private void putUpdateStoredBlock(StoredBlock storedBlock, boolean wasUndoable)
throws SQLException {
try {
PreparedStatement s =
conn.get()
.prepareStatement(
"INSERT INTO headers(hash, chainWork, height, header, wasUndoable)"
+ " VALUES(?, ?, ?, ?, ?)");
// We skip the first 4 bytes because (on prodnet) the minimum target has 4 0-bytes
byte[] hashBytes = new byte[28];
System.arraycopy(storedBlock.getHeader().getHash().getBytes(), 3, hashBytes, 0, 28);
s.setBytes(1, hashBytes);
s.setBytes(2, storedBlock.getChainWork().toByteArray());
s.setInt(3, storedBlock.getHeight());
s.setBytes(4, storedBlock.getHeader().unsafeRimbitSerialize());
s.setBoolean(5, wasUndoable);
s.executeUpdate();
s.close();
} catch (SQLException e) {
// It is possible we try to add a duplicate StoredBlock if we upgraded
// In that case, we just update the entry to mark it wasUndoable
if (!(e.getSQLState().equals(POSTGRES_DUPLICATE_KEY_ERROR_CODE)) || !wasUndoable) throw e;
PreparedStatement s =
conn.get().prepareStatement("UPDATE headers SET wasUndoable=? WHERE hash=?");
s.setBoolean(1, true);
// We skip the first 4 bytes because (on prodnet) the minimum target has 4 0-bytes
byte[] hashBytes = new byte[28];
System.arraycopy(storedBlock.getHeader().getHash().getBytes(), 3, hashBytes, 0, 28);
s.setBytes(2, hashBytes);
s.executeUpdate();
s.close();
}
}
/** Gets the median timestamp of the last 11 blocks */
private static long getMedianTimestampOfRecentBlocks(StoredBlock storedBlock, BlockStore store)
throws BlockStoreException {
long[] timestamps = new long[11];
int unused = 9;
timestamps[10] = storedBlock.getHeader().getTimeSeconds();
while (unused >= 0 && (storedBlock = storedBlock.getPrev(store)) != null)
timestamps[unused--] = storedBlock.getHeader().getTimeSeconds();
Arrays.sort(timestamps, unused + 1, 11);
return timestamps[unused + (11 - unused) / 2];
}
private synchronized boolean add(Block block, boolean tryConnecting)
throws BlockStoreException, VerificationException, ScriptException {
if (System.currentTimeMillis() - statsLastTime > 1000) {
// More than a second passed since last stats logging.
log.info("{} blocks per second", statsBlocksAdded);
statsLastTime = System.currentTimeMillis();
statsBlocksAdded = 0;
}
// We check only the chain head for double adds here to avoid potentially expensive block chain
// misses.
if (block.equals(chainHead.getHeader())) {
// Duplicate add of the block at the top of the chain, can be a natural artifact of the
// download process.
return true;
}
// Prove the block is internally valid: hash is lower than target, merkle root is correct and so
// on.
try {
block.verify();
} catch (VerificationException e) {
log.error("Failed to verify block:", e);
log.error(block.toString());
throw e;
}
// Try linking it to a place in the currently known blocks.
StoredBlock storedPrev = blockStore.get(block.getPrevBlockHash());
if (storedPrev == null) {
// We can't find the previous block. Probably we are still in the process of downloading the
// chain and a
// block was solved whilst we were doing it. We put it to one side and try to connect it later
// when we
// have more blocks.
log.warn("Block does not connect: {}", block.getHashAsString());
unconnectedBlocks.add(block);
return false;
} else {
// It connects to somewhere on the chain. Not necessarily the top of the best known chain.
//
// Create a new StoredBlock from this block. It will throw away the transaction data so when
// block goes
// out of scope we will reclaim the used memory.
StoredBlock newStoredBlock = storedPrev.build(block);
checkDifficultyTransitions(storedPrev, newStoredBlock);
blockStore.put(newStoredBlock);
// block.transactions may be null here if we received only a header and not a full block. This
// does not
// happen currently but might in future if getheaders is implemented.
connectBlock(newStoredBlock, storedPrev, block.transactions);
}
if (tryConnecting) tryConnectingUnconnected();
statsBlocksAdded++;
return true;
}
/**
* Returns an estimate of when the given block will be reached, assuming a perfect 10 minute
* average for each block. This is useful for turning transaction lock times into human readable
* times. Note that a height in the past will still be estimated, even though the time of solving
* is actually known (we won't scan backwards through the chain to obtain the right answer).
