Package org.bitcoinj.core

Class Block

  • public class Block
extends Message

    A block is a group of transactions, and is one of the fundamental data structures of the Bitcoin system. It records a set of Transactions together with some data that links it into a place in the global block chain, and proves that a difficult calculation was done over its contents. See the Bitcoin technical paper for more detail on blocks.

    To get a block, you can either build one from the raw bytes you can get from another implementation, or request one specifically using Peer.getBlock(Sha256Hash), or grab one from a downloaded BlockChain.

    Instances of this class are not safe for use by multiple threads.

    • Field Detail

      • HEADER_SIZE

        public static final int HEADER_SIZE
        How many bytes are required to represent a block header WITHOUT the trailing 00 length byte.
        See Also:
        Constant Field Values

      • MAX_BLOCK_SIZE

        public static final int MAX_BLOCK_SIZE
        A constant shared by the entire network: how large in bytes a block is allowed to be. One day we may have to upgrade everyone to change this, so Bitcoin can continue to grow. For now it exists as an anti-DoS measure to avoid somebody creating a titanically huge but valid block and forcing everyone to download/store it forever.
        See Also:
        Constant Field Values

      • MAX_BLOCK_SIGOPS

        public static final int MAX_BLOCK_SIGOPS
        A "sigop" is a signature verification operation. Because they're expensive we also impose a separate limit on the number in a block to prevent somebody mining a huge block that has way more sigops than normal, so is very expensive/slow to verify.
        See Also:
        Constant Field Values

      • STANDARD_MAX_DIFFICULTY_TARGET

        public static final long STANDARD_MAX_DIFFICULTY_TARGET
        Standard maximum value for difficultyTarget (nBits) (Bitcoin MainNet and TestNet)
        See Also:
        Constant Field Values

      • EASIEST_DIFFICULTY_TARGET

        public static final long EASIEST_DIFFICULTY_TARGET
        A value for difficultyTarget (nBits) that allows (slightly less than) half of all possible hash solutions. Used in unit testing.
        See Also:
        Constant Field Values

      • BLOCK_HEIGHT_UNKNOWN

        public static final int BLOCK_HEIGHT_UNKNOWN
        Value to use if the block height is unknown
        See Also:
        Constant Field Values

      • BLOCK_HEIGHT_GENESIS

        public static final int BLOCK_HEIGHT_GENESIS
        Height of the first block
        See Also:
        Constant Field Values

      • BLOCK_VERSION_BIP34

        public static final long BLOCK_VERSION_BIP34
        Block version introduced in BIP 34: Height in coinbase
        See Also:
        Constant Field Values

      • BLOCK_VERSION_BIP66

        public static final long BLOCK_VERSION_BIP66
        Block version introduced in BIP 66: Strict DER signatures
        See Also:
        Constant Field Values

      • BLOCK_VERSION_BIP65

        public static final long BLOCK_VERSION_BIP65
        Block version introduced in BIP 65: OP_CHECKLOCKTIMEVERIFY
        See Also:
        Constant Field Values

      • headerBytesValid

        protected boolean headerBytesValid

      • transactionBytesValid

        protected boolean transactionBytesValid

      • optimalEncodingMessageSize

        protected int optimalEncodingMessageSize

    • Constructor Detail

      • Block

        public Block​(NetworkParameters params,
             byte[] payloadBytes,
             MessageSerializer serializer,
             int length)
      throws ProtocolException
        Construct a block object from the Bitcoin wire format.
        Parameters:
        params - NetworkParameters object.
        payloadBytes - the payload to extract the block from.
        serializer - the serializer to use for this message.
        length - The length of message if known. Usually this is provided when deserializing of the wire as the length will be provided as part of the header. If unknown then set to Message.UNKNOWN_LENGTH
        Throws:
        ProtocolException

      • Block

        public Block​(NetworkParameters params,
             byte[] payloadBytes,
             int offset,
             MessageSerializer serializer,
             int length)
      throws ProtocolException
        Construct a block object from the Bitcoin wire format.
        Parameters:
        params - NetworkParameters object.
        payloadBytes - the payload to extract the block from.
        offset - The location of the first payload byte within the array.
        serializer - the serializer to use for this message.
        length - The length of message if known. Usually this is provided when deserializing of the wire as the length will be provided as part of the header. If unknown then set to Message.UNKNOWN_LENGTH
        Throws:
        ProtocolException

