test: test OP_CSV empty stack fail in feature_csv_activation.py

With BIP112 activated, the operation OP_CHECKSEQUENCEVERIFY (former OP_NOP3)
leads to script interpreter termination with an error if one of the following
conditions is true:
    -> stack is empty
    -> top item on stack is negative (< 0)
    -> top item on stack has disable flag unset and at least one of
       four other conditions is true (contains the core CSV logic)

This commits adds the missing empty stack failure test to the functional test
by prepending a valid scriptSig with just OP_CHECKSEQUENCEVERIFY. If BIP112 is
inactive, the operator just behaves as a NOP (for both tx versions 1 and 2) and
the transaction remains valid -- if it is active, the tx is invalid due to an
empty stack (for both tx versions 1 and 2, as well).

Author: theStack

test/functional/feature_csv_activation.py

@@ -35,6 +35,7 @@
 bip112txs_vary_OP_CSV - 16 txs with nSequence = 10 evaluated against varying {relative_locktimes of 10} OP_CSV OP_DROP
 bip112txs_vary_OP_CSV_9 - 16 txs with nSequence = 9 evaluated against varying {relative_locktimes of 10} OP_CSV OP_DROP
 bip112tx_special - test negative argument to OP_CSV
+bip112tx_emptystack - test empty stack (= no argument) OP_CSV
 """
 from decimal import Decimal
 from itertools import product
@@ -95,6 +96,13 @@ def create_bip112special(node, input, txversion, address):
     signtx.vin[0].scriptSig = CScript([-1, OP_CHECKSEQUENCEVERIFY, OP_DROP] + list(CScript(signtx.vin[0].scriptSig)))
     return signtx
 
+def create_bip112emptystack(node, input, txversion, address):
+    tx = create_transaction(node, input, address, amount=Decimal("49.98"))
+    tx.nVersion = txversion
+    signtx = sign_transaction(node, tx)
+    signtx.vin[0].scriptSig = CScript([OP_CHECKSEQUENCEVERIFY] + list(CScript(signtx.vin[0].scriptSig)))
+    return signtx
+
 def send_generic_input_tx(node, coinbases, address):
     return node.sendrawtransaction(ToHex(sign_transaction(node, create_transaction(node, node.getblock(coinbases.pop())['tx'][0], address, amount=Decimal("49.99")))))
 
@@ -179,15 +187,15 @@ def run_test(self):
         self.log.info("Generate blocks in the past for coinbase outputs.")
         long_past_time = int(time.time()) - 600 * 1000  # enough to build up to 1000 blocks 10 minutes apart without worrying about getting into the future
         self.nodes[0].setmocktime(long_past_time - 100)  # enough so that the generated blocks will still all be before long_past_time
-        self.coinbase_blocks = self.nodes[0].generate(1 + 16 + 2 * 32 + 1)  # 82 blocks generated for inputs
+        self.coinbase_blocks = self.nodes[0].generate(1 + 16 + 2 * 32 + 2)  # 83 blocks generated for inputs
         self.nodes[0].setmocktime(0)  # set time back to present so yielded blocks aren't in the future as we advance last_block_time
-        self.tipheight = 82  # height of the next block to build
+        self.tipheight = 83  # height of the next block to build
         self.last_block_time = long_past_time
         self.tip = int(self.nodes[0].getbestblockhash(), 16)
         self.nodeaddress = self.nodes[0].getnewaddress()
 
         # Activation height is hardcoded
-        test_blocks = self.generate_blocks(345)
+        test_blocks = self.generate_blocks(344)
         self.send_blocks(test_blocks)
         assert not softfork_active(self.nodes[0], 'csv')
 
@@ -218,6 +226,8 @@ def run_test(self):
 
         # 1 special input with -1 OP_CSV OP_DROP (actually will be prepended to spending scriptSig)
         bip112specialinput = send_generic_input_tx(self.nodes[0], self.coinbase_blocks, self.nodeaddress)
+        # 1 special input with (empty stack) OP_CSV (actually will be prepended to spending scriptSig)
+        bip112emptystackinput = send_generic_input_tx(self.nodes[0],self.coinbase_blocks, self.nodeaddress)
 
