fix ife input spend challenge using wrong index

plasma_framework/contracts/src/exits/payment/controllers/PaymentChallengeIFEInputSpent.sol

@@ -136,7 +136,8 @@ library PaymentChallengeIFEInputSpent {
         GenericTransaction.Transaction memory challengingTx = GenericTransaction.decode(data.args.challengingTx);
 
         GenericTransaction.Transaction memory inputTx = GenericTransaction.decode(data.args.inputTx);
-        GenericTransaction.Output memory output = GenericTransaction.getOutput(inputTx, data.args.challengingTxInputIndex);
+        PosLib.Position memory utxoPos = PosLib.decode(data.args.inputUtxoPos);
+        GenericTransaction.Output memory output = GenericTransaction.getOutput(inputTx, utxoPos.outputIndex);
 
         ISpendingCondition condition = data.controller.spendingConditionRegistry.spendingConditions(
             output.outputType, challengingTx.txType

plasma_framework/python_tests/tests/contracts/root_chain/test_challenge_in_flight_exit_input_spent.py

@@ -1,11 +1,13 @@
 import pytest
 from eth_tester.exceptions import TransactionFailed
 from plasma_core.constants import NULL_ADDRESS
+from plasma_core.utils.transactions import decode_utxo_id, encode_utxo_id
+from tests_utils.constants import PAYMENT_TX_MAX_INPUT_SIZE, PAYMENT_TX_MAX_OUTPUT_SIZE
 
 
 # should succeed even when phase 2 of in-flight exit is over
-@pytest.mark.parametrize("period", [1, 2, 4])
-def test_challenge_in_flight_exit_input_spent_should_succeed(testlang, period):
+@pytest.mark.parametrize("period", [0, 1, 2, 3])
+def test_challenge_in_flight_exit_input_spent_should_succeed_for_all_periods(testlang, period):
     owner_1, owner_2, amount = testlang.accounts[0], testlang.accounts[1], 100
     deposit_id = testlang.deposit(owner_1, amount)
     spend_id = testlang.spend_utxo([deposit_id], [owner_1], [(owner_1.address, NULL_ADDRESS, 100)])
@@ -20,6 +22,56 @@ def test_challenge_in_flight_exit_input_spent_should_succeed(testlang, period):
     assert not in_flight_exit.input_piggybacked(0)
 
 
+@pytest.mark.parametrize(
+    "double_spend_output_index,challenge_input_index",
+    [(i, j) for i in range(PAYMENT_TX_MAX_OUTPUT_SIZE) for j in range(PAYMENT_TX_MAX_INPUT_SIZE)]
+)
+def test_challenge_in_flight_exit_input_spent_should_succeed_for_all_indices(
+    testlang, double_spend_output_index, challenge_input_index
+):
+    alice, bob, carol = testlang.accounts[0], testlang.accounts[1], testlang.accounts[2]
+    deposit_amount = 100
+    deposit_id = testlang.deposit(alice, deposit_amount)
+
+    tx_output_amount = deposit_amount // PAYMENT_TX_MAX_OUTPUT_SIZE
+    outputs = [(alice.address, NULL_ADDRESS, tx_output_amount)] * PAYMENT_TX_MAX_OUTPUT_SIZE
+
+    input_tx_id = testlang.spend_utxo([deposit_id], [alice], outputs=outputs)
+    blknum, tx_index, _ = decode_utxo_id(input_tx_id)
+    double_spend_utxo = encode_utxo_id(blknum, tx_index, double_spend_output_index)
+
+    ife_output_amount = tx_output_amount
+    ife_tx_id = testlang.spend_utxo(
+        [double_spend_utxo],
+        [alice],
+        [(bob.address, NULL_ADDRESS, ife_output_amount)]
+    )
+
+    inputs = []
+    for i in range(0, PAYMENT_TX_MAX_INPUT_SIZE):
+        if i == challenge_input_index:
+            inputs.append(double_spend_utxo)
+        else:
+            inputs.append(testlang.deposit(alice, tx_output_amount))
+
+    challenge_tx_id = testlang.spend_utxo(
+        inputs,
+        [alice] * PAYMENT_TX_MAX_INPUT_SIZE,
+        [
+            (carol.address, NULL_ADDRESS, tx_output_amount),
+        ],
+        force_invalid=True
+    )
+
+    testlang.start_in_flight_exit(ife_tx_id, sender=bob)
+    testlang.piggyback_in_flight_exit_input(ife_tx_id, 0, alice)
+    testlang.challenge_in_flight_exit_input_spent(ife_tx_id, challenge_tx_id, carol)
+
+    in_flight_exit = testlang.get_in_flight_exit(ife_tx_id)
+    for i in range(0, PAYMENT_TX_MAX_INPUT_SIZE):
+        assert not in_flight_exit.input_piggybacked(i)
+
+
 def test_challenge_in_flight_exit_input_spent_not_piggybacked_should_fail(testlang):
     owner_1, owner_2, amount = testlang.accounts[0], testlang.accounts[1], 100
     deposit_id = testlang.deposit(owner_1, amount)

plasma_framework/python_tests/tests/tests_utils/constants.py

@@ -11,3 +11,6 @@
 START_GAS = GAS_LIMIT - 1000000
 
 INITIAL_ETH = 10000 * 10 ** 18
+
+PAYMENT_TX_MAX_INPUT_SIZE = 4
+PAYMENT_TX_MAX_OUTPUT_SIZE = 4