wallet: implement cancelling tx by double-spending to self ("dscancel")

electrum/gui/qt/history_list.py

@@ -698,6 +698,8 @@ class HistoryList(MyTreeView, AcceptFileDragDrop):
                 child_tx = self.wallet.cpfp(tx, 0)
                 if child_tx:
                     menu.addAction(_("Child pays for parent"), lambda: self.parent.cpfp(tx, child_tx))
+            if tx_details.can_dscancel and tx_details.fee is not None:
+                menu.addAction(_("Cancel (double-spend)"), lambda: self.parent.dscancel_dialog(tx))
         invoices = self.wallet.get_relevant_invoices_for_tx(tx)
         if len(invoices) == 1:
             menu.addAction(_("View invoice"), lambda inv=invoices[0]: self.parent.show_onchain_invoice(inv))

electrum/gui/qt/main_window.py

@@ -67,7 +67,8 @@ from electrum.invoices import PR_PAID, PR_FAILED, pr_expiration_values, LNInvoic
 from electrum.transaction import (Transaction, PartialTxInput,
                                   PartialTransaction, PartialTxOutput)
 from electrum.wallet import (Multisig_Wallet, CannotBumpFee, Abstract_Wallet,
-                             sweep_preparations, InternalAddressCorruption)
+                             sweep_preparations, InternalAddressCorruption,
+                             CannotDoubleSpendTx)
 from electrum.version import ELECTRUM_VERSION
 from electrum.network import Network, TxBroadcastError, BestEffortRequestFailed, UntrustedServerReturnedError
 from electrum.exchange_rate import FxThread
@@ -486,7 +487,7 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger):
         run_hook('close_wallet', self.wallet)
 
     @profiler
-    def load_wallet(self, wallet):
+    def load_wallet(self, wallet: Abstract_Wallet):
         wallet.thread = TaskThread(self, self.on_error)
         self.update_recently_visited(wallet.storage.path)
         if wallet.has_lightning():
@@ -3236,6 +3237,56 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger):
             new_tx.set_rbf(False)
         self.show_transaction(new_tx, tx_desc=tx_label)
 
+    def dscancel_dialog(self, tx: Transaction):
+        txid = tx.txid()
+        assert txid
+        fee = self.wallet.get_tx_fee(txid)
+        if fee is None:
+            self.show_error(_('Cannot cancel transaction') + ': ' + _('unknown fee for original transaction'))
+            return
+        tx_size = tx.estimated_size()
+        old_fee_rate = fee / tx_size  # sat/vbyte
+        d = WindowModalDialog(self, _('Cancel transaction'))
+        vbox = QVBoxLayout(d)
+        vbox.addWidget(WWLabel(_("Cancel an unconfirmed RBF transaction by double-spending "
+                                 "its inputs back to your wallet with a higher fee.")))
+
+        grid = QGridLayout()
+        grid.addWidget(QLabel(_('Current Fee') + ':'), 0, 0)
+        grid.addWidget(QLabel(self.format_amount(fee) + ' ' + self.base_unit()), 0, 1)
+        grid.addWidget(QLabel(_('Current Fee rate') + ':'), 1, 0)
+        grid.addWidget(QLabel(self.format_fee_rate(1000 * old_fee_rate)), 1, 1)
+
+        grid.addWidget(QLabel(_('New Fee rate') + ':'), 2, 0)
+        def on_textedit_rate():
+            fee_slider.deactivate()
+        feerate_e = FeerateEdit(lambda: 0)
+        feerate_e.setAmount(max(old_fee_rate * 1.5, old_fee_rate + 1))
+        feerate_e.textEdited.connect(on_textedit_rate)
+        grid.addWidget(feerate_e, 2, 1)
+
+        def on_slider_rate(dyn, pos, fee_rate):
+            fee_slider.activate()
+            if fee_rate is not None:
+                feerate_e.setAmount(fee_rate / 1000)
+        fee_slider = FeeSlider(self, self.config, on_slider_rate)
+        fee_combo = FeeComboBox(fee_slider)
+        fee_slider.deactivate()
+        grid.addWidget(fee_slider, 3, 1)
+        grid.addWidget(fee_combo, 3, 2)
+
+        vbox.addLayout(grid)
+        vbox.addLayout(Buttons(CancelButton(d), OkButton(d)))
+        if not d.exec_():
+            return
+        new_fee_rate = feerate_e.get_amount()
+        try:
+            new_tx = self.wallet.dscancel(tx=tx, new_fee_rate=new_fee_rate)
+        except CannotDoubleSpendTx as e:
+            self.show_error(str(e))
+            return
+        self.show_transaction(new_tx)
+
     def save_transaction_into_wallet(self, tx: Transaction):
         win = self.top_level_window()
         try:

