Merge #990: [RPC] Correct getblockstats fee calculation

95c4740 getblockstats: Consider ct_fee as tx fee if available (Zannick)

Pull request description:

  Current implementation always performs a subtraction `ins - outs` to calculate fee, which is only correct for basecoin-to-basecoin, and results in zerocoin spends appearing as the fee. CT/RingCT and Zerocoin Minting/Spending include a ct_fee output that we can use (ZC spends have a ct_fee of 0 but at least that lets us skip the subtraction).

Tree-SHA512: df1c7b2ee500f011280cab73a79de2bcaf9e861a3fe60860be00f5eec7ea7952b285d571338778311598d573191088daff1dc2f9562d227602dee9964dc3edd6

Author: codeofalltrades

src/rpc/blockchain.cpp

@@ -2076,10 +2076,6 @@ static UniValue getblockstats(const JSONRPCRequest& request)
         if (tx->IsCoinStake()) {
             continue;
         }
-        if (tx->vin[0].IsAnonInput()) {
-            // Can't really do much with a ringCT transaction
-            continue;
-        }
 
         inputs += tx->vin.size(); // Don't count coinbase's fake input
         total_out += tx_total_out; // Don't count coinbase reward
@@ -2110,34 +2106,46 @@ static UniValue getblockstats(const JSONRPCRequest& request)
 
         if (loop_inputs) {
 
-            if (!g_txindex) {
-                throw JSONRPCError(RPC_INVALID_PARAMETER, "One or more of the selected stats requires -txindex enabled");
-            }
-            CAmount tx_total_in = 0;
-            for (const CTxIn& in : tx->vin) {
-                if (!in.IsZerocoinSpend()) {
-                    CTransactionRef tx_in;
-                    uint256 hashBlock;
-                    if (!GetTransaction(in.prevout.hash, tx_in, Params().GetConsensus(), hashBlock, false)) {
-                        throw JSONRPCError(RPC_INTERNAL_ERROR, std::string("Unexpected internal error (tx index seems corrupt)"));
+            CAmount txfee;
+            if (tx->vin[0].IsAnonInput()) {
+                if (!tx->GetCTFee(txfee)) {
+                    // Can't really do much with a ringCT transaction with no fee
+                    continue;
+                }
+            } else {
+                if (!g_txindex) {
+                    throw JSONRPCError(RPC_INVALID_PARAMETER, "One or more of the selected stats requires -txindex enabled");
+                }
+                // Total up the utxo_size_inc even if we have a ct_fee
+                CAmount tx_total_in = 0;
+                for (const CTxIn& in : tx->vin) {
+                    if (!in.IsZerocoinSpend()) {
+                        CTransactionRef tx_in;
+                        uint256 hashBlock;
+                        if (!GetTransaction(in.prevout.hash, tx_in, Params().GetConsensus(), hashBlock, false)) {
+                            throw JSONRPCError(RPC_INTERNAL_ERROR, std::string("Unexpected internal error (tx index seems corrupt)"));
+                        }
+
+                        auto prevoutput = tx_in->vpout[in.prevout.n];
+
+                        tx_total_in += prevoutput->GetValue();
+                        CDataStream ss(SER_NETWORK, PROTOCOL_VERSION);
+                        ss << *prevoutput.get();
+                        utxo_size_inc -= ss.size() + PER_UTXO_OVERHEAD;
+                    } else {
+                        tx_total_in += in.GetZerocoinSpent();
+                    }
+                }
+                // Prefer the ct_fee over the difference
+                if (!tx->GetCTFee(txfee)) {
+                    txfee = tx_total_in - tx_total_out;
+                    if (tx_total_in < tx_total_out) {
+                        // RingCT with hidden inputs, can't count it
+                        continue;
                     }
-
-                    auto prevoutput = tx_in->vpout[in.prevout.n];
-
-                    tx_total_in += prevoutput->GetValue();
-                    CDataStream ss(SER_NETWORK, PROTOCOL_VERSION);
-                    ss << *prevoutput.get();
-                    utxo_size_inc -= ss.size() + PER_UTXO_OVERHEAD;
-                } else {
-                    tx_total_in += in.GetZerocoinSpent();
                 }
             }
 
-            CAmount txfee = tx_total_in - tx_total_out;
-            if (tx_total_in < tx_total_out) {
-                // RingCT with hidden inputs, can't count it
-                continue;
-            }
             assert(MoneyRange(txfee));
             if (do_medianfee) {
                 fee_array.push_back(txfee);