[fees] introduce configurable hard dust limit

Co-authored-by: Ross Nicoll <[email protected]>

7 files changed, 118 insertions, 1 deletions

diff --git a/qa/pull-tester/rpc-tests.py b/qa/pull-tester/rpc-tests.py
index f7a2deb0d..fd78d3701 100755
--- a/qa/pull-tester/rpc-tests.py
+++ b/qa/pull-tester/rpc-tests.py
@@ -153,6 +153,7 @@ testScripts = [
     'signmessages.py',
     # 'nulldummy.py',
     'import-rescan.py',
+    'harddustlimit.py',
     # While fee bumping should work in Doge, these tests depend on free transactions, which we don't support.
     # Disable until we can do a full rewrite of the tests (possibly upstream), or revise fee schedule, or something
     'bumpfee.py',
diff --git a/qa/rpc-tests/harddustlimit.py b/qa/rpc-tests/harddustlimit.py
new file mode 100644
index 000000000..9d56febb7
--- /dev/null
+++ b/qa/rpc-tests/harddustlimit.py
@@ -0,0 +1,82 @@
+#!/usr/bin/env python3
+# Copyright (c) 2021 The Dogecoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Hard dust limit QA test.
+
+# Tests nodes with differing -dustlimits
+"""
+
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import *
+from decimal import Decimal
+
+class HardDustLimitTest(BitcoinTestFramework):
+
+    def __init__(self):
+        super().__init__()
+        self.setup_clean_chain = True
+        self.num_nodes = 3
+
+    def setup_network(self, split=False):
+        self.nodes = []
+        self.nodes.append(start_node(0, self.options.tmpdir, ["-dustlimit=0.1", "-debug"]))
+        self.nodes.append(start_node(1, self.options.tmpdir, ["-dustlimit=1", "-debug"]))
+        self.nodes.append(start_node(2, self.options.tmpdir, ["-dustlimit=0.01", "-debug"]))
+
+        connect_nodes_bi(self.nodes,0,1)
+        connect_nodes_bi(self.nodes,1,2)
+        connect_nodes_bi(self.nodes,0,2)
+
+        self.is_network_split=False
+        self.sync_all()
+
+    def run_test(self):
+
+        self.fee = Decimal("1")
+        self.seed = 1000
+        self.coinselector = {'minimumAmount': self.fee * 10, 'maximumAmount': self.seed}
+
+        # set up addresses
+        n0a1 = self.nodes[0].getnewaddress()
+        n0a2 = self.nodes[0].getnewaddress()
+        n0a3 = self.nodes[0].getnewaddress()
+        n1a1 = self.nodes[1].getnewaddress()
+        n2a1 = self.nodes[2].getnewaddress()
+        n2a2 = self.nodes[2].getnewaddress()
+        n2a3 = self.nodes[2].getnewaddress()
+        n2a4 = self.nodes[2].getnewaddress()
+
+        # mine some blocks and prepare some coins
+        self.nodes[2].generate(1)
+        self.sync_all()
+        self.nodes[0].generate(101)
+        self.sync_all()
+        self.nodes[0].sendtoaddress(n0a1, self.seed)
+        self.nodes[0].sendtoaddress(n2a1, self.seed)
+        self.sync_all()
