Package org.bitcoinj.core

Class AbstractBlockChain

  • Direct Known Subclasses:
    BlockChain, FullPrunedBlockChain
    public abstract class AbstractBlockChain
extends java.lang.Object

    An AbstractBlockChain holds a series of Block objects, links them together, and knows how to verify that the chain follows the rules of the NetworkParameters for this chain.

    It can be connected to a Wallet, and also TransactionReceivedInBlockListeners that can receive transactions and notifications of re-organizations.

    An AbstractBlockChain implementation must be connected to a BlockStore implementation. The chain object by itself doesn't store any data, that's delegated to the store. Which store you use is a decision best made by reading the getting started guide, but briefly, fully validating block chains need fully validating stores. In the lightweight SPV mode, a SPVBlockStore is the right choice.

    This class implements an abstract class which makes it simple to create a BlockChain that does/doesn't do full verification. It verifies headers and is implements most of what is required to implement SPV mode, but also provides callback hooks which can be used to do full verification.

    There are two subclasses of AbstractBlockChain that are useful: BlockChain, which is the simplest class and implements simplified payment verification. This is a lightweight and efficient mode that does not verify the contents of blocks, just their headers. A FullPrunedBlockChain paired with a MemoryFullPrunedBlockStore implements full verification, which is equivalent to Bitcoin Core. To learn more about the alternative security models, please consult the articles on the website.

    Theory

    The 'chain' is actually a tree although in normal operation it operates mostly as a list of Blocks. When multiple new head blocks are found simultaneously, there are multiple stories of the economy competing to become the one true consensus. This can happen naturally when two miners solve a block within a few seconds of each other, or it can happen when the chain is under attack.

    A reference to the head block of the best known chain is stored. If you can reach the genesis block by repeatedly walking through the prevBlock pointers, then we say this is a full chain. If you cannot reach the genesis block we say it is an orphan chain. Orphan chains can occur when blocks are solved and received during the initial block chain download, or if we connect to a peer that doesn't send us blocks in order.

    A reorganize occurs when the blocks that make up the best known chain change. Note that simply adding a new block to the top of the best chain isn't a reorganize, but that a reorganize is always triggered by adding a new block that connects to some other (non best head) block. By "best" we mean the chain representing the largest amount of work done.

    Every so often the block chain passes a difficulty transition point. At that time, all the blocks in the last 2016 blocks are examined and a new difficulty target is calculated from them.

    • Field Detail

      • lock

        protected final java.util.concurrent.locks.ReentrantLock lock
        synchronization lock

      • chainHead

        protected StoredBlock chainHead
        Tracks the top of the best known chain.

        Following this one down to the genesis block produces the story of the economy from the creation of Bitcoin until the present day. The chain head can change if a new set of blocks is received that results in a chain of greater work than the one obtained by following this one down. In that case a reorganize is triggered, potentially invalidating transactions in our wallet.

      • FP_ESTIMATOR_ALPHA

        public static final double FP_ESTIMATOR_ALPHA
        False positive estimation uses a double exponential moving average.
        See Also:
        Constant Field Values

      • FP_ESTIMATOR_BETA

        public static final double FP_ESTIMATOR_BETA
        False positive estimation uses a double exponential moving average.
        See Also:
        Constant Field Values

    • Constructor Detail

      • AbstractBlockChain

        public AbstractBlockChain​(NetworkParameters params,
                          java.util.List<? extends Wallet> wallets,
                          BlockStore blockStore)
                   throws BlockStoreException
        Constructs a BlockChain connected to the given list of listeners (wallets) and a store.
        Parameters:
        params - network parameters for this chain
        wallets - list of listeners (wallets)
        blockStore - where to store blocks
        Throws:
        BlockStoreException - if a failure occurs while storing a block

    • Method Detail

      • addWallet

        public final void addWallet​(Wallet wallet)
        Add a wallet to the BlockChain. Note that the wallet will be unaffected by any blocks received while it was not part of this BlockChain. This method is useful if the wallet has just been created, and its keys have never been in use, or if the wallet has been loaded along with the BlockChain. Note that adding multiple wallets is not well tested!
        Parameters:
        wallet - wallet to add

      • removeWallet

        public void removeWallet​(Wallet wallet)
        Remove a wallet from the chain.
        Parameters:
        wallet - wallet to remove

      • addNewBestBlockListener

        public final void addNewBestBlockListener​(java.util.concurrent.Executor executor,
                                          NewBestBlockListener listener)
        Adds a NewBestBlockListener listener to the chain.
        Parameters:
        executor - executor to listen on
        listener - listener to add

