From eecffe50efc3944d713c701fa375dacbf17fb7cf Mon Sep 17 00:00:00 2001
From: Matt Corallo <git@bluematt.me>
Date: Tue, 1 Nov 2016 11:03:18 -0400
Subject: [PATCH] Remove redundant duplicate-input check from CheckTransaction

---
 src/main.cpp | 20 +++++++++++---------
 src/main.h   |  2 +-
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index 7e5b9528b..c8af01983 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1104,7 +1104,7 @@ int64_t GetTransactionSigOpCost(const CTransaction& tx, const CCoinsViewCache& i
 
 
 
-bool CheckTransaction(const CTransaction& tx, CValidationState &state)
+bool CheckTransaction(const CTransaction& tx, CValidationState &state, bool fCheckDuplicateInputs)
 {
     // Basic checks that don't depend on any context
     if (tx.vin.empty())
@@ -1128,13 +1128,15 @@ bool CheckTransaction(const CTransaction& tx, CValidationState &state)
             return state.DoS(100, false, REJECT_INVALID, "bad-txns-txouttotal-toolarge");
     }
 
-    // Check for duplicate inputs
-    set<COutPoint> vInOutPoints;
-    for (const auto& txin : tx.vin)
-    {
-        if (vInOutPoints.count(txin.prevout))
-            return state.DoS(100, false, REJECT_INVALID, "bad-txns-inputs-duplicate");
-        vInOutPoints.insert(txin.prevout);
+    // Check for duplicate inputs - note that this check is slow so we skip it in CheckBlock
+    if (fCheckDuplicateInputs) {
+        set<COutPoint> vInOutPoints;
+        for (const auto& txin : tx.vin)
+        {
+            if (vInOutPoints.count(txin.prevout))
+                return state.DoS(100, false, REJECT_INVALID, "bad-txns-inputs-duplicate");
+            vInOutPoints.insert(txin.prevout);
+        }
     }
 
     if (tx.IsCoinBase())
@@ -3461,7 +3463,7 @@ bool CheckBlock(const CBlock& block, CValidationState& state, const Consensus::P
 
     // Check transactions
     for (const auto& tx : block.vtx)
-        if (!CheckTransaction(tx, state))
+        if (!CheckTransaction(tx, state, false))
             return state.Invalid(false, state.GetRejectCode(), state.GetRejectReason(),
                                  strprintf("Transaction check failed (tx hash %s) %s", tx.GetHash().ToString(), state.GetDebugMessage()));
 
diff --git a/src/main.h b/src/main.h
index 934333058..21829b6c2 100644
--- a/src/main.h
+++ b/src/main.h
@@ -343,7 +343,7 @@ void UpdateCoins(const CTransaction& tx, CCoinsViewCache& inputs, int nHeight);
 /** Transaction validation functions */
 
 /** Context-independent validity checks */
-bool CheckTransaction(const CTransaction& tx, CValidationState& state);
+bool CheckTransaction(const CTransaction& tx, CValidationState& state, bool fCheckDuplicateInputs=true);
 
 namespace Consensus {