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Implement SequenceLocks functions

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SequenceLocks functions are used to evaluate sequence lock times or heights per BIP 68.

The majority of this code is copied from maaku in #6312
Further credit: btcdrak, sipa, NicolasDorier
This commit is contained in:
Alex Morcos
2015-12-07 15:44:16 -05:00
parent dc0305d15a
commit c6c2f0fd78
10 changed files with 300 additions and 49 deletions
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150
src/main.cpp
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@@ -667,9 +667,10 @@ bool IsFinalTx(const CTransaction &tx, int nBlockHeight, int64_t nBlockTime)
return true;
if ((int64_t)tx.nLockTime < ((int64_t)tx.nLockTime < LOCKTIME_THRESHOLD ? (int64_t)nBlockHeight : nBlockTime))
return true;
BOOST_FOREACH(const CTxIn& txin, tx.vin)
if (!txin.IsFinal())
BOOST_FOREACH(const CTxIn& txin, tx.vin) {
if (!(txin.nSequence == CTxIn::SEQUENCE_FINAL))
return false;
}
return true;
}
@@ -705,6 +706,128 @@ bool CheckFinalTx(const CTransaction &tx, int flags)
return IsFinalTx(tx, nBlockHeight, nBlockTime);
}
/**
* Calculates the block height and previous block's median time past at
* which the transaction will be considered final in the context of BIP 68.
* Also removes from the vector of input heights any entries which did not
* correspond to sequence locked inputs as they do not affect the calculation.
*/
static std::pair<int, int64_t> CalculateSequenceLocks(const CTransaction &tx, int flags, std::vector<int>* prevHeights, const CBlockIndex& block)
{
assert(prevHeights->size() == tx.vin.size());
// Will be set to the equivalent height- and time-based nLockTime
// values that would be necessary to satisfy all relative lock-
// time constraints given our view of block chain history.
// The semantics of nLockTime are the last invalid height/time, so
// use -1 to have the effect of any height or time being valid.
int nMinHeight = -1;
int64_t nMinTime = -1;
// tx.nVersion is signed integer so requires cast to unsigned otherwise
// we would be doing a signed comparison and half the range of nVersion
// wouldn't support BIP 68.
bool fEnforceBIP68 = static_cast<uint32_t>(tx.nVersion) >= 2
&& flags & LOCKTIME_VERIFY_SEQUENCE;
// Do not enforce sequence numbers as a relative lock time
// unless we have been instructed to
if (!fEnforceBIP68) {
return std::make_pair(nMinHeight, nMinTime);
}
for (size_t txinIndex = 0; txinIndex < tx.vin.size(); txinIndex++) {
const CTxIn& txin = tx.vin[txinIndex];
// Sequence numbers with the most significant bit set are not
// treated as relative lock-times, nor are they given any
// consensus-enforced meaning at this point.
if (txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_DISABLE_FLAG) {
// The height of this input is not relevant for sequence locks
(*prevHeights)[txinIndex] = 0;
continue;
}
int nCoinHeight = (*prevHeights)[txinIndex];
if (txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_TYPE_FLAG) {
int64_t nCoinTime = block.GetAncestor(std::max(nCoinHeight-1, 0))->GetMedianTimePast();
// NOTE: Subtract 1 to maintain nLockTime semantics
// BIP 68 relative lock times have the semantics of calculating
// the first block or time at which the transaction would be
// valid. When calculating the effective block time or height
// for the entire transaction, we switch to using the
// semantics of nLockTime which is the last invalid block
// time or height. Thus we subtract 1 from the calculated
// time or height.
// Time-based relative lock-times are measured from the
// smallest allowed timestamp of the block containing the
// txout being spent, which is the median time past of the
// block prior.
