src/wallet/feebumper.cpp

   1 // Copyright (c) 2017 The Bitcoin Core developers
   2 // Distributed under the MIT software license, see the accompanying
   3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   4
   5 #include <consensus/validation.h>
   6 #include <wallet/coincontrol.h>
   7 #include <wallet/feebumper.h>
   8 #include <wallet/fees.h>
   9 #include <wallet/wallet.h>
  10 #include <policy/fees.h>
  11 #include <policy/policy.h>
  12 #include <policy/rbf.h>
  13 #include <validation.h> //for mempool access
  14 #include <txmempool.h>
  15 #include <utilmoneystr.h>
  16 #include <util.h>
  17 #include <net.h>
  18
  19 // Calculate the size of the transaction assuming all signatures are max size
  20 // Use DummySignatureCreator, which inserts 72 byte signatures everywhere.
  21 // TODO: re-use this in CWallet::CreateTransaction (right now
  22 // CreateTransaction uses the constructed dummy-signed tx to do a priority
  23 // calculation, but we should be able to refactor after priority is removed).
  24 // NOTE: this requires that all inputs must be in mapWallet (eg the tx should
  25 // be IsAllFromMe).
  26 static int64_t CalculateMaximumSignedTxSize(const CTransaction &tx, const CWallet *wallet)
  27 {
  28     CMutableTransaction txNew(tx);
  29     std::vector<CInputCoin> vCoins;
  30     // Look up the inputs.  We should have already checked that this transaction
  31     // IsAllFromMe(ISMINE_SPENDABLE), so every input should already be in our
  32     // wallet, with a valid index into the vout array.
  33     for (auto& input : tx.vin) {
  34         const auto mi = wallet->mapWallet.find(input.prevout.hash);
  35         assert(mi != wallet->mapWallet.end() && input.prevout.n < mi->second.tx->vout.size());
  36         vCoins.emplace_back(CInputCoin(&(mi->second), input.prevout.n));
  37     }
  38     if (!wallet->DummySignTx(txNew, vCoins)) {
  39         // This should never happen, because IsAllFromMe(ISMINE_SPENDABLE)
  40         // implies that we can sign for every input.
  41         return -1;
  42     }
  43     return GetVirtualTransactionSize(txNew);
  44 }
  45
  46 //! Check whether transaction has descendant in wallet or mempool, or has been
  47 //! mined, or conflicts with a mined transaction. Return a feebumper::Result.
  48 static feebumper::Result PreconditionChecks(const CWallet* wallet, const CWalletTx& wtx, std::vector<std::string>& errors)
  49 {
  50     if (wallet->HasWalletSpend(wtx.GetHash())) {
  51         errors.push_back("Transaction has descendants in the wallet");
  52         return feebumper::Result::INVALID_PARAMETER;
  53     }
  54
  55     {
  56         LOCK(mempool.cs);
  57         auto it_mp = mempool.mapTx.find(wtx.GetHash());
  58         if (it_mp != mempool.mapTx.end() && it_mp->GetCountWithDescendants() > 1) {
  59             errors.push_back("Transaction has descendants in the mempool");
  60             return feebumper::Result::INVALID_PARAMETER;
  61         }
  62     }
  63
  64     if (wtx.GetDepthInMainChain() != 0) {
  65         errors.push_back("Transaction has been mined, or is conflicted with a mined transaction");
  66         return feebumper::Result::WALLET_ERROR;
  67     }
  68     return feebumper::Result::OK;
  69 }
  70
  71 namespace feebumper {
  72
  73 bool TransactionCanBeBumped(CWallet* wallet, const uint256& txid)
