MOVEONLY: CWallet transaction code out of wallet.cpp/.h

This commit just moves functions without making any changes. It can be
reviewed with `git log -p -n1 --color-moved=dimmed_zebra`

Motivation for this change is to make wallet.cpp/h less monolithic and
start to make wallet transaction state tracking comprehensible so bugs
in
https://github.com/bitcoin-core/bitcoin-devwiki/wiki/Wallet-Transaction-Conflict-Tracking
can be fixed safely without introducing new problems.

This commit moves wallet classes and methods that deal with transactions
out of wallet.cpp/.h into better organized files:

- transaction.cpp/.h - CWalletTx and CMerkleTx class definitions
- receive.cpp/.h - functions checking received transactions and computing balances
- spend.cpp/.h - functions creating transactions and finding spendable coins

After #20773, when loading is separated from syncing it will also be
possible to move more wallet.cpp/.h functions to:

- sync.cpp/.h - functions handling chain notifications and rescanning

This commit arranges receive.cpp and spend.cpp functions in dependency
order so it's possible to skim receive.cpp and get an idea of how
computing balances works, and skim spend.cpp and get an idea of how
transactions are created, without having to jump all over wallet.cpp
where functions are not in order and there is a lot of unrelated code.

Followup commit "refactor: Detach wallet transaction methods" in
https://github.com/bitcoin/bitcoin/pull/21206 follows up this PR and
tweaks function names and arguments to reflect new locations. The two
commits are split into separate PRs because this commit is more work to
maintain and less work to review, while the other commit is less work to
maintain and more work to review, so hopefully this commit can be merged
earlier.

1 files changed, 978 insertions, 0 deletions

diff --git a/src/wallet/spend.cpp b/src/wallet/spend.cpp
new file mode 100644
index 0000000000..97fc7acca5
--- /dev/null
+++ b/src/wallet/spend.cpp
@@ -0,0 +1,978 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <consensus/validation.h>
+#include <interfaces/chain.h>
+#include <policy/policy.h>
+#include <util/check.h>
+#include <util/fees.h>
+#include <util/moneystr.h>
+#include <util/rbf.h>
+#include <util/translation.h>
+#include <wallet/coincontrol.h>
+#include <wallet/fees.h>
+#include <wallet/receive.h>
+#include <wallet/spend.h>
+#include <wallet/transaction.h>
+#include <wallet/wallet.h>
+
+using interfaces::FoundBlock;
+
+static constexpr size_t OUTPUT_GROUP_MAX_ENTRIES{100};
+
+std::string COutput::ToString() const
+{
+    return strprintf("COutput(%s, %d, %d) [%s]", tx->GetHash().ToString(), i, nDepth, FormatMoney(tx->tx->vout[i].nValue));
+}
+
+int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* wallet, bool use_max_sig)
+{
+    CMutableTransaction txn;
+    txn.vin.push_back(CTxIn(COutPoint()));
+    if (!wallet->DummySignInput(txn.vin[0], txout, use_max_sig)) {
+        return -1;
+    }
+    return GetVirtualTransactionInputSize(txn.vin[0]);
+}
+
+// txouts needs to be in the order of tx.vin
+TxSize CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, const std::vector<CTxOut>& txouts, bool use_max_sig)
+{
+    CMutableTransaction txNew(tx);
+    if (!wallet->DummySignTx(txNew, txouts, use_max_sig)) {
+        return TxSize{-1, -1};
+    }
+    CTransaction ctx(txNew);
+    int64_t vsize = GetVirtualTransactionSize(ctx);
+    int64_t weight = GetTransactionWeight(ctx);
+    return TxSize{vsize, weight};
+}
+
+TxSize CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, bool use_max_sig)
+{
+    std::vector<CTxOut> txouts;
+    for (const CTxIn& input : tx.vin) {
+        const auto mi = wallet->mapWallet.find(input.prevout.hash);
+        // Can not estimate size without knowing the input details
+        if (mi == wallet->mapWallet.end()) {
+            return TxSize{-1, -1};
+        }
+        assert(input.prevout.n < mi->second.tx->vout.size());
+        txouts.emplace_back(mi->second.tx->vout[input.prevout.n]);
+    }
+    return CalculateMaximumSignedTxSize(tx, wallet, txouts, use_max_sig);
+}
+
+void CWallet::AvailableCoins(std::vector<COutput>& vCoins, const CCoinControl* coinControl, const CAmount& nMinimumAmount, const CAmount& nMaximumAmount, const CAmount& nMinimumSumAmount, const uint64_t nMaximumCount) const
+{
+    AssertLockHeld(cs_wallet);
+
+    vCoins.clear();
+    CAmount nTotal = 0;
+    // Either the WALLET_FLAG_AVOID_REUSE flag is not set (in which case we always allow), or we default to avoiding, and only in the case where
+    // a coin control object is provided, and has the avoid address reuse flag set to false, do we allow already used addresses
+    bool allow_used_addresses = !IsWalletFlagSet(WALLET_FLAG_AVOID_REUSE) || (coinControl && !coinControl->m_avoid_address_reuse);
+    const int min_depth = {coinControl ? coinControl->m_min_depth : DEFAULT_MIN_DEPTH};
+    const int max_depth = {coinControl ? coinControl->m_max_depth : DEFAULT_MAX_DEPTH};
+    const bool only_safe = {coinControl ? !coinControl->m_include_unsafe_inputs : true};
+
+    std::set<uint256> trusted_parents;
+    for (const auto& entry : mapWallet)
+    {
+        const uint256& wtxid = entry.first;
+        const CWalletTx& wtx = entry.second;
+
+        if (!chain().checkFinalTx(*wtx.tx)) {
+            continue;
+        }
+
+        if (wtx.IsImmatureCoinBase())
+            continue;
+
+        int nDepth = wtx.GetDepthInMainChain();
+        if (nDepth < 0)
+            continue;
+
+        // We should not consider coins which aren't at least in our mempool
+        // It's possible for these to be conflicted via ancestors which we may never be able to detect
+        if (nDepth == 0 && !wtx.InMempool())
+            continue;
+
+        bool safeTx = IsTrusted(wtx, trusted_parents);
+
+        // We should not consider coins from transactions that are replacing
+        // other transactions.
