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spend.cpp
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// Copyright (c) 2021-2022 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 <algorithm>
#include <consensus/amount.h>
#include <consensus/validation.h>
#include <interfaces/chain.h>
#include <numeric>
#include <policy/policy.h>
#include <primitives/transaction.h>
#include <script/signingprovider.h>
#include <util/check.h>
#include <util/fees.h>
#include <util/moneystr.h>
#include <util/rbf.h>
#include <util/trace.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>
#include <cmath>
using interfaces::FoundBlock;
namespace wallet {
static constexpr size_t OUTPUT_GROUP_MAX_ENTRIES{100};
int CalculateMaximumSignedInputSize(const CTxOut& txout, const COutPoint outpoint, const SigningProvider* provider, const CCoinControl* coin_control)
{
CMutableTransaction txn;
txn.vin.push_back(CTxIn(outpoint));
if (!provider || !DummySignInput(*provider, txn.vin[0], txout, coin_control)) {
return -1;
}
return GetVirtualTransactionInputSize(txn.vin[0]);
}
int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* wallet, const CCoinControl* coin_control)
{
const std::unique_ptr<SigningProvider> provider = wallet->GetSolvingProvider(txout.scriptPubKey);
return CalculateMaximumSignedInputSize(txout, COutPoint(), provider.get(), coin_control);
}
// txouts needs to be in the order of tx.vin
TxSize CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, const std::vector<CTxOut>& txouts, const CCoinControl* coin_control)
{
CMutableTransaction txNew(tx);
if (!wallet->DummySignTx(txNew, txouts, coin_control)) {
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, const CCoinControl* coin_control)
{
std::vector<CTxOut> txouts;
// Look up the inputs. The inputs are either in the wallet, or in coin_control.
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()) {
assert(input.prevout.n < mi->second.tx->vout.size());
txouts.emplace_back(mi->second.tx->vout.at(input.prevout.n));
} else if (coin_control) {
CTxOut txout;
if (!coin_control->GetExternalOutput(input.prevout, txout)) {
return TxSize{-1, -1};
}
txouts.emplace_back(txout);
} else {
return TxSize{-1, -1};
}
}
return CalculateMaximumSignedTxSize(tx, wallet, txouts, coin_control);
}
size_t CoinsResult::Size() const
{
size_t size{0};
for (const auto& it : coins) {
size += it.second.size();
}
return size;
}
std::vector<COutput> CoinsResult::All() const
{
std::vector<COutput> all;
all.reserve(coins.size());
for (const auto& it : coins) {
all.insert(all.end(), it.second.begin(), it.second.end());
}
return all;
}
void CoinsResult::Clear() {
coins.clear();
}
void CoinsResult::Erase(const std::unordered_set<COutPoint, SaltedOutpointHasher>& coins_to_remove)
{
for (auto& [type, vec] : coins) {
auto remove_it = std::remove_if(vec.begin(), vec.end(), [&](const COutput& coin) {
// remove it if it's on the set
if (coins_to_remove.count(coin.outpoint) == 0) return false;
// update cached amounts
total_amount -= coin.txout.nValue;
if (coin.HasEffectiveValue()) total_effective_amount = *total_effective_amount - coin.GetEffectiveValue();
return true;
});
vec.erase(remove_it, vec.end());
}
}
void CoinsResult::Shuffle(FastRandomContext& rng_fast)
{
for (auto& it : coins) {
::Shuffle(it.second.begin(), it.second.end(), rng_fast);
}
}
void CoinsResult::Add(OutputType type, const COutput& out)
{
coins[type].emplace_back(out);
total_amount += out.txout.nValue;
if (out.HasEffectiveValue()) {
total_effective_amount = total_effective_amount.has_value() ?
