Merge branch 'master' into single_prodname

1 files changed, 592 insertions, 0 deletions

diff --git a/qa/rpc-tests/replace-by-fee.py b/qa/rpc-tests/replace-by-fee.py
new file mode 100755
index 0000000000..ba1956853a
--- /dev/null
+++ b/qa/rpc-tests/replace-by-fee.py
@@ -0,0 +1,592 @@
+#!/usr/bin/env python2
+# Copyright (c) 2014-2015 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#
+# Test replace by fee code
+#
+
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import *
+from test_framework.script import *
+from test_framework.mininode import *
+import binascii
+
+COIN = 100000000
+MAX_REPLACEMENT_LIMIT = 100
+
+def satoshi_round(amount):
+    return Decimal(amount).quantize(Decimal('0.00000001'), rounding=ROUND_DOWN)
+
+def txToHex(tx):
+    return binascii.hexlify(tx.serialize()).decode('utf-8')
+
+def make_utxo(node, amount, confirmed=True, scriptPubKey=CScript([1])):
+    """Create a txout with a given amount and scriptPubKey
+
+    Mines coins as needed.
+
+    confirmed - txouts created will be confirmed in the blockchain;
+                unconfirmed otherwise.
+    """
+    fee = 1*COIN
+    while node.getbalance() < satoshi_round((amount + fee)/COIN):
+        node.generate(100)
+        #print (node.getbalance(), amount, fee)
+
+    new_addr = node.getnewaddress()
+    #print new_addr
+    txid = node.sendtoaddress(new_addr, satoshi_round((amount+fee)/COIN))
+    tx1 = node.getrawtransaction(txid, 1)
+    txid = int(txid, 16)
+    i = None
+
+    for i, txout in enumerate(tx1['vout']):
+        #print i, txout['scriptPubKey']['addresses']
+        if txout['scriptPubKey']['addresses'] == [new_addr]:
+            #print i
+            break
+    assert i is not None
+
+    tx2 = CTransaction()
+    tx2.vin = [CTxIn(COutPoint(txid, i))]
+    tx2.vout = [CTxOut(amount, scriptPubKey)]
+    tx2.rehash()
+
+    binascii.hexlify(tx2.serialize()).decode('utf-8')
+
+    signed_tx = node.signrawtransaction(binascii.hexlify(tx2.serialize()).decode('utf-8'))
+
+    txid = node.sendrawtransaction(signed_tx['hex'], True)
+
+    # If requested, ensure txouts are confirmed.
+    if confirmed:
+        mempool_size = len(node.getrawmempool())
+        while mempool_size > 0:
+            node.generate(1)
+            new_size = len(node.getrawmempool())
+            # Error out if we have something stuck in the mempool, as this
+            # would likely be a bug.
+            assert(new_size < mempool_size)
+            mempool_size = new_size
+
+    return COutPoint(int(txid, 16), 0)
+
+class ReplaceByFeeTest(BitcoinTestFramework):
+
+    def setup_network(self):
+        self.nodes = []
+        self.nodes.append(start_node(0, self.options.tmpdir, ["-maxorphantx=1000", "-debug",
+                                                              "-relaypriority=0", "-whitelist=127.0.0.1",
+                                                              "-limitancestorcount=50",
+                                                              "-limitancestorsize=101",
+                                                              "-limitdescendantcount=200",
+                                                              "-limitdescendantsize=101"
+                                                              ]))
+        self.is_network_split = False
+
+    def run_test(self):
+        make_utxo(self.nodes[0], 1*COIN)
+
+        print "Running test simple doublespend..."
+        self.test_simple_doublespend()
+
+        print "Running test doublespend chain..."
+        self.test_doublespend_chain()
+
+        print "Running test doublespend tree..."
+        self.test_doublespend_tree()
+
+        print "Running test replacement feeperkb..."
+        self.test_replacement_feeperkb()
+
+        print "Running test spends of conflicting outputs..."
+        self.test_spends_of_conflicting_outputs()
+
+        print "Running test new unconfirmed inputs..."
+        self.test_new_unconfirmed_inputs()
+
+        print "Running test too many replacements..."
+        self.test_too_many_replacements()
+
+        print "Running test opt-in..."
+        self.test_opt_in()
+
+        print "Running test prioritised transactions..."
