Merge #8498: Near-Bugfix: Optimization: Minimize the number of times it is checked that no money...

4e955c5 Near-Bugfix: Reestablish consensus check removed in 8d7849b (Jorge Timón)
3e8c916 Introduce CheckInputsAndUpdateCoins static wrapper in txmempool.cpp (Jorge Timón)
832e074 Optimization: Minimize the number of times it is checked that no money is created (Jorge Timón)
3f0ee3e Proper indentation for CheckTxInputs and other minor fixes (Jorge Timón)

Pull request description:

  ...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)

  For more motivation:

  ~~https://github.com/bitcoin/bitcoin/blob/master/src/main.cpp#L1493~~
  https://github.com/jtimon/bitcoin/compare/0.13-consensus-inputs...jtimon:0.13-consensus-inputs-comments

  EDIT: partially replaces #6445

  Near-Bugfix as pointed out in https://github.com/bitcoin/bitcoin/pull/8498#discussion_r124346132

Tree-SHA512: c71188e7c7c2425c9170ed7b803896755a92fd22f43b136eedaa6e554106696f0b10271d0ef0d0127c1eaafbc31d12eb19143df4f1b6882feecedf6ef05ea346

4 files changed, 69 insertions, 62 deletions

diff --git a/src/consensus/tx_verify.cpp b/src/consensus/tx_verify.cpp
index 0a71915d1d..70aa9d7006 100644
--- a/src/consensus/tx_verify.cpp
+++ b/src/consensus/tx_verify.cpp
@@ -13,7 +13,7 @@
 #include "chain.h"
 #include "coins.h"
 #include "utilmoneystr.h"
- 
+
 bool IsFinalTx(const CTransaction &tx, int nBlockHeight, int64_t nBlockTime)
 {
     if (tx.nLockTime == 0)
@@ -205,46 +205,46 @@ 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.
-        if (!inputs.HaveInputs(tx))
-            return state.Invalid(false, 0, "", "Inputs unavailable");
-
-        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);
-            assert(!coin.IsSpent());
-
-            // If prev is coinbase, check that it's matured
-            if (coin.IsCoinBase()) {
-                if (nSpendHeight - coin.nHeight < COINBASE_MATURITY)
-                    return state.Invalid(false,
-                        REJECT_INVALID, "bad-txns-premature-spend-of-coinbase",
-                        strprintf("tried to spend coinbase at depth %d", nSpendHeight - coin.nHeight));
-            }
-
-            // Check for negative or overflow input values
-            nValueIn += coin.out.nValue;
-            if (!MoneyRange(coin.out.nValue) || !MoneyRange(nValueIn))
-                return state.DoS(100, false, REJECT_INVALID, "bad-txns-inputvalues-outofrange");
+    // are the actual inputs available?
+    if (!inputs.HaveInputs(tx)) {
+        return state.DoS(100, false, REJECT_INVALID, "bad-txns-inputs-missingorspent", false,
+                         strprintf("%s: inputs missing/spent", __func__));
+    }
+
+    CAmount nValueIn = 0;
+    for (unsigned int i = 0; i < tx.vin.size(); ++i) {
+        const COutPoint &prevout = tx.vin[i].prevout;
+        const Coin& coin = inputs.AccessCoin(prevout);
+        assert(!coin.IsSpent());
+
+        // If prev is coinbase, check that it's matured
+        if (coin.IsCoinBase() && nSpendHeight - coin.nHeight < COINBASE_MATURITY) {
+            return state.Invalid(false,
+                REJECT_INVALID, "bad-txns-premature-spend-of-coinbase",
+                strprintf("tried to spend coinbase at depth %d", nSpendHeight - coin.nHeight));
+        }
 
+        // Check for negative or overflow input values
+        nValueIn += coin.out.nValue;
+        if (!MoneyRange(coin.out.nValue) || !MoneyRange(nValueIn)) {
+            return state.DoS(100, false, REJECT_INVALID, "bad-txns-inputvalues-outofrange");
         }
+    }
+
+    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(value_out)));
+    }
+
+    // Tally transaction fees
+    const CAmount txfee_aux = nValueIn - value_out;
+    if (!MoneyRange(txfee_aux)) {
+        return state.DoS(100, false, REJECT_INVALID, "bad-txns-fee-outofrange");
+    }
 
