wallet: Refactor dummy signature signing for reusability

src/wallet/wallet.cpp

@@ -2583,21 +2583,9 @@ bool CWallet::CreateTransaction(const vector<CRecipient>& vecSend, CWalletTx& wt
                                               std::numeric_limits<unsigned int>::max() - (fWalletRbf ? 2 : 1)));
 
                 // Fill in dummy signatures for fee calculation.
-                int nIn = 0;
+                if (!DummySignTx(txNew, setCoins)) {
-                for (const auto& coin : setCoins)
-                {
-                    const CScript& scriptPubKey = coin.first->tx->vout[coin.second].scriptPubKey;
-                    SignatureData sigdata;
-
-                    if (!ProduceSignature(DummySignatureCreator(this), scriptPubKey, sigdata))
-                    {
                     strFailReason = _("Signing transaction failed");
                     return false;
-                    } else {
-                        UpdateTransaction(txNew, nIn, sigdata);
-                    }
-
-                    nIn++;
                 }
 
                 unsigned int nBytes = GetVirtualTransactionSize(txNew);

src/wallet/wallet.h

@@ -13,6 +13,7 @@
 #include "utilstrencodings.h"
 #include "validationinterface.h"
 #include "script/ismine.h"
+#include "script/sign.h"
 #include "wallet/crypter.h"
 #include "wallet/walletdb.h"
 #include "wallet/rpcwallet.h"
@@ -796,6 +797,8 @@ public:
     void ListAccountCreditDebit(const std::string& strAccount, std::list<CAccountingEntry>& entries);
     bool AddAccountingEntry(const CAccountingEntry&);
     bool AddAccountingEntry(const CAccountingEntry&, CWalletDB *pwalletdb);
+    template <typename ContainerType>
+    bool DummySignTx(CMutableTransaction &txNew, const ContainerType &coins);
 
     static CFeeRate minTxFee;
     static CFeeRate fallbackFee;
@@ -1028,4 +1031,28 @@ public:
     }
 };
 
+// Helper for producing a bunch of max-sized low-S signatures (eg 72 bytes)
+// ContainerType is meant to hold pair<CWalletTx *, int>, and be iterable
+// so that each entry corresponds to each vIn, in order.
+template <typename ContainerType>
+bool CWallet::DummySignTx(CMutableTransaction &txNew, const ContainerType &coins)
+{
+    // Fill in dummy signatures for fee calculation.
+    int nIn = 0;
+    for (const auto& coin : coins)
+    {
+        const CScript& scriptPubKey = coin.first->tx->vout[coin.second].scriptPubKey;
+        SignatureData sigdata;
+
+        if (!ProduceSignature(DummySignatureCreator(this), scriptPubKey, sigdata))
+        {
+            return false;
+        } else {
+            UpdateTransaction(txNew, nIn, sigdata);
+        }
+
+        nIn++;
+    }
+    return true;
+}
 #endif // BITCOIN_WALLET_WALLET_H