+        self.test_prioritised_transactions()
+
+        print "Passed\n"
+
+    def test_simple_doublespend(self):
+        """Simple doublespend"""
+        tx0_outpoint = make_utxo(self.nodes[0], 1.1*COIN)
+
+        tx1a = CTransaction()
+        tx1a.vin = [CTxIn(tx0_outpoint, nSequence=0)]
+        tx1a.vout = [CTxOut(1*COIN, CScript([b'a']))]
+        tx1a_hex = txToHex(tx1a)
+        tx1a_txid = self.nodes[0].sendrawtransaction(tx1a_hex, True)
+
+        # Should fail because we haven't changed the fee
+        tx1b = CTransaction()
+        tx1b.vin = [CTxIn(tx0_outpoint, nSequence=0)]
+        tx1b.vout = [CTxOut(1*COIN, CScript([b'b']))]
+        tx1b_hex = txToHex(tx1b)
+
+        try:
+            tx1b_txid = self.nodes[0].sendrawtransaction(tx1b_hex, True)
+        except JSONRPCException as exp:
+            assert_equal(exp.error['code'], -26) # insufficient fee
+        else:
+            assert(False)
+
+        # Extra 0.1 BTC fee
+        tx1b = CTransaction()
+        tx1b.vin = [CTxIn(tx0_outpoint, nSequence=0)]
+        tx1b.vout = [CTxOut(0.9*COIN, CScript([b'b']))]
+        tx1b_hex = txToHex(tx1b)
+        tx1b_txid = self.nodes[0].sendrawtransaction(tx1b_hex, True)
+
+        mempool = self.nodes[0].getrawmempool()
+
+        assert (tx1a_txid not in mempool)
+        assert (tx1b_txid in mempool)
+
+        assert_equal(tx1b_hex, self.nodes[0].getrawtransaction(tx1b_txid))
+
+    def test_doublespend_chain(self):
+        """Doublespend of a long chain"""
+
+        initial_nValue = 50*COIN
+        tx0_outpoint = make_utxo(self.nodes[0], initial_nValue)
+
+        prevout = tx0_outpoint
+        remaining_value = initial_nValue
+        chain_txids = []
+        while remaining_value > 10*COIN:
+            remaining_value -= 1*COIN
+            tx = CTransaction()
+            tx.vin = [CTxIn(prevout, nSequence=0)]
+            tx.vout = [CTxOut(remaining_value, CScript([1]))]
+            tx_hex = txToHex(tx)
+            txid = self.nodes[0].sendrawtransaction(tx_hex, True)
+            chain_txids.append(txid)
+            prevout = COutPoint(int(txid, 16), 0)
+
+        # Whether the double-spend is allowed is evaluated by including all
+        # child fees - 40 BTC - so this attempt is rejected.
+        dbl_tx = CTransaction()
+        dbl_tx.vin = [CTxIn(tx0_outpoint, nSequence=0)]
+        dbl_tx.vout = [CTxOut(initial_nValue - 30*COIN, CScript([1]))]
+        dbl_tx_hex = txToHex(dbl_tx)
+
+        try:
+            self.nodes[0].sendrawtransaction(dbl_tx_hex, True)
+        except JSONRPCException as exp:
+            assert_equal(exp.error['code'], -26) # insufficient fee
+        else:
+            assert(False) # transaction mistakenly accepted!
+
+        # Accepted with sufficient fee
+        dbl_tx = CTransaction()
+        dbl_tx.vin = [CTxIn(tx0_outpoint, nSequence=0)]
+        dbl_tx.vout = [CTxOut(1*COIN, CScript([1]))]
+        dbl_tx_hex = txToHex(dbl_tx)
+        self.nodes[0].sendrawtransaction(dbl_tx_hex, True)
+
+        mempool = self.nodes[0].getrawmempool()
+        for doublespent_txid in chain_txids:
+            assert(doublespent_txid not in mempool)
+
+    def test_doublespend_tree(self):
+        """Doublespend of a big tree of transactions"""
+
+        initial_nValue = 50*COIN
+        tx0_outpoint = make_utxo(self.nodes[0], initial_nValue)
+
+        def branch(prevout, initial_value, max_txs, tree_width=5, fee=0.0001*COIN, _total_txs=None):
+            if _total_txs is None:
+                _total_txs = [0]
+            if _total_txs[0] >= max_txs:
+                return
+
