[functional test] opportunistic 1p1c package submission

3 files changed, 581 insertions, 0 deletions

diff --git a/test/functional/p2p_1p1c_network.py b/test/functional/p2p_1p1c_network.py
new file mode 100755
index 0000000000..e88c826962
--- /dev/null
+++ b/test/functional/p2p_1p1c_network.py
@@ -0,0 +1,165 @@
+#!/usr/bin/env python3
+# Copyright (c) 2024-present 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 that 1p1c package submission allows a 1p1c package to propagate in a "network" of nodes. Send
+various packages from different nodes on a network in which some nodes have already received some of
+the transactions (and submitted them to mempool, kept them as orphans or rejected them as
+too-low-feerate transactions). The packages should be received and accepted by all nodes.
+"""
+
+from decimal import Decimal
+from math import ceil
+
+from test_framework.messages import (
+    msg_tx,
+)
+from test_framework.p2p import (
+    P2PInterface,
+)
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import (
+    assert_equal,
+    assert_greater_than,
+    fill_mempool,
+)
+from test_framework.wallet import (
+    MiniWallet,
+    MiniWalletMode,
+)
+
+# 1sat/vB feerate denominated in BTC/KvB
+FEERATE_1SAT_VB = Decimal("0.00001000")
+
+class PackageRelayTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.setup_clean_chain = True
+        self.num_nodes = 4
+        # hugely speeds up the test, as it involves multiple hops of tx relay.
+        self.noban_tx_relay = True
+        self.extra_args = [[
+            "-datacarriersize=100000",
+            "-maxmempool=5",
+        ]] * self.num_nodes
+        self.supports_cli = False
+
+    def raise_network_minfee(self):
+        filler_wallet = MiniWallet(self.nodes[0])
+        fill_mempool(self, self.nodes[0], filler_wallet)
+
+        self.log.debug("Wait for the network to sync mempools")
+        self.sync_mempools()
+
+        self.log.debug("Check that all nodes' mempool minimum feerates are above min relay feerate")
+        for node in self.nodes:
+            assert_equal(node.getmempoolinfo()['minrelaytxfee'], FEERATE_1SAT_VB)
+            assert_greater_than(node.getmempoolinfo()['mempoolminfee'], FEERATE_1SAT_VB)
+
+    def create_basic_1p1c(self, wallet):
+        low_fee_parent = wallet.create_self_transfer(fee_rate=FEERATE_1SAT_VB, confirmed_only=True)
+        high_fee_child = wallet.create_self_transfer(utxo_to_spend=low_fee_parent["new_utxo"], fee_rate=999*FEERATE_1SAT_VB)
+        package_hex_basic = [low_fee_parent["hex"], high_fee_child["hex"]]
+        return package_hex_basic, low_fee_parent["tx"], high_fee_child["tx"]
+
+    def create_package_2outs(self, wallet):
+        # First create a tester tx to see the vsize, and then adjust the fees
+        utxo_for_2outs = wallet.get_utxo(confirmed_only=True)
+
+        low_fee_parent_2outs_tester = wallet.create_self_transfer_multi(
+            utxos_to_spend=[utxo_for_2outs],
+            num_outputs=2,
+        )
+
+        # Target 1sat/vB so the number of satoshis is equal to the vsize.
+        # Round up. The goal is to be between min relay feerate and mempool min feerate.
