Merge bitcoin/bitcoin#26720: wallet: coin selection, don't return results that exceed the max allowed weight

25ab14712b9d80276016f9fc9bff7fb9c1d09635 refactor: coinselector_tests, unify wallet creation code (furszy)
ba9431c505e1590db6103b9632134985cd4704dc test: coverage for bnb max weight (furszy)
5a2bc45ee0b123e461c5191322ed0b43524c3d82 wallet: clean post coin selection max weight filter (furszy)
2d112584e384de10021c64e4700455d71326824e coin selection: BnB, don't return selection if exceeds max allowed tx weight (furszy)
d3a1c098e4b5df2ebbae20c6e390c3d783950e93 test: coin selection, add coverage for SRD (furszy)
9d9689e5a657956db8a30829c994600ec7d3098b coin selection: heap-ify SRD, don't return selection if exceeds max tx weight (furszy)
6107ec2229c5f5b4e944a6b10d38010c850094ac coin selection: knapsack, select closest UTXO above target if result exceeds max tx size (furszy)
1284223691127e76135a46d251c52416104f0ff1 wallet: refactor coin selection algos to return util::Result (furszy)

Pull request description:

  Coming from the following comment https://github.com/bitcoin/bitcoin/pull/25729#discussion_r1029324367.

  The reason why we are adding hundreds of UTXO from different sources when the target
  amount is covered only by one of them is because only SRD returns a usable result.

  Context:
  In the test, we create 1515 UTXOs with 0.033 BTC each, and 1 UTXO with 50 BTC. Then
  perform Coin Selection to fund 49.5 BTC.

  As the selection of the 1515 small UTXOs exceeds the max allowed tx size, the
  expectation here is to receive a selection result that only contain the big UTXO.
  Which is not happening for the following reason:

  Knapsack returns a result that exceeds the max allowed transaction size, when
  it should return the closest utxo above the target, so we fallback to SRD who
  selects coins randomly up until the target is met. So we end up with a selection
  result with lot more coins than what is needed.

ACKs for top commit:
  S3RK:
    ACK 25ab14712b9d80276016f9fc9bff7fb9c1d09635
  achow101:
    ACK 25ab14712b9d80276016f9fc9bff7fb9c1d09635
  Xekyo:
    reACK 25ab14712b9d80276016f9fc9bff7fb9c1d09635
  theStack:
    Code-review ACK 25ab14712b9d80276016f9fc9bff7fb9c1d09635

Tree-SHA512: 2425de4cc479b4db999b3b2e02eb522a2130a06379cca0418672a51c4076971a1d427191173820db76a0f85a8edfff100114e1c38fb3b5dc51598d07cabe1a60

5 files changed, 285 insertions, 102 deletions

diff --git a/src/wallet/coinselection.cpp b/src/wallet/coinselection.cpp
index 9cf61dbe51..f704d03b5f 100644
--- a/src/wallet/coinselection.cpp
+++ b/src/wallet/coinselection.cpp
@@ -13,8 +13,16 @@
 
 #include <numeric>
 #include <optional>
+#include <queue>
 
 namespace wallet {
+// Common selection error across the algorithms
+static util::Result<SelectionResult> ErrorMaxWeightExceeded()
+{
+    return util::Error{_("The inputs size exceeds the maximum weight. "
+                         "Please try sending a smaller amount or manually consolidating your wallet's UTXOs")};
+}
+
 // Descending order comparator
 struct {
     bool operator()(const OutputGroup& a, const OutputGroup& b) const
@@ -63,11 +71,13 @@ struct {
 
 static const size_t TOTAL_TRIES = 100000;
 
-std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, const CAmount& cost_of_change)
+util::Result<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, const CAmount& cost_of_change,
+                                             int max_weight)
 {
     SelectionResult result(selection_target, SelectionAlgorithm::BNB);
     CAmount curr_value = 0;
     std::vector<size_t> curr_selection; // selected utxo indexes
+    int curr_selection_weight = 0; // sum of selected utxo weight
 
     // Calculate curr_available_value
     CAmount curr_available_value = 0;
@@ -78,7 +88,7 @@ std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_poo
         curr_available_value += utxo.GetSelectionAmount();
     }
     if (curr_available_value < selection_target) {
-        return std::nullopt;
+        return util::Error();
     }
 
     // Sort the utxo_pool
@@ -89,6 +99,7 @@ std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_poo
     CAmount best_waste = MAX_MONEY;
 
     bool is_feerate_high = utxo_pool.at(0).fee > utxo_pool.at(0).long_term_fee;
+    bool max_tx_weight_exceeded = false;
 
