bitcoin/test/functional/feature_rbf.py

#!/usr/bin/env python3
# Copyright (c) 2014-2020 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 the RBF code."""

from copy import deepcopy
from decimal import Decimal

from test_framework.messages import (
    BIP125_SEQUENCE_NUMBER,
    COIN,
    COutPoint,
    CTransaction,
    CTxIn,
    CTxOut,
)
from test_framework.script import CScript, OP_DROP
from test_framework.test_framework import BitcoinTestFramework
from test_framework.util import (
    assert_equal,
    assert_greater_than,
    assert_raises_rpc_error,
)
from test_framework.script_util import (
    DUMMY_P2WPKH_SCRIPT,
    DUMMY_2_P2WPKH_SCRIPT,
)
from test_framework.wallet import MiniWallet


MAX_REPLACEMENT_LIMIT = 100
class ReplaceByFeeTest(BitcoinTestFramework):
    def set_test_params(self):
        self.num_nodes = 1
        self.extra_args = [
            [
                "-acceptnonstdtxn=1",
                "-maxorphantx=1000",
                "-limitancestorcount=50",
                "-limitancestorsize=101",
                "-limitdescendantcount=200",
                "-limitdescendantsize=101",
            ],
        ]
        self.supports_cli = False

    def skip_test_if_missing_module(self):
        self.skip_if_no_wallet()

    def run_test(self):
        self.wallet = MiniWallet(self.nodes[0])
        # the pre-mined test framework chain contains coinbase outputs to the
        # MiniWallet's default address ADDRESS_BCRT1_P2WSH_OP_TRUE in blocks
        # 76-100 (see method BitcoinTestFramework._initialize_chain())
        self.wallet.rescan_utxos()

        self.log.info("Running test simple doublespend...")
        self.test_simple_doublespend()

        self.log.info("Running test doublespend chain...")
        self.test_doublespend_chain()

        self.log.info("Running test doublespend tree...")
        self.test_doublespend_tree()

        self.log.info("Running test replacement feeperkb...")
        self.test_replacement_feeperkb()

        self.log.info("Running test spends of conflicting outputs...")
        self.test_spends_of_conflicting_outputs()

        self.log.info("Running test new unconfirmed inputs...")
        self.test_new_unconfirmed_inputs()

        self.log.info("Running test too many replacements...")
        self.test_too_many_replacements()

        self.log.info("Running test opt-in...")
        self.test_opt_in()

        self.log.info("Running test RPC...")
        self.test_rpc()

        self.log.info("Running test prioritised transactions...")
        self.test_prioritised_transactions()

        self.log.info("Running test no inherited signaling...")
        self.test_no_inherited_signaling()

        self.log.info("Running test replacement relay fee...")
        self.test_replacement_relay_fee()

        self.log.info("Passed")

    def make_utxo(self, node, amount, confirmed=True, scriptPubKey=DUMMY_P2WPKH_SCRIPT):
        """Create a txout with a given amount and scriptPubKey

        Assumes that MiniWallet has enough funds to cover the amount and the fixed fee
        (from it's internal utxos, the one with the largest value is taken).

        confirmed - txouts created will be confirmed in the blockchain;
                    unconfirmed otherwise.
        """
        # MiniWallet only supports sweeping utxos to its own internal scriptPubKey, so in
        # order to create an output with arbitrary amount/scriptPubKey, we have to add it
        # manually after calling the create_self_transfer method. The MiniWallet output's
        # nValue has to be adapted accordingly (amount and fee deduction). To keep things
        # simple, we use a fixed fee of 1000 Satoshis here.
        fee = 1000
        tx = self.wallet.create_self_transfer(from_node=node, fee_rate=0, mempool_valid=False)['tx']
        assert_greater_than(tx.vout[0].nValue, amount + fee)
        tx.vout[0].nValue -= (amount + fee)           # change output -> MiniWallet
        tx.vout.append(CTxOut(amount, scriptPubKey))  # desired output -> to be returned
        txid = self.wallet.sendrawtransaction(from_node=node, tx_hex=tx.serialize().hex())

