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rpc: bumpfee: use correct maximum signed tx size for fee calculation

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More accurate than simply adding one byte per input, and properly handles the
case where the original transaction happened to have very small signatures
This commit is contained in:
Suhas Daftuar 2017-01-26 12:59:32 -05:00 committed by Suhas Daftuar
parent d625b907a1
commit f62659448c
1 changed files with 35 additions and 4 deletions
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39
src/wallet/rpcwallet.cpp
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@ -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)) {
@ -2769,9 +2796,9 @@ 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 +2872,12 @@ 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);
}
}