wallet: CreateTransaction(): return out-params as (optional) struct

src/wallet/feebumper.cpp

@@ -218,21 +218,20 @@ Result CreateRateBumpTransaction(CWallet& wallet, const uint256& txid, const CCo
     // We cannot source new unconfirmed inputs(bip125 rule 2)
     new_coin_control.m_min_depth = 1;
 
-    CTransactionRef tx_new;
+    constexpr int RANDOM_CHANGE_POSITION = -1;
-    CAmount fee_ret;
-    int change_pos_in_out = -1; // No requested location for change
     bilingual_str fail_reason;
     FeeCalculation fee_calc_out;
-    if (!CreateTransaction(wallet, recipients, tx_new, fee_ret, change_pos_in_out, fail_reason, new_coin_control, fee_calc_out, false)) {
+    std::optional<CreatedTransactionResult> txr = CreateTransaction(wallet, recipients, RANDOM_CHANGE_POSITION, fail_reason, new_coin_control, fee_calc_out, false);
+    if (!txr) {
         errors.push_back(Untranslated("Unable to create transaction.") + Untranslated(" ") + fail_reason);
         return Result::WALLET_ERROR;
     }
 
     // Write back new fee if successful
-    new_fee = fee_ret;
+    new_fee = txr->fee;
 
     // Write back transaction
-    mtx = CMutableTransaction(*tx_new);
+    mtx = CMutableTransaction(*txr->tx);
 
     return Result::OK;
 }

src/wallet/interfaces.cpp

@@ -257,13 +257,14 @@ public:
         bilingual_str& fail_reason) override
     {
         LOCK(m_wallet->cs_wallet);
-        CTransactionRef tx;
         FeeCalculation fee_calc_out;
-        if (!CreateTransaction(*m_wallet, recipients, tx, fee, change_pos,
+        std::optional<CreatedTransactionResult> txr = CreateTransaction(*m_wallet, recipients, change_pos,
-                fail_reason, coin_control, fee_calc_out, sign)) {
+                fail_reason, coin_control, fee_calc_out, sign);
-            return {};
+        if (!txr) return {};
-        }
+        fee = txr->fee;
-        return tx;
+        change_pos = txr->change_pos;
+
+        return txr->tx;
     }
     void commitTransaction(CTransactionRef tx,
         WalletValueMap value_map,

src/wallet/rpc/spend.cpp

@@ -155,15 +155,14 @@ UniValue SendMoney(CWallet& wallet, const CCoinControl &coin_control, std::vecto
     std::shuffle(recipients.begin(), recipients.end(), FastRandomContext());
 
     // Send
-    CAmount nFeeRequired = 0;
+    constexpr int RANDOM_CHANGE_POSITION = -1;
-    int nChangePosRet = -1;
     bilingual_str error;
-    CTransactionRef tx;
     FeeCalculation fee_calc_out;
-    const bool fCreated = CreateTransaction(wallet, recipients, tx, nFeeRequired, nChangePosRet, error, coin_control, fee_calc_out, true);
+    std::optional<CreatedTransactionResult> txr = CreateTransaction(wallet, recipients, RANDOM_CHANGE_POSITION, error, coin_control, fee_calc_out, true);
-    if (!fCreated) {
+    if (!txr) {
         throw JSONRPCError(RPC_WALLET_INSUFFICIENT_FUNDS, error.original);
     }
+    CTransactionRef tx = txr->tx;
     wallet.CommitTransaction(tx, std::move(map_value), {} /* orderForm */);
     if (verbose) {
         UniValue entry(UniValue::VOBJ);

src/wallet/spend.cpp

@@ -961,14 +961,10 @@ static std::optional<CreatedTransactionResult> CreateTransactionInternal(
     return CreatedTransactionResult(tx, nFeeRet, nChangePosInOut);
 }
 
-// TODO: also return std::optional<CreatedTransactionResult> here in order
+std::optional<CreatedTransactionResult> CreateTransaction(
-//       to eliminate the out parameters and to simplify the function
-bool CreateTransaction(
         CWallet& wallet,
         const std::vector<CRecipient>& vecSend,
-        CTransactionRef& tx,
+        int change_pos,
-        CAmount& nFeeRet,
-        int& nChangePosInOut,
         bilingual_str& error,
         const CCoinControl& coin_control,
         FeeCalculation& fee_calc_out,
@@ -976,54 +972,37 @@ bool CreateTransaction(
 {
     if (vecSend.empty()) {
         error = _("Transaction must have at least one recipient");
-        return false;
+        return std::nullopt;
     }
 
     if (std::any_of(vecSend.cbegin(), vecSend.cend(), [](const auto& recipient){ return recipient.nAmount < 0; })) {
         error = _("Transaction amounts must not be negative");
-        return false;
+        return std::nullopt;
     }
 