*/
public Date estimateBlockTime(int height) {
synchronized (chainHeadLock) {
long offset = height - chainHead.getHeight();
long headTime = chainHead.getHeader().getTimeSeconds();
long estimated =
(headTime * 1000) + (1000L * 30L * 1L * offset); // 2 blocks per minute
return new Date(estimated);
}
}
/** Constructs a BlockChain connected to the given list of listeners (eg, wallets) and a store. */
public AbstractBlockChain(
Context context, List<BlockChainListener> listeners, BlockStore blockStore)
throws BlockStoreException {
this.blockStore = blockStore;
chainHead = blockStore.getChainHead();
log.info("chain head is at height {}:\n{}", chainHead.getHeight(), chainHead.getHeader());
this.params = context.getParams();
this.listeners = new CopyOnWriteArrayList<ListenerRegistration<BlockChainListener>>();
for (BlockChainListener l : listeners) addListener(l, Threading.SAME_THREAD);
}
/**
* Constructs a BlockChain connected to the given wallet and store. To obtain a {@link Wallet} you
* can construct one from scratch, or you can deserialize a saved wallet from disk using {@link
* Wallet#loadFromFile(java.io.File)}
*
* <p>For the store you can use a {@link MemoryBlockStore} if you don't care about saving the
* downloaded data, or a {@link BoundedOverheadBlockStore} if you'd like to ensure fast startup
* the next time you run the program.
*/
public BlockChain(NetworkParameters params, Wallet wallet, BlockStore blockStore) {
try {
this.blockStore = blockStore;
chainHead = blockStore.getChainHead();
log.info("chain head is:\n{}", chainHead.getHeader());
} catch (BlockStoreException e) {
throw new RuntimeException(e);
}
this.params = params;
this.wallet = wallet;
}
/**
* Called as part of connecting a block when the new block results in a different chain having
* higher total work.
*/
private void handleNewBestChain(StoredBlock newChainHead)
throws BlockStoreException, VerificationException {
// This chain has overtaken the one we currently believe is best. Reorganize is required.
//
// Firstly, calculate the block at which the chain diverged. We only need to examine the
// chain from beyond this block to find differences.
StoredBlock splitPoint = findSplit(newChainHead, chainHead);
log.info("Re-organize after split at height {}", splitPoint.getHeight());
log.info("Old chain head: {}", chainHead.getHeader().getHashAsString());
log.info("New chain head: {}", newChainHead.getHeader().getHashAsString());
log.info("Split at block: {}", splitPoint.getHeader().getHashAsString());
// Then build a list of all blocks in the old part of the chain and the new part.
List<StoredBlock> oldBlocks = getPartialChain(chainHead, splitPoint);
List<StoredBlock> newBlocks = getPartialChain(newChainHead, splitPoint);
// Now inform the wallet. This is necessary so the set of currently active transactions (that we
// can spend)
// can be updated to take into account the re-organize. We might also have received new coins we
// didn't have
// before and our previous spends might have been undone.
wallet.reorganize(oldBlocks, newBlocks);
// Update the pointer to the best known block.
setChainHead(newChainHead);
}
@Override
public void setChainHead(StoredBlock chainHead) throws BlockStoreException {
final MappedByteBuffer buffer = this.buffer;
if (buffer == null) throw new BlockStoreException("Store closed");
lock.lock();
try {
lastChainHead = chainHead;
byte[] headHash = chainHead.getHeader().getHash().getBytes();
buffer.position(8);
buffer.put(headHash);
} finally {
lock.unlock();
}
}
public void setChainHead(StoredBlock chainHead) throws BlockStoreException {
Sha256Hash hash = chainHead.getHeader().getHash();
this.chainHeadHash = hash;
this.chainHeadBlock = chainHead;
maybeConnect();
try {
PreparedStatement s =
conn.get().prepareStatement("UPDATE settings SET value = ? WHERE name = ?");
s.setString(2, CHAIN_HEAD_SETTING);
s.setBytes(1, hash.getBytes());
s.executeUpdate();
s.close();
} catch (SQLException ex) {
throw new BlockStoreException(ex);
}
}
public void setVerifiedChainHead(StoredBlock chainHead) throws BlockStoreException {
Sha256Hash hash = chainHead.getHeader().getHash();
this.verifiedChainHeadHash = hash;
this.verifiedChainHeadBlock = chainHead;
maybeConnect();
try {
PreparedStatement s =
conn.get().prepareStatement("UPDATE settings SET value = ? WHERE name = ?");
s.setString(2, VERIFIED_CHAIN_HEAD_SETTING);
s.setBytes(1, hash.getBytes());
s.executeUpdate();
s.close();
} catch (SQLException ex) {
throw new BlockStoreException(ex);
}
if (this.chainHeadBlock.getHeight() < chainHead.getHeight()) setChainHead(chainHead);
removeUndoableBlocksWhereHeightIsLessThan(chainHead.getHeight() - fullStoreDepth);
}
private void connectBlock(
StoredBlock newStoredBlock, StoredBlock storedPrev, List<Transaction> newTransactions)
throws BlockStoreException, VerificationException {
if (storedPrev.equals(chainHead)) {
// This block connects to the best known block, it is a normal continuation of the system.
