Use 72 byte dummy signatures when watching only inputs may be used

With watching only inputs, we do not know how large the signatures
for those inputs will be as their signers may not have implemented
71 byte signatures. Thus we estimate their fees using the 72 byte
dummy signature to ensure that we pay enough fees.

This only effects fundrawtransaction when includeWatching is true.

1 files changed, 14 insertions, 15 deletions

diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 173f1b786c..3a473e4de3 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -1541,29 +1541,28 @@ int64_t CWalletTx::GetTxTime() const
 }
 
 // Helper for producing a max-sized low-S low-R signature (eg 71 bytes)
-bool CWallet::DummySignInput(CTxIn &tx_in, const CTxOut &txout) const
+// or a max-sized low-S signature (e.g. 72 bytes) if use_max_sig is true
+bool CWallet::DummySignInput(CTxIn &tx_in, const CTxOut &txout, bool use_max_sig) const
 {
     // Fill in dummy signatures for fee calculation.
     const CScript& scriptPubKey = txout.scriptPubKey;
     SignatureData sigdata;
 
-    if (!ProduceSignature(*this, DUMMY_SIGNATURE_CREATOR, scriptPubKey, sigdata))
-    {
+    if (!ProduceSignature(*this, use_max_sig ? DUMMY_MAXIMUM_SIGNATURE_CREATOR : DUMMY_SIGNATURE_CREATOR, scriptPubKey, sigdata)) {
         return false;
-    } else {
-        UpdateInput(tx_in, sigdata);
     }
+    UpdateInput(tx_in, sigdata);
     return true;
 }
 
 // Helper for producing a bunch of max-sized low-S low-R signatures (eg 71 bytes)
-bool CWallet::DummySignTx(CMutableTransaction &txNew, const std::vector<CTxOut> &txouts) const
+bool CWallet::DummySignTx(CMutableTransaction &txNew, const std::vector<CTxOut> &txouts, bool use_max_sig) const
 {
     // Fill in dummy signatures for fee calculation.
     int nIn = 0;
     for (const auto& txout : txouts)
     {
-        if (!DummySignInput(txNew.vin[nIn], txout)) {
+        if (!DummySignInput(txNew.vin[nIn], txout, use_max_sig)) {
             return false;
         }
 
@@ -1572,7 +1571,7 @@ bool CWallet::DummySignTx(CMutableTransaction &txNew, const std::vector<CTxOut>
     return true;
 }
 
-int64_t CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet)
+int64_t CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, bool use_max_sig)
 {
     std::vector<CTxOut> txouts;
     // Look up the inputs.  We should have already checked that this transaction
@@ -1586,14 +1585,14 @@ int64_t CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wall
         assert(input.prevout.n < mi->second.tx->vout.size());
         txouts.emplace_back(mi->second.tx->vout[input.prevout.n]);
     }
-    return CalculateMaximumSignedTxSize(tx, wallet, txouts);
+    return CalculateMaximumSignedTxSize(tx, wallet, txouts, use_max_sig);
 }
 
 // txouts needs to be in the order of tx.vin
-int64_t CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, const std::vector<CTxOut>& txouts)
+int64_t CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, const std::vector<CTxOut>& txouts, bool use_max_sig)
 {
     CMutableTransaction txNew(tx);
-    if (!wallet->DummySignTx(txNew, txouts)) {
+    if (!wallet->DummySignTx(txNew, txouts, use_max_sig)) {
         // This should never happen, because IsAllFromMe(ISMINE_SPENDABLE)
         // implies that we can sign for every input.
         return -1;
@@ -1601,11 +1600,11 @@ int64_t CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wall
     return GetVirtualTransactionSize(txNew);
 }
 
-int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* wallet)
+int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* wallet, bool use_max_sig)
 {
     CMutableTransaction txn;
     txn.vin.push_back(CTxIn(COutPoint()));
-    if (!wallet->DummySignInput(txn.vin[0], txout)) {
+    if (!wallet->DummySignInput(txn.vin[0], txout, use_max_sig)) {
         // This should never happen, because IsAllFromMe(ISMINE_SPENDABLE)
         // implies that we can sign for every input.
         return -1;
@@ -2332,7 +2331,7 @@ void CWallet::AvailableCoins(std::vector<COutput> &vCoins, bool fOnlySafe, const
             bool solvable = IsSolvable(*this, pcoin->tx->vout[i].scriptPubKey);
             bool spendable = ((mine & ISMINE_SPENDABLE) != ISMINE_NO) || (((mine & ISMINE_WATCH_ONLY) != ISMINE_NO) && (coinControl && coinControl->fAllowWatchOnly && solvable));
 
-            vCoins.push_back(COutput(pcoin, i, nDepth, spendable, solvable, safeTx));
+            vCoins.push_back(COutput(pcoin, i, nDepth, spendable, solvable, safeTx, (coinControl && coinControl->fAllowWatchOnly)));
 
             // Checks the sum amount of all UTXO's.
             if (nMinimumSumAmount != MAX_MONEY) {
@@ -2881,7 +2880,7 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend, CTransac
                     txNew.vin.push_back(CTxIn(coin.outpoint,CScript()));
                 }
 
-                nBytes = CalculateMaximumSignedTxSize(txNew, this);
+                nBytes = CalculateMaximumSignedTxSize(txNew, this, coin_control.fAllowWatchOnly);
                 if (nBytes < 0) {
                     strFailReason = _("Signing transaction failed");
                     return false;