+        fee_2outs = ceil(low_fee_parent_2outs_tester["tx"].get_vsize() / 2)
+
+        low_fee_parent_2outs = wallet.create_self_transfer_multi(
+            utxos_to_spend=[utxo_for_2outs],
+            num_outputs=2,
+            fee_per_output=fee_2outs,
+        )
+
+        # Now create the child
+        high_fee_child_2outs = wallet.create_self_transfer_multi(
+            utxos_to_spend=low_fee_parent_2outs["new_utxos"][::-1],
+            fee_per_output=fee_2outs*100,
+        )
+        return [low_fee_parent_2outs["hex"], high_fee_child_2outs["hex"]], low_fee_parent_2outs["tx"], high_fee_child_2outs["tx"]
+
+    def create_package_2p1c(self, wallet):
+        parent1 = wallet.create_self_transfer(fee_rate=FEERATE_1SAT_VB*10, confirmed_only=True)
+        parent2 = wallet.create_self_transfer(fee_rate=FEERATE_1SAT_VB*20, confirmed_only=True)
+        child = wallet.create_self_transfer_multi(
+            utxos_to_spend=[parent1["new_utxo"], parent2["new_utxo"]],
+            fee_per_output=999*parent1["tx"].get_vsize(),
+        )
+        return [parent1["hex"], parent2["hex"], child["hex"]], parent1["tx"], parent2["tx"], child["tx"]
+
+    def create_packages(self):
+        # 1: Basic 1-parent-1-child package, parent 1sat/vB, child 999sat/vB
+        package_hex_1, parent_1, child_1 = self.create_basic_1p1c(self.wallet)
+
+        # 2: same as 1, parent's txid is the same as its wtxid.
+        package_hex_2, parent_2, child_2 = self.create_basic_1p1c(self.wallet_nonsegwit)
+
+        # 3: 2-parent-1-child package. Both parents are above mempool min feerate. No package submission happens.
+        # We require packages to be child-with-unconfirmed-parents and only allow 1-parent-1-child packages.
+        package_hex_3, parent_31, parent_32, child_3 = self.create_package_2p1c(self.wallet)
+
+        # 4: parent + child package where the child spends 2 different outputs from the parent.
+        package_hex_4, parent_4, child_4 = self.create_package_2outs(self.wallet)
+
+        # Assemble return results
+        packages_to_submit = [package_hex_1, package_hex_2, package_hex_3, package_hex_4]
+        # node0: sender
+        # node1: pre-received the children (orphan)
+        # node3: pre-received the parents (too low fee)
+        # All nodes receive parent_31 ahead of time.
+        txns_to_send = [
+            [],
+            [child_1, child_2, parent_31, child_3, child_4],
+            [parent_31],
+            [parent_1, parent_2, parent_31, parent_4]
+        ]
+
+        return packages_to_submit, txns_to_send
+
+    def run_test(self):
+        self.wallet = MiniWallet(self.nodes[1])
+        self.wallet_nonsegwit = MiniWallet(self.nodes[2], mode=MiniWalletMode.RAW_P2PK)
+        self.generate(self.wallet_nonsegwit, 10)
+        self.generate(self.wallet, 120)
+
+        self.log.info("Fill mempools with large transactions to raise mempool minimum feerates")
+        self.raise_network_minfee()
+
+        # Create the transactions.
+        self.wallet.rescan_utxos(include_mempool=True)
+        packages_to_submit, transactions_to_presend = self.create_packages()
+
+        self.peers = [self.nodes[i].add_p2p_connection(P2PInterface()) for i in range(self.num_nodes)]
+
+        self.log.info("Pre-send some transactions to nodes")
+        for (i, peer) in enumerate(self.peers):
+            for tx in transactions_to_presend[i]:
+                peer.send_and_ping(msg_tx(tx))
+            # This disconnect removes any sent orphans from the orphanage (EraseForPeer) and times
+            # out the in-flight requests.  It is currently required for the test to pass right now,
+            # because the node will not reconsider an orphan tx and will not (re)try requesting
+            # orphan parents from multiple peers if the first one didn't respond.
+            # TODO: remove this in the future if the node tries orphan resolution with multiple peers.
