Merge bitcoin/bitcoin#25481: wallet: unify max signature logic

d54c5c8b1b1a38b5b38e6878aea0fa8d6c1ad7e9 wallet: use CCoinControl to estimate signature size (S3RK)
a94659c84ee10ac5915eb5a6b654435183d88521 wallet: replace GetTxSpendSize with CalculateMaximumSignedInputSize (S3RK)

Pull request description:

  Currently `DummySignTx` and `DummySignInput` use different ways to determine signature size.
  This PR unifies the way wallet estimates signature size for various inputs.
  Instead of passing boolean flags from calling code the `use_max_sig` is now calculated at the place of signature creation using information available in `CCoinControl`

ACKs for top commit:
  achow101:
    ACK d54c5c8b1b1a38b5b38e6878aea0fa8d6c1ad7e9
  theStack:
    Code-review ACK d54c5c8b1b1a38b5b38e6878aea0fa8d6c1ad7e9

Tree-SHA512: e790903ad4683067070aa7dbf7434a1bd142282a5bc425112e64d88d27559f1a2cd60c68d6022feaf6b845237035cb18ece10f6243d719ba28173b69bd99110a

6 files changed, 27 insertions, 36 deletions

diff --git a/src/bench/coin_selection.cpp b/src/bench/coin_selection.cpp
index b2958bcc9f..eaefb9b63a 100644
--- a/src/bench/coin_selection.cpp
+++ b/src/bench/coin_selection.cpp
@@ -58,7 +58,8 @@ static void CoinSelection(benchmark::Bench& bench)
     // Create coins
     std::vector<COutput> coins;
     for (const auto& wtx : wtxs) {
-        coins.emplace_back(COutPoint(wtx->GetHash(), 0), wtx->tx->vout.at(0), /*depth=*/6 * 24, GetTxSpendSize(wallet, *wtx, 0), /*spendable=*/true, /*solvable=*/true, /*safe=*/true, wtx->GetTxTime(), /*from_me=*/true, /*fees=*/ 0);
+        const auto txout = wtx->tx->vout.at(0);
+        coins.emplace_back(COutPoint(wtx->GetHash(), 0), txout, /*depth=*/6 * 24, CalculateMaximumSignedInputSize(txout, &wallet, /*coin_control=*/nullptr), /*spendable=*/true, /*solvable=*/true, /*safe=*/true, wtx->GetTxTime(), /*from_me=*/true, /*fees=*/ 0);
     }
 
     const CoinEligibilityFilter filter_standard(1, 6, 0);
diff --git a/src/wallet/spend.cpp b/src/wallet/spend.cpp
index 1d22d0993e..21007f5a92 100644
--- a/src/wallet/spend.cpp
+++ b/src/wallet/spend.cpp
@@ -27,25 +27,20 @@ using interfaces::FoundBlock;
 namespace wallet {
 static constexpr size_t OUTPUT_GROUP_MAX_ENTRIES{100};
 
-int GetTxSpendSize(const CWallet& wallet, const CWalletTx& wtx, unsigned int out, bool use_max_sig)
-{
-    return CalculateMaximumSignedInputSize(wtx.tx->vout[out], &wallet, use_max_sig);
-}
-
-int CalculateMaximumSignedInputSize(const CTxOut& txout, const SigningProvider* provider, bool use_max_sig)
+int CalculateMaximumSignedInputSize(const CTxOut& txout, const COutPoint outpoint, const SigningProvider* provider, const CCoinControl* coin_control)
 {
     CMutableTransaction txn;
-    txn.vin.push_back(CTxIn(COutPoint()));
-    if (!provider || !DummySignInput(*provider, txn.vin[0], txout, use_max_sig)) {
+    txn.vin.push_back(CTxIn(outpoint));
+    if (!provider || !DummySignInput(*provider, txn.vin[0], txout, coin_control)) {
         return -1;
     }
     return GetVirtualTransactionInputSize(txn.vin[0]);
 }
 
-int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* wallet, bool use_max_sig)
+int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* wallet, const CCoinControl* coin_control)
 {
     const std::unique_ptr<SigningProvider> provider = wallet->GetSolvingProvider(txout.scriptPubKey);
-    return CalculateMaximumSignedInputSize(txout, provider.get(), use_max_sig);
+    return CalculateMaximumSignedInputSize(txout, COutPoint(), provider.get(), coin_control);
 }
 
 // txouts needs to be in the order of tx.vin
@@ -198,7 +193,7 @@ CoinsResult AvailableCoins(const CWallet& wallet,
             // Filter by spendable outputs only
             if (!spendable && only_spendable) continue;
 
