to keep lock on mempool
         view.SetBackend(dummy);
 
@@ -531,6 +528,12 @@ static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool
         // CoinsViewCache instead of create its own
         if (!CheckSequenceLocks(tx, STANDARD_LOCKTIME_VERIFY_FLAGS, &lp))
             return state.DoS(0, false, REJECT_NONSTANDARD, "non-BIP68-final");
+
+        } // end LOCK(pool.cs)
+
+        CAmount nFees = 0;
+        if (!Consensus::CheckTxInputs(tx, state, view, GetSpendHeight(view), nFees)) {
+            return error("%s: Consensus::CheckTxInputs: %s, %s", __func__, tx.GetHash().ToString(), FormatStateMessage(state));
         }
 
         // Check for non-standard pay-to-script-hash in inputs
@@ -543,8 +546,6 @@ static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool
 
         int64_t nSigOpsCost = GetTransactionSigOpCost(tx, view, STANDARD_SCRIPT_VERIFY_FLAGS);
 
-        CAmount nValueOut = tx.GetValueOut();
-        CAmount nFees = nValueIn-nValueOut;
         // nModifiedFees includes any fee deltas from PrioritiseTransaction
         CAmount nModifiedFees = nFees;
         pool.ApplyDelta(hash, nModifiedFees);
@@ -1161,9 +1162,6 @@ static bool CheckInputs(const CTransaction& tx, CValidationState &state, const C
 {
     if (!tx.IsCoinBase())
     {
-        if (!Consensus::CheckTxInputs(tx, state, inputs, GetSpendHeight(inputs)))
-            return false;
-
         if (pvChecks)
             pvChecks->reserve(tx.vin.size());
 
@@ -1635,9 +1633,11 @@ static bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockInd
 
         if (!tx.IsCoinBase())
         {
-            if (!view.HaveInputs(tx))
-                return state.DoS(100, error("ConnectBlock(): inputs missing/spent"),
-                                 REJECT_INVALID, "bad-txns-inputs-missingorspent");
+            CAmount txfee = 0;
+            if (!Consensus::CheckTxInputs(tx, state, view, pindex->nHeight, txfee)) {
+                return error("%s: Consensus::CheckTxInputs: %s, %s", __func__, tx.GetHash().ToString(), FormatStateMessage(state));
+            }
+            nFees += txfee;
 
             // Check that transaction is BIP68 final
             // BIP68 lock checks (as opposed to nLockTime checks) must
@@ -1665,8 +1665,6 @@ static bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockInd
         txdata.emplace_back(tx);
         if (!tx.IsCoinBase())
         {
-            nFees += view.GetValueIn(tx)-tx.GetValueOut();
-
             std::vector<CScriptCheck> vChecks;
             bool fCacheResults = fJustCheck; /* Don't cache results if we're actually connecting blocks (still consult the cache, though) */
             if (!CheckInputs(tx, state, view, fScriptChecks, flags, fCacheResults, txdata[i], nScriptCheckThreads ? &vChecks : NULL))