+        //
+        // Example: There is a transaction A which is replaced by bumpfee
+        // transaction B. In this case, we want to prevent creation of
+        // a transaction B' which spends an output of B.
+        //
+        // Reason: If transaction A were initially confirmed, transactions B
+        // and B' would no longer be valid, so the user would have to create
+        // a new transaction C to replace B'. However, in the case of a
+        // one-block reorg, transactions B' and C might BOTH be accepted,
+        // when the user only wanted one of them. Specifically, there could
+        // be a 1-block reorg away from the chain where transactions A and C
+        // were accepted to another chain where B, B', and C were all
+        // accepted.
+        if (nDepth == 0 && wtx.mapValue.count("replaces_txid")) {
+            safeTx = false;
+        }
+
+        // Similarly, we should not consider coins from transactions that
+        // have been replaced. In the example above, we would want to prevent
+        // creation of a transaction A' spending an output of A, because if
+        // transaction B were initially confirmed, conflicting with A and
+        // A', we wouldn't want to the user to create a transaction D
+        // intending to replace A', but potentially resulting in a scenario
+        // where A, A', and D could all be accepted (instead of just B and
+        // D, or just A and A' like the user would want).
+        if (nDepth == 0 && wtx.mapValue.count("replaced_by_txid")) {
+            safeTx = false;
+        }
+
+        if (only_safe && !safeTx) {
+            continue;
+        }
+
+        if (nDepth < min_depth || nDepth > max_depth) {
+            continue;
+        }
+
+        for (unsigned int i = 0; i < wtx.tx->vout.size(); i++) {
+            // Only consider selected coins if add_inputs is false
+            if (coinControl && !coinControl->m_add_inputs && !coinControl->IsSelected(COutPoint(entry.first, i))) {
+                continue;
+            }
+
+            if (wtx.tx->vout[i].nValue < nMinimumAmount || wtx.tx->vout[i].nValue > nMaximumAmount)
+                continue;
+
+            if (coinControl && coinControl->HasSelected() && !coinControl->fAllowOtherInputs && !coinControl->IsSelected(COutPoint(entry.first, i)))
+                continue;
+
+            if (IsLockedCoin(entry.first, i))
+                continue;
+
+            if (IsSpent(wtxid, i))
+                continue;
+
+            isminetype mine = IsMine(wtx.tx->vout[i]);
+
+            if (mine == ISMINE_NO) {
+                continue;
+            }
+
+            if (!allow_used_addresses && IsSpentKey(wtxid, i)) {
+                continue;
+            }
+
+            std::unique_ptr<SigningProvider> provider = GetSolvingProvider(wtx.tx->vout[i].scriptPubKey);
+
+            bool solvable = provider ? IsSolvable(*provider, wtx.tx->vout[i].scriptPubKey) : false;
+            bool spendable = ((mine & ISMINE_SPENDABLE) != ISMINE_NO) || (((mine & ISMINE_WATCH_ONLY) != ISMINE_NO) && (coinControl && coinControl->fAllowWatchOnly && solvable));
+
+            vCoins.push_back(COutput(&wtx, i, nDepth, spendable, solvable, safeTx, (coinControl && coinControl->fAllowWatchOnly)));
+
+            // Checks the sum amount of all UTXO's.
+            if (nMinimumSumAmount != MAX_MONEY) {
+                nTotal += wtx.tx->vout[i].nValue;
+
+                if (nTotal >= nMinimumSumAmount) {
+                    return;
+                }
+            }
+
+            // Checks the maximum number of UTXO's.
+            if (nMaximumCount > 0 && vCoins.size() >= nMaximumCount) {
+                return;
+            }
+        }
+    }
+}
+
+CAmount CWallet::GetAvailableBalance(const CCoinControl* coinControl) const
+{
+    LOCK(cs_wallet);
+
+    CAmount balance = 0;
+    std::vector<COutput> vCoins;
+    AvailableCoins(vCoins, coinControl);
+    for (const COutput& out : vCoins) {
+        if (out.fSpendable) {
+            balance += out.tx->tx->vout[out.i].nValue;
+        }
+    }
+    return balance;
+}
+
+const CTxOut& CWallet::FindNonChangeParentOutput(const CTransaction& tx, int output) const
+{
+    AssertLockHeld(cs_wallet);
+    const CTransaction* ptx = &tx;
+    int n = output;
+    while (IsChange(ptx->vout[n]) && ptx->vin.size() > 0) {
+        const COutPoint& prevout = ptx->vin[0].prevout;
+        auto it = mapWallet.find(prevout.hash);
+        if (it == mapWallet.end() || it->second.tx->vout.size() <= prevout.n ||
+            !IsMine(it->second.tx->vout[prevout.n])) {
+            break;
+        }
+        ptx = it->second.tx.get();
+        n = prevout.n;
+    }
+    return ptx->vout[n];
+}
+
+std::map<CTxDestination, std::vector<COutput>> CWallet::ListCoins() const
+{
+    AssertLockHeld(cs_wallet);
+
+    std::map<CTxDestination, std::vector<COutput>> result;
+    std::vector<COutput> availableCoins;
+
+    AvailableCoins(availableCoins);
+
+    for (const COutput& coin : availableCoins) {
+        CTxDestination address;
+        if ((coin.fSpendable || (IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS) && coin.fSolvable)) &&
+            ExtractDestination(FindNonChangeParentOutput(*coin.tx->tx, coin.i).scriptPubKey, address)) {
+            result[address].emplace_back(std::move(coin));
+        }
+    }
+
+    std::vector<COutPoint> lockedCoins;
+    ListLockedCoins(lockedCoins);
+    // Include watch-only for LegacyScriptPubKeyMan wallets without private keys
+    const bool include_watch_only = GetLegacyScriptPubKeyMan() && IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS);
+    const isminetype is_mine_filter = include_watch_only ? ISMINE_WATCH_ONLY : ISMINE_SPENDABLE;
+    for (const COutPoint& output : lockedCoins) {
+        auto it = mapWallet.find(output.hash);
+        if (it != mapWallet.end()) {
+            int depth = it->second.GetDepthInMainChain();
+            if (depth >= 0 && output.n < it->second.tx->vout.size() &&
+                IsMine(it->second.tx->vout[output.n]) == is_mine_filter
+            ) {
+                CTxDestination address;
+                if (ExtractDestination(FindNonChangeParentOutput(*it->second.tx, output.n).scriptPubKey, address)) {
+                    result[address].emplace_back(
+                        &it->second, output.n, depth, true /* spendable */, true /* solvable */, false /* safe */);
+                }
+            }
+        }
+    }
+
+    return result;
+}
+
+std::vector<OutputGroup> CWallet::GroupOutputs(const std::vector<COutput>& outputs, const CoinSelectionParams& coin_sel_params, const CoinEligibilityFilter& filter, bool positive_only) const
+{
+    std::vector<OutputGroup> groups_out;
+
+    if (!coin_sel_params.m_avoid_partial_spends) {
+        // Allowing partial spends  means no grouping. Each COutput gets its own OutputGroup.