+        self.nodes[0].generate(1)
+        self.sync_all()
+
+        # create dusty transactions
+        self.send_dusty_tx(self.nodes[2], n2a2, n0a2, Decimal("0.9"))
+        self.send_dusty_tx(self.nodes[2], n2a3, n0a3, Decimal("0.09"))
+        self.send_dusty_tx(self.nodes[0], n2a4, n1a1, Decimal("1"))
+
+        # wait 10 seconds to sync mempools
+        time.sleep(10)
+
+        assert_equal(self.nodes[2].getmempoolinfo()['size'], 3)
+        assert_equal(self.nodes[1].getmempoolinfo()['size'], 1)
+        assert_equal(self.nodes[0].getmempoolinfo()['size'], 2)
+
+    def send_dusty_tx(self, n, addr1, addr2, dust):
+        avail = n.listunspent(0, 1000, [], True, self.coinselector)
+        inputs = [ {'txid': avail[0]['txid'], 'vout': avail[0]['vout']}]
+        outputs = { addr1 : avail[0]['amount'] - self.fee - dust , addr2: dust }
+        rawtx = n.createrawtransaction(inputs, outputs)
+        rawtx = n.signrawtransaction(rawtx)
+        n.sendrawtransaction(rawtx['hex'])
+
+if __name__ == '__main__':
+    HardDustLimitTest().main()
diff --git a/src/init.cpp b/src/init.cpp
index 22dc45929..dd1942133 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -475,6 +475,7 @@ std::string HelpMessage(HelpMessageMode mode)
         strUsage += HelpMessageOpt("-incrementalrelayfee=<amt>", strprintf("Fee rate (in %s/kB) used to define cost of relay, used for mempool limiting and BIP 125 replacement. (default: %s)", CURRENCY_UNIT, FormatMoney(DEFAULT_INCREMENTAL_RELAY_FEE)));
         strUsage += HelpMessageOpt("-dustrelayfee=<amt>", strprintf("Fee rate (in %s/kB) used to defined dust, the value of an output such that it will cost about 1/3 of its value in fees at this fee rate to spend it. (default: %s)", CURRENCY_UNIT, FormatMoney(DUST_RELAY_TX_FEE)));
     }
+    strUsage += HelpMessageOpt("-dustlimit=<amt>", strprintf(_("Amount under which a transaction output is considered dust, in %s (default: %s)"), CURRENCY_UNIT, FormatMoney(DEFAULT_DUST_LIMIT)));
     strUsage += HelpMessageOpt("-bytespersigop", strprintf(_("Equivalent bytes per sigop in transactions for relay and mining (default: %u)"), DEFAULT_BYTES_PER_SIGOP));
     strUsage += HelpMessageOpt("-datacarrier", strprintf(_("Relay and mine data carrier transactions (default: %u)"), DEFAULT_ACCEPT_DATACARRIER));
     strUsage += HelpMessageOpt("-datacarriersize", strprintf(_("Maximum size of data in data carrier transactions we relay and mine (default: %u)"), MAX_OP_RETURN_RELAY));
@@ -1043,6 +1044,14 @@ bool AppInitParameterInteraction()
         return InitError(strprintf("acceptnonstdtxn is not currently supported for %s chain", chainparams.NetworkIDString()));
     nBytesPerSigOp = GetArg("-bytespersigop", nBytesPerSigOp);
 
