Disable wallet fallbackfee by default on mainnet

src/chainparams.cpp

@@ -175,6 +175,9 @@ public:
                         //   (the tx=... number in the SetBestChain debug.log lines)
             3.5         // * estimated number of transactions per second after that timestamp
         };
+
+        /* disable fallback fee on mainnet */
+        m_fallback_fee_enabled = false;
     }
 };
 
@@ -266,6 +269,8 @@ public:
             0.09
         };
 
+        /* enable fallback fee on testnet */
+        m_fallback_fee_enabled = true;
     }
 };
 
@@ -343,6 +348,9 @@ public:
         base58Prefixes[EXT_SECRET_KEY] = {0x04, 0x35, 0x83, 0x94};
 
         bech32_hrp = "bcrt";
+
+        /* enable fallback fee on regtest */
+        m_fallback_fee_enabled = true;
     }
 };
 

src/chainparams.h

@@ -65,6 +65,8 @@ public:
     bool MineBlocksOnDemand() const { return fMineBlocksOnDemand; }
     /** Return the BIP70 network string (main, test or regtest) */
     std::string NetworkIDString() const { return strNetworkID; }
+    /** Return true if the fallback fee is by default enabled for this network */
+    bool IsFallbackFeeEnabled() const { return m_fallback_fee_enabled; }
     /** Return the list of hostnames to look up for DNS seeds */
     const std::vector<std::string>& DNSSeeds() const { return vSeeds; }
     const std::vector<unsigned char>& Base58Prefix(Base58Type type) const { return base58Prefixes[type]; }
@@ -91,6 +93,7 @@ protected:
     bool fMineBlocksOnDemand;
     CCheckpointData checkpointData;
     ChainTxData chainTxData;
+    bool m_fallback_fee_enabled;
 };
 
 /**

src/qt/test/wallettests.cpp

@@ -158,6 +158,8 @@ void TestGUI()
         test.CreateAndProcessBlock({}, GetScriptForRawPubKey(test.coinbaseKey.GetPubKey()));
     }
     bitdb.MakeMock();
+    g_wallet_allow_fallback_fee = true;
+
     std::unique_ptr<CWalletDBWrapper> dbw(new CWalletDBWrapper(&bitdb, "wallet_test.dat"));
     CWallet wallet(std::move(dbw));
     bool firstRun;

src/wallet/fees.cpp

@@ -53,6 +53,9 @@ CAmount GetMinimumFee(unsigned int nTxBytes, const CCoinControl& coin_control, c
             // if we don't have enough data for estimateSmartFee, then use fallbackFee
             fee_needed = CWallet::fallbackFee.GetFee(nTxBytes);
             if (feeCalc) feeCalc->reason = FeeReason::FALLBACK;
+
+            // directly return if fallback fee is disabled (feerate 0 == disabled)
+            if (CWallet::fallbackFee.GetFee(1000) == 0) return fee_needed;
         }
         // Obey mempool min fee when using smart fee estimation
         CAmount min_mempool_fee = pool.GetMinFee(gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000).GetFee(nTxBytes);

src/wallet/init.cpp

@@ -5,6 +5,7 @@
 
 #include <wallet/init.h>
 
+#include <chainparams.h>
 #include <net.h>
 #include <util.h>
 #include <utilmoneystr.h>
@@ -123,6 +124,8 @@ bool WalletParameterInteraction()
                         _("This is the minimum transaction fee you pay on every transaction."));
         CWallet::minTxFee = CFeeRate(n);
     }
+
+    g_wallet_allow_fallback_fee = Params().IsFallbackFeeEnabled();
     if (gArgs.IsArgSet("-fallbackfee"))
     {
         CAmount nFeePerK = 0;
@@ -132,6 +135,7 @@ bool WalletParameterInteraction()
             InitWarning(AmountHighWarn("-fallbackfee") + " " +
                         _("This is the transaction fee you may pay when fee estimates are not available."));
         CWallet::fallbackFee = CFeeRate(nFeePerK);
+        g_wallet_allow_fallback_fee = nFeePerK != 0; //disable fallback fee in case value was set to 0, enable if non-null value
     }
     if (gArgs.IsArgSet("-discardfee"))
     {

src/wallet/test/wallet_test_fixture.cpp

@@ -11,6 +11,7 @@ WalletTestingSetup::WalletTestingSetup(const std::string& chainName):
     TestingSetup(chainName)
 {
     bitdb.MakeMock();
+    g_wallet_allow_fallback_fee = true;
 
     bool fFirstRun;
     g_address_type = OUTPUT_TYPE_DEFAULT;

src/wallet/wallet.cpp

@@ -44,6 +44,7 @@ bool bSpendZeroConfChange = DEFAULT_SPEND_ZEROCONF_CHANGE;
 bool fWalletRbf = DEFAULT_WALLET_RBF;
 OutputType g_address_type = OUTPUT_TYPE_NONE;
 OutputType g_change_type = OUTPUT_TYPE_NONE;
+bool g_wallet_allow_fallback_fee = false; //<! will be defined via chainparams
 
 const char * DEFAULT_WALLET_DAT = "wallet.dat";
 const uint32_t BIP32_HARDENED_KEY_LIMIT = 0x80000000;
@@ -2922,6 +2923,11 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend, CWalletT
                 }
 
                 nFeeNeeded = GetMinimumFee(nBytes, coin_control, ::mempool, ::feeEstimator, &feeCalc);
+                if (feeCalc.reason == FeeReason::FALLBACK && !g_wallet_allow_fallback_fee) {
+                    // eventually allow a fallback fee
+                    strFailReason = _("Fee estimation failed. Fallbackfee is disabled. Wait a few blocks or enable -fallbackfee.");
+                    return false;
+                }
 
                 // If we made it here and we aren't even able to meet the relay fee on the next pass, give up
                 // because we must be at the maximum allowed fee.

src/wallet/wallet.h

@@ -39,6 +39,7 @@ extern CFeeRate payTxFee;
 extern unsigned int nTxConfirmTarget;
 extern bool bSpendZeroConfChange;
 extern bool fWalletRbf;
+extern bool g_wallet_allow_fallback_fee;
 
 static const unsigned int DEFAULT_KEYPOOL_SIZE = 1000;
 //! -paytxfee default
@@ -65,6 +66,7 @@ static const unsigned int DEFAULT_TX_CONFIRM_TARGET = 6;
 static const bool DEFAULT_WALLET_RBF = false;
 static const bool DEFAULT_WALLETBROADCAST = true;
 static const bool DEFAULT_DISABLE_WALLET = false;
+static const bool DEFAULT_WALLET_ALLOW_FALLBACKFEE = true;
 
 extern const char * DEFAULT_WALLET_DAT;