     // Depth First search loop for choosing the UTXOs
     for (size_t curr_try = 0, utxo_pool_index = 0; curr_try < TOTAL_TRIES; ++curr_try, ++utxo_pool_index) {
@@ -98,6 +109,9 @@ std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_poo
             curr_value > selection_target + cost_of_change || // Selected value is out of range, go back and try other branch
             (curr_waste > best_waste && is_feerate_high)) { // Don't select things which we know will be more wasteful if the waste is increasing
             backtrack = true;
+        } else if (curr_selection_weight > max_weight) { // Exceeding weight for standard tx, cannot find more solutions by adding more inputs
+            max_tx_weight_exceeded = true; // at least one selection attempt exceeded the max weight
+            backtrack = true;
         } else if (curr_value >= selection_target) {       // Selected value is within range
             curr_waste += (curr_value - selection_target); // This is the excess value which is added to the waste for the below comparison
             // Adding another UTXO after this check could bring the waste down if the long term fee is higher than the current fee.
@@ -127,6 +141,7 @@ std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_poo
             OutputGroup& utxo = utxo_pool.at(utxo_pool_index);
             curr_value -= utxo.GetSelectionAmount();
             curr_waste -= utxo.fee - utxo.long_term_fee;
+            curr_selection_weight -= utxo.m_weight;
             curr_selection.pop_back();
         } else { // Moving forwards, continuing down this branch
             OutputGroup& utxo = utxo_pool.at(utxo_pool_index);
@@ -146,13 +161,14 @@ std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_poo
                 curr_selection.push_back(utxo_pool_index);
                 curr_value += utxo.GetSelectionAmount();
                 curr_waste += utxo.fee - utxo.long_term_fee;
+                curr_selection_weight += utxo.m_weight;
             }
         }
     }
 
     // Check for solution
     if (best_selection.empty()) {
-        return std::nullopt;
+        return max_tx_weight_exceeded ? ErrorMaxWeightExceeded() : util::Error();
     }
 
     // Set output set
@@ -165,9 +181,20 @@ std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_poo
     return result;
 }
 
-std::optional<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& utxo_pool, CAmount target_value, FastRandomContext& rng)
+class MinOutputGroupComparator
+{
+public:
+    int operator() (const OutputGroup& group1, const OutputGroup& group2) const
+    {
+        return group1.GetSelectionAmount() > group2.GetSelectionAmount();
+    }
+};
+
+util::Result<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& utxo_pool, CAmount target_value, FastRandomContext& rng,
+                                             int max_weight)
 {
     SelectionResult result(target_value, SelectionAlgorithm::SRD);
+    std::priority_queue<OutputGroup, std::vector<OutputGroup>, MinOutputGroupComparator> heap;
 
     // Include change for SRD as we want to avoid making really small change if the selection just
     // barely meets the target. Just use the lower bound change target instead of the randomly
@@ -181,16 +208,40 @@ std::optional<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& ut
     Shuffle(indexes.begin(), indexes.end(), rng);
 
     CAmount selected_eff_value = 0;
+    int weight = 0;
+    bool max_tx_weight_exceeded = false;
     for (const size_t i : indexes) {
         const OutputGroup& group = utxo_pool.at(i);
         Assume(group.GetSelectionAmount() > 0);
+
+        // Add group to selection
+        heap.push(group);
         selected_eff_value += group.GetSelectionAmount();
-        result.AddInput(group);
+        weight += group.m_weight;
+
+        // If the selection weight exceeds the maximum allowed size, remove the least valuable inputs until we
+        // are below max weight.
+        if (weight > max_weight) {
+            max_tx_weight_exceeded = true; // mark it in case we don't find any useful result.
+            do {
+                const OutputGroup& to_remove_group = heap.top();
+                selected_eff_value -= to_remove_group.GetSelectionAmount();
+                weight -= to_remove_group.m_weight;
+                heap.pop();
+            } while (!heap.empty() && weight > max_weight);
+        }
+
+        // Now check if we are above the target
         if (selected_eff_value >= target_value) {
+            // Result found, add it.
+            while (!heap.empty()) {
+                result.AddInput(heap.top());
+                heap.pop();
+            }
             return result;
         }
     }
-    return std::nullopt;
+    return max_tx_weight_exceeded ? ErrorMaxWeightExceeded() : util::Error();
 }
 
 /** Find a subset of the OutputGroups that is at least as large as, but as close as possible to, the
@@ -252,8 +303,8 @@ static void ApproximateBestSubset(FastRandomContext& insecure_rand, const std::v
     }
 }
 
-std::optional<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups, const CAmount& nTargetValue,
-                                              CAmount change_target, FastRandomContext& rng)
+util::Result<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups, const CAmount& nTargetValue,
+                                             CAmount change_target, FastRandomContext& rng, int max_weight)
 {
     SelectionResult result(nTargetValue, SelectionAlgorithm::KNAPSACK);
 
@@ -286,7 +337,7 @@ std::optional<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups,
     }
 
     if (nTotalLower < nTargetValue) {
-        if (!lowest_larger) return std::nullopt;
+        if (!lowest_larger) return util::Error();
         result.AddInput(*lowest_larger);
         return result;
     }
@@ -313,6 +364,16 @@ std::optional<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups,
             }
         }
 