electrum/tests/test_wallet_vertical.py

@@ -1558,6 +1558,202 @@ class TestWalletSending(TestCaseForTestnet):
         self.assertFalse(any([wallet_frost.is_mine(txin.address) for txin in tx.inputs()]))
         self.assertFalse(any([wallet_frost.is_mine(txout.address) for txout in tx.outputs()]))
 
+    @mock.patch.object(wallet.Abstract_Wallet, 'save_db')
+    def test_dscancel(self, mock_save_db):
+        self.maxDiff = None
+        config = SimpleConfig({'electrum_path': self.electrum_path})
+        config.set_key('coin_chooser_output_rounding', False)
+
+        for simulate_moving_txs in (False, True):
+            with self.subTest(msg="_dscancel_when_all_outputs_are_ismine", simulate_moving_txs=simulate_moving_txs):
+                self._dscancel_when_all_outputs_are_ismine(
+                    simulate_moving_txs=simulate_moving_txs,
+                    config=config)
+            with self.subTest(msg="_dscancel_p2wpkh_when_there_is_a_change_address", simulate_moving_txs=simulate_moving_txs):
+                self._dscancel_p2wpkh_when_there_is_a_change_address(
+                    simulate_moving_txs=simulate_moving_txs,
+                    config=config)
+            with self.subTest(msg="_dscancel_when_user_sends_max", simulate_moving_txs=simulate_moving_txs):
+                self._dscancel_when_user_sends_max(
+                    simulate_moving_txs=simulate_moving_txs,
+                    config=config)
+
+    def _dscancel_when_all_outputs_are_ismine(self, *, simulate_moving_txs, config):
+        wallet = self.create_standard_wallet_from_seed('fold object utility erase deputy output stadium feed stereo usage modify bean',
+                                                       config=config)
+
+        # bootstrap wallet
+        funding_tx = Transaction('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')
+        funding_txid = funding_tx.txid()
+        funding_output_value = 10000000
+        self.assertEqual('03052739fcfa2ead5f8e57e26021b0c2c546bcd3d74c6e708d5046dc58d90762', funding_txid)
+        wallet.receive_tx_callback(funding_txid, funding_tx, TX_HEIGHT_UNCONFIRMED)
+
+        # create tx
+        outputs = [PartialTxOutput.from_address_and_value('miFLSDZBXUo4on8PGhTRTAufUn4mP61uoH', '!')]
+        coins = wallet.get_spendable_coins(domain=None)
+        tx = wallet.make_unsigned_transaction(coins=coins, outputs=outputs, fee=5000)
+        tx.set_rbf(True)
+        tx.locktime = 1859362
+        tx.version = 2
+        if simulate_moving_txs:
+            partial_tx = tx.serialize_as_bytes().hex()
+            self.assertEqual("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",
+                             partial_tx)
+            tx = tx_from_any(partial_tx)  # simulates moving partial txn between cosigners
+        wallet.sign_transaction(tx, password=None)
+
+        self.assertTrue(tx.is_complete())
+        self.assertFalse(tx.is_segwit())
+        self.assertEqual(1, len(tx.inputs()))
+        tx_copy = tx_from_any(tx.serialize())
+        self.assertTrue(wallet.is_mine(wallet.get_txin_address(tx_copy.inputs()[0])))
+
+        self.assertEqual(tx.txid(), tx_copy.txid())
+        self.assertEqual(tx.wtxid(), tx_copy.wtxid())
