wallet: return CreatedTransactionResult from FundTransaction

Instead of using the output parameters, return CreatedTransactionResult
from FundTransaction in the same way that CreateTransaction does.
Additionally, instead of modifying the original CMutableTransaction, the
result from CreateTransactionInternal is used.

Author: achow101

src/wallet/rpc/spend.cpp

@@ -489,13 +489,13 @@ static std::vector<RPCArg> FundTxDoc(bool solving_data = true)
     return args;
 }
 
-void FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& fee_out, int& change_position, const UniValue& options, CCoinControl& coinControl, bool override_min_fee)
+CreatedTransactionResult FundTransaction(CWallet& wallet, const CMutableTransaction& tx, const UniValue& options, CCoinControl& coinControl, bool override_min_fee)
 {
     // Make sure the results are valid at least up to the most recent block
     // the user could have gotten from another RPC command prior to now
     wallet.BlockUntilSyncedToCurrentChain();
 
-    change_position = -1;
+    std::optional<unsigned int> change_position;
     bool lockUnspents = false;
     UniValue subtractFeeFromOutputs;
     std::set<int> setSubtractFeeFromOutputs;
@@ -553,7 +553,11 @@ void FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& fee_out,
         }
 
         if (options.exists("changePosition") || options.exists("change_position")) {
-            change_position = (options.exists("change_position") ? options["change_position"] : options["changePosition"]).getInt<int>();
+            int pos = (options.exists("change_position") ? options["change_position"] : options["changePosition"]).getInt<int>();
+            if (pos < 0 || (unsigned int)pos > tx.vout.size()) {
+                throw JSONRPCError(RPC_INVALID_PARAMETER, "changePosition out of bounds");
+            }
+            change_position = (unsigned int)pos;
         }
 
         if (options.exists("change_type")) {
@@ -703,9 +707,6 @@ void FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& fee_out,
     if (tx.vout.size() == 0)
         throw JSONRPCError(RPC_INVALID_PARAMETER, "TX must have at least one output");
 
-    if (change_position != -1 && (change_position < 0 || (unsigned int)change_position > tx.vout.size()))
-        throw JSONRPCError(RPC_INVALID_PARAMETER, "changePosition out of bounds");
-
     for (unsigned int idx = 0; idx < subtractFeeFromOutputs.size(); idx++) {
         int pos = subtractFeeFromOutputs[idx].getInt<int>();
         if (setSubtractFeeFromOutputs.count(pos))
@@ -717,11 +718,11 @@ void FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& fee_out,
         setSubtractFeeFromOutputs.insert(pos);
     }
 
-    bilingual_str error;
-
-    if (!FundTransaction(wallet, tx, fee_out, change_position, error, lockUnspents, setSubtractFeeFromOutputs, coinControl)) {
-        throw JSONRPCError(RPC_WALLET_ERROR, error.original);
+    auto txr = FundTransaction(wallet, tx, change_position, lockUnspents, setSubtractFeeFromOutputs, coinControl);
+    if (!txr) {
+        throw JSONRPCError(RPC_WALLET_ERROR, ErrorString(txr).original);
     }
+    return *txr;
 }
 
 static void SetOptionsInputWeights(const UniValue& inputs, UniValue& options)
@@ -844,17 +845,15 @@ RPCHelpMan fundrawtransaction()
         throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "TX decode failed");
     }
 
-    CAmount fee;
-    int change_position;
     CCoinControl coin_control;
     // Automatically select (additional) coins. Can be overridden by options.add_inputs.
     coin_control.m_allow_other_inputs = true;
-    FundTransaction(*pwallet, tx, fee, change_position, request.params[1], coin_control, /*override_min_fee=*/true);
+    auto txr = FundTransaction(*pwallet, tx, request.params[1], coin_control, /*override_min_fee=*/true);
 
     UniValue result(UniValue::VOBJ);
-    result.pushKV("hex", EncodeHexTx(CTransaction(tx)));
-    result.pushKV("fee", ValueFromAmount(fee));
-    result.pushKV("changepos", change_position);
+    result.pushKV("hex", EncodeHexTx(*txr.tx));
+    result.pushKV("fee", ValueFromAmount(txr.fee));
+    result.pushKV("changepos", txr.change_pos ? (int)*txr.change_pos : -1);
 
     return result;
 },
@@ -1272,18 +1271,16 @@ RPCHelpMan send()
             PreventOutdatedOptions(options);
 
 
-            CAmount fee;
-            int change_position;
             bool rbf{options.exists("replaceable") ? options["replaceable"].get_bool() : pwallet->m_signal_rbf};
             CMutableTransaction rawTx = ConstructTransaction(options["inputs"], request.params[0], options["locktime"], rbf);
             CCoinControl coin_control;
             // Automatically select coins, unless at least one is manually selected. Can
             // be overridden by options.add_inputs.
             coin_control.m_allow_other_inputs = rawTx.vin.size() == 0;
             SetOptionsInputWeights(options["inputs"], options);
-            FundTransaction(*pwallet, rawTx, fee, change_position, options, coin_control, /*override_min_fee=*/false);
+            auto txr = FundTransaction(*pwallet, rawTx, options, coin_control, /*override_min_fee=*/false);
 
-            return FinishTransaction(pwallet, options, rawTx);
+            return FinishTransaction(pwallet, options, CMutableTransaction(*txr.tx));
         }
     };
 }
@@ -1699,8 +1696,6 @@ RPCHelpMan walletcreatefundedpsbt()
 