+        // If the result exceeds the maximum allowed size, return closest UTXO above the target
+        if (result.GetWeight() > max_weight) {
+            // No coin above target, nothing to do.
+            if (!lowest_larger) return ErrorMaxWeightExceeded();
+
+            // Return closest UTXO above target
+            result.Clear();
+            result.AddInput(*lowest_larger);
+        }
+
         if (LogAcceptCategory(BCLog::SELECTCOINS, BCLog::Level::Debug)) {
             std::string log_message{"Coin selection best subset: "};
             for (unsigned int i = 0; i < applicable_groups.size(); i++) {
diff --git a/src/wallet/coinselection.h b/src/wallet/coinselection.h
index 5a7b748be1..723f5bbfb3 100644
--- a/src/wallet/coinselection.h
+++ b/src/wallet/coinselection.h
@@ -13,6 +13,7 @@
 #include <random.h>
 #include <util/system.h>
 #include <util/check.h>
+#include <util/result.h>
 
 #include <optional>
 
@@ -408,20 +409,24 @@ public:
     int GetWeight() const { return m_weight; }
 };
 
-std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, const CAmount& cost_of_change);
+util::Result<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, const CAmount& cost_of_change,
+                                             int max_weight);
 
 /** Select coins by Single Random Draw. OutputGroups are selected randomly from the eligible
  * outputs until the target is satisfied
  *
  * @param[in]  utxo_pool    The positive effective value OutputGroups eligible for selection
  * @param[in]  target_value The target value to select for
- * @returns If successful, a SelectionResult, otherwise, std::nullopt
+ * @param[in]  rng The randomness source to shuffle coins
+ * @param[in]  max_weight The maximum allowed weight for a selection result to be valid
+ * @returns If successful, a valid SelectionResult, otherwise, util::Error
  */
-std::optional<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& utxo_pool, CAmount target_value, FastRandomContext& rng);
+util::Result<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& utxo_pool, CAmount target_value, FastRandomContext& rng,
+                                             int max_weight);
 
 // Original coin selection algorithm as a fallback
-std::optional<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups, const CAmount& nTargetValue,
-                                              CAmount change_target, FastRandomContext& rng);
+util::Result<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups, const CAmount& nTargetValue,
+                                             CAmount change_target, FastRandomContext& rng, int max_weight);
 } // namespace wallet
 
 #endif // BITCOIN_WALLET_COINSELECTION_H
diff --git a/src/wallet/spend.cpp b/src/wallet/spend.cpp
index 57f3785a3a..c3303419d4 100644
--- a/src/wallet/spend.cpp
+++ b/src/wallet/spend.cpp
@@ -559,42 +559,45 @@ util::Result<SelectionResult> ChooseSelectionResult(const CAmount& nTargetValue,
 {
     // Vector of results. We will choose the best one based on waste.
     std::vector<SelectionResult> results;
+    std::vector<util::Result<SelectionResult>> errors;
+    auto append_error = [&] (const util::Result<SelectionResult>& result) {
+        // If any specific error message appears here, then something different from a simple "no selection found" happened.
+        // Let's save it, so it can be retrieved to the user if no other selection algorithm succeeded.
+        if (HasErrorMsg(result)) {
+            errors.emplace_back(result);
+        }
+    };
+
+    // Maximum allowed weight
+    int max_inputs_weight = MAX_STANDARD_TX_WEIGHT - (coin_selection_params.tx_noinputs_size * WITNESS_SCALE_FACTOR);
 
-    if (auto bnb_result{SelectCoinsBnB(groups.positive_group, nTargetValue, coin_selection_params.m_cost_of_change)}) {
+    if (auto bnb_result{SelectCoinsBnB(groups.positive_group, nTargetValue, coin_selection_params.m_cost_of_change, max_inputs_weight)}) {
         results.push_back(*bnb_result);
-    }
+    } else append_error(bnb_result);
+
+    // As Knapsack and SRD can create change, also deduce change weight.
+    max_inputs_weight -= (coin_selection_params.change_output_size * WITNESS_SCALE_FACTOR);
 
     // 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.
-    if (auto knapsack_result{KnapsackSolver(groups.mixed_group, nTargetValue, coin_selection_params.m_min_change_target, coin_selection_params.rng_fast)}) {
+    if (auto knapsack_result{KnapsackSolver(groups.mixed_group, nTargetValue, coin_selection_params.m_min_change_target, coin_selection_params.rng_fast, max_inputs_weight)}) {
         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);
-    }
+    } else append_error(knapsack_result);
 
-    if (auto srd_result{SelectCoinsSRD(groups.positive_group, nTargetValue, coin_selection_params.rng_fast)}) {
+    if (auto srd_result{SelectCoinsSRD(groups.positive_group, nTargetValue, coin_selection_params.rng_fast, max_inputs_weight)}) {
         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);
-    }
+    } else append_error(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")};
+        // No solution found, retrieve the first explicit error (if any).
+        // future: add 'severity level' to errors so the worst one can be retrieved instead of the first one.
+        return errors.empty() ? util::Error() : errors.front();
     }
 
     // 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;
+    return *std::min_element(results.begin(), results.end());
 }
 
 util::Result<SelectionResult> SelectCoins(const CWallet& wallet, CoinsResult& available_coins, const PreSelectedInputs& pre_set_inputs,
diff --git a/src/wallet/test/coinselector_tests.cpp b/src/wallet/test/coinselector_tests.cpp
index 8f626addde..7f66179517 100644
--- a/src/wallet/test/coinselector_tests.cpp
+++ b/src/wallet/test/coinselector_tests.cpp
@@ -68,7 +68,7 @@ static void add_coin(const CAmount& nValue, int nInput, CoinSet& set, CAmount fe
     set.insert(std::make_shared<COutput>(coin));
 }
 
-static void add_coin(CoinsResult& available_coins, CWallet& wallet, const CAmount& nValue, CFeeRate feerate = CFeeRate(0), int nAge = 6*24, bool fIsFromMe = false, int nInput =0, bool spendable = false)
+static void add_coin(CoinsResult& available_coins, CWallet& wallet, const CAmount& nValue, CFeeRate feerate = CFeeRate(0), int nAge = 6*24, bool fIsFromMe = false, int nInput =0, bool spendable = false, int custom_size = 0)
 {
     CMutableTransaction tx;
     tx.nLockTime = nextLockTime++;        // so all transactions get different hashes
@@ -84,7 +84,21 @@ static void add_coin(CoinsResult& available_coins, CWallet& wallet, const CAmoun
     assert(ret.second);
     CWalletTx& wtx = (*ret.first).second;
     const auto& txout = wtx.tx->vout.at(nInput);
-    available_coins.Add(OutputType::BECH32, {COutPoint(wtx.GetHash(), nInput), txout, nAge, CalculateMaximumSignedInputSize(txout, &wallet, /*coin_control=*/nullptr), /*spendable=*/ true, /*solvable=*/ true, /*safe=*/ true, wtx.GetTxTime(), fIsFromMe, feerate});
+    available_coins.Add(OutputType::BECH32, {COutPoint(wtx.GetHash(), nInput), txout, nAge, custom_size == 0 ? CalculateMaximumSignedInputSize(txout, &wallet, /*coin_control=*/nullptr) : custom_size, /*spendable=*/ true, /*solvable=*/ true, /*safe=*/ true, wtx.GetTxTime(), fIsFromMe, feerate});
+}
+
+// Helpers
+std::optional<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups, const CAmount& nTargetValue,
+                                              CAmount change_target, FastRandomContext& rng)
+{
+    auto res{KnapsackSolver(groups, nTargetValue, change_target, rng, MAX_STANDARD_TX_WEIGHT)};
+    return res ? std::optional<SelectionResult>(*res) : std::nullopt;
+}
+
+std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, const CAmount& cost_of_change)
+{
+    auto res{SelectCoinsBnB(utxo_pool, selection_target, cost_of_change, MAX_STANDARD_TX_WEIGHT)};
+    return res ? std::optional<SelectionResult>(*res) : std::nullopt;
 }
 
 /** Check if SelectionResult a is equivalent to SelectionResult b.
@@ -128,13 +142,15 @@ static CAmount make_hard_case(int utxos, std::vector<COutput>& utxo_pool)
     return target;
 }
 
-inline std::vector<OutputGroup>& GroupCoins(const std::vector<COutput>& available_coins)
+inline std::vector<OutputGroup>& GroupCoins(const std::vector<COutput>& available_coins, bool subtract_fee_outputs = false)
 {
     static std::vector<OutputGroup> static_groups;
     static_groups.clear();
     for (auto& coin : available_coins) {
         static_groups.emplace_back();
-        static_groups.back().Insert(std::make_shared<COutput>(coin), /*ancestors=*/ 0, /*descendants=*/ 0);
+        OutputGroup& group = static_groups.back();
+        group.Insert(std::make_shared<COutput>(coin), /*ancestors=*/ 0, /*descendants=*/ 0);
+        group.m_subtract_fee_outputs = subtract_fee_outputs;
     }
     return static_groups;
 }
@@ -158,6 +174,16 @@ inline std::vector<OutputGroup>& KnapsackGroupOutputs(const CoinsResult& availab
     return static_groups.all_groups.mixed_group;
 }
 