+        for (const COutput& output : outputs) {
+            // Skip outputs we cannot spend
+            if (!output.fSpendable) continue;
+
+            size_t ancestors, descendants;
+            chain().getTransactionAncestry(output.tx->GetHash(), ancestors, descendants);
+            CInputCoin input_coin = output.GetInputCoin();
+
+            // Make an OutputGroup containing just this output
+            OutputGroup group{coin_sel_params};
+            group.Insert(input_coin, output.nDepth, output.tx->IsFromMe(ISMINE_ALL), ancestors, descendants, positive_only);
+
+            // Check the OutputGroup's eligibility. Only add the eligible ones.
+            if (positive_only && group.GetSelectionAmount() <= 0) continue;
+            if (group.m_outputs.size() > 0 && group.EligibleForSpending(filter)) groups_out.push_back(group);
+        }
+        return groups_out;
+    }
+
+    // We want to combine COutputs that have the same scriptPubKey into single OutputGroups
+    // except when there are more than OUTPUT_GROUP_MAX_ENTRIES COutputs grouped in an OutputGroup.
+    // To do this, we maintain a map where the key is the scriptPubKey and the value is a vector of OutputGroups.
+    // For each COutput, we check if the scriptPubKey is in the map, and if it is, the COutput's CInputCoin is added
+    // to the last OutputGroup in the vector for the scriptPubKey. When the last OutputGroup has
+    // OUTPUT_GROUP_MAX_ENTRIES CInputCoins, a new OutputGroup is added to the end of the vector.
+    std::map<CScript, std::vector<OutputGroup>> spk_to_groups_map;
+    for (const auto& output : outputs) {
+        // Skip outputs we cannot spend
+        if (!output.fSpendable) continue;
+
+        size_t ancestors, descendants;
+        chain().getTransactionAncestry(output.tx->GetHash(), ancestors, descendants);
+        CInputCoin input_coin = output.GetInputCoin();
+        CScript spk = input_coin.txout.scriptPubKey;
+
+        std::vector<OutputGroup>& groups = spk_to_groups_map[spk];
+
+        if (groups.size() == 0) {
+            // No OutputGroups for this scriptPubKey yet, add one
+            groups.emplace_back(coin_sel_params);
+        }
+
+        // Get the last OutputGroup in the vector so that we can add the CInputCoin to it
+        // A pointer is used here so that group can be reassigned later if it is full.
+        OutputGroup* group = &groups.back();
+
+        // Check if this OutputGroup is full. We limit to OUTPUT_GROUP_MAX_ENTRIES when using -avoidpartialspends
+        // to avoid surprising users with very high fees.
+        if (group->m_outputs.size() >= OUTPUT_GROUP_MAX_ENTRIES) {
+            // The last output group is full, add a new group to the vector and use that group for the insertion
+            groups.emplace_back(coin_sel_params);
+            group = &groups.back();
+        }
+
+        // Add the input_coin to group
+        group->Insert(input_coin, output.nDepth, output.tx->IsFromMe(ISMINE_ALL), ancestors, descendants, positive_only);
+    }
+
+    // Now we go through the entire map and pull out the OutputGroups
+    for (const auto& spk_and_groups_pair: spk_to_groups_map) {
+        const std::vector<OutputGroup>& groups_per_spk= spk_and_groups_pair.second;
+
+        // Go through the vector backwards. This allows for the first item we deal with being the partial group.
+        for (auto group_it = groups_per_spk.rbegin(); group_it != groups_per_spk.rend(); group_it++) {
+            const OutputGroup& group = *group_it;
+
+            // Don't include partial groups if there are full groups too and we don't want partial groups
+            if (group_it == groups_per_spk.rbegin() && groups_per_spk.size() > 1 && !filter.m_include_partial_groups) {
+                continue;
+            }
+
+            // Check the OutputGroup's eligibility. Only add the eligible ones.
+            if (positive_only && group.GetSelectionAmount() <= 0) continue;
+            if (group.m_outputs.size() > 0 && group.EligibleForSpending(filter)) groups_out.push_back(group);
+        }
+    }
+
+    return groups_out;
+}
+
+bool CWallet::SelectCoinsMinConf(const CAmount& nTargetValue, const CoinEligibilityFilter& eligibility_filter, std::vector<COutput> coins,
+                                 std::set<CInputCoin>& setCoinsRet, CAmount& nValueRet, const CoinSelectionParams& coin_selection_params) const
+{
+    setCoinsRet.clear();
+    nValueRet = 0;
+
+    // Note that unlike KnapsackSolver, we do not include the fee for creating a change output as BnB will not create a change output.
+    std::vector<OutputGroup> positive_groups = GroupOutputs(coins, coin_selection_params, eligibility_filter, true /* positive_only */);
+    if (SelectCoinsBnB(positive_groups, nTargetValue, coin_selection_params.m_cost_of_change, setCoinsRet, nValueRet)) {
+        return true;
+    }
+    // The knapsack solver has some legacy behavior where it will spend dust outputs. We retain this behavior, so don't filter for positive only here.