  74 {
  75     LOCK2(cs_main, wallet->cs_wallet);
  76     const CWalletTx* wtx = wallet->GetWalletTx(txid);
  77     return wtx && SignalsOptInRBF(*wtx->tx) && !wtx->mapValue.count("replaced_by_txid");
  78 }
  79
  80 Result CreateTransaction(const CWallet* wallet, const uint256& txid, const CCoinControl& coin_control, CAmount total_fee, std::vector<std::string>& errors,
  81                          CAmount& old_fee, CAmount& new_fee, CMutableTransaction& mtx)
  82 {
  83     LOCK2(cs_main, wallet->cs_wallet);
  84     errors.clear();
  85     auto it = wallet->mapWallet.find(txid);
  86     if (it == wallet->mapWallet.end()) {
  87         errors.push_back("Invalid or non-wallet transaction id");
  88         return Result::INVALID_ADDRESS_OR_KEY;
  89     }
  90     const CWalletTx& wtx = it->second;
  91
  92     Result result = PreconditionChecks(wallet, wtx, errors);
  93     if (result != Result::OK) {
  94         return result;
  95     }
  96
  97     if (!SignalsOptInRBF(*wtx.tx)) {
  98         errors.push_back("Transaction is not BIP 125 replaceable");
  99         return Result::WALLET_ERROR;
 100     }
 101
 102     if (wtx.mapValue.count("replaced_by_txid")) {
 103         errors.push_back(strprintf("Cannot bump transaction %s which was already bumped by transaction %s", txid.ToString(), wtx.mapValue.at("replaced_by_txid")));
 104         return Result::WALLET_ERROR;
 105     }
 106
 107     // check that original tx consists entirely of our inputs
 108     // if not, we can't bump the fee, because the wallet has no way of knowing the value of the other inputs (thus the fee)
 109     if (!wallet->IsAllFromMe(*wtx.tx, ISMINE_SPENDABLE)) {
 110         errors.push_back("Transaction contains inputs that don't belong to this wallet");
 111         return Result::WALLET_ERROR;
 112     }
 113
 114     // figure out which output was change
 115     // if there was no change output or multiple change outputs, fail
 116     int nOutput = -1;
 117     for (size_t i = 0; i < wtx.tx->vout.size(); ++i) {
 118         if (wallet->IsChange(wtx.tx->vout[i])) {
 119             if (nOutput != -1) {
 120                 errors.push_back("Transaction has multiple change outputs");
 121                 return Result::WALLET_ERROR;
 122             }
 123             nOutput = i;
 124         }
 125     }
 126     if (nOutput == -1) {
 127         errors.push_back("Transaction does not have a change output");
 128         return Result::WALLET_ERROR;
 129     }
 130
 131     // Calculate the expected size of the new transaction.
 132     int64_t txSize = GetVirtualTransactionSize(*(wtx.tx));
 133     const int64_t maxNewTxSize = CalculateMaximumSignedTxSize(*wtx.tx, wallet);
 134     if (maxNewTxSize < 0) {
 135         errors.push_back("Transaction contains inputs that cannot be signed");
 136         return Result::INVALID_ADDRESS_OR_KEY;
 137     }
 138
 139     // calculate the old fee and fee-rate
 140     old_fee = wtx.GetDebit(ISMINE_SPENDABLE) - wtx.tx->GetValueOut();
 141     CFeeRate nOldFeeRate(old_fee, txSize);
 142     CFeeRate nNewFeeRate;
 143     // The wallet uses a conservative WALLET_INCREMENTAL_RELAY_FEE value to
 144     // future proof against changes to network wide policy for incremental relay
 145     // fee that our node may not be aware of.