setChainHead(newStoredBlock);
log.trace("Chain is now {} blocks high", chainHead.getHeight());
if (newTransactions != null)
sendTransactionsToWallet(newStoredBlock, NewBlockType.BEST_CHAIN, newTransactions);
} else {
// This block connects to somewhere other than the top of the best known chain. We treat these
// differently.
//
// Note that we send the transactions to the wallet FIRST, even if we're about to re-organize
// this block
// to become the new best chain head. This simplifies handling of the re-org in the Wallet
// class.
boolean haveNewBestChain = newStoredBlock.moreWorkThan(chainHead);
if (haveNewBestChain) {
log.info("Block is causing a re-organize");
} else {
StoredBlock splitPoint = findSplit(newStoredBlock, chainHead);
String splitPointHash = splitPoint != null ? splitPoint.getHeader().getHashAsString() : "?";
log.info(
"Block forks the chain at {}, but it did not cause a reorganize:\n{}",
splitPointHash,
newStoredBlock);
}
// We may not have any transactions if we received only a header. That never happens today but
// will in
// future when getheaders is used as an optimization.
if (newTransactions != null) {
sendTransactionsToWallet(newStoredBlock, NewBlockType.SIDE_CHAIN, newTransactions);
}
if (haveNewBestChain) handleNewBestChain(newStoredBlock);
}
}
@Override
public void put(StoredBlock block) throws BlockStoreException {
final MappedByteBuffer buffer = this.buffer;
if (buffer == null) throw new BlockStoreException("Store closed");
lock.lock();
try {
int cursor = getRingCursor(buffer);
if (cursor == getFileSize()) {
// Wrapped around.
cursor = FILE_PROLOGUE_BYTES;
}
buffer.position(cursor);
Sha256Hash hash = block.getHeader().getHash();
notFoundCache.remove(hash);
buffer.put(hash.getBytes());
block.serializeCompact(buffer);
setRingCursor(buffer, buffer.position());
blockCache.put(hash, block);
} finally {
lock.unlock();
}
}
/**
* Called as part of connecting a block when the new block results in a different chain having
* higher total work.
*
* <p>if (shouldVerifyTransactions) Either newChainHead needs to be in the block store as a
* FullStoredBlock, or (block != null && block.transactions != null)
*/
private void handleNewBestChain(
StoredBlock storedPrev, StoredBlock newChainHead, Block block, boolean expensiveChecks)
throws BlockStoreException, VerificationException, PrunedException {
checkState(lock.isHeldByCurrentThread());
// This chain has overtaken the one we currently believe is best. Reorganize is required.
//
// Firstly, calculate the block at which the chain diverged. We only need to examine the
// chain from beyond this block to find differences.
StoredBlock head = getChainHead();
final StoredBlock splitPoint = findSplit(newChainHead, head, blockStore);
log.info("Re-organize after split at height {}", splitPoint.getHeight());
log.info("Old chain head: {}", head.getHeader().getHashAsString());
log.info("New chain head: {}", newChainHead.getHeader().getHashAsString());
log.info("Split at block: {}", splitPoint.getHeader().getHashAsString());
// Then build a list of all blocks in the old part of the chain and the new part.
final LinkedList<StoredBlock> oldBlocks = getPartialChain(head, splitPoint, blockStore);
final LinkedList<StoredBlock> newBlocks = getPartialChain(newChainHead, splitPoint, blockStore);
// Disconnect each transaction in the previous main chain that is no longer in the new main
// chain
StoredBlock storedNewHead = splitPoint;
if (shouldVerifyTransactions()) {
for (StoredBlock oldBlock : oldBlocks) {
try {
disconnectTransactions(oldBlock);
} catch (PrunedException e) {
// We threw away the data we need to re-org this deep! We need to go back to a peer with
// full
// block contents and ask them for the relevant data then rebuild the indexs. Or we could
// just
// give up and ask the human operator to help get us unstuck (eg, rescan from the genesis
// block).
