From 6b563cae92957dc30dc35103a7c321fdb0115ef3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Aur=C3=A8le=20Oul=C3=A8s?= <aurele@oules.com>
Date: Tue, 4 Oct 2022 14:17:11 +0200
Subject: wallet: Check max tx weight in coin selector

Co-authored-by: Andrew Chow <github@achow101.com>
---
 src/wallet/coinselection.cpp | 14 ++++++++++++++
 src/wallet/coinselection.h   |  7 +++++++
 src/wallet/spend.cpp         | 29 +++++++++++++++++++----------
 3 files changed, 40 insertions(+), 10 deletions(-)

(limited to 'src/wallet')

diff --git a/src/wallet/coinselection.cpp b/src/wallet/coinselection.cpp
index b889d31928..ba1d60fe44 100644
--- a/src/wallet/coinselection.cpp
+++ b/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
diff --git a/src/wallet/coinselection.h b/src/wallet/coinselection.h
index 2ab4061a9b..ecfc5bfd6b 100644
--- a/src/wallet/coinselection.h
+++ b/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 @@ private:
     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 @@ public:
     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);
diff --git a/src/wallet/spend.cpp b/src/wallet/spend.cpp
index 52d10b74b5..1724b11268 100644
--- a/src/wallet/spend.cpp
+++ b/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
-- 
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