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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 <consensus/amount.h>
#include <policy/fees.h>
#include <script/solver.h>
#include <validation.h>
#include <wallet/coincontrol.h>
#include <wallet/spend.h>
#include <wallet/test/util.h>
#include <wallet/test/wallet_test_fixture.h>
#include <boost/test/unit_test.hpp>
namespace wallet {
BOOST_FIXTURE_TEST_SUITE(spend_tests, WalletTestingSetup)
BOOST_FIXTURE_TEST_CASE(SubtractFee, TestChain100Setup)
{
CreateAndProcessBlock({}, GetScriptForRawPubKey(coinbaseKey.GetPubKey()));
auto wallet = CreateSyncedWallet(*m_node.chain, WITH_LOCK(Assert(m_node.chainman)->GetMutex(), return m_node.chainman->ActiveChain()), coinbaseKey);
// Check that a subtract-from-recipient transaction slightly less than the
// coinbase input amount does not create a change output (because it would
// be uneconomical to add and spend the output), and make sure it pays the
// leftover input amount which would have been change to the recipient
// instead of the miner.
auto check_tx = [&wallet](CAmount leftover_input_amount) {
CRecipient recipient{PubKeyDestination({}), 50 * COIN - leftover_input_amount, /*subtract_fee=*/true};
CCoinControl coin_control;
coin_control.m_feerate.emplace(10000);
coin_control.fOverrideFeeRate = true;
// We need to use a change type with high cost of change so that the leftover amount will be dropped to fee instead of added as a change output
coin_control.m_change_type = OutputType::LEGACY;
auto res = CreateTransaction(*wallet, {recipient}, /*change_pos=*/std::nullopt, coin_control);
BOOST_CHECK(res);
const auto& txr = *res;
BOOST_CHECK_EQUAL(txr.tx->vout.size(), 1);
BOOST_CHECK_EQUAL(txr.tx->vout[0].nValue, recipient.nAmount + leftover_input_amount - txr.fee);
BOOST_CHECK_GT(txr.fee, 0);
return txr.fee;
};
// Send full input amount to recipient, check that only nonzero fee is
// subtracted (to_reduce == fee).
const CAmount fee{check_tx(0)};
// Send slightly less than full input amount to recipient, check leftover
// input amount is paid to recipient not the miner (to_reduce == fee - 123)
BOOST_CHECK_EQUAL(fee, check_tx(123));
// Send full input minus fee amount to recipient, check leftover input
// amount is paid to recipient not the miner (to_reduce == 0)
BOOST_CHECK_EQUAL(fee, check_tx(fee));
// Send full input minus more than the fee amount to recipient, check
// leftover input amount is paid to recipient not the miner (to_reduce ==
// -123). This overpays the recipient instead of overpaying the miner more
// than double the necessary fee.
BOOST_CHECK_EQUAL(fee, check_tx(fee + 123));
}
BOOST_FIXTURE_TEST_CASE(wallet_duplicated_preset_inputs_test, TestChain100Setup)
{
// Verify that the wallet's Coin Selection process does not include pre-selected inputs twice in a transaction.
// Add 4 spendable UTXO, 50 BTC each, to the wallet (total balance 200 BTC)
for (int i = 0; i < 4; i++) CreateAndProcessBlock({}, GetScriptForRawPubKey(coinbaseKey.GetPubKey()));
auto wallet = CreateSyncedWallet(*m_node.chain, WITH_LOCK(Assert(m_node.chainman)->GetMutex(), return m_node.chainman->ActiveChain()), coinbaseKey);
LOCK(wallet->cs_wallet);
auto available_coins = AvailableCoins(*wallet);
std::vector<COutput> coins = available_coins.All();
// Preselect the first 3 UTXO (150 BTC total)
std::set<COutPoint> preset_inputs = {coins[0].outpoint, coins[1].outpoint, coins[2].outpoint};
// Try to create a tx that spends more than what preset inputs + wallet selected inputs are covering for.
// The wallet can cover up to 200 BTC, and the tx target is 299 BTC.
std::vector<CRecipient> recipients{{*Assert(wallet->GetNewDestination(OutputType::BECH32, "dummy")),
/*nAmount=*/299 * COIN, /*fSubtractFeeFromAmount=*/true}};
CCoinControl coin_control;
coin_control.m_allow_other_inputs = true;
for (const auto& outpoint : preset_inputs) {
coin_control.Select(outpoint);
}
// Attempt to send 299 BTC from a wallet that only has 200 BTC. The wallet should exclude
// the preset inputs from the pool of available coins, realize that there is not enough
// money to fund the 299 BTC payment, and fail with "Insufficient funds".
//
// Even with SFFO, the wallet can only afford to send 200 BTC.
// If the wallet does not properly exclude preset inputs from the pool of available coins
// prior to coin selection, it may create a transaction that does not fund the full payment
// amount or, through SFFO, incorrectly reduce the recipient's amount by the difference
// between the original target and the wrongly counted inputs (in this case 99 BTC)
// so that the recipient's amount is no longer equal to the user's selected target of 299 BTC.
// First case, use 'subtract_fee_from_outputs=true'
BOOST_CHECK(!CreateTransaction(*wallet, recipients, /*change_pos=*/std::nullopt, coin_control));
// Second case, don't use 'subtract_fee_from_outputs'.
recipients[0].fSubtractFeeFromAmount = false;
BOOST_CHECK(!CreateTransaction(*wallet, recipients, /*change_pos=*/std::nullopt, coin_control));
}
BOOST_AUTO_TEST_SUITE_END()
} // namespace wallet
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