Introduce WALLET_INCREMENTAL_RELAY_FEE

Have wallet's default bump value be higher than the default incrementalRelayFee to future proof against changes to incremental relay fee.  Only applies when not setting the fee rate directly.

src/wallet/rpcwallet.cpp

@@ -2786,11 +2786,19 @@ UniValue bumpfee(const JSONRPCRequest& request)
     CFeeRate nOldFeeRate(nOldFee, txSize);
     CAmount nNewFee;
     CFeeRate nNewFeeRate;
+    // The wallet uses a conservative WALLET_INCREMENTAL_RELAY_FEE value to
+    // future proof against changes to network wide policy for incremental relay
+    // fee that our node may not be aware of.
+    CFeeRate walletIncrementalRelayFee = CFeeRate(WALLET_INCREMENTAL_RELAY_FEE);
+    if (::incrementalRelayFee > walletIncrementalRelayFee) {
+        walletIncrementalRelayFee = ::incrementalRelayFee;
+    }
 
     if (totalFee > 0) {
         CAmount minTotalFee = nOldFeeRate.GetFee(maxNewTxSize) + ::incrementalRelayFee.GetFee(maxNewTxSize);
         if (totalFee < minTotalFee) {
-            throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Invalid totalFee, must be at least %s (oldFee %s + relayFee %s)", FormatMoney(minTotalFee), nOldFeeRate.GetFee(maxNewTxSize), ::incrementalRelayFee.GetFee(maxNewTxSize)));
+            throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Insufficient totalFee, must be at least %s (oldFee %s + incrementalFee %s)",
+                                                                FormatMoney(minTotalFee), FormatMoney(nOldFeeRate.GetFee(maxNewTxSize)), FormatMoney(::incrementalRelayFee.GetFee(maxNewTxSize))));
         }
         nNewFee = totalFee;
         nNewFeeRate = CFeeRate(totalFee, maxNewTxSize);
@@ -2806,9 +2814,9 @@ UniValue bumpfee(const JSONRPCRequest& request)
 
         nNewFeeRate = CFeeRate(nNewFee, maxNewTxSize);
 
-        // new fee rate must be at least old rate + minimum incremental relay rate
-        if (nNewFeeRate.GetFeePerK() < nOldFeeRate.GetFeePerK() + ::incrementalRelayFee.GetFeePerK()) {
-            nNewFeeRate = CFeeRate(nOldFeeRate.GetFeePerK() + ::incrementalRelayFee.GetFeePerK());
+        // New fee rate must be at least old rate + minimum incremental relay rate
+        if (nNewFeeRate.GetFeePerK() < nOldFeeRate.GetFeePerK() + walletIncrementalRelayFee.GetFeePerK()) {
+            nNewFeeRate = CFeeRate(nOldFeeRate.GetFeePerK() + walletIncrementalRelayFee.GetFeePerK());
             nNewFee = nNewFeeRate.GetFee(maxNewTxSize);
         }
     }

src/wallet/wallet.h

@@ -48,6 +48,8 @@ static const CAmount DEFAULT_TRANSACTION_FEE = 0;
 static const CAmount DEFAULT_FALLBACK_FEE = 20000;
 //! -mintxfee default
 static const CAmount DEFAULT_TRANSACTION_MINFEE = 1000;
+//! minimum recommended increment for BIP 125 replacement txs
+static const CAmount WALLET_INCREMENTAL_RELAY_FEE = 5000;
 //! target minimum change amount
 static const CAmount MIN_CHANGE = CENT;
 //! final minimum change amount after paying for fees