*total_effective_amount + out.GetEffectiveValue() : out.GetEffectiveValue();
}
}
static OutputType GetOutputType(TxoutType type, bool is_from_p2sh)
{
switch (type) {
case TxoutType::WITNESS_V1_TAPROOT:
return OutputType::BECH32M;
case TxoutType::WITNESS_V0_KEYHASH:
case TxoutType::WITNESS_V0_SCRIPTHASH:
if (is_from_p2sh) return OutputType::P2SH_SEGWIT;
else return OutputType::BECH32;
case TxoutType::SCRIPTHASH:
case TxoutType::PUBKEYHASH:
return OutputType::LEGACY;
default:
return OutputType::UNKNOWN;
}
}
// Fetch and validate the coin control selected inputs.
// Coins could be internal (from the wallet) or external.
util::Result<PreSelectedInputs> FetchSelectedInputs(const CWallet& wallet, const CCoinControl& coin_control,
const CoinSelectionParams& coin_selection_params) EXCLUSIVE_LOCKS_REQUIRED(wallet.cs_wallet)
{
PreSelectedInputs result;
std::vector<COutPoint> vPresetInputs;
coin_control.ListSelected(vPresetInputs);
for (const COutPoint& outpoint : vPresetInputs) {
int input_bytes = -1;
CTxOut txout;
if (auto ptr_wtx = wallet.GetWalletTx(outpoint.hash)) {
// Clearly invalid input, fail
if (ptr_wtx->tx->vout.size() <= outpoint.n) {
return util::Error{strprintf(_("Invalid pre-selected input %s"), outpoint.ToString())};
}
txout = ptr_wtx->tx->vout.at(outpoint.n);
input_bytes = CalculateMaximumSignedInputSize(txout, &wallet, &coin_control);
} else {
// The input is external. We did not find the tx in mapWallet.
if (!coin_control.GetExternalOutput(outpoint, txout)) {
return util::Error{strprintf(_("Not found pre-selected input %s"), outpoint.ToString())};
}
}
if (input_bytes == -1) {
input_bytes = CalculateMaximumSignedInputSize(txout, outpoint, &coin_control.m_external_provider, &coin_control);
}
// If available, override calculated size with coin control specified size
if (coin_control.HasInputWeight(outpoint)) {
input_bytes = GetVirtualTransactionSize(coin_control.GetInputWeight(outpoint), 0, 0);
}
if (input_bytes == -1) {
return util::Error{strprintf(_("Not solvable pre-selected input %s"), outpoint.ToString())}; // Not solvable, can't estimate size for fee
}
/* Set some defaults for depth, spendable, solvable, safe, time, and from_me as these don't matter for preset inputs since no selection is being done. */
COutput output(outpoint, txout, /*depth=*/ 0, input_bytes, /*spendable=*/ true, /*solvable=*/ true, /*safe=*/ true, /*time=*/ 0, /*from_me=*/ false, coin_selection_params.m_effective_feerate);
result.Insert(output, coin_selection_params.m_subtract_fee_outputs);
}
return result;
}
CoinsResult AvailableCoins(const CWallet& wallet,
const CCoinControl* coinControl,
std::optional<CFeeRate> feerate,
const CoinFilterParams& params)
{
AssertLockHeld(wallet.cs_wallet);
CoinsResult result;
// 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 = !wallet.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 : wallet.mapWallet)
{
const uint256& wtxid = entry.first;
const CWalletTx& wtx = entry.second;
if (wallet.IsTxImmatureCoinBase(wtx) && !params.include_immature_coinbase)
continue;
int nDepth = wallet.GetTxDepthInMainChain(wtx);
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 = CachedTxIsTrusted(wallet, 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;
}
bool tx_from_me = CachedTxIsFromMe(wallet, wtx, ISMINE_ALL);
for (unsigned int i = 0; i < wtx.tx->vout.size(); i++) {
const CTxOut& output = wtx.tx->vout[i];
const COutPoint outpoint(wtxid, i);
if (output.nValue < params.min_amount || output.nValue > params.max_amount)
continue;
// Skip manually selected coins (the caller can fetch them directly)
if (coinControl && coinControl->HasSelected() && coinControl->IsSelected(outpoint))
continue;
if (wallet.IsLockedCoin(outpoint) && params.skip_locked)
continue;
if (wallet.IsSpent(outpoint))
continue;
isminetype mine = wallet.IsMine(output);
if (mine == ISMINE_NO) {
continue;
}
if (!allow_used_addresses && wallet.IsSpentKey(output.scriptPubKey)) {
continue;
}
std::unique_ptr<SigningProvider> provider = wallet.GetSolvingProvider(output.scriptPubKey);
int input_bytes = CalculateMaximumSignedInputSize(output, COutPoint(), provider.get(), coinControl);
// Because CalculateMaximumSignedInputSize just uses ProduceSignature and makes a dummy signature,
// it is safe to assume that this input is solvable if input_bytes is greater -1.