// TODO: Retry adding this block when we get a block with hash e.getHash()
throw e;
}
}
StoredBlock cursor;
// Walk in ascending chronological order.
for (Iterator<StoredBlock> it = newBlocks.descendingIterator(); it.hasNext(); ) {
cursor = it.next();
Block cursorBlock = cursor.getHeader();
if (expensiveChecks
&& cursorBlock.getTimeSeconds()
<= getMedianTimestampOfRecentBlocks(cursor.getPrev(blockStore), blockStore))
throw new VerificationException("Block's timestamp is too early during reorg");
TransactionOutputChanges txOutChanges;
if (cursor != newChainHead || block == null) txOutChanges = connectTransactions(cursor);
else txOutChanges = connectTransactions(newChainHead.getHeight(), block);
storedNewHead = addToBlockStore(storedNewHead, cursorBlock.cloneAsHeader(), txOutChanges);
}
} else {
// (Finally) write block to block store
storedNewHead = addToBlockStore(storedPrev, newChainHead.getHeader());
}
// Now inform the listeners. This is necessary so the set of currently active transactions (that
// we can spend)
// can be updated to take into account the re-organize. We might also have received new coins we
// didn't have
// before and our previous spends might have been undone.
for (final ListenerRegistration<BlockChainListener> registration : listeners) {
if (registration.executor == Threading.SAME_THREAD) {
// Short circuit the executor so we can propagate any exceptions.
// TODO: Do we really need to do this or should it be irrelevant?
registration.listener.reorganize(splitPoint, oldBlocks, newBlocks);
} else {
registration.executor.execute(
new Runnable() {
@Override
public void run() {
try {
registration.listener.reorganize(splitPoint, oldBlocks, newBlocks);
} catch (VerificationException e) {
log.error("Block chain listener threw exception during reorg", e);
}
}
});
}
}
// Update the pointer to the best known block.
setChainHead(storedNewHead);
}
// expensiveChecks enables checks that require looking at blocks further back in the chain
// than the previous one when connecting (eg median timestamp check)
// It could be exposed, but for now we just set it to shouldVerifyTransactions()
private void connectBlock(
final Block block,
StoredBlock storedPrev,
boolean expensiveChecks,
@Nullable final List<Sha256Hash> filteredTxHashList,
@Nullable final Map<Sha256Hash, Transaction> filteredTxn)
throws BlockStoreException, VerificationException, PrunedException {
checkState(lock.isHeldByCurrentThread());
boolean filtered = filteredTxHashList != null && filteredTxn != null;
// Check that we aren't connecting a block that fails a checkpoint check
if (!params.passesCheckpoint(storedPrev.getHeight() + 1, block.getHash()))
throw new VerificationException(
"Block failed checkpoint lockin at " + (storedPrev.getHeight() + 1));
if (shouldVerifyTransactions()) {
checkNotNull(block.transactions);
for (Transaction tx : block.transactions)
if (!tx.isFinal(storedPrev.getHeight() + 1, block.getTimeSeconds()))
throw new VerificationException("Block contains non-final transaction");
}
StoredBlock head = getChainHead();
if (storedPrev.equals(head)) {
if (filtered && filteredTxn.size() > 0) {
log.debug(
"Block {} connects to top of best chain with {} transaction(s) of which we were sent {}",
block.getHashAsString(),
filteredTxHashList.size(),
filteredTxn.size());
for (Sha256Hash hash : filteredTxHashList) log.debug(" matched tx {}", hash);
}
if (expensiveChecks
&& block.getTimeSeconds() <= getMedianTimestampOfRecentBlocks(head, blockStore))
throw new VerificationException("Block's timestamp is too early");
// This block connects to the best known block, it is a normal continuation of the system.