     UniValue options{request.params[3].isNull() ? UniValue::VOBJ : request.params[3]};
 
-    CAmount fee;
-    int change_position;
     const UniValue &replaceable_arg = options["replaceable"];
     const bool rbf{replaceable_arg.isNull() ? wallet.m_signal_rbf : replaceable_arg.get_bool()};
     CMutableTransaction rawTx = ConstructTransaction(request.params[0], request.params[1], request.params[2], rbf);
@@ -1709,10 +1704,10 @@ RPCHelpMan walletcreatefundedpsbt()
     // be overridden by options.add_inputs.
     coin_control.m_allow_other_inputs = rawTx.vin.size() == 0;
     SetOptionsInputWeights(request.params[0], options);
-    FundTransaction(wallet, rawTx, fee, change_position, options, coin_control, /*override_min_fee=*/true);
+    auto txr = FundTransaction(wallet, rawTx, options, coin_control, /*override_min_fee=*/true);
 
     // Make a blank psbt
-    PartiallySignedTransaction psbtx(rawTx);
+    PartiallySignedTransaction psbtx(CMutableTransaction(*txr.tx));
 
     // Fill transaction with out data but don't sign
     bool bip32derivs = request.params[4].isNull() ? true : request.params[4].get_bool();
@@ -1728,8 +1723,8 @@ RPCHelpMan walletcreatefundedpsbt()
 
     UniValue result(UniValue::VOBJ);
     result.pushKV("psbt", EncodeBase64(ssTx.str()));
-    result.pushKV("fee", ValueFromAmount(fee));
-    result.pushKV("changepos", change_position);
+    result.pushKV("fee", ValueFromAmount(txr.fee));
+    result.pushKV("changepos", txr.change_pos ? (int)*txr.change_pos : -1);
     return result;
 },
     };

src/wallet/spend.cpp

@@ -1314,7 +1314,7 @@ util::Result<CreatedTransactionResult> CreateTransaction(
     return res;
 }
 
-bool FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& nFeeRet, int& nChangePosInOut, bilingual_str& error, bool lockUnspents, const std::set<int>& setSubtractFeeFromOutputs, CCoinControl coinControl)
+util::Result<CreatedTransactionResult> FundTransaction(CWallet& wallet, const CMutableTransaction& tx, std::optional<unsigned int> change_pos, bool lockUnspents, const std::set<int>& setSubtractFeeFromOutputs, CCoinControl coinControl)
 {
     std::vector<CRecipient> vecSend;
 
@@ -1348,8 +1348,7 @@ bool FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& nFeeRet,
         PreselectedInput& preset_txin = coinControl.Select(outPoint);
         if (!wallet.IsMine(outPoint)) {
             if (coins[outPoint].out.IsNull()) {
-                error = _("Unable to find UTXO for external input");
-                return false;
+                return util::Error{_("Unable to find UTXO for external input")};
             }
 
             // The input was not in the wallet, but is in the UTXO set, so select as external
@@ -1360,38 +1359,17 @@ bool FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& nFeeRet,
         preset_txin.SetScriptWitness(txin.scriptWitness);
     }
 
-    auto res = CreateTransaction(wallet, vecSend, nChangePosInOut == -1 ? std::nullopt : std::optional<unsigned int>((unsigned int)nChangePosInOut), coinControl, false);
+    auto res = CreateTransaction(wallet, vecSend, change_pos, coinControl, false);
     if (!res) {
-        error = util::ErrorString(res);
-        return false;
-    }
-    const auto& txr = *res;
-    CTransactionRef tx_new = txr.tx;
-    nFeeRet = txr.fee;
-    nChangePosInOut = txr.change_pos ? *txr.change_pos : -1;
-
-    if (nChangePosInOut != -1) {
-        tx.vout.insert(tx.vout.begin() + nChangePosInOut, tx_new->vout[nChangePosInOut]);
-    }
-
-    // Copy output sizes from new transaction; they may have had the fee
-    // subtracted from them.
-    for (unsigned int idx = 0; idx < tx.vout.size(); idx++) {
-        tx.vout[idx].nValue = tx_new->vout[idx].nValue;
+        return res;
     }
 
-    // Add new txins while keeping original txin scriptSig/order.
-    for (const CTxIn& txin : tx_new->vin) {
-        if (!coinControl.IsSelected(txin.prevout)) {
-            tx.vin.push_back(txin);
-
-        }
-        if (lockUnspents) {
+    if (lockUnspents) {
+        for (const CTxIn& txin : res->tx->vin) {
             wallet.LockCoin(txin.prevout);
         }
-
     }
 
-    return true;
+    return res;
 }
 } // namespace wallet

src/wallet/spend.h

@@ -222,7 +222,7 @@ util::Result<CreatedTransactionResult> CreateTransaction(CWallet& wallet, const
  * Insert additional inputs into the transaction by
  * calling CreateTransaction();
  */
-bool FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& nFeeRet, int& nChangePosInOut, bilingual_str& error, bool lockUnspents, const std::set<int>& setSubtractFeeFromOutputs, CCoinControl);
+util::Result<CreatedTransactionResult> FundTransaction(CWallet& wallet, const CMutableTransaction& tx, std::optional<unsigned int> change_pos, bool lockUnspents, const std::set<int>& setSubtractFeeFromOutputs, CCoinControl);
 } // namespace wallet
 
 #endif // BITCOIN_WALLET_SPEND_H