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Merge bitcoin/bitcoin#18096: doc: IsFinalTx comment about nSequence & OP_CLTV

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f9e37f33ce doc: IsFinalTx comment about nSequence & OP_CLTV (Yuval Kogman)

Pull request description:

  It's somewhat surprising that a transaction's `nLockTime` field is ignored
  when all `nSequence` fields are final, so this change aims to clarify this
  behavior and cross reference relevant details of `OP_CHECKLOCKTIMEVERIFY`.

ACKs for top commit:
  MarcoFalke:
    ACK f9e37f33ce

Tree-SHA512: 88460dacbe4b8115fb1948715f09b21d4f34ba1da9e88d52f0b774a969f845e9eddc5940e7fee66eacdd3062dc40d6d44c3f282b0e5144411fd47eb2320b44f5
This commit is contained in:
MarcoFalke 2021-06-30 09:43:16 +02:00
commit e1a13f12e1
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2 changed files with 12 additions and 3 deletions
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9
src/consensus/tx_verify.cpp
View file

@ -20,6 +20,15 @@ bool IsFinalTx(const CTransaction &tx, int nBlockHeight, int64_t nBlockTime)
return true; return true;
if ((int64_t)tx.nLockTime < ((int64_t)tx.nLockTime < LOCKTIME_THRESHOLD ? (int64_t)nBlockHeight : nBlockTime)) if ((int64_t)tx.nLockTime < ((int64_t)tx.nLockTime < LOCKTIME_THRESHOLD ? (int64_t)nBlockHeight : nBlockTime))
return true; return true;
// Even if tx.nLockTime isn't satisfied by nBlockHeight/nBlockTime, a
// transaction is still considered final if all inputs' nSequence ==
// SEQUENCE_FINAL (0xffffffff), in which case nLockTime is ignored.
//
// Because of this behavior OP_CHECKLOCKTIMEVERIFY/CheckLockTime() will
// also check that the spending input's nSequence != SEQUENCE_FINAL,
// ensuring that an unsatisfied nLockTime value will actually cause
// IsFinalTx() to return false here:
for (const auto& txin : tx.vin) { for (const auto& txin : tx.vin) {
if (!(txin.nSequence == CTxIn::SEQUENCE_FINAL)) if (!(txin.nSequence == CTxIn::SEQUENCE_FINAL))
return false; return false;

6
src/script/interpreter.cpp
View file

@ -1740,9 +1740,9 @@ bool GenericTransactionSignatureChecker<T>::CheckLockTime(const CScriptNum& nLoc
if (nLockTime > (int64_t)txTo->nLockTime) if (nLockTime > (int64_t)txTo->nLockTime)
return false; return false;
// Finally the nLockTime feature can be disabled and thus // Finally the nLockTime feature can be disabled in IsFinalTx()
// CHECKLOCKTIMEVERIFY bypassed if every txin has been // and thus CHECKLOCKTIMEVERIFY bypassed if every txin has
// finalized by setting nSequence to maxint. The // been finalized by setting nSequence to maxint. The
// transaction would be allowed into the blockchain, making // transaction would be allowed into the blockchain, making
// the opcode ineffective. // the opcode ineffective.
// //