Add 'subtractFeeFromOutputs' option to 'fundrawtransaction'.

2 files changed, 77 insertions, 3 deletions

diff --git a/qa/rpc-tests/fundrawtransaction.py b/qa/rpc-tests/fundrawtransaction.py
index 82e148c55a..b97e9aecdf 100755
--- a/qa/rpc-tests/fundrawtransaction.py
+++ b/qa/rpc-tests/fundrawtransaction.py
@@ -660,5 +660,75 @@ class RawTransactionsTest(BitcoinTestFramework):
         assert_fee_amount(result2['fee'], count_bytes(result2['hex']), 2 * result_fee_rate)
         assert_fee_amount(result3['fee'], count_bytes(result3['hex']), 10 * result_fee_rate)
 
+        ######################################
+        # Test subtractFeeFromOutputs option #
+        ######################################
+
+        # Make sure there is exactly one input so coin selection can't skew the result
+        assert_equal(len(self.nodes[3].listunspent(1)), 1)
+
+        inputs = []
+        outputs = {self.nodes[2].getnewaddress(): 1}
+        rawtx = self.nodes[3].createrawtransaction(inputs, outputs)
+
+        result = [self.nodes[3].fundrawtransaction(rawtx), # uses min_relay_tx_fee (set by settxfee)
+                  self.nodes[3].fundrawtransaction(rawtx, {"subtractFeeFromOutputs": []}), # empty subtraction list
+                  self.nodes[3].fundrawtransaction(rawtx, {"subtractFeeFromOutputs": [0]}), # uses min_relay_tx_fee (set by settxfee)
+                  self.nodes[3].fundrawtransaction(rawtx, {"feeRate": 2*min_relay_tx_fee}),
+                  self.nodes[3].fundrawtransaction(rawtx, {"feeRate": 2*min_relay_tx_fee, "subtractFeeFromOutputs": [0]})]
+
+        dec_tx = [self.nodes[3].decoderawtransaction(tx['hex']) for tx in result]
+        output = [d['vout'][1 - r['changepos']]['value'] for d, r in zip(dec_tx, result)]
+        change = [d['vout'][r['changepos']]['value'] for d, r in zip(dec_tx, result)]
+
+        assert_equal(result[0]['fee'], result[1]['fee'], result[2]['fee'])
+        assert_equal(result[3]['fee'], result[4]['fee'])
+        assert_equal(change[0], change[1])
+        assert_equal(output[0], output[1])
+        assert_equal(output[0], output[2] + result[2]['fee'])
+        assert_equal(change[0] + result[0]['fee'], change[2])
+        assert_equal(output[3], output[4] + result[4]['fee'])
+        assert_equal(change[3] + result[3]['fee'], change[4])
+
+        inputs = []
+        outputs = {self.nodes[2].getnewaddress(): value for value in (1.0, 1.1, 1.2, 1.3)}
+        keys = list(outputs.keys())
+        rawtx = self.nodes[3].createrawtransaction(inputs, outputs)
+
+        result = [self.nodes[3].fundrawtransaction(rawtx),
+                  # split the fee between outputs 0, 2, and 3, but not output 1
+                  self.nodes[3].fundrawtransaction(rawtx, {"subtractFeeFromOutputs": [0, 2, 3]})]
+
+        dec_tx = [self.nodes[3].decoderawtransaction(result[0]['hex']),
+                  self.nodes[3].decoderawtransaction(result[1]['hex'])]
+
+        # Nested list of non-change output amounts for each transaction
+        output = [[out['value'] for i, out in enumerate(d['vout']) if i != r['changepos']]
+                  for d, r in zip(dec_tx, result)]
+
+        # List of differences in output amounts between normal and subtractFee transactions
+        share = [o0 - o1 for o0, o1 in zip(output[0], output[1])]
+
+        # output 1 is the same in both transactions
+        assert_equal(share[1], 0)
+
+        # the other 3 outputs are smaller as a result of subtractFeeFromOutputs
+        assert_greater_than(share[0], 0)
+        assert_greater_than(share[2], 0)
+        assert_greater_than(share[3], 0)
+
+        # outputs 2 and 3 take the same share of the fee
+        assert_equal(share[2], share[3])
+
+        # output 0 takes at least as much share of the fee, and no more than 2 satoshis more, than outputs 2 and 3
+        assert_greater_than_or_equal(share[0], share[2])
+        assert_greater_than_or_equal(share[2] + Decimal(2e-8), share[0])
+
+        # the fee is the same in both transactions
+        assert_equal(result[0]['fee'], result[1]['fee'])
+
+        # the total subtracted from the outputs is equal to the fee
+        assert_equal(share[0] + share[2] + share[3], result[0]['fee'])
+
 if __name__ == '__main__':
     RawTransactionsTest().main()
diff --git a/qa/rpc-tests/test_framework/util.py b/qa/rpc-tests/test_framework/util.py
index 85898d9f32..57f8218cf0 100644
--- a/qa/rpc-tests/test_framework/util.py
+++ b/qa/rpc-tests/test_framework/util.py
@@ -524,14 +524,18 @@ def assert_fee_amount(fee, tx_size, fee_per_kB):
     if fee > (tx_size + 2) * fee_per_kB / 1000:
         raise AssertionError("Fee of %s BTC too high! (Should be %s BTC)"%(str(fee), str(target_fee)))
 
-def assert_equal(thing1, thing2):
-    if thing1 != thing2:
-        raise AssertionError("%s != %s"%(str(thing1),str(thing2)))
+def assert_equal(thing1, thing2, *args):
+    if thing1 != thing2 or any(thing1 != arg for arg in args):
+        raise AssertionError("not(%s)" % " == ".join(str(arg) for arg in (thing1, thing2) + args))
 
 def assert_greater_than(thing1, thing2):
     if thing1 <= thing2:
         raise AssertionError("%s <= %s"%(str(thing1),str(thing2)))
 
+def assert_greater_than_or_equal(thing1, thing2):
+    if thing1 < thing2:
+        raise AssertionError("%s < %s"%(str(thing1),str(thing2)))
+
 def assert_raises(exc, fun, *args, **kwds):
     assert_raises_message(exc, None, fun, *args, **kwds)