Introduce -dustrelayfee

src/init.cpp

@@ -468,6 +468,7 @@ std::string HelpMessage(HelpMessageMode mode)
     if (showDebug) {
         strUsage += HelpMessageOpt("-acceptnonstdtxn", strprintf("Relay and mine \"non-standard\" transactions (%sdefault: %u)", "testnet/regtest only; ", !Params(CBaseChainParams::TESTNET).RequireStandard()));
         strUsage += HelpMessageOpt("-incrementalrelayfee=<amt>", strprintf("Fee rate (in %s/kB) used to define cost of relay, used for mempool limiting and BIP 125 replacement. (default: %s)", CURRENCY_UNIT, FormatMoney(DEFAULT_INCREMENTAL_RELAY_FEE)));
+        strUsage += HelpMessageOpt("-dustrelayfee=<amt>", strprintf("Fee rate (in %s/kB) used to defined dust, the value of an output such that it will cost about 1/3 of its value in fees at this fee rate to spend it. (default: %s)", CURRENCY_UNIT, FormatMoney(DUST_RELAY_TX_FEE)));
     }
     strUsage += HelpMessageOpt("-bytespersigop", strprintf(_("Equivalent bytes per sigop in transactions for relay and mining (default: %u)"), DEFAULT_BYTES_PER_SIGOP));
     strUsage += HelpMessageOpt("-datacarrier", strprintf(_("Relay and mine data carrier transactions (default: %u)"), DEFAULT_ACCEPT_DATACARRIER));
@@ -995,6 +996,16 @@ bool AppInitParameterInteraction()
             return InitError(AmountErrMsg("blockmintxfee", GetArg("-blockmintxfee", "")));
     }
 
+    // Feerate used to define dust.  Shouldn't be changed lightly as old
+    // implementations may inadvertently create non-standard transactions
+    if (IsArgSet("-dustrelayfee"))
+    {
+        CAmount n = 0;
+        if (!ParseMoney(GetArg("-dustrelayfee", ""), n) || 0 == n)
+            return InitError(AmountErrMsg("dustrelayfee", GetArg("-dustrelayfee", "")));
+        dustRelayFee = CFeeRate(n);
+    }
+
     fRequireStandard = !GetBoolArg("-acceptnonstdtxn", !chainparams.RequireStandard());
     if (chainparams.RequireStandard() && !fRequireStandard)
         return InitError(strprintf("acceptnonstdtxn is not currently supported for %s chain", chainparams.NetworkIDString()));

src/policy/policy.cpp

@@ -105,7 +105,7 @@ bool IsStandardTx(const CTransaction& tx, std::string& reason, const bool witnes
         else if ((whichType == TX_MULTISIG) && (!fIsBareMultisigStd)) {
             reason = "bare-multisig";
             return false;
-        } else if (txout.IsDust(::minRelayTxFee)) {
+        } else if (txout.IsDust(dustRelayFee)) {
             reason = "dust";
             return false;
         }
@@ -207,6 +207,7 @@ bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
 }
 
 CFeeRate incrementalRelayFee = CFeeRate(DEFAULT_INCREMENTAL_RELAY_FEE);
+CFeeRate dustRelayFee = CFeeRate(DUST_RELAY_TX_FEE);
 unsigned int nBytesPerSigOp = DEFAULT_BYTES_PER_SIGOP;
 
 int64_t GetVirtualTransactionSize(int64_t nWeight, int64_t nSigOpCost)