-        if (nValueIn < tx.GetValueOut())
-            return state.DoS(100, false, REJECT_INVALID, "bad-txns-in-belowout", false,
-                strprintf("value in (%s) < value out (%s)", FormatMoney(nValueIn), FormatMoney(tx.GetValueOut())));
-
-        // 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))
-            return state.DoS(100, false, REJECT_INVALID, "bad-txns-fee-outofrange");
+    txfee = txfee_aux;
     return true;
 }
diff --git a/src/consensus/tx_verify.h b/src/consensus/tx_verify.h
index d46d3294ca..288892462d 100644
--- a/src/consensus/tx_verify.h
+++ b/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) */
diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index 776d3f36ca..b0306811cb 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -607,6 +607,15 @@ void CTxMemPool::clear()
     _clear();
 }
 
+static void CheckInputsAndUpdateCoins(const CTransaction& tx, CCoinsViewCache& mempoolDuplicate, const int64_t spendheight)
+{
+    CValidationState state;
+    CAmount txfee = 0;
+    bool fCheckResult = tx.IsCoinBase() || Consensus::CheckTxInputs(tx, state, mempoolDuplicate, spendheight, txfee);
+    assert(fCheckResult);
+    UpdateCoins(tx, mempoolDuplicate, 1000000);
+}
+
 void CTxMemPool::check(const CCoinsViewCache *pcoins) const
 {
     if (nCheckFrequency == 0)
@@ -621,7 +630,7 @@ 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;
@@ -700,11 +709,7 @@ void CTxMemPool::check(const CCoinsViewCache *pcoins) const
         if (fDependsWait)
             waitingOnDependants.push_back(&(*it));
         else {
-            CValidationState state;
-            bool fCheckResult = tx.IsCoinBase() ||
-                Consensus::CheckTxInputs(tx, state, mempoolDuplicate, nSpendHeight);
-            assert(fCheckResult);
-            UpdateCoins(tx, mempoolDuplicate, 1000000);
+            CheckInputsAndUpdateCoins(tx, mempoolDuplicate, spendheight);
         }
     }
     unsigned int stepsSinceLastRemove = 0;
@@ -717,10 +722,7 @@ void CTxMemPool::check(const CCoinsViewCache *pcoins) const
             stepsSinceLastRemove++;
             assert(stepsSinceLastRemove < waitingOnDependants.size());
         } else {
-            bool fCheckResult = entry->GetTx().IsCoinBase() ||
-                Consensus::CheckTxInputs(entry->GetTx(), state, mempoolDuplicate, nSpendHeight);
-            assert(fCheckResult);
-            UpdateCoins(entry->GetTx(), mempoolDuplicate, 1000000);
+            CheckInputsAndUpdateCoins(entry->GetTx(), mempoolDuplicate, spendheight);
             stepsSinceLastRemove = 0;
         }
     }
diff --git a/src/validation.cpp b/src/validation.cpp
index e098de5d3d..a073e3d1c0 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -534,7 +534,6 @@ static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool
         CCoinsView dummy;
         CCoinsViewCache view(&dummy);
 
-        CAmount nValueIn = 0;
         LockPoints lp;
         {
         LOCK(pool.cs);
@@ -565,8 +564,6 @@ 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);
 
@@ -577,6 +574,12 @@ 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
@@ -589,8 +592,6 @@ 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);
@@ -1247,9 +1248,6 @@ bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsVi
 {
     if (!tx.IsCoinBase())
     {
-        if (!Consensus::CheckTxInputs(tx, state, inputs, GetSpendHeight(inputs)))
-            return false;
-
         if (pvChecks)
             pvChecks->reserve(tx.vin.size());
 
@@ -1762,9 +1760,15 @@ 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;
+            if (!MoneyRange(nFees)) {
+                return state.DoS(100, error("%s: accumulated fee in the block out of range.", __func__),
+                                 REJECT_INVALID, "bad-txns-accumulated-fee-outofrange");
+            }
 
             // Check that transaction is BIP68 final
             // BIP68 lock checks (as opposed to nLockTime checks) must
@@ -1792,8 +1796,6 @@ 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, fCacheResults, txdata[i], nScriptCheckThreads ? &vChecks : nullptr))