+            txout_value = (initial_value - fee) // tree_width
+            if txout_value < fee:
+                return
+
+            vout = [CTxOut(txout_value, CScript([i+1]))
+                    for i in range(tree_width)]
+            tx = CTransaction()
+            tx.vin = [CTxIn(prevout, nSequence=0)]
+            tx.vout = vout
+            tx_hex = txToHex(tx)
+
+            assert(len(tx.serialize()) < 100000)
+            txid = self.nodes[0].sendrawtransaction(tx_hex, True)
+            yield tx
+            _total_txs[0] += 1
+
+            txid = int(txid, 16)
+
+            for i, txout in enumerate(tx.vout):
+                for x in branch(COutPoint(txid, i), txout_value,
+                                  max_txs,
+                                  tree_width=tree_width, fee=fee,
+                                  _total_txs=_total_txs):
+                    yield x
+
+        fee = 0.0001*COIN
+        n = MAX_REPLACEMENT_LIMIT
+        tree_txs = list(branch(tx0_outpoint, initial_nValue, n, fee=fee))
+        assert_equal(len(tree_txs), n)
+
+        # Attempt double-spend, will fail because too little fee paid
+        dbl_tx = CTransaction()
+        dbl_tx.vin = [CTxIn(tx0_outpoint, nSequence=0)]
+        dbl_tx.vout = [CTxOut(initial_nValue - fee*n, CScript([1]))]
+        dbl_tx_hex = txToHex(dbl_tx)
+        try:
+            self.nodes[0].sendrawtransaction(dbl_tx_hex, True)
+        except JSONRPCException as exp:
+            assert_equal(exp.error['code'], -26) # insufficient fee
+        else:
+            assert(False)
+
+        # 1 BTC fee is enough
+        dbl_tx = CTransaction()
+        dbl_tx.vin = [CTxIn(tx0_outpoint, nSequence=0)]
+        dbl_tx.vout = [CTxOut(initial_nValue - fee*n - 1*COIN, CScript([1]))]
+        dbl_tx_hex = txToHex(dbl_tx)
+        self.nodes[0].sendrawtransaction(dbl_tx_hex, True)
+
+        mempool = self.nodes[0].getrawmempool()
+
+        for tx in tree_txs:
+            tx.rehash()
+            assert (tx.hash not in mempool)
+
+        # Try again, but with more total transactions than the "max txs
+        # double-spent at once" anti-DoS limit.
+        for n in (MAX_REPLACEMENT_LIMIT+1, MAX_REPLACEMENT_LIMIT*2):
+            fee = 0.0001*COIN
+            tx0_outpoint = make_utxo(self.nodes[0], initial_nValue)
+            tree_txs = list(branch(tx0_outpoint, initial_nValue, n, fee=fee))
+            assert_equal(len(tree_txs), n)
+
+            dbl_tx = CTransaction()
+            dbl_tx.vin = [CTxIn(tx0_outpoint, nSequence=0)]
+            dbl_tx.vout = [CTxOut(initial_nValue - 2*fee*n, CScript([1]))]
+            dbl_tx_hex = txToHex(dbl_tx)
+            try:
+                self.nodes[0].sendrawtransaction(dbl_tx_hex, True)
+            except JSONRPCException as exp:
+                assert_equal(exp.error['code'], -26)
+                assert_equal("too many potential replacements" in exp.error['message'], True)
+            else:
+                assert(False)
+
+            for tx in tree_txs:
+                tx.rehash()
+                self.nodes[0].getrawtransaction(tx.hash)
+
+    def test_replacement_feeperkb(self):
+        """Replacement requires fee-per-KB to be higher"""
+        tx0_outpoint = make_utxo(self.nodes[0], 1.1*COIN)
+
+        tx1a = CTransaction()
+        tx1a.vin = [CTxIn(tx0_outpoint, nSequence=0)]
+        tx1a.vout = [CTxOut(1*COIN, CScript([b'a']))]
+        tx1a_hex = txToHex(tx1a)
+        tx1a_txid = self.nodes[0].sendrawtransaction(tx1a_hex, True)
+
+        # Higher fee, but the fee per KB is much lower, so the replacement is
+        # rejected.
+        tx1b = CTransaction()
+        tx1b.vin = [CTxIn(tx0_outpoint, nSequence=0)]
+        tx1b.vout = [CTxOut(0.001*COIN, CScript([b'a'*999000]))]
+        tx1b_hex = txToHex(tx1b)
+
+        try:
+            tx1b_txid = self.nodes[0].sendrawtransaction(tx1b_hex, True)
+        except JSONRPCException as exp:
+            assert_equal(exp.error['code'], -26) # insufficient fee
+        else:
+            assert(False)
+
+    def test_spends_of_conflicting_outputs(self):
+        """Replacements that spend conflicting tx outputs are rejected"""
+        utxo1 = make_utxo(self.nodes[0], 1.2*COIN)
+        utxo2 = make_utxo(self.nodes[0], 3.0*COIN)
+
+        tx1a = CTransaction()
+        tx1a.vin = [CTxIn(utxo1, nSequence=0)]
+        tx1a.vout = [CTxOut(1.1*COIN, CScript([b'a']))]
+        tx1a_hex = txToHex(tx1a)
+        tx1a_txid = self.nodes[0].sendrawtransaction(tx1a_hex, True)
+
+        tx1a_txid = int(tx1a_txid, 16)
+
+        # Direct spend an output of the transaction we're replacing.
+        tx2 = CTransaction()
+        tx2.vin = [CTxIn(utxo1, nSequence=0), CTxIn(utxo2, nSequence=0)]
+        tx2.vin.append(CTxIn(COutPoint(tx1a_txid, 0), nSequence=0))
+        tx2.vout = tx1a.vout
+        tx2_hex = txToHex(tx2)
+
+        try:
+            tx2_txid = self.nodes[0].sendrawtransaction(tx2_hex, True)
+        except JSONRPCException as exp:
+            assert_equal(exp.error['code'], -26)
+        else:
+            assert(False)
+
+        # Spend tx1a's output to test the indirect case.
+        tx1b = CTransaction()
+        tx1b.vin = [CTxIn(COutPoint(tx1a_txid, 0), nSequence=0)]
+        tx1b.vout = [CTxOut(1.0*COIN, CScript([b'a']))]
+        tx1b_hex = txToHex(tx1b)
+        tx1b_txid = self.nodes[0].sendrawtransaction(tx1b_hex, True)
+        tx1b_txid = int(tx1b_txid, 16)
+
+        tx2 = CTransaction()
+        tx2.vin = [CTxIn(utxo1, nSequence=0), CTxIn(utxo2, nSequence=0),
+                   CTxIn(COutPoint(tx1b_txid, 0))]
+        tx2.vout = tx1a.vout
+        tx2_hex = txToHex(tx2)
+
+        try:
+            tx2_txid = self.nodes[0].sendrawtransaction(tx2_hex, True)
+        except JSONRPCException as exp:
+            assert_equal(exp.error['code'], -26)
+        else:
+            assert(False)
+
+    def test_new_unconfirmed_inputs(self):
+        """Replacements that add new unconfirmed inputs are rejected"""
+        confirmed_utxo = make_utxo(self.nodes[0], 1.1*COIN)
+        unconfirmed_utxo = make_utxo(self.nodes[0], 0.1*COIN, False)
+
+        tx1 = CTransaction()
+        tx1.vin = [CTxIn(confirmed_utxo)]
+        tx1.vout = [CTxOut(1.0*COIN, CScript([b'a']))]
+        tx1_hex = txToHex(tx1)
+        tx1_txid = self.nodes[0].sendrawtransaction(tx1_hex, True)
+
+        tx2 = CTransaction()
+        tx2.vin = [CTxIn(confirmed_utxo), CTxIn(unconfirmed_utxo)]
+        tx2.vout = tx1.vout
+        tx2_hex = txToHex(tx2)
+
+        try:
+            tx2_txid = self.nodes[0].sendrawtransaction(tx2_hex, True)
+        except JSONRPCException as exp:
+            assert_equal(exp.error['code'], -26)
+        else:
+            assert(False)
+
+    def test_too_many_replacements(self):
+        """Replacements that evict too many transactions are rejected"""
+        # Try directly replacing more than MAX_REPLACEMENT_LIMIT
+        # transactions
+
+        # Start by creating a single transaction with many outputs
+        initial_nValue = 10*COIN
+        utxo = make_utxo(self.nodes[0], initial_nValue)
+        fee = 0.0001*COIN
+        split_value = int((initial_nValue-fee)/(MAX_REPLACEMENT_LIMIT+1))
+        actual_fee = initial_nValue - split_value*(MAX_REPLACEMENT_LIMIT+1)
+
+        outputs = []
+        for i in range(MAX_REPLACEMENT_LIMIT+1):
+            outputs.append(CTxOut(split_value, CScript([1])))
+
+        splitting_tx = CTransaction()
+        splitting_tx.vin = [CTxIn(utxo, nSequence=0)]
+        splitting_tx.vout = outputs
+        splitting_tx_hex = txToHex(splitting_tx)
+
+        txid = self.nodes[0].sendrawtransaction(splitting_tx_hex, True)
+        txid = int(txid, 16)
+
+        # Now spend each of those outputs individually
+        for i in range(MAX_REPLACEMENT_LIMIT+1):
+            tx_i = CTransaction()
+            tx_i.vin = [CTxIn(COutPoint(txid, i), nSequence=0)]
+            tx_i.vout = [CTxOut(split_value-fee, CScript([b'a']))]
+            tx_i_hex = txToHex(tx_i)
+            self.nodes[0].sendrawtransaction(tx_i_hex, True)
+
+        # Now create doublespend of the whole lot; should fail.
