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Discourage fee sniping with nLockTime

This commit is contained in:
Peter Todd 2013-08-25 14:13:25 -04:00
parent fe36e031cd
commit ba7fcc8de0
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GPG Key ID: 2481403DA5F091FB
1 changed files with 27 additions and 1 deletions
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28
src/wallet.cpp
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@ -1347,6 +1347,28 @@ bool CWallet::CreateTransaction(const vector<pair<CScript, CAmount> >& vecSend,
wtxNew.BindWallet(this);
CMutableTransaction txNew;
// Discourage fee sniping.
//
// However because of a off-by-one-error in previous versions we need to
// neuter it by setting nLockTime to at least one less than nBestHeight.
// Secondly currently propagation of transactions created for block heights
// corresponding to blocks that were just mined may be iffy - transactions
// aren't re-accepted into the mempool - we additionally neuter the code by
// going ten blocks back. Doesn't yet do anything for sniping, but does act
// to shake out wallet bugs like not showing nLockTime'd transactions at
// all.
txNew.nLockTime = std::max(0, chainActive.Height() - 10);
// Secondly occasionally randomly pick a nLockTime even further back, so
// that transactions that are delayed after signing for whatever reason,
// e.g. high-latency mix networks and some CoinJoin implementations, have
// better privacy.
if (GetRandInt(10) == 0)
txNew.nLockTime = std::max(0, (int)txNew.nLockTime - GetRandInt(100));
assert(txNew.nLockTime <= (unsigned int)chainActive.Height());
assert(txNew.nLockTime < LOCKTIME_THRESHOLD);
{
LOCK2(cs_main, cs_wallet);
{
@ -1440,8 +1462,12 @@ bool CWallet::CreateTransaction(const vector<pair<CScript, CAmount> >& vecSend,
reservekey.ReturnKey();
// Fill vin
//
// Note how the sequence number is set to max()-1 so that the
// nLockTime set above actually works.
BOOST_FOREACH(const PAIRTYPE(const CWalletTx*,unsigned int)& coin, setCoins)
txNew.vin.push_back(CTxIn(coin.first->GetHash(),coin.second));
txNew.vin.push_back(CTxIn(coin.first->GetHash(),coin.second,CScript(),
std::numeric_limits<unsigned int>::max()-1));
// Sign
int nIn = 0;