Consensus: Minimal way to move dust out of consensus

Author: jtimon

src/policy/policy.cpp

@@ -15,6 +15,43 @@
 
 #include <boost/foreach.hpp>
 
+CAmount GetDustThreshold(const CTxOut& txout, const CFeeRate& dustRelayFee)
+{
+    // "Dust" is defined in terms of dustRelayFee,
+    // which has units satoshis-per-kilobyte.
+    // If you'd pay more than 1/3 in fees
+    // to spend something, then we consider it dust.
+    // A typical spendable non-segwit txout is 34 bytes big, and will
+    // need a CTxIn of at least 148 bytes to spend:
+    // so dust is a spendable txout less than
+    // 546*dustRelayFee/1000 (in satoshis).
+    // A typical spendable segwit txout is 31 bytes big, and will
+    // need a CTxIn of at least 67 bytes to spend:
+    // so dust is a spendable txout less than
+    // 294*dustRelayFee/1000 (in satoshis).
+    if (txout.scriptPubKey.IsUnspendable())
+        return 0;
+
+    size_t nSize = GetSerializeSize(txout, SER_DISK, 0);
+    int witnessversion = 0;
+    std::vector<unsigned char> witnessprogram;
+
+    if (txout.scriptPubKey.IsWitnessProgram(witnessversion, witnessprogram)) {
+        // sum the sizes of the parts of a transaction input
+        // with 75% segwit discount applied to the script size.
+        nSize += (32 + 4 + 1 + (107 / WITNESS_SCALE_FACTOR) + 4);
+    } else {
+        nSize += (32 + 4 + 1 + 107 + 4); // the 148 mentioned above
+    }
+
+    return 3 * dustRelayFee.GetFee(nSize);
+}
+
+bool IsDust(const CTxOut& txout, const CFeeRate& dustRelayFee)
+{
+    return (txout.nValue < GetDustThreshold(txout, dustRelayFee));
+}
+
     /**
      * Check transaction inputs to mitigate two
      * potential denial-of-service attacks:
@@ -106,7 +143,7 @@ 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(dustRelayFee)) {
+        } else if (IsDust(txout, ::dustRelayFee)) {
             reason = "dust";
             return false;
         }

src/policy/policy.h

@@ -13,6 +13,7 @@
 #include <string>
 
 class CCoinsViewCache;
+class CTxOut;
 
 /** Default for -blockmaxsize, which controls the maximum size of block the mining code will create **/
 static const unsigned int DEFAULT_BLOCK_MAX_SIZE = 750000;
@@ -72,6 +73,10 @@ static const unsigned int STANDARD_NOT_MANDATORY_VERIFY_FLAGS = STANDARD_SCRIPT_
 static const unsigned int STANDARD_LOCKTIME_VERIFY_FLAGS = LOCKTIME_VERIFY_SEQUENCE |
                                                            LOCKTIME_MEDIAN_TIME_PAST;
 
+CAmount GetDustThreshold(const CTxOut& txout, const CFeeRate& dustRelayFee);
+
+bool IsDust(const CTxOut& txout, const CFeeRate& dustRelayFee);
+
 bool IsStandard(const CScript& scriptPubKey, txnouttype& whichType, const bool witnessEnabled = false);
     /**
      * Check for standard transaction types

