Merge bitcoin/bitcoin#25729: wallet: Check max transaction weight in CoinSelection

c7c7ee9 test: Check max transaction weight in CoinSelection (Aurèle Oulès)
6b563ca wallet: Check max tx weight in coin selector (Aurèle Oulès)

Pull request description:

  This PR is an attempt to fix #5782.

  I have added 4 test scenarios, 3 of them provided here bitcoin/bitcoin#5782 (comment) (slightly modified to use a segwit wallet).

  Here are my benchmarks :
  ## PR
  |               ns/op |                op/s |    err% |          ins/op |          cyc/op |    IPC |         bra/op |   miss% |     total | benchmark
  |--------------------:|--------------------:|--------:|----------------:|----------------:|-------:|---------------:|--------:|----------:|:----------
  |        1,466,341.00 |              681.97 |    0.6% |   11,176,762.00 |    3,358,752.00 |  3.328 |   1,897,839.00 |    0.3% |      0.02 | `CoinSelection`

  ## Master

  |               ns/op |                op/s |    err% |          ins/op |          cyc/op |    IPC |         bra/op |   miss% |     total | benchmark
  |--------------------:|--------------------:|--------:|----------------:|----------------:|-------:|---------------:|--------:|----------:|:----------
  |        1,526,029.00 |              655.30 |    0.5% |   11,142,188.00 |    3,499,200.00 |  3.184 |   1,994,156.00 |    0.2% |      0.02 | `CoinSelection`

ACKs for top commit:
  achow101:
    reACK c7c7ee9
  w0xlt:
    ACK bitcoin/bitcoin@c7c7ee9
  furszy:
    diff ACK c7c7ee9

Tree-SHA512: ef0b28576ff845174651ba494aa9adee234c96e6f886d0e032eceb7050296e45b099dda0039d1dfb9944469f067627b2101f3ff855c70353cf39d1fc7ee81828

Author: achow101

src/wallet/coinselection.cpp

@@ -5,6 +5,7 @@
 #include <wallet/coinselection.h>
 
 #include <consensus/amount.h>
+#include <consensus/consensus.h>
 #include <policy/feerate.h>
 #include <util/check.h>
 #include <util/system.h>
@@ -354,6 +355,10 @@ void OutputGroup::Insert(const COutput& output, size_t ancestors, size_t descend
     // descendants is the count as seen from the top ancestor, not the descendants as seen from the
     // coin itself; thus, this value is counted as the max, not the sum
     m_descendants = std::max(m_descendants, descendants);
+
+    if (output.input_bytes > 0) {
+        m_weight += output.input_bytes * WITNESS_SCALE_FACTOR;
+    }
 }
 
 bool OutputGroup::EligibleForSpending(const CoinEligibilityFilter& eligibility_filter) const
@@ -436,18 +441,25 @@ void SelectionResult::Clear()
 {
     m_selected_inputs.clear();
     m_waste.reset();
+    m_weight = 0;
 }
 
 void SelectionResult::AddInput(const OutputGroup& group)
 {
     util::insert(m_selected_inputs, group.m_outputs);
     m_use_effective = !group.m_subtract_fee_outputs;
+
+    m_weight += group.m_weight;
 }
 
 void SelectionResult::AddInputs(const std::set<COutput>& inputs, bool subtract_fee_outputs)
 {
     util::insert(m_selected_inputs, inputs);
     m_use_effective = !subtract_fee_outputs;
+
+    m_weight += std::accumulate(inputs.cbegin(), inputs.cend(), 0, [](int sum, const auto& coin) {
+        return sum + std::max(coin.input_bytes, 0) * WITNESS_SCALE_FACTOR;
+    });
 }
 
 void SelectionResult::Merge(const SelectionResult& other)
@@ -462,6 +474,8 @@ void SelectionResult::Merge(const SelectionResult& other)
     }
     util::insert(m_selected_inputs, other.m_selected_inputs);
     assert(m_selected_inputs.size() == expected_count);
+
+    m_weight += other.m_weight;
 }
 
 const std::set<COutput>& SelectionResult::GetInputSet() const

src/wallet/coinselection.h

@@ -6,6 +6,7 @@
 #define BITCOIN_WALLET_COINSELECTION_H
 
 #include <consensus/amount.h>
+#include <consensus/consensus.h>
 #include <policy/feerate.h>
 #include <primitives/transaction.h>
 #include <random.h>
@@ -223,6 +224,8 @@ struct OutputGroup
     /** Indicate that we are subtracting the fee from outputs.
      * When true, the value that is used for coin selection is the UTXO's real value rather than effective value */
     bool m_subtract_fee_outputs{false};
+    /** Total weight of the UTXOs in this group. */
+    int m_weight{0};
 
     OutputGroup() {}
     OutputGroup(const CoinSelectionParams& params) :
@@ -295,6 +298,8 @@ struct SelectionResult
     bool m_use_effective{false};
     /** The computed waste */
     std::optional<CAmount> m_waste;
+    /** Total weight of the selected inputs */
+    int m_weight{0};
 
 public:
     explicit SelectionResult(const CAmount target, SelectionAlgorithm algo)
@@ -353,6 +358,8 @@ struct SelectionResult
     CAmount GetTarget() const { return m_target; }
 
     SelectionAlgorithm GetAlgo() const { return m_algo; }
+
+    int GetWeight() const { return m_weight; }
 };
 
 std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, const CAmount& cost_of_change);

src/wallet/spend.cpp

@@ -2,9 +2,11 @@
 // 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 <script/signingprovider.h>
 #include <util/check.h>
@@ -555,14 +557,24 @@ std::optional<SelectionResult> ChooseSelectionResult(const CWallet& wallet, cons
         results.push_back(*srd_result);
     }
 
-    if (results.size() == 0) {
+    if (results.empty()) {
         // No solution found
         return std::nullopt;
     }
 
+    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 std::nullopt;
+    }
+
     // 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(results.begin(), results.end());
+    auto& best_result = *std::min_element(eligible_results.begin(), eligible_results.end());
     return best_result;
 }
 
@@ -867,19 +879,16 @@ static util::Result<CreatedTransactionResult> CreateTransactionInternal(
     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
-    if (!coin_selection_params.m_subtract_fee_outputs) {
-        coin_selection_params.tx_noinputs_size = 10; // 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 += GetSizeOfCompactSize(vecSend.size()); // bytes for output count
-    }
     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);
-        }
+        coin_selection_params.tx_noinputs_size += ::GetSerializeSize(txout, PROTOCOL_VERSION);
 
         if (IsDust(txout, wallet.chain().relayDustFee())) {
             return util::Error{_("Transaction amount too small")};
@@ -888,7 +897,7 @@ static util::Result<CreatedTransactionResult> CreateTransactionInternal(
     }
 
     // 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);
+    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

src/wallet/test/coinselector_tests.cpp

@@ -4,6 +4,7 @@
 
 #include <consensus/amount.h>
 #include <node/context.h>
+#include <policy/policy.h>
 #include <primitives/transaction.h>
 #include <random.h>
 #include <test/util/setup_common.h>
@@ -930,6 +931,124 @@ BOOST_AUTO_TEST_CASE(effective_value_test)
     BOOST_CHECK_EQUAL(output5.GetEffectiveValue(), nValue); // The effective value should be equal to the absolute value if input_bytes is -1
 }
 