nMinTime = std::max(nMinTime, nCoinTime + (int64_t)((txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_MASK) << CTxIn::SEQUENCE_LOCKTIME_GRANULARITY) - 1);
} else {
nMinHeight = std::max(nMinHeight, nCoinHeight + (int)(txin.nSequence & CTxIn::SEQUENCE_LOCKTIME_MASK) - 1);
}
}
return std::make_pair(nMinHeight, nMinTime);
}
static bool EvaluateSequenceLocks(const CBlockIndex& block, std::pair<int, int64_t> lockPair)
{
assert(block.pprev);
int64_t nBlockTime = block.pprev->GetMedianTimePast();
if (lockPair.first >= block.nHeight || lockPair.second >= nBlockTime)
return false;
return true;
}
bool SequenceLocks(const CTransaction &tx, int flags, std::vector<int>* prevHeights, const CBlockIndex& block)
{
return EvaluateSequenceLocks(block, CalculateSequenceLocks(tx, flags, prevHeights, block));
}
bool CheckSequenceLocks(const CTransaction &tx, int flags)
{
AssertLockHeld(cs_main);
AssertLockHeld(mempool.cs);
CBlockIndex* tip = chainActive.Tip();
CBlockIndex index;
index.pprev = tip;
// CheckSequenceLocks() uses chainActive.Height()+1 to evaluate
// height based locks because when SequenceLocks() is called within
// CBlock::AcceptBlock(), the height of the block *being*
// evaluated is what is used. Thus if we want to know if a
// transaction can be part of the *next* block, we need to call
// SequenceLocks() with one more than chainActive.Height().
index.nHeight = tip->nHeight + 1;
// pcoinsTip contains the UTXO set for chainActive.Tip()
CCoinsViewMemPool viewMemPool(pcoinsTip, mempool);
std::vector<int> prevheights;
prevheights.resize(tx.vin.size());
for (size_t txinIndex = 0; txinIndex < tx.vin.size(); txinIndex++) {
const CTxIn& txin = tx.vin[txinIndex];
CCoins coins;
if (!viewMemPool.GetCoins(txin.prevout.hash, coins)) {
return error("%s: Missing input", __func__);
}
if (coins.nHeight == MEMPOOL_HEIGHT) {
// Assume all mempool transaction confirm in the next block
prevheights[txinIndex] = tip->nHeight + 1;
} else {
prevheights[txinIndex] = coins.nHeight;
}
}
std::pair<int, int64_t> lockPair = CalculateSequenceLocks(tx, flags, &prevheights, index);
return EvaluateSequenceLocks(index, lockPair);
}
unsigned int GetLegacySigOpCount(const CTransaction& tx)
{
unsigned int nSigOps = 0;
@@ -949,6 +1072,14 @@ bool AcceptToMemoryPoolWorker(CTxMemPool& pool, CValidationState &state, const C
// we have all inputs cached now, so switch back to dummy, so we don't need to keep lock on mempool
view.SetBackend(dummy);
// Only accept BIP68 sequence locked transactions that can be mined in the next
// block; we don't want our mempool filled up with transactions that can't
// be mined yet.
// Must keep pool.cs for this unless we change CheckSequenceLocks to take a
// CoinsViewCache instead of create its own
if (!CheckSequenceLocks(tx, STANDARD_LOCKTIME_VERIFY_FLAGS))
return state.DoS(0, false, REJECT_NONSTANDARD, "non-BIP68-final");
}
// Check for non-standard pay-to-script-hash in inputs
@@ -2075,6 +2206,8 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
CCheckQueueControl<CScriptCheck> control(fScriptChecks && nScriptCheckThreads ? &scriptcheckqueue : NULL);
std::vector<int> prevheights;
int nLockTimeFlags = 0;
CAmount nFees = 0;
int nInputs = 0;
unsigned int nSigOps = 0;
@@ -2098,6 +2231,19 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
return state.DoS(100, error("ConnectBlock(): inputs missing/spent"),
REJECT_INVALID, "bad-txns-inputs-missingorspent");
// Check that transaction is BIP68 final
// BIP68 lock checks (as opposed to nLockTime checks) must
// be in ConnectBlock because they require the UTXO set
prevheights.resize(tx.vin.size());
for (size_t j = 0; j < tx.vin.size(); j++) {
prevheights[j] = view.AccessCoins(tx.vin[j].prevout.hash)->nHeight;
}
if (!SequenceLocks(tx, nLockTimeFlags, &prevheights, *pindex)) {
return state.DoS(100, error("ConnectBlock(): contains a non-BIP68-final transaction", __func__),
REJECT_INVALID, "bad-txns-nonfinal");
}
if (fStrictPayToScriptHash)
{
// Add in sigops done by pay-to-script-hash inputs;