Merge #21053: rpc, test: document {previous,next}blockhash as optional

ba7e17e rpc, test: document {previous,next}blockhash as optional (Sebastian Falbesoner)

Pull request description:

  This PR updates the result help of the following RPCs w.r.t. the `previousblockhash` and `nextblockhash` fields:
  - getblockheader
  - getblock

  Also adds trivial tests on genesis block (should not contain "previousblockhash") and best block (should not contain "nextblockhash").

Top commit has no ACKs.

Tree-SHA512: ef42c5c773fc436e1b4a67be14e2532e800e1e30e45e54a57431c6abb714d2c069c70d40ea4012d549293b823a1973b3f569484b3273679683b28ed40abf46bb

Author: MarcoFalke

src/rpc/blockchain.cpp

@@ -800,8 +800,8 @@ static RPCHelpMan getblockheader()
                             {RPCResult::Type::NUM, "difficulty", "The difficulty"},
                             {RPCResult::Type::STR_HEX, "chainwork", "Expected number of hashes required to produce the current chain"},
                             {RPCResult::Type::NUM, "nTx", "The number of transactions in the block"},
-                            {RPCResult::Type::STR_HEX, "previousblockhash", "The hash of the previous block"},
-                            {RPCResult::Type::STR_HEX, "nextblockhash", "The hash of the next block"},
+                            {RPCResult::Type::STR_HEX, "previousblockhash", /* optional */ true, "The hash of the previous block (if available)"},
+                            {RPCResult::Type::STR_HEX, "nextblockhash", /* optional */ true, "The hash of the next block (if available)"},
                         }},
                     RPCResult{"for verbose=false",
                         RPCResult::Type::STR_HEX, "", "A string that is serialized, hex-encoded data for block 'hash'"},
@@ -908,8 +908,8 @@ static RPCHelpMan getblock()
                     {RPCResult::Type::NUM, "difficulty", "The difficulty"},
                     {RPCResult::Type::STR_HEX, "chainwork", "Expected number of hashes required to produce the chain up to this block (in hex)"},
                     {RPCResult::Type::NUM, "nTx", "The number of transactions in the block"},
-                    {RPCResult::Type::STR_HEX, "previousblockhash", "The hash of the previous block"},
-                    {RPCResult::Type::STR_HEX, "nextblockhash", "The hash of the next block"},
+                    {RPCResult::Type::STR_HEX, "previousblockhash", /* optional */ true, "The hash of the previous block (if available)"},
+                    {RPCResult::Type::STR_HEX, "nextblockhash", /* optional */ true, "The hash of the next block (if available)"},
                 }},
                     RPCResult{"for verbosity = 2",
                 RPCResult::Type::OBJ, "", "",

test/functional/rpc_blockchain.py

@@ -316,6 +316,9 @@ def _test_getblockheader(self):
         header.calc_sha256()
         assert_equal(header.hash, besthash)
 
+        assert 'previousblockhash' not in node.getblockheader(node.getblockhash(0))
+        assert 'nextblockhash' not in node.getblockheader(node.getbestblockhash())
+
     def _test_getdifficulty(self):
         difficulty = self.nodes[0].getdifficulty()
         # 1 hash in 2 should be valid, so difficulty should be 1/2**31
@@ -420,6 +423,9 @@ def move_block_file(old, new):
         # Restore chain state
         move_block_file('rev_wrong', 'rev00000.dat')
 
+        assert 'previousblockhash' not in node.getblock(node.getblockhash(0))
+        assert 'nextblockhash' not in node.getblock(node.getbestblockhash())
+
 
 if __name__ == '__main__':
     BlockchainTest().main()