Merge bitcoin/bitcoin#33446: rpc: fix getblock(header) returns target for tip

bf7996cbc3 rpc: fix getblock(header) returns target for tip (Sjors Provoost)
4c3c1f42cf test: add block 2016 to mock mainnet (Sjors Provoost)

Pull request description:

  A `target` field was added to the `getblock` and `getblockheader` RPC calls in #31583, but it mistakingly always used the tip value.

  This PR fixes it to return the target for the given block. Because regtest does not have difficulty adjustment, the mainnet test is expanded to cover the fix.

  A preliminary commit deals with mining block 2016 that's needed for the test. It also:
  - renames the `create_coinbase` `retarget_period` argument to `halving_period`. Before #31583 this was hardcoded for regtest where these values are the same.
  - drops unused `fees` argument from `mine` helper
  - expands the CPU miner instructions for generating the alternative mainnet chain

  Fixes #33440

ACKs for top commit:
  sipa:
    utACK bf7996cbc3
  luke-jr:
    crACK bf7996cbc3
  TheCharlatan:
    ACK bf7996cbc3
  ismaelsadeeq:
    Code review ACK bf7996cbc3

Tree-SHA512: 2a2e11efd91f4aaccf9d2ec4dff9fd82c366b8a7e797ce5981dca2e6f08028f69154f4e6a27aef20d78b0e6c3304416789267c2fad42d7aa5072f8537d0c8b0d

src/rpc/blockchain.cpp

@@ -166,7 +166,7 @@ UniValue blockheaderToJSON(const CBlockIndex& tip, const CBlockIndex& blockindex
     result.pushKV("mediantime", blockindex.GetMedianTimePast());
     result.pushKV("nonce", blockindex.nNonce);
     result.pushKV("bits", strprintf("%08x", blockindex.nBits));
-    result.pushKV("target", GetTarget(tip, pow_limit).GetHex());
+    result.pushKV("target", GetTarget(blockindex, pow_limit).GetHex());
     result.pushKV("difficulty", GetDifficulty(blockindex));
     result.pushKV("chainwork", blockindex.nChainWork.GetHex());
     result.pushKV("nTx", blockindex.nTx);

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
@@ -82,10 +82,13 @@ 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)
+            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)
 
@@ -102,5 +105,21 @@ 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)
+
+        mining_info = node.getmininginfo()
+        assert_equal(mining_info['difficulty'], 4)
+
+        self.log.info("getblock RPC should show historical target")
+        block_info = node.getblock(node.getblockhash(1))
+
+        assert_equal(block_info['difficulty'], 1)
+        assert_equal(block_info['bits'], nbits_str(DIFF_1_N_BITS))
+        assert_equal(block_info['target'], target_str(DIFF_1_TARGET))
+
+
 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: