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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2021 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_MERKLEBLOCK_H
#define BITCOIN_MERKLEBLOCK_H
#include <common/bloom.h>
#include <primitives/block.h>
#include <serialize.h>
#include <uint256.h>
#include <set>
#include <vector>
// Helper functions for serialization.
std::vector<unsigned char> BitsToBytes(const std::vector<bool>& bits);
std::vector<bool> BytesToBits(const std::vector<unsigned char>& bytes);
/** Data structure that represents a partial merkle tree.
*
* It represents a subset of the txid's of a known block, in a way that
* allows recovery of the list of txid's and the merkle root, in an
* authenticated way.
*
* 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 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.
*/
class CPartialMerkleTree
{
protected:
/** the total number of transactions in the block */
unsigned int nTransactions;
/** node-is-parent-of-matched-txid bits */
std::vector<bool> vBits;
/** txids and internal hashes */
std::vector<uint256> vHash;
/** flag set when encountering invalid data */
bool fBad;
/** helper function to efficiently calculate the number of nodes at given height in the merkle tree */
unsigned int CalcTreeWidth(int height) const {
return (nTransactions+(1 << height)-1) >> height;
}
/** calculate the hash of a node in the merkle tree (at leaf level: the txid's themselves) */
uint256 CalcHash(int height, unsigned int pos, const std::vector<uint256> &vTxid);
/** recursive function that traverses tree nodes, storing the data as bits and hashes */
void TraverseAndBuild(int height, unsigned int pos, const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch);
/**
* recursive function that traverses tree nodes, consuming the bits and hashes produced by TraverseAndBuild.
* it returns the hash of the respective node and its respective index.
*/
uint256 TraverseAndExtract(int height, unsigned int pos, unsigned int &nBitsUsed, unsigned int &nHashUsed, std::vector<uint256> &vMatch, std::vector<unsigned int> &vnIndex);
public:
SERIALIZE_METHODS(CPartialMerkleTree, obj)
{
READWRITE(obj.nTransactions, obj.vHash);
std::vector<unsigned char> bytes;
SER_WRITE(obj, bytes = BitsToBytes(obj.vBits));
READWRITE(bytes);
SER_READ(obj, obj.vBits = BytesToBits(bytes));
SER_READ(obj, obj.fBad = false);
}
/** Construct a partial merkle tree from a list of transaction ids, and a mask that selects a subset of them */
CPartialMerkleTree(const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch);
CPartialMerkleTree();
/**
* extract the matching txid's represented by this partial merkle tree
* and their respective indices within the partial tree.
* returns the merkle root, or 0 in case of failure
*/
uint256 ExtractMatches(std::vector<uint256> &vMatch, std::vector<unsigned int> &vnIndex);
/** Get number of transactions the merkle proof is indicating for cross-reference with
* local blockchain knowledge.
*/
unsigned int GetNumTransactions() const { return nTransactions; };
};
/**
* Used to relay blocks as header + vector<merkle branch>
* to filtered nodes.
*
* NOTE: The class assumes that the given CBlock has *at least* 1 transaction. If the CBlock has 0 txs, it will hit an assertion.
*/
class CMerkleBlock
{
public:
/** Public only for unit testing */
CBlockHeader header;
CPartialMerkleTree txn;
/**
* Public only for unit testing and relay testing (not relayed).
*
* Used only when a bloom filter is specified to allow
* testing the transactions which matched the bloom filter.
*/
std::vector<std::pair<unsigned int, uint256> > vMatchedTxn;
/**
* Create from a CBlock, filtering transactions according to filter
* Note that this will call IsRelevantAndUpdate on the filter for each transaction,
* thus the filter will likely be modified.
*/
CMerkleBlock(const CBlock& block, CBloomFilter& filter) : CMerkleBlock(block, &filter, nullptr) { }
// Create from a CBlock, matching the txids in the set
CMerkleBlock(const CBlock& block, const std::set<Txid>& txids) : CMerkleBlock{block, nullptr, &txids} {}
CMerkleBlock() {}
SERIALIZE_METHODS(CMerkleBlock, obj) { READWRITE(obj.header, obj.txn); }
private:
// Combined constructor to consolidate code
CMerkleBlock(const CBlock& block, CBloomFilter* filter, const std::set<Txid>* txids);
};
#endif // BITCOIN_MERKLEBLOCK_H
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