+    std::vector<OutputGroup> all_groups = GroupOutputs(coins, coin_selection_params, eligibility_filter, false /* positive_only */);
+    // While nTargetValue includes the transaction fees for non-input things, it does not include the fee for creating a change output.
+    // So we need to include that for KnapsackSolver as well, as we are expecting to create a change output.
+    return KnapsackSolver(nTargetValue + coin_selection_params.m_change_fee, all_groups, setCoinsRet, nValueRet);
+}
+
+bool CWallet::SelectCoins(const std::vector<COutput>& vAvailableCoins, const CAmount& nTargetValue, std::set<CInputCoin>& setCoinsRet, CAmount& nValueRet, const CCoinControl& coin_control, CoinSelectionParams& coin_selection_params) const
+{
+    std::vector<COutput> vCoins(vAvailableCoins);
+    CAmount value_to_select = nTargetValue;
+
+    // coin control -> return all selected outputs (we want all selected to go into the transaction for sure)
+    if (coin_control.HasSelected() && !coin_control.fAllowOtherInputs)
+    {
+        for (const COutput& out : vCoins)
+        {
+            if (!out.fSpendable)
+                 continue;
+            nValueRet += out.tx->tx->vout[out.i].nValue;
+            setCoinsRet.insert(out.GetInputCoin());
+        }
+        return (nValueRet >= nTargetValue);
+    }
+
+    // calculate value from preset inputs and store them
+    std::set<CInputCoin> setPresetCoins;
+    CAmount nValueFromPresetInputs = 0;
+
+    std::vector<COutPoint> vPresetInputs;
+    coin_control.ListSelected(vPresetInputs);
+    for (const COutPoint& outpoint : vPresetInputs)
+    {
+        std::map<uint256, CWalletTx>::const_iterator it = mapWallet.find(outpoint.hash);
+        if (it != mapWallet.end())
+        {
+            const CWalletTx& wtx = it->second;
+            // Clearly invalid input, fail
+            if (wtx.tx->vout.size() <= outpoint.n) {
+                return false;
+            }
+            // Just to calculate the marginal byte size
+            CInputCoin coin(wtx.tx, outpoint.n, wtx.GetSpendSize(outpoint.n, false));
+            nValueFromPresetInputs += coin.txout.nValue;
+            if (coin.m_input_bytes <= 0) {
+                return false; // Not solvable, can't estimate size for fee
+            }
+            coin.effective_value = coin.txout.nValue - coin_selection_params.m_effective_feerate.GetFee(coin.m_input_bytes);
+            if (coin_selection_params.m_subtract_fee_outputs) {
+                value_to_select -= coin.txout.nValue;
+            } else {
+                value_to_select -= coin.effective_value;
+            }
+            setPresetCoins.insert(coin);
+        } else {
+            return false; // TODO: Allow non-wallet inputs
+        }
+    }
+
+    // remove preset inputs from vCoins so that Coin Selection doesn't pick them.
+    for (std::vector<COutput>::iterator it = vCoins.begin(); it != vCoins.end() && coin_control.HasSelected();)
+    {
+        if (setPresetCoins.count(it->GetInputCoin()))
+            it = vCoins.erase(it);
+        else
+            ++it;
+    }
+
+    unsigned int limit_ancestor_count = 0;
+    unsigned int limit_descendant_count = 0;
+    chain().getPackageLimits(limit_ancestor_count, limit_descendant_count);
+    const size_t max_ancestors = (size_t)std::max<int64_t>(1, limit_ancestor_count);
+    const size_t max_descendants = (size_t)std::max<int64_t>(1, limit_descendant_count);
+    const bool fRejectLongChains = gArgs.GetBoolArg("-walletrejectlongchains", DEFAULT_WALLET_REJECT_LONG_CHAINS);
+
+    // form groups from remaining coins; note that preset coins will not
+    // automatically have their associated (same address) coins included
+    if (coin_control.m_avoid_partial_spends && vCoins.size() > OUTPUT_GROUP_MAX_ENTRIES) {
+        // Cases where we have 101+ outputs all pointing to the same destination may result in
+        // privacy leaks as they will potentially be deterministically sorted. We solve that by
+        // explicitly shuffling the outputs before processing
+        Shuffle(vCoins.begin(), vCoins.end(), FastRandomContext());
+    }
+
+    // Coin Selection attempts to select inputs from a pool of eligible UTXOs to fund the
+    // transaction at a target feerate. If an attempt fails, more attempts may be made using a more
+    // permissive CoinEligibilityFilter.
+    const bool res = [&] {
+        // Pre-selected inputs already cover the target amount.
+        if (value_to_select <= 0) return true;
+
+        // If possible, fund the transaction with confirmed UTXOs only. Prefer at least six
+        // confirmations on outputs received from other wallets and only spend confirmed change.
+        if (SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(1, 6, 0), vCoins, setCoinsRet, nValueRet, coin_selection_params)) return true;
+        if (SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(1, 1, 0), vCoins, setCoinsRet, nValueRet, coin_selection_params)) return true;
+
+        // Fall back to using zero confirmation change (but with as few ancestors in the mempool as
+        // possible) if we cannot fund the transaction otherwise.
+        if (m_spend_zero_conf_change) {
+            if (SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, 2), vCoins, setCoinsRet, nValueRet, coin_selection_params)) return true;
+            if (SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, std::min((size_t)4, max_ancestors/3), std::min((size_t)4, max_descendants/3)),
+                                   vCoins, setCoinsRet, nValueRet, coin_selection_params)) {
+                return true;
+            }
+            if (SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, max_ancestors/2, max_descendants/2),
+                                   vCoins, setCoinsRet, nValueRet, coin_selection_params)) {
+                return true;
+            }
+            // If partial groups are allowed, relax the requirement of spending OutputGroups (groups
+            // of UTXOs sent to the same address, which are obviously controlled by a single wallet)
+            // in their entirety.
