Consensus: Minimal way to move dust out of consensus

coming from btc@330bb5a456a5f9c26703fa742e4c80691e1455ab

src/policy/policy.cpp

@@ -16,6 +16,29 @@
 
 bool fIsBareMultisigStd = DEFAULT_PERMIT_BAREMULTISIG;
 
+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 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).
+    if (txout.scriptPubKey.IsUnspendable())
+        return 0;
+
+    size_t nSize = GetSerializeSize(txout, SER_DISK, 0);
+    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:
@@ -132,7 +155,7 @@ bool IsStandardTx(const CTransaction& tx, std::string& reason)
         else if ((whichType == TX_MULTISIG) && (!fIsBareMultisigStd)) {
             reason = "bare-multisig";
             return false;
-        } else if (txout.IsDust(::minRelayTxFee)) {
+        } else if (IsDust(txout, ::minRelayTxFee)) {
             reason = "dust";
             return false;
         }

src/policy/policy.h

@@ -14,6 +14,7 @@
 
 class CChainParams;
 class CCoinsViewCache;
+class CTxOut;
 
 /** Default for -blockmaxsize and -blockminsize, which control the range of sizes the mining code will create **/
 static const unsigned int DEFAULT_BLOCK_MAX_SIZE = 750000;
@@ -48,6 +49,10 @@ static constexpr unsigned int STANDARD_NOT_MANDATORY_VERIFY_FLAGS = STANDARD_SCR
 BOOST_STATIC_ASSERT(DEFAULT_BLOCK_MAX_SIZE <= MAX_BLOCK_SIZE_CURRENT);
 BOOST_STATIC_ASSERT(DEFAULT_BLOCK_PRIORITY_SIZE <= DEFAULT_BLOCK_MAX_SIZE);
 
+CAmount GetDustThreshold(const CTxOut& txout, const CFeeRate& dustRelayFee);
+
+bool IsDust(const CTxOut& txout, const CFeeRate& dustRelayFee);
+
 bool IsStandard(const CScript& scriptPubKey, txnouttype& whichType);
 
 /** Check for standard transaction types

src/primitives/transaction.h

@@ -194,28 +194,6 @@ class CTxOut
     uint256 GetHash() const;
     bool GetKeyIDFromUTXO(CKeyID& keyIDRet) const;
 
-    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 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 satoshis
-        // with default minRelayTxFee.
-        if (scriptPubKey.IsUnspendable())
-            return 0;
-
-        size_t nSize = GetSerializeSize(*this, SER_DISK, 0) + 148u;
-        return 3 * minRelayTxFee.GetFee(nSize);
-    }
-
-    bool IsDust(const CFeeRate& minRelayTxFee) const
-    {
-        return (nValue < GetDustThreshold(minRelayTxFee));
-    }
-
     bool IsZerocoinMint() const;
 
     friend bool operator==(const CTxOut& a, const CTxOut& b)

src/qt/coincontroldialog.cpp

@@ -13,6 +13,7 @@
 #include "guiutil.h"
 #include "init.h"
 #include "optionsmodel.h"
+#include "policy/policy.h"
 #include "txmempool.h"
 #include "wallet/wallet.h"
 #include "walletmodel.h"
@@ -566,7 +567,7 @@ void CoinControlDialog::updateLabels()
         nPayAmount += amount;
         if (amount > 0) {
             CTxOut txout(amount, (CScript)std::vector<unsigned char>(24, 0));
-            if (txout.IsDust(::minRelayTxFee))
+            if (IsDust(txout, ::minRelayTxFee))
                 fDust = true;
         }
     }
@@ -669,7 +670,7 @@ void CoinControlDialog::updateLabels()
             // Never create dust outputs; if we would, just add the dust to the fee.
             if (nChange > 0 && nChange < CENT) {
                 CTxOut txout(nChange, (CScript)std::vector<unsigned char>(24, 0));
-                if (txout.IsDust(::minRelayTxFee)) {
+                if (IsDust(txout, ::minRelayTxFee)) {
                     nPayFee += nChange;
                     nChange = 0;
                 }

src/qt/guiutil.cpp

@@ -12,6 +12,7 @@
 #include "walletmodel.h"
 
 #include "init.h"
+#include "policy/policy.h"
 #include "primitives/transaction.h"
 #include "protocol.h"
 #include "script/script.h"
@@ -246,7 +247,7 @@ bool isDust(const QString& address, const CAmount& amount)
     CTxDestination dest = DecodeDestination(address.toStdString());
     CScript script = GetScriptForDestination(dest);
     CTxOut txOut(amount, script);
-    return txOut.IsDust(::minRelayTxFee);
+    return IsDust(txOut, ::minRelayTxFee);
 }
 
 QString HtmlEscape(const QString& str, bool fMultiLine)

src/qt/paymentserver.cpp

@@ -9,6 +9,7 @@
 #include "bitcoinunits.h"
 #include "guiutil.h"
 #include "optionsmodel.h"
+#include "policy/policy.h"
 
 #include "base58.h"
 #include "chainparams.h"
@@ -515,7 +516,7 @@ bool PaymentServer::processPaymentRequest(PaymentRequestPlus& request, SendCoins
 
         // Extract and check amounts
         CTxOut txOut(sendingTo.second, sendingTo.first);
-        if (txOut.IsDust(::minRelayTxFee)) {
+        if (IsDust(txOut, ::minRelayTxFee)) {
             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/wallet.cpp

@@ -2593,7 +2593,7 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend,
                 if (coinControl && !coinControl->fSplitBlock) {
                     for (const CRecipient& rec : vecSend) {
                         CTxOut txout(rec.nAmount, rec.scriptPubKey);
-                        if (txout.IsDust(::minRelayTxFee)) {
+                        if (IsDust(txout, ::minRelayTxFee)) {
                             strFailReason = _("Transaction amount too small");
                             return false;
                         }
@@ -2700,7 +2700,7 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend,
 
                         // Never create dust outputs; if we would, just
                         // add the dust to the fee.
-                        if (newTxOut.IsDust(::minRelayTxFee)) {
+                        if (IsDust(newTxOut, ::minRelayTxFee)) {
                             nFeeRet += nChange;
                             nChange = 0;
                             reservekey.ReturnKey();