test: add block 2016 to mock mainnet

The next commit requires an additional mainnet block which changes the difficulty.

Also fix a few minor mistakes in the test (suite):
- rename the create_coinbase retarger_period argument to halving_period. Before bitcoin#31583 this was hardcoded for regtest where these values are the same.
- drop unused fees argument from mine helper

Finally the CPU miner instructions for generating the alternative mainnet chain are expanded.

test/functional/data/README.md

@@ -11,9 +11,10 @@ The alternate mainnet chain was generated as follows:
 - restart node with a faketime 2 minutes later
 
 ```sh
-for i in {1..2015}
+for i in {1..2016}
 do
- faketime "`date -d @"$(( 1231006505 + $i * 120 ))"  +'%Y-%m-%d %H:%M:%S'`" \
+ t=$(( 1231006505 + $i * 120 ))
+ faketime "`date -d @$t  +'%Y-%m-%d %H:%M:%S'`" \
  bitcoind -connect=0 -nocheckpoints -stopatheight=$i
 done
 ```
@@ -21,7 +22,9 @@ done
 The CPU miner is kept running as follows:
 
 ```sh
-./minerd --coinbase-addr 1NQpH6Nf8QtR2HphLRcvuVqfhXBXsiWn8r --no-stratum --algo sha256d --no-longpoll --scantime 3 --retry-pause 1
+./minerd -u ... -p ... -o http://127.0.0.1:8332 --no-stratum \
+        --coinbase-addr 1NQpH6Nf8QtR2HphLRcvuVqfhXBXsiWn8r \
+        --algo sha256d --no-longpoll --scantime 3 --retry-pause 1
 ```
 
 The payout address is derived from first BIP32 test vector master key:
@@ -40,3 +43,8 @@ The timestamp was not kept constant because at difficulty 1 it's not sufficient
 to only grind the nonce. Grinding the extra_nonce or version field instead
 would have required additional (stratum) software. It would also make it more
 complicated to reconstruct the blocks in this test.
+
+The `getblocktemplate` RPC code needs to be patched to ignore not being connected
+to any peers, and to ignore the IBD status check.
+
+On macOS use `faketime "@$t"` instead.

test/functional/data/mainnet_alt.json

@@ -2014,7 +2014,8 @@
       1231247971,
       1231248071,
       1231248198,
-      1231248322
+      1231248322,
+      1231248621
     ],
     "nonces": [
       2345621585,
@@ -4031,6 +4032,7 @@
       3658502865,
       2519048297,
       1915965760,
-      1183846025
+      1183846025,
+      2713372123
     ]
 }

test/functional/mining_mainnet.py

@@ -53,15 +53,15 @@ class MiningMainnetTest(BitcoinTestFramework):
             help='Block data file (default: %(default)s)',
         )
 
-    def mine(self, height, prev_hash, blocks, node, fees=0):
+    def mine(self, height, prev_hash, blocks, node):
         self.log.debug(f"height={height}")
         block = CBlock()
         block.nVersion = 0x20000000
         block.hashPrevBlock = int(prev_hash, 16)
         block.nTime = blocks['timestamps'][height - 1]
-        block.nBits = DIFF_1_N_BITS
+        block.nBits = DIFF_1_N_BITS if height < 2016 else DIFF_4_N_BITS
         block.nNonce = blocks['nonces'][height - 1]
-        block.vtx = [create_coinbase(height=height, script_pubkey=bytes.fromhex(COINBASE_SCRIPT_PUBKEY), retarget_period=2016)]
+        block.vtx = [create_coinbase(height=height, script_pubkey=bytes.fromhex(COINBASE_SCRIPT_PUBKEY), halving_period=210000)]
         # The alternate mainnet chain was mined with non-timelocked coinbase txs.
         block.vtx[0].nLockTime = 0
         block.vtx[0].vin[0].nSequence = SEQUENCE_FINAL
@@ -82,12 +82,15 @@ class MiningMainnetTest(BitcoinTestFramework):
         self.log.info("Load alternative mainnet blocks")
         path = os.path.join(os.path.dirname(os.path.realpath(__file__)), self.options.datafile)
         prev_hash = node.getbestblockhash()
+        blocks = None
         with open(path, encoding='utf-8') as f:
             blocks = json.load(f)
             n_blocks = len(blocks['timestamps'])
-            assert_equal(n_blocks, 2015)
-            for i in range(2015):
-                prev_hash = self.mine(i + 1, prev_hash, blocks, node)
+            assert_equal(n_blocks, 2016)
+
+        # Mine up to the last block of the first retarget period
+        for i in range(2015):
+            prev_hash = self.mine(i + 1, prev_hash, blocks, node)
 
         assert_equal(node.getblockcount(), 2015)
 
@@ -102,5 +105,9 @@ class MiningMainnetTest(BitcoinTestFramework):
         assert_equal(mining_info['next']['bits'], nbits_str(DIFF_4_N_BITS))
         assert_equal(mining_info['next']['target'], target_str(DIFF_4_TARGET))
 
+        # Mine first block of the second retarget period
+        height = 2016
+        prev_hash = self.mine(height, prev_hash, blocks, node)
+        assert_equal(node.getblockcount(), height)
 if __name__ == '__main__':
     MiningMainnetTest(__file__).main()

test/functional/test_framework/blocktools.py

@@ -144,7 +144,7 @@ def script_BIP34_coinbase_height(height):
     return CScript([CScriptNum(height)])
 
 
-def create_coinbase(height, pubkey=None, *, script_pubkey=None, extra_output_script=None, fees=0, nValue=50, retarget_period=REGTEST_RETARGET_PERIOD):
+def create_coinbase(height, pubkey=None, *, script_pubkey=None, extra_output_script=None, fees=0, nValue=50, halving_period=REGTEST_RETARGET_PERIOD):
     """Create a coinbase transaction.
 
     If pubkey is passed in, the coinbase output will be a P2PK output;
@@ -158,7 +158,7 @@ def create_coinbase(height, pubkey=None, *, script_pubkey=None, extra_output_scr
     coinbaseoutput = CTxOut()
     coinbaseoutput.nValue = nValue * COIN
     if nValue == 50:
-        halvings = int(height / retarget_period)
+        halvings = int(height / halving_period)
         coinbaseoutput.nValue >>= halvings
         coinbaseoutput.nValue += fees
     if pubkey is not None: