Calculate and store the number of bytes required to spend an input

src/consensus/validation.h

@@ -101,5 +101,10 @@ static inline int64_t GetBlockWeight(const CBlock& block)
 {
     return ::GetSerializeSize(block, SER_NETWORK, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS) * (WITNESS_SCALE_FACTOR - 1) + ::GetSerializeSize(block, SER_NETWORK, PROTOCOL_VERSION);
 }
+static inline int64_t GetTransationInputWeight(const CTxIn& txin)
+{
+    // scriptWitness size is added here because witnesses and txins are split up in segwit serialization.
+    return ::GetSerializeSize(txin, SER_NETWORK, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS) * (WITNESS_SCALE_FACTOR - 1) + ::GetSerializeSize(txin, SER_NETWORK, PROTOCOL_VERSION) + ::GetSerializeSize(txin.scriptWitness.stack, SER_NETWORK, PROTOCOL_VERSION);
+}
 
 #endif // BITCOIN_CONSENSUS_VALIDATION_H

src/policy/policy.cpp

@@ -258,3 +258,8 @@ int64_t GetVirtualTransactionSize(const CTransaction& tx, int64_t nSigOpCost)
 {
     return GetVirtualTransactionSize(GetTransactionWeight(tx), nSigOpCost);
 }
+
+int64_t GetVirtualTransactionInputSize(const CTxIn& txin, int64_t nSigOpCost)
+{
+    return GetVirtualTransactionSize(GetTransationInputWeight(txin), nSigOpCost);
+}

src/policy/policy.h

@@ -102,5 +102,6 @@ extern unsigned int nBytesPerSigOp;
 /** Compute the virtual transaction size (weight reinterpreted as bytes). */
 int64_t GetVirtualTransactionSize(int64_t nWeight, int64_t nSigOpCost);
 int64_t GetVirtualTransactionSize(const CTransaction& tx, int64_t nSigOpCost = 0);
+int64_t GetVirtualTransactionInputSize(const CTxIn& tx, int64_t nSigOpCost = 0);
 
 #endif // BITCOIN_POLICY_POLICY_H

src/script/sign.cpp

@@ -194,11 +194,16 @@ SignatureData DataFromTransaction(const CMutableTransaction& tx, unsigned int nI
     return data;
 }
 
+void UpdateInput(CTxIn& input, const SignatureData& data)
+{
+    input.scriptSig = data.scriptSig;
+    input.scriptWitness = data.scriptWitness;
+}
+
 void UpdateTransaction(CMutableTransaction& tx, unsigned int nIn, const SignatureData& data)
 {
     assert(tx.vin.size() > nIn);
-    tx.vin[nIn].scriptSig = data.scriptSig;
-    tx.vin[nIn].scriptWitness = data.scriptWitness;
+    UpdateInput(tx.vin[nIn], data);
 }
 
 bool SignSignature(const CKeyStore &keystore, const CScript& fromPubKey, CMutableTransaction& txTo, unsigned int nIn, const CAmount& amount, int nHashType)

src/script/sign.h

@@ -80,6 +80,7 @@ SignatureData CombineSignatures(const CScript& scriptPubKey, const BaseSignature
 /** Extract signature data from a transaction, and insert it. */
 SignatureData DataFromTransaction(const CMutableTransaction& tx, unsigned int nIn);
 void UpdateTransaction(CMutableTransaction& tx, unsigned int nIn, const SignatureData& data);
+void UpdateInput(CTxIn& input, const SignatureData& data);
 
 /* Check whether we know how to sign for an output like this, assuming we
  * have all private keys. While this function does not need private keys, the passed

src/wallet/feebumper.cpp

@@ -16,33 +16,6 @@
 #include <util.h>
 #include <net.h>
 
-// Calculate the size of the transaction assuming all signatures are max size
-// Use DummySignatureCreator, which inserts 72 byte signatures everywhere.
-// TODO: re-use this in CWallet::CreateTransaction (right now
-// CreateTransaction uses the constructed dummy-signed tx to do a priority
-// calculation, but we should be able to refactor after priority is removed).
-// NOTE: this requires that all inputs must be in mapWallet (eg the tx should
-// be IsAllFromMe).
-static int64_t CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet)
-{
-    CMutableTransaction txNew(tx);
-    std::vector<CInputCoin> vCoins;
-    // Look up the inputs.  We should have already checked that this transaction
-    // IsAllFromMe(ISMINE_SPENDABLE), so every input should already be in our
-    // wallet, with a valid index into the vout array.
-    for (auto& input : tx.vin) {
-        const auto mi = wallet->mapWallet.find(input.prevout.hash);
-        assert(mi != wallet->mapWallet.end() && input.prevout.n < mi->second.tx->vout.size());
-        vCoins.emplace_back(CInputCoin(&(mi->second), input.prevout.n));
-    }
-    if (!wallet->DummySignTx(txNew, vCoins)) {
-        // This should never happen, because IsAllFromMe(ISMINE_SPENDABLE)
-        // implies that we can sign for every input.
-        return -1;
-    }
-    return GetVirtualTransactionSize(txNew);
-}
-
 //! Check whether transaction has descendant in wallet or mempool, or has been
 //! mined, or conflicts with a mined transaction. Return a feebumper::Result.
 static feebumper::Result PreconditionChecks(const CWallet* wallet, const CWalletTx& wtx, std::vector<std::string>& errors)

src/wallet/wallet.cpp

@@ -1543,6 +1543,79 @@ int CWalletTx::GetRequestCount() const
     return nRequests;
 }
 
+// Helper for producing a max-sized low-S signature (eg 72 bytes)
+bool CWallet::DummySignInput(CTxIn &tx_in, const CTxOut &txout) const
+{
+    // Fill in dummy signatures for fee calculation.
+    const CScript& scriptPubKey = txout.scriptPubKey;
+    SignatureData sigdata;
+
+    if (!ProduceSignature(DummySignatureCreator(this), scriptPubKey, sigdata))
+    {
+        return false;
+    } else {
+        UpdateInput(tx_in, sigdata);
+    }
+    return true;
+}
+
+// Helper for producing a bunch of max-sized low-S signatures (eg 72 bytes)
+bool CWallet::DummySignTx(CMutableTransaction &txNew, const std::vector<CTxOut> &txouts) const
+{
+    // Fill in dummy signatures for fee calculation.
+    int nIn = 0;
+    for (const auto& txout : txouts)
+    {
+        if (!DummySignInput(txNew.vin[nIn], txout)) {
+            return false;
+        }
+
+        nIn++;
+    }
+    return true;
+}
+
+int64_t CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet)
+{
+    std::vector<CTxOut> txouts;
+    // Look up the inputs.  We should have already checked that this transaction
+    // IsAllFromMe(ISMINE_SPENDABLE), so every input should already be in our
+    // wallet, with a valid index into the vout array, and the ability to sign.
+    for (auto& input : tx.vin) {
+        const auto mi = wallet->mapWallet.find(input.prevout.hash);
+        if (mi == wallet->mapWallet.end()) {
+            return -1;
+        }
+        assert(input.prevout.n < mi->second.tx->vout.size());
+        txouts.emplace_back(mi->second.tx->vout[input.prevout.n]);
+    }
+    return CalculateMaximumSignedTxSize(tx, wallet, txouts);
+}
+
+// txouts needs to be in the order of tx.vin
+int64_t CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, const std::vector<CTxOut>& txouts)
+{
+    CMutableTransaction txNew(tx);
+    if (!wallet->DummySignTx(txNew, txouts)) {
+        // This should never happen, because IsAllFromMe(ISMINE_SPENDABLE)
+        // implies that we can sign for every input.
+        return -1;
+    }
+    return GetVirtualTransactionSize(txNew);
+}
+
+int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* wallet)
+{
+    CMutableTransaction txn;
+    txn.vin.push_back(CTxIn(COutPoint()));
+    if (!wallet->DummySignInput(txn.vin[0], txout)) {
+        // This should never happen, because IsAllFromMe(ISMINE_SPENDABLE)
+        // implies that we can sign for every input.
+        return -1;
+    }
+    return GetVirtualTransactionInputSize(txn.vin[0]);
+}
+
 void CWalletTx::GetAmounts(std::list<COutputEntry>& listReceived,
                            std::list<COutputEntry>& listSent, CAmount& nFee, std::string& strSentAccount, const isminefilter& filter) const
 {
@@ -2752,7 +2825,7 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend, CWalletT
     assert(txNew.nLockTime < LOCKTIME_THRESHOLD);
     FeeCalculation feeCalc;
     CAmount nFeeNeeded;
-    unsigned int nBytes;
+    int nBytes;
     {
         std::set<CInputCoin> setCoins;
         LOCK2(cs_main, cs_wallet);
@@ -2903,20 +2976,12 @@ bool CWallet::CreateTransaction(const std::vector<CRecipient>& vecSend, CWalletT
                     txNew.vin.push_back(CTxIn(coin.outpoint,CScript(),
                                               nSequence));
 
-                // Fill in dummy signatures for fee calculation.
-                if (!DummySignTx(txNew, setCoins)) {
+                nBytes = CalculateMaximumSignedTxSize(txNew, this);
+                if (nBytes < 0) {
                     strFailReason = _("Signing transaction failed");
                     return false;
                 }
 