+            if (SelectCoinsMinConf(value_to_select, CoinEligibilityFilter(0, 1, max_ancestors-1, max_descendants-1, true /* include_partial_groups */),
+                                   vCoins, setCoinsRet, nValueRet, coin_selection_params)) {
+                return true;
+            }
+            // Try with unsafe inputs if they are allowed. This may spend unconfirmed outputs
+            // received from other wallets.
+            if (coin_control.m_include_unsafe_inputs
+                && SelectCoinsMinConf(value_to_select,
+                    CoinEligibilityFilter(0 /* conf_mine */, 0 /* conf_theirs */, max_ancestors-1, max_descendants-1, true /* include_partial_groups */),
+                    vCoins, setCoinsRet, nValueRet, coin_selection_params)) {
+                return true;
+            }
+            // Try with unlimited ancestors/descendants. The transaction will still need to meet
+            // mempool ancestor/descendant policy to be accepted to mempool and broadcasted, but
+            // OutputGroups use heuristics that may overestimate ancestor/descendant counts.
+            if (!fRejectLongChains && SelectCoinsMinConf(value_to_select,
+                                      CoinEligibilityFilter(0, 1, std::numeric_limits<uint64_t>::max(), std::numeric_limits<uint64_t>::max(), true /* include_partial_groups */),
+                                      vCoins, setCoinsRet, nValueRet, coin_selection_params)) {
+                return true;
+            }
+        }
+        // Coin Selection failed.
+        return false;
+    }();
+
+    // SelectCoinsMinConf clears setCoinsRet, so add the preset inputs from coin_control to the coinset
+    util::insert(setCoinsRet, setPresetCoins);
+
+    // add preset inputs to the total value selected
+    nValueRet += nValueFromPresetInputs;
+
+    return res;
+}
+
+static bool IsCurrentForAntiFeeSniping(interfaces::Chain& chain, const uint256& block_hash)
+{
+    if (chain.isInitialBlockDownload()) {
+        return false;
+    }
+    constexpr int64_t MAX_ANTI_FEE_SNIPING_TIP_AGE = 8 * 60 * 60; // in seconds
+    int64_t block_time;
+    CHECK_NONFATAL(chain.findBlock(block_hash, FoundBlock().time(block_time)));
+    if (block_time < (GetTime() - MAX_ANTI_FEE_SNIPING_TIP_AGE)) {
+        return false;
+    }
+    return true;
+}
+
+/**
+ * Return a height-based locktime for new transactions (uses the height of the
+ * current chain tip unless we are not synced with the current chain
+ */
+static uint32_t GetLocktimeForNewTransaction(interfaces::Chain& chain, const uint256& block_hash, int block_height)
+{
+    uint32_t locktime;
+    // Discourage fee sniping.
+    //
+    // For a large miner the value of the transactions in the best block and
+    // the mempool can exceed the cost of deliberately attempting to mine two
+    // blocks to orphan the current best block. By setting nLockTime such that
+    // only the next block can include the transaction, we discourage this
+    // practice as the height restricted and limited blocksize gives miners
+    // considering fee sniping fewer options for pulling off this attack.
+    //
+    // A simple way to think about this is from the wallet's point of view we
+    // always want the blockchain to move forward. By setting nLockTime this
+    // way we're basically making the statement that we only want this
+    // transaction to appear in the next block; we don't want to potentially
+    // encourage reorgs by allowing transactions to appear at lower heights
+    // than the next block in forks of the best chain.
+    //
+    // Of course, the subsidy is high enough, and transaction volume low
+    // enough, that fee sniping isn't a problem yet, but by implementing a fix
+    // now we ensure code won't be written that makes assumptions about
+    // nLockTime that preclude a fix later.
+    if (IsCurrentForAntiFeeSniping(chain, block_hash)) {
+        locktime = block_height;
+
+        // Secondly occasionally randomly pick a nLockTime even further back, so
+        // that transactions that are delayed after signing for whatever reason,
+        // e.g. high-latency mix networks and some CoinJoin implementations, have
+        // better privacy.
+        if (GetRandInt(10) == 0)
+            locktime = std::max(0, (int)locktime - GetRandInt(100));
+    } else {
+        // If our chain is lagging behind, we can't discourage fee sniping nor help
+        // the privacy of high-latency transactions. To avoid leaking a potentially
+        // unique "nLockTime fingerprint", set nLockTime to a constant.
+        locktime = 0;
+    }
+    assert(locktime < LOCKTIME_THRESHOLD);
+    return locktime;
+}
+
+bool CWallet::CreateTransactionInternal(
+        const std::vector<CRecipient>& vecSend,
+        CTransactionRef& tx,
+        CAmount& nFeeRet,
+        int& nChangePosInOut,
+        bilingual_str& error,
+        const CCoinControl& coin_control,
+        FeeCalculation& fee_calc_out,
+        bool sign)
+{
+    CAmount nValue = 0;
+    const OutputType change_type = TransactionChangeType(coin_control.m_change_type ? *coin_control.m_change_type : m_default_change_type, vecSend);
+    ReserveDestination reservedest(this, change_type);
+    unsigned int nSubtractFeeFromAmount = 0;
+    for (const auto& recipient : vecSend)
+    {
+        if (nValue < 0 || recipient.nAmount < 0)
+        {
+            error = _("Transaction amounts must not be negative");
+            return false;
+        }
+        nValue += recipient.nAmount;
+
+        if (recipient.fSubtractFeeFromAmount)
+            nSubtractFeeFromAmount++;
+    }
+    if (vecSend.empty())
+    {
+        error = _("Transaction must have at least one recipient");
+        return false;
+    }
+
+    CMutableTransaction txNew;
+    FeeCalculation feeCalc;
+    TxSize tx_sizes;
+    int nBytes;
+    {
+        std::set<CInputCoin> setCoins;
+        LOCK(cs_wallet);
+        txNew.nLockTime = GetLocktimeForNewTransaction(chain(), GetLastBlockHash(), GetLastBlockHeight());
+        {
+            std::vector<COutput> vAvailableCoins;
+            AvailableCoins(vAvailableCoins, &coin_control, 1, MAX_MONEY, MAX_MONEY, 0);
+            CoinSelectionParams coin_selection_params; // Parameters for coin selection, init with dummy
+            coin_selection_params.m_avoid_partial_spends = coin_control.m_avoid_partial_spends;
+
+            // Create change script that will be used if we need change
+            // TODO: pass in scriptChange instead of reservedest so
+            // change transaction isn't always pay-to-bitcoin-address
+            CScript scriptChange;
+
+            // coin control: send change to custom address
+            if (!std::get_if<CNoDestination>(&coin_control.destChange)) {
+                scriptChange = GetScriptForDestination(coin_control.destChange);
+            } else { // no coin control: send change to newly generated address
+                // Note: We use a new key here to keep it from being obvious which side is the change.
