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

src/wallet/spend.cpp

@@ -656,12 +656,10 @@ static void DiscourageFeeSniping(CMutableTransaction& tx, FastRandomContext& rng
     }
 }
 
-static bool CreateTransactionInternal(
+static std::optional<CreatedTransactionResult> CreateTransactionInternal(
         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,
@@ -669,6 +667,11 @@ static bool CreateTransactionInternal(
 {
     AssertLockHeld(wallet.cs_wallet);
 
+    // out variables, to be packed into returned result structure
+    CTransactionRef tx;
+    CAmount nFeeRet;
+    int nChangePosInOut = change_pos;
+
     FastRandomContext rng_fast;
     CMutableTransaction txNew; // The resulting transaction that we make
 
@@ -742,12 +745,12 @@ static bool CreateTransactionInternal(
     // provided one
     if (coin_control.m_feerate && coin_selection_params.m_effective_feerate > *coin_control.m_feerate) {
         error = strprintf(_("Fee rate (%s) is lower than the minimum fee rate setting (%s)"), coin_control.m_feerate->ToString(FeeEstimateMode::SAT_VB), coin_selection_params.m_effective_feerate.ToString(FeeEstimateMode::SAT_VB));
-        return false;
+        return std::nullopt;
     }
     if (feeCalc.reason == FeeReason::FALLBACK && !wallet.m_allow_fallback_fee) {
         // eventually allow a fallback fee
         error = _("Fee estimation failed. Fallbackfee is disabled. Wait a few blocks or enable -fallbackfee.");
-        return false;
+        return std::nullopt;
     }
 
     // Calculate the cost of change
@@ -774,7 +777,7 @@ static bool CreateTransactionInternal(
         if (IsDust(txout, wallet.chain().relayDustFee()))
         {
             error = _("Transaction amount too small");
-            return false;
+            return std::nullopt;
         }
         txNew.vout.push_back(txout);
     }
@@ -791,7 +794,7 @@ static bool CreateTransactionInternal(
     std::optional<SelectionResult> result = SelectCoins(wallet, vAvailableCoins, /*nTargetValue=*/selection_target, coin_control, coin_selection_params);
     if (!result) {
         error = _("Insufficient funds");
-        return false;
+        return std::nullopt;
     }
     TRACE5(coin_selection, selected_coins, wallet.GetName().c_str(), GetAlgorithmName(result->m_algo).c_str(), result->m_target, result->GetWaste(), result->GetSelectedValue());
 
@@ -808,7 +811,7 @@ static bool CreateTransactionInternal(
     else if ((unsigned int)nChangePosInOut > txNew.vout.size())
     {
         error = _("Transaction change output index out of range");
-        return false;
+        return std::nullopt;
     }
 
     assert(nChangePosInOut != -1);
@@ -836,7 +839,7 @@ static bool CreateTransactionInternal(
     int nBytes = tx_sizes.vsize;
     if (nBytes == -1) {
         error = _("Missing solving data for estimating transaction size");
-        return false;
+        return std::nullopt;
     }
     nFeeRet = coin_selection_params.m_effective_feerate.GetFee(nBytes);
 
@@ -900,7 +903,7 @@ static bool CreateTransactionInternal(
                     } else {
                         error = _("The transaction amount is too small to send after the fee has been deducted");
                     }
-                    return false;
+                    return std::nullopt;
                 }
             }
             ++i;
@@ -910,12 +913,12 @@ static bool CreateTransactionInternal(
 
     // Give up if change keypool ran out and change is required
     if (scriptChange.empty() && nChangePosInOut != -1) {
-        return false;
+        return std::nullopt;
     }
 
     if (sign && !wallet.SignTransaction(txNew)) {
         error = _("Signing transaction failed");
-        return false;
+        return std::nullopt;
     }
 