        # If requested, ensure txouts are confirmed.
        if confirmed:
            mempool_size = len(node.getrawmempool())
            while mempool_size > 0:
                self.generate(node, 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), 1)

    def test_simple_doublespend(self):
        """Simple doublespend"""
        # we use MiniWallet to create a transaction template with inputs correctly set,
        # and modify the output (amount, scriptPubKey) according to our needs
        tx_template = self.wallet.create_self_transfer(from_node=self.nodes[0])['tx']

        tx1a = deepcopy(tx_template)
        tx1a.vout = [CTxOut(1 * COIN, DUMMY_P2WPKH_SCRIPT)]
        tx1a_hex = tx1a.serialize().hex()
        tx1a_txid = self.nodes[0].sendrawtransaction(tx1a_hex, 0)

        # Should fail because we haven't changed the fee
        tx1b = deepcopy(tx_template)
        tx1b.vout = [CTxOut(1 * COIN, DUMMY_2_P2WPKH_SCRIPT)]
        tx1b_hex = tx1b.serialize().hex()

        # This will raise an exception due to insufficient fee
        assert_raises_rpc_error(-26, "insufficient fee", self.nodes[0].sendrawtransaction, tx1b_hex, 0)

        # Extra 0.1 BTC fee
        tx1b.vout[0].nValue -= int(0.1 * COIN)
        tx1b_hex = tx1b.serialize().hex()
        # Works when enabled
        tx1b_txid = self.nodes[0].sendrawtransaction(tx1b_hex, 0)

        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 = 5 * COIN
        tx0_outpoint = self.make_utxo(self.nodes[0], initial_nValue)

        prevout = tx0_outpoint
        remaining_value = initial_nValue
        chain_txids = []
        while remaining_value > 1 * COIN:
            remaining_value -= int(0.1 * COIN)
            tx = CTransaction()
            tx.vin = [CTxIn(prevout, nSequence=0)]
            tx.vout = [CTxOut(remaining_value, CScript([1, OP_DROP] * 15 + [1]))]
            tx_hex = tx.serialize().hex()
            txid = self.nodes[0].sendrawtransaction(tx_hex, 0)
            chain_txids.append(txid)
            prevout = COutPoint(int(txid, 16), 0)

        # Whether the double-spend is allowed is evaluated by including all
        # child fees - 4 BTC - so this attempt is rejected.
        dbl_tx = CTransaction()
        dbl_tx.vin = [CTxIn(tx0_outpoint, nSequence=0)]
        dbl_tx.vout = [CTxOut(initial_nValue - 3 * COIN, DUMMY_P2WPKH_SCRIPT)]
        dbl_tx_hex = dbl_tx.serialize().hex()

        # This will raise an exception due to insufficient fee
        assert_raises_rpc_error(-26, "insufficient fee", self.nodes[0].sendrawtransaction, dbl_tx_hex, 0)

        # Accepted with sufficient fee
        dbl_tx = CTransaction()
        dbl_tx.vin = [CTxIn(tx0_outpoint, nSequence=0)]
        dbl_tx.vout = [CTxOut(int(0.1 * COIN), DUMMY_P2WPKH_SCRIPT)]
        dbl_tx_hex = dbl_tx.serialize().hex()
        self.nodes[0].sendrawtransaction(dbl_tx_hex, 0)

        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 = 5 * COIN
        tx0_outpoint = self.make_utxo(self.nodes[0], initial_nValue)

        def branch(prevout, initial_value, max_txs, tree_width=5, fee=0.00001 * 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 = tx.serialize().hex()

            assert len(tx.serialize()) < 100000
            txid = self.nodes[0].sendrawtransaction(tx_hex, 0)
            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 = int(0.00001 * 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, DUMMY_P2WPKH_SCRIPT)]
        dbl_tx_hex = dbl_tx.serialize().hex()
        # This will raise an exception due to insufficient fee
        assert_raises_rpc_error(-26, "insufficient fee", self.nodes[0].sendrawtransaction, dbl_tx_hex, 0)

