rpc: fix getblock(header) returns target for tip

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

Because regtest does not have difficulty adjustment, a test is added for mainnet instead.

Author: Sjors

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/mining_mainnet.py

@@ -109,5 +109,17 @@ def run_test(self):
         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()