+                //  The drawback is that by not reusing a previous key, the change may be lost if a
+                //  backup is restored, if the backup doesn't have the new private key for the change.
+                //  If we reused the old key, it would be possible to add code to look for and
+                //  rediscover unknown transactions that were written with keys of ours to recover
+                //  post-backup change.
+
+                // Reserve a new key pair from key pool. If it fails, provide a dummy
+                // destination in case we don't need change.
+                CTxDestination dest;
+                if (!reservedest.GetReservedDestination(dest, true)) {
+                    error = _("Transaction needs a change address, but we can't generate it. Please call keypoolrefill first.");
+                }
+                scriptChange = GetScriptForDestination(dest);
+                // A valid destination implies a change script (and
+                // vice-versa). An empty change script will abort later, if the
+                // change keypool ran out, but change is required.
+                CHECK_NONFATAL(IsValidDestination(dest) != scriptChange.empty());
+            }
+            CTxOut change_prototype_txout(0, scriptChange);
+            coin_selection_params.change_output_size = GetSerializeSize(change_prototype_txout);
+
+            // Get size of spending the change output
+            int change_spend_size = CalculateMaximumSignedInputSize(change_prototype_txout, this);
+            // If the wallet doesn't know how to sign change output, assume p2sh-p2wpkh
+            // as lower-bound to allow BnB to do it's thing
+            if (change_spend_size == -1) {
+                coin_selection_params.change_spend_size = DUMMY_NESTED_P2WPKH_INPUT_SIZE;
+            } else {
+                coin_selection_params.change_spend_size = (size_t)change_spend_size;
+            }
+
+            // Set discard feerate
+            coin_selection_params.m_discard_feerate = GetDiscardRate(*this);
+
+            // Get the fee rate to use effective values in coin selection
+            coin_selection_params.m_effective_feerate = GetMinimumFeeRate(*this, coin_control, &feeCalc);
+            // Do not, ever, assume that it's fine to change the fee rate if the user has explicitly
+            // provided one
+            if (coin_control.m_feerate && coin_selection_params.m_effective_feerate > *coin_control.m_feerate) {
+                error = strprintf(_("Fee rate (%s) is lower than the minimum fee rate setting (%s)"), coin_control.m_feerate->ToString(FeeEstimateMode::SAT_VB), coin_selection_params.m_effective_feerate.ToString(FeeEstimateMode::SAT_VB));
+                return false;
+            }
+            if (feeCalc.reason == FeeReason::FALLBACK && !m_allow_fallback_fee) {
+                // eventually allow a fallback fee
+                error = _("Fee estimation failed. Fallbackfee is disabled. Wait a few blocks or enable -fallbackfee.");
+                return false;
+            }
+
+            // Get long term estimate
+            CCoinControl cc_temp;
+            cc_temp.m_confirm_target = chain().estimateMaxBlocks();
+            coin_selection_params.m_long_term_feerate = GetMinimumFeeRate(*this, cc_temp, nullptr);
+
+            // Calculate the cost of change
+            // Cost of change is the cost of creating the change output + cost of spending the change output in the future.
+            // For creating the change output now, we use the effective feerate.
+            // For spending the change output in the future, we use the discard feerate for now.
+            // So cost of change = (change output size * effective feerate) + (size of spending change output * discard feerate)
+            coin_selection_params.m_change_fee = coin_selection_params.m_effective_feerate.GetFee(coin_selection_params.change_output_size);
+            coin_selection_params.m_cost_of_change = coin_selection_params.m_discard_feerate.GetFee(coin_selection_params.change_spend_size) + coin_selection_params.m_change_fee;
+
+            coin_selection_params.m_subtract_fee_outputs = nSubtractFeeFromAmount != 0; // If we are doing subtract fee from recipient, don't use effective values
+
+            // vouts to the payees
+            if (!coin_selection_params.m_subtract_fee_outputs) {
+                coin_selection_params.tx_noinputs_size = 11; // Static vsize overhead + outputs vsize. 4 nVersion, 4 nLocktime, 1 input count, 1 output count, 1 witness overhead (dummy, flag, stack size)
+            }
+            for (const auto& recipient : vecSend)
+            {
+                CTxOut txout(recipient.nAmount, recipient.scriptPubKey);
+
+                // Include the fee cost for outputs.
+                if (!coin_selection_params.m_subtract_fee_outputs) {
+                    coin_selection_params.tx_noinputs_size += ::GetSerializeSize(txout, PROTOCOL_VERSION);
+                }
+
+                if (IsDust(txout, chain().relayDustFee()))
+                {
+                    error = _("Transaction amount too small");
+                    return false;
+                }
+                txNew.vout.push_back(txout);
+            }
+
+            // Include the fees for things that aren't inputs, excluding the change output
+            const CAmount not_input_fees = coin_selection_params.m_effective_feerate.GetFee(coin_selection_params.tx_noinputs_size);
+            CAmount nValueToSelect = nValue + not_input_fees;
+
+            // Choose coins to use
+            CAmount inputs_sum = 0;
+            setCoins.clear();
+            if (!SelectCoins(vAvailableCoins, /* nTargetValue */ nValueToSelect, setCoins, inputs_sum, coin_control, coin_selection_params))
+            {
+                error = _("Insufficient funds");
+                return false;
+            }
+
+            // Always make a change output
+            // We will reduce the fee from this change output later, and remove the output if it is too small.
