From b583f73354c617ede9145f9738f13cedf1c13e08 Mon Sep 17 00:00:00 2001
From: Andrew Chow <achow101-github@achow101.com>
Date: Mon, 17 May 2021 16:31:06 -0400
Subject: [PATCH] Move vin filling to before final fee setting

It's unnecessary to fill in the vin with dummy inputs, calculate the
fee, then fill in the vin with the actual inputs. Just fill the vin with
the actual inputs the first time.
---
 src/wallet/spend.cpp | 35 ++++++++++++++---------------------
 1 file changed, 14 insertions(+), 21 deletions(-)

diff --git a/src/wallet/spend.cpp b/src/wallet/spend.cpp
index dbe5d165c8..e3bea9bd33 100644
--- a/src/wallet/spend.cpp
+++ b/src/wallet/spend.cpp
@@ -729,10 +729,21 @@ bool CWallet::CreateTransactionInternal(
     assert(nChangePosInOut != -1);
     auto change_position = txNew.vout.insert(txNew.vout.begin() + nChangePosInOut, newTxOut);
 
-    // Dummy fill vin for maximum size estimation
+    // Shuffle selected coins and fill in final vin
+    std::vector<CInputCoin> selected_coins(setCoins.begin(), setCoins.end());
+    Shuffle(selected_coins.begin(), selected_coins.end(), FastRandomContext());
+
+    // Note how the sequence number is set to non-maxint so that
+    // the nLockTime set above actually works.
     //
-    for (const auto& coin : setCoins) {
-        txNew.vin.push_back(CTxIn(coin.outpoint,CScript()));
+    // BIP125 defines opt-in RBF as any nSequence < maxint-1, so
+    // we use the highest possible value in that range (maxint-2)
+    // to avoid conflicting with other possible uses of nSequence,
+    // and in the spirit of "smallest possible change from prior
+    // behavior."
+    const uint32_t nSequence = coin_control.m_signal_bip125_rbf.value_or(m_signal_rbf) ? MAX_BIP125_RBF_SEQUENCE : (CTxIn::SEQUENCE_FINAL - 1);
+    for (const auto& coin : selected_coins) {
+        txNew.vin.push_back(CTxIn(coin.outpoint, CScript(), nSequence));
     }
 
     // Calculate the transaction fee
@@ -813,24 +824,6 @@ bool CWallet::CreateTransactionInternal(
         return false;
     }
 
-    // Shuffle selected coins and fill in final vin
-    txNew.vin.clear();
-    std::vector<CInputCoin> selected_coins(setCoins.begin(), setCoins.end());
-    Shuffle(selected_coins.begin(), selected_coins.end(), FastRandomContext());
-
-    // Note how the sequence number is set to non-maxint so that
-    // the nLockTime set above actually works.
-    //
-    // BIP125 defines opt-in RBF as any nSequence < maxint-1, so
-    // we use the highest possible value in that range (maxint-2)
-    // to avoid conflicting with other possible uses of nSequence,
-    // and in the spirit of "smallest possible change from prior
-    // behavior."
-    const uint32_t nSequence = coin_control.m_signal_bip125_rbf.value_or(m_signal_rbf) ? MAX_BIP125_RBF_SEQUENCE : (CTxIn::SEQUENCE_FINAL - 1);
-    for (const auto& coin : selected_coins) {
-        txNew.vin.push_back(CTxIn(coin.outpoint, CScript(), nSequence));
-    }
-
     if (sign && !SignTransaction(txNew)) {
         error = _("Signing transaction failed");
         return false;