Package org.bitcoinj.core

Class Block

java.lang.Object
org.bitcoinj.core.BaseMessage
org.bitcoinj.core.Block
All Implemented Interfaces:
Message
public class Block extends BaseMessage

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 Details

    • 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:

    • 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:

    • 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:

    • STANDARD_MAX_DIFFICULTY_TARGET

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

    • 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:

    • BLOCK_HEIGHT_UNKNOWN

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

    • BLOCK_HEIGHT_GENESIS

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

    • BLOCK_VERSION_GENESIS

      public static final long BLOCK_VERSION_GENESIS
      See Also:

    • BLOCK_VERSION_BIP34

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

    • BLOCK_VERSION_BIP66

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

    • BLOCK_VERSION_BIP65

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

  • Constructor Details

    • Block

      public Block(long version, Sha256Hash prevBlockHash, Sha256Hash merkleRoot, Instant time, long difficultyTarget, long nonce, @Nullable List<Transaction> transactions)
      Construct a block initialized with all the given fields.
      Parameters:
      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 - 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, or null for header-only blocks

    • Block

      @Deprecated public Block(long version, Sha256Hash prevBlockHash, Sha256Hash merkleRoot, long time, long difficultyTarget, long nonce, @Nullable List<Transaction> transactions)
      Deprecated.
      use Block(long, Sha256Hash, Sha256Hash, Instant, long, long, List)
      Construct a block initialized with all the given fields.
      Parameters:
      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 seconds 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, or null for header-only blocks

  • Method Details

    • read

      public static Block read(ByteBuffer payload) throws BufferUnderflowException, ProtocolException
      Deserialize this message from a given payload.
      Parameters:
      payload - payload to deserialize from
      Returns:
      read message
      Throws:
      BufferUnderflowException - if the read message extends beyond the remaining bytes of the payload
      ProtocolException

    • createGenesis

      public static Block createGenesis(Instant time, long difficultyTarget)

    • createGenesis

      public static Block createGenesis(Instant time, long difficultyTarget, long nonce)

    • messageSize

      public int messageSize()
      Description copied from class: BaseMessage
      Return the size of the serialized message. Note that if the message was deserialized from a payload, this size can differ from the size of the original payload.
      Specified by:
      messageSize in interface Message
      Overrides:
      messageSize in class BaseMessage
      Returns:
      size of this object when serialized (in bytes)

    • bitcoinSerializeToStream

      protected void bitcoinSerializeToStream(OutputStream stream) throws IOException
      Description copied from class: BaseMessage
      Serializes this message to the provided stream. If you just want the raw bytes use BaseMessage.serialize().
      Specified by:
      bitcoinSerializeToStream in class BaseMessage
      Throws:
      IOException

    • unCache

      protected void unCache()

    • getHashAsString

      public 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.

    • getWork

      public 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 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 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 BigInteger getDifficultyTargetAsInteger()
      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.
      Returns:
      difficulty target as 256-bit value

    • checkProofOfWork

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

    • equals

      public boolean equals(Object o)
      Overrides:
      equals in class Object

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class 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.

    • time

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

    • getTimeSeconds

      @Deprecated public long getTimeSeconds()
      Deprecated.
      use time()
      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

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

    • 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.

    • 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.

    • getTransactions

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

    • createNextBlock

      public Block createNextBlock(@Nullable Address to, long version, Instant time, int height)
      Returns a solved block that builds on top of this one. This exists for unit tests.
      Parameters:
      to - if not null, 50 coins are sent to the address
      version - version of the block to create
      time - time of the block to create
      height - block height if known, or -1 otherwise
      Returns:
      created block

    • createNextBlock

      public Block createNextBlock(@Nullable Address to, TransactionOutPoint prevOut)
      This method is intended for test use only.
      Parameters:
      to - if not null, 50 coins are sent to the address
      prevOut - previous output to spend by the "50 coins transaction"
      Returns:
      created block

    • createNextBlock

      public Block createNextBlock(@Nullable Address to, Coin coinbaseValue)
      This method is intended for test use only.
      Parameters:
      to - if not null, 50 coins are sent to the address
      coinbaseValue - for the coinbase
      Returns:
      created block

    • createNextBlock

      public Block createNextBlock(@Nullable Address to)
      This method is intended for test use only.
      Parameters:
      to - if not null, 50 coins are sent to the address
      Returns:
      created block

    • createNextBlockWithCoinbase

      public Block createNextBlockWithCoinbase(long version, byte[] pubKey, Coin coinbaseValue, int height)
      This method is intended for test use only.
      Parameters:
      version - version of the block to create
      pubKey - for the coinbase
      coinbaseValue - for the coinbase
      height - block height if known, or -1 otherwise
      Returns:
      created block

    • hasTransactions

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

    • isBIP34

      public boolean isBIP34()
      Returns whether this block conforms to BIP34: Height in Coinbase.

    • isBIP66

      public boolean isBIP66()
      Returns whether this block conforms to BIP66: Strict DER signatures.

    • isBIP65

      public boolean isBIP65()
      Returns whether this block conforms to BIP65: OP_CHECKLOCKTIMEVERIFY.

    • verify

      public static void verify(NetworkParameters params, Block block, int height, EnumSet<Block.VerifyFlag> flags) throws VerificationException
      Verifies both the header and that the transactions hash to the merkle root.
      Parameters:
      params - parameters for the verification rules
      block - block to verify
      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 at least one of the rules is violated

    • verifyHeader

      public static void verifyHeader(Block block) 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.
      Parameters:
      block - block to verify
      Throws:
      VerificationException - if at least one of the rules is violated

    • verifyTransactions

      public static void verifyTransactions(NetworkParameters params, Block block, int height, EnumSet<Block.VerifyFlag> flags) throws VerificationException
      Checks the block contents
      Parameters:
      params - parameters for the verification rules
      block - block to verify
      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 at least one of the rules is violated