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       1                 :            : // Copyright (c) 2021-2022 The Bitcoin Core developers
       2                 :            : // Distributed under the MIT software license, see the accompanying
       3                 :            : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
       4                 :            : 
       5                 :            : #include <consensus/amount.h>
       6                 :            : #include <policy/fees.h>
       7                 :            : #include <script/solver.h>
       8                 :            : #include <validation.h>
       9                 :            : #include <wallet/coincontrol.h>
      10                 :            : #include <wallet/spend.h>
      11                 :            : #include <wallet/test/util.h>
      12                 :            : #include <wallet/test/wallet_test_fixture.h>
      13                 :            : 
      14                 :            : #include <boost/test/unit_test.hpp>
      15                 :            : 
      16                 :            : namespace wallet {
      17                 :          0 : BOOST_FIXTURE_TEST_SUITE(spend_tests, WalletTestingSetup)
      18                 :          0 : 
      19                 :          0 : BOOST_FIXTURE_TEST_CASE(SubtractFee, TestChain100Setup)
      20                 :            : {
      21                 :          0 :     CreateAndProcessBlock({}, GetScriptForRawPubKey(coinbaseKey.GetPubKey()));
      22                 :          0 :     auto wallet = CreateSyncedWallet(*m_node.chain, WITH_LOCK(Assert(m_node.chainman)->GetMutex(), return m_node.chainman->ActiveChain()), coinbaseKey);
      23                 :            : 
      24                 :            :     // Check that a subtract-from-recipient transaction slightly less than the
      25                 :            :     // coinbase input amount does not create a change output (because it would
      26                 :            :     // be uneconomical to add and spend the output), and make sure it pays the
      27                 :          0 :     // leftover input amount which would have been change to the recipient
      28                 :            :     // instead of the miner.
      29                 :          0 :     auto check_tx = [&wallet](CAmount leftover_input_amount) {
      30                 :          0 :         CRecipient recipient{PubKeyDestination({}), 50 * COIN - leftover_input_amount, /*subtract_fee=*/true};
      31                 :          0 :         constexpr int RANDOM_CHANGE_POSITION = -1;
      32                 :          0 :         CCoinControl coin_control;
      33                 :          0 :         coin_control.m_feerate.emplace(10000);
      34                 :          0 :         coin_control.fOverrideFeeRate = true;
      35                 :          0 :         // 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
      36                 :          0 :         coin_control.m_change_type = OutputType::LEGACY;
      37                 :          0 :         auto res = CreateTransaction(*wallet, {recipient}, RANDOM_CHANGE_POSITION, coin_control);
      38                 :          0 :         BOOST_CHECK(res);
      39                 :          0 :         const auto& txr = *res;
      40                 :          0 :         BOOST_CHECK_EQUAL(txr.tx->vout.size(), 1);
      41                 :          0 :         BOOST_CHECK_EQUAL(txr.tx->vout[0].nValue, recipient.nAmount + leftover_input_amount - txr.fee);
      42                 :          0 :         BOOST_CHECK_GT(txr.fee, 0);
      43                 :          0 :         return txr.fee;
      44                 :          0 :     };
      45                 :            : 
      46                 :            :     // Send full input amount to recipient, check that only nonzero fee is
      47                 :            :     // subtracted (to_reduce == fee).
      48                 :          0 :     const CAmount fee{check_tx(0)};
      49                 :            : 
      50                 :            :     // Send slightly less than full input amount to recipient, check leftover
      51                 :            :     // input amount is paid to recipient not the miner (to_reduce == fee - 123)
      52                 :          0 :     BOOST_CHECK_EQUAL(fee, check_tx(123));
      53                 :          0 : 
      54                 :            :     // Send full input minus fee amount to recipient, check leftover input
      55                 :            :     // amount is paid to recipient not the miner (to_reduce == 0)
      56                 :          0 :     BOOST_CHECK_EQUAL(fee, check_tx(fee));
      57                 :            : 
      58                 :            :     // Send full input minus more than the fee amount to recipient, check
      59                 :            :     // leftover input amount is paid to recipient not the miner (to_reduce ==
      60                 :            :     // -123). This overpays the recipient instead of overpaying the miner more
      61                 :            :     // than double the necessary fee.
