1// Copyright (c) 2009-2010 Satoshi Nakamoto
2// Copyright (c) 2009-present 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.
19std::vector<unsigned char> BitsToBytes(const std::vector<bool>& bits);
20std::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 */
56class CPartialMerkleTree
57{
58protected:
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    unsigned int CalcTreeWidth(int height) const {
73        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
88public:
89
90    SERIALIZE_METHODS(CPartialMerkleTree, obj)
91    {
92        READWRITE(obj.nTransactions, obj.vHash);
93        std::vector<unsigned char> bytes;
94        SER_WRITE(obj, bytes = BitsToBytes(obj.vBits));
95        READWRITE(bytes);
96        SER_READ(obj, obj.vBits = BytesToBits(bytes));
97        SER_READ(obj, obj.fBad = false);
98    }
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    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 */
126class CMerkleBlock
127{
128public:
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    CMerkleBlock(const CBlock& block, CBloomFilter& filter) : CMerkleBlock(block, &filter, nullptr) { }
147
148    // Create from a CBlock, matching the txids in the set
149    CMerkleBlock(const CBlock& block, const std::set<Txid>& txids) : CMerkleBlock{block, nullptr, &txids} {}
150
151    CMerkleBlock() = default;
152
153    SERIALIZE_METHODS(CMerkleBlock, obj) { READWRITE(obj.header, obj.txn); }
154
155private:
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
161