        # 0.1 BTC fee is enough
        dbl_tx = CTransaction()
        dbl_tx.vin = [CTxIn(tx0_outpoint, nSequence=0)]
        dbl_tx.vout = [CTxOut(initial_nValue - fee * n - int(0.1 * COIN), DUMMY_P2WPKH_SCRIPT)]
        dbl_tx_hex = dbl_tx.serialize().hex()
        self.nodes[0].sendrawtransaction(dbl_tx_hex, 0)

        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 = int(0.00001 * COIN)
            tx0_outpoint = self.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, DUMMY_P2WPKH_SCRIPT)]
            dbl_tx_hex = dbl_tx.serialize().hex()
            # This will raise an exception
            assert_raises_rpc_error(-26, "too many potential replacements", self.nodes[0].sendrawtransaction, dbl_tx_hex, 0)

            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 = self.make_utxo(self.nodes[0], int(1.1 * COIN))

        tx1a = CTransaction()
        tx1a.vin = [CTxIn(tx0_outpoint, nSequence=0)]
        tx1a.vout = [CTxOut(1 * COIN, DUMMY_P2WPKH_SCRIPT)]
        tx1a_hex = tx1a.serialize().hex()
        self.nodes[0].sendrawtransaction(tx1a_hex, 0)

        # 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(int(0.001 * COIN), CScript([b'a' * 999000]))]
        tx1b_hex = tx1b.serialize().hex()

        # This will raise an exception due to insufficient fee
        assert_raises_rpc_error(-26, "insufficient fee", self.nodes[0].sendrawtransaction, tx1b_hex, 0)

    def test_spends_of_conflicting_outputs(self):
        """Replacements that spend conflicting tx outputs are rejected"""
        utxo1 = self.make_utxo(self.nodes[0], int(1.2 * COIN))
        utxo2 = self.make_utxo(self.nodes[0], 3 * COIN)

        tx1a = CTransaction()
        tx1a.vin = [CTxIn(utxo1, nSequence=0)]
        tx1a.vout = [CTxOut(int(1.1 * COIN), DUMMY_P2WPKH_SCRIPT)]
        tx1a_hex = tx1a.serialize().hex()
        tx1a_txid = self.nodes[0].sendrawtransaction(tx1a_hex, 0)

        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 = tx2.serialize().hex()

        # This will raise an exception
        assert_raises_rpc_error(-26, "bad-txns-spends-conflicting-tx", self.nodes[0].sendrawtransaction, tx2_hex, 0)

        # Spend tx1a's output to test the indirect case.
        tx1b = CTransaction()
        tx1b.vin = [CTxIn(COutPoint(tx1a_txid, 0), nSequence=0)]
        tx1b.vout = [CTxOut(1 * COIN, DUMMY_P2WPKH_SCRIPT)]
        tx1b_hex = tx1b.serialize().hex()
        tx1b_txid = self.nodes[0].sendrawtransaction(tx1b_hex, 0)
        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 = tx2.serialize().hex()

        # This will raise an exception
        assert_raises_rpc_error(-26, "bad-txns-spends-conflicting-tx", self.nodes[0].sendrawtransaction, tx2_hex, 0)

    def test_new_unconfirmed_inputs(self):
        """Replacements that add new unconfirmed inputs are rejected"""
        confirmed_utxo = self.make_utxo(self.nodes[0], int(1.1 * COIN))
        unconfirmed_utxo = self.make_utxo(self.nodes[0], int(0.1 * COIN), False)

        tx1 = CTransaction()
        tx1.vin = [CTxIn(confirmed_utxo)]
        tx1.vout = [CTxOut(1 * COIN, DUMMY_P2WPKH_SCRIPT)]
        tx1_hex = tx1.serialize().hex()
        self.nodes[0].sendrawtransaction(tx1_hex, 0)

        tx2 = CTransaction()
        tx2.vin = [CTxIn(confirmed_utxo), CTxIn(unconfirmed_utxo)]
        tx2.vout = tx1.vout
        tx2_hex = tx2.serialize().hex()

        # This will raise an exception
        assert_raises_rpc_error(-26, "replacement-adds-unconfirmed", self.nodes[0].sendrawtransaction, tx2_hex, 0)