+static std::unique_ptr<CWallet> NewWallet(const node::NodeContext& m_node, const std::string& wallet_name = "")
+{
+    std::unique_ptr<CWallet> wallet = std::make_unique<CWallet>(m_node.chain.get(), wallet_name, CreateMockWalletDatabase());
+    BOOST_CHECK(wallet->LoadWallet() == DBErrors::LOAD_OK);
+    LOCK(wallet->cs_wallet);
+    wallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
+    wallet->SetupDescriptorScriptPubKeyMans();
+    return wallet;
+}
+
 // Branch and bound coin selection tests
 BOOST_AUTO_TEST_CASE(bnb_search_test)
 {
@@ -294,11 +320,7 @@ BOOST_AUTO_TEST_CASE(bnb_search_test)
     coin_selection_params_bnb.m_subtract_fee_outputs = true;
 
     {
-        std::unique_ptr<CWallet> wallet = std::make_unique<CWallet>(m_node.chain.get(), "", CreateMockWalletDatabase());
-        wallet->LoadWallet();
-        LOCK(wallet->cs_wallet);
-        wallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
-        wallet->SetupDescriptorScriptPubKeyMans();
+        std::unique_ptr<CWallet> wallet = NewWallet(m_node);
 
         CoinsResult available_coins;
 
@@ -316,11 +338,7 @@ BOOST_AUTO_TEST_CASE(bnb_search_test)
     }
 
     {
-        std::unique_ptr<CWallet> wallet = std::make_unique<CWallet>(m_node.chain.get(), "", CreateMockWalletDatabase());
-        wallet->LoadWallet();
-        LOCK(wallet->cs_wallet);
-        wallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
-        wallet->SetupDescriptorScriptPubKeyMans();
+        std::unique_ptr<CWallet> wallet = NewWallet(m_node);
 
         CoinsResult available_coins;
 
@@ -335,15 +353,13 @@ BOOST_AUTO_TEST_CASE(bnb_search_test)
         selected_input.Insert(select_coin, coin_selection_params_bnb.m_subtract_fee_outputs);
         available_coins.Erase({available_coins.coins[OutputType::BECH32].begin()->outpoint});
         coin_selection_params_bnb.m_effective_feerate = CFeeRate(0);
+        LOCK(wallet->cs_wallet);
         const auto result10 = SelectCoins(*wallet, available_coins, selected_input, 10 * CENT, coin_control, coin_selection_params_bnb);
         BOOST_CHECK(result10);
     }
     {
-        std::unique_ptr<CWallet> wallet = std::make_unique<CWallet>(m_node.chain.get(), "", CreateMockWalletDatabase());
-        wallet->LoadWallet();
-        LOCK(wallet->cs_wallet);
-        wallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
-        wallet->SetupDescriptorScriptPubKeyMans();
+        std::unique_ptr<CWallet> wallet = NewWallet(m_node);
+        LOCK(wallet->cs_wallet); // Every 'SelectCoins' call requires it
 
         CoinsResult available_coins;
 
@@ -397,6 +413,37 @@ BOOST_AUTO_TEST_CASE(bnb_search_test)
         const auto result13 = SelectCoins(*wallet, available_coins, selected_input, 10 * CENT, coin_control, coin_selection_params_bnb);
         BOOST_CHECK(EquivalentResult(expected_result, *result13));
     }
+
+    {
+        // Test bnb max weight exceeded
+        // Inputs set [10, 9, 8, 5, 3, 1], Selection Target = 16 and coin 5 exceeding the max weight.
+
+        std::unique_ptr<CWallet> wallet = NewWallet(m_node);
+
+        CoinsResult available_coins;
+        add_coin(available_coins, *wallet, 10 * CENT, coin_selection_params_bnb.m_effective_feerate, 6 * 24, false, 0, true);
+        add_coin(available_coins, *wallet, 9 * CENT, coin_selection_params_bnb.m_effective_feerate, 6 * 24, false, 0, true);
+        add_coin(available_coins, *wallet, 8 * CENT, coin_selection_params_bnb.m_effective_feerate, 6 * 24, false, 0, true);
+        add_coin(available_coins, *wallet, 5 * CENT, coin_selection_params_bnb.m_effective_feerate, 6 * 24, false, 0, true, /*custom_size=*/MAX_STANDARD_TX_WEIGHT);
+        add_coin(available_coins, *wallet, 3 * CENT, coin_selection_params_bnb.m_effective_feerate, 6 * 24, false, 0, true);
+        add_coin(available_coins, *wallet, 1 * CENT, coin_selection_params_bnb.m_effective_feerate, 6 * 24, false, 0, true);
+
+        CAmount selection_target = 16 * CENT;
+        const auto& no_res = SelectCoinsBnB(GroupCoins(available_coins.All(), /*subtract_fee_outputs*/true),
+                                            selection_target, /*cost_of_change=*/0, MAX_STANDARD_TX_WEIGHT);
+        BOOST_ASSERT(!no_res);
+        BOOST_CHECK(util::ErrorString(no_res).original.find("The inputs size exceeds the maximum weight") != std::string::npos);
+
+        // Now add same coin value with a good size and check that it gets selected
+        add_coin(available_coins, *wallet, 5 * CENT, coin_selection_params_bnb.m_effective_feerate, 6 * 24, false, 0, true);
+        const auto& res = SelectCoinsBnB(GroupCoins(available_coins.All(), /*subtract_fee_outputs*/true), selection_target, /*cost_of_change=*/0);
+
+        expected_result.Clear();
+        add_coin(8 * CENT, 2, expected_result);
+        add_coin(5 * CENT, 2, expected_result);
+        add_coin(3 * CENT, 2, expected_result);
+        BOOST_CHECK(EquivalentResult(expected_result, *res));
+    }
 }
 
