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validation: Add minimum witness commitment size constant

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Per BIP 141, the witness commitment structure is atleast 38 bytes,
OP_RETURN (0x6a) + 36 (0x24) + 4 byte header (0xaa21a9ed) + 32 byte
SHA256 hash. It can be longer, however any additional data has no
consensus meaning.
This commit is contained in:
fanquake 2020-04-26 20:01:46 +08:00
parent ba348dbc51
commit 06442549f8
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2 changed files with 11 additions and 2 deletions
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11
src/validation.cpp
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@ -3386,7 +3386,14 @@ int GetWitnessCommitmentIndex(const CBlock& block)
int commitpos = -1;
if (!block.vtx.empty()) {
for (size_t o = 0; o < block.vtx[0]->vout.size(); o++) {
if (block.vtx[0]->vout[o].scriptPubKey.size() >= 38 && block.vtx[0]->vout[o].scriptPubKey[0] == OP_RETURN && block.vtx[0]->vout[o].scriptPubKey[1] == 0x24 && block.vtx[0]->vout[o].scriptPubKey[2] == 0xaa && block.vtx[0]->vout[o].scriptPubKey[3] == 0x21 && block.vtx[0]->vout[o].scriptPubKey[4] == 0xa9 && block.vtx[0]->vout[o].scriptPubKey[5] == 0xed) {
const CTxOut& vout = block.vtx[0]->vout[o];
if (vout.scriptPubKey.size() >= MINIMUM_WITNESS_COMMITMENT &&
vout.scriptPubKey[0] == OP_RETURN &&
vout.scriptPubKey[1] == 0x24 &&
vout.scriptPubKey[2] == 0xaa &&
vout.scriptPubKey[3] == 0x21 &&
vout.scriptPubKey[4] == 0xa9 &&
vout.scriptPubKey[5] == 0xed) {
commitpos = o;
}
}
@ -3417,7 +3424,7 @@ std::vector<unsigned char> GenerateCoinbaseCommitment(CBlock& block, const CBloc
CHash256().Write(witnessroot.begin(), 32).Write(ret.data(), 32).Finalize(witnessroot.begin());
CTxOut out;
out.nValue = 0;
out.scriptPubKey.resize(38);
out.scriptPubKey.resize(MINIMUM_WITNESS_COMMITMENT);
out.scriptPubKey[0] = OP_RETURN;
out.scriptPubKey[1] = 0x24;
out.scriptPubKey[2] = 0xaa;

2
src/validation.h
View file

@ -92,6 +92,8 @@ static const unsigned int DEFAULT_CHECKLEVEL = 3;
// one 128MB block file + added 15% undo data = 147MB greater for a total of 545MB
// Setting the target to >= 550 MiB will make it likely we can respect the target.
static const uint64_t MIN_DISK_SPACE_FOR_BLOCK_FILES = 550 * 1024 * 1024;
/** Minimum size of a witness commitment structure. Defined in BIP 141. **/
static constexpr size_t MINIMUM_WITNESS_COMMITMENT{38};
struct BlockHasher
{