    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 = self.make_utxo(self.nodes[0], initial_nValue)
        fee = int(0.0001 * COIN)
        split_value = int((initial_nValue - fee) / (MAX_REPLACEMENT_LIMIT + 1))

        outputs = []
        for _ 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 = splitting_tx.serialize().hex()

        txid = self.nodes[0].sendrawtransaction(splitting_tx_hex, 0)
        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, DUMMY_P2WPKH_SCRIPT)]
            tx_i_hex = tx_i.serialize().hex()
            self.nodes[0].sendrawtransaction(tx_i_hex, 0)

        # 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 = double_tx.serialize().hex()

        # This will raise an exception
        assert_raises_rpc_error(-26, "too many potential replacements", self.nodes[0].sendrawtransaction, double_tx_hex, 0)

        # 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 = double_tx.serialize().hex()
        self.nodes[0].sendrawtransaction(double_tx_hex, 0)

    def test_opt_in(self):
        """Replacing should only work if orig tx opted in"""
        tx0_outpoint = self.make_utxo(self.nodes[0], int(1.1 * COIN))

        # Create a non-opting in transaction
        tx1a = CTransaction()
        tx1a.vin = [CTxIn(tx0_outpoint, nSequence=0xffffffff)]
        tx1a.vout = [CTxOut(1 * COIN, DUMMY_P2WPKH_SCRIPT)]
        tx1a_hex = tx1a.serialize().hex()
        tx1a_txid = self.nodes[0].sendrawtransaction(tx1a_hex, 0)

        # This transaction isn't shown as replaceable
        assert_equal(self.nodes[0].getmempoolentry(tx1a_txid)['bip125-replaceable'], False)

        # Shouldn't be able to double-spend
        tx1b = CTransaction()
        tx1b.vin = [CTxIn(tx0_outpoint, nSequence=0)]
        tx1b.vout = [CTxOut(int(0.9 * COIN), DUMMY_P2WPKH_SCRIPT)]
        tx1b_hex = tx1b.serialize().hex()

        # This will raise an exception
        assert_raises_rpc_error(-26, "txn-mempool-conflict", self.nodes[0].sendrawtransaction, tx1b_hex, 0)

        tx1_outpoint = self.make_utxo(self.nodes[0], int(1.1 * COIN))

        # Create a different non-opting in transaction
        tx2a = CTransaction()
        tx2a.vin = [CTxIn(tx1_outpoint, nSequence=0xfffffffe)]
        tx2a.vout = [CTxOut(1 * COIN, DUMMY_P2WPKH_SCRIPT)]
        tx2a_hex = tx2a.serialize().hex()
        tx2a_txid = self.nodes[0].sendrawtransaction(tx2a_hex, 0)

        # Still shouldn't be able to double-spend
        tx2b = CTransaction()
        tx2b.vin = [CTxIn(tx1_outpoint, nSequence=0)]
        tx2b.vout = [CTxOut(int(0.9 * COIN), DUMMY_P2WPKH_SCRIPT)]
        tx2b_hex = tx2b.serialize().hex()

        # This will raise an exception
        assert_raises_rpc_error(-26, "txn-mempool-conflict", self.nodes[0].sendrawtransaction, tx2b_hex, 0)

        # 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(int(0.9 * COIN), CScript([b'c'])), CTxOut(int(0.9 * COIN), CScript([b'd']))]
        tx3a_hex = tx3a.serialize().hex()

        tx3a_txid = self.nodes[0].sendrawtransaction(tx3a_hex, 0)

        # This transaction is shown as replaceable
        assert_equal(self.nodes[0].getmempoolentry(tx3a_txid)['bip125-replaceable'], True)

        tx3b = CTransaction()
        tx3b.vin = [CTxIn(COutPoint(tx1a_txid, 0), nSequence=0)]
        tx3b.vout = [CTxOut(int(0.5 * COIN), DUMMY_P2WPKH_SCRIPT)]
        tx3b_hex = tx3b.serialize().hex()

        tx3c = CTransaction()
        tx3c.vin = [CTxIn(COutPoint(tx2a_txid, 0), nSequence=0)]
        tx3c.vout = [CTxOut(int(0.5 * COIN), DUMMY_P2WPKH_SCRIPT)]
        tx3c_hex = tx3c.serialize().hex()

        self.nodes[0].sendrawtransaction(tx3b_hex, 0)
        # If tx3b was accepted, tx3c won't look like a replacement,
        # but make sure it is accepted anyway
        self.nodes[0].sendrawtransaction(tx3c_hex, 0)