+            peer.peer_disconnect()
+
+        self.log.info("Submit full packages to node0")
+        for package_hex in packages_to_submit:
+            submitpackage_result = self.nodes[0].submitpackage(package_hex)
+            assert_equal(submitpackage_result["package_msg"], "success")
+
+        self.log.info("Wait for mempools to sync")
+        self.sync_mempools(timeout=20)
+
+
+if __name__ == '__main__':
+    PackageRelayTest().main()
diff --git a/test/functional/p2p_opportunistic_1p1c.py b/test/functional/p2p_opportunistic_1p1c.py
new file mode 100755
index 0000000000..e07acd5481
--- /dev/null
+++ b/test/functional/p2p_opportunistic_1p1c.py
@@ -0,0 +1,414 @@
+#!/usr/bin/env python3
+# Copyright (c) 2024-present 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 opportunistic 1p1c package submission logic.
+"""
+
+from decimal import Decimal
+import time
+from test_framework.messages import (
+    CInv,
+    CTxInWitness,
+    MAX_BIP125_RBF_SEQUENCE,
+    MSG_WTX,
+    msg_inv,
+    msg_tx,
+    tx_from_hex,
+)
+from test_framework.p2p import (
+    P2PInterface,
+)
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import (
+    assert_equal,
+    assert_greater_than,
+    fill_mempool,
+)
+from test_framework.wallet import (
+    MiniWallet,
+    MiniWalletMode,
+)
+
+# 1sat/vB feerate denominated in BTC/KvB
+FEERATE_1SAT_VB = Decimal("0.00001000")
+# Number of seconds to wait to ensure no getdata is received
+GETDATA_WAIT = 60
+
+def cleanup(func):
+    def wrapper(self, *args, **kwargs):
+        try:
+            func(self, *args, **kwargs)
+        finally:
+            self.nodes[0].disconnect_p2ps()
+            # Do not clear the node's mempool, as each test requires mempool min feerate > min
+            # relay feerate. However, do check that this is the case.
+            assert self.nodes[0].getmempoolinfo()["mempoolminfee"] > self.nodes[0].getnetworkinfo()["relayfee"]
+            # Ensure we do not try to spend the same UTXOs in subsequent tests, as they will look like RBF attempts.
+            self.wallet.rescan_utxos(include_mempool=True)
+
+            # Resets if mocktime was used
+            self.nodes[0].setmocktime(0)
+    return wrapper
+
+class PackageRelayTest(BitcoinTestFramework):
+    def set_test_params(self):
+        self.setup_clean_chain = True
+        self.num_nodes = 1
+        self.extra_args = [[
+            "-datacarriersize=100000",
+            "-maxmempool=5",
+        ]]
+        self.supports_cli = False
+
+    def create_tx_below_mempoolminfee(self, wallet):
+        """Create a 1-input 1sat/vB transaction using a confirmed UTXO. Decrement and use
+        self.sequence so that subsequent calls to this function result in unique transactions."""
+
+        self.sequence -= 1
+        assert_greater_than(self.nodes[0].getmempoolinfo()["mempoolminfee"], FEERATE_1SAT_VB)
+
+        return wallet.create_self_transfer(fee_rate=FEERATE_1SAT_VB, sequence=self.sequence, confirmed_only=True)
+
+    @cleanup
+    def test_basic_child_then_parent(self):
+        node = self.nodes[0]
+        self.log.info("Check that opportunistic 1p1c logic works when child is received before parent")
+
+        low_fee_parent = self.create_tx_below_mempoolminfee(self.wallet)
+        high_fee_child = self.wallet.create_self_transfer(utxo_to_spend=low_fee_parent["new_utxo"], fee_rate=20*FEERATE_1SAT_VB)
+
+        peer_sender = node.add_p2p_connection(P2PInterface())
+
+        # 1. Child is received first (perhaps the low feerate parent didn't meet feefilter or the requests were sent to different nodes). It is missing an input.
+        high_child_wtxid_int = int(high_fee_child["tx"].getwtxid(), 16)
+        peer_sender.send_and_ping(msg_inv([CInv(t=MSG_WTX, h=high_child_wtxid_int)]))
+        peer_sender.wait_for_getdata([high_child_wtxid_int])
+        peer_sender.send_and_ping(msg_tx(high_fee_child["tx"]))
+
+        # 2. Node requests the missing parent by txid.
