blockchain

Documentation

Index

• Constants
• Variables
• func BuildMerkleTreeStore(transactions []*qtumsuite.Tx, witness bool) []*chainhash.Hash
• func HashMerkleBranches(left *chainhash.Hash, right *chainhash.Hash) *chainhash.Hash

Constants

const (
	// CoinbaseWitnessDataLen is the required length of the only element within
	// the coinbase's witness data if the coinbase transaction contains a
	// witness commitment.
	CoinbaseWitnessDataLen = 32

	// CoinbaseWitnessPkScriptLength is the length of the public key script
	// containing an OP_RETURN, the WitnessMagicBytes, and the witness
	// commitment itself. In order to be a valid candidate for the output
	// containing the witness commitment
	CoinbaseWitnessPkScriptLength = 38
)

Variables

var (
	// WitnessMagicBytes is the prefix marker within the public key script
	// of a coinbase output to indicate that this output holds the witness
	// commitment for a block.
	WitnessMagicBytes = []byte{
		txscript.OP_RETURN,
		txscript.OP_DATA_36,
		0xaa,
		0x21,
		0xa9,
		0xed,
	}
)

Functions

func BuildMerkleTreeStore

func BuildMerkleTreeStore(transactions []*qtumsuite.Tx, witness bool) []*chainhash.Hash

BuildMerkleTreeStore creates a merkle tree from a slice of transactions, stores it using a linear array, and returns a slice of the backing array. A linear array was chosen as opposed to an actual tree structure since it uses about half as much memory. The following describes a merkle tree and how it is stored in a linear array.

A merkle tree is a tree in which every non-leaf node is the hash of its children nodes. A diagram depicting how this works for bitcoin transactions where h(x) is a double sha256 follows:

         root = h1234 = h(h12 + h34)
        /                           \
  h12 = h(h1 + h2)            h34 = h(h3 + h4)
   /            \              /            \
h1 = h(tx1)  h2 = h(tx2)    h3 = h(tx3)  h4 = h(tx4)

The above stored as a linear array is as follows:

[h1 h2 h3 h4 h12 h34 root]

As the above shows, the merkle root is always the last element in the array.

The number of inputs is not always a power of two which results in a balanced tree structure as above. In that case, parent nodes with no children are also zero and parent nodes with only a single left node are calculated by concatenating the left node with itself before hashing. Since this function uses nodes that are pointers to the hashes, empty nodes will be nil.

The additional bool parameter indicates if we are generating the merkle tree using witness transaction id's rather than regular transaction id's. This also presents an additional case wherein the wtxid of the coinbase transaction is the zeroHash.

func HashMerkleBranches

func HashMerkleBranches(left *chainhash.Hash, right *chainhash.Hash) *chainhash.Hash

HashMerkleBranches takes two hashes, treated as the left and right tree nodes, and returns the hash of their concatenation. This is a helper function used to aid in the generation of a merkle tree.