+    if (IsArgSet("-dustlimit"))
+    {
+        CAmount n = nDustLimit;
+        if (!ParseMoney(GetArg("-dustlimit", ""), n))
+            return InitError(AmountErrMsg("dustlimit", GetArg("-dustlimit", "")));
+        nDustLimit = n;
+    }
+
 #ifdef ENABLE_WALLET
     if (!CWallet::ParameterInteraction())
         return false;
diff --git a/src/policy/policy.cpp b/src/policy/policy.cpp
index ec398f662..7b2b23964 100644
--- a/src/policy/policy.cpp
+++ b/src/policy/policy.cpp
@@ -209,6 +209,7 @@ bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
 CFeeRate incrementalRelayFee = CFeeRate(DEFAULT_INCREMENTAL_RELAY_FEE);
 CFeeRate dustRelayFee = CFeeRate(DUST_RELAY_TX_FEE);
 unsigned int nBytesPerSigOp = DEFAULT_BYTES_PER_SIGOP;
+unsigned int nDustLimit = DEFAULT_DUST_LIMIT;
 
 int64_t GetVirtualTransactionSize(int64_t nWeight, int64_t nSigOpCost)
 {
diff --git a/src/policy/policy.h b/src/policy/policy.h
index a7fc8b78e..be34b9156 100644
--- a/src/policy/policy.h
+++ b/src/policy/policy.h
@@ -47,6 +47,13 @@ static const unsigned int MAX_STANDARD_P2WSH_SCRIPT_SIZE = 3600;
  * outputs below the new threshold */
 static const unsigned int DUST_RELAY_TX_FEE = 1000;
 /**
+ * Dogecoin: Default dust limit that is evaluated when considering whether a
+ * transaction output is required to pay additional fee for relay and inclusion
+ * in blocks. Overridden by -dustlimit
+ */
+static const unsigned int DEFAULT_DUST_LIMIT = 100000000;
+
+/**
  * Standard script verification flags that standard transactions will comply
  * with. However scripts violating these flags may still be present in valid
  * blocks and we must accept those blocks.
@@ -96,6 +103,7 @@ bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
 extern CFeeRate incrementalRelayFee;
 extern CFeeRate dustRelayFee;
 extern unsigned int nBytesPerSigOp;
+extern unsigned int nDustLimit;
 
 /** Compute the virtual transaction size (weight reinterpreted as bytes). */
 int64_t GetVirtualTransactionSize(int64_t nWeight, int64_t nSigOpCost);
diff --git a/src/primitives/transaction.h b/src/primitives/transaction.h
index 16a92bf2e..0d0ceda54 100644
--- a/src/primitives/transaction.h
+++ b/src/primitives/transaction.h
@@ -15,6 +15,8 @@ static const int SERIALIZE_TRANSACTION_NO_WITNESS = 0x40000000;
 
 static const int WITNESS_SCALE_FACTOR = 4;
 
+extern unsigned int nDustLimit;
+
 /** An outpoint - a combination of a transaction hash and an index n into its vout */
 class COutPoint
 {
@@ -195,7 +197,7 @@ public:
         */
 
         // Dogecoin: Anything below 1 DOGE is always dust
-        return COIN;
+        return nDustLimit;
     }
 
     bool IsDust(const CFeeRate &minRelayTxFeeRate) const
diff --git a/src/wallet/test/wallet_tests.cpp b/src/wallet/test/wallet_tests.cpp
index 4e84bb688..79a994bf6 100644
--- a/src/wallet/test/wallet_tests.cpp
+++ b/src/wallet/test/wallet_tests.cpp
@@ -36,6 +36,8 @@ std::vector<std::unique_ptr<CWalletTx>> wtxn;
 
 typedef set<pair<const CWalletTx*,unsigned int> > CoinSet;
 
+extern unsigned int nDustLimit;
+
 BOOST_FIXTURE_TEST_SUITE(wallet_tests, WalletTestingSetup)
 
 static const CWallet wallet;
@@ -524,6 +526,18 @@ BOOST_AUTO_TEST_CASE(GetMinimumFee_dust_test)
     BOOST_CHECK_EQUAL(CWallet::GetMinimumFee(tx, 963, 0, pool), 2 * nMinTxFee);
     BOOST_CHECK_EQUAL(CWallet::GetMinimumFee(tx, 1000, 0, pool), 2 * nMinTxFee);
     BOOST_CHECK_EQUAL(CWallet::GetMinimumFee(tx, 1999, 0, pool), 3 * nMinTxFee);
+
+    // change the hard dust limit
+
+    nDustLimit = COIN / 10;
+
+    // Confirm dust penalty fees are not added
+
+    BOOST_CHECK_EQUAL(CWallet::GetMinimumFee(tx, 963, 0, pool), 1 * nMinTxFee);
+    BOOST_CHECK_EQUAL(CWallet::GetMinimumFee(tx, 1000, 0, pool), 1 * nMinTxFee);
+    BOOST_CHECK_EQUAL(CWallet::GetMinimumFee(tx, 1999, 0, pool), 2 * nMinTxFee);
+
+    nDustLimit = COIN;
 }
 
 BOOST_AUTO_TEST_SUITE_END()