 146     CFeeRate walletIncrementalRelayFee = CFeeRate(WALLET_INCREMENTAL_RELAY_FEE);
 147     if (::incrementalRelayFee > walletIncrementalRelayFee) {
 148         walletIncrementalRelayFee = ::incrementalRelayFee;
 149     }
 150
 151     if (total_fee > 0) {
 152         CAmount minTotalFee = nOldFeeRate.GetFee(maxNewTxSize) + ::incrementalRelayFee.GetFee(maxNewTxSize);
 153         if (total_fee < minTotalFee) {
 154             errors.push_back(strprintf("Insufficient totalFee, must be at least %s (oldFee %s + incrementalFee %s)",
 155                                                                 FormatMoney(minTotalFee), FormatMoney(nOldFeeRate.GetFee(maxNewTxSize)), FormatMoney(::incrementalRelayFee.GetFee(maxNewTxSize))));
 156             return Result::INVALID_PARAMETER;
 157         }
 158         CAmount requiredFee = GetRequiredFee(maxNewTxSize);
 159         if (total_fee < requiredFee) {
 160             errors.push_back(strprintf("Insufficient totalFee (cannot be less than required fee %s)",
 161                                                                 FormatMoney(requiredFee)));
 162             return Result::INVALID_PARAMETER;
 163         }
 164         new_fee = total_fee;
 165         nNewFeeRate = CFeeRate(total_fee, maxNewTxSize);
 166     } else {
 167         new_fee = GetMinimumFee(maxNewTxSize, coin_control, mempool, ::feeEstimator, nullptr /* FeeCalculation */);
 168         nNewFeeRate = CFeeRate(new_fee, maxNewTxSize);
 169
 170         // New fee rate must be at least old rate + minimum incremental relay rate
 171         // walletIncrementalRelayFee.GetFeePerK() should be exact, because it's initialized
 172         // in that unit (fee per kb).
 173         // However, nOldFeeRate is a calculated value from the tx fee/size, so
 174         // add 1 satoshi to the result, because it may have been rounded down.
 175         if (nNewFeeRate.GetFeePerK() < nOldFeeRate.GetFeePerK() + 1 + walletIncrementalRelayFee.GetFeePerK()) {
 176             nNewFeeRate = CFeeRate(nOldFeeRate.GetFeePerK() + 1 + walletIncrementalRelayFee.GetFeePerK());
 177             new_fee = nNewFeeRate.GetFee(maxNewTxSize);
 178         }
 179     }
 180
 181     // Check that in all cases the new fee doesn't violate maxTxFee
 182      if (new_fee > maxTxFee) {
 183          errors.push_back(strprintf("Specified or calculated fee %s is too high (cannot be higher than maxTxFee %s)",
 184                                FormatMoney(new_fee), FormatMoney(maxTxFee)));
 185          return Result::WALLET_ERROR;
 186      }
 187
 188     // check that fee rate is higher than mempool's minimum fee
 189     // (no point in bumping fee if we know that the new tx won't be accepted to the mempool)
 190     // This may occur if the user set TotalFee or paytxfee too low, if fallbackfee is too low, or, perhaps,
 191     // in a rare situation where the mempool minimum fee increased significantly since the fee estimation just a
 192     // moment earlier. In this case, we report an error to the user, who may use total_fee to make an adjustment.
 193     CFeeRate minMempoolFeeRate = mempool.GetMinFee(gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000);
 194     if (nNewFeeRate.GetFeePerK() < minMempoolFeeRate.GetFeePerK()) {
 195         errors.push_back(strprintf(
 196             "New fee rate (%s) is lower than the minimum fee rate (%s) to get into the mempool -- "
 197             "the totalFee value should be at least %s or the settxfee value should be at least %s to add transaction",
 198             FormatMoney(nNewFeeRate.GetFeePerK()),
 199             FormatMoney(minMempoolFeeRate.GetFeePerK()),
 200             FormatMoney(minMempoolFeeRate.GetFee(maxNewTxSize)),
 201             FormatMoney(minMempoolFeeRate.GetFeePerK())));
 202         return Result::WALLET_ERROR;
 203     }
 204
 205     // Now modify the output to increase the fee.
 206     // If the output is not large enough to pay the fee, fail.