      • addReorganizeListener

        public void addReorganizeListener​(ReorganizeListener listener)
        Adds a generic ReorganizeListener listener to the chain.
        Parameters:
        listener - listener to add

      • addReorganizeListener

        public final void addReorganizeListener​(java.util.concurrent.Executor executor,
                                        ReorganizeListener listener)
        Adds a generic ReorganizeListener listener to the chain.
        Parameters:
        executor - executor to listen on
        listener - listener to add

      • removeNewBestBlockListener

        public void removeNewBestBlockListener​(NewBestBlockListener listener)
        Removes the given NewBestBlockListener from the chain.
        Parameters:
        listener - listener to remove

      • removeReorganizeListener

        public void removeReorganizeListener​(ReorganizeListener listener)
        Removes the given ReorganizeListener from the chain.
        Parameters:
        listener - listener to remove

      • getBlockStore

        public BlockStore getBlockStore()
        Returns the BlockStore the chain was constructed with. You can use this to iterate over the chain.
        Returns:
        the BlockStore the chain was constructed with

      • rollbackBlockStore

        protected abstract void rollbackBlockStore​(int height)
                                    throws BlockStoreException
        Rollback the block store to a given height. This is currently only supported by BlockChain instances.
        Parameters:
        height - height to roll back to
        Throws:
        BlockStoreException - if the operation fails or is unsupported.

      • doSetChainHead

        protected abstract void doSetChainHead​(StoredBlock chainHead)
                                throws BlockStoreException
        Called before setting chain head in memory. Should write the new head to block store and then commit any database transactions that were started by disconnectTransactions/connectTransactions.
        Parameters:
        chainHead - chain head to set
        Throws:
        BlockStoreException - if a failure occurs while storing a block

      • notSettingChainHead

        protected abstract void notSettingChainHead()
                                     throws BlockStoreException
        Called if we (possibly) previously called disconnectTransaction/connectTransactions, but will not be calling preSetChainHead as a block failed verification. Can be used to abort database transactions that were started by disconnectTransactions/connectTransactions.
        Throws:
        BlockStoreException - if a failure occurs while storing a block

      • getStoredBlockInCurrentScope

        protected abstract StoredBlock getStoredBlockInCurrentScope​(Sha256Hash hash)
                                                     throws BlockStoreException
        For a standard BlockChain, this should return blockStore.get(hash), for a FullPrunedBlockChain blockStore.getOnceUndoableStoredBlock(hash)
        Parameters:
        hash - hash of block to fetch
        Returns:
        block with matching hash
        Throws:
        BlockStoreException - if a failure occurs while storing a block

      • add

        public boolean add​(Block block)
            throws VerificationException,
                   PrunedException
        Processes a received block and tries to add it to the chain. If there's something wrong with the block an exception is thrown. If the block is OK but cannot be connected to the chain at this time, returns false. If the block can be connected to the chain, returns true. Accessing block's transactions in another thread while this method runs may result in undefined behavior.
        Parameters:
        block - block to add
        Returns:
        true if block can be connected, false if block is valid but can't be connected
        Throws:
        VerificationException - block is invalid or contains invalid transactions
        PrunedException - a reorg that is too-long for our stored block data has occurred

      • add

        public boolean add​(FilteredBlock block)
            throws VerificationException,
                   PrunedException
        Processes a received block and tries to add it to the chain. If there's something wrong with the block an exception is thrown. If the block is OK but cannot be connected to the chain at this time, returns false. If the block can be connected to the chain, returns true.
        Parameters:
        block - received block
        Returns:
        true if block can be connected, false if block is valid but can't be connected
        Throws:
        VerificationException - if invalid block
        PrunedException - a reorg that is too-long for our stored block data has occurred

      • shouldVerifyTransactions

        protected abstract boolean shouldVerifyTransactions()
        Whether or not we are maintaining a set of unspent outputs and are verifying all transactions. Also indicates that all calls to add() should provide a block containing transactions
        Returns:
        true if we are verifying all transactions

      • connectTransactions

        protected abstract TransactionOutputChanges connectTransactions​(int height,
                                                                Block block)
                                                         throws VerificationException,
                                                                BlockStoreException
        Connect each transaction in block.transactions, verifying them as we go and removing spent outputs If an error is encountered in a transaction, no changes should be made to the underlying BlockStore. and a VerificationException should be thrown. Only called if(shouldVerifyTransactions())
        Parameters:
        height - block height to attach at
        block - block to connect
        Returns:
        The full set of all changes made to the set of open transaction outputs.
        Throws:
        VerificationException - if an attempt was made to spend an already-spent output, or if a transaction incorrectly solved an output script.
        BlockStoreException - if the block store had an underlying error.