 BOOST_AUTO_TEST_CASE(knapsack_solver_test)
@@ -404,11 +451,7 @@ BOOST_AUTO_TEST_CASE(knapsack_solver_test)
     FastRandomContext rand{};
     const auto temp1{[&rand](std::vector<OutputGroup>& g, const CAmount& v, CAmount c) { return KnapsackSolver(g, v, c, rand); }};
     const auto KnapsackSolver{temp1};
-    std::unique_ptr<CWallet> wallet = std::make_unique<CWallet>(m_node.chain.get(), "", CreateMockWalletDatabase());
-    wallet->LoadWallet();
-    LOCK(wallet->cs_wallet);
-    wallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
-    wallet->SetupDescriptorScriptPubKeyMans();
+    std::unique_ptr<CWallet> wallet = NewWallet(m_node);
 
     CoinsResult available_coins;
 
@@ -714,11 +757,7 @@ BOOST_AUTO_TEST_CASE(knapsack_solver_test)
 BOOST_AUTO_TEST_CASE(ApproximateBestSubset)
 {
     FastRandomContext rand{};
-    std::unique_ptr<CWallet> wallet = std::make_unique<CWallet>(m_node.chain.get(), "", CreateMockWalletDatabase());
-    wallet->LoadWallet();
-    LOCK(wallet->cs_wallet);
-    wallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
-    wallet->SetupDescriptorScriptPubKeyMans();
+    std::unique_ptr<CWallet> wallet = NewWallet(m_node);
 
     CoinsResult available_coins;
 
@@ -736,11 +775,8 @@ BOOST_AUTO_TEST_CASE(ApproximateBestSubset)
 // Tests that with the ideal conditions, the coin selector will always be able to find a solution that can pay the target value
 BOOST_AUTO_TEST_CASE(SelectCoins_test)
 {
-    std::unique_ptr<CWallet> wallet = std::make_unique<CWallet>(m_node.chain.get(), "", CreateMockWalletDatabase());
-    wallet->LoadWallet();
-    LOCK(wallet->cs_wallet);
-    wallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
-    wallet->SetupDescriptorScriptPubKeyMans();
+    std::unique_ptr<CWallet> wallet = NewWallet(m_node);
+    LOCK(wallet->cs_wallet); // Every 'SelectCoins' call requires it
 
     // Random generator stuff
     std::default_random_engine generator;
@@ -921,16 +957,101 @@ 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 util::Result<SelectionResult> select_coins(const CAmount& target, const CoinSelectionParams& cs_params, const CCoinControl& cc, std::function<CoinsResult(CWallet&)> coin_setup, interfaces::Chain* chain)
+
+static util::Result<SelectionResult> SelectCoinsSRD(const CAmount& target,
+                                                    const CoinSelectionParams& cs_params,
+                                                    const node::NodeContext& m_node,
+                                                    int max_weight,
+                                                    std::function<CoinsResult(CWallet&)> coin_setup)
 {
-    std::unique_ptr<CWallet> wallet = std::make_unique<CWallet>(chain, "", CreateMockWalletDatabase());
-    wallet->LoadWallet();
-    LOCK(wallet->cs_wallet);
-    wallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
-    wallet->SetupDescriptorScriptPubKeyMans();
+    std::unique_ptr<CWallet> wallet = NewWallet(m_node);
+    CoinEligibilityFilter filter(0, 0, 0); // accept all coins without ancestors
+    Groups group = GroupOutputs(*wallet, coin_setup(*wallet), cs_params, {{filter}})[filter].all_groups;
+    return SelectCoinsSRD(group.positive_group, target, cs_params.rng_fast, max_weight);
+}
+
+BOOST_AUTO_TEST_CASE(srd_tests)
+{
+    // Test SRD:
+    // 1) Insufficient funds, select all provided coins and fail.
+    // 2) Exceeded max weight, coin selection always surpasses the max allowed weight.
+    // 3) Select coins without surpassing the max weight (some coins surpasses the max allowed weight, some others not)
+
+    FastRandomContext rand;
+    CoinSelectionParams dummy_params{ // Only used to provide the 'avoid_partial' flag.
+            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,
+    };
+
+    {
+        // #########################################################
+        // 1) Insufficient funds, select all provided coins and fail
+        // #########################################################
+        CAmount target = 49.5L * COIN;
+        int max_weight = 10000; // high enough to not fail for this reason.
+        const auto& res = SelectCoinsSRD(target, dummy_params, m_node, max_weight, [&](CWallet& wallet) {
+            CoinsResult available_coins;
+            for (int j = 0; j < 10; ++j) {
+                add_coin(available_coins, wallet, CAmount(1 * COIN));
+                add_coin(available_coins, wallet, CAmount(2 * COIN));
+            }
+            return available_coins;
+        });
+        BOOST_CHECK(!res);
+        BOOST_CHECK(util::ErrorString(res).empty()); // empty means "insufficient funds"
+    }
+
+    {
+        // ###########################
+        // 2) Test max weight exceeded
+        // ###########################
+        CAmount target = 49.5L * COIN;
+        int max_weight = 3000;
+        const auto& res = SelectCoinsSRD(target, dummy_params, m_node, max_weight, [&](CWallet& wallet) {
+            CoinsResult available_coins;
+            for (int j = 0; j < 10; ++j) {
+                add_coin(available_coins, wallet, CAmount(1 * COIN), CFeeRate(0), 144, false, 0, true);
+                add_coin(available_coins, wallet, CAmount(2 * COIN), CFeeRate(0), 144, false, 0, true);
+            }
+            return available_coins;
+        });
+        BOOST_CHECK(!res);
+        BOOST_CHECK(util::ErrorString(res).original.find("The inputs size exceeds the maximum weight") != std::string::npos);
+    }
 
