fix: disabling "use change addresses" did not work correctly

lib/coinchooser.py

@@ -25,7 +25,7 @@
 from collections import defaultdict, namedtuple
 from math import floor, log10
 
-from .bitcoin import sha256, COIN, TYPE_ADDRESS
+from .bitcoin import sha256, COIN, TYPE_ADDRESS, is_address
 from .transaction import Transaction
 from .util import NotEnoughFunds, PrintError
 
@@ -240,6 +240,13 @@ class CoinChooserBase(PrintError):
         tx.add_inputs([coin for b in buckets for coin in b.coins])
         tx_weight = get_tx_weight(buckets)
 
+        # change is sent back to sending address unless specified
+        if not change_addrs:
+            change_addrs = [tx.inputs()[0]['address']]
+            # note: this is not necessarily the final "first input address"
+            # because the inputs had not been sorted at this point
+            assert is_address(change_addrs[0])
+
         # This takes a count of change outputs and returns a tx fee
         output_weight = 4 * Transaction.estimated_output_size(change_addrs[0])
         fee = lambda count: fee_estimator_w(tx_weight + count * output_weight)

lib/wallet.py

@@ -1123,7 +1123,8 @@ class Abstract_Wallet(PrintError):
                 if not change_addrs:
                     change_addrs = [random.choice(addrs)]
             else:
-                change_addrs = [inputs[0]['address']]
+                # coin_chooser will set change address
+                change_addrs = []
 
         # Fee estimator
         if fixed_fee is None: