wallet: Remove sendfree

This removes the option from the wallet to not pay a fee on "small"
transactions which spend "old" inputs.

This code is no longer worth keeping around, as almost all miners
prefer not to include transactions which pay no fee at all.

contrib/debian/examples/bitcoin.conf

@@ -118,9 +118,6 @@
 
 # Transaction Fee Changes in 0.10.0
 
-# Send transactions as zero-fee transactions if possible (default: 0)
-#sendfreetransactions=0
-
 # Create transactions that have enough fees (or priority) so they are likely to begin confirmation within n blocks (default: 1).
 # This setting is over-ridden by the -paytxfee option.
 #txconfirmtarget=n

contrib/devtools/check-doc.py

@@ -21,7 +21,7 @@ CMD_GREP_DOCS = r"egrep -r -I 'HelpMessageOpt\(\"\-[^\"=]+?(=|\")' %s" % (CMD_RO
 REGEX_ARG = re.compile(r'(?:map(?:Multi)?Args(?:\.count\(|\[)|Get(?:Bool)?Arg\()\"(\-[^\"]+?)\"')
 REGEX_DOC = re.compile(r'HelpMessageOpt\(\"(\-[^\"=]+?)(?:=|\")')
 # list unsupported, deprecated and duplicate args as they need no documentation
-SET_DOC_OPTIONAL = set(['-rpcssl', '-benchmark', '-h', '-help', '-socks', '-tor', '-debugnet', '-whitelistalwaysrelay', '-prematurewitness', '-walletprematurewitness', '-promiscuousmempoolflags', '-blockminsize'])
+SET_DOC_OPTIONAL = set(['-rpcssl', '-benchmark', '-h', '-help', '-socks', '-tor', '-debugnet', '-whitelistalwaysrelay', '-prematurewitness', '-walletprematurewitness', '-promiscuousmempoolflags', '-blockminsize', '-sendfreetransactions'])
 
 def main():
   used = check_output(CMD_GREP_ARGS, shell=True)

src/qt/coincontroldialog.cpp

@@ -444,11 +444,7 @@ void CoinControlDialog::updateLabels(WalletModel *model, QDialog* dialog)
     CAmount nChange             = 0;
     unsigned int nBytes         = 0;
     unsigned int nBytesInputs   = 0;
-    double dPriority            = 0;
-    double dPriorityInputs      = 0;
     unsigned int nQuantity      = 0;
-    int nQuantityUncompressed   = 0;
-    bool fAllowFree             = false;
     bool fWitness               = false;
 
     std::vector<COutPoint> vCoinControl;
@@ -473,9 +469,6 @@ void CoinControlDialog::updateLabels(WalletModel *model, QDialog* dialog)
         // Amount
         nAmount += out.tx->tx->vout[out.i].nValue;
 
-        // Priority
-        dPriorityInputs += (double)out.tx->tx->vout[out.i].nValue * (out.nDepth+1);
-
         // Bytes
         CTxDestination address;
         int witnessversion = 0;
@@ -492,8 +485,6 @@ void CoinControlDialog::updateLabels(WalletModel *model, QDialog* dialog)
             if (keyid && model->getPubKey(*keyid, pubkey))
             {
                 nBytesInputs += (pubkey.IsCompressed() ? 148 : 180);
-                if (!pubkey.IsCompressed())
-                    nQuantityUncompressed++;
             }
             else
                 nBytesInputs += 148; // in all error cases, simply assume 148 here
@@ -525,17 +516,6 @@ void CoinControlDialog::updateLabels(WalletModel *model, QDialog* dialog)
         if (nPayFee > 0 && coinControl->nMinimumTotalFee > nPayFee)
             nPayFee = coinControl->nMinimumTotalFee;
 
-
-        // Allow free? (require at least hard-coded threshold and default to that if no estimate)
-        double mempoolEstimatePriority = mempool.estimateSmartPriority(nTxConfirmTarget);
-        dPriority = dPriorityInputs / (nBytes - nBytesInputs + (nQuantityUncompressed * 29)); // 29 = 180 - 151 (uncompressed public keys are over the limit. max 151 bytes of the input are ignored for priority)
-        double dPriorityNeeded = std::max(mempoolEstimatePriority, AllowFreeThreshold());
-        fAllowFree = (dPriority >= dPriorityNeeded);
-
-        if (fSendFreeTransactions)
-            if (fAllowFree && nBytes <= MAX_FREE_TRANSACTION_CREATE_SIZE)
-                nPayFee = 0;
-
         if (nPayAmount > 0)
         {
             nChange = nAmount - nPayAmount;

src/wallet/wallet.cpp

@@ -39,7 +39,6 @@ CWallet* pwalletMain = NULL;
 CFeeRate payTxFee(DEFAULT_TRANSACTION_FEE);
 unsigned int nTxConfirmTarget = DEFAULT_TX_CONFIRM_TARGET;
 bool bSpendZeroConfChange = DEFAULT_SPEND_ZEROCONF_CHANGE;
-bool fSendFreeTransactions = DEFAULT_SEND_FREE_TRANSACTIONS;
 bool fWalletRbf = DEFAULT_WALLET_RBF;
 
 const char * DEFAULT_WALLET_DAT = "wallet.dat";
@@ -2449,7 +2448,6 @@ bool CWallet::CreateTransaction(const vector<CRecipient>& vecSend, CWalletTx& wt
                 CAmount nValueToSelect = nValue;
                 if (nSubtractFeeFromAmount == 0)
                     nValueToSelect += nFeeRet;
-                double dPriority = 0;
                 // vouts to the payees
                 for (const auto& recipient : vecSend)
                 {
@@ -2490,19 +2488,6 @@ bool CWallet::CreateTransaction(const vector<CRecipient>& vecSend, CWalletTx& wt
                     strFailReason = _("Insufficient funds");
                     return false;
                 }
-                for (const auto& pcoin : setCoins)
-                {
-                    CAmount nCredit = pcoin.first->tx->vout[pcoin.second].nValue;
-                    //The coin age after the next block (depth+1) is used instead of the current,
-                    //reflecting an assumption the user would accept a bit more delay for
-                    //a chance at a free transaction.
-                    //But mempool inputs might still be in the mempool, so their age stays 0
-                    int age = pcoin.first->GetDepthInMainChain();
-                    assert(age >= 0);
-                    if (age != 0)
-                        age += 1;
-                    dPriority += (double)nCredit * age;
-                }
 
                 const CAmount nChange = nValueIn - nValueToSelect;
                 if (nChange > 0)
@@ -2614,7 +2599,6 @@ bool CWallet::CreateTransaction(const vector<CRecipient>& vecSend, CWalletTx& wt
                 unsigned int nBytes = GetVirtualTransactionSize(txNew);
 
                 CTransaction txNewConst(txNew);
-                dPriority = txNewConst.ComputePriority(dPriority, nBytes);
 
                 // Remove scriptSigs to eliminate the fee calculation dummy signatures
                 for (auto& vin : txNew.vin) {
@@ -2627,16 +2611,6 @@ bool CWallet::CreateTransaction(const vector<CRecipient>& vecSend, CWalletTx& wt
                 if (coinControl && coinControl->nConfirmTarget > 0)
                     currentConfirmationTarget = coinControl->nConfirmTarget;
 
