private void unCacheHeader() {
maybeParseHeader();
headerBytesValid = false;
if (!transactionBytesValid) bytes = null;
hash = null;
checksum = null;
}
private void checkTimestamp() throws VerificationException {
maybeParseHeader();
// Allow injection of a fake clock to allow unit testing.
long currentTime = fakeClock != 0 ? fakeClock : System.currentTimeMillis() / 1000;
if (time > currentTime + ALLOWED_TIME_DRIFT)
throw new VerificationException("Block too far in future");
}
/**
* Returns the difficulty target as a 320 bit value that can be compared to a scrypt hash. Inside
* a block the target is represented using a compact form. If this form decodes to a value that is
* out of bounds, an exception is thrown.
*/
public BigInteger getDifficultyTargetAsInteger() throws VerificationException {
maybeParseHeader();
BigInteger target = Utils.decodeCompactBits(difficultyTarget);
if (target.compareTo(BigInteger.ZERO) <= 0 || target.compareTo(params.proofOfWorkLimit) > 0)
throw new VerificationException(
"Difficulty target is bad: " + target.toString() + " or " + difficultyTarget);
return target;
}
/**
* In lazy parsing mode access to getters and setters may throw an unchecked LazyParseException.
* If guaranteed safe access is required this method will force parsing to occur immediately thus
* ensuring LazyParseExeption will never be thrown from this Message. If the Message contains
* child messages (e.g. a Block containing Transaction messages) this will not force child
* messages to parse.
*
* <p>This method ensures parsing of headers only.
*
* @throws ProtocolException
*/
public void ensureParsedHeader() throws ProtocolException {
try {
maybeParseHeader();
} catch (LazyParseException e) {
if (e.getCause() instanceof ProtocolException) throw (ProtocolException) e.getCause();
throw new ProtocolException(e);
}
}
/** Returns the merkle root in big endian form, calculating it from transactions if necessary. */
public Sha256Hash getMerkleRoot() {
maybeParseHeader();
if (merkleRoot == null) {
// TODO check if this is really necessary.
unCacheHeader();
merkleRoot = calculateMerkleRoot();
}
return merkleRoot;
}
/**
* Checks the block data to ensure it follows the rules laid out in the network parameters.
* Specifically, throws an exception if the proof of work is invalid, or if the timestamp is too
* far from what it should be. This is <b>not</b> everything that is required for a block to be
* valid, only what is checkable independent of the chain and without a transaction index.
*
* @throws VerificationException
*/
public void verifyHeader() throws VerificationException {
// Prove that this block is OK. It might seem that we can just ignore most of these checks given
// that the
// network is also verifying the blocks, but we cannot as it'd open us to a variety of obscure
// attacks.
//
// Firstly we need to ensure this block does in fact represent real work done. If the difficulty
// is high
// enough, it's probably been done by the network.
maybeParseHeader();
checkProofOfWork(true);
checkTimestamp();
}
/**
* Finds a value of nonce that makes the blocks hash lower than the difficulty target. This is
* called mining, but solve() is far too slow to do real mining with. It exists only for unit
* testing purposes and is not a part of the public API.
*
* <p>This can loop forever if a solution cannot be found solely by incrementing nonce. It doesn't
* change extraNonce.
*/
void solve() {
maybeParseHeader();
while (true) {
try {
// Is our proof of work valid yet?
if (checkProofOfWork(false)) return;
// No, so increment the nonce and try again.
setNonce(getNonce() + 1);
} catch (VerificationException e) {
throw new RuntimeException(e); // Cannot happen.
}
}
}
/** Returns a copy of the block, but without any transactions. */
public Block cloneAsHeader() {
maybeParseHeader();
Block block = new Block(params);
block.nonce = nonce;
block.prevBlockHash = prevBlockHash.duplicate();
block.merkleRoot = getMerkleRoot().duplicate();
block.version = version;
block.time = time;
block.difficultyTarget = difficultyTarget;
block.transactions = null;
block.hash = getHash().duplicate();
return block;
}
// default for testing
void writeHeader(OutputStream stream) throws IOException {
// try for cached write first
if (headerBytesValid && bytes != null && bytes.length >= offset + HEADER_SIZE) {
stream.write(bytes, offset, HEADER_SIZE);
return;
}
// fall back to manual write
maybeParseHeader();
Utils.uint32ToByteStreamLE(version, stream);
stream.write(Utils.reverseBytes(prevBlockHash.getBytes()));
stream.write(Utils.reverseBytes(getMerkleRoot().getBytes()));
Utils.uint32ToByteStreamLE(time, stream);
Utils.uint32ToByteStreamLE(difficultyTarget, stream);
Utils.uint32ToByteStreamLE(nonce, stream);
}
/**
* Returns the nonce, an arbitrary value that exists only to make the hash of the block header
* fall below the difficulty target.
*/
public long getNonce() {
maybeParseHeader();
return nonce;
}
/**
* Returns the difficulty of the proof of work that this block should meet encoded <b>in compact
* form</b>. The {@link BlockChain} verifies that this is not too easy by looking at the length of
* the chain when the block is added. To find the actual value the hash should be compared
* against, use {@link net.usecredits.credits.core.Block#getDifficultyTargetAsInteger()}. Note
* that this is <b>not</b> the same as the difficulty value reported by the Litecoin
* "getdifficulty" RPC that you may see on various block explorers. That number is the result of
* applying a formula to the underlying difficulty to normalize the minimum to 1. Calculating the
* difficulty that way is currently unsupported.
*/
public long getDifficultyTarget() {
maybeParseHeader();
return difficultyTarget;
}
/**
* Returns the time at which the block was solved and broadcast, according to the clock of the
* solving node. This is measured in seconds since the UNIX epoch (midnight Jan 1st 1970).
*/
public long getTimeSeconds() {
maybeParseHeader();
return time;
}
/** Returns the hash of the previous block in the chain, as defined by the block header. */
public Sha256Hash getPrevBlockHash() {
maybeParseHeader();
return prevBlockHash;
}
/** Returns the version of the block data structure as defined by the Litecoin protocol. */
public long getVersion() {
maybeParseHeader();
return version;
}