      62                 :          0 :     BOOST_CHECK_EQUAL(fee, check_tx(fee + 123));
      63                 :          0 : }
      64                 :            : 
      65                 :          0 : BOOST_FIXTURE_TEST_CASE(wallet_duplicated_preset_inputs_test, TestChain100Setup)
      66                 :            : {
      67                 :            :     // Verify that the wallet's Coin Selection process does not include pre-selected inputs twice in a transaction.
      68                 :            : 
      69                 :            :     // Add 4 spendable UTXO, 50 BTC each, to the wallet (total balance 200 BTC)
      70                 :          0 :     for (int i = 0; i < 4; i++) CreateAndProcessBlock({}, GetScriptForRawPubKey(coinbaseKey.GetPubKey()));
      71                 :          0 :     auto wallet = CreateSyncedWallet(*m_node.chain, WITH_LOCK(Assert(m_node.chainman)->GetMutex(), return m_node.chainman->ActiveChain()), coinbaseKey);
      72                 :            : 
      73                 :          0 :     LOCK(wallet->cs_wallet);
      74                 :          0 :     auto available_coins = AvailableCoins(*wallet);
      75                 :          0 :     std::vector<COutput> coins = available_coins.All();
      76                 :            :     // Preselect the first 3 UTXO (150 BTC total)
      77                 :          0 :     std::set<COutPoint> preset_inputs = {coins[0].outpoint, coins[1].outpoint, coins[2].outpoint};
      78                 :            : 
      79                 :            :     // Try to create a tx that spends more than what preset inputs + wallet selected inputs are covering for.
      80                 :            :     // The wallet can cover up to 200 BTC, and the tx target is 299 BTC.
      81                 :          0 :     std::vector<CRecipient> recipients = {{GetScriptForDestination(*Assert(wallet->GetNewDestination(OutputType::BECH32, "dummy"))),
      82                 :            :                                            /*nAmount=*/299 * COIN, /*fSubtractFeeFromAmount=*/true}};
      83                 :          0 :     CCoinControl coin_control;
      84                 :          0 :     coin_control.m_allow_other_inputs = true;
      85                 :          0 :     for (const auto& outpoint : preset_inputs) {
      86                 :          0 :         coin_control.Select(outpoint);
      87                 :            :     }
      88                 :            : 
      89                 :            :     // Attempt to send 299 BTC from a wallet that only has 200 BTC. The wallet should exclude
      90                 :            :     // the preset inputs from the pool of available coins, realize that there is not enough
      91                 :          0 :     // money to fund the 299 BTC payment, and fail with "Insufficient funds".
      92                 :            :     //
      93                 :            :     // Even with SFFO, the wallet can only afford to send 200 BTC.
      94                 :            :     // If the wallet does not properly exclude preset inputs from the pool of available coins
      95                 :            :     // prior to coin selection, it may create a transaction that does not fund the full payment
      96                 :            :     // amount or, through SFFO, incorrectly reduce the recipient's amount by the difference
      97                 :            :     // between the original target and the wrongly counted inputs (in this case 99 BTC)
      98                 :            :     // so that the recipient's amount is no longer equal to the user's selected target of 299 BTC.
      99                 :          0 : 
     100                 :            :     // First case, use 'subtract_fee_from_outputs=true'
     101                 :          0 :     util::Result<CreatedTransactionResult> res_tx = CreateTransaction(*wallet, recipients, /*change_pos*/-1, coin_control);
     102                 :          0 :     BOOST_CHECK(!res_tx.has_value());
     103                 :            : 
     104                 :            :     // Second case, don't use 'subtract_fee_from_outputs'.
     105                 :          0 :     recipients[0].fSubtractFeeFromAmount = false;
     106                 :          0 :     res_tx = CreateTransaction(*wallet, recipients, /*change_pos*/-1, coin_control);
     107                 :          0 :     BOOST_CHECK(!res_tx.has_value());
     108                 :          0 : }
     109                 :            : 
     110                 :          0 : BOOST_AUTO_TEST_SUITE_END()
     111                 :            : } // namespace wallet