      • Block

        public Block​(NetworkParameters params,
             byte[] payloadBytes,
             int offset,
             @Nullable
             Message parent,
             MessageSerializer serializer,
             int length)
      throws ProtocolException
        Construct a block object from the Bitcoin wire format. Used in the case of a block contained within another message (i.e. for AuxPoW header).
        Parameters:
        params - NetworkParameters object.
        payloadBytes - Bitcoin protocol formatted byte array containing message content.
        offset - The location of the first payload byte within the array.
        parent - The message element which contains this block, maybe null for no parent.
        serializer - the serializer to use for this block.
        length - The length of message if known. Usually this is provided when deserializing of the wire as the length will be provided as part of the header. If unknown then set to Message.UNKNOWN_LENGTH
        Throws:
        ProtocolException

      • Block

        public Block​(NetworkParameters params,
             long version,
             Sha256Hash prevBlockHash,
             Sha256Hash merkleRoot,
             long time,
             long difficultyTarget,
             long nonce,
             java.util.List<Transaction> transactions)
        Construct a block initialized with all the given fields.
        Parameters:
        params - Which network the block is for.
        version - This should usually be set to 1 or 2, depending on if the height is in the coinbase input.
        prevBlockHash - Reference to previous block in the chain or Sha256Hash.ZERO_HASH if genesis.
        merkleRoot - The root of the merkle tree formed by the transactions.
        time - UNIX time when the block was mined.
        difficultyTarget - Number which this block hashes lower than.
        nonce - Arbitrary number to make the block hash lower than the target.
        transactions - List of transactions including the coinbase.

    • Method Detail

      • parseTransactions

        protected void parseTransactions​(int transactionsOffset)
                          throws ProtocolException
        Parse transactions from the block.
        Parameters:
        transactionsOffset - Offset of the transactions within the block. Useful for non-Bitcoin chains where the block header may not be a fixed size.
        Throws:
        ProtocolException

      • getOptimalEncodingMessageSize

        public int getOptimalEncodingMessageSize()

      • bitcoinSerialize

        public byte[] bitcoinSerialize()
        Special handling to check if we have a valid byte array for both header and transactions
        Overrides:
        bitcoinSerialize in class Message
        Returns:
        a freshly allocated serialized byte array

      • bitcoinSerializeToStream

        protected void bitcoinSerializeToStream​(java.io.OutputStream stream)
                                 throws java.io.IOException
        Description copied from class: Message
        Serializes this message to the provided stream. If you just want the raw bytes use bitcoinSerialize().
        Overrides:
        bitcoinSerializeToStream in class Message
        Throws:
        java.io.IOException

      • unCache

        protected void unCache()
        Description copied from class: Message

        To be called before any change of internal values including any setters. This ensures any cached byte array is removed.

        Child messages of this object(e.g. Transactions belonging to a Block) will not have their internal byte caches invalidated unless they are also modified internally.

        Overrides:
        unCache in class Message

      • getHashAsString

        public java.lang.String getHashAsString()
        Returns the hash of the block (which for a valid, solved block should be below the target) in the form seen on the block explorer. If you call this on block 1 in the mainnet chain you will get "00000000839a8e6886ab5951d76f411475428afc90947ee320161bbf18eb6048".

      • getHash

        public Sha256Hash getHash()
        Returns the hash of the block (which for a valid, solved block should be below the target). Big endian.
        Overrides:
        getHash in class Message

      • getWork

        public java.math.BigInteger getWork()
                             throws VerificationException
        Returns the work represented by this block.

        Work is defined as the number of tries needed to solve a block in the average case. Consider a difficulty target that covers 5% of all possible hash values. Then the work of the block will be 20. As the target gets lower, the amount of work goes up.

        Throws:
        VerificationException

      • cloneAsHeader

        public Block cloneAsHeader()
        Returns a copy of the block, but without any transactions.
        Returns:
        new, header-only Block

      • toString

        public java.lang.String toString()
        Returns a multi-line string containing a description of the contents of the block. Use for debugging purposes only.
        Overrides:
        toString in class java.lang.Object

      • solve

        public void solve()

        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.