+        parent_txid_int = int(low_fee_parent["txid"], 16)
+        peer_sender.wait_for_getdata([parent_txid_int])
+
+        # 3. Sender relays the parent. Parent+Child are evaluated as a package and accepted.
+        peer_sender.send_and_ping(msg_tx(low_fee_parent["tx"]))
+
+        # 4. Both transactions should now be in mempool.
+        node_mempool = node.getrawmempool()
+        assert low_fee_parent["txid"] in node_mempool
+        assert high_fee_child["txid"] in node_mempool
+
+        node.disconnect_p2ps()
+
+    @cleanup
+    def test_basic_parent_then_child(self, wallet):
+        node = self.nodes[0]
+        low_fee_parent = self.create_tx_below_mempoolminfee(wallet)
+        high_fee_child = wallet.create_self_transfer(utxo_to_spend=low_fee_parent["new_utxo"], fee_rate=20*FEERATE_1SAT_VB)
+
+        peer_sender = node.add_outbound_p2p_connection(P2PInterface(), p2p_idx=1, connection_type="outbound-full-relay")
+        peer_ignored = node.add_outbound_p2p_connection(P2PInterface(), p2p_idx=2, connection_type="outbound-full-relay")
+
+        # 1. Parent is relayed first. It is too low feerate.
+        parent_wtxid_int = int(low_fee_parent["tx"].getwtxid(), 16)
+        peer_sender.send_and_ping(msg_inv([CInv(t=MSG_WTX, h=parent_wtxid_int)]))
+        peer_sender.wait_for_getdata([parent_wtxid_int])
+        peer_sender.send_and_ping(msg_tx(low_fee_parent["tx"]))
+        assert low_fee_parent["txid"] not in node.getrawmempool()
+
+        # Send again from peer_ignored, check that it is ignored
+        peer_ignored.send_and_ping(msg_inv([CInv(t=MSG_WTX, h=parent_wtxid_int)]))
+        assert "getdata" not in peer_ignored.last_message
+
+        # 2. Child is relayed next. It is missing an input.
+        high_child_wtxid_int = int(high_fee_child["tx"].getwtxid(), 16)
+        peer_sender.send_and_ping(msg_inv([CInv(t=MSG_WTX, h=high_child_wtxid_int)]))
+        peer_sender.wait_for_getdata([high_child_wtxid_int])
+        peer_sender.send_and_ping(msg_tx(high_fee_child["tx"]))
+
+        # 3. Node requests the missing parent by txid.
+        # It should do so even if it has previously rejected that parent for being too low feerate.
+        parent_txid_int = int(low_fee_parent["txid"], 16)
+        peer_sender.wait_for_getdata([parent_txid_int])
+
+        # 4. Sender re-relays the parent. Parent+Child are evaluated as a package and accepted.
+        peer_sender.send_and_ping(msg_tx(low_fee_parent["tx"]))
+
+        # 5. Both transactions should now be in mempool.
+        node_mempool = node.getrawmempool()
+        assert low_fee_parent["txid"] in node_mempool
+        assert high_fee_child["txid"] in node_mempool
+
+    @cleanup
+    def test_low_and_high_child(self, wallet):
+        node = self.nodes[0]
+        low_fee_parent = self.create_tx_below_mempoolminfee(wallet)
+        # This feerate is above mempoolminfee, but not enough to also bump the low feerate parent.
+        feerate_just_above = node.getmempoolinfo()["mempoolminfee"]
+        med_fee_child = wallet.create_self_transfer(utxo_to_spend=low_fee_parent["new_utxo"], fee_rate=feerate_just_above)
+        high_fee_child = wallet.create_self_transfer(utxo_to_spend=low_fee_parent["new_utxo"], fee_rate=999*FEERATE_1SAT_VB)
+
+        peer_sender = node.add_outbound_p2p_connection(P2PInterface(), p2p_idx=1, connection_type="outbound-full-relay")
+        peer_ignored = node.add_outbound_p2p_connection(P2PInterface(), p2p_idx=2, connection_type="outbound-full-relay")
+
+        self.log.info("Check that tx caches low fee parent + low fee child package rejections")
+
+        # 1. Send parent, rejected for being low feerate.