-            int input_bytes = GetTxSpendSize(wallet, wtx, i, (coinControl && coinControl->fAllowWatchOnly));
+            int input_bytes = CalculateMaximumSignedInputSize(output, COutPoint(), provider.get(), coinControl);
             result.coins.emplace_back(outpoint, output, nDepth, input_bytes, spendable, solvable, safeTx, wtx.GetTxTime(), tx_from_me, feerate);
             result.total_amount += output.nValue;
 
@@ -289,8 +284,9 @@ std::map<CTxDestination, std::vector<COutput>> ListCoins(const CWallet& wallet)
             ) {
                 CTxDestination address;
                 if (ExtractDestination(FindNonChangeParentOutput(wallet, *wtx.tx, output.n).scriptPubKey, address)) {
+                    const auto out = wtx.tx->vout.at(output.n);
                     result[address].emplace_back(
-                        COutPoint(wtx.GetHash(), output.n), wtx.tx->vout.at(output.n), depth, GetTxSpendSize(wallet, wtx, output.n), /*spendable=*/ true, /*solvable=*/ true, /*safe=*/ false, wtx.GetTxTime(), CachedTxIsFromMe(wallet, wtx, ISMINE_ALL));
+                            COutPoint(wtx.GetHash(), output.n), out, depth, CalculateMaximumSignedInputSize(out, &wallet, /*coin_control=*/nullptr), /*spendable=*/ true, /*solvable=*/ true, /*safe=*/ false, wtx.GetTxTime(), CachedTxIsFromMe(wallet, wtx, ISMINE_ALL));
                 }
             }
         }
@@ -450,14 +446,14 @@ std::optional<SelectionResult> SelectCoins(const CWallet& wallet, const std::vec
             if (ptr_wtx->tx->vout.size() <= outpoint.n) {
                 return std::nullopt;
             }
-            input_bytes = GetTxSpendSize(wallet, *ptr_wtx, outpoint.n, false);
             txout = ptr_wtx->tx->vout.at(outpoint.n);
+            input_bytes = CalculateMaximumSignedInputSize(txout, &wallet, &coin_control);
         } else {
             // The input is external. We did not find the tx in mapWallet.
             if (!coin_control.GetExternalOutput(outpoint, txout)) {
                 return std::nullopt;
             }
-            input_bytes = CalculateMaximumSignedInputSize(txout, &coin_control.m_external_provider, /*use_max_sig=*/true);
+            input_bytes = CalculateMaximumSignedInputSize(txout, outpoint, &coin_control.m_external_provider, &coin_control);
         }
         // If available, override calculated size with coin control specified size
         if (coin_control.HasInputWeight(outpoint)) {
diff --git a/src/wallet/spend.h b/src/wallet/spend.h
index cba42d6fae..21f0095e77 100644
--- a/src/wallet/spend.h
+++ b/src/wallet/spend.h
@@ -14,23 +14,16 @@
 
 namespace wallet {
 /** Get the marginal bytes if spending the specified output from this transaction.
- * use_max_sig indicates whether to use the maximum sized, 72 byte signature when calculating the
- * size of the input spend. This should only be set when watch-only outputs are allowed */
-int GetTxSpendSize(const CWallet& wallet, const CWalletTx& wtx, unsigned int out, bool use_max_sig = false);
-
-//Get the marginal bytes of spending the specified output
-int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* pwallet, bool use_max_sig = false);
-int CalculateMaximumSignedInputSize(const CTxOut& txout, const SigningProvider* pwallet, bool use_max_sig = false);
-
+ * Use CoinControl to determine whether to expect signature grinding when calculating the size of the input spend. */
+int CalculateMaximumSignedInputSize(const CTxOut& txout, const CWallet* pwallet, const CCoinControl* coin_control = nullptr);
+int CalculateMaximumSignedInputSize(const CTxOut& txout, const COutPoint outpoint, const SigningProvider* pwallet, const CCoinControl* coin_control = nullptr);
 struct TxSize {
     int64_t vsize{-1};
     int64_t weight{-1};
 };
 
-/** Calculate the size of the transaction assuming all signatures are max size
-* Use DummySignatureCreator, which inserts 71 byte signatures everywhere.
-* NOTE: this requires that all inputs must be in mapWallet (eg the tx should
-* be AllInputsMine). */
+/** Calculate the size of the transaction using CoinControl to determine
+ * whether to expect signature grinding when calculating the size of the input spend. */
 TxSize CalculateMaximumSignedTxSize(const CTransaction& tx, const CWallet* wallet, const std::vector<CTxOut>& txouts, const CCoinControl* coin_control = nullptr);
 TxSize CalculateMaximumSignedTxSize(const CTransaction& tx, const CWallet* wallet, const CCoinControl* coin_control = nullptr) EXCLUSIVE_LOCKS_REQUIRED(wallet->cs_wallet);
 