+        # Need a big enough fee to cover all spending transactions and have
+        # a higher fee rate
+        double_spend_value = (split_value-100*fee)*(MAX_REPLACEMENT_LIMIT+1)
+        inputs = []
+        for i in range(MAX_REPLACEMENT_LIMIT+1):
+            inputs.append(CTxIn(COutPoint(txid, i), nSequence=0))
+        double_tx = CTransaction()
+        double_tx.vin = inputs
+        double_tx.vout = [CTxOut(double_spend_value, CScript([b'a']))]
+        double_tx_hex = txToHex(double_tx)
+
+        try:
+            self.nodes[0].sendrawtransaction(double_tx_hex, True)
+        except JSONRPCException as exp:
+            assert_equal(exp.error['code'], -26)
+            assert_equal("too many potential replacements" in exp.error['message'], True)
+        else:
+            assert(False)
+
+        # If we remove an input, it should pass
+        double_tx = CTransaction()
+        double_tx.vin = inputs[0:-1]
+        double_tx.vout = [CTxOut(double_spend_value, CScript([b'a']))]
+        double_tx_hex = txToHex(double_tx)
+        self.nodes[0].sendrawtransaction(double_tx_hex, True)
+
+    def test_opt_in(self):
+        """ Replacing should only work if orig tx opted in """
+        tx0_outpoint = make_utxo(self.nodes[0], 1.1*COIN)
+
+        # Create a non-opting in transaction
+        tx1a = CTransaction()
+        tx1a.vin = [CTxIn(tx0_outpoint, nSequence=0xffffffff)]
+        tx1a.vout = [CTxOut(1*COIN, CScript([b'a']))]
+        tx1a_hex = txToHex(tx1a)
+        tx1a_txid = self.nodes[0].sendrawtransaction(tx1a_hex, True)
+
+        # Shouldn't be able to double-spend
+        tx1b = CTransaction()
+        tx1b.vin = [CTxIn(tx0_outpoint, nSequence=0)]
+        tx1b.vout = [CTxOut(0.9*COIN, CScript([b'b']))]
+        tx1b_hex = txToHex(tx1b)
+
+        try:
+            tx1b_txid = self.nodes[0].sendrawtransaction(tx1b_hex, True)
+        except JSONRPCException as exp:
+            assert_equal(exp.error['code'], -26)
+        else:
+            print tx1b_txid
+            assert(False)
+
+        tx1_outpoint = make_utxo(self.nodes[0], 1.1*COIN)
+
+        # Create a different non-opting in transaction
+        tx2a = CTransaction()
+        tx2a.vin = [CTxIn(tx1_outpoint, nSequence=0xfffffffe)]
+        tx2a.vout = [CTxOut(1*COIN, CScript([b'a']))]
+        tx2a_hex = txToHex(tx2a)
+        tx2a_txid = self.nodes[0].sendrawtransaction(tx2a_hex, True)
+
+        # Still shouldn't be able to double-spend
+        tx2b = CTransaction()
+        tx2b.vin = [CTxIn(tx1_outpoint, nSequence=0)]
+        tx2b.vout = [CTxOut(0.9*COIN, CScript([b'b']))]
+        tx2b_hex = txToHex(tx2b)
+
+        try:
+            tx2b_txid = self.nodes[0].sendrawtransaction(tx2b_hex, True)
+        except JSONRPCException as exp:
+            assert_equal(exp.error['code'], -26)
+        else:
+            assert(False)
+
+        # Now create a new transaction that spends from tx1a and tx2a
+        # opt-in on one of the inputs
+        # Transaction should be replaceable on either input
+
+        tx1a_txid = int(tx1a_txid, 16)
+        tx2a_txid = int(tx2a_txid, 16)
+
+        tx3a = CTransaction()
+        tx3a.vin = [CTxIn(COutPoint(tx1a_txid, 0), nSequence=0xffffffff),
+                    CTxIn(COutPoint(tx2a_txid, 0), nSequence=0xfffffffd)]
+        tx3a.vout = [CTxOut(0.9*COIN, CScript([b'c'])), CTxOut(0.9*COIN, CScript([b'd']))]