+    {
+        // ################################################################################################################
+        // 3) Test selection when some coins surpass the max allowed weight while others not. --> must find a good solution
+        // ################################################################################################################
+        CAmount target = 25.33L * COIN;
+        int max_weight = 10000; // WU
+        const auto& res = SelectCoinsSRD(target, dummy_params, m_node, max_weight, [&](CWallet& wallet) {
+            CoinsResult available_coins;
+            for (int j = 0; j < 60; ++j) { // 60 UTXO --> 19,8 BTC total --> 60 × 272 WU = 16320 WU
+                add_coin(available_coins, wallet, CAmount(0.33 * COIN), CFeeRate(0), 144, false, 0, true);
+            }
+            for (int i = 0; i < 10; i++) { // 10 UTXO --> 20 BTC total --> 10 × 272 WU = 2720 WU
+                add_coin(available_coins, wallet, CAmount(2 * COIN), CFeeRate(0), 144, false, 0, true);
+            }
+            return available_coins;
+        });
+        BOOST_CHECK(res);
+    }
+}
+
+static util::Result<SelectionResult> select_coins(const CAmount& target, const CoinSelectionParams& cs_params, const CCoinControl& cc, std::function<CoinsResult(CWallet&)> coin_setup, const node::NodeContext& m_node)
+{
+    std::unique_ptr<CWallet> wallet = NewWallet(m_node);
     auto available_coins = coin_setup(*wallet);
 
+    LOCK(wallet->cs_wallet);
     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)
@@ -964,8 +1085,6 @@ BOOST_AUTO_TEST_CASE(check_max_weight)
         /*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
@@ -984,10 +1103,13 @@ BOOST_AUTO_TEST_CASE(check_max_weight)
                 add_coin(available_coins, wallet, CAmount(50 * COIN), CFeeRate(0), 144, false, 0, true);
                 return available_coins;
             },
-            chain);
+            m_node);
 
         BOOST_CHECK(result);
-        BOOST_CHECK(has_coin(result->GetInputSet(), CAmount(50 * COIN)));
+        // Verify that only the 50 BTC UTXO was selected
+        const auto& selection_res = result->GetInputSet();
+        BOOST_CHECK(selection_res.size() == 1);
+        BOOST_CHECK((*selection_res.begin())->GetEffectiveValue() == 50 * COIN);
     }
 
     {
@@ -1009,7 +1131,7 @@ BOOST_AUTO_TEST_CASE(check_max_weight)
                 }
                 return available_coins;
             },
-            chain);
+            m_node);
 
         BOOST_CHECK(has_coin(result->GetInputSet(), CAmount(0.0625 * COIN)));
         BOOST_CHECK(has_coin(result->GetInputSet(), CAmount(0.025 * COIN)));
@@ -1030,7 +1152,7 @@ BOOST_AUTO_TEST_CASE(check_max_weight)
                 }
                 return available_coins;
             },
-            chain);
+            m_node);
 
         // No results
         // 1515 inputs * 68 bytes = 103,020 bytes
@@ -1045,20 +1167,11 @@ BOOST_AUTO_TEST_CASE(SelectCoins_effective_value_test)
     // This test creates a coin whose value is higher than the target but whose effective value is lower than the target.
     // The coin is selected using coin control, with m_allow_other_inputs = false. SelectCoins should fail due to insufficient funds.
 