+        parent_wtxid_int = int(low_fee_parent["tx"].getwtxid(), 16)
+        peer_sender.send_and_ping(msg_inv([CInv(t=MSG_WTX, h=parent_wtxid_int)]))
+        peer_sender.wait_for_getdata([parent_wtxid_int])
+        peer_sender.send_and_ping(msg_tx(low_fee_parent["tx"]))
+        assert low_fee_parent["txid"] not in node.getrawmempool()
+
+        # Send again from peer_ignored, check that it is ignored
+        peer_ignored.send_and_ping(msg_inv([CInv(t=MSG_WTX, h=parent_wtxid_int)]))
+        assert "getdata" not in peer_ignored.last_message
+
+        # 2. Send an (orphan) child that has a higher feerate, but not enough to bump the parent.
+        med_child_wtxid_int = int(med_fee_child["tx"].getwtxid(), 16)
+        peer_sender.send_and_ping(msg_inv([CInv(t=MSG_WTX, h=med_child_wtxid_int)]))
+        peer_sender.wait_for_getdata([med_child_wtxid_int])
+        peer_sender.send_and_ping(msg_tx(med_fee_child["tx"]))
+
+        # 3. Node requests the orphan's missing parent.
+        parent_txid_int = int(low_fee_parent["txid"], 16)
+        peer_sender.wait_for_getdata([parent_txid_int])
+
+        # 4. The low parent + low child are submitted as a package. They are not accepted due to low package feerate.
+        peer_sender.send_and_ping(msg_tx(low_fee_parent["tx"]))
+
+        assert low_fee_parent["txid"] not in node.getrawmempool()
+        assert med_fee_child["txid"] not in node.getrawmempool()
+
+        # If peer_ignored announces the low feerate child, it should be ignored
+        peer_ignored.send_and_ping(msg_inv([CInv(t=MSG_WTX, h=med_child_wtxid_int)]))
+        assert "getdata" not in peer_ignored.last_message
+        # If either peer sends the parent again, package evaluation should not be attempted
+        peer_sender.send_and_ping(msg_tx(low_fee_parent["tx"]))
+        peer_ignored.send_and_ping(msg_tx(low_fee_parent["tx"]))
+
+        assert low_fee_parent["txid"] not in node.getrawmempool()
+        assert med_fee_child["txid"] not in node.getrawmempool()
+
+        # 5. Send the high feerate (orphan) child
+        high_child_wtxid_int = int(high_fee_child["tx"].getwtxid(), 16)
+        peer_sender.send_and_ping(msg_inv([CInv(t=MSG_WTX, h=high_child_wtxid_int)]))
+        peer_sender.wait_for_getdata([high_child_wtxid_int])
+        peer_sender.send_and_ping(msg_tx(high_fee_child["tx"]))
+
+        # 6. Node requests the orphan's parent, even though it has already been rejected, both by
+        # itself and with a child. This is necessary, otherwise high_fee_child can be censored.
+        parent_txid_int = int(low_fee_parent["txid"], 16)
+        peer_sender.wait_for_getdata([parent_txid_int])
+
+        # 7. The low feerate parent + high feerate child are submitted as a package.
+        peer_sender.send_and_ping(msg_tx(low_fee_parent["tx"]))
+
+        # 8. Both transactions should now be in mempool
+        node_mempool = node.getrawmempool()
+        assert low_fee_parent["txid"] in node_mempool
+        assert high_fee_child["txid"] in node_mempool
+        assert med_fee_child["txid"] not in node_mempool
+
+    @cleanup
+    def test_orphan_consensus_failure(self):
+        self.log.info("Check opportunistic 1p1c logic with consensus-invalid orphan causes disconnect of the correct peer")
+        node = self.nodes[0]
+        low_fee_parent = self.create_tx_below_mempoolminfee(self.wallet)
+        coin = low_fee_parent["new_utxo"]
+        address = node.get_deterministic_priv_key().address
+        # Create raw transaction spending the parent, but with no signature (a consensus error).
+        hex_orphan_no_sig = node.createrawtransaction([{"txid": coin["txid"], "vout": coin["vout"]}], {address : coin["value"] - Decimal("0.0001")})
+        tx_orphan_bad_wit = tx_from_hex(hex_orphan_no_sig)
+        tx_orphan_bad_wit.wit.vtxinwit.append(CTxInWitness())
+        tx_orphan_bad_wit.wit.vtxinwit[0].scriptWitness.stack = [b'garbage']
+
+        bad_orphan_sender = node.add_p2p_connection(P2PInterface())
+        parent_sender = node.add_p2p_connection(P2PInterface())
+
+        # 1. Child is received first. It is missing an input.
+        child_wtxid_int = int(tx_orphan_bad_wit.getwtxid(), 16)
+        bad_orphan_sender.send_and_ping(msg_inv([CInv(t=MSG_WTX, h=child_wtxid_int)]))
+        bad_orphan_sender.wait_for_getdata([child_wtxid_int])
+        bad_orphan_sender.send_and_ping(msg_tx(tx_orphan_bad_wit))
+
+        # 2. Node requests the missing parent by txid.
+        parent_txid_int = int(low_fee_parent["txid"], 16)
+        bad_orphan_sender.wait_for_getdata([parent_txid_int])
+
+        # 3. A different peer relays the parent. Parent+Child are evaluated as a package and rejected.
+        parent_sender.send_message(msg_tx(low_fee_parent["tx"]))
+
+        # 4. Transactions should not be in mempool.
+        node_mempool = node.getrawmempool()
+        assert low_fee_parent["txid"] not in node_mempool
+        assert tx_orphan_bad_wit.rehash() not in node_mempool
+
+        # 5. Peer that sent a consensus-invalid transaction should be disconnected.
+        bad_orphan_sender.wait_for_disconnect()
+
+        # The peer that didn't provide the orphan should not be disconnected.
+        parent_sender.sync_with_ping()
+
+    @cleanup
+    def test_parent_consensus_failure(self):
+        self.log.info("Check opportunistic 1p1c logic with consensus-invalid parent causes disconnect of the correct peer")
+        node = self.nodes[0]
+        low_fee_parent = self.create_tx_below_mempoolminfee(self.wallet)
+        high_fee_child = self.wallet.create_self_transfer(utxo_to_spend=low_fee_parent["new_utxo"], fee_rate=999*FEERATE_1SAT_VB)
+
+        # Create invalid version of parent with a bad signature.
+        tx_parent_bad_wit = tx_from_hex(low_fee_parent["hex"])
+        tx_parent_bad_wit.wit.vtxinwit.append(CTxInWitness())
+        tx_parent_bad_wit.wit.vtxinwit[0].scriptWitness.stack = [b'garbage']
+
+        package_sender = node.add_p2p_connection(P2PInterface())
+        fake_parent_sender = node.add_p2p_connection(P2PInterface())
+
+        # 1. Child is received first. It is missing an input.
+        child_wtxid_int = int(high_fee_child["tx"].getwtxid(), 16)
+        package_sender.send_and_ping(msg_inv([CInv(t=MSG_WTX, h=child_wtxid_int)]))
+        package_sender.wait_for_getdata([child_wtxid_int])
+        package_sender.send_and_ping(msg_tx(high_fee_child["tx"]))
+
+        # 2. Node requests the missing parent by txid.