bool solvable = input_bytes > -1;
bool spendable = ((mine & ISMINE_SPENDABLE) != ISMINE_NO) || (((mine & ISMINE_WATCH_ONLY) != ISMINE_NO) && (coinControl && coinControl->fAllowWatchOnly && solvable));
// Filter by spendable outputs only
if (!spendable && params.only_spendable) continue;
// Obtain script type
std::vector<std::vector<uint8_t>> script_solutions;
TxoutType type = Solver(output.scriptPubKey, script_solutions);
// If the output is P2SH and solvable, we want to know if it is
// a P2SH (legacy) or one of P2SH-P2WPKH, P2SH-P2WSH (P2SH-Segwit). We can determine
// this from the redeemScript. If the output is not solvable, it will be classified
// as a P2SH (legacy), since we have no way of knowing otherwise without the redeemScript
bool is_from_p2sh{false};
if (type == TxoutType::SCRIPTHASH && solvable) {
CScript script;
if (!provider->GetCScript(CScriptID(uint160(script_solutions[0])), script)) continue;
type = Solver(script, script_solutions);
is_from_p2sh = true;
}
result.Add(GetOutputType(type, is_from_p2sh),
COutput(outpoint, output, nDepth, input_bytes, spendable, solvable, safeTx, wtx.GetTxTime(), tx_from_me, feerate));
// Checks the sum amount of all UTXO's.
if (params.min_sum_amount != MAX_MONEY) {
if (result.GetTotalAmount() >= params.min_sum_amount) {
return result;
}
}
// Checks the maximum number of UTXO's.
if (params.max_count > 0 && result.Size() >= params.max_count) {
return result;
}
}
}
return result;
}
CoinsResult AvailableCoinsListUnspent(const CWallet& wallet, const CCoinControl* coinControl, CoinFilterParams params)
{
params.only_spendable = false;
return AvailableCoins(wallet, coinControl, /*feerate=*/ std::nullopt, params);
}
CAmount GetAvailableBalance(const CWallet& wallet, const CCoinControl* coinControl)
{
LOCK(wallet.cs_wallet);
return AvailableCoins(wallet, coinControl).GetTotalAmount();
}
const CTxOut& FindNonChangeParentOutput(const CWallet& wallet, const COutPoint& outpoint)
{
AssertLockHeld(wallet.cs_wallet);
const CWalletTx* wtx{Assert(wallet.GetWalletTx(outpoint.hash))};
const CTransaction* ptx = wtx->tx.get();
int n = outpoint.n;
while (OutputIsChange(wallet, ptx->vout[n]) && ptx->vin.size() > 0) {
const COutPoint& prevout = ptx->vin[0].prevout;
const CWalletTx* it = wallet.GetWalletTx(prevout.hash);
if (!it || it->tx->vout.size() <= prevout.n ||
!wallet.IsMine(it->tx->vout[prevout.n])) {
break;
}
ptx = it->tx.get();
n = prevout.n;
}
return ptx->vout[n];
}
std::map<CTxDestination, std::vector<COutput>> ListCoins(const CWallet& wallet)
{
AssertLockHeld(wallet.cs_wallet);
std::map<CTxDestination, std::vector<COutput>> result;
CCoinControl coin_control;
// Include watch-only for LegacyScriptPubKeyMan wallets without private keys
coin_control.fAllowWatchOnly = wallet.GetLegacyScriptPubKeyMan() && wallet.IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS);
CoinFilterParams coins_params;
coins_params.only_spendable = false;
coins_params.skip_locked = false;
for (const COutput& coin : AvailableCoins(wallet, &coin_control, /*feerate=*/std::nullopt, coins_params).All()) {
CTxDestination address;
if ((coin.spendable || (wallet.IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS) && coin.solvable)) &&
ExtractDestination(FindNonChangeParentOutput(wallet, coin.outpoint).scriptPubKey, address)) {
