wallet: try -avoidpartialspends mode and use its result if fees are below threshold

The threshold is defined by a new max avoid partial spends fee flag, which defaults to 0 (i.e. if fees are unchanged, use the grouped option).

1 files changed, 13 insertions, 0 deletions

diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index a761caf38c..6d9512f59a 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -72,6 +72,16 @@ static const CAmount DEFAULT_FALLBACK_FEE = 0;
 static const CAmount DEFAULT_DISCARD_FEE = 10000;
 //! -mintxfee default
 static const CAmount DEFAULT_TRANSACTION_MINFEE = 1000;
+/**
+ * maximum fee increase allowed to do partial spend avoidance, even for nodes with this feature disabled by default
+ *
+ * A value of -1 disables this feature completely.
+ * A value of 0 (current default) means to attempt to do partial spend avoidance, and use its results if the fees remain *unchanged*
+ * A value > 0 means to do partial spend avoidance if the fee difference against a regular coin selection instance is in the range [0..value].
+ */
+static const CAmount DEFAULT_MAX_AVOIDPARTIALSPEND_FEE = 0;
+//! discourage APS fee higher than this amount
+constexpr CAmount HIGH_APS_FEE{COIN / 10000};
 //! minimum recommended increment for BIP 125 replacement txs
 static const CAmount WALLET_INCREMENTAL_RELAY_FEE = 5000;
 //! Default for -spendzeroconfchange
@@ -719,6 +729,8 @@ private:
     // ScriptPubKeyMan::GetID. In many cases it will be the hash of an internal structure
     std::map<uint256, std::unique_ptr<ScriptPubKeyMan>> m_spk_managers;
 
+    bool CreateTransactionInternal(const std::vector<CRecipient>& vecSend, CTransactionRef& tx, CAmount& nFeeRet, int& nChangePosInOut, bilingual_str& error, const CCoinControl& coin_control, bool sign);
+
 public:
     /*
      * Main wallet lock.
@@ -1008,6 +1020,7 @@ public:
      */
     CFeeRate m_fallback_fee{DEFAULT_FALLBACK_FEE};
     CFeeRate m_discard_rate{DEFAULT_DISCARD_FEE};
+    CAmount m_max_aps_fee{DEFAULT_MAX_AVOIDPARTIALSPEND_FEE}; //!< note: this is absolute fee, not fee rate
     OutputType m_default_address_type{DEFAULT_ADDRESS_TYPE};
     /**
      * Default output type for change outputs. When unset, automatically choose type