Add logic to reject long chains to CreateTransaction.

src/wallet/wallet.cpp

@@ -278,6 +278,22 @@ unsigned int CTransparentTxout::GetDepthInMainChain() const {
     return wallet->mapWallet.at(GetHash()).GetDepthInMainChain();
 }
 
+unsigned int CTransparentTxout::GetDepthInMempool() const {
+    if (_isMockup)
+        return GetDepthInMainChain() ? 0 : 1;
+
+    assert(wallet);
+    AssertLockHeld(wallet->cs_wallet);
+    AssertLockHeld(mempool.cs);
+
+    auto entry = mempool.mapTx.find(GetHash());
+    if (entry == mempool.mapTx.end())
+        return 0;
+
+    uint64_t nAncestors = entry->GetCountWithAncestors();
+    return nAncestors;
+}
+
 const uint256 CMerkleTx::ABANDON_HASH(uint256S("0000000000000000000000000000000000000000000000000000000000000001"));
 
 /** @defgroup mapWallet
@@ -4321,7 +4337,7 @@ void CWallet::CheckTransparentTransactionSanity(CMutableTransaction& tx,
         throw std::runtime_error("txFee > maxTxFee. This is probably a bug.");
 
     bool fHasDataOut = false;
-    for (CTxOut& txout: tx.vout) {
+    for (const CTxOut& txout: tx.vout) {
         txnouttype whichType;
 
         if (!::IsStandard(txout.scriptPubKey, whichType, false))
@@ -4357,6 +4373,18 @@ void CWallet::CheckTransparentTransactionSanity(CMutableTransaction& tx,
     for (CTxOut& txout: tx.vout) totalOutputValue += txout.nValue;
     assert(totalInputValue == totalOutputValue + nFee);
     assert(totalInputValue > 0);
+
+    if (GetBoolArg("-walletrejectlongchains", DEFAULT_WALLET_REJECT_LONG_CHAINS)) {
+        // We should probably not make these transactions in the first place, but throwing this exception instead is the
+        // backwards compatible behaviour.
+        size_t nTotalMempoolAncestors = 0;
+
+        for (const CTransparentTxout& txin: vInputTxs)
+            nTotalMempoolAncestors += txin.GetDepthInMempool();
+
+        if (nTotalMempoolAncestors >= GetArg("-limitancestorcount", DEFAULT_ANCESTOR_LIMIT))
+            throw std::runtime_error("mempool chain");
+    }
 }
 
 // Create a transaction to vecSend, placing it in wtxNew. reservekey is the keypool. nFeeRet will be populated with the
@@ -4386,6 +4414,7 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend, CWalletT
                                 CAmount& nFeeRet, int& nChangePosInOut, std::string& strFailReason,
                                 const CCoinControl* coinControl, bool sign, int nExtraPayloadSize,
                                 bool fUseInstantSend, const std::vector<CTransparentTxout>& vTransparentTxouts) {
+    LOCK(mempool.cs);
     AssertLockHeld(cs_main);
 
     if (!coinControl || coinControl->destChange.which() == 0)

src/wallet/wallet.h

@@ -14,6 +14,7 @@
 #include "tinyformat.h"
 #include "ui_interface.h"
 #include "utilstrencodings.h"
+#include "validation.h"
 #include "validationinterface.h"
 #include "script/ismine.h"
 #include "script/sign.h"
@@ -668,6 +669,7 @@ class CTransparentTxout {
     bool IsCoinBase() const;
     bool IsFromMe() const;
     unsigned int GetDepthInMainChain() const;
+    unsigned int GetDepthInMempool() const;
 
 private:
     const CWallet* wallet = nullptr;
@@ -736,6 +738,9 @@ class CWallet : public CCryptoKeyStore, public CValidationInterface
         if (coinControl && coinControl->nCoinType == CoinType::WITH_MINTS)
             throw std::runtime_error("CoinType::WITH_MINTS is not supported for any transactions.");
 
+        unsigned int nMaxMempoolDepth = GetArg("-limitancestorcount", DEFAULT_ANCESTOR_LIMIT);
+        bool fRejectLongChains = GetBoolArg("-walletrejectlongchains", DEFAULT_WALLET_REJECT_LONG_CHAINS);
+
         for (const AbstractTxout& tx: vRelevantTransactions) {
             bool isSelected = coinControl && coinControl->HasSelected() && coinControl->IsSelected(tx.GetOutpoint());
 
@@ -754,6 +759,7 @@ class CWallet : public CCryptoKeyStore, public CValidationInterface
                 (!fUseInstantSend || !tx.IsLLMQInstantSendLocked()) &&
                 ((coinControl && !coinControl->fAllowUnconfirmed) || !tx.IsFromMe())
             ) continue;
+            if (fRejectLongChains && tx.GetDepthInMempool() + 1 >= nMaxMempoolDepth) continue;
 
             if (isSelected) vCoinControlInputs.push_back(tx);
             else vAvailableInputs.push_back(tx);
@@ -801,6 +807,7 @@ class CWallet : public CCryptoKeyStore, public CValidationInterface
         nCollectedRet = 0;
 
         size_t nMaxSize = coinControl && coinControl->nMaxSize ? coinControl->nMaxSize : (MAX_STANDARD_TX_WEIGHT / 4);
+        size_t nMaxAncestors = GetArg("-limitancestorcount", DEFAULT_ANCESTOR_LIMIT);
 
         if (nRequired < 0)
             throw std::runtime_error("Transaction amounts must be positive");