     LOCK(wallet.cs_wallet);
 
-    int nChangePosIn = nChangePosInOut;
+    std::optional<CreatedTransactionResult> txr_ungrouped = CreateTransactionInternal(wallet, vecSend, change_pos, error, coin_control, fee_calc_out, sign);
-    Assert(!tx); // tx is an out-param. TODO change the return type from bool to tx (or nullptr)
+    TRACE4(coin_selection, normal_create_tx_internal, wallet.GetName().c_str(), txr_ungrouped.has_value(),
-    std::optional<CreatedTransactionResult> txr_ungrouped = CreateTransactionInternal(wallet, vecSend, nChangePosInOut, error, coin_control, fee_calc_out, sign);
+           txr_ungrouped.has_value() ? txr_ungrouped->fee : 0, txr_ungrouped.has_value() ? txr_ungrouped->change_pos : 0);
-    bool res = false;
+    if (!txr_ungrouped) return std::nullopt;
-    if (txr_ungrouped) {
-        tx = txr_ungrouped->tx;
-        nFeeRet = txr_ungrouped->fee;
-        nChangePosInOut = txr_ungrouped->change_pos;
-        res = true;
-    }
-    TRACE4(coin_selection, normal_create_tx_internal, wallet.GetName().c_str(), res, nFeeRet, nChangePosInOut);
     // try with avoidpartialspends unless it's enabled already
-    if (res && nFeeRet > 0 /* 0 means non-functional fee rate estimation */ && wallet.m_max_aps_fee > -1 && !coin_control.m_avoid_partial_spends) {
+    if (txr_ungrouped->fee > 0 /* 0 means non-functional fee rate estimation */ && wallet.m_max_aps_fee > -1 && !coin_control.m_avoid_partial_spends) {
         TRACE1(coin_selection, attempting_aps_create_tx, wallet.GetName().c_str());
         CCoinControl tmp_cc = coin_control;
         tmp_cc.m_avoid_partial_spends = true;
-        CAmount nFeeRet2;
-        CTransactionRef tx2;
-        int nChangePosInOut2 = nChangePosIn;
         bilingual_str error2; // fired and forgotten; if an error occurs, we discard the results
-        std::optional<CreatedTransactionResult> txr_grouped = CreateTransactionInternal(wallet, vecSend, nChangePosInOut2, error2, tmp_cc, fee_calc_out, sign);
+        std::optional<CreatedTransactionResult> txr_grouped = CreateTransactionInternal(wallet, vecSend, change_pos, error2, tmp_cc, fee_calc_out, sign);
         if (txr_grouped) {
-            tx2 = txr_grouped->tx;
-            nFeeRet2 = txr_grouped->fee;
-            nChangePosInOut2 = txr_grouped->change_pos;
-
             // if fee of this alternative one is within the range of the max fee, we use this one
-            const bool use_aps = nFeeRet2 <= nFeeRet + wallet.m_max_aps_fee;
+            const bool use_aps = txr_grouped->fee <= txr_ungrouped->fee + wallet.m_max_aps_fee;
-            wallet.WalletLogPrintf("Fee non-grouped = %lld, grouped = %lld, using %s\n", nFeeRet, nFeeRet2, use_aps ? "grouped" : "non-grouped");
+            wallet.WalletLogPrintf("Fee non-grouped = %lld, grouped = %lld, using %s\n",
-            TRACE5(coin_selection, aps_create_tx_internal, wallet.GetName().c_str(), use_aps, res, nFeeRet2, nChangePosInOut2);
+                txr_ungrouped->fee, txr_grouped->fee, use_aps ? "grouped" : "non-grouped");
-            if (use_aps) {
+            TRACE5(coin_selection, aps_create_tx_internal, wallet.GetName().c_str(), use_aps, true, txr_grouped->fee, txr_grouped->change_pos);
-                tx = tx2;
+            if (use_aps) return txr_grouped;
-                nFeeRet = nFeeRet2;
-                nChangePosInOut = nChangePosInOut2;
-            }
         }
     }
-    return res;
+    return txr_ungrouped;
 }
 
 bool FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& nFeeRet, int& nChangePosInOut, bilingual_str& error, bool lockUnspents, const std::set<int>& setSubtractFeeFromOutputs, CCoinControl coinControl)
@@ -1047,11 +1026,12 @@ bool FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& nFeeRet,
     // CreateTransaction call and LockCoin calls (when lockUnspents is true).
     LOCK(wallet.cs_wallet);
 
