imported wallets: respect "use_change" option; default off

Imported wallets used to send change back to the "from address".
We keep this behaviour as default.

There has already been an option "Use change addresses" (exposed in GUI),
ignored so far by imported wallets (was only used by HD wallets).
With this change, imported wallets no longer ignore that option, and if set,
they will send change to a random unused imported address, instead of back to "from address".
If all addresses are used, it falls back to sending change back to the "from address".

see: #7330
see: #5353

electrum/tests/test_wallet_vertical.py

@@ -2197,6 +2197,123 @@ def test_wallet_does_not_create_zero_input_tx(self, mock_save_db):
             self.assertEqual(1, len(tx.inputs()))
             self.assertEqual(2, len(tx.outputs()))
 
+    @mock.patch.object(wallet.Abstract_Wallet, 'save_db')
+    def test_imported_wallet_usechange_off(self, mock_save_db):
+        wallet = restore_wallet_from_text(
+            "p2wpkh:cVcwSp488C8Riguq55Tuktgi6TpzuyLdDwUxkBDBz3yzV7FW4af2 p2wpkh:cPWyoPvnv2hiyyxbhMkhX3gPEENzB6DqoP9bbR8SDTg5njK5SL9n",
+            path='if_this_exists_mocking_failed_648151893',
+            config=self.config)['wallet']  # type: Abstract_Wallet
+
+        # bootstrap wallet
+        funding_tx = Transaction('02000000000101c6edaaf0157020a38de8b07810b22ffe331d5b79c83b680dad24da15c572ae7d0000000000fdffffff026080010000000000160014eabbd791df76eeeaa3ed273cac4e1dde3be295cca0860100000000001600147a65e09bb1da80abfc65d545388a2e61aab7c7210247304402203cb8b2f84ed4fb8de5f51a07b2159bc0d8d474e5dba0f77cc66ab641cf48621b022076fb3c6b4bc76aa06dd29ebe1dd081c063cdbd2949ffcf4ab4bd8bddae6c948b0121029f16b602a6b3c738b66a03dd5133abe810169a377bbc2fdf5c5363f59b8d9bdec3951e00')
+        funding_txid = funding_tx.txid()
+        self.assertEqual('9bed2a210b4154183295bc7b78c8841a3a6116197713f744e5cd95ab0c0c01ce', funding_txid)
+        wallet.receive_tx_callback(funding_txid, funding_tx, TX_HEIGHT_UNCONFIRMED)
+
+        # imported wallets do not send change to change addresses by default
+        # (they send it back to the "from address")
+        self.assertFalse(wallet.use_change)
+
+        outputs = [PartialTxOutput.from_address_and_value('tb1qq4pypzwxf5uanfyckmsu3ejxxf6rrvjqchza3v', 49646)]
+        coins = wallet.get_spendable_coins(domain=None)
+        tx = wallet.make_unsigned_transaction(coins=coins, outputs=outputs, fee=1000)
+        tx.set_rbf(True)
+        tx.locktime = 2004420
+        tx.version = 2
+
+        # check that change is sent back to the "from address"
+        self.assertEqual(2, len(tx.outputs()))
+        self.assertTrue(tx.output_value_for_address("tb1q0fj7pxa3m2q2hlr964zn3z3wvx4t03ep5fgnhy") > 0)
+        self.assertEqual(49646, tx.output_value_for_address("tb1qq4pypzwxf5uanfyckmsu3ejxxf6rrvjqchza3v"))
+
+        self.assertEqual("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",
+                         tx.serialize_as_bytes().hex())
+        wallet.sign_transaction(tx, password=None)
+        tx_copy = tx_from_any(tx.serialize())
+        self.assertEqual('02000000000101ce010c0cab95cde544f713771916613a1a84c8787bbc95321854410b212aed9b0100000000fdffffff02cac00000000000001600147a65e09bb1da80abfc65d545388a2e61aab7c721eec100000000000016001405424089c64d39d9a498b6e1c8e646327431b240024730440220526eac6c56cba19842b67f6c9e45af113b1a2d44fb229335bdeaf08cb2cc164e0220087fba65619016fd3f62f6c8717070e48f94b45743b86d8e0517698d2b9c3afc012102d67eaa10463f5c786271feb9ae3456c27d35c3cf6c7d881617e915d1f32cb875c4951e00',
+                         str(tx_copy))
+
+    @mock.patch.object(wallet.Abstract_Wallet, 'save_db')
+    def test_imported_wallet_usechange_on(self, mock_save_db):
+        wallet = restore_wallet_from_text(
+            "p2wpkh:cVcwSp488C8Riguq55Tuktgi6TpzuyLdDwUxkBDBz3yzV7FW4af2 p2wpkh:cPWyoPvnv2hiyyxbhMkhX3gPEENzB6DqoP9bbR8SDTg5njK5SL9n",
+            path='if_this_exists_mocking_failed_648151893',
+            config=self.config)['wallet']  # type: Abstract_Wallet
+
+        # bootstrap wallet
+        funding_tx = Transaction('02000000000101c6edaaf0157020a38de8b07810b22ffe331d5b79c83b680dad24da15c572ae7d0000000000fdffffff026080010000000000160014eabbd791df76eeeaa3ed273cac4e1dde3be295cca0860100000000001600147a65e09bb1da80abfc65d545388a2e61aab7c7210247304402203cb8b2f84ed4fb8de5f51a07b2159bc0d8d474e5dba0f77cc66ab641cf48621b022076fb3c6b4bc76aa06dd29ebe1dd081c063cdbd2949ffcf4ab4bd8bddae6c948b0121029f16b602a6b3c738b66a03dd5133abe810169a377bbc2fdf5c5363f59b8d9bdec3951e00')
+        funding_txid = funding_tx.txid()
+        self.assertEqual('9bed2a210b4154183295bc7b78c8841a3a6116197713f744e5cd95ab0c0c01ce', funding_txid)
+        wallet.receive_tx_callback(funding_txid, funding_tx, TX_HEIGHT_UNCONFIRMED)
+
+        # instead of sending the change back to the "from address", we want it sent to another unused address
+        wallet.use_change = True
+
+        outputs = [PartialTxOutput.from_address_and_value('tb1qq4pypzwxf5uanfyckmsu3ejxxf6rrvjqchza3v', 49646)]
+        coins = wallet.get_spendable_coins(domain=None)
+        tx = wallet.make_unsigned_transaction(coins=coins, outputs=outputs, fee=1000)
+        tx.set_rbf(True)
+        tx.locktime = 2004420
+        tx.version = 2
+
+        # check that change is sent to another unused imported address
+        self.assertEqual(2, len(tx.outputs()))
+        self.assertTrue(tx.output_value_for_address("tb1qetcgdwuzlpdnt5fmzxxdpczjhadz06cynpttpv") > 0)
+        self.assertEqual(49646, tx.output_value_for_address("tb1qq4pypzwxf5uanfyckmsu3ejxxf6rrvjqchza3v"))
+
+        self.assertEqual("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",
+                         tx.serialize_as_bytes().hex())
+        wallet.sign_transaction(tx, password=None)
+        tx_copy = tx_from_any(tx.serialize())
+        self.assertEqual('02000000000101ce010c0cab95cde544f713771916613a1a84c8787bbc95321854410b212aed9b0100000000fdffffff02cac0000000000000160014caf086bb82f85b35d13b118cd0e052bf5a27eb04eec100000000000016001405424089c64d39d9a498b6e1c8e646327431b24002473044022006dfe30f851b0174e5c920fd5b2e294a25fe5d449b17b422f3fda485d514c39b022047a6760f9d6ddfac5273094bed1f640fc1622a42938ebfb0b5f61cce7b161a00012102d67eaa10463f5c786271feb9ae3456c27d35c3cf6c7d881617e915d1f32cb875c4951e00',
+                         str(tx_copy))
+
+    @mock.patch.object(wallet.Abstract_Wallet, 'save_db')
+    def test_imported_wallet_usechange_on__no_more_unused_addresses(self, mock_save_db):
+        wallet = restore_wallet_from_text(
+            "p2wpkh:cVcwSp488C8Riguq55Tuktgi6TpzuyLdDwUxkBDBz3yzV7FW4af2 p2wpkh:cPWyoPvnv2hiyyxbhMkhX3gPEENzB6DqoP9bbR8SDTg5njK5SL9n",
+            path='if_this_exists_mocking_failed_648151893',
+            config=self.config)['wallet']  # type: Abstract_Wallet
+
+        # bootstrap wallet
+        funding_tx = Transaction('02000000000101c6edaaf0157020a38de8b07810b22ffe331d5b79c83b680dad24da15c572ae7d0000000000fdffffff026080010000000000160014eabbd791df76eeeaa3ed273cac4e1dde3be295cca0860100000000001600147a65e09bb1da80abfc65d545388a2e61aab7c7210247304402203cb8b2f84ed4fb8de5f51a07b2159bc0d8d474e5dba0f77cc66ab641cf48621b022076fb3c6b4bc76aa06dd29ebe1dd081c063cdbd2949ffcf4ab4bd8bddae6c948b0121029f16b602a6b3c738b66a03dd5133abe810169a377bbc2fdf5c5363f59b8d9bdec3951e00')
+        funding_txid = funding_tx.txid()
+        self.assertEqual('9bed2a210b4154183295bc7b78c8841a3a6116197713f744e5cd95ab0c0c01ce', funding_txid)
+        wallet.receive_tx_callback(funding_txid, funding_tx, TX_HEIGHT_UNCONFIRMED)
+        # add more txs so that all addresses become used
+        _txs = [
+            ("077c8f7a3b0cbb660192c3e35d01a65694f7b90b10e4c6434713912c44cdbfb7", "02000000000101bc125beec2014e3b89679207116e28bcf5bf85cab63ac2903119c8c21ab84cac0100000000fdffffff02daff000000000000160014caf086bb82f85b35d13b118cd0e052bf5a27eb04814201000000000016001491145275b4c4a4814b733fbd28f2a519a5874bad02473044022008ae14e4f7802639a34e92348db7eef95c9fb5d480d7a110d4b11e7d0c45a0cc02205d29414eebcdc76a07f5e2422ed3e560cd663de4b733a0f9c7b3ad7102a733510121030438b8bdbe8121b6a6508e54247b9d1b0547d9ac94c4d3154afd7d7376fe7ae6b6951e00"),
+            ("5f8e17612ad4e04819f1b1cf9039509518e230db07140b2eec81582a8647f8d6", "02000000000101b7bfcd442c91134743c6e4100bb9f79456a6015de3c3920166bb0c3b7a8f7c070000000000fdffffff016cff0000000000001600146a84f3681e545d13fa41de090b6e404401198e7d0247304402204e16704d836cb6e1fffa34244c42578267853e8c3933a3d367bd6a236c24596a0220025a7be9483eeba06a433b96b5cb35a6a4b117ffa884569b09cedc4a5f3d6381012103c19caa2ced1b74bf31ba7885d83eeda35c0011e740273ebdf6750e0298588cc5c7951e00"),
+        ]
+        for txid, rawtx in _txs:
+            tx = Transaction(rawtx)
+            self.assertEqual(txid, tx.txid())
+            wallet.receive_tx_callback(txid, tx, TX_HEIGHT_UNCONFIRMED)
+
+        # instead of sending the change back to the "from address", we want it sent to another unused address.
+        # (except all our addresses are used! so we expect change sent back to "from address")
+        wallet.use_change = True
+
+        outputs = [PartialTxOutput.from_address_and_value('tb1qq4pypzwxf5uanfyckmsu3ejxxf6rrvjqchza3v', 49646)]
+        coins = wallet.get_spendable_coins(domain=None)
+        tx = wallet.make_unsigned_transaction(coins=coins, outputs=outputs, fee=1000)
+        tx.set_rbf(True)
+        tx.locktime = 2004420
+        tx.version = 2
+
+        # check that change is sent back to the "from address"
+        self.assertEqual(2, len(tx.outputs()))
+        self.assertTrue(tx.output_value_for_address("tb1q0fj7pxa3m2q2hlr964zn3z3wvx4t03ep5fgnhy") > 0)
+        self.assertEqual(49646, tx.output_value_for_address("tb1qq4pypzwxf5uanfyckmsu3ejxxf6rrvjqchza3v"))
+
+        self.assertEqual("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",
+                         tx.serialize_as_bytes().hex())
+        wallet.sign_transaction(tx, password=None)
+        tx_copy = tx_from_any(tx.serialize())
+        self.assertEqual('02000000000101ce010c0cab95cde544f713771916613a1a84c8787bbc95321854410b212aed9b0100000000fdffffff02cac00000000000001600147a65e09bb1da80abfc65d545388a2e61aab7c721eec100000000000016001405424089c64d39d9a498b6e1c8e646327431b240024730440220526eac6c56cba19842b67f6c9e45af113b1a2d44fb229335bdeaf08cb2cc164e0220087fba65619016fd3f62f6c8717070e48f94b45743b86d8e0517698d2b9c3afc012102d67eaa10463f5c786271feb9ae3456c27d35c3cf6c7d881617e915d1f32cb875c4951e00',
+                         str(tx_copy))
+
+
 