-                nBytes = GetVirtualTransactionSize(txNew);
-
-                // Remove scriptSigs to eliminate the fee calculation dummy signatures
-                for (auto& vin : txNew.vin) {
-                    vin.scriptSig = CScript();
-                    vin.scriptWitness.SetNull();
-                }
-
                 nFeeNeeded = GetMinimumFee(nBytes, coin_control, ::mempool, ::feeEstimator, &feeCalc);
                 if (feeCalc.reason == FeeReason::FALLBACK && !g_wallet_allow_fallback_fee) {
                     // eventually allow a fallback fee

src/wallet/wallet.h

@@ -269,6 +269,9 @@ public:
     bool IsCoinBase() const { return tx->IsCoinBase(); }
 };
 
+//Get the marginal bytes of spending the specified output
+int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* pwallet);
+
 /** 
  * A transaction with a bunch of additional info that only the owner cares about.
  * It includes any unrecorded transactions needed to link it back to the block chain.
@@ -462,6 +465,12 @@ public:
     CAmount GetAvailableWatchOnlyCredit(const bool fUseCache=true) const;
     CAmount GetChange() const;
 
+    // Get the marginal bytes if spending the specified output from this transaction
+    int GetSpendSize(unsigned int out) const
+    {
+        return CalculateMaximumSignedInputSize(tx->vout[out], pwallet);
+    }
+
     void GetAmounts(std::list<COutputEntry>& listReceived,
                     std::list<COutputEntry>& listSent, CAmount& nFee, std::string& strSentAccount, const isminefilter& filter) const;
 
@@ -525,6 +534,9 @@ public:
     int i;
     int nDepth;
 
+    /** Pre-computed estimated size of this output as a fully-signed input in a transaction. Can be -1 if it could not be calculated */
+    int nInputBytes;
+
     /** Whether we have the private keys to spend this output */
     bool fSpendable;
 
@@ -540,7 +552,12 @@ public:
 
     COutput(const CWalletTx *txIn, int iIn, int nDepthIn, bool fSpendableIn, bool fSolvableIn, bool fSafeIn)
     {
-        tx = txIn; i = iIn; nDepth = nDepthIn; fSpendable = fSpendableIn; fSolvable = fSolvableIn; fSafe = fSafeIn;
+        tx = txIn; i = iIn; nDepth = nDepthIn; fSpendable = fSpendableIn; fSolvable = fSolvableIn; fSafe = fSafeIn; nInputBytes = -1;
+        // If known and signable by the given wallet, compute nInputBytes
+        // Failure will keep this value -1
+        if (fSpendable && tx) {
+            nInputBytes = tx->GetSpendSize(i);
+        }
     }
 
     std::string ToString() const;
@@ -981,8 +998,14 @@ 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) const;
+    bool DummySignTx(CMutableTransaction &txNew, const std::set<CTxOut> &txouts) const
+    {
+        std::vector<CTxOut> v_txouts(txouts.size());
+        std::copy(txouts.begin(), txouts.end(), v_txouts.begin());
+        return DummySignTx(txNew, v_txouts);
+    }
+    bool DummySignTx(CMutableTransaction &txNew, const std::vector<CTxOut> &txouts) const;
+    bool DummySignInput(CTxIn &tx_in, const CTxOut &txout) const;
 
     static CFeeRate minTxFee;
     static CFeeRate fallbackFee;
@@ -1227,31 +1250,6 @@ 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) const
-{
-    // Fill in dummy signatures for fee calculation.
-    int nIn = 0;
-    for (const auto& coin : coins)
-    {
-        const CScript& scriptPubKey = coin.txout.scriptPubKey;
-        SignatureData sigdata;
-
-        if (!ProduceSignature(DummySignatureCreator(this), scriptPubKey, sigdata))
-        {
-            return false;
-        } else {
-            UpdateTransaction(txNew, nIn, sigdata);
-        }
-
-        nIn++;
-    }
-    return true;
-}
-
 OutputType ParseOutputType(const std::string& str, OutputType default_type = OUTPUT_TYPE_DEFAULT);
 const std::string& FormatOutputType(OutputType type);
 
@@ -1299,4 +1297,10 @@ public:
     }
 };
 
+// Calculate the size of the transaction assuming all signatures are max size
+// Use DummySignatureCreator, which inserts 72 byte signatures everywhere.
+// NOTE: this requires that all inputs must be in mapWallet (eg the tx should
+// be IsAllFromMe).
+int64_t CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet);
+int64_t CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet, const std::vector<CTxOut>& txouts);
 #endif // BITCOIN_WALLET_WALLET_H