Merge pull request #6822

e20d924 [trivial] init: Use defaults MIN_RELAY_TX_FEE & TRANSACTION_MAXFEE (MarcoFalke)
536766c [trivial] New DEFAULT_MIN_RELAY_TX_FEE = 1000 (MarcoFalke)
5f46a7d transaction_tests: Be more strict checking dust (MarcoFalke)

src/init.cpp

@@ -385,7 +385,7 @@ std::string HelpMessage(HelpMessageMode mode)
     strUsage += HelpMessageOpt("-spendzeroconfchange", strprintf(_("Spend unconfirmed change when sending transactions (default: %u)"), 1));
     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("-maxtxfee=<amt>", strprintf(_("Maximum total fees (in %s) to use in a single wallet transaction; setting this too low may abort large transactions (default: %s)"),
-        CURRENCY_UNIT, FormatMoney(maxTxFee)));
+        CURRENCY_UNIT, FormatMoney(DEFAULT_TRANSACTION_MAXFEE)));
     strUsage += HelpMessageOpt("-upgradewallet", _("Upgrade wallet to latest format on startup"));
     strUsage += HelpMessageOpt("-wallet=<file>", _("Specify wallet file (within data directory)") + " " + strprintf(_("(default: %s)"), "wallet.dat"));
     strUsage += HelpMessageOpt("-walletbroadcast", _("Make the wallet broadcast transactions") + " " + strprintf(_("(default: %u)"), true));
@@ -440,7 +440,7 @@ std::string HelpMessage(HelpMessageMode mode)
         strUsage += HelpMessageOpt("-maxsigcachesize=<n>", strprintf("Limit size of signature cache to <n> entries (default: %u)", 50000));
     }
     strUsage += HelpMessageOpt("-minrelaytxfee=<amt>", strprintf(_("Fees (in %s/kB) smaller than this are considered zero fee for relaying, mining and transaction creation (default: %s)"),
-        CURRENCY_UNIT, FormatMoney(::minRelayTxFee.GetFeePerK())));
+        CURRENCY_UNIT, FormatMoney(DEFAULT_MIN_RELAY_TX_FEE)));
     strUsage += HelpMessageOpt("-printtoconsole", _("Send trace/debug info to console instead of debug.log file"));
     if (showDebug)
     {

src/main.cpp

@@ -75,7 +75,7 @@ uint64_t nPruneTarget = 0;
 bool fAlerts = DEFAULT_ALERTS;
 
 /** Fees smaller than this (in satoshi) are considered zero fee (for relaying, mining and transaction creation) */
-CFeeRate minRelayTxFee = CFeeRate(1000);
+CFeeRate minRelayTxFee = CFeeRate(DEFAULT_MIN_RELAY_TX_FEE);
 
 CTxMemPool mempool(::minRelayTxFee);
 

src/main.h

@@ -41,6 +41,8 @@ struct CNodeStateStats;
 
 /** Default for accepting alerts from the P2P network. */
 static const bool DEFAULT_ALERTS = true;
+/** Default for -minrelaytxfee, minimum relay fee for transactions */
+static const unsigned int DEFAULT_MIN_RELAY_TX_FEE = 1000;
 /** Default for -maxorphantx, maximum number of orphan transactions kept in memory */
 static const unsigned int DEFAULT_MAX_ORPHAN_TRANSACTIONS = 100;
 /** Default for -limitancestorcount, max number of in-mempool ancestors */

src/primitives/transaction.h

@@ -143,8 +143,8 @@ public:
         // 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.
+        // so dust is a spendable txout less than
+        // 546*minRelayTxFee/1000 (in satoshis)
         if (scriptPubKey.IsUnspendable())
             return 0;
 

src/test/transaction_tests.cpp

@@ -342,11 +342,26 @@ BOOST_AUTO_TEST_CASE(test_IsStandard)
     string reason;
     BOOST_CHECK(IsStandardTx(t, reason));
 
-    t.vout[0].nValue = 501; // dust
+    // Check dust with default relay fee:
+    CAmount nDustThreshold = 182 * minRelayTxFee.GetFeePerK()/1000 * 3;
+    BOOST_CHECK_EQUAL(nDustThreshold, 546);
+    // dust:
+    t.vout[0].nValue = nDustThreshold - 1;
     BOOST_CHECK(!IsStandardTx(t, reason));
+    // not dust:
+    t.vout[0].nValue = nDustThreshold;
+    BOOST_CHECK(IsStandardTx(t, reason));
 
-    t.vout[0].nValue = 2730; // not dust
+    // Check dust with odd relay fee to verify rounding:
+    // nDustThreshold = 182 * 1234 / 1000 * 3
+    minRelayTxFee = CFeeRate(1234);
+    // dust:
+    t.vout[0].nValue = 672 - 1;
+    BOOST_CHECK(!IsStandardTx(t, reason));
+    // not dust:
+    t.vout[0].nValue = 672;
     BOOST_CHECK(IsStandardTx(t, reason));
+    minRelayTxFee = CFeeRate(DEFAULT_MIN_RELAY_TX_FEE);
 
     t.vout[0].scriptPubKey = CScript() << OP_1;
     BOOST_CHECK(!IsStandardTx(t, reason));