        This can loop forever if a solution cannot be found solely by incrementing nonce. It doesn't change extraNonce.

      • getDifficultyTargetAsInteger

        public java.math.BigInteger getDifficultyTargetAsInteger()
                                                  throws VerificationException
        Returns the difficulty target as a 256 bit value that can be compared to a SHA-256 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.
        Throws:
        VerificationException

      • checkProofOfWork

        protected boolean checkProofOfWork​(boolean throwException)
                            throws VerificationException
        Returns true if the hash of the block is OK (lower than difficulty target).
        Throws:
        VerificationException

      • verifyHeader

        public void verifyHeader()
                  throws VerificationException
        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 not 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

      • verifyTransactions

        public void verifyTransactions​(int height,
                               java.util.EnumSet<Block.VerifyFlag> flags)
                        throws VerificationException
        Checks the block contents
        Parameters:
        height - block height, if known, or -1 otherwise. If valid, used to validate the coinbase input script of v2 and above blocks.
        flags - flags to indicate which tests should be applied (i.e. whether to test for height in the coinbase transaction).
        Throws:
        VerificationException - if there was an error verifying the block.

      • verify

        public void verify​(int height,
                   java.util.EnumSet<Block.VerifyFlag> flags)
            throws VerificationException
        Verifies both the header and that the transactions hash to the merkle root.
        Parameters:
        height - block height, if known, or -1 otherwise.
        flags - flags to indicate which tests should be applied (i.e. whether to test for height in the coinbase transaction).
        Throws:
        VerificationException - if there was an error verifying the block.

      • equals

        public boolean equals​(java.lang.Object o)
        Overrides:
        equals in class java.lang.Object

      • hashCode

        public int hashCode()
        Overrides:
        hashCode in class java.lang.Object

      • getMerkleRoot

        public Sha256Hash getMerkleRoot()
        Returns the merkle root in big endian form, calculating it from transactions if necessary.

      • getWitnessRoot

        public Sha256Hash getWitnessRoot()
        Returns the witness root in big endian form, calculating it from transactions if necessary.

      • addTransaction

        public void addTransaction​(Transaction t)
        Adds a transaction to this block. The nonce and merkle root are invalid after this.

      • getVersion

        public long getVersion()
        Returns the version of the block data structure as defined by the Bitcoin protocol.

      • getPrevBlockHash

        public Sha256Hash getPrevBlockHash()
        Returns the hash of the previous block in the chain, as defined by the block header.

      • getTimeSeconds

        public long getTimeSeconds()
        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).

      • getTime

        public java.util.Date getTime()
        Returns the time at which the block was solved and broadcast, according to the clock of the solving node.

      • setTime

        public void setTime​(long time)

      • getDifficultyTarget

        public long getDifficultyTarget()
        Returns the difficulty of the proof of work that this block should meet encoded in compact form. The 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 getDifficultyTargetAsInteger(). Note that this is not the same as the difficulty value reported by the Bitcoin "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.

      • setDifficultyTarget

        public void setDifficultyTarget​(long compactForm)
        Sets the difficulty target in compact form.

      • getNonce

        public long getNonce()
        Returns the nonce, an arbitrary value that exists only to make the hash of the block header fall below the difficulty target.

      • setNonce

        public void setNonce​(long nonce)
        Sets the nonce and clears any cached data.

      • getTransactions

        @Nullable
public java.util.List<Transaction> getTransactions()
        Returns an immutable list of transactions held in this block, or null if this object represents just a header.

      • createNextBlock

        public Block createNextBlock​(Address to,
                             long version,
                             long time,
                             int blockHeight)
        Returns a solved block that builds on top of this one. This exists for unit tests.

      • createNextBlock

        public Block createNextBlock​(@Nullable
                             Address to,
                             Coin value)

      • createNextBlock

        public Block createNextBlock​(@Nullable
                             Address to)

      • createNextBlockWithCoinbase

        public Block createNextBlockWithCoinbase​(long version,
                                         byte[] pubKey,
                                         Coin coinbaseValue,
                                         int height)

      • hasTransactions

        public boolean hasTransactions()
        Return whether this block contains any transactions.
        Returns:
        true if the block contains transactions, false otherwise (is purely a header).