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