      • connectTransactions

        protected abstract TransactionOutputChanges connectTransactions​(StoredBlock newBlock)
                                                         throws VerificationException,
                                                                BlockStoreException,
                                                                PrunedException
        Load newBlock from BlockStore and connect its transactions, returning changes to the set of unspent transactions. If an error is encountered in a transaction, no changes should be made to the underlying BlockStore. Only called if(shouldVerifyTransactions())
        Parameters:
        newBlock - block to load
        Returns:
        The full set of all changes made to the set of open transaction outputs.
        Throws:
        PrunedException - if newBlock does not exist as a StoredUndoableBlock in the block store.
        VerificationException - if an attempt was made to spend an already-spent output, or if a transaction incorrectly solved an output script.
        BlockStoreException - if the block store had an underlying error or newBlock does not exist in the block store at all.

      • drainOrphanBlocks

        public java.util.Set<Sha256Hash> drainOrphanBlocks()
        Returns the hashes of the currently stored orphan blocks and then deletes them from this objects storage. Used by Peer when a filter exhaustion event has occurred and thus any orphan blocks that have been downloaded might be inaccurate/incomplete.
        Returns:
        hashes of deleted blocks

      • disconnectTransactions

        protected abstract void disconnectTransactions​(StoredBlock block)
                                        throws PrunedException,
                                               BlockStoreException
        Disconnect each transaction in the block (after reading it from the block store) Only called if(shouldVerifyTransactions())
        Parameters:
        block - block to disconnect
        Throws:
        PrunedException - if block does not exist as a StoredUndoableBlock in the block store.
        BlockStoreException - if the block store had an underlying error or block does not exist in the block store at all.

      • getBestChainHeight

        public final int getBestChainHeight()
        Returns:
        the height of the best known chain, convenience for getChainHead().getHeight().

      • getChainHead

        public StoredBlock getChainHead()
        Returns the block at the head of the current best chain. This is the block which represents the greatest amount of cumulative work done.
        Returns:
        block at the head of the current best chain

      • getOrphanRoot

        @Nullable
public Block getOrphanRoot​(Sha256Hash from)
        An orphan block is one that does not connect to the chain anywhere (ie we can't find its parent, therefore it's an orphan). Typically, this occurs when we are downloading the chain and didn't reach the head yet, and/or if a block is solved whilst we are downloading. It's possible that we see a small amount of orphan blocks which chain together, this method tries walking backwards through the known orphan blocks to find the bottom-most.
        Parameters:
        from - hash of block to walk backwards from
        Returns:
        from or one of froms parents, or null if "from" does not identify an orphan block

      • isOrphan

        public boolean isOrphan​(Sha256Hash block)
        Returns true if the given block is currently in the orphan blocks list.
        Parameters:
        block - block to check
        Returns:
        true if block is an orphan

      • estimateBlockTimeInstant

        public java.time.Instant estimateBlockTimeInstant​(int height)
        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).
        Parameters:
        height - block time to estimate
        Returns:
        estimated time block will be mined

      • getHeightFuture

        public ListenableCompletableFuture<StoredBlock> getHeightFuture​(int height)
        Returns a future that completes when the block chain has reached the given height. Yields the StoredBlock of the block that reaches that height first. The future completes on a peer thread.
        Parameters:
        height - desired height
        Returns:
        future that will complete when height is reached

      • getFalsePositiveRate

        public double getFalsePositiveRate()
        The false positive rate is the average over all blockchain transactions of: - 1.0 if the transaction was false-positive (was irrelevant to all listeners) - 0.0 if the transaction was relevant or filtered out
        Returns:
        the false positive rate

      • trackFilteredTransactions

        protected void trackFilteredTransactions​(int count)
        We completed handling of a filtered block. Update false-positive estimate based on the total number of transactions in the original block. count includes filtered transactions, transactions that were passed in and were relevant and transactions that were false positives (i.e. includes all transactions in the block).
        Parameters:
        count - total number of transactions in original block

      • resetFalsePositiveEstimate

        public void resetFalsePositiveEstimate()
        Resets estimates of false positives. Used when the filter is sent to the peer.

      • getVersionTally

        protected VersionTally getVersionTally()
        Returns:
        version tally (not thread safe!)