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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 <primitives/transaction_identifier.h>
12 : : #include <serialize.h>
13 : : #include <uint256.h>
14 : :
15 : : #include <set>
16 : : #include <vector>
17 : :
18 : : // Helper functions for serialization.
19 : : std::vector<unsigned char> BitsToBytes(const std::vector<bool>& bits);
20 : : std::vector<bool> BytesToBits(const std::vector<unsigned char>& bytes);
21 : :
22 : : /** Data structure that represents a partial merkle tree.
23 : : *
24 : : * It represents a subset of the txid's of a known block, in a way that
25 : : * allows recovery of the list of txid's and the merkle root, in an
26 : : * authenticated way.
27 : : *
28 : : * The encoding works as follows: we traverse the tree in depth-first order,
29 : : * storing a bit for each traversed node, signifying whether the node is the
30 : : * parent of at least one matched leaf txid (or a matched txid itself). In
31 : : * case we are at the leaf level, or this bit is 0, its merkle node hash is
32 : : * stored, and its children are not explored further. Otherwise, no hash is
33 : : * stored, but we recurse into both (or the only) child branch. During
34 : : * decoding, the same depth-first traversal is performed, consuming bits and
35 : : * hashes as they written during encoding.
36 : : *
37 : : * The serialization is fixed and provides a hard guarantee about the
38 : : * encoded size:
39 : : *
40 : : * SIZE <= 10 + ceil(32.25*N)
41 : : *
42 : : * Where N represents the number of leaf nodes of the partial tree. N itself
43 : : * is bounded by:
44 : : *
45 : : * N <= total_transactions
46 : : * N <= 1 + matched_transactions*tree_height
47 : : *
48 : : * The serialization format:
49 : : * - uint32 total_transactions (4 bytes)
50 : : * - varint number of hashes (1-3 bytes)
51 : : * - uint256[] hashes in depth-first order (<= 32*N bytes)
52 : : * - varint number of bytes of flag bits (1-3 bytes)
53 : : * - byte[] flag bits, packed per 8 in a byte, least significant bit first (<= 2*N-1 bits)
54 : : * The size constraints follow from this.
55 : : */
56 : 2376 : class CPartialMerkleTree
57 : : {
58 : : protected:
59 : : /** the total number of transactions in the block */
60 : : unsigned int nTransactions;
61 : :
62 : : /** node-is-parent-of-matched-txid bits */
63 : : std::vector<bool> vBits;
64 : :
65 : : /** txids and internal hashes */
66 : : std::vector<uint256> vHash;
67 : :
68 : : /** flag set when encountering invalid data */
69 : : bool fBad;
70 : :
71 : : /** helper function to efficiently calculate the number of nodes at given height in the merkle tree */
72 : 524950 : unsigned int CalcTreeWidth(int height) const {
73 [ + + + + : 524950 : return (nTransactions+(1 << height)-1) >> height;
+ + + + +
+ ]
74 : : }
75 : :
76 : : /** calculate the hash of a node in the merkle tree (at leaf level: the txid's themselves) */
77 : : uint256 CalcHash(int height, unsigned int pos, const std::vector<Txid> &vTxid);
78 : :
79 : : /** recursive function that traverses tree nodes, storing the data as bits and hashes */
80 : : void TraverseAndBuild(int height, unsigned int pos, const std::vector<Txid> &vTxid, const std::vector<bool> &vMatch);
81 : :
82 : : /**
83 : : * recursive function that traverses tree nodes, consuming the bits and hashes produced by TraverseAndBuild.
84 : : * it returns the hash of the respective node and its respective index.
85 : : */
86 : : uint256 TraverseAndExtract(int height, unsigned int pos, unsigned int &nBitsUsed, unsigned int &nHashUsed, std::vector<Txid> &vMatch, std::vector<unsigned int> &vnIndex);
87 : :
88 : : public:
89 : :
90 : 2455 : SERIALIZE_METHODS(CPartialMerkleTree, obj)
91 : : {
92 : 1921 : READWRITE(obj.nTransactions, obj.vHash);
93 : 1860 : std::vector<unsigned char> bytes;
94 [ # # ]: 4952 : SER_WRITE(obj, bytes = BitsToBytes(obj.vBits));
[ + + + - ]
95 : 1830 : READWRITE(bytes);
96 [ + - ]: 2398 : SER_READ(obj, obj.vBits = BytesToBits(bytes));
97 : 1830 : SER_READ(obj, obj.fBad = false);
98 : 1830 : }
99 : :
100 : : /** Construct a partial merkle tree from a list of transaction ids, and a mask that selects a subset of them */
101 : : CPartialMerkleTree(const std::vector<Txid> &vTxid, const std::vector<bool> &vMatch);
102 : :
103 : : CPartialMerkleTree();
104 : :
105 : : /**
106 : : * extract the matching txid's represented by this partial merkle tree
107 : : * and their respective indices within the partial tree.
108 : : * returns the merkle root, or 0 in case of failure
109 : : */
110 : : uint256 ExtractMatches(std::vector<Txid> &vMatch, std::vector<unsigned int> &vnIndex);
111 : :
112 : : /** Get number of transactions the merkle proof is indicating for cross-reference with
113 : : * local blockchain knowledge.
114 : : */
115 [ # # ]: 0 : unsigned int GetNumTransactions() const { return nTransactions; };
116 : :
117 : : };
118 : :
119 : :
120 : : /**
121 : : * Used to relay blocks as header + vector<merkle branch>
122 : : * to filtered nodes.
123 : : *
124 : : * NOTE: The class assumes that the given CBlock has *at least* 1 transaction. If the CBlock has 0 txs, it will hit an assertion.
125 : : */
126 : : class CMerkleBlock
127 : : {
128 : : public:
129 : : /** Public only for unit testing */
130 : : CBlockHeader header;
131 : : CPartialMerkleTree txn;
132 : :
133 : : /**
134 : : * Public only for unit testing and relay testing (not relayed).
135 : : *
136 : : * Used only when a bloom filter is specified to allow
137 : : * testing the transactions which matched the bloom filter.
138 : : */
139 : : std::vector<std::pair<unsigned int, Txid> > vMatchedTxn;
140 : :
141 : : /**
142 : : * Create from a CBlock, filtering transactions according to filter
143 : : * Note that this will call IsRelevantAndUpdate on the filter for each transaction,
144 : : * thus the filter will likely be modified.
145 : : */
146 [ + - ]: 1455 : CMerkleBlock(const CBlock& block, CBloomFilter& filter) : CMerkleBlock(block, &filter, nullptr) { }
147 : :
148 : : // Create from a CBlock, matching the txids in the set
149 [ + - ]: 119 : CMerkleBlock(const CBlock& block, const std::set<Txid>& txids) : CMerkleBlock{block, nullptr, &txids} {}
150 : :
151 : 2303 : CMerkleBlock() = default;
152 : :
153 : 1806 : SERIALIZE_METHODS(CMerkleBlock, obj) { READWRITE(obj.header, obj.txn); }
154 : :
155 : : private:
156 : : // Combined constructor to consolidate code
157 : : CMerkleBlock(const CBlock& block, CBloomFilter* filter, const std::set<Txid>* txids);
158 : : };
159 : :
160 : : #endif // BITCOIN_MERKLEBLOCK_H
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