+        self.assertEqual('02000000016207d958dc46508d706e4cd7d3bc46c5c2b02160e2578e5fad2efafc39270503000000006a47304402200c1ad6499cfd7a808c2463e211e0aaf503a571c85b679e69af215b76f05ad74d022066fccfec30164ad62686734ec3eca024e33e935b1bf30a98df85d87f01ba1b5f012102a807c07bd7975211078e916bdda061d97e98d59a3631a804aada2f9a3f5b587afdffffff01f8829800000000001976a9141df43441a3a3ee563e560d3ddc7e07cc9f9c3cdb88ac225f1c00',
+                         str(tx_copy))
+        self.assertEqual('200d5173d3113e9cec7a63e885b64836245572d93b6dda4035f3ed44341b6277', tx_copy.txid())
+        self.assertEqual('200d5173d3113e9cec7a63e885b64836245572d93b6dda4035f3ed44341b6277', tx_copy.wtxid())
+
+        wallet.receive_tx_callback(tx.txid(), tx, TX_HEIGHT_UNCONFIRMED)
+        self.assertEqual((0, funding_output_value - 5000, 0), wallet.get_balance())
+
+        # cancel tx
+        tx_details = wallet.get_tx_info(tx_from_any(tx.serialize()))
+        self.assertFalse(tx_details.can_dscancel)
+
+    def _dscancel_p2wpkh_when_there_is_a_change_address(self, *, simulate_moving_txs, config):
+        wallet = self.create_standard_wallet_from_seed('frost repair depend effort salon ring foam oak cancel receive save usage',
+                                                       config=config)
+
+        # bootstrap wallet
+        funding_tx = Transaction('01000000000102acd6459dec7c3c51048eb112630da756f5d4cb4752b8d39aa325407ae0885cba020000001716001455c7f5e0631d8e6f5f05dddb9f676cec48845532fdffffffd146691ef6a207b682b13da5f2388b1f0d2a2022c8cfb8dc27b65434ec9ec8f701000000171600147b3be8a7ceaf15f57d7df2a3d216bc3c259e3225fdffffff02a9875b000000000017a914ea5a99f83e71d1c1dfc5d0370e9755567fe4a141878096980000000000160014d4ca56fcbad98fb4dcafdc573a75d6a6fffb09b702483045022100dde1ba0c9a2862a65791b8d91295a6603207fb79635935a67890506c214dd96d022046c6616642ef5971103c1db07ac014e63fa3b0e15c5729eacdd3e77fcb7d2086012103a72410f185401bb5b10aaa30989c272b554dc6d53bda6da85a76f662723421af024730440220033d0be8f74e782fbcec2b396647c7715d2356076b442423f23552b617062312022063c95cafdc6d52ccf55c8ee0f9ceb0f57afb41ea9076eb74fe633f59c50c6377012103b96a4954d834fbcfb2bbf8cf7de7dc2b28bc3d661c1557d1fd1db1bfc123a94abb391400')
+        funding_txid = funding_tx.txid()
+        funding_output_value = 10000000
+        self.assertEqual('52e669a20a26c8b3df5b41e5e6309b18bcde8e1ad7ea17a18f63b6dc6c8becc0', funding_txid)
+        wallet.receive_tx_callback(funding_txid, funding_tx, TX_HEIGHT_UNCONFIRMED)
+
+        # create tx
+        outputs = [PartialTxOutput.from_address_and_value('2N1VTMMFb91SH9SNRAkT7z8otP5eZEct4KL', 2500000)]
+        coins = wallet.get_spendable_coins(domain=None)
+        tx = wallet.make_unsigned_transaction(coins=coins, outputs=outputs, fee=5000)
+        tx.set_rbf(True)
+        tx.locktime = 1325499
+        tx.version = 1
+        if simulate_moving_txs:
+            partial_tx = tx.serialize_as_bytes().hex()
+            self.assertEqual("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",
+                             partial_tx)
+            tx = tx_from_any(partial_tx)  # simulates moving partial txn between cosigners
+        wallet.sign_transaction(tx, password=None)
+
+        self.assertTrue(tx.is_complete())
+        self.assertTrue(tx.is_segwit())
+        self.assertEqual(1, len(tx.inputs()))
+        tx_copy = tx_from_any(tx.serialize())
+        self.assertTrue(wallet.is_mine(wallet.get_txin_address(tx_copy.inputs()[0])))
+
+        self.assertEqual(tx.txid(), tx_copy.txid())