+        tx3a_hex = txToHex(tx3a)
+
+        self.nodes[0].sendrawtransaction(tx3a_hex, True)
+
+        tx3b = CTransaction()
+        tx3b.vin = [CTxIn(COutPoint(tx1a_txid, 0), nSequence=0)]
+        tx3b.vout = [CTxOut(0.5*COIN, CScript([b'e']))]
+        tx3b_hex = txToHex(tx3b)
+
+        tx3c = CTransaction()
+        tx3c.vin = [CTxIn(COutPoint(tx2a_txid, 0), nSequence=0)]
+        tx3c.vout = [CTxOut(0.5*COIN, CScript([b'f']))]
+        tx3c_hex = txToHex(tx3c)
+
+        self.nodes[0].sendrawtransaction(tx3b_hex, True)
+        # If tx3b was accepted, tx3c won't look like a replacement,
+        # but make sure it is accepted anyway
+        self.nodes[0].sendrawtransaction(tx3c_hex, True)
+
+    def test_prioritised_transactions(self):
+        # Ensure that fee deltas used via prioritisetransaction are
+        # correctly used by replacement logic
+
+        # 1. Check that feeperkb uses modified fees
+        tx0_outpoint = make_utxo(self.nodes[0], 1.1*COIN)
+
+        tx1a = CTransaction()
+        tx1a.vin = [CTxIn(tx0_outpoint, nSequence=0)]
+        tx1a.vout = [CTxOut(1*COIN, CScript([b'a']))]
+        tx1a_hex = txToHex(tx1a)
+        tx1a_txid = self.nodes[0].sendrawtransaction(tx1a_hex, True)
+
+        # Higher fee, but the actual fee per KB is much lower.
+        tx1b = CTransaction()
+        tx1b.vin = [CTxIn(tx0_outpoint, nSequence=0)]
+        tx1b.vout = [CTxOut(0.001*COIN, CScript([b'a'*740000]))]
+        tx1b_hex = txToHex(tx1b)
+
+        # Verify tx1b cannot replace tx1a.
+        try:
+            tx1b_txid = self.nodes[0].sendrawtransaction(tx1b_hex, True)
+        except JSONRPCException as exp:
+            assert_equal(exp.error['code'], -26)
+        else:
+            assert(False)
+
+        # Use prioritisetransaction to set tx1a's fee to 0.
+        self.nodes[0].prioritisetransaction(tx1a_txid, 0, int(-0.1*COIN))
+
+        # Now tx1b should be able to replace tx1a
+        tx1b_txid = self.nodes[0].sendrawtransaction(tx1b_hex, True)
+
+        assert(tx1b_txid in self.nodes[0].getrawmempool())
+
+        # 2. Check that absolute fee checks use modified fee.
+        tx1_outpoint = make_utxo(self.nodes[0], 1.1*COIN)
+
+        tx2a = CTransaction()
+        tx2a.vin = [CTxIn(tx1_outpoint, nSequence=0)]
+        tx2a.vout = [CTxOut(1*COIN, CScript([b'a']))]
+        tx2a_hex = txToHex(tx2a)
+        tx2a_txid = self.nodes[0].sendrawtransaction(tx2a_hex, True)
+
+        # Lower fee, but we'll prioritise it
+        tx2b = CTransaction()
+        tx2b.vin = [CTxIn(tx1_outpoint, nSequence=0)]
+        tx2b.vout = [CTxOut(1.01*COIN, CScript([b'a']))]
+        tx2b.rehash()
+        tx2b_hex = txToHex(tx2b)
+
+        # Verify tx2b cannot replace tx2a.
+        try:
+            tx2b_txid = self.nodes[0].sendrawtransaction(tx2b_hex, True)
+        except JSONRPCException as exp:
+            assert_equal(exp.error['code'], -26)
+        else:
+            assert(False)
+
+        # Now prioritise tx2b to have a higher modified fee
+        self.nodes[0].prioritisetransaction(tx2b.hash, 0, int(0.1*COIN))
+
+        # tx2b should now be accepted
+        tx2b_txid = self.nodes[0].sendrawtransaction(tx2b_hex, True)
+
+        assert(tx2b_txid in self.nodes[0].getrawmempool())
+
+if __name__ == '__main__':
+    ReplaceByFeeTest().main()