gettxoutproof() should return consistent result

We can call gettxoutproof() with a list of transactions. Currently, if
the first transaction is unspent (and all other transactions are in the
same block), then the call will succeed. If the first transaction has
been spent, then the call will fail. The means that the following two
calls will return different results:

gettxoutproof(unspent_tx1, spent_tx1)
gettxoutproof(spent_tx1, unspent_tx1)

This commit makes behaviour independent of transaction ordering by looping
through all transactions provided and trying to find which block they're in.

This commit also increases the test coverage and tests more failure
cases for gettxoutproof()

src/rpc/rawtransaction.cpp

@@ -219,9 +219,13 @@ UniValue gettxoutproof(const JSONRPCRequest& request)
             throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found");
         pblockindex = mapBlockIndex[hashBlock];
     } else {
-        const Coin& coin = AccessByTxid(*pcoinsTip, oneTxid);
-        if (!coin.IsSpent() && coin.nHeight > 0 && coin.nHeight <= chainActive.Height()) {
-            pblockindex = chainActive[coin.nHeight];
+        // Loop through txids and try to find which block they're in. Exit loop once a block is found.
+        for (const auto& tx : setTxids) {
+            const Coin& coin = AccessByTxid(*pcoinsTip, tx);
+            if (!coin.IsSpent()) {
+                pblockindex = chainActive[coin.nHeight];
+                break;
+            }
         }
     }
 
@@ -244,7 +248,7 @@ UniValue gettxoutproof(const JSONRPCRequest& request)
         if (setTxids.count(tx->GetHash()))
             ntxFound++;
     if (ntxFound != setTxids.size())
-        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "(Not all) transactions not found in specified block");
+        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Not all transactions found in specified or retrieved block");
 
     CDataStream ssMB(SER_NETWORK, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS);
     CMerkleBlock mb(block, setTxids);

test/functional/merkle_blocks.py

@@ -39,7 +39,8 @@ class MerkleBlockTest(BitcoinTestFramework):
         txid1 = self.nodes[0].sendrawtransaction(self.nodes[0].signrawtransaction(tx1)["hex"])
         tx2 = self.nodes[0].createrawtransaction([node0utxos.pop()], {self.nodes[1].getnewaddress(): 49.99})
         txid2 = self.nodes[0].sendrawtransaction(self.nodes[0].signrawtransaction(tx2)["hex"])
-        assert_raises(JSONRPCException, self.nodes[0].gettxoutproof, [txid1])
+        # This will raise an exception because the transaction is not yet in a block
+        assert_raises_jsonrpc(-5, "Transaction not yet in block", self.nodes[0].gettxoutproof, [txid1])
 
         self.nodes[0].generate(1)
         blockhash = self.nodes[0].getblockhash(chain_height + 1)
@@ -56,7 +57,7 @@ class MerkleBlockTest(BitcoinTestFramework):
 
         txin_spent = self.nodes[1].listunspent(1).pop()
         tx3 = self.nodes[1].createrawtransaction([txin_spent], {self.nodes[0].getnewaddress(): 49.98})
-        self.nodes[0].sendrawtransaction(self.nodes[1].signrawtransaction(tx3)["hex"])
+        txid3 = self.nodes[0].sendrawtransaction(self.nodes[1].signrawtransaction(tx3)["hex"])
         self.nodes[0].generate(1)
         self.sync_all()
 
@@ -64,17 +65,21 @@ class MerkleBlockTest(BitcoinTestFramework):
         txid_unspent = txid1 if txin_spent["txid"] != txid1 else txid2
 
         # We can't find the block from a fully-spent tx
-        assert_raises(JSONRPCException, self.nodes[2].gettxoutproof, [txid_spent])
-        # ...but we can if we specify the block
+        assert_raises_jsonrpc(-5, "Transaction not yet in block", self.nodes[2].gettxoutproof, [txid_spent])
+        # We can get the proof if we specify the block
         assert_equal(self.nodes[2].verifytxoutproof(self.nodes[2].gettxoutproof([txid_spent], blockhash)), [txid_spent])
-        # ...or if the first tx is not fully-spent
+        # We can't get the proof if we specify a non-existent block
+        assert_raises_jsonrpc(-5, "Block not found", self.nodes[2].gettxoutproof, [txid_spent], "00000000000000000000000000000000")
+        # We can get the proof if the transaction is unspent
         assert_equal(self.nodes[2].verifytxoutproof(self.nodes[2].gettxoutproof([txid_unspent])), [txid_unspent])
-        try:
-            assert_equal(self.nodes[2].verifytxoutproof(self.nodes[2].gettxoutproof([txid1, txid2])), txlist)
-        except JSONRPCException:
-            assert_equal(self.nodes[2].verifytxoutproof(self.nodes[2].gettxoutproof([txid2, txid1])), txlist)
-        # ...or if we have a -txindex
+        # 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.
+        assert_equal(sorted(self.nodes[2].verifytxoutproof(self.nodes[2].gettxoutproof([txid1, txid2]))), sorted(txlist))
+        assert_equal(sorted(self.nodes[2].verifytxoutproof(self.nodes[2].gettxoutproof([txid2, txid1]))), sorted(txlist))
+        # We can always get a proof if we have a -txindex
         assert_equal(self.nodes[2].verifytxoutproof(self.nodes[3].gettxoutproof([txid_spent])), [txid_spent])
+        # We can't get a proof if we specify transactions from different blocks
+        assert_raises_jsonrpc(-5, "Not all transactions found in specified or retrieved block", self.nodes[2].gettxoutproof, [txid1, txid3])
+
 
 if __name__ == '__main__':
     MerkleBlockTest().main()