src/primitives/transaction.h

@@ -161,43 +161,6 @@ class CTxOut
         return (nValue == -1);
     }
 
-    CAmount GetDustThreshold(const CFeeRate &minRelayTxFee) const
-    {
-        // "Dust" is defined in terms of CTransaction::minRelayTxFee,
-        // which has units satoshis-per-kilobyte.
-        // If you'd pay more than 1/3 in fees
-        // to spend something, then we consider it dust.
-        // A typical spendable non-segwit txout is 34 bytes big, and will
-        // need a CTxIn of at least 148 bytes to spend:
-        // so dust is a spendable txout less than
-        // 546*minRelayTxFee/1000 (in satoshis).
-        // A typical spendable segwit txout is 31 bytes big, and will
-        // need a CTxIn of at least 67 bytes to spend:
-        // so dust is a spendable txout less than
-        // 294*minRelayTxFee/1000 (in satoshis).
-        if (scriptPubKey.IsUnspendable())
-            return 0;
-
-        size_t nSize = GetSerializeSize(*this, SER_DISK, 0);
-        int witnessversion = 0;
-        std::vector<unsigned char> witnessprogram;
-
-        if (scriptPubKey.IsWitnessProgram(witnessversion, witnessprogram)) {
-            // sum the sizes of the parts of a transaction input
-            // with 75% segwit discount applied to the script size.
-            nSize += (32 + 4 + 1 + (107 / WITNESS_SCALE_FACTOR) + 4);
-        } else {
-            nSize += (32 + 4 + 1 + 107 + 4); // the 148 mentioned above
-        }
-
-        return 3 * minRelayTxFee.GetFee(nSize);
-    }
-
-    bool IsDust(const CFeeRate &minRelayTxFee) const
-    {
-        return (nValue < GetDustThreshold(minRelayTxFee));
-    }
-
     friend bool operator==(const CTxOut& a, const CTxOut& b)
     {
         return (a.nValue       == b.nValue &&

src/qt/coincontroldialog.cpp

@@ -434,8 +434,7 @@ 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(dustRelayFee))
-               fDust = true;
+            fDust |= IsDust(txout, ::dustRelayFee);
         }
     }
 
@@ -527,10 +526,10 @@ 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(dustRelayFee))
+                if (IsDust(txout, ::dustRelayFee))
                 {
                     if (CoinControlDialog::fSubtractFeeFromAmount) // dust-change will be raised until no dust
-                        nChange = txout.GetDustThreshold(dustRelayFee);
+                        nChange = GetDustThreshold(txout, ::dustRelayFee);
                     else
                     {
                         nPayFee += nChange;

src/qt/guiutil.cpp

@@ -251,7 +251,7 @@ 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(dustRelayFee);
+    return IsDust(txOut, ::dustRelayFee);
 }
 
 QString HtmlEscape(const QString& str, bool fMultiLine)

src/qt/paymentserver.cpp

@@ -580,7 +580,7 @@ bool PaymentServer::processPaymentRequest(const PaymentRequestPlus& request, Sen
 
         // Extract and check amounts
         CTxOut txOut(sendingTo.second, sendingTo.first);
-        if (txOut.IsDust(dustRelayFee)) {
+        if (IsDust(txOut, ::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/wallet/feebumper.cpp

@@ -214,7 +214,7 @@ CFeeBumper::CFeeBumper(const CWallet *pWallet, const uint256 txidIn, int newConf
 
     // If the output would become dust, discard it (converting the dust to fee)
     poutput->nValue -= nDelta;
-    if (poutput->nValue <= poutput->GetDustThreshold(::dustRelayFee)) {
+    if (poutput->nValue <= GetDustThreshold(*poutput, ::dustRelayFee)) {
         LogPrint(BCLog::RPC, "Bumping fee and discarding dust output\n");
         nNewFee += poutput->nValue;
         mtx.vout.erase(mtx.vout.begin() + nOutput);

src/wallet/wallet.cpp

@@ -2449,7 +2449,7 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend, CWalletT
                         }
                     }
 
-                    if (txout.IsDust(dustRelayFee))
+                    if (IsDust(txout, ::dustRelayFee))
                     {
                         if (recipient.fSubtractFeeFromAmount && nFeeRet > 0)
                         {
@@ -2514,16 +2514,16 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend, CWalletT
                     // 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(dustRelayFee))
+                    if (nSubtractFeeFromAmount > 0 && IsDust(newTxOut, ::dustRelayFee))
                     {
-                        CAmount nDust = newTxOut.GetDustThreshold(dustRelayFee) - newTxOut.nValue;
+                        CAmount nDust = GetDustThreshold(newTxOut, ::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(dustRelayFee))
+                                if (IsDust(txNew.vout[i], ::dustRelayFee))
                                 {
                                     strFailReason = _("The transaction amount is too small to send after the fee has been deducted");
                                     return false;
@@ -2535,7 +2535,7 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend, CWalletT
 
                     // Never create dust outputs; if we would, just
                     // add the dust to the fee.
-                    if (newTxOut.IsDust(dustRelayFee))
+                    if (IsDust(newTxOut, ::dustRelayFee))
                     {
                         nChangePosInOut = -1;
                         nFeeRet += nChange;