test: add functional test for non-standard txs with too large scriptSig

A transaction is rejected by the mempool with reason "scriptsig-size" if any of
the inputs' scriptSig is larger than 1650 bytes.

Author: theStack

test/functional/mempool_accept.py

@@ -267,6 +267,12 @@ def run_test(self):
             rawtxs=[tx.serialize().hex()],
         )
         tx.deserialize(BytesIO(hex_str_to_bytes(raw_tx_reference)))
+        tx.vin[0].scriptSig = CScript([b'a' * 1648]) # Some too large scriptSig (>1650 bytes)
+        self.check_mempool_result(
+            result_expected=[{'txid': tx.rehash(), 'allowed': False, 'reject-reason': 'scriptsig-size'}],
+            rawtxs=[tx.serialize().hex()],
+        )
+        tx.deserialize(BytesIO(hex_str_to_bytes(raw_tx_reference)))
         output_p2sh_burn = CTxOut(nValue=540, scriptPubKey=CScript([OP_HASH160, hash160(b'burn'), OP_EQUAL]))
         num_scripts = 100000 // len(output_p2sh_burn.serialize())  # Use enough outputs to make the tx too large for our policy
         tx.vout = [output_p2sh_burn] * num_scripts