+        self.assertEqual(tx.wtxid(), tx_copy.wtxid())
+        self.assertEqual('01000000000101c0ec8b6cdcb6638fa117ead71a8edebc189b30e6e5415bdfb3c8260aa269e6520100000000fdffffff02a02526000000000017a9145a71fc1a7a98ddd67be935ade1600981c0d066f987585d720000000000160014f0fe5c1867a174a12e70165e728a072619455ed50247304402205442705e988abe74bf391b293bb1b886674284a92ed0788c33024f9336d60aef022013a93049d3bed693254cd31a704d70bb988a36750f0b74d0a5b4d9e29c54ca9d0121028d4c44ca36d2c4bff3813df8d5d3c0278357521ecb892cd694c473c03970e4c5bb391400',
+                         str(tx_copy))
+        self.assertEqual('b019bbad45a46ed25365e46e4cae6428fb12ae425977eb93011ffb294cb4977e', tx_copy.txid())
+        self.assertEqual('ba87313e2b3b42f1cc478843d4d53c72d6e06f6c66ac8cfbe2a59cdac2fd532d', tx_copy.wtxid())
+
+        wallet.receive_tx_callback(tx.txid(), tx, TX_HEIGHT_UNCONFIRMED)
+        self.assertEqual((0, funding_output_value - 2500000 - 5000, 0), wallet.get_balance())
+
+        # cancel tx
+        tx_details = wallet.get_tx_info(tx_from_any(tx.serialize()))
+        self.assertTrue(tx_details.can_dscancel)
+        tx = wallet.dscancel(tx=tx_from_any(tx.serialize()), new_fee_rate=70.0)
+        tx.locktime = 1859397
+        tx.version = 2
+        if simulate_moving_txs:
+            partial_tx = tx.serialize_as_bytes().hex()
+            self.assertEqual("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",
+                             partial_tx)
+            tx = tx_from_any(partial_tx)  # simulates moving partial txn between cosigners
+        self.assertFalse(tx.is_complete())
+
+        wallet.sign_transaction(tx, password=None)
+        self.assertTrue(tx.is_complete())
+        self.assertTrue(tx.is_segwit())
+        tx_copy = tx_from_any(tx.serialize())
+        self.assertEqual('02000000000101c0ec8b6cdcb6638fa117ead71a8edebc189b30e6e5415bdfb3c8260aa269e6520100000000fdffffff016c78980000000000160014f0fe5c1867a174a12e70165e728a072619455ed50247304402201e706f7ab50e4212a98782e483476102cd6579dad91196002b13dedec79a9a6302205ae30e6c3cf6dd8c566ddae090eeedaac09ba0adc4c0205dfa77bc627621a6b70121028d4c44ca36d2c4bff3813df8d5d3c0278357521ecb892cd694c473c03970e4c5455f1c00',
+                         str(tx_copy))
+        self.assertEqual('165f82b1440cd3a31c005cec660cf834917a1e0a89011805a620c702840fc46a', tx_copy.txid())
+        self.assertEqual('a164fff4f4231a09e8745eb27d0fe636c5c291400b8506d932b0bde6ff8cf9ee', tx_copy.wtxid())
+
+        wallet.receive_tx_callback(tx.txid(), tx, TX_HEIGHT_UNCONFIRMED)
+        self.assertEqual((0, 9992300, 0), wallet.get_balance())
+
+    def _dscancel_when_user_sends_max(self, *, simulate_moving_txs, config):
+        wallet = self.create_standard_wallet_from_seed('frost repair depend effort salon ring foam oak cancel receive save usage',
+                                                       config=config)
+
+        # bootstrap wallet
+        funding_tx = Transaction('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')
+        funding_txid = funding_tx.txid()
+        self.assertEqual('52e669a20a26c8b3df5b41e5e6309b18bcde8e1ad7ea17a18f63b6dc6c8becc0', funding_txid)
+        wallet.receive_tx_callback(funding_txid, funding_tx, TX_HEIGHT_UNCONFIRMED)
+
+        # create tx
+        outputs = [PartialTxOutput.from_address_and_value('2N1VTMMFb91SH9SNRAkT7z8otP5eZEct4KL', '!')]
+        coins = wallet.get_spendable_coins(domain=None)