result[address].emplace_back(coin);
}
}
return result;
}
std::vector<OutputGroup> GroupOutputs(const CWallet& wallet, const std::vector<COutput>& outputs, const CoinSelectionParams& coin_sel_params, const CoinEligibilityFilter& filter, bool positive_only)
{
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.spendable) continue;
size_t ancestors, descendants;
wallet.chain().getTransactionAncestry(output.outpoint.hash, ancestors, descendants);
// Make an OutputGroup containing just this output
OutputGroup group{coin_sel_params};
group.Insert(output, 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 is added
// to the last OutputGroup in the vector for the scriptPubKey. When the last OutputGroup has
// OUTPUT_GROUP_MAX_ENTRIES COutputs, 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.spendable) continue;
size_t ancestors, descendants;
wallet.chain().getTransactionAncestry(output.outpoint.hash, ancestors, descendants);
CScript spk = output.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 COutput 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 output to group
group->Insert(output, 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;
}
// Returns true if the result contains an error and the message is not empty
static bool HasErrorMsg(const util::Result<SelectionResult>& res) { return !util::ErrorString(res).empty(); }
util::Result<SelectionResult> AttemptSelection(const CWallet& wallet, const CAmount& nTargetValue, const CoinEligibilityFilter& eligibility_filter, const CoinsResult& available_coins,
const CoinSelectionParams& coin_selection_params, bool allow_mixed_output_types)
{
// Run coin selection on each OutputType and compute the Waste Metric
std::vector<SelectionResult> results;
for (const auto& it : available_coins.coins) {
auto result{ChooseSelectionResult(wallet, nTargetValue, eligibility_filter, it.second, coin_selection_params)};
// If any specific error message appears here, then something particularly wrong happened.
if (HasErrorMsg(result)) return result; // So let's return the specific error.
// Append the favorable result.
if (result) results.push_back(*result);
}
// If we have at least one solution for funding the transaction without mixing, choose the minimum one according to waste metric
// and return the result
if (results.size() > 0) return *std::min_element(results.begin(), results.end());
// If we can't fund the transaction from any individual OutputType, run coin selection one last time
// over all available coins, which would allow mixing.
// If TypesCount() <= 1, there is nothing to mix.
if (allow_mixed_output_types && available_coins.TypesCount() > 1) {
return ChooseSelectionResult(wallet, nTargetValue, eligibility_filter, available_coins.All(), coin_selection_params);
}
// Either mixing is not allowed and we couldn't find a solution from any single OutputType, or mixing was allowed and we still couldn't
// find a solution using all available coins
return util::Error();
};
util::Result<SelectionResult> ChooseSelectionResult(const CWallet& wallet, const CAmount& nTargetValue, const CoinEligibilityFilter& eligibility_filter, const std::vector<COutput>& available_coins, const CoinSelectionParams& coin_selection_params)
{
// Vector of results. We will choose the best one based on waste.