+        parent_txid_int = int(tx_parent_bad_wit.rehash(), 16)
+        package_sender.wait_for_getdata([parent_txid_int])
+
+        # 3. A different node relays the parent. The parent is first evaluated by itself and
+        # rejected for being too low feerate. Then it is evaluated as a package and, after passing
+        # feerate checks, rejected for having a bad signature (consensus error).
+        fake_parent_sender.send_message(msg_tx(tx_parent_bad_wit))
+
+        # 4. Transactions should not be in mempool.
+        node_mempool = node.getrawmempool()
+        assert tx_parent_bad_wit.rehash() not in node_mempool
+        assert high_fee_child["txid"] not in node_mempool
+
+        # 5. Peer sent a consensus-invalid transaction.
+        fake_parent_sender.wait_for_disconnect()
+
+        self.log.info("Check that fake parent does not cause orphan to be deleted and real package can still be submitted")
+        # 6. Child-sending should not have been punished and the orphan should remain in orphanage.
+        # It can send the "real" parent transaction, and the package is accepted.
+        parent_wtxid_int = int(low_fee_parent["tx"].getwtxid(), 16)
+        package_sender.send_and_ping(msg_inv([CInv(t=MSG_WTX, h=parent_wtxid_int)]))
+        package_sender.wait_for_getdata([parent_wtxid_int])
+        package_sender.send_and_ping(msg_tx(low_fee_parent["tx"]))
+
+        node_mempool = node.getrawmempool()
+        assert low_fee_parent["txid"] in node_mempool
+        assert high_fee_child["txid"] in node_mempool
+
+    @cleanup
+    def test_multiple_parents(self):
+        self.log.info("Check that node does not request more than 1 previously-rejected low feerate parent")
+
+        node = self.nodes[0]
+        node.setmocktime(int(time.time()))
+
+        # 2-parent-1-child package where both parents are below mempool min feerate
+        parent_low_1 = self.create_tx_below_mempoolminfee(self.wallet_nonsegwit)
+        parent_low_2 = self.create_tx_below_mempoolminfee(self.wallet_nonsegwit)
+        child_bumping = self.wallet_nonsegwit.create_self_transfer_multi(
+            utxos_to_spend=[parent_low_1["new_utxo"], parent_low_2["new_utxo"]],
+            fee_per_output=999*parent_low_1["tx"].get_vsize(),
+        )
+
+        peer_sender = node.add_outbound_p2p_connection(P2PInterface(), p2p_idx=1, connection_type="outbound-full-relay")
+
+        # 1. Send both parents. Each should be rejected for being too low feerate.
+        # Send unsolicited so that we can later check that no "getdata" was ever received.
+        peer_sender.send_and_ping(msg_tx(parent_low_1["tx"]))
+        peer_sender.send_and_ping(msg_tx(parent_low_2["tx"]))
+
+        # parent_low_1 and parent_low_2 are rejected for being low feerate.
+        assert parent_low_1["txid"] not in node.getrawmempool()
+        assert parent_low_2["txid"] not in node.getrawmempool()
+
+        # 2. Send child.
+        peer_sender.send_and_ping(msg_tx(child_bumping["tx"]))
+
+        # 3. Node should not request any parents, as it should recognize that it will not accept
+        # multi-parent-1-child packages.
+        node.bumpmocktime(GETDATA_WAIT)
+        peer_sender.sync_with_ping()
+        assert "getdata" not in peer_sender.last_message
+
+    @cleanup
+    def test_other_parent_in_mempool(self):
+        self.log.info("Check opportunistic 1p1c fails if child already has another parent in mempool")
+        node = self.nodes[0]
+
+        # This parent needs CPFP
+        parent_low = self.create_tx_below_mempoolminfee(self.wallet)
+        # This parent does not need CPFP and can be submitted alone ahead of time
+        parent_high = self.wallet.create_self_transfer(fee_rate=FEERATE_1SAT_VB*10, confirmed_only=True)
+        child = self.wallet.create_self_transfer_multi(
+            utxos_to_spend=[parent_high["new_utxo"], parent_low["new_utxo"]],
+            fee_per_output=999*parent_low["tx"].get_vsize(),
+        )
+
+        peer_sender = node.add_outbound_p2p_connection(P2PInterface(), p2p_idx=1, connection_type="outbound-full-relay")
+
+        # 1. Send first parent which will be accepted.
