rpc: Improve gettxoutproof error when only header is available.

src/rpc/txoutproof.cpp

@@ -10,6 +10,7 @@
 #include <merkleblock.h>
 #include <node/blockstorage.h>
 #include <primitives/transaction.h>
+#include <rpc/blockchain.h>
 #include <rpc/server.h>
 #include <rpc/server_util.h>
 #include <rpc/util.h>
@@ -96,6 +97,10 @@ static RPCHelpMan gettxoutproof()
                 }
             }
 
+            {
+                LOCK(cs_main);
+                CheckBlockDataAvailability(chainman.m_blockman, *pblockindex, /*check_for_undo=*/false);
+            }
             CBlock block;
             if (!chainman.m_blockman.ReadBlockFromDisk(block, *pblockindex)) {
                 throw JSONRPCError(RPC_INTERNAL_ERROR, "Can't read block from disk");

test/functional/rpc_txoutproof.py

@@ -67,6 +67,10 @@ class MerkleBlockTest(BitcoinTestFramework):
         assert_equal(self.nodes[0].verifytxoutproof(self.nodes[0].gettxoutproof([txid_spent], blockhash)), [txid_spent])
         # We can't get the proof if we specify a non-existent block
         assert_raises_rpc_error(-5, "Block not found", self.nodes[0].gettxoutproof, [txid_spent], "0000000000000000000000000000000000000000000000000000000000000000")
+        # We can't get the proof if we only have the header of the specified block
+        block = self.generateblock(self.nodes[0], output="raw(55)", transactions=[], submit=False)
+        self.nodes[0].submitheader(block["hex"])
+        assert_raises_rpc_error(-1, "Block not available (not fully downloaded)", self.nodes[0].gettxoutproof, [txid_spent], block['hash'])
         # We can get the proof if the transaction is unspent
         assert_equal(self.nodes[0].verifytxoutproof(self.nodes[0].gettxoutproof([txid_unspent])), [txid_unspent])
         # We can get the proof if we provide a list of transactions and one of them is unspent. The ordering of the list should not matter.