std::vector<SelectionResult> results;
std::vector<OutputGroup> positive_groups = GroupOutputs(wallet, available_coins, coin_selection_params, eligibility_filter, /*positive_only=*/true);
if (auto bnb_result{SelectCoinsBnB(positive_groups, nTargetValue, coin_selection_params.m_cost_of_change)}) {
results.push_back(*bnb_result);
}
// 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(wallet, available_coins, coin_selection_params, eligibility_filter, /*positive_only=*/false);
if (auto knapsack_result{KnapsackSolver(all_groups, nTargetValue, coin_selection_params.m_min_change_target, coin_selection_params.rng_fast)}) {
knapsack_result->ComputeAndSetWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee);
results.push_back(*knapsack_result);
}
if (auto srd_result{SelectCoinsSRD(positive_groups, nTargetValue, coin_selection_params.rng_fast)}) {
srd_result->ComputeAndSetWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee);
results.push_back(*srd_result);
}
if (results.empty()) {
// No solution found
return util::Error();
}
std::vector<SelectionResult> eligible_results;
std::copy_if(results.begin(), results.end(), std::back_inserter(eligible_results), [coin_selection_params](const SelectionResult& result) {
const auto initWeight{coin_selection_params.tx_noinputs_size * WITNESS_SCALE_FACTOR};
return initWeight + result.GetWeight() <= static_cast<int>(MAX_STANDARD_TX_WEIGHT);
});
if (eligible_results.empty()) {
return util::Error{_("The inputs size exceeds the maximum weight. "
"Please try sending a smaller amount or manually consolidating your wallet's UTXOs")};
}
// Choose the result with the least waste
// If the waste is the same, choose the one which spends more inputs.
auto& best_result = *std::min_element(eligible_results.begin(), eligible_results.end());
return best_result;
}
util::Result<SelectionResult> SelectCoins(const CWallet& wallet, CoinsResult& available_coins, const PreSelectedInputs& pre_set_inputs,
const CAmount& nTargetValue, const CCoinControl& coin_control,
const CoinSelectionParams& coin_selection_params)
{
// Deduct preset inputs amount from the search target
CAmount selection_target = nTargetValue - pre_set_inputs.total_amount;
// Return if automatic coin selection is disabled, and we don't cover the selection target
if (!coin_control.m_allow_other_inputs && selection_target > 0) {
return util::Error{_("The preselected coins total amount does not cover the transaction target. "
"Please allow other inputs to be automatically selected or include more coins manually")};
}
// Return if we can cover the target only with the preset inputs
if (selection_target <= 0) {
SelectionResult result(nTargetValue, SelectionAlgorithm::MANUAL);
result.AddInputs(pre_set_inputs.coins, coin_selection_params.m_subtract_fee_outputs);
result.ComputeAndSetWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee);
return result;
}
// Return early if we cannot cover the target with the wallet's UTXO.
// We use the total effective value if we are not subtracting fee from outputs and 'available_coins' contains the data.
CAmount available_coins_total_amount = coin_selection_params.m_subtract_fee_outputs ? available_coins.GetTotalAmount() :
(available_coins.GetEffectiveTotalAmount().has_value() ? *available_coins.GetEffectiveTotalAmount() : 0);
if (selection_target > available_coins_total_amount) {
return util::Error(); // Insufficient funds
}
// Start wallet Coin Selection procedure
auto op_selection_result = AutomaticCoinSelection(wallet, available_coins, selection_target, coin_control, coin_selection_params);
if (!op_selection_result) return op_selection_result;
// If needed, add preset inputs to the automatic coin selection result
if (!pre_set_inputs.coins.empty()) {
SelectionResult preselected(pre_set_inputs.total_amount, SelectionAlgorithm::MANUAL);
preselected.AddInputs(pre_set_inputs.coins, coin_selection_params.m_subtract_fee_outputs);
op_selection_result->Merge(preselected);
op_selection_result->ComputeAndSetWaste(coin_selection_params.min_viable_change,
coin_selection_params.m_cost_of_change,
coin_selection_params.m_change_fee);
}
return op_selection_result;
}
struct SelectionFilter {
CoinEligibilityFilter filter;
bool allow_mixed_output_types{true};
};
util::Result<SelectionResult> AutomaticCoinSelection(const CWallet& wallet, CoinsResult& available_coins, const CAmount& value_to_select, const CCoinControl& coin_control, const CoinSelectionParams& coin_selection_params)
{
unsigned int limit_ancestor_count = 0;
unsigned int limit_descendant_count = 0;
wallet.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 && available_coins.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
available_coins.Shuffle(coin_selection_params.rng_fast);
}
// 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.
util::Result<SelectionResult> res = [&] {
// Place coins eligibility filters on a scope increasing order.
std::vector<SelectionFilter> ordered_filters{
// 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.
{CoinEligibilityFilter(1, 6, 0), /*allow_mixed_output_types=*/false},
{CoinEligibilityFilter(1, 1, 0)},
};
// 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 (wallet.m_spend_zero_conf_change) {
ordered_filters.push_back({CoinEligibilityFilter(0, 1, 2)});
ordered_filters.push_back({CoinEligibilityFilter(0, 1, std::min(size_t{4}, max_ancestors/3), std::min(size_t{4}, max_descendants/3))});
ordered_filters.push_back({CoinEligibilityFilter(0, 1, max_ancestors/2, max_descendants/2)});
// 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.
ordered_filters.push_back({CoinEligibilityFilter(0, 1, max_ancestors-1, max_descendants-1, /*include_partial=*/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) {
ordered_filters.push_back({CoinEligibilityFilter(/*conf_mine=*/0, /*conf_theirs*/0, max_ancestors-1, max_descendants-1, /*include_partial=*/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) {
ordered_filters.push_back({CoinEligibilityFilter(0, 1, std::numeric_limits<uint64_t>::max(),
std::numeric_limits<uint64_t>::max(),
/*include_partial=*/true)});
}
}
// Walk-through the filters until the solution gets found.
// If no solution is found, return the first detailed error (if any).
// future: add "error level" so the worst one can be picked instead.
std::vector<util::Result<SelectionResult>> res_detailed_errors;
for (const auto& select_filter : ordered_filters) {
if (auto res{AttemptSelection(wallet, value_to_select, select_filter.filter, available_coins,
coin_selection_params, select_filter.allow_mixed_output_types)}) {
return res; // result found
} else {
// If any specific error message appears here, then something particularly wrong might have happened.
// Save the error and continue the selection process. So if no solutions gets found, we can return
// the detailed error to the upper layers.
if (HasErrorMsg(res)) res_detailed_errors.emplace_back(res);
}
}
// Coin Selection failed.
return res_detailed_errors.empty() ? util::Result<SelectionResult>(util::Error()) : res_detailed_errors.front();
}();
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;
}
/**
* Set 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 void DiscourageFeeSniping(CMutableTransaction& tx, FastRandomContext& rng_fast,
interfaces::Chain& chain, const uint256& block_hash, int block_height)
{
// All inputs must be added by now
assert(!tx.vin.empty());
// 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)) {
tx.nLockTime = 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 (rng_fast.randrange(10) == 0) {
tx.nLockTime = std::max(0, int(tx.nLockTime) - int(rng_fast.randrange(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.
tx.nLockTime = 0;
}
// Sanity check all values
assert(tx.nLockTime < LOCKTIME_THRESHOLD); // Type must be block height
assert(tx.nLockTime <= uint64_t(block_height));
for (const auto& in : tx.vin) {
// Can not be FINAL for locktime to work
assert(in.nSequence != CTxIn::SEQUENCE_FINAL);
// May be MAX NONFINAL to disable both BIP68 and BIP125
if (in.nSequence == CTxIn::MAX_SEQUENCE_NONFINAL) continue;
// May be MAX BIP125 to disable BIP68 and enable BIP125
if (in.nSequence == MAX_BIP125_RBF_SEQUENCE) continue;
// The wallet does not support any other sequence-use right now.
