Bug fix: validate scripts before utxo update to avoid missing referen…

…ced utxo

core/chain/blockchain.go

@@ -177,7 +177,6 @@ func (chain *BlockChain) ProcessBlock(block *types.Block, broadcast bool) (bool,
 		logger.Error(err)
 		return false, false, err
 	}
-
 	prevHash := block.Header.PrevBlockHash
 	if prevHashExists := chain.blockExists(prevHash); !prevHashExists {
 		// Orphan block.
@@ -350,6 +349,11 @@ func (chain *BlockChain) tryConnectBlockToMainChain(block *types.Block, utxoSet
 	// 	str := "the coinbase for the genesis block is not spendable"
 	// 	return ErrMissingTxOut
 	// }
+	// Validate scripts here before utxoSet is updated; otherwise it may fail mistakenly
+	if err := validateBlockScripts(utxoSet, block); err != nil {
+		return err
+	}
+
 	transactions := block.Txs
 	// Perform several checks on the inputs for each transaction.
 	// Also accumulate the total fees.
@@ -400,9 +404,6 @@ func (chain *BlockChain) tryConnectBlockToMainChain(block *types.Block, utxoSet
 		}
 	}
 
-	if err := validateBlockScripts(utxoSet, block); err != nil {
-		return err
-	}
 	chain.SetTailBlock(block, utxoSet)
 	// Notify others such as mempool.
 	chain.notifyBlockConnectionUpdate(block, true)

core/chain/validate.go

@@ -168,9 +168,12 @@ func ValidateTxScripts(utxoSet *UtxoSet, tx *types.Transaction) error {
 	for txInIdx, txIn := range tx.Vin {
 		// Ensure the referenced input transaction exists and is not spent.
 		utxo := utxoSet.FindUtxo(txIn.PrevOutPoint)
-		if utxo == nil || utxo.IsSpent {
-			logger.Errorf("output %v referenced from transaction %s:%d does not exist or"+
-				"has already been spent", txIn.PrevOutPoint, txHash, txInIdx)
+		if utxo == nil {
+			logger.Errorf("output %v referenced from transaction %s:%d does not exist", txIn.PrevOutPoint, txHash, txInIdx)
+			return core.ErrMissingTxOut
+		}
+		if utxo.IsSpent {
+			logger.Errorf("output %v referenced from transaction %s:%d has already been spent", txIn.PrevOutPoint, txHash, txInIdx)
 			return core.ErrMissingTxOut
 		}