+static std::optional<SelectionResult> select_coins(const CAmount& target, const CoinSelectionParams& cs_params, const CCoinControl& cc, std::function<CoinsResult(CWallet&)> coin_setup, interfaces::Chain* chain, const ArgsManager& args)
+{
+    std::unique_ptr<CWallet> wallet = std::make_unique<CWallet>(chain, "", args, CreateMockWalletDatabase());
+    wallet->LoadWallet();
+    LOCK(wallet->cs_wallet);
+    wallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
+    wallet->SetupDescriptorScriptPubKeyMans();
+
+    auto available_coins = coin_setup(*wallet);
+
+    const auto result = SelectCoins(*wallet, available_coins, /*pre_set_inputs=*/ {}, target, cc, cs_params);
+    if (result) {
+        const auto signedTxSize = 10 + 34 + 68 * result->GetInputSet().size(); // static header size + output size + inputs size (P2WPKH)
+        BOOST_CHECK_LE(signedTxSize * WITNESS_SCALE_FACTOR, MAX_STANDARD_TX_WEIGHT);
+
+        BOOST_CHECK_GE(result->GetSelectedValue(), target);
+    }
+    return result;
+}
+
+static bool has_coin(const CoinSet& set, CAmount amount)
+{
+    return std::any_of(set.begin(), set.end(), [&](const auto& coin) { return coin.GetEffectiveValue() == amount; });
+}
+
+BOOST_AUTO_TEST_CASE(check_max_weight)
+{
+    const CAmount target = 49.5L * COIN;
+    CCoinControl cc;
+
+    FastRandomContext rand;
+    CoinSelectionParams cs_params{
+        rand,
+        /*change_output_size=*/34,
+        /*change_spend_size=*/68,
+        /*min_change_target=*/CENT,
+        /*effective_feerate=*/CFeeRate(0),
+        /*long_term_feerate=*/CFeeRate(0),
+        /*discard_feerate=*/CFeeRate(0),
+        /*tx_noinputs_size=*/10 + 34, // static header size + output size
+        /*avoid_partial=*/false,
+    };
+
+    auto chain{m_node.chain.get()};
+
+    {
+        // Scenario 1:
+        // The actor starts with 1x 50.0 BTC and 1515x 0.033 BTC (~100.0 BTC total) unspent outputs
+        // Then tries to spend 49.5 BTC
+        // The 50.0 BTC output should be selected, because the transaction would otherwise be too large
+
+        // Perform selection
+
+        const auto result = select_coins(
+            target, cs_params, cc, [&](CWallet& wallet) {
+                CoinsResult available_coins;
+                for (int j = 0; j < 1515; ++j) {
+                    add_coin(available_coins, wallet, CAmount(0.033 * COIN), CFeeRate(0), 144, false, 0, true);
+                }
+
+                add_coin(available_coins, wallet, CAmount(50 * COIN), CFeeRate(0), 144, false, 0, true);
+                return available_coins;
+            },
+            chain, m_args);
+
+        BOOST_CHECK(result);
+        BOOST_CHECK(has_coin(result->GetInputSet(), CAmount(50 * COIN)));
+    }
+
+    {
+        // Scenario 2:
+
+        // The actor starts with 400x 0.0625 BTC and 2000x 0.025 BTC (75.0 BTC total) unspent outputs
+        // Then tries to spend 49.5 BTC
+        // A combination of coins should be selected, such that the created transaction is not too large
+
+        // Perform selection
+        const auto result = select_coins(
+            target, cs_params, cc, [&](CWallet& wallet) {
+                CoinsResult available_coins;
+                for (int j = 0; j < 400; ++j) {
+                    add_coin(available_coins, wallet, CAmount(0.0625 * COIN), CFeeRate(0), 144, false, 0, true);
+                }
+                for (int j = 0; j < 2000; ++j) {
+                    add_coin(available_coins, wallet, CAmount(0.025 * COIN), CFeeRate(0), 144, false, 0, true);
+                }
+                return available_coins;
+            },
+            chain, m_args);
+
+        BOOST_CHECK(has_coin(result->GetInputSet(), CAmount(0.0625 * COIN)));
+        BOOST_CHECK(has_coin(result->GetInputSet(), CAmount(0.025 * COIN)));
+    }
+
+    {
+        // Scenario 3:
+
+        // The actor starts with 1515x 0.033 BTC (49.995 BTC total) unspent outputs
+        // No results should be returned, because the transaction would be too large
+
+        // Perform selection
+        const auto result = select_coins(
+            target, cs_params, cc, [&](CWallet& wallet) {
+                CoinsResult available_coins;
+                for (int j = 0; j < 1515; ++j) {
+                    add_coin(available_coins, wallet, CAmount(0.033 * COIN), CFeeRate(0), 144, false, 0, true);
+                }
+                return available_coins;
+            },
+            chain, m_args);
+
+        // No results
+        // 1515 inputs * 68 bytes = 103,020 bytes
+        // 103,020 bytes * 4 = 412,080 weight, which is above the MAX_STANDARD_TX_WEIGHT of 400,000
+        BOOST_CHECK(!result);
+    }
+}
+
 BOOST_AUTO_TEST_CASE(SelectCoins_effective_value_test)
 {
     // Test that the effective value is used to check whether preset inputs provide sufficient funds when subtract_fee_outputs is not used.

test/functional/rpc_fundrawtransaction.py

@@ -987,7 +987,7 @@ def test_transaction_too_large(self):
             outputs[recipient.getnewaddress()] = 0.1
         wallet.sendmany("", outputs)
         self.generate(self.nodes[0], 10)
-        assert_raises_rpc_error(-4, "Transaction too large", recipient.fundrawtransaction, rawtx)
+        assert_raises_rpc_error(-4, "Insufficient funds", recipient.fundrawtransaction, rawtx)
         self.nodes[0].unloadwallet("large")
 
     def test_external_inputs(self):