+            const CAmount change_and_fee = inputs_sum - nValue;
+            assert(change_and_fee >= 0);
+            CTxOut newTxOut(change_and_fee, scriptChange);
+
+            if (nChangePosInOut == -1)
+            {
+                // Insert change txn at random position:
+                nChangePosInOut = GetRandInt(txNew.vout.size()+1);
+            }
+            else if ((unsigned int)nChangePosInOut > txNew.vout.size())
+            {
+                error = _("Change index out of range");
+                return false;
+            }
+
+            assert(nChangePosInOut != -1);
+            auto change_position = txNew.vout.insert(txNew.vout.begin() + nChangePosInOut, newTxOut);
+
+            // Dummy fill vin for maximum size estimation
+            //
+            for (const auto& coin : setCoins) {
+                txNew.vin.push_back(CTxIn(coin.outpoint,CScript()));
+            }
+
+            // Calculate the transaction fee
+            tx_sizes = CalculateMaximumSignedTxSize(CTransaction(txNew), this, coin_control.fAllowWatchOnly);
+            nBytes = tx_sizes.vsize;
+            if (nBytes < 0) {
+                error = _("Signing transaction failed");
+                return false;
+            }
+            nFeeRet = coin_selection_params.m_effective_feerate.GetFee(nBytes);
+
+            // Subtract fee from the change output if not subtrating it from recipient outputs
+            CAmount fee_needed = nFeeRet;
+            if (nSubtractFeeFromAmount == 0) {
+                change_position->nValue -= fee_needed;
+            }
+
+            // We want to drop the change to fees if:
+            // 1. The change output would be dust
+            // 2. The change is within the (almost) exact match window, i.e. it is less than or equal to the cost of the change output (cost_of_change)
+            CAmount change_amount = change_position->nValue;
+            if (IsDust(*change_position, coin_selection_params.m_discard_feerate) || change_amount <= coin_selection_params.m_cost_of_change)
+            {
+                nChangePosInOut = -1;
+                change_amount = 0;
+                txNew.vout.erase(change_position);
+
+                // Because we have dropped this change, the tx size and required fee will be different, so let's recalculate those
+                tx_sizes = CalculateMaximumSignedTxSize(CTransaction(txNew), this, coin_control.fAllowWatchOnly);
+                nBytes = tx_sizes.vsize;
+                fee_needed = coin_selection_params.m_effective_feerate.GetFee(nBytes);
+            }
+
+            // Update nFeeRet in case fee_needed changed due to dropping the change output
+            if (fee_needed <= change_and_fee - change_amount) {
+                nFeeRet = change_and_fee - change_amount;
+            }
+
+            // Reduce output values for subtractFeeFromAmount
+            if (nSubtractFeeFromAmount != 0) {
+                CAmount to_reduce = fee_needed + change_amount - change_and_fee;
+                int i = 0;
+                bool fFirst = true;
+                for (const auto& recipient : vecSend)
+                {
+                    if (i == nChangePosInOut) {
+                        ++i;
+                    }
+                    CTxOut& txout = txNew.vout[i];
+
+                    if (recipient.fSubtractFeeFromAmount)
+                    {
+                        txout.nValue -= to_reduce / nSubtractFeeFromAmount; // Subtract fee equally from each selected recipient
+
+                        if (fFirst) // first receiver pays the remainder not divisible by output count
+                        {
+                            fFirst = false;
+                            txout.nValue -= to_reduce % nSubtractFeeFromAmount;
+                        }
+
+                        // Error if this output is reduced to be below dust
+                        if (IsDust(txout, chain().relayDustFee())) {
+                            if (txout.nValue < 0) {
+                                error = _("The transaction amount is too small to pay the fee");
+                            } else {
+                                error = _("The transaction amount is too small to send after the fee has been deducted");
+                            }
+                            return false;
+                        }
+                    }
+                    ++i;
+                }
+                nFeeRet = fee_needed;
+            }
+
+            // Give up if change keypool ran out and change is required
+            if (scriptChange.empty() && nChangePosInOut != -1) {
+                return false;
+            }
+        }
+
+        // Shuffle selected coins and fill in final vin
+        txNew.vin.clear();
+        std::vector<CInputCoin> selected_coins(setCoins.begin(), setCoins.end());
+        Shuffle(selected_coins.begin(), selected_coins.end(), FastRandomContext());
+
+        // Note how the sequence number is set to non-maxint so that
+        // the nLockTime set above actually works.
+        //
+        // BIP125 defines opt-in RBF as any nSequence < maxint-1, so
+        // we use the highest possible value in that range (maxint-2)
+        // to avoid conflicting with other possible uses of nSequence,
+        // and in the spirit of "smallest possible change from prior
+        // behavior."
+        const uint32_t nSequence = coin_control.m_signal_bip125_rbf.value_or(m_signal_rbf) ? MAX_BIP125_RBF_SEQUENCE : (CTxIn::SEQUENCE_FINAL - 1);
+        for (const auto& coin : selected_coins) {
+            txNew.vin.push_back(CTxIn(coin.outpoint, CScript(), nSequence));
+        }
+
+        if (sign && !SignTransaction(txNew)) {
+            error = _("Signing transaction failed");
+            return false;
+        }
+
+        // Return the constructed transaction data.
+        tx = MakeTransactionRef(std::move(txNew));
+
+        // Limit size
+        if ((sign && GetTransactionWeight(*tx) > MAX_STANDARD_TX_WEIGHT) ||
+            (!sign && tx_sizes.weight > MAX_STANDARD_TX_WEIGHT))
+        {
+            error = _("Transaction too large");
+            return false;
+        }
+    }
+
+    if (nFeeRet > m_default_max_tx_fee) {
+        error = TransactionErrorString(TransactionError::MAX_FEE_EXCEEDED);
+        return false;
+    }
+
+    if (gArgs.GetBoolArg("-walletrejectlongchains", DEFAULT_WALLET_REJECT_LONG_CHAINS)) {
+        // Lastly, ensure this tx will pass the mempool's chain limits
+        if (!chain().checkChainLimits(tx)) {
+            error = _("Transaction has too long of a mempool chain");
+            return false;
+        }
+    }
+
+    // Before we return success, we assume any change key will be used to prevent
+    // accidental re-use.
