send: refactor CreateTransaction flow to return a BResult<CTransactionRef>

1 files changed, 43 insertions, 54 deletions

diff --git a/src/wallet/spend.cpp b/src/wallet/spend.cpp
index 9846335da7..4a54a5f671 100644
--- a/src/wallet/spend.cpp
+++ b/src/wallet/spend.cpp
@@ -656,18 +656,16 @@ static void DiscourageFeeSniping(CMutableTransaction& tx, FastRandomContext& rng
     }
 }
 
-static std::optional<CreatedTransactionResult> CreateTransactionInternal(
+static BResult<CreatedTransactionResult> CreateTransactionInternal(
         CWallet& wallet,
         const std::vector<CRecipient>& vecSend,
         int change_pos,
-        bilingual_str& error,
         const CCoinControl& coin_control,
         bool sign) EXCLUSIVE_LOCKS_REQUIRED(wallet.cs_wallet)
 {
     AssertLockHeld(wallet.cs_wallet);
 
     // out variables, to be packed into returned result structure
-    CTransactionRef tx;
     CAmount nFeeRet;
     int nChangePosInOut = change_pos;
 
@@ -696,6 +694,7 @@ static std::optional<CreatedTransactionResult> CreateTransactionInternal(
 
     // Create change script that will be used if we need change
     CScript scriptChange;
+    bilingual_str error; // possible error str
 
     // coin control: send change to custom address
     if (!std::get_if<CNoDestination>(&coin_control.destChange)) {
@@ -743,13 +742,11 @@ static std::optional<CreatedTransactionResult> CreateTransactionInternal(
     // Do not, ever, assume that it's fine to change the fee rate if the user has explicitly
     // 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 std::nullopt;
+        return 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));
     }
     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 std::nullopt;
+        return _("Fee estimation failed. Fallbackfee is disabled. Wait a few blocks or enable -fallbackfee.");
     }
 
     // Calculate the cost of change
@@ -774,10 +771,8 @@ static std::optional<CreatedTransactionResult> CreateTransactionInternal(
             coin_selection_params.tx_noinputs_size += ::GetSerializeSize(txout, PROTOCOL_VERSION);
         }
 
-        if (IsDust(txout, wallet.chain().relayDustFee()))
-        {
-            error = _("Transaction amount too small");
-            return std::nullopt;
+        if (IsDust(txout, wallet.chain().relayDustFee())) {
+            return _("Transaction amount too small");
         }
         txNew.vout.push_back(txout);
     }
@@ -798,8 +793,7 @@ static std::optional<CreatedTransactionResult> CreateTransactionInternal(
     // Choose coins to use
     std::optional<SelectionResult> result = SelectCoins(wallet, res_available_coins.coins, /*nTargetValue=*/selection_target, coin_control, coin_selection_params);
     if (!result) {
-        error = _("Insufficient funds");
-        return std::nullopt;
+        return _("Insufficient funds");
     }
     TRACE5(coin_selection, selected_coins, wallet.GetName().c_str(), GetAlgorithmName(result->m_algo).c_str(), result->m_target, result->GetWaste(), result->GetSelectedValue());
 
@@ -813,10 +807,8 @@ static std::optional<CreatedTransactionResult> CreateTransactionInternal(
         // Insert change txn at random position:
         nChangePosInOut = rng_fast.randrange(txNew.vout.size() + 1);
     }
-    else if ((unsigned int)nChangePosInOut > txNew.vout.size())
-    {
-        error = _("Transaction change output index out of range");
-        return std::nullopt;
+    else if ((unsigned int)nChangePosInOut > txNew.vout.size()) {
+        return _("Transaction change output index out of range");
     }
 
     assert(nChangePosInOut != -1);
@@ -843,8 +835,7 @@ static std::optional<CreatedTransactionResult> CreateTransactionInternal(
     TxSize tx_sizes = CalculateMaximumSignedTxSize(CTransaction(txNew), &wallet, &coin_control);
     int nBytes = tx_sizes.vsize;
     if (nBytes == -1) {
-        error = _("Missing solving data for estimating transaction size");
-        return std::nullopt;
+        return _("Missing solving data for estimating transaction size");
     }
     nFeeRet = coin_selection_params.m_effective_feerate.GetFee(nBytes);
 
@@ -904,11 +895,10 @@ static std::optional<CreatedTransactionResult> CreateTransactionInternal(
                 // Error if this output is reduced to be below dust
                 if (IsDust(txout, wallet.chain().relayDustFee())) {
                     if (txout.nValue < 0) {
-                        error = _("The transaction amount is too small to pay the fee");
+                        return _("The transaction amount is too small to pay the fee");
                     } else {
-                        error = _("The transaction amount is too small to send after the fee has been deducted");
+                        return _("The transaction amount is too small to send after the fee has been deducted");
                     }
-                    return std::nullopt;
                 }
             }
             ++i;
@@ -918,35 +908,31 @@ static std::optional<CreatedTransactionResult> CreateTransactionInternal(
 
     // Give up if change keypool ran out and change is required
     if (scriptChange.empty() && nChangePosInOut != -1) {
-        return std::nullopt;
+        return error;
     }
 
     if (sign && !wallet.SignTransaction(txNew)) {
-        error = _("Signing transaction failed");
-        return std::nullopt;
+        return _("Signing transaction failed");
     }
 
     // Return the constructed transaction data.
-    tx = MakeTransactionRef(std::move(txNew));
+    CTransactionRef tx = MakeTransactionRef(std::move(txNew));
 