src/policy/policy.h

@@ -40,6 +40,12 @@ static const unsigned int MAX_STANDARD_P2WSH_STACK_ITEMS = 100;
 static const unsigned int MAX_STANDARD_P2WSH_STACK_ITEM_SIZE = 80;
 /** The maximum size of a standard witnessScript */
 static const unsigned int MAX_STANDARD_P2WSH_SCRIPT_SIZE = 3600;
+/** Min feerate for defining dust. Historically this has been the same as the
+ * minRelayTxFee, however changing the dust limit changes which transactions are
+ * standard and should be done with care and ideally rarely. It makes sense to
+ * only increase the dust limit after prior releases were already not creating
+ * outputs below the new threshold */
+static const unsigned int DUST_RELAY_TX_FEE = 1000;
 /**
  * Standard script verification flags that standard transactions will comply
  * with. However scripts violating these flags may still be present in valid
@@ -88,6 +94,7 @@ bool AreInputsStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
 bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs);
 
 extern CFeeRate incrementalRelayFee;
+extern CFeeRate dustRelayFee;
 extern unsigned int nBytesPerSigOp;
 
 /** Compute the virtual transaction size (weight reinterpreted as bytes). */

src/qt/coincontroldialog.cpp

@@ -15,7 +15,8 @@
 
 #include "wallet/coincontrol.h"
 #include "init.h"
-#include "validation.h" // For minRelayTxFee
+#include "policy/policy.h"
+#include "validation.h" // For mempool
 #include "wallet/wallet.h"
 
 #include <boost/assign/list_of.hpp> // for 'map_list_of()'
@@ -432,7 +433,7 @@ void CoinControlDialog::updateLabels(WalletModel *model, QDialog* dialog)
         {
             CTxOut txout(amount, (CScript)std::vector<unsigned char>(24, 0));
             txDummy.vout.push_back(txout);
-            if (txout.IsDust(::minRelayTxFee))
+            if (txout.IsDust(dustRelayFee))
                fDust = true;
         }
     }
@@ -545,10 +546,10 @@ void CoinControlDialog::updateLabels(WalletModel *model, QDialog* dialog)
             if (nChange > 0 && nChange < MIN_CHANGE)
             {
                 CTxOut txout(nChange, (CScript)std::vector<unsigned char>(24, 0));
-                if (txout.IsDust(::minRelayTxFee))
+                if (txout.IsDust(dustRelayFee))
                 {
                     if (CoinControlDialog::fSubtractFeeFromAmount) // dust-change will be raised until no dust
-                        nChange = txout.GetDustThreshold(::minRelayTxFee);
+                        nChange = txout.GetDustThreshold(dustRelayFee);
                     else
                     {
                         nPayFee += nChange;

src/qt/guiutil.cpp

@@ -11,7 +11,7 @@
 
 #include "primitives/transaction.h"
 #include "init.h"
-#include "validation.h" // For minRelayTxFee
+#include "policy/policy.h"
 #include "protocol.h"
 #include "script/script.h"
 #include "script/standard.h"
@@ -257,7 +257,7 @@ bool isDust(const QString& address, const CAmount& amount)
     CTxDestination dest = CBitcoinAddress(address.toStdString()).Get();
     CScript script = GetScriptForDestination(dest);
     CTxOut txOut(amount, script);
-    return txOut.IsDust(::minRelayTxFee);
+    return txOut.IsDust(dustRelayFee);
 }
 
 QString HtmlEscape(const QString& str, bool fMultiLine)

src/qt/paymentserver.cpp

@@ -10,7 +10,7 @@
 
 #include "base58.h"
 #include "chainparams.h"
-#include "validation.h" // For minRelayTxFee
+#include "policy/policy.h"
 #include "ui_interface.h"
 #include "util.h"
 #include "wallet/wallet.h"
@@ -582,7 +582,7 @@ bool PaymentServer::processPaymentRequest(const PaymentRequestPlus& request, Sen
 
         // Extract and check amounts
         CTxOut txOut(sendingTo.second, sendingTo.first);
-        if (txOut.IsDust(::minRelayTxFee)) {
+        if (txOut.IsDust(dustRelayFee)) {
             Q_EMIT message(tr("Payment request error"), tr("Requested payment amount of %1 is too small (considered dust).")
                 .arg(BitcoinUnits::formatWithUnit(optionsModel->getDisplayUnit(), sendingTo.second)),
                 CClientUIInterface::MSG_ERROR);

src/test/transaction_tests.cpp

@@ -692,7 +692,7 @@ BOOST_AUTO_TEST_CASE(test_IsStandard)
     BOOST_CHECK(IsStandardTx(t, reason));
 
     // Check dust with default relay fee:
-    CAmount nDustThreshold = 182 * minRelayTxFee.GetFeePerK()/1000 * 3;
+    CAmount nDustThreshold = 182 * dustRelayFee.GetFeePerK()/1000 * 3;
     BOOST_CHECK_EQUAL(nDustThreshold, 546);
     // dust:
     t.vout[0].nValue = nDustThreshold - 1;
@@ -703,14 +703,14 @@ BOOST_AUTO_TEST_CASE(test_IsStandard)
 
     // Check dust with odd relay fee to verify rounding:
     // nDustThreshold = 182 * 1234 / 1000 * 3
-    minRelayTxFee = CFeeRate(1234);
+    dustRelayFee = CFeeRate(1234);
     // dust:
     t.vout[0].nValue = 672 - 1;
     BOOST_CHECK(!IsStandardTx(t, reason));
     // not dust:
     t.vout[0].nValue = 672;
     BOOST_CHECK(IsStandardTx(t, reason));
-    minRelayTxFee = CFeeRate(DEFAULT_MIN_RELAY_TX_FEE);
+    dustRelayFee = CFeeRate(DUST_RELAY_TX_FEE);
 
     t.vout[0].scriptPubKey = CScript() << OP_1;
     BOOST_CHECK(!IsStandardTx(t, reason));

src/wallet/wallet.cpp

@@ -2335,7 +2335,7 @@ bool CWallet::CreateTransaction(const vector<CRecipient>& vecSend, CWalletTx& wt
                         }
                     }
 
-                    if (txout.IsDust(::minRelayTxFee))
+                    if (txout.IsDust(dustRelayFee))
                     {
                         if (recipient.fSubtractFeeFromAmount && nFeeRet > 0)
                         {
@@ -2413,16 +2413,16 @@ bool CWallet::CreateTransaction(const vector<CRecipient>& vecSend, CWalletTx& wt
                     // We do not move dust-change to fees, because the sender would end up paying more than requested.
                     // This would be against the purpose of the all-inclusive feature.
                     // So instead we raise the change and deduct from the recipient.
-                    if (nSubtractFeeFromAmount > 0 && newTxOut.IsDust(::minRelayTxFee))
+                    if (nSubtractFeeFromAmount > 0 && newTxOut.IsDust(dustRelayFee))
                     {
-                        CAmount nDust = newTxOut.GetDustThreshold(::minRelayTxFee) - newTxOut.nValue;
+                        CAmount nDust = newTxOut.GetDustThreshold(dustRelayFee) - newTxOut.nValue;
                         newTxOut.nValue += nDust; // raise change until no more dust
                         for (unsigned int i = 0; i < vecSend.size(); i++) // subtract from first recipient
                         {
                             if (vecSend[i].fSubtractFeeFromAmount)
                             {
                                 txNew.vout[i].nValue -= nDust;
-                                if (txNew.vout[i].IsDust(::minRelayTxFee))
+                                if (txNew.vout[i].IsDust(dustRelayFee))
                                 {
                                     strFailReason = _("The transaction amount is too small to send after the fee has been deducted");
                                     return false;
@@ -2434,7 +2434,7 @@ bool CWallet::CreateTransaction(const vector<CRecipient>& vecSend, CWalletTx& wt
 
                     // Never create dust outputs; if we would, just
                     // add the dust to the fee.
-                    if (newTxOut.IsDust(::minRelayTxFee))
+                    if (newTxOut.IsDust(dustRelayFee))
                     {
                         nChangePosInOut = -1;
                         nFeeRet += nChange;