assert(false);
}
}
static util::Result<CreatedTransactionResult> CreateTransactionInternal(
CWallet& wallet,
const std::vector<CRecipient>& vecSend,
int change_pos,
const CCoinControl& coin_control,
bool sign) EXCLUSIVE_LOCKS_REQUIRED(wallet.cs_wallet)
{
AssertLockHeld(wallet.cs_wallet);
// out variables, to be packed into returned result structure
int nChangePosInOut = change_pos;
FastRandomContext rng_fast;
CMutableTransaction txNew; // The resulting transaction that we make
CoinSelectionParams coin_selection_params{rng_fast}; // Parameters for coin selection, init with dummy
coin_selection_params.m_avoid_partial_spends = coin_control.m_avoid_partial_spends;
// Set the long term feerate estimate to the wallet's consolidate feerate
coin_selection_params.m_long_term_feerate = wallet.m_consolidate_feerate;
CAmount recipients_sum = 0;
const OutputType change_type = wallet.TransactionChangeType(coin_control.m_change_type ? *coin_control.m_change_type : wallet.m_default_change_type, vecSend);
ReserveDestination reservedest(&wallet, change_type);
unsigned int outputs_to_subtract_fee_from = 0; // The number of outputs which we are subtracting the fee from
for (const auto& recipient : vecSend) {
recipients_sum += recipient.nAmount;
if (recipient.fSubtractFeeFromAmount) {
outputs_to_subtract_fee_from++;
coin_selection_params.m_subtract_fee_outputs = true;
}
}
// Create change script that will be used if we need change
CScript scriptChange;
bilingual_str error; // possible error str
// 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;
auto op_dest = reservedest.GetReservedDestination(true);
if (!op_dest) {
error = _("Transaction needs a change address, but we can't generate it.") + Untranslated(" ") + util::ErrorString(op_dest);
} else {
dest = *op_dest;
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, &wallet);
// 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(wallet);
// Get the fee rate to use effective values in coin selection
FeeCalculation feeCalc;
coin_selection_params.m_effective_feerate = GetMinimumFeeRate(wallet, 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) {
return util::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))};
}
if (feeCalc.reason == FeeReason::FALLBACK && !wallet.m_allow_fallback_fee) {
// eventually allow a fallback fee
return util::Error{_("Fee estimation failed. Fallbackfee is disabled. Wait a few blocks or enable -fallbackfee.")};
}
// 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_min_change_target = GenerateChangeTarget(std::floor(recipients_sum / vecSend.size()), coin_selection_params.m_change_fee, rng_fast);
// The smallest change amount should be:
// 1. at least equal to dust threshold
// 2. at least 1 sat greater than fees to spend it at m_discard_feerate
const auto dust = GetDustThreshold(change_prototype_txout, coin_selection_params.m_discard_feerate);
const auto change_spend_fee = coin_selection_params.m_discard_feerate.GetFee(coin_selection_params.change_spend_size);
coin_selection_params.min_viable_change = std::max(change_spend_fee + 1, dust);
// Static vsize overhead + outputs vsize. 4 nVersion, 4 nLocktime, 1 input count, 1 witness overhead (dummy, flag, stack size)
coin_selection_params.tx_noinputs_size = 10 + GetSizeOfCompactSize(vecSend.size()); // bytes for output count
// vouts to the payees
for (const auto& recipient : vecSend)
{
CTxOut txout(recipient.nAmount, recipient.scriptPubKey);
// Include the fee cost for outputs.