         # 1 normal input
         bip113input = send_generic_input_tx(self.nodes[0], self.coinbase_blocks, self.nodeaddress)
@@ -228,7 +238,7 @@ def run_test(self):
         self.tip = int(inputblockhash, 16)
         self.tipheight += 1
         self.last_block_time += 600
-        assert_equal(len(self.nodes[0].getblock(inputblockhash, True)["tx"]), 82 + 1)
+        assert_equal(len(self.nodes[0].getblock(inputblockhash, True)["tx"]), 83 + 1)
 
         # 2 more version 4 blocks
         test_blocks = self.generate_blocks(2)
@@ -267,18 +277,22 @@ def run_test(self):
         # -1 OP_CSV OP_DROP input
         bip112tx_special_v1 = create_bip112special(self.nodes[0], bip112specialinput, 1, self.nodeaddress)
         bip112tx_special_v2 = create_bip112special(self.nodes[0], bip112specialinput, 2, self.nodeaddress)
+        # (empty stack) OP_CSV input
+        bip112tx_emptystack_v1 = create_bip112emptystack(self.nodes[0], bip112emptystackinput, 1, self.nodeaddress)
+        bip112tx_emptystack_v2 = create_bip112emptystack(self.nodes[0], bip112emptystackinput, 2, self.nodeaddress)
 
         self.log.info("TESTING")
 
         self.log.info("Pre-Soft Fork Tests. All txs should pass.")
         self.log.info("Test version 1 txs")
 
         success_txs = []
-        # add BIP113 tx and -1 CSV tx
+        # BIP113 tx, -1 CSV tx and empty stack CSV tx should succeed
         bip113tx_v1.nLockTime = self.last_block_time - 600 * 5  # = MTP of prior block (not <) but < time put on current block
         bip113signed1 = sign_transaction(self.nodes[0], bip113tx_v1)
         success_txs.append(bip113signed1)
         success_txs.append(bip112tx_special_v1)
+        success_txs.append(bip112tx_emptystack_v1)
         # add BIP 68 txs
         success_txs.extend(all_rlt_txs(bip68txs_v1))
         # add BIP 112 with seq=10 txs
@@ -293,11 +307,12 @@ def run_test(self):
         self.log.info("Test version 2 txs")
 
         success_txs = []
-        # add BIP113 tx and -1 CSV tx
+        # BIP113 tx, -1 CSV tx and empty stack CSV tx should succeed
         bip113tx_v2.nLockTime = self.last_block_time - 600 * 5  # = MTP of prior block (not <) but < time put on current block
         bip113signed2 = sign_transaction(self.nodes[0], bip113tx_v2)
         success_txs.append(bip113signed2)
         success_txs.append(bip112tx_special_v2)
+        success_txs.append(bip112tx_emptystack_v2)
         # add BIP 68 txs
         success_txs.extend(all_rlt_txs(bip68txs_v2))
         # add BIP 112 with seq=10 txs
@@ -385,8 +400,9 @@ def run_test(self):
         self.log.info("BIP 112 tests")
         self.log.info("Test version 1 txs")
 
-        # -1 OP_CSV tx should fail
+        # -1 OP_CSV tx and (empty stack) OP_CSV tx should fail
         self.send_blocks([self.create_test_block([bip112tx_special_v1])], success=False)
+        self.send_blocks([self.create_test_block([bip112tx_emptystack_v1])], success=False)
         # If SEQUENCE_LOCKTIME_DISABLE_FLAG is set in argument to OP_CSV, version 1 txs should still pass
 
         success_txs = [tx['tx'] for tx in bip112txs_vary_OP_CSV_v1 if tx['sdf']]
@@ -404,8 +420,9 @@ def run_test(self):
 
         self.log.info("Test version 2 txs")
 
-        # -1 OP_CSV tx should fail
+        # -1 OP_CSV tx and (empty stack) OP_CSV tx should fail
         self.send_blocks([self.create_test_block([bip112tx_special_v2])], success=False)
+        self.send_blocks([self.create_test_block([bip112tx_emptystack_v2])], success=False)
 
         # If SEQUENCE_LOCKTIME_DISABLE_FLAG is set in argument to OP_CSV, version 2 txs should pass (all sequence locks are met)
         success_txs = [tx['tx'] for tx in bip112txs_vary_OP_CSV_v2 if tx['sdf']]
@@ -449,7 +466,5 @@ def run_test(self):
         self.send_blocks([self.create_test_block(time_txs)])
         self.nodes[0].invalidateblock(self.nodes[0].getbestblockhash())
 
-        # TODO: Test empty stack fails
-
 if __name__ == '__main__':
     BIP68_112_113Test().main()