TransactionOutputChanges txOutChanges = null;
if (shouldVerifyTransactions())
txOutChanges = connectTransactions(storedPrev.getHeight() + 1, block);
StoredBlock newStoredBlock =
addToBlockStore(
storedPrev, block.transactions == null ? block : block.cloneAsHeader(), txOutChanges);
setChainHead(newStoredBlock);
log.debug("Chain is now {} blocks high, running listeners", newStoredBlock.getHeight());
informListenersForNewBlock(
block, NewBlockType.BEST_CHAIN, filteredTxHashList, filteredTxn, newStoredBlock);
} else {
// This block connects to somewhere other than the top of the best known chain. We treat these
// differently.
//
// Note that we send the transactions to the wallet FIRST, even if we're about to re-organize
// this block
// to become the new best chain head. This simplifies handling of the re-org in the Wallet
// class.
StoredBlock newBlock = storedPrev.build(block);
boolean haveNewBestChain = newBlock.moreWorkThan(head);
if (haveNewBestChain) {
log.info("Block is causing a re-organize");
} else {
StoredBlock splitPoint = findSplit(newBlock, head, blockStore);
if (splitPoint != null && splitPoint.equals(newBlock)) {
// newStoredBlock is a part of the same chain, there's no fork. This happens when we
// receive a block
// that we already saw and linked into the chain previously, which isn't the chain head.
// Re-processing it is confusing for the wallet so just skip.
log.warn(
"Saw duplicated block in main chain at height {}: {}",
newBlock.getHeight(),
newBlock.getHeader().getHash());
return;
}
if (splitPoint == null) {
// This should absolutely never happen
// (lets not write the full block to disk to keep any bugs which allow this to happen
// from writing unreasonable amounts of data to disk)
throw new VerificationException("Block forks the chain but splitPoint is null");
} else {
// We aren't actually spending any transactions (yet) because we are on a fork
addToBlockStore(storedPrev, block);
int splitPointHeight = splitPoint.getHeight();
String splitPointHash = splitPoint.getHeader().getHashAsString();
log.info(
"Block forks the chain at height {}/block {}, but it did not cause a reorganize:\n{}",
splitPointHeight,
splitPointHash,
newBlock.getHeader().getHashAsString());
}
}
// We may not have any transactions if we received only a header, which can happen during fast
// catchup.
// If we do, send them to the wallet but state that they are on a side chain so it knows not
// to try and
// spend them until they become activated.
if (block.transactions != null || filtered) {
informListenersForNewBlock(
block, NewBlockType.SIDE_CHAIN, filteredTxHashList, filteredTxn, newBlock);
}
if (haveNewBestChain) handleNewBestChain(storedPrev, newBlock, block, expensiveChecks);
}
}
public void put(StoredBlock storedBlock, StoredUndoableBlock undoableBlock)
throws BlockStoreException {
maybeConnect();
// We skip the first 4 bytes because (on prodnet) the minimum target has 4 0-bytes
byte[] hashBytes = new byte[28];
System.arraycopy(storedBlock.getHeader().getHash().getBytes(), 3, hashBytes, 0, 28);
int height = storedBlock.getHeight();
byte[] transactions = null;
byte[] txOutChanges = null;
try {
ByteArrayOutputStream bos = new ByteArrayOutputStream();
if (undoableBlock.getTxOutChanges() != null) {
undoableBlock.getTxOutChanges().serializeToStream(bos);
txOutChanges = bos.toByteArray();
} else {
int numTxn = undoableBlock.getTransactions().size();
bos.write((int) (0xFF & (numTxn >> 0)));
bos.write((int) (0xFF & (numTxn >> 8)));
bos.write((int) (0xFF & (numTxn >> 16)));
bos.write((int) (0xFF & (numTxn >> 24)));
for (Transaction tx : undoableBlock.getTransactions()) tx.rimbitSerialize(bos);
transactions = bos.toByteArray();
}
bos.close();
} catch (IOException e) {
throw new BlockStoreException(e);
}
try {
if (log.isDebugEnabled())
log.debug("Looking for undoable block with hash: " + Utils.bytesToHexString(hashBytes));
PreparedStatement findS =
conn.get().prepareStatement("select 1 from undoableBlocks where hash = ?");
findS.setBytes(1, hashBytes);
ResultSet rs = findS.executeQuery();
if (rs.next()) {
// We already have this output, update it.