diff --git a/src/wallet/test/coinselector_tests.cpp b/src/wallet/test/coinselector_tests.cpp
index 27202cd7f3..85f3cd7f3c 100644
--- a/src/wallet/test/coinselector_tests.cpp
+++ b/src/wallet/test/coinselector_tests.cpp
@@ -86,7 +86,8 @@ static void add_coin(std::vector<COutput>& coins, CWallet& wallet, const CAmount
     auto ret = wallet.mapWallet.emplace(std::piecewise_construct, std::forward_as_tuple(txid), std::forward_as_tuple(MakeTransactionRef(std::move(tx)), TxStateInactive{}));
     assert(ret.second);
     CWalletTx& wtx = (*ret.first).second;
-    coins.emplace_back(COutPoint(wtx.GetHash(), nInput), wtx.tx->vout.at(nInput), nAge, GetTxSpendSize(wallet, wtx, nInput), /*spendable=*/ true, /*solvable=*/ true, /*safe=*/ true, wtx.GetTxTime(), fIsFromMe, feerate);
+    const auto& txout = wtx.tx->vout.at(nInput);
+    coins.emplace_back(COutPoint(wtx.GetHash(), nInput), txout, nAge, CalculateMaximumSignedInputSize(txout, &wallet, /*coin_control=*/nullptr), /*spendable=*/ true, /*solvable=*/ true, /*safe=*/ true, wtx.GetTxTime(), fIsFromMe, feerate);
 }
 
 /** Check if SelectionResult a is equivalent to SelectionResult b.
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index bd2882dacb..3349b119cc 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -1504,13 +1504,16 @@ bool CWallet::AddWalletFlags(uint64_t flags)
 }
 
 // Helper for producing a max-sized low-S low-R signature (eg 71 bytes)
-// or a max-sized low-S signature (e.g. 72 bytes) if use_max_sig is true
-bool DummySignInput(const SigningProvider& provider, CTxIn &tx_in, const CTxOut &txout, bool use_max_sig)
+// or a max-sized low-S signature (e.g. 72 bytes) depending on coin_control
+bool DummySignInput(const SigningProvider& provider, CTxIn &tx_in, const CTxOut &txout, const CCoinControl* coin_control)
 {
     // Fill in dummy signatures for fee calculation.
     const CScript& scriptPubKey = txout.scriptPubKey;
     SignatureData sigdata;
 
+    // Use max sig if watch only inputs were used or if this particular input is an external input
+    // to ensure a sufficient fee is attained for the requested feerate.
+    const bool use_max_sig = coin_control && (coin_control->fAllowWatchOnly || coin_control->IsExternalSelected(tx_in.prevout));
     if (!ProduceSignature(provider, use_max_sig ? DUMMY_MAXIMUM_SIGNATURE_CREATOR : DUMMY_SIGNATURE_CREATOR, scriptPubKey, sigdata)) {
         return false;
     }
@@ -1577,12 +1580,9 @@ bool CWallet::DummySignTx(CMutableTransaction &txNew, const std::vector<CTxOut>
             nIn++;
             continue;
         }
-        // Use max sig if watch only inputs were used or if this particular input is an external input
-        // to ensure a sufficient fee is attained for the requested feerate.
-        const bool use_max_sig = coin_control && (coin_control->fAllowWatchOnly || coin_control->IsExternalSelected(txin.prevout));
         const std::unique_ptr<SigningProvider> provider = GetSolvingProvider(txout.scriptPubKey);
-        if (!provider || !DummySignInput(*provider, txin, txout, use_max_sig)) {
-            if (!coin_control || !DummySignInput(coin_control->m_external_provider, txin, txout, use_max_sig)) {
+        if (!provider || !DummySignInput(*provider, txin, txout, coin_control)) {
+            if (!coin_control || !DummySignInput(coin_control->m_external_provider, txin, txout, coin_control)) {
                 return false;
             }
         }
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index 6b12752c34..669aa8d195 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -955,7 +955,7 @@ bool AddWalletSetting(interfaces::Chain& chain, const std::string& wallet_name);
 //! Remove wallet name from persistent configuration so it will not be loaded on startup.
 bool RemoveWalletSetting(interfaces::Chain& chain, const std::string& wallet_name);
 
-bool DummySignInput(const SigningProvider& provider, CTxIn &tx_in, const CTxOut &txout, bool use_max_sig);
+bool DummySignInput(const SigningProvider& provider, CTxIn &tx_in, const CTxOut &txout, const CCoinControl* coin_control = nullptr);
 
 bool FillInputToWeight(CTxIn& txin, int64_t target_weight);
 } // namespace wallet