 class TestWalletOfflineSigning(TestCaseForTestnet):
 

electrum/wallet.py

@@ -2640,6 +2640,7 @@ class Imported_Wallet(Simple_Wallet):
 
     def __init__(self, db, storage, *, config):
         Abstract_Wallet.__init__(self, db, storage, config=config)
+        self.use_change = db.get('use_change', False)
 
     def is_watching_only(self):
         return self.keystore is None
@@ -2682,7 +2683,7 @@ def get_receiving_addresses(self, **kwargs):
         return self.get_addresses()
 
     def get_change_addresses(self, **kwargs):
-        return []
+        return self.get_addresses()
 
     def import_addresses(self, addresses: List[str], *,
                          write_to_disk=True) -> Tuple[List[str], List[Tuple[str, str]]]:
@@ -2749,6 +2750,22 @@ def delete_address(self, address: str) -> None:
                 self.save_keystore()
         self.save_db()
 
+    def get_change_addresses_for_new_transaction(self, *args, **kwargs) -> List[str]:
+        # for an imported wallet, if all "change addresses" are already used,
+        # it is probably better to send change back to the "from address", than to
+        # send it to another random used address and link them together, hence
+        # we force "allow_reusing_used_change_addrs=False"
+        return super().get_change_addresses_for_new_transaction(
+            *args,
+            **{**kwargs, "allow_reusing_used_change_addrs": False},
+        )
+
+    def calc_unused_change_addresses(self) -> Sequence[str]:
+        with self.lock:
+            unused_addrs = [addr for addr in self.get_change_addresses()
+                            if not self.is_used(addr) and not self.is_address_reserved(addr)]
+            return unused_addrs
+
     def is_mine(self, address) -> bool:
         if not address: return False
         return self.db.has_imported_address(address)