test: refactor IPC mining test to use script_BIP34_coinbase_height

Needed in a later commit to correctly derive the BIP34 prefix
for heights <= 16.

Add a padding parameter to script_BIP34_coinbase_height() that
controls whether the OP_0 dummy extranonce is appended for
heights <= 16.

Use this helper with padding=False in the IPC mining test's
build_coinbase_test().

test/functional/interface_ipc_mining.py

@@ -7,7 +7,7 @@ import asyncio
 import time
 from contextlib import AsyncExitStack
 from io import BytesIO
-from test_framework.blocktools import NULL_OUTPOINT
+from test_framework.blocktools import NULL_OUTPOINT, script_BIP34_coinbase_height
 from test_framework.messages import (
     MAX_BLOCK_WEIGHT,
     CBlockHeader,
@@ -20,10 +20,6 @@ from test_framework.messages import (
     from_hex,
     msg_headers,
 )
-from test_framework.script import (
-    CScript,
-    CScriptNum,
-)
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
     assert_equal,
@@ -79,8 +75,8 @@ class IPCMiningTest(BitcoinTestFramework):
 
         # Verify there's no dummy extraNonce in the coinbase scriptSig
         current_block_height = self.nodes[0].getchaintips()[0]["height"]
-        expected_scriptsig = CScript([CScriptNum(current_block_height + 1)])
-        assert_equal(coinbase_res.scriptSigPrefix.hex(), expected_scriptsig.hex())
+        bip34_prefix = script_BIP34_coinbase_height(current_block_height + 1, padding=False)
+        assert_equal(coinbase_res.scriptSigPrefix, bip34_prefix)
 
         # Typically a mining pool appends its name and an extraNonce
         coinbase_tx.vin[0].scriptSig = coinbase_res.scriptSigPrefix

test/functional/test_framework/blocktools.py

@@ -161,11 +161,13 @@ def add_witness_commitment(block, nonce=0):
     block.hashMerkleRoot = block.calc_merkle_root()
 
 
-def script_BIP34_coinbase_height(height):
+def script_BIP34_coinbase_height(height, *, padding=True):
     if height <= 16:
         res = CScriptOp.encode_op_n(height)
-        # Append dummy extraNonce to increase scriptSig size to 2 (see bad-cb-length consensus rule)
-        return CScript([res, OP_0])
+        if padding:
+            # Append dummy extraNonce to increase scriptSig size to 2 (see bad-cb-length consensus rule)
+            return CScript([res, OP_0])
+        return CScript([res])
     return CScript([CScriptNum(height)])