Package org.bitcoinj.core

Class PartialMerkleTree

java.lang.Object
org.bitcoinj.core.PartialMerkleTree
public class PartialMerkleTree extends Object

A data structure that contains proofs of block inclusion for one or more transactions, in an efficient manner.

The encoding works as follows: we traverse the tree in depth-first order, storing a bit for each traversed node, signifying whether the node is the parent of at least one matched leaf txid (or a matched txid itself). In case we are at the leaf level, or this bit is 0, its merkle node hash is stored, and its children are not explored further. Otherwise, no hash is stored, but we recurse into both (or the only) child branch. During decoding, the same depth-first traversal is performed, consuming bits and hashes as they were written during encoding.

The serialization is fixed and provides a hard guarantee about the encoded size, SIZE <= 10 + ceil(32.25*N) where N represents the number of leaf nodes of the partial tree. N itself is bounded by:

N <= total_transactions
N <= 1 + matched_transactions*tree_height

The serialization format:

  - uint32     total_transactions (4 bytes)
  - varint     number of hashes   (1-3 bytes)
  - uint256[]  hashes in depth-first order (<= 32*N bytes)
  - varint     number of bytes of flag bits (1-3 bytes)
  - byte[]     flag bits, packed per 8 in a byte, least significant bit first (<= 2*N-1 bits)

The size constraints follow from this.

  • Constructor Details

    • PartialMerkleTree

      public PartialMerkleTree(int origTxCount, List<Sha256Hash> hashes, byte[] bits)
      Constructs a new PMT with the given bit set (little endian) and the raw list of hashes including internal hashes, taking ownership of the list.

  • Method Details

    • read

      public static PartialMerkleTree read(ByteBuffer payload) throws BufferUnderflowException, ProtocolException
      Deserialize a partial merkle tree 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

    • buildFromLeaves

      public static PartialMerkleTree buildFromLeaves(byte[] includeBits, List<Sha256Hash> allLeafHashes)
      Calculates a PMT given the list of leaf hashes and which leaves need to be included. The relevant interior hashes are calculated and a new PMT returned.

    • write

      public ByteBuffer write(ByteBuffer buf) throws BufferOverflowException
      Write this partial merkle tree into the given buffer.
      Parameters:
      buf - buffer to write into
      Returns:
      the buffer
      Throws:
      BufferOverflowException - if the partial merkle tree doesn't fit the remaining buffer

    • serialize

      public byte[] serialize()
      Allocates a byte array and writes this partial merkle tree into it.
      Returns:
      byte array containing the partial merkle tree

    • messageSize

      public int messageSize()
      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.
      Returns:
      size of the serialized message in bytes

    • getMessageSize

      @Deprecated public int getMessageSize()
      Deprecated.
      Use messageSize()

    • getTxnHashAndMerkleRoot

      public Sha256Hash getTxnHashAndMerkleRoot(List<Sha256Hash> matchedHashesOut) throws VerificationException
      Extracts tx hashes that are in this merkle tree and returns the merkle root of this tree. The returned root should be checked against the merkle root contained in the block header for security.
      Parameters:
      matchedHashesOut - A list which will contain the matched txn (will be cleared).
      Returns:
      the merkle root of this merkle tree
      Throws:
      ProtocolException - if this partial merkle tree is invalid
      VerificationException

    • getTransactionCount

      public int getTransactionCount()

    • equals

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

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object

    • toString

      public String toString()
      Overrides:
      toString in class Object