    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 = self.make_utxo(self.nodes[0], int(1.1 * COIN))

        tx1a = CTransaction()
        tx1a.vin = [CTxIn(tx0_outpoint, nSequence=0)]
        tx1a.vout = [CTxOut(1 * COIN, DUMMY_P2WPKH_SCRIPT)]
        tx1a_hex = tx1a.serialize().hex()
        tx1a_txid = self.nodes[0].sendrawtransaction(tx1a_hex, 0)

        # Higher fee, but the actual fee per KB is much lower.
        tx1b = CTransaction()
        tx1b.vin = [CTxIn(tx0_outpoint, nSequence=0)]
        tx1b.vout = [CTxOut(int(0.001 * COIN), CScript([b'a' * 740000]))]
        tx1b_hex = tx1b.serialize().hex()

        # Verify tx1b cannot replace tx1a.
        assert_raises_rpc_error(-26, "insufficient fee", self.nodes[0].sendrawtransaction, tx1b_hex, 0)

        # Use prioritisetransaction to set tx1a's fee to 0.
        self.nodes[0].prioritisetransaction(txid=tx1a_txid, fee_delta=int(-0.1 * COIN))

        # Now tx1b should be able to replace tx1a
        tx1b_txid = self.nodes[0].sendrawtransaction(tx1b_hex, 0)

        assert tx1b_txid in self.nodes[0].getrawmempool()

        # 2. Check that absolute fee checks use modified fee.
        tx1_outpoint = self.make_utxo(self.nodes[0], int(1.1 * COIN))

        tx2a = CTransaction()
        tx2a.vin = [CTxIn(tx1_outpoint, nSequence=0)]
        tx2a.vout = [CTxOut(1 * COIN, DUMMY_P2WPKH_SCRIPT)]
        tx2a_hex = tx2a.serialize().hex()
        self.nodes[0].sendrawtransaction(tx2a_hex, 0)

        # Lower fee, but we'll prioritise it
        tx2b = CTransaction()
        tx2b.vin = [CTxIn(tx1_outpoint, nSequence=0)]
        tx2b.vout = [CTxOut(int(1.01 * COIN), DUMMY_P2WPKH_SCRIPT)]
        tx2b.rehash()
        tx2b_hex = tx2b.serialize().hex()

        # Verify tx2b cannot replace tx2a.
        assert_raises_rpc_error(-26, "insufficient fee", self.nodes[0].sendrawtransaction, tx2b_hex, 0)

        # Now prioritise tx2b to have a higher modified fee
        self.nodes[0].prioritisetransaction(txid=tx2b.hash, fee_delta=int(0.1 * COIN))

        # tx2b should now be accepted
        tx2b_txid = self.nodes[0].sendrawtransaction(tx2b_hex, 0)

        assert tx2b_txid in self.nodes[0].getrawmempool()

    def test_rpc(self):
        us0 = self.nodes[0].listunspent()[0]
        ins = [us0]
        outs = {self.nodes[0].getnewaddress(): Decimal(1.0000000)}
        rawtx0 = self.nodes[0].createrawtransaction(ins, outs, 0, True)
        rawtx1 = self.nodes[0].createrawtransaction(ins, outs, 0, False)
        json0 = self.nodes[0].decoderawtransaction(rawtx0)
        json1 = self.nodes[0].decoderawtransaction(rawtx1)
        assert_equal(json0["vin"][0]["sequence"], 4294967293)
        assert_equal(json1["vin"][0]["sequence"], 4294967295)

        rawtx2 = self.nodes[0].createrawtransaction([], outs)
        frawtx2a = self.nodes[0].fundrawtransaction(rawtx2, {"replaceable": True})
        frawtx2b = self.nodes[0].fundrawtransaction(rawtx2, {"replaceable": False})

        json0 = self.nodes[0].decoderawtransaction(frawtx2a['hex'])
        json1 = self.nodes[0].decoderawtransaction(frawtx2b['hex'])
        assert_equal(json0["vin"][0]["sequence"], 4294967293)
        assert_equal(json1["vin"][0]["sequence"], 4294967294)

    def test_no_inherited_signaling(self):
        confirmed_utxo = self.wallet.get_utxo()

