Require sufficent priority for relay of free transactions

qa/pull-tester/run-bitcoind-for-test.sh.in

@@ -10,7 +10,7 @@ touch "$DATADIR/regtest/debug.log"
 tail -q -n 1 -F "$DATADIR/regtest/debug.log" | grep -m 1 -q "Done loading" &
 WAITER=$!
 PORT=`expr 10000 + $$ % 55536`
-"@abs_top_builddir@/src/bitcoind@EXEEXT@" -connect=0.0.0.0 -datadir="$DATADIR" -rpcuser=user -rpcpassword=pass -listen -keypool=3 -debug -debug=net -logtimestamps -checkmempool=0 -port=$PORT -whitelist=127.0.0.1 -regtest -rpcport=`expr $PORT + 1` &
+"@abs_top_builddir@/src/bitcoind@EXEEXT@" -connect=0.0.0.0 -datadir="$DATADIR" -rpcuser=user -rpcpassword=pass -listen -keypool=3 -debug -debug=net -logtimestamps -checkmempool=0 -relaypriority=0 -port=$PORT -whitelist=127.0.0.1 -regtest -rpcport=`expr $PORT + 1` &
 BITCOIND=$!
 
 #Install a watchdog.

src/init.cpp

@@ -324,6 +324,7 @@ std::string HelpMessage(HelpMessageMode mode)
     if (GetBoolArg("-help-debug", false))
     {
         strUsage += "  -limitfreerelay=<n>    " + strprintf(_("Continuously rate-limit free transactions to <n>*1000 bytes per minute (default:%u)"), 15) + "\n";
+        strUsage += "  -relaypriority         " + strprintf(_("Require high priority for relaying free or low-fee transactions (default:%u)"), 1) + "\n";
         strUsage += "  -maxsigcachesize=<n>   " + strprintf(_("Limit size of signature cache to <n> entries (default: %u)"), 50000) + "\n";
     }
     strUsage += "  -minrelaytxfee=<amt>   " + strprintf(_("Fees (in BTC/Kb) smaller than this are considered zero fee for relaying (default: %s)"), FormatMoney(::minRelayTxFee.GetFeePerK())) + "\n";

src/main.cpp

@@ -1029,6 +1029,11 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
                                       hash.ToString(), nFees, txMinFee),
                              REJECT_INSUFFICIENTFEE, "insufficient fee");
 
+        // Require that free transactions have sufficient priority to be mined in the next block.
+        if (GetBoolArg("-relaypriority", true) && nFees < ::minRelayTxFee.GetFee(nSize) && !AllowFree(view.GetPriority(tx, chainActive.Height() + 1))) {
+            return state.DoS(0, false, REJECT_INSUFFICIENTFEE, "insufficient priority");
+        }
+
         // Continuously rate-limit free (really, very-low-fee) transactions
         // This mitigates 'penny-flooding' -- sending thousands of free transactions just to
         // be annoying or make others' transactions take longer to confirm.
@@ -1048,7 +1053,7 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
             // At default rate it would take over a month to fill 1GB
             if (dFreeCount >= GetArg("-limitfreerelay", 15)*10*1000)
                 return state.DoS(0, error("AcceptToMemoryPool : free transaction rejected by rate limiter"),
-                                 REJECT_INSUFFICIENTFEE, "insufficient priority");
+                                 REJECT_INSUFFICIENTFEE, "rate limited free transaction");
             LogPrint("mempool", "Rate limit dFreeCount: %g => %g\n", dFreeCount, dFreeCount+nSize);
             dFreeCount += nSize;
         }