     // Return the constructed transaction data.
@@ -926,19 +929,19 @@ static bool CreateTransactionInternal(
         (!sign && tx_sizes.weight > MAX_STANDARD_TX_WEIGHT))
     {
         error = _("Transaction too large");
-        return false;
+        return std::nullopt;
     }
 
     if (nFeeRet > wallet.m_default_max_tx_fee) {
         error = TransactionErrorString(TransactionError::MAX_FEE_EXCEEDED);
-        return false;
+        return std::nullopt;
     }
 
     if (gArgs.GetBoolArg("-walletrejectlongchains", DEFAULT_WALLET_REJECT_LONG_CHAINS)) {
         // Lastly, ensure this tx will pass the mempool's chain limits
         if (!wallet.chain().checkChainLimits(tx)) {
             error = _("Transaction has too long of a mempool chain");
-            return false;
+            return std::nullopt;
         }
     }
 
@@ -955,9 +958,11 @@ static bool CreateTransactionInternal(
               feeCalc.est.fail.start, feeCalc.est.fail.end,
               (feeCalc.est.fail.totalConfirmed + feeCalc.est.fail.inMempool + feeCalc.est.fail.leftMempool) > 0.0 ? 100 * feeCalc.est.fail.withinTarget / (feeCalc.est.fail.totalConfirmed + feeCalc.est.fail.inMempool + feeCalc.est.fail.leftMempool) : 0.0,
               feeCalc.est.fail.withinTarget, feeCalc.est.fail.totalConfirmed, feeCalc.est.fail.inMempool, feeCalc.est.fail.leftMempool);
-    return true;
+    return CreatedTransactionResult(tx, nFeeRet, nChangePosInOut);
 }
 
+// TODO: also return std::optional<CreatedTransactionResult> here in order
+//       to eliminate the out parameters and to simplify the function
 bool CreateTransaction(
         CWallet& wallet,
         const std::vector<CRecipient>& vecSend,
@@ -983,7 +988,14 @@ bool CreateTransaction(
 
     int nChangePosIn = nChangePosInOut;
     Assert(!tx); // tx is an out-param. TODO change the return type from bool to tx (or nullptr)
-    bool res = CreateTransactionInternal(wallet, vecSend, tx, nFeeRet, nChangePosInOut, error, coin_control, fee_calc_out, sign);
+    std::optional<CreatedTransactionResult> txr_ungrouped = CreateTransactionInternal(wallet, vecSend, nChangePosInOut, error, coin_control, fee_calc_out, sign);
+    bool res = false;
+    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) {
@@ -994,7 +1006,12 @@ bool CreateTransaction(
         CTransactionRef tx2;
         int nChangePosInOut2 = nChangePosIn;
         bilingual_str error2; // fired and forgotten; if an error occurs, we discard the results
-        if (CreateTransactionInternal(wallet, vecSend, tx2, nFeeRet2, nChangePosInOut2, error2, tmp_cc, fee_calc_out, sign)) {
+        std::optional<CreatedTransactionResult> txr_grouped = CreateTransactionInternal(wallet, vecSend, nChangePosInOut2, 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;
             wallet.WalletLogPrintf("Fee non-grouped = %lld, grouped = %lld, using %s\n", nFeeRet, nFeeRet2, use_aps ? "grouped" : "non-grouped");

src/wallet/spend.h

@@ -82,6 +82,16 @@ std::optional<SelectionResult> AttemptSelection(const CWallet& wallet, const CAm
 std::optional<SelectionResult> SelectCoins(const CWallet& wallet, const std::vector<COutput>& vAvailableCoins, const CAmount& nTargetValue, const CCoinControl& coin_control,
                  const CoinSelectionParams& coin_selection_params) EXCLUSIVE_LOCKS_REQUIRED(wallet.cs_wallet);
 
+struct CreatedTransactionResult
+{
+    CTransactionRef tx;
+    CAmount fee;
+    int change_pos;
+
+    CreatedTransactionResult(CTransactionRef tx, CAmount fee, int change_pos)
+        : tx(tx), fee(fee), change_pos(change_pos) {}
+};
+
 /**
  * Create a new transaction paying the recipients with a set of coins
  * selected by SelectCoins(); Also create the change output, when needed