        # Create an explicitly opt-in parent transaction
        optin_parent_tx = self.wallet.send_self_transfer(
            from_node=self.nodes[0],
            utxo_to_spend=confirmed_utxo,
            sequence=BIP125_SEQUENCE_NUMBER,
            fee_rate=Decimal('0.01'),
        )
        assert_equal(True, self.nodes[0].getmempoolentry(optin_parent_tx['txid'])['bip125-replaceable'])

        replacement_parent_tx = self.wallet.create_self_transfer(
            from_node=self.nodes[0],
            utxo_to_spend=confirmed_utxo,
            sequence=BIP125_SEQUENCE_NUMBER,
            fee_rate=Decimal('0.02'),
        )

        # Test if parent tx can be replaced.
        res = self.nodes[0].testmempoolaccept(rawtxs=[replacement_parent_tx['hex']])[0]

        # Parent can be replaced.
        assert_equal(res['allowed'], True)

        # Create an opt-out child tx spending the opt-in parent
        parent_utxo = self.wallet.get_utxo(txid=optin_parent_tx['txid'])
        optout_child_tx = self.wallet.send_self_transfer(
            from_node=self.nodes[0],
            utxo_to_spend=parent_utxo,
            sequence=0xffffffff,
            fee_rate=Decimal('0.01'),
        )

        # Reports true due to inheritance
        assert_equal(True, self.nodes[0].getmempoolentry(optout_child_tx['txid'])['bip125-replaceable'])

        replacement_child_tx = self.wallet.create_self_transfer(
            from_node=self.nodes[0],
            utxo_to_spend=parent_utxo,
            sequence=0xffffffff,
            fee_rate=Decimal('0.02'),
            mempool_valid=False,
        )

        # Broadcast replacement child tx
        # BIP 125 :
        # 1. The original transactions signal replaceability explicitly or through inheritance as described in the above
        # Summary section.
        # The original transaction (`optout_child_tx`) doesn't signal RBF but its parent (`optin_parent_tx`) does.
        # The replacement transaction (`replacement_child_tx`) should be able to replace the original transaction.
        # See CVE-2021-31876 for further explanations.
        assert_equal(True, self.nodes[0].getmempoolentry(optin_parent_tx['txid'])['bip125-replaceable'])
        assert_raises_rpc_error(-26, 'txn-mempool-conflict', self.nodes[0].sendrawtransaction, replacement_child_tx["hex"], 0)

        self.log.info('Check that the child tx can still be replaced (via a tx that also replaces the parent)')
        replacement_parent_tx = self.wallet.send_self_transfer(
            from_node=self.nodes[0],
            utxo_to_spend=confirmed_utxo,
            sequence=0xffffffff,
            fee_rate=Decimal('0.03'),
        )
        # Check that child is removed and update wallet utxo state
        assert_raises_rpc_error(-5, 'Transaction not in mempool', self.nodes[0].getmempoolentry, optout_child_tx['txid'])
        self.wallet.get_utxo(txid=optout_child_tx['txid'])

    def test_replacement_relay_fee(self):
        tx = self.wallet.send_self_transfer(from_node=self.nodes[0])['tx']

        # Higher fee, higher feerate, different txid, but the replacement does not provide a relay
        # fee conforming to node's `incrementalrelayfee` policy of 1000 sat per KB.
        tx.vout[0].nValue -= 1
        assert_raises_rpc_error(-26, "insufficient fee", self.nodes[0].sendrawtransaction, tx.serialize().hex())

if __name__ == '__main__':
    ReplaceByFeeTest().main()