coin_selection_params.tx_noinputs_size += ::GetSerializeSize(txout, PROTOCOL_VERSION);
if (IsDust(txout, wallet.chain().relayDustFee())) {
return util::Error{_("Transaction amount too small")};
}
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.m_subtract_fee_outputs ? 0 : coin_selection_params.tx_noinputs_size);
CAmount selection_target = recipients_sum + not_input_fees;
// Fetch manually selected coins
PreSelectedInputs preset_inputs;
if (coin_control.HasSelected()) {
auto res_fetch_inputs = FetchSelectedInputs(wallet, coin_control, coin_selection_params);
if (!res_fetch_inputs) return util::Error{util::ErrorString(res_fetch_inputs)};
preset_inputs = *res_fetch_inputs;
}
// Fetch wallet available coins if "other inputs" are
// allowed (coins automatically selected by the wallet)
CoinsResult available_coins;
if (coin_control.m_allow_other_inputs) {
available_coins = AvailableCoins(wallet, &coin_control, coin_selection_params.m_effective_feerate);
}
// Choose coins to use
auto select_coins_res = SelectCoins(wallet, available_coins, preset_inputs, /*nTargetValue=*/selection_target, coin_control, coin_selection_params);
if (!select_coins_res) {
// 'SelectCoins' either returns a specific error message or, if empty, means a general "Insufficient funds".
const bilingual_str& err = util::ErrorString(select_coins_res);
return util::Error{err.empty() ?_("Insufficient funds") : err};
}
const SelectionResult& result = *select_coins_res;
TRACE5(coin_selection, selected_coins, wallet.GetName().c_str(), GetAlgorithmName(result.GetAlgo()).c_str(), result.GetTarget(), result.GetWaste(), result.GetSelectedValue());
const CAmount change_amount = result.GetChange(coin_selection_params.min_viable_change, coin_selection_params.m_change_fee);
if (change_amount > 0) {
CTxOut newTxOut(change_amount, scriptChange);
if (nChangePosInOut == -1) {
// Insert change txn at random position:
nChangePosInOut = rng_fast.randrange(txNew.vout.size() + 1);
} else if ((unsigned int)nChangePosInOut > txNew.vout.size()) {
return util::Error{_("Transaction change output index out of range")};
}
txNew.vout.insert(txNew.vout.begin() + nChangePosInOut, newTxOut);
} else {
nChangePosInOut = -1;
}
// Shuffle selected coins and fill in final vin
std::vector<COutput> selected_coins = result.GetShuffledInputVector();
// The sequence number is set to non-maxint so that DiscourageFeeSniping
// 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(wallet.m_signal_rbf) ? MAX_BIP125_RBF_SEQUENCE : CTxIn::MAX_SEQUENCE_NONFINAL};
for (const auto& coin : selected_coins) {
txNew.vin.push_back(CTxIn(coin.outpoint, CScript(), nSequence));
}
DiscourageFeeSniping(txNew, rng_fast, wallet.chain(), wallet.GetLastBlockHash(), wallet.GetLastBlockHeight());
// Calculate the transaction fee
TxSize tx_sizes = CalculateMaximumSignedTxSize(CTransaction(txNew), &wallet, &coin_control);
int nBytes = tx_sizes.vsize;
if (nBytes == -1) {
return util::Error{_("Missing solving data for estimating transaction size")};
}
CAmount fee_needed = coin_selection_params.m_effective_feerate.GetFee(nBytes);
const CAmount output_value = CalculateOutputValue(txNew);
Assume(recipients_sum + change_amount == output_value);
CAmount current_fee = result.GetSelectedValue() - output_value;
// Sanity check that the fee cannot be negative as that means we have more output value than input value
if (current_fee < 0) {
return util::Error{Untranslated(STR_INTERNAL_BUG("Fee paid < 0"))};
}
// If there is a change output and we overpay the fees then increase the change to match the fee needed
if (nChangePosInOut != -1 && fee_needed < current_fee) {
auto& change = txNew.vout.at(nChangePosInOut);
change.nValue += current_fee - fee_needed;
current_fee = result.GetSelectedValue() - CalculateOutputValue(txNew);
if (fee_needed != current_fee) {
return util::Error{Untranslated(STR_INTERNAL_BUG("Change adjustment: Fee needed != fee paid"))};
}
}
// Reduce output values for subtractFeeFromAmount
if (coin_selection_params.m_subtract_fee_outputs) {
CAmount to_reduce = fee_needed - current_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 / outputs_to_subtract_fee_from; // 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 % outputs_to_subtract_fee_from;
}
// Error if this output is reduced to be below dust