-                // Can we complete this as a free transaction?
-                if (fSendFreeTransactions && nBytes <= MAX_FREE_TRANSACTION_CREATE_SIZE)
-                {
-                    // Not enough fee: enough priority?
-                    double dPriorityNeeded = mempool.estimateSmartPriority(currentConfirmationTarget);
-                    // Require at least hard-coded AllowFree.
-                    if (dPriority >= dPriorityNeeded && AllowFree(dPriority))
-                        break;
-                }
-
                 CAmount nFeeNeeded = GetMinimumFee(nBytes, currentConfirmationTarget, mempool);
                 if (coinControl && nFeeNeeded > 0 && coinControl->nMinimumTotalFee > nFeeNeeded) {
                     nFeeNeeded = coinControl->nMinimumTotalFee;
@@ -3548,8 +3522,6 @@ std::string CWallet::GetWalletHelpString(bool showDebug)
                                                             CURRENCY_UNIT, FormatMoney(payTxFee.GetFeePerK())));
     strUsage += HelpMessageOpt("-rescan", _("Rescan the block chain for missing wallet transactions on startup"));
     strUsage += HelpMessageOpt("-salvagewallet", _("Attempt to recover private keys from a corrupt wallet on startup"));
-    if (showDebug)
-        strUsage += HelpMessageOpt("-sendfreetransactions", strprintf(_("Send transactions as zero-fee transactions if possible (default: %u)"), DEFAULT_SEND_FREE_TRANSACTIONS));
     strUsage += HelpMessageOpt("-spendzeroconfchange", strprintf(_("Spend unconfirmed change when sending transactions (default: %u)"), DEFAULT_SPEND_ZEROCONF_CHANGE));
     strUsage += HelpMessageOpt("-txconfirmtarget=<n>", strprintf(_("If paytxfee is not set, include enough fee so transactions begin confirmation on average within n blocks (default: %u)"), DEFAULT_TX_CONFIRM_TARGET));
     strUsage += HelpMessageOpt("-usehd", _("Use hierarchical deterministic key generation (HD) after BIP32. Only has effect during wallet creation/first start") + " " + strprintf(_("(default: %u)"), DEFAULT_USE_HD_WALLET));
@@ -3868,11 +3840,10 @@ bool CWallet::ParameterInteraction()
     }
     nTxConfirmTarget = GetArg("-txconfirmtarget", DEFAULT_TX_CONFIRM_TARGET);
     bSpendZeroConfChange = GetBoolArg("-spendzeroconfchange", DEFAULT_SPEND_ZEROCONF_CHANGE);
-    fSendFreeTransactions = GetBoolArg("-sendfreetransactions", DEFAULT_SEND_FREE_TRANSACTIONS);
     fWalletRbf = GetBoolArg("-walletrbf", DEFAULT_WALLET_RBF);
 
-    if (fSendFreeTransactions && GetArg("-limitfreerelay", DEFAULT_LIMITFREERELAY) <= 0)
-        return InitError("Creation of free transactions with their relay disabled is not supported.");
+    if (GetBoolArg("-sendfreetransactions", false))
+        InitWarning("The argument -sendfreetransactions is no longer supported.");
 
     return true;
 }

src/wallet/wallet.h

@@ -39,7 +39,6 @@ extern CWallet* pwalletMain;
 extern CFeeRate payTxFee;
 extern unsigned int nTxConfirmTarget;
 extern bool bSpendZeroConfChange;
-extern bool fSendFreeTransactions;
 extern bool fWalletRbf;
 
 static const unsigned int DEFAULT_KEYPOOL_SIZE = 100;
@@ -57,16 +56,12 @@ static const CAmount MIN_CHANGE = CENT;
 static const CAmount MIN_FINAL_CHANGE = MIN_CHANGE/2;
 //! Default for -spendzeroconfchange
 static const bool DEFAULT_SPEND_ZEROCONF_CHANGE = true;
-//! Default for -sendfreetransactions
-static const bool DEFAULT_SEND_FREE_TRANSACTIONS = false;
 //! Default for -walletrejectlongchains
 static const bool DEFAULT_WALLET_REJECT_LONG_CHAINS = false;
 //! -txconfirmtarget default
 static const unsigned int DEFAULT_TX_CONFIRM_TARGET = 6;
 //! -walletrbf default
 static const bool DEFAULT_WALLET_RBF = false;
-//! Largest (in bytes) free transaction we're willing to create
-static const unsigned int MAX_FREE_TRANSACTION_CREATE_SIZE = 1000;
 static const bool DEFAULT_WALLETBROADCAST = true;
 static const bool DEFAULT_DISABLE_WALLET = false;
 //! if set, all keys will be derived by using BIP32