[qt] Properly display required fee instead of minTxFee

Zcash: Only includes non-QT parts

src/wallet/wallet.cpp

@@ -3636,6 +3636,11 @@ bool CWallet::CommitTransaction(CWalletTx& wtxNew, boost::optional<CReserveKey&>
     return true;
 }
 
+CAmount CWallet::GetRequiredFee(unsigned int nTxBytes)
+{
+    return std::max(minTxFee.GetFee(nTxBytes), ::minRelayTxFee.GetFee(nTxBytes));
+}
+
 CAmount CWallet::GetMinimumFee(unsigned int nTxBytes, unsigned int nConfirmTarget, const CTxMemPool& pool)
 {
     // payTxFee is user-set "I want to pay this much"
@@ -3647,9 +3652,9 @@ CAmount CWallet::GetMinimumFee(unsigned int nTxBytes, unsigned int nConfirmTarge
     if (nFeeNeeded == 0)
         nFeeNeeded = pool.estimateFee(nConfirmTarget).GetFee(nTxBytes);
     // ... unless we don't have enough mempool data, in which case fall
-    // back to a hard-coded fee
+    // back to the required fee
     if (nFeeNeeded == 0)
-        nFeeNeeded = minTxFee.GetFee(nTxBytes);
+        nFeeNeeded = GetRequiredFee(nTxBytes);
     // prevent user from paying a non-sense fee (like 1 satoshi): 0 < fee < minRelayFee
     if (nFeeNeeded < ::minRelayTxFee.GetFee(nTxBytes))
         nFeeNeeded = ::minRelayTxFee.GetFee(nTxBytes);

src/wallet/wallet.h

@@ -1176,7 +1176,16 @@ public:
     bool CommitTransaction(CWalletTx& wtxNew, boost::optional<CReserveKey&> reservekey);
 
     static CFeeRate minTxFee;
+    /**
+     * Estimate the minimum fee considering user set parameters
+     * and the required fee
+     */
     static CAmount GetMinimumFee(unsigned int nTxBytes, unsigned int nConfirmTarget, const CTxMemPool& pool);
+    /**
+     * Return the minimum required fee taking into account the
+     * floating relay fee and user set minimum transaction fee
+     */
+    static CAmount GetRequiredFee(unsigned int nTxBytes);
 
     bool NewKeyPool();
     bool TopUpKeyPool(unsigned int kpSize = 0);