Enforce minRelayTxFee on wallet created tx and add a maxtxfee option.

Previously the minRelayTxFee was only enforced on user specified values.

It was possible for smartfee to produce a fee below minRelayTxFee which
 would just result in the transaction getting stuck because it can't be
 relayed.

This also introduces a maxtxfee option which sets an absolute maximum
 for any fee created by the wallet, with an intention of increasing
 user confidence that the automatic fees won't burn them. This was
 frequently a concern even before smartfees.

If the configured fee policy won't even allow the wallet to meet the relay
 fee the transaction creation may be aborted.

1 files changed, 15 insertions, 0 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 11329c16aa..c5ced8654e 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -288,6 +288,7 @@ std::string HelpMessage(HelpMessageMode mode)
     strUsage += "  -sendfreetransactions  " + strprintf(_("Send transactions as zero-fee transactions if possible (default: %u)"), 0) + "\n";
     strUsage += "  -spendzeroconfchange   " + strprintf(_("Spend unconfirmed change when sending transactions (default: %u)"), 1) + "\n";
     strUsage += "  -txconfirmtarget=<n>   " + strprintf(_("If paytxfee is not set, include enough fee so transactions are confirmed on average within n blocks (default: %u)"), 1) + "\n";
+    strUsage += "  -maxtxfee=<amt>        " + strprintf(_("Maximum total fees to use in a single wallet transaction, setting too low may abort large transactions (default: %s)"), FormatMoney(maxTxFee)) + "\n";
     strUsage += "  -upgradewallet         " + _("Upgrade wallet to latest format") + " " + _("on startup") + "\n";
     strUsage += "  -wallet=<file>         " + _("Specify wallet file (within data directory)") + " " + strprintf(_("(default: %s)"), "wallet.dat") + "\n";
     strUsage += "  -walletnotify=<cmd>    " + _("Execute command when a wallet transaction changes (%s in cmd is replaced by TxID)") + "\n";
@@ -697,6 +698,20 @@ bool AppInit2(boost::thread_group& threadGroup)
                                        mapArgs["-paytxfee"], ::minRelayTxFee.ToString()));
         }
     }
+    if (mapArgs.count("-maxtxfee"))
+    {
+        CAmount nMaxFee = 0;
+        if (!ParseMoney(mapArgs["-maxtxfee"], nMaxFee))
+            return InitError(strprintf(_("Invalid amount for -maxtxfee=<amount>: '%s'"), mapArgs["-maptxfee"]));
+        if (nMaxFee > nHighTransactionMaxFeeWarning)
+            InitWarning(_("Warning: -maxtxfee is set very high! Fees this large could be paid on a single transaction."));
+        maxTxFee = nMaxFee;
+        if (CFeeRate(maxTxFee, 1000) < ::minRelayTxFee)
+        {
+            return InitError(strprintf(_("Invalid amount for -maxtxfee=<amount>: '%s' (must be at least the minrelay fee of %s to prevent stuck transactions)"),
+                                       mapArgs["-maxtxfee"], ::minRelayTxFee.ToString()));
+        }
+    }
     nTxConfirmTarget = GetArg("-txconfirmtarget", 1);
     bSpendZeroConfChange = GetArg("-spendzeroconfchange", true);
     fSendFreeTransactions = GetArg("-sendfreetransactions", false);