 207     CAmount nDelta = new_fee - old_fee;
 208     assert(nDelta > 0);
 209     mtx =  *wtx.tx;
 210     CTxOut* poutput = &(mtx.vout[nOutput]);
 211     if (poutput->nValue < nDelta) {
 212         errors.push_back("Change output is too small to bump the fee");
 213         return Result::WALLET_ERROR;
 214     }
 215
 216     // If the output would become dust, discard it (converting the dust to fee)
 217     poutput->nValue -= nDelta;
 218     if (poutput->nValue <= GetDustThreshold(*poutput, ::dustRelayFee)) {
 219         LogPrint(BCLog::RPC, "Bumping fee and discarding dust output\n");
 220         new_fee += poutput->nValue;
 221         mtx.vout.erase(mtx.vout.begin() + nOutput);
 222     }
 223
 224     // Mark new tx not replaceable, if requested.
 225     if (!coin_control.signalRbf) {
 226         for (auto& input : mtx.vin) {
 227             if (input.nSequence < 0xfffffffe) input.nSequence = 0xfffffffe;
 228         }
 229     }
 230
 231     return Result::OK;
 232 }
 233
 234 bool SignTransaction(CWallet* wallet, CMutableTransaction& mtx) {
 235     LOCK2(cs_main, wallet->cs_wallet);
 236     return wallet->SignTransaction(mtx);
 237 }
 238
 239 Result CommitTransaction(CWallet* wallet, const uint256& txid, CMutableTransaction&& mtx, std::vector<std::string>& errors, uint256& bumped_txid)
 240 {
 241     LOCK2(cs_main, wallet->cs_wallet);
 242     if (!errors.empty()) {
 243         return Result::MISC_ERROR;
 244     }
 245     auto it = txid.IsNull() ? wallet->mapWallet.end() : wallet->mapWallet.find(txid);
 246     if (it == wallet->mapWallet.end()) {
 247         errors.push_back("Invalid or non-wallet transaction id");
 248         return Result::MISC_ERROR;
 249     }
 250     CWalletTx& oldWtx = it->second;
 251
 252     // make sure the transaction still has no descendants and hasn't been mined in the meantime
 253     Result result = PreconditionChecks(wallet, oldWtx, errors);
 254     if (result != Result::OK) {
 255         return result;
 256     }
 257
 258     CWalletTx wtxBumped(wallet, MakeTransactionRef(std::move(mtx)));
 259     // commit/broadcast the tx
 260     CReserveKey reservekey(wallet);
 261     wtxBumped.mapValue = oldWtx.mapValue;
 262     wtxBumped.mapValue["replaces_txid"] = oldWtx.GetHash().ToString();
 263     wtxBumped.vOrderForm = oldWtx.vOrderForm;
 264     wtxBumped.strFromAccount = oldWtx.strFromAccount;
 265     wtxBumped.fTimeReceivedIsTxTime = true;
 266     wtxBumped.fFromMe = true;
 267     CValidationState state;
 268     if (!wallet->CommitTransaction(wtxBumped, reservekey, g_connman.get(), state)) {
 269         // NOTE: CommitTransaction never returns false, so this should never happen.
 270         errors.push_back(strprintf("The transaction was rejected: %s", state.GetRejectReason()));
 271         return Result::WALLET_ERROR;
 272     }
 273
 274     bumped_txid = wtxBumped.GetHash();
 275     if (state.IsInvalid()) {
 276         // This can happen if the mempool rejected the transaction.  Report
 277         // what happened in the "errors" response.
 278         errors.push_back(strprintf("Error: The transaction was rejected: %s", FormatStateMessage(state)));
 279     }
 280
 281     // mark the original tx as bumped
 282     if (!wallet->MarkReplaced(oldWtx.GetHash(), wtxBumped.GetHash())) {
 283         // TODO: see if JSON-RPC has a standard way of returning a response
 284         // along with an exception. It would be good to return information about
 285         // wtxBumped to the caller even if marking the original transaction
 286         // replaced does not succeed for some reason.
 287         errors.push_back("Created new bumpfee transaction but could not mark the original transaction as replaced");
 288     }
 289     return Result::OK;
 290 }
 291
 292 } // namespace feebumper
 293