+    reservedest.KeepDestination();
+    fee_calc_out = feeCalc;
+
+    WalletLogPrintf("Fee Calculation: Fee:%d Bytes:%u Tgt:%d (requested %d) Reason:\"%s\" Decay %.5f: Estimation: (%g - %g) %.2f%% %.1f/(%.1f %d mem %.1f out) Fail: (%g - %g) %.2f%% %.1f/(%.1f %d mem %.1f out)\n",
+              nFeeRet, nBytes, feeCalc.returnedTarget, feeCalc.desiredTarget, StringForFeeReason(feeCalc.reason), feeCalc.est.decay,
+              feeCalc.est.pass.start, feeCalc.est.pass.end,
+              (feeCalc.est.pass.totalConfirmed + feeCalc.est.pass.inMempool + feeCalc.est.pass.leftMempool) > 0.0 ? 100 * feeCalc.est.pass.withinTarget / (feeCalc.est.pass.totalConfirmed + feeCalc.est.pass.inMempool + feeCalc.est.pass.leftMempool) : 0.0,
+              feeCalc.est.pass.withinTarget, feeCalc.est.pass.totalConfirmed, feeCalc.est.pass.inMempool, feeCalc.est.pass.leftMempool,
+              feeCalc.est.fail.start, feeCalc.est.fail.end,
+              (feeCalc.est.fail.totalConfirmed + feeCalc.est.fail.inMempool + feeCalc.est.fail.leftMempool) > 0.0 ? 100 * feeCalc.est.fail.withinTarget / (feeCalc.est.fail.totalConfirmed + feeCalc.est.fail.inMempool + feeCalc.est.fail.leftMempool) : 0.0,
+              feeCalc.est.fail.withinTarget, feeCalc.est.fail.totalConfirmed, feeCalc.est.fail.inMempool, feeCalc.est.fail.leftMempool);
+    return true;
+}
+
+bool CWallet::CreateTransaction(
+        const std::vector<CRecipient>& vecSend,
+        CTransactionRef& tx,
+        CAmount& nFeeRet,
+        int& nChangePosInOut,
+        bilingual_str& error,
+        const CCoinControl& coin_control,
+        FeeCalculation& fee_calc_out,
+        bool sign)
+{
+    int nChangePosIn = nChangePosInOut;
+    Assert(!tx); // tx is an out-param. TODO change the return type from bool to tx (or nullptr)
+    bool res = CreateTransactionInternal(vecSend, tx, nFeeRet, nChangePosInOut, error, coin_control, fee_calc_out, sign);
+    // try with avoidpartialspends unless it's enabled already
+    if (res && nFeeRet > 0 /* 0 means non-functional fee rate estimation */ && m_max_aps_fee > -1 && !coin_control.m_avoid_partial_spends) {
+        CCoinControl tmp_cc = coin_control;
+        tmp_cc.m_avoid_partial_spends = true;
+        CAmount nFeeRet2;
+        CTransactionRef tx2;
+        int nChangePosInOut2 = nChangePosIn;
+        bilingual_str error2; // fired and forgotten; if an error occurs, we discard the results
+        if (CreateTransactionInternal(vecSend, tx2, nFeeRet2, nChangePosInOut2, error2, tmp_cc, fee_calc_out, sign)) {
+            // if fee of this alternative one is within the range of the max fee, we use this one
+            const bool use_aps = nFeeRet2 <= nFeeRet + m_max_aps_fee;
+            WalletLogPrintf("Fee non-grouped = %lld, grouped = %lld, using %s\n", nFeeRet, nFeeRet2, use_aps ? "grouped" : "non-grouped");
+            if (use_aps) {
+                tx = tx2;
+                nFeeRet = nFeeRet2;
+                nChangePosInOut = nChangePosInOut2;
+            }
+        }
+    }
+    return res;
+}
+
+bool CWallet::FundTransaction(CMutableTransaction& tx, CAmount& nFeeRet, int& nChangePosInOut, bilingual_str& error, bool lockUnspents, const std::set<int>& setSubtractFeeFromOutputs, CCoinControl coinControl)
+{
+    std::vector<CRecipient> vecSend;
+
+    // Turn the txout set into a CRecipient vector.
+    for (size_t idx = 0; idx < tx.vout.size(); idx++) {
+        const CTxOut& txOut = tx.vout[idx];
+        CRecipient recipient = {txOut.scriptPubKey, txOut.nValue, setSubtractFeeFromOutputs.count(idx) == 1};
+        vecSend.push_back(recipient);
+    }
+
+    coinControl.fAllowOtherInputs = true;
+
+    for (const CTxIn& txin : tx.vin) {
+        coinControl.Select(txin.prevout);
+    }
+
+    // Acquire the locks to prevent races to the new locked unspents between the
+    // CreateTransaction call and LockCoin calls (when lockUnspents is true).
+    LOCK(cs_wallet);
+
+    CTransactionRef tx_new;
+    FeeCalculation fee_calc_out;
+    if (!CreateTransaction(vecSend, tx_new, nFeeRet, nChangePosInOut, error, coinControl, fee_calc_out, false)) {
+        return false;
+    }
+
+    if (nChangePosInOut != -1) {
+        tx.vout.insert(tx.vout.begin() + nChangePosInOut, tx_new->vout[nChangePosInOut]);
+    }
+
+    // Copy output sizes from new transaction; they may have had the fee
+    // subtracted from them.
+    for (unsigned int idx = 0; idx < tx.vout.size(); idx++) {
+        tx.vout[idx].nValue = tx_new->vout[idx].nValue;
+    }
+
+    // Add new txins while keeping original txin scriptSig/order.
+    for (const CTxIn& txin : tx_new->vin) {
+        if (!coinControl.IsSelected(txin.prevout)) {
+            tx.vin.push_back(txin);
+
+        }
+        if (lockUnspents) {
+            LockCoin(txin.prevout);
+        }
+
+    }
+
+    return true;
+}