-    std::unique_ptr<CWallet> wallet = std::make_unique<CWallet>(m_node.chain.get(), "", CreateMockWalletDatabase());
-    wallet->LoadWallet();
-    LOCK(wallet->cs_wallet);
-    wallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
-    wallet->SetupDescriptorScriptPubKeyMans();
+    std::unique_ptr<CWallet> wallet = NewWallet(m_node);
 
     CoinsResult available_coins;
     {
-        std::unique_ptr<CWallet> dummyWallet = std::make_unique<CWallet>(m_node.chain.get(), "dummy", CreateMockWalletDatabase());
-        dummyWallet->LoadWallet();
-        LOCK(dummyWallet->cs_wallet);
-        dummyWallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
-        dummyWallet->SetupDescriptorScriptPubKeyMans();
-
+        std::unique_ptr<CWallet> dummyWallet = NewWallet(m_node, /*wallet_name=*/"dummy");
         add_coin(available_coins, *dummyWallet, 100000); // 0.001 BTC
     }
 
@@ -1082,6 +1195,7 @@ BOOST_AUTO_TEST_CASE(SelectCoins_effective_value_test)
     cc.SetInputWeight(output.outpoint, 148);
     cc.SelectExternal(output.outpoint, output.txout);
 
+    LOCK(wallet->cs_wallet);
     const auto preset_inputs = *Assert(FetchSelectedInputs(*wallet, cc, cs_params));
     available_coins.Erase({available_coins.coins[OutputType::BECH32].begin()->outpoint});
 
@@ -1094,11 +1208,7 @@ BOOST_FIXTURE_TEST_CASE(wallet_coinsresult_test, BasicTestingSetup)
     // Test case to verify CoinsResult object sanity.
     CoinsResult available_coins;
     {
-        std::unique_ptr<CWallet> dummyWallet = std::make_unique<CWallet>(m_node.chain.get(), "dummy", CreateMockWalletDatabase());
-        BOOST_CHECK_EQUAL(dummyWallet->LoadWallet(), DBErrors::LOAD_OK);
-        LOCK(dummyWallet->cs_wallet);
-        dummyWallet->SetWalletFlag(WALLET_FLAG_DESCRIPTORS);
-        dummyWallet->SetupDescriptorScriptPubKeyMans();
+        std::unique_ptr<CWallet> dummyWallet = NewWallet(m_node, /*wallet_name=*/"dummy");
 
         // Add some coins to 'available_coins'
         for (int i=0; i<10; i++) {
diff --git a/src/wallet/test/fuzz/coinselection.cpp b/src/wallet/test/fuzz/coinselection.cpp
index 304190eec1..9be8efab62 100644
--- a/src/wallet/test/fuzz/coinselection.cpp
+++ b/src/wallet/test/fuzz/coinselection.cpp
@@ -3,6 +3,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <policy/feerate.h>
+#include <policy/policy.h>
 #include <primitives/transaction.h>
 #include <test/fuzz/FuzzedDataProvider.h>
 #include <test/fuzz/fuzz.h>
@@ -44,6 +45,9 @@ static void GroupCoins(FuzzedDataProvider& fuzzed_data_provider, const std::vect
     if (valid_outputgroup) output_groups.push_back(output_group);
 }
 
+// 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(); }
+
 FUZZ_TARGET(coinselection)
 {
     FuzzedDataProvider fuzzed_data_provider{buffer.data(), buffer.size()};
@@ -84,18 +88,18 @@ FUZZ_TARGET(coinselection)
     GroupCoins(fuzzed_data_provider, utxo_pool, coin_params, /*positive_only=*/false, group_all);
 
     // Run coinselection algorithms
-    const auto result_bnb = SelectCoinsBnB(group_pos, target, cost_of_change);
+    const auto result_bnb = SelectCoinsBnB(group_pos, target, cost_of_change, MAX_STANDARD_TX_WEIGHT);
 
-    auto result_srd = SelectCoinsSRD(group_pos, target, fast_random_context);
+    auto result_srd = SelectCoinsSRD(group_pos, target, fast_random_context, MAX_STANDARD_TX_WEIGHT);
     if (result_srd) result_srd->ComputeAndSetWaste(cost_of_change, cost_of_change, 0);
 
     CAmount change_target{GenerateChangeTarget(target, coin_params.m_change_fee, fast_random_context)};
-    auto result_knapsack = KnapsackSolver(group_all, target, change_target, fast_random_context);
+    auto result_knapsack = KnapsackSolver(group_all, target, change_target, fast_random_context, MAX_STANDARD_TX_WEIGHT);
     if (result_knapsack) result_knapsack->ComputeAndSetWaste(cost_of_change, cost_of_change, 0);
 
     // If the total balance is sufficient for the target and we are not using
-    // effective values, Knapsack should always find a solution.
-    if (total_balance >= target && subtract_fee_outputs) {
+    // effective values, Knapsack should always find a solution (unless the selection exceeded the max tx weight).
+    if (total_balance >= target && subtract_fee_outputs && !HasErrorMsg(result_knapsack)) {
         assert(result_knapsack);
     }
 }