+        tx = wallet.make_unsigned_transaction(coins=coins, outputs=outputs, fee=5000)
+        tx.set_rbf(True)
+        tx.locktime = 1325499
+        tx.version = 1
+        if simulate_moving_txs:
+            partial_tx = tx.serialize_as_bytes().hex()
+            self.assertEqual("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",
+                             partial_tx)
+            tx = tx_from_any(partial_tx)  # simulates moving partial txn between cosigners
+        wallet.sign_transaction(tx, password=None)
+
+        self.assertTrue(tx.is_complete())
+        self.assertTrue(tx.is_segwit())
+        self.assertEqual(1, len(tx.inputs()))
+        tx_copy = tx_from_any(tx.serialize())
+        self.assertTrue(wallet.is_mine(wallet.get_txin_address(tx_copy.inputs()[0])))
+
+        self.assertEqual(tx.txid(), tx_copy.txid())
+        self.assertEqual(tx.wtxid(), tx_copy.wtxid())
+        self.assertEqual('01000000000101c0ec8b6cdcb6638fa117ead71a8edebc189b30e6e5415bdfb3c8260aa269e6520100000000fdffffff01f88298000000000017a9145a71fc1a7a98ddd67be935ade1600981c0d066f987024730440220520ab41536d5d0fac8ad44e6aa4a8258a266121bab1eb6599f1ee86bbc65719d02205944c2fb765fca4753a850beadac49f5305c6722410c347c08cec4d90e3eb4430121028d4c44ca36d2c4bff3813df8d5d3c0278357521ecb892cd694c473c03970e4c5bb391400',
+                         str(tx_copy))
+        self.assertEqual('dc4b622f3225f00edb886011fa02b74630cdbc24cebdd3210d5ea3b68bef5cc9', tx_copy.txid())
+        self.assertEqual('a00340ee8c90673e05f2cf368601b6bba6a7f0513bd974feb218a326e39b1874', tx_copy.wtxid())
+
+        wallet.receive_tx_callback(tx.txid(), tx, TX_HEIGHT_UNCONFIRMED)
+        self.assertEqual((0, 0, 0), wallet.get_balance())
+
+        # cancel tx
+        tx_details = wallet.get_tx_info(tx_from_any(tx.serialize()))
+        self.assertTrue(tx_details.can_dscancel)
+        tx = wallet.dscancel(tx=tx_from_any(tx.serialize()), new_fee_rate=70.0)
+        tx.locktime = 1859455
+        tx.version = 2
+        if simulate_moving_txs:
+            partial_tx = tx.serialize_as_bytes().hex()
+            self.assertEqual("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",
+                             partial_tx)
+            tx = tx_from_any(partial_tx)  # simulates moving partial txn between cosigners
+        self.assertFalse(tx.is_complete())
+
+        wallet.sign_transaction(tx, password=None)
+        self.assertTrue(tx.is_complete())
+        self.assertTrue(tx.is_segwit())
+        tx_copy = tx_from_any(tx.serialize())
+        self.assertEqual('02000000000101c0ec8b6cdcb6638fa117ead71a8edebc189b30e6e5415bdfb3c8260aa269e6520100000000fdffffff016c78980000000000160014f0fe5c1867a174a12e70165e728a072619455ed502473044022013892ba1580bd8b35fe74cb7a0dceb6914b01ed5cfef6435b94ac0256866971c02200290d08d5f199fcdbba1a2dc4884f5cdea0177cb88e423d8588480d6a5fd62740121028d4c44ca36d2c4bff3813df8d5d3c0278357521ecb892cd694c473c03970e4c57f5f1c00',
+                         str(tx_copy))
+        self.assertEqual('42e222b8faff6cb7fcb82697e04f7bc88a5ed57293773a57a5e400ce0450203e', tx_copy.txid())
+        self.assertEqual('0c6511d0c008604948ea68b0f8cb3da00966c5a97a08a220716ff47eecd4922d', tx_copy.wtxid())
+
+        wallet.receive_tx_callback(tx.txid(), tx, TX_HEIGHT_UNCONFIRMED)
+        self.assertEqual((0, 9992300, 0), wallet.get_balance())
+
 