-    CTransactionRef tx_new;
     FeeCalculation fee_calc_out;
-    if (!CreateTransaction(wallet, vecSend, tx_new, nFeeRet, nChangePosInOut, error, coinControl, fee_calc_out, false)) {
+    std::optional<CreatedTransactionResult> txr = CreateTransaction(wallet, vecSend, nChangePosInOut, error, coinControl, fee_calc_out, false);
-        return false;
+    if (!txr) return false;
-    }
+    CTransactionRef tx_new = txr->tx;
+    nFeeRet = txr->fee;
+    nChangePosInOut = txr->change_pos;
 
     if (nChangePosInOut != -1) {
         tx.vout.insert(tx.vout.begin() + nChangePosInOut, tx_new->vout[nChangePosInOut]);

src/wallet/spend.h

@@ -10,6 +10,8 @@
 #include <wallet/transaction.h>
 #include <wallet/wallet.h>
 
+#include <optional>
+
 namespace wallet {
 /** Get the marginal bytes if spending the specified output from this transaction.
  * use_max_sig indicates whether to use the maximum sized, 72 byte signature when calculating the
@@ -95,9 +97,9 @@ struct CreatedTransactionResult
 /**
  * Create a new transaction paying the recipients with a set of coins
  * selected by SelectCoins(); Also create the change output, when needed
- * @note passing nChangePosInOut as -1 will result in setting a random position
+ * @note passing change_pos as -1 will result in setting a random position
  */
-bool CreateTransaction(CWallet& wallet, const std::vector<CRecipient>& vecSend, CTransactionRef& tx, CAmount& nFeeRet, int& nChangePosInOut, bilingual_str& error, const CCoinControl& coin_control, FeeCalculation& fee_calc_out, bool sign = true);
+std::optional<CreatedTransactionResult> CreateTransaction(CWallet& wallet, const std::vector<CRecipient>& vecSend, int change_pos, bilingual_str& error, const CCoinControl& coin_control, FeeCalculation& fee_calc_out, bool sign = true);
 
 /**
  * Insert additional inputs into the transaction by

src/wallet/test/spend_tests.cpp

@@ -27,9 +27,7 @@ BOOST_FIXTURE_TEST_CASE(SubtractFee, TestChain100Setup)
     // instead of the miner.
     auto check_tx = [&wallet](CAmount leftover_input_amount) {
         CRecipient recipient{GetScriptForRawPubKey({}), 50 * COIN - leftover_input_amount, true /* subtract fee */};
-        CTransactionRef tx;
+        constexpr int RANDOM_CHANGE_POSITION = -1;
-        CAmount fee;
-        int change_pos = -1;
         bilingual_str error;
         CCoinControl coin_control;
         coin_control.m_feerate.emplace(10000);
@@ -37,11 +35,12 @@ BOOST_FIXTURE_TEST_CASE(SubtractFee, TestChain100Setup)
         // We need to use a change type with high cost of change so that the leftover amount will be dropped to fee instead of added as a change output
         coin_control.m_change_type = OutputType::LEGACY;
         FeeCalculation fee_calc;
-        BOOST_CHECK(CreateTransaction(*wallet, {recipient}, tx, fee, change_pos, error, coin_control, fee_calc));
+        std::optional<CreatedTransactionResult> txr = CreateTransaction(*wallet, {recipient}, RANDOM_CHANGE_POSITION, error, coin_control, fee_calc);
-        BOOST_CHECK_EQUAL(tx->vout.size(), 1);
+        BOOST_CHECK(txr.has_value());
-        BOOST_CHECK_EQUAL(tx->vout[0].nValue, recipient.nAmount + leftover_input_amount - fee);
+        BOOST_CHECK_EQUAL(txr->tx->vout.size(), 1);
-        BOOST_CHECK_GT(fee, 0);
+        BOOST_CHECK_EQUAL(txr->tx->vout[0].nValue, recipient.nAmount + leftover_input_amount - txr->fee);
-        return fee;
+        BOOST_CHECK_GT(txr->fee, 0);
+        return txr->fee;
     };
 
     // Send full input amount to recipient, check that only nonzero fee is

src/wallet/test/wallet_tests.cpp

@@ -521,13 +521,14 @@ public:
     CWalletTx& AddTx(CRecipient recipient)
     {
         CTransactionRef tx;
-        CAmount fee;
-        int changePos = -1;
         bilingual_str error;
         CCoinControl dummy;
         FeeCalculation fee_calc_out;
         {
-            BOOST_CHECK(CreateTransaction(*wallet, {recipient}, tx, fee, changePos, error, dummy, fee_calc_out));
+            constexpr int RANDOM_CHANGE_POSITION = -1;
+            std::optional<CreatedTransactionResult> txr = CreateTransaction(*wallet, {recipient}, RANDOM_CHANGE_POSITION, error, dummy, fee_calc_out);
+            BOOST_CHECK(txr.has_value());
+            tx = txr->tx;
         }
         wallet->CommitTransaction(tx, {}, {});
         CMutableTransaction blocktx;