Use fee/priority estimates in wallet CreateTransaction

The wallet now uses the mempool fee estimator with a new
command-line option: -txconfirmtarget (default: 1) instead
of using hard-coded fees or priorities.

A new bitcoind that hasn't seen enough transactions to estimate
will fall back to the old hard-coded minimum priority or
transaction fee.

-paytxfee option overrides -txconfirmtarget.

Relaying and mining code isn't changed.

For Qt, the coin control dialog now uses priority estimates to
label transaction priority (instead of hard-coded constants);
unspent outputs were consistently labeled with a much higher
priority than is justified by the free transactions actually
being accepted into blocks.

I did not implement any GUI for setting -txconfirmtarget; I would
suggest getting rid of the "Pay transaction fee" GUI and replace
it with either "target number of confirmations" or maybe
a "faster confirmation <--> lower fee" slider or select box.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 2dd141a735..3ee0f2aa39 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -254,6 +254,7 @@ std::string HelpMessage(HelpMessageMode mode)
     strUsage += "\n" + _("Wallet options:") + "\n";
     strUsage += "  -disablewallet         " + _("Do not load the wallet and disable wallet RPC calls") + "\n";
     strUsage += "  -paytxfee=<amt>        " + strprintf(_("Fee (in BTC/kB) to add to transactions you send (default: %s)"), FormatMoney(payTxFee.GetFeePerK())) + "\n";
+    strUsage += "  -txconfirmtarget=<n>   " + _("If paytxfee is not set, include enough fee so transactions are confirmed on average within n blocks (default: 1)") + "\n";
     strUsage += "  -rescan                " + _("Rescan the block chain for missing wallet transactions") + " " + _("on startup") + "\n";
     strUsage += "  -salvagewallet         " + _("Attempt to recover private keys from a corrupt wallet.dat") + " " + _("on startup") + "\n";
     strUsage += "  -spendzeroconfchange   " + _("Spend unconfirmed change when sending transactions (default: 1)") + "\n";
@@ -635,7 +636,13 @@ bool AppInit2(boost::thread_group& threadGroup)
         if (nFeePerK > nHighTransactionFeeWarning)
             InitWarning(_("Warning: -paytxfee is set very high! This is the transaction fee you will pay if you send a transaction."));
         payTxFee = CFeeRate(nFeePerK, 1000);
+        if (payTxFee < CTransaction::minRelayTxFee)
+        {
+            return InitError(strprintf(_("Invalid amount for -paytxfee=<amount>: '%s' (must be at least %s)"),
+                                       mapArgs["-paytxfee"], CTransaction::minRelayTxFee.ToString()));
+        }
     }
+    nTxConfirmTarget = GetArg("-txconfirmtarget", 1);
     bSpendZeroConfChange = GetArg("-spendzeroconfchange", true);
 
     std::string strWalletFile = GetArg("-wallet", "wallet.dat");