[doc] for CheckInputsFromMempoolAndCache

Author: glozow

src/validation.cpp

@@ -404,10 +404,16 @@ static void UpdateMempoolForReorg(CTxMemPool& mempool, DisconnectedBlockTransact
     LimitMempoolSize(mempool, gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000, std::chrono::hours{gArgs.GetArg("-mempoolexpiry", DEFAULT_MEMPOOL_EXPIRY)});
 }
 
-// Used to avoid mempool polluting consensus critical paths if CCoinsViewMempool
-// were somehow broken and returning the wrong scriptPubKeys
-static bool CheckInputsFromMempoolAndCache(const CTransaction& tx, TxValidationState& state, const CCoinsViewCache& view, const CTxMemPool& pool,
-                 unsigned int flags, PrecomputedTransactionData& txdata) EXCLUSIVE_LOCKS_REQUIRED(cs_main, pool.cs) {
+/**
+* Checks to avoid mempool polluting consensus critical paths since cached
+* signature and script validity results will be reused if we validate this
+* transaction again during block validation.
+* */
+static bool CheckInputsFromMempoolAndCache(const CTransaction& tx, TxValidationState& state,
+                const CCoinsViewCache& view, const CTxMemPool& pool,
+                unsigned int flags, PrecomputedTransactionData& txdata)
+                EXCLUSIVE_LOCKS_REQUIRED(cs_main, pool.cs)
+{
     AssertLockHeld(cs_main);
     AssertLockHeld(pool.cs);
 
@@ -420,16 +426,19 @@ static bool CheckInputsFromMempoolAndCache(const CTransaction& tx, TxValidationS
         Assume(!coin.IsSpent());
         if (coin.IsSpent()) return false;
 
-        // Check equivalence for available inputs.
+        // If the Coin is available, there are 2 possibilities:
+        // it is available in our current ChainstateActive UTXO set,
+        // or it's a UTXO provided by a transaction in our mempool.
+        // Ensure the scriptPubKeys in Coins from CoinsView are correct.
         const CTransactionRef& txFrom = pool.get(txin.prevout.hash);
         if (txFrom) {
             assert(txFrom->GetHash() == txin.prevout.hash);
             assert(txFrom->vout.size() > txin.prevout.n);
             assert(txFrom->vout[txin.prevout.n] == coin.out);
         } else {
-            const Coin& coinFromDisk = ::ChainstateActive().CoinsTip().AccessCoin(txin.prevout);
-            assert(!coinFromDisk.IsSpent());
-            assert(coinFromDisk.out == coin.out);
+            const Coin& coinFromUTXOSet = ::ChainstateActive().CoinsTip().AccessCoin(txin.prevout);
+            assert(!coinFromUTXOSet.IsSpent());
+            assert(coinFromUTXOSet.out == coin.out);
         }
     }