Merge #9640: Bumpfee: bugfixes for error handling and feerate calculation

9522b53 rpc: bumpfee: handle errors more gracefully (Suhas Daftuar)
f626594 rpc: bumpfee: use correct maximum signed tx size for fee calculation (Suhas Daftuar)
d625b90 wallet: Refactor dummy signature signing for reusability (Suhas Daftuar)

3 files changed, 77 insertions, 21 deletions

diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index bfc738afad..8b135b0e0f 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -2664,6 +2664,33 @@ UniValue fundrawtransaction(const JSONRPCRequest& request)
     return result;
 }
 
+// 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).
+int64_t CalculateMaximumSignedTxSize(const CTransaction &tx)
+{
+    CMutableTransaction txNew(tx);
+    std::vector<pair<CWalletTx *, unsigned int>> 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 = pwalletMain->mapWallet.find(input.prevout.hash);
+        assert(mi != pwalletMain->mapWallet.end() && input.prevout.n < mi->second.tx->vout.size());
+        vCoins.emplace_back(make_pair(&(mi->second), input.prevout.n));
+    }
+    if (!pwalletMain->DummySignTx(txNew, vCoins)) {
+        // This should never happen, because IsAllFromMe(ISMINE_SPENDABLE)
+        // implies that we can sign for every input.
+        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Transaction contains inputs that cannot be signed");
+    }
+    return GetVirtualTransactionSize(txNew);
+}
+
 UniValue bumpfee(const JSONRPCRequest& request)
 {
     if (!EnsureWalletIsAvailable(request.fHelp)) {
@@ -2706,6 +2733,7 @@ UniValue bumpfee(const JSONRPCRequest& request)
             "  \"txid\":    \"value\",   (string)  The id of the new transaction\n"
             "  \"origfee\":  n,         (numeric) Fee of the replaced transaction\n"
             "  \"fee\":      n,         (numeric) Fee of the new transaction\n"
+            "  \"errors\":  [ str... ] (json array of strings) Errors encountered during processing (may be empty)\n"
             "}\n"
             "\nExamples:\n"
             "\nBump the fee, get the new transaction\'s txid\n" +
@@ -2769,9 +2797,9 @@ UniValue bumpfee(const JSONRPCRequest& request)
         throw JSONRPCError(RPC_MISC_ERROR, "Transaction does not have a change output");
     }
 
-    // signature sizes can vary by a byte, so add 1 for each input when calculating the new fee
+    // Calculate the expected size of the new transaction.
     int64_t txSize = GetVirtualTransactionSize(*(wtx.tx));
-    const int64_t maxNewTxSize = txSize + wtx.tx->vin.size();
+    const int64_t maxNewTxSize = CalculateMaximumSignedTxSize(*wtx.tx);
 
     // optional parameters
     bool specifiedConfirmTarget = false;
@@ -2845,8 +2873,12 @@ UniValue bumpfee(const JSONRPCRequest& request)
         nNewFeeRate = CFeeRate(nNewFee, maxNewTxSize);
 
         // New fee rate must be at least old rate + minimum incremental relay rate
-        if (nNewFeeRate.GetFeePerK() < nOldFeeRate.GetFeePerK() + walletIncrementalRelayFee.GetFeePerK()) {
-            nNewFeeRate = CFeeRate(nOldFeeRate.GetFeePerK() + walletIncrementalRelayFee.GetFeePerK());
+        // walletIncrementalRelayFee.GetFeePerK() should be exact, because it's initialized
+        // in that unit (fee per kb).
+        // However, nOldFeeRate is a calculated value from the tx fee/size, so
+        // add 1 satoshi to the result, because it may have been rounded down.
+        if (nNewFeeRate.GetFeePerK() < nOldFeeRate.GetFeePerK() + 1 + walletIncrementalRelayFee.GetFeePerK()) {
+            nNewFeeRate = CFeeRate(nOldFeeRate.GetFeePerK() + 1 + walletIncrementalRelayFee.GetFeePerK());
             nNewFee = nNewFeeRate.GetFee(maxNewTxSize);
         }
     }
@@ -2914,23 +2946,32 @@ UniValue bumpfee(const JSONRPCRequest& request)
     CWalletTx wtxBumped(pwalletMain, MakeTransactionRef(std::move(tx)));
     wtxBumped.mapValue["replaces_txid"] = hash.ToString();
     CValidationState state;
-    if (!pwalletMain->CommitTransaction(wtxBumped, reservekey, g_connman.get(), state) || !state.IsValid()) {
+    if (!pwalletMain->CommitTransaction(wtxBumped, reservekey, g_connman.get(), state)) {
+        // NOTE: CommitTransaction never returns false, so this should never happen.
         throw JSONRPCError(RPC_WALLET_ERROR, strprintf("Error: The transaction was rejected! Reason given: %s", state.GetRejectReason()));
     }
 
+    UniValue vErrors(UniValue::VARR);
+    if (state.IsInvalid()) {
+        // This can happen if the mempool rejected the transaction.  Report
+        // what happened in the "errors" response.
+        vErrors.push_back(strprintf("Error: The transaction was rejected: %s", FormatStateMessage(state)));
+    }
+
     // mark the original tx as bumped
     if (!pwalletMain->MarkReplaced(wtx.GetHash(), wtxBumped.GetHash())) {
         // TODO: see if JSON-RPC has a standard way of returning a response
         // along with an exception. It would be good to return information about
         // wtxBumped to the caller even if marking the original transaction
         // replaced does not succeed for some reason.
-        throw JSONRPCError(RPC_WALLET_ERROR, "Error: Created new bumpfee transaction but could not mark the original transaction as replaced.");
+        vErrors.push_back("Error: Created new bumpfee transaction but could not mark the original transaction as replaced.");
     }
 
     UniValue result(UniValue::VOBJ);
     result.push_back(Pair("txid", wtxBumped.GetHash().GetHex()));
     result.push_back(Pair("origfee", ValueFromAmount(nOldFee)));
     result.push_back(Pair("fee", ValueFromAmount(nNewFee)));
+    result.push_back(Pair("errors", vErrors));
 
     return result;
 }
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index 9a5f35b6e3..a7b8022bd9 100644
--- a/src/wallet/wallet.cpp
+++ b/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;
-                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++;
+                if (!DummySignTx(txNew, setCoins)) {
+                    strFailReason = _("Signing transaction failed");
+                    return false;
                 }
 
                 unsigned int nBytes = GetVirtualTransactionSize(txNew);
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index 200ec0cba2..1de04ae16a 100644
--- a/src/wallet/wallet.h
+++ b/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