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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 <vector>
15 : :
16 : : // Helper functions for serialization.
17 : : std::vector<unsigned char> BitsToBytes(const std::vector<bool>& bits);
18 : : std::vector<bool> BytesToBits(const std::vector<unsigned char>& bytes);
19 : :
20 : : /** Data structure that represents a partial merkle tree.
21 : : *
22 : : * It represents a subset of the txid's of a known block, in a way that
23 : : * allows recovery of the list of txid's and the merkle root, in an
24 : : * authenticated way.
25 : : *
26 : : * The encoding works as follows: we traverse the tree in depth-first order,
27 : : * storing a bit for each traversed node, signifying whether the node is the
28 : : * parent of at least one matched leaf txid (or a matched txid itself). In
29 : : * case we are at the leaf level, or this bit is 0, its merkle node hash is
30 : : * stored, and its children are not explored further. Otherwise, no hash is
31 : : * stored, but we recurse into both (or the only) child branch. During
32 : : * decoding, the same depth-first traversal is performed, consuming bits and
33 : : * hashes as they written during encoding.
34 : : *
35 : : * The serialization is fixed and provides a hard guarantee about the
36 : : * encoded size:
37 : : *
38 : : * SIZE <= 10 + ceil(32.25*N)
39 : : *
40 : : * Where N represents the number of leaf nodes of the partial tree. N itself
41 : : * is bounded by:
42 : : *
43 : : * N <= total_transactions
44 : : * N <= 1 + matched_transactions*tree_height
45 : : *
46 : : * The serialization format:
47 : : * - uint32 total_transactions (4 bytes)
48 : : * - varint number of hashes (1-3 bytes)
49 : : * - uint256[] hashes in depth-first order (<= 32*N bytes)
50 : : * - varint number of bytes of flag bits (1-3 bytes)
51 : : * - byte[] flag bits, packed per 8 in a byte, least significant bit first (<= 2*N-1 bits)
52 : : * The size constraints follow from this.
53 : : */
54 : : class CPartialMerkleTree
55 : : {
56 : : protected:
57 : : /** the total number of transactions in the block */
58 : : unsigned int nTransactions;
59 : :
60 : : /** node-is-parent-of-matched-txid bits */
61 : : std::vector<bool> vBits;
62 : :
63 : : /** txids and internal hashes */
64 : : std::vector<uint256> vHash;
65 : :
66 : : /** flag set when encountering invalid data */
67 : : bool fBad;
68 : :
69 : : /** helper function to efficiently calculate the number of nodes at given height in the merkle tree */
70 : 291977 : unsigned int CalcTreeWidth(int height) const {
71 : 291977 : return (nTransactions+(1 << height)-1) >> height;
72 : : }
73 : :
74 : : /** calculate the hash of a node in the merkle tree (at leaf level: the txid's themselves) */
75 : : uint256 CalcHash(int height, unsigned int pos, const std::vector<uint256> &vTxid);
76 : :
77 : : /** recursive function that traverses tree nodes, storing the data as bits and hashes */
78 : : void TraverseAndBuild(int height, unsigned int pos, const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch);
79 : :
80 : : /**
81 : : * recursive function that traverses tree nodes, consuming the bits and hashes produced by TraverseAndBuild.
82 : : * it returns the hash of the respective node and its respective index.
83 : : */
84 : : uint256 TraverseAndExtract(int height, unsigned int pos, unsigned int &nBitsUsed, unsigned int &nHashUsed, std::vector<uint256> &vMatch, std::vector<unsigned int> &vnIndex);
85 : :
86 : : public:
87 : :
88 : 8790 : SERIALIZE_METHODS(CPartialMerkleTree, obj)
89 : : {
90 : 2930 : READWRITE(obj.nTransactions, obj.vHash);
91 : 2930 : std::vector<unsigned char> bytes;
92 [ + + + + ]: 5654 : SER_WRITE(obj, bytes = BitsToBytes(obj.vBits));
93 [ + + + + ]: 2893 : READWRITE(bytes);
94 [ + - + - ]: 3044 : SER_READ(obj, obj.vBits = BytesToBits(bytes));
95 [ + + + + ]: 3044 : SER_READ(obj, obj.fBad = false);
96 : 2930 : }
97 : :
98 : : /** Construct a partial merkle tree from a list of transaction ids, and a mask that selects a subset of them */
99 : : CPartialMerkleTree(const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch);
100 : :
101 : : CPartialMerkleTree();
102 : :
103 : : /**
104 : : * extract the matching txid's represented by this partial merkle tree
105 : : * and their respective indices within the partial tree.
106 : : * returns the merkle root, or 0 in case of failure
107 : : */
108 : : uint256 ExtractMatches(std::vector<uint256> &vMatch, std::vector<unsigned int> &vnIndex);
109 : :
110 : : /** Get number of transactions the merkle proof is indicating for cross-reference with
111 : : * local blockchain knowledge.
112 : : */
113 : 237 : unsigned int GetNumTransactions() const { return nTransactions; };
114 : :
115 : : };
116 : :
117 : :
118 : : /**
119 : : * Used to relay blocks as header + vector<merkle branch>
120 : : * to filtered nodes.
121 : : *
122 : : * NOTE: The class assumes that the given CBlock has *at least* 1 transaction. If the CBlock has 0 txs, it will hit an assertion.
123 : : */
124 : : class CMerkleBlock
125 : : {
126 : : public:
127 : : /** Public only for unit testing */
128 : : CBlockHeader header;
129 : : CPartialMerkleTree txn;
130 : :
131 : : /**
132 : : * Public only for unit testing and relay testing (not relayed).
133 : : *
134 : : * Used only when a bloom filter is specified to allow
135 : : * testing the transactions which matched the bloom filter.
136 : : */
137 : : std::vector<std::pair<unsigned int, uint256> > vMatchedTxn;
138 : :
139 : : /**
140 : : * Create from a CBlock, filtering transactions according to filter
141 : : * Note that this will call IsRelevantAndUpdate on the filter for each transaction,
142 : : * thus the filter will likely be modified.
143 : : */
144 : 2658 : CMerkleBlock(const CBlock& block, CBloomFilter& filter) : CMerkleBlock(block, &filter, nullptr) { }
145 : :
146 : : // Create from a CBlock, matching the txids in the set
147 : 62 : CMerkleBlock(const CBlock& block, const std::set<uint256>& txids) : CMerkleBlock(block, nullptr, &txids) { }
148 : :
149 : 25861 : CMerkleBlock() {}
150 : :
151 : 8361 : SERIALIZE_METHODS(CMerkleBlock, obj) { READWRITE(obj.header, obj.txn); }
152 : :
153 : : private:
154 : : // Combined constructor to consolidate code
155 : : CMerkleBlock(const CBlock& block, CBloomFilter* filter, const std::set<uint256>* txids);
156 : : };
157 : :
158 : : #endif // BITCOIN_MERKLEBLOCK_H
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