+        peer_sender.send_and_ping(msg_tx(parent_high["tx"]))
+        assert parent_high["txid"] in node.getrawmempool()
+
+        # 2. Send child.
+        peer_sender.send_and_ping(msg_tx(child["tx"]))
+
+        # 3. Node requests parent_low. However, 1p1c fails because package-not-child-with-unconfirmed-parents
+        parent_low_txid_int = int(parent_low["txid"], 16)
+        peer_sender.wait_for_getdata([parent_low_txid_int])
+        peer_sender.send_and_ping(msg_tx(parent_low["tx"]))
+
+        node_mempool = node.getrawmempool()
+        assert parent_high["txid"] in node_mempool
+        assert parent_low["txid"] not in node_mempool
+        assert child["txid"] not in node_mempool
+
+        # Same error if submitted through submitpackage without parent_high
+        package_hex_missing_parent = [parent_low["hex"], child["hex"]]
+        result_missing_parent = node.submitpackage(package_hex_missing_parent)
+        assert_equal(result_missing_parent["package_msg"], "package-not-child-with-unconfirmed-parents")
+
+    def run_test(self):
+        node = self.nodes[0]
+        # To avoid creating transactions with the same txid (can happen if we set the same feerate
+        # and reuse the same input as a previous transaction that wasn't successfully submitted),
+        # we give each subtest a different nSequence for its transactions.
+        self.sequence = MAX_BIP125_RBF_SEQUENCE
+
+        self.wallet = MiniWallet(node)
+        self.wallet_nonsegwit = MiniWallet(node, mode=MiniWalletMode.RAW_P2PK)
+        self.generate(self.wallet_nonsegwit, 10)
+        self.generate(self.wallet, 20)
+
+        filler_wallet = MiniWallet(node)
+        fill_mempool(self, node, filler_wallet)
+
+        self.log.info("Check opportunistic 1p1c logic when parent (txid != wtxid) is received before child")
+        self.test_basic_parent_then_child(self.wallet)
+
+        self.log.info("Check opportunistic 1p1c logic when parent (txid == wtxid) is received before child")
+        self.test_basic_parent_then_child(self.wallet_nonsegwit)
+
+        self.log.info("Check opportunistic 1p1c logic when child is received before parent")
+        self.test_basic_child_then_parent()
+
+        self.log.info("Check opportunistic 1p1c logic when 2 candidate children exist (parent txid != wtxid)")
+        self.test_low_and_high_child(self.wallet)
+
+        self.log.info("Check opportunistic 1p1c logic when 2 candidate children exist (parent txid == wtxid)")
+        self.test_low_and_high_child(self.wallet_nonsegwit)
+
+        self.test_orphan_consensus_failure()
+        self.test_parent_consensus_failure()
+        self.test_multiple_parents()
+        self.test_other_parent_in_mempool()
+
+
+if __name__ == '__main__':
+    PackageRelayTest().main()
diff --git a/test/functional/test_runner.py b/test/functional/test_runner.py
index 3f6e47d410..629c9d025a 100755
--- a/test/functional/test_runner.py
+++ b/test/functional/test_runner.py
@@ -199,6 +199,8 @@ BASE_SCRIPTS = [
     'wallet_txn_clone.py --segwit',
     'rpc_getchaintips.py',
     'rpc_misc.py',
+    'p2p_1p1c_network.py',
+    'p2p_opportunistic_1p1c.py',
     'interface_rest.py',
     'mempool_spend_coinbase.py',
     'wallet_avoid_mixing_output_types.py --descriptors',