findS.close();
// Postgres insert-or-updates are very complex (and finnicky). This level of transaction
// isolation
// seems to work for rimbitj
PreparedStatement s =
conn.get()
.prepareStatement(
"UPDATE undoableBlocks SET txOutChanges=?, transactions=?" + " WHERE hash = ?");
s.setBytes(3, hashBytes);
if (log.isDebugEnabled())
log.debug("Updating undoable block with hash: " + Utils.bytesToHexString(hashBytes));
if (transactions == null) {
s.setBytes(1, txOutChanges);
s.setNull(2, Types.BINARY);
} else {
s.setNull(1, Types.BINARY);
s.setBytes(2, transactions);
}
s.executeUpdate();
s.close();
return;
}
PreparedStatement s =
conn.get()
.prepareStatement(
"INSERT INTO undoableBlocks(hash, height, txOutChanges, transactions)"
+ " VALUES(?, ?, ?, ?)");
s.setBytes(1, hashBytes);
s.setInt(2, height);
if (log.isDebugEnabled())
log.debug(
"Inserting undoable block with hash: "
+ Utils.bytesToHexString(hashBytes)
+ " at height "
+ height);
if (transactions == null) {
s.setBytes(3, txOutChanges);
s.setNull(4, Types.BINARY);
} else {
s.setNull(3, Types.BINARY);
s.setBytes(4, transactions);
}
s.executeUpdate();
s.close();
try {
putUpdateStoredBlock(storedBlock, true);
} catch (SQLException e) {
throw new BlockStoreException(e);
}
} catch (SQLException e) {
if (!e.getSQLState().equals(POSTGRES_DUPLICATE_KEY_ERROR_CODE))
throw new BlockStoreException(e);
}
}
/** Throws an exception if the blocks difficulty is not correct. */
private void checkDifficultyTransitions(StoredBlock storedPrev, StoredBlock storedNext)
throws BlockStoreException, VerificationException {
Block prev = storedPrev.getHeader();
Block next = storedNext.getHeader();
// Is this supposed to be a difficulty transition point?
if ((storedPrev.getHeight() + 1) % params.interval != 0) {
// No ... so check the difficulty didn't actually change.
if (next.getDifficultyTarget() != prev.getDifficultyTarget())
throw new VerificationException(
"Unexpected change in difficulty at height "
+ storedPrev.getHeight()
+ ": "
+ Long.toHexString(next.getDifficultyTarget())
+ " vs "
+ Long.toHexString(prev.getDifficultyTarget()));
return;
}
// We need to find a block far back in the chain. It's OK that this is expensive because it only
// occurs every
// two weeks after the initial block chain download.
long now = System.currentTimeMillis();
StoredBlock cursor = blockStore.get(prev.getHash());
for (int i = 0; i < params.interval - 1; i++) {
if (cursor == null) {
// This should never happen. If it does, it means we are following an incorrect or busted
// chain.
throw new VerificationException(
"Difficulty transition point but we did not find a way back to the genesis block.");
}
cursor = blockStore.get(cursor.getHeader().getPrevBlockHash());
}
log.info("Difficulty transition traversal took {}msec", System.currentTimeMillis() - now);
Block blockIntervalAgo = cursor.getHeader();
int timespan = (int) (prev.getTime() - blockIntervalAgo.getTime());
// Limit the adjustment step.
if (timespan < params.targetTimespan / 4) timespan = params.targetTimespan / 4;
if (timespan > params.targetTimespan * 4) timespan = params.targetTimespan * 4;
BigInteger newDifficulty = Utils.decodeCompactBits(blockIntervalAgo.getDifficultyTarget());
newDifficulty = newDifficulty.multiply(BigInteger.valueOf(timespan));
newDifficulty = newDifficulty.divide(BigInteger.valueOf(params.targetTimespan));
if (newDifficulty.compareTo(params.proofOfWorkLimit) > 0) {
log.warn("Difficulty hit proof of work limit: {}", newDifficulty.toString(16));
newDifficulty = params.proofOfWorkLimit;
}
int accuracyBytes = (int) (next.getDifficultyTarget() >>> 24) - 3;
BigInteger receivedDifficulty = next.getDifficultyTargetAsInteger();
// The calculated difficulty is to a higher precision than received, so reduce here.
BigInteger mask = BigInteger.valueOf(0xFFFFFFL).shiftLeft(accuracyBytes * 8);
newDifficulty = newDifficulty.and(mask);
if (newDifficulty.compareTo(receivedDifficulty) != 0)
throw new VerificationException(
"Network provided difficulty bits do not match what was calculated: "
+ receivedDifficulty.toString(16)
+ " vs "
+ newDifficulty.toString(16));
}