 class TestWalletOfflineSigning(TestCaseForTestnet):
 

electrum/wallet.py

@@ -35,6 +35,7 @@ import copy
 import errno
 import traceback
 import operator
+import math
 from functools import partial
 from collections import defaultdict
 from numbers import Number
@@ -211,6 +212,9 @@ def get_locktime_for_new_transaction(network: 'Network') -> int:
 class CannotBumpFee(Exception): pass
 
 
+class CannotDoubleSpendTx(Exception): pass
+
+
 class InternalAddressCorruption(Exception):
     def __str__(self):
         return _("Wallet file corruption detected. "
@@ -223,6 +227,7 @@ class TxWalletDetails(NamedTuple):
     label: str
     can_broadcast: bool
     can_bump: bool
+    can_dscancel: bool  # whether user can double-spend to self
     can_save_as_local: bool
     amount: Optional[int]
     fee: Optional[int]
@@ -566,6 +571,7 @@ class Abstract_Wallet(AddressSynchronizer, ABC):
                       and is_relevant
                       # don't offer during common signing flow, e.g. when watch-only wallet starts creating a tx:
                       and bool(tx_we_already_have_in_db))
+        can_dscancel = False
         if tx.is_complete():
             if tx_we_already_have_in_db:
                 label = self.get_label(tx_hash)
@@ -583,6 +589,8 @@ class Abstract_Wallet(AddressSynchronizer, ABC):
                         fee_per_byte = fee / size
                         exp_n = self.config.fee_to_depth(fee_per_byte)
                     can_bump = is_mine and not tx.is_final()
+                    can_dscancel = (is_mine and not tx.is_final()
+                                    and not all([self.is_mine(txout.address) for txout in tx.outputs()]))
                 else:
                     status = _('Local')
                     can_broadcast = self.network is not None
@@ -614,6 +622,7 @@ class Abstract_Wallet(AddressSynchronizer, ABC):
             label=label,
             can_broadcast=can_broadcast,
             can_bump=can_bump,
+            can_dscancel=can_dscancel,
             can_save_as_local=can_save_as_local,
             amount=amount,
             fee=fee,
@@ -1471,6 +1480,53 @@ class Abstract_Wallet(AddressSynchronizer, ABC):
         tx_new.add_info_from_wallet(self)
         return tx_new
 
+    def dscancel(
+            self, *, tx: Transaction, new_fee_rate: Union[int, float, Decimal]
+    ) -> PartialTransaction:
+        """Double-Spend-Cancel: cancel an unconfirmed tx by double-spending
+        its inputs, paying ourselves.
+        'new_fee_rate' is the target min rate in sat/vbyte
+        """
+        if tx.is_final():
+            raise CannotDoubleSpendTx(_('Cannot cancel transaction') + ': ' + _('transaction is final'))
+        new_fee_rate = quantize_feerate(new_fee_rate)  # strip excess precision
+        old_tx_size = tx.estimated_size()
+        old_txid = tx.txid()
+        assert old_txid
+        old_fee = self.get_tx_fee(old_txid)
+        if old_fee is None:
+            raise CannotDoubleSpendTx(_('Cannot cancel transaction') + ': ' + _('current fee unknown'))
+        old_fee_rate = old_fee / old_tx_size  # sat/vbyte
+        if new_fee_rate <= old_fee_rate:
+            raise CannotDoubleSpendTx(_('Cannot cancel transaction') + ': ' + _("The new fee rate needs to be higher than the old fee rate."))
+
+        tx = PartialTransaction.from_tx(tx)
+        tx.add_info_from_wallet(self)
+
+        # grab all ismine inputs
+        inputs = [txin for txin in tx.inputs()
+                  if self.is_mine(self.get_txin_address(txin))]
+        value = sum([txin.value_sats() for txin in tx.inputs()])
+        # figure out output address
+        old_change_addrs = [o.address for o in tx.outputs() if self.is_mine(o.address)]
+        out_address = (self.get_single_change_address_for_new_transaction(old_change_addrs)
+                       or self.get_receiving_address())
+
+        locktime = get_locktime_for_new_transaction(self.network)
+
+        outputs = [PartialTxOutput.from_address_and_value(out_address, value)]
+        tx_new = PartialTransaction.from_io(inputs, outputs, locktime=locktime)
+        new_tx_size = tx_new.estimated_size()
+        new_fee = max(
+            new_fee_rate * new_tx_size,
+            old_fee + self.relayfee() * new_tx_size / Decimal(1000),  # BIP-125 rules 3 and 4
+        )
+        new_fee = int(math.ceil(new_fee))
+        outputs = [PartialTxOutput.from_address_and_value(out_address, value - new_fee)]
+        tx_new = PartialTransaction.from_io(inputs, outputs, locktime=locktime)
+        tx_new.add_info_from_wallet(self)
+        return tx_new
+
     @abstractmethod
     def _add_input_sig_info(self, txin: PartialTxInput, address: str, *, only_der_suffix: bool = True) -> None:
         pass