1  // Copyright (c) 2009-2010 Satoshi Nakamoto
  2  // Copyright (c) 2009-2021 The Bitcoin Core developers
  3  // Distributed under the MIT software license, see the accompanying
  4  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  5  
  6  #ifndef BITCOIN_MERKLEBLOCK_H
  7  #define BITCOIN_MERKLEBLOCK_H
  8  
  9  #include <common/bloom.h>
 10  #include <primitives/block.h>
 11  #include <serialize.h>
 12  #include <uint256.h>
 13  
 14  #include <set>
 15  #include <vector>
 16  
 17  // Helper functions for serialization.
 18  std::vector<unsigned char> BitsToBytes(const std::vector<bool>& bits);
 19  std::vector<bool> BytesToBits(const std::vector<unsigned char>& bytes);
 20  
 21  /** Data structure that represents a partial merkle tree.
 22   *
 23   * It represents a subset of the txid's of a known block, in a way that
 24   * allows recovery of the list of txid's and the merkle root, in an
 25   * authenticated way.
 26   *
 27   * The encoding works as follows: we traverse the tree in depth-first order,
 28   * storing a bit for each traversed node, signifying whether the node is the
 29   * parent of at least one matched leaf txid (or a matched txid itself). In
 30   * case we are at the leaf level, or this bit is 0, its merkle node hash is
 31   * stored, and its children are not explored further. Otherwise, no hash is
 32   * stored, but we recurse into both (or the only) child branch. During
 33   * decoding, the same depth-first traversal is performed, consuming bits and
 34   * hashes as they written during encoding.
 35   *
 36   * The serialization is fixed and provides a hard guarantee about the
 37   * encoded size:
 38   *
 39   *   SIZE <= 10 + ceil(32.25*N)
 40   *
 41   * Where N represents the number of leaf nodes of the partial tree. N itself
 42   * is bounded by:
 43   *
 44   *   N <= total_transactions
 45   *   N <= 1 + matched_transactions*tree_height
 46   *
 47   * The serialization format:
 48   *  - uint32     total_transactions (4 bytes)
 49   *  - varint     number of hashes   (1-3 bytes)
 50   *  - uint256[]  hashes in depth-first order (<= 32*N bytes)
 51   *  - varint     number of bytes of flag bits (1-3 bytes)
 52   *  - byte[]     flag bits, packed per 8 in a byte, least significant bit first (<= 2*N-1 bits)
 53   * The size constraints follow from this.
 54   */
 55  class CPartialMerkleTree
 56  {
 57  protected:
 58      /** the total number of transactions in the block */
 59      unsigned int nTransactions;
 60  
 61      /** node-is-parent-of-matched-txid bits */
 62      std::vector<bool> vBits;
 63  
 64      /** txids and internal hashes */
 65      std::vector<uint256> vHash;
 66  
 67      /** flag set when encountering invalid data */
 68      bool fBad;
 69  
 70      /** helper function to efficiently calculate the number of nodes at given height in the merkle tree */
 71      unsigned int CalcTreeWidth(int height) const {
 72          return (nTransactions+(1 << height)-1) >> height;
 73      }
 74  
 75      /** calculate the hash of a node in the merkle tree (at leaf level: the txid's themselves) */
 76      uint256 CalcHash(int height, unsigned int pos, const std::vector<uint256> &vTxid);
 77  
 78      /** recursive function that traverses tree nodes, storing the data as bits and hashes */
 79      void TraverseAndBuild(int height, unsigned int pos, const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch);
 80  
 81      /**
 82       * recursive function that traverses tree nodes, consuming the bits and hashes produced by TraverseAndBuild.
 83       * it returns the hash of the respective node and its respective index.
 84       */
 85      uint256 TraverseAndExtract(int height, unsigned int pos, unsigned int &nBitsUsed, unsigned int &nHashUsed, std::vector<uint256> &vMatch, std::vector<unsigned int> &vnIndex);
 86  
 87  public:
 88  
 89      SERIALIZE_METHODS(CPartialMerkleTree, obj)
 90      {
 91          READWRITE(obj.nTransactions, obj.vHash);
 92          std::vector<unsigned char> bytes;
 93          SER_WRITE(obj, bytes = BitsToBytes(obj.vBits));
 94          READWRITE(bytes);
 95          SER_READ(obj, obj.vBits = BytesToBits(bytes));
 96          SER_READ(obj, obj.fBad = false);
 97      }
 98  
 99      /** Construct a partial merkle tree from a list of transaction ids, and a mask that selects a subset of them */
100      CPartialMerkleTree(const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch);
101  
102      CPartialMerkleTree();
103  
104      /**
105       * extract the matching txid's represented by this partial merkle tree
106       * and their respective indices within the partial tree.
107       * returns the merkle root, or 0 in case of failure
108       */
109      uint256 ExtractMatches(std::vector<uint256> &vMatch, std::vector<unsigned int> &vnIndex);
110  
111      /** Get number of transactions the merkle proof is indicating for cross-reference with
112       * local blockchain knowledge.
113       */
114      unsigned int GetNumTransactions() const { return nTransactions; };
115  
116  };
117  
118  
119  /**
120   * Used to relay blocks as header + vector<merkle branch>
121   * to filtered nodes.
122   *
123   * NOTE: The class assumes that the given CBlock has *at least* 1 transaction. If the CBlock has 0 txs, it will hit an assertion.
124   */
125  class CMerkleBlock
126  {
127  public:
128      /** Public only for unit testing */
129      CBlockHeader header;
130      CPartialMerkleTree txn;
131  
132      /**
133       * Public only for unit testing and relay testing (not relayed).
134       *
135       * Used only when a bloom filter is specified to allow
136       * testing the transactions which matched the bloom filter.
137       */
138      std::vector<std::pair<unsigned int, uint256> > vMatchedTxn;
139  
140      /**
141       * Create from a CBlock, filtering transactions according to filter
142       * Note that this will call IsRelevantAndUpdate on the filter for each transaction,
143       * thus the filter will likely be modified.
144       */
145      CMerkleBlock(const CBlock& block, CBloomFilter& filter) : CMerkleBlock(block, &filter, nullptr) { }
146  
147      // Create from a CBlock, matching the txids in the set
148      CMerkleBlock(const CBlock& block, const std::set<Txid>& txids) : CMerkleBlock{block, nullptr, &txids} {}
149  
150      CMerkleBlock() {}
151  
152      SERIALIZE_METHODS(CMerkleBlock, obj) { READWRITE(obj.header, obj.txn); }
153  
154  private:
155      // Combined constructor to consolidate code
156      CMerkleBlock(const CBlock& block, CBloomFilter* filter, const std::set<Txid>* txids);
157  };
158  
159  #endif // BITCOIN_MERKLEBLOCK_H