Uncache input txn in utxo cache if a tx is not accepted to mempool

Author: TheBlueMatt

src/main.cpp

@@ -835,8 +835,9 @@ std::string FormatStateMessage(const CValidationState &state)
         state.GetRejectCode());
 }
 
-bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransaction &tx, bool fLimitFree,
-                        bool* pfMissingInputs, bool fOverrideMempoolLimit, bool fRejectAbsurdFee)
+bool AcceptToMemoryPoolWorker(CTxMemPool& pool, CValidationState &state, const CTransaction &tx, bool fLimitFree,
+                              bool* pfMissingInputs, bool fOverrideMempoolLimit, bool fRejectAbsurdFee,
+                              std::vector<uint256>& vHashTxnToUncache)
 {
     AssertLockHeld(cs_main);
     if (pfMissingInputs)
@@ -917,13 +918,19 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
         view.SetBackend(viewMemPool);
 
         // do we already have it?
-        if (view.HaveCoins(hash))
+        bool fHadTxInCache = pcoinsTip->HaveCoinsInCache(hash);
+        if (view.HaveCoins(hash)) {
+            if (!fHadTxInCache)
+                vHashTxnToUncache.push_back(hash);
             return state.Invalid(false, REJECT_ALREADY_KNOWN, "txn-already-known");
+        }
 
         // do all inputs exist?
         // Note that this does not check for the presence of actual outputs (see the next check for that),
         // and only helps with filling in pfMissingInputs (to determine missing vs spent).
         BOOST_FOREACH(const CTxIn txin, tx.vin) {
+            if (!pcoinsTip->HaveCoinsInCache(txin.prevout.hash))
+                vHashTxnToUncache.push_back(txin.prevout.hash);
             if (!view.HaveCoins(txin.prevout.hash)) {
                 if (pfMissingInputs)
                     *pfMissingInputs = true;
@@ -1232,6 +1239,18 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
     return true;
 }
 
+bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransaction &tx, bool fLimitFree,
+                        bool* pfMissingInputs, bool fOverrideMempoolLimit, bool fRejectAbsurdFee)
+{
+    std::vector<uint256> vHashTxToUncache;
+    bool res = AcceptToMemoryPoolWorker(pool, state, tx, fLimitFree, pfMissingInputs, fOverrideMempoolLimit, fRejectAbsurdFee, vHashTxToUncache);
+    if (!res) {
+        BOOST_FOREACH(const uint256& hashTx, vHashTxToUncache)
+            pcoinsTip->Uncache(hashTx);
+    }
+    return res;
+}
+
 /** Return transaction in tx, and if it was found inside a block, its hash is placed in hashBlock */
 bool GetTransaction(const uint256 &hash, CTransaction &txOut, const Consensus::Params& consensusParams, uint256 &hashBlock, bool fAllowSlow)
 {