     // Limit size
     if ((sign && GetTransactionWeight(*tx) > MAX_STANDARD_TX_WEIGHT) ||
         (!sign && tx_sizes.weight > MAX_STANDARD_TX_WEIGHT))
     {
-        error = _("Transaction too large");
-        return std::nullopt;
+        return _("Transaction too large");
     }
 
     if (nFeeRet > wallet.m_default_max_tx_fee) {
-        error = TransactionErrorString(TransactionError::MAX_FEE_EXCEEDED);
-        return std::nullopt;
+        return TransactionErrorString(TransactionError::MAX_FEE_EXCEEDED);
     }
 
     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 std::nullopt;
+            return _("Transaction has too long of a mempool chain");
         }
     }
 
@@ -965,48 +951,47 @@ static std::optional<CreatedTransactionResult> CreateTransactionInternal(
     return CreatedTransactionResult(tx, nFeeRet, nChangePosInOut, feeCalc);
 }
 
-std::optional<CreatedTransactionResult> CreateTransaction(
+BResult<CreatedTransactionResult> CreateTransaction(
         CWallet& wallet,
         const std::vector<CRecipient>& vecSend,
         int change_pos,
-        bilingual_str& error,
         const CCoinControl& coin_control,
         bool sign)
 {
     if (vecSend.empty()) {
-        error = _("Transaction must have at least one recipient");
-        return std::nullopt;
+        return _("Transaction must have at least one recipient");
     }
 
     if (std::any_of(vecSend.cbegin(), vecSend.cend(), [](const auto& recipient){ return recipient.nAmount < 0; })) {
-        error = _("Transaction amounts must not be negative");
-        return std::nullopt;
+        return _("Transaction amounts must not be negative");
     }
 
     LOCK(wallet.cs_wallet);
 
-    std::optional<CreatedTransactionResult> txr_ungrouped = CreateTransactionInternal(wallet, vecSend, change_pos, error, coin_control, sign);
-    TRACE4(coin_selection, normal_create_tx_internal, wallet.GetName().c_str(), txr_ungrouped.has_value(),
-           txr_ungrouped.has_value() ? txr_ungrouped->fee : 0, txr_ungrouped.has_value() ? txr_ungrouped->change_pos : 0);
-    if (!txr_ungrouped) return std::nullopt;
+    auto res = CreateTransactionInternal(wallet, vecSend, change_pos, coin_control, sign);
+    TRACE4(coin_selection, normal_create_tx_internal, wallet.GetName().c_str(), res.HasRes(),
+           res ? res.GetObj().fee : 0, res ? res.GetObj().change_pos : 0);
+    if (!res) return res;
+    const auto& txr_ungrouped = res.GetObj();
     // try with avoidpartialspends unless it's enabled already
-    if (txr_ungrouped->fee > 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;
-        bilingual_str error2; // fired and forgotten; if an error occurs, we discard the results
-        std::optional<CreatedTransactionResult> txr_grouped = CreateTransactionInternal(wallet, vecSend, change_pos, error2, tmp_cc, sign);
+        auto res_tx_grouped = CreateTransactionInternal(wallet, vecSend, change_pos, tmp_cc, sign);
+        // Helper optional class for now
+        std::optional<CreatedTransactionResult> txr_grouped{res_tx_grouped.HasRes() ? std::make_optional(res_tx_grouped.GetObj()) : std::nullopt};
         // if fee of this alternative one is within the range of the max fee, we use this one
-        const bool use_aps{txr_grouped.has_value() ? (txr_grouped->fee <= txr_ungrouped->fee + wallet.m_max_aps_fee) : false};
+        const bool use_aps{txr_grouped.has_value() ? (txr_grouped->fee <= txr_ungrouped.fee + wallet.m_max_aps_fee) : false};
         TRACE5(coin_selection, aps_create_tx_internal, wallet.GetName().c_str(), use_aps, txr_grouped.has_value(),
                txr_grouped.has_value() ? txr_grouped->fee : 0, txr_grouped.has_value() ? txr_grouped->change_pos : 0);
         if (txr_grouped) {
             wallet.WalletLogPrintf("Fee non-grouped = %lld, grouped = %lld, using %s\n",
-                txr_ungrouped->fee, txr_grouped->fee, use_aps ? "grouped" : "non-grouped");
-            if (use_aps) return txr_grouped;
+                txr_ungrouped.fee, txr_grouped->fee, use_aps ? "grouped" : "non-grouped");
+            if (use_aps) return res_tx_grouped;
         }
     }
-    return txr_ungrouped;
+    return res;
 }
 
 bool FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& nFeeRet, int& nChangePosInOut, bilingual_str& error, bool lockUnspents, const std::set<int>& setSubtractFeeFromOutputs, CCoinControl coinControl)
@@ -1042,11 +1027,15 @@ bool FundTransaction(CWallet& wallet, CMutableTransaction& tx, CAmount& nFeeRet,
         }
     }
 
-    std::optional<CreatedTransactionResult> txr = CreateTransaction(wallet, vecSend, nChangePosInOut, error, coinControl, false);
-    if (!txr) return false;
-    CTransactionRef tx_new = txr->tx;
-    nFeeRet = txr->fee;
-    nChangePosInOut = txr->change_pos;
+    auto res = CreateTransaction(wallet, vecSend, nChangePosInOut, coinControl, false);
+    if (!res) {
+        error = res.GetError();
+        return false;
+    }
+    const auto& txr = res.GetObj();
+    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]);