1// Copyright (c) 2018-present The Bitcoin Core developers
2// Distributed under the MIT software license, see the accompanying
3// file COPYING or http://www.opensource.org/licenses/mit-license.php.
4
5#ifndef BITCOIN_BLOCKFILTER_H
6#define BITCOIN_BLOCKFILTER_H
7
8#include <cstddef>
9#include <cstdint>
10#include <ios>
11#include <set>
12#include <string>
13#include <string_view>
14#include <unordered_set>
15#include <utility>
16#include <vector>
17
18#include <attributes.h>
19#include <uint256.h>
20#include <util/bytevectorhash.h>
21
22class CBlock;
23class CBlockUndo;
24
25/**
26 * This implements a Golomb-coded set as defined in BIP 158. It is a
27 * compact, probabilistic data structure for testing set membership.
28 */
29class GCSFilter
30{
31public:
32    typedef std::vector<unsigned char> Element;
33    typedef std::unordered_set<Element, ByteVectorHash> ElementSet;
34
35    struct Params
36    {
37        uint64_t m_siphash_k0;
38        uint64_t m_siphash_k1;
39        uint8_t m_P;  //!< Golomb-Rice coding parameter
40        uint32_t m_M;  //!< Inverse false positive rate
41
42        Params(uint64_t siphash_k0 = 0, uint64_t siphash_k1 = 0, uint8_t P = 0, uint32_t M = 1)
43            : m_siphash_k0(siphash_k0), m_siphash_k1(siphash_k1), m_P(P), m_M(M)
44        {}
45    };
46
47private:
48    Params m_params;
49    uint32_t m_N;  //!< Number of elements in the filter
50    uint64_t m_F;  //!< Range of element hashes, F = N * M
51    std::vector<unsigned char> m_encoded;
52
53    /** Hash a data element to an integer in the range [0, N * M). */
54    uint64_t HashToRange(const Element& element) const;
55
56    std::vector<uint64_t> BuildHashedSet(const ElementSet& elements) const;
57
58    /** Helper method used to implement Match and MatchAny */
59    bool MatchInternal(const uint64_t* sorted_element_hashes, size_t size) const;
60
61public:
62
63    /** Constructs an empty filter. */
64    explicit GCSFilter(const Params& params = Params());
65
66    /** Reconstructs an already-created filter from an encoding. */
67    GCSFilter(const Params& params, std::vector<unsigned char> encoded_filter, bool skip_decode_check);
68
69    /** Builds a new filter from the params and set of elements. */
70    GCSFilter(const Params& params, const ElementSet& elements);
71
72    uint32_t GetN() const { return m_N; }
73    const Params& GetParams() const LIFETIMEBOUND { return m_params; }
74    const std::vector<unsigned char>& GetEncoded() const LIFETIMEBOUND { return m_encoded; }
75
76    /**
77     * Checks if the element may be in the set. False positives are possible
78     * with probability 1/M.
79     */
80    bool Match(const Element& element) const;
81
82    /**
83     * Checks if any of the given elements may be in the set. False positives
84     * are possible with probability 1/M per element checked. This is more
85     * efficient that checking Match on multiple elements separately.
86     */
87    bool MatchAny(const ElementSet& elements) const;
88};
89
90inline constexpr uint8_t BASIC_FILTER_P = 19;
91inline constexpr uint32_t BASIC_FILTER_M = 784931;
92
93enum class BlockFilterType : uint8_t
94{
95    BASIC = 0,
96    INVALID = 255,
97};
98
99/** Get the human-readable name for a filter type. Returns empty string for unknown types. */
100const std::string& BlockFilterTypeName(BlockFilterType filter_type);
101
102/** Find a filter type by its human-readable name. */
103bool BlockFilterTypeByName(std::string_view name, BlockFilterType& filter_type);
104
105/** Get a list of known filter types. */
106const std::set<BlockFilterType>& AllBlockFilterTypes();
107
108/** Get a comma-separated list of known filter type names. */
109const std::string& ListBlockFilterTypes();
110
111/**
112 * Complete block filter struct as defined in BIP 157. Serialization matches
113 * payload of "cfilter" messages.
114 */
115class BlockFilter
116{
117private:
118    BlockFilterType m_filter_type = BlockFilterType::INVALID;
119    uint256 m_block_hash;
120    GCSFilter m_filter;
121
122    bool BuildParams(GCSFilter::Params& params) const;
123
124public:
125
126    BlockFilter() = default;
127
128    //! Reconstruct a BlockFilter from parts.
129    BlockFilter(BlockFilterType filter_type, const uint256& block_hash,
130                std::vector<unsigned char> filter, bool skip_decode_check);
131
132    //! Construct a new BlockFilter of the specified type from a block.
133    BlockFilter(BlockFilterType filter_type, const CBlock& block, const CBlockUndo& block_undo);
134
135    BlockFilterType GetFilterType() const { return m_filter_type; }
136    const uint256& GetBlockHash() const LIFETIMEBOUND { return m_block_hash; }
137    const GCSFilter& GetFilter() const LIFETIMEBOUND { return m_filter; }
138
139    const std::vector<unsigned char>& GetEncodedFilter() const LIFETIMEBOUND
140    {
141        return m_filter.GetEncoded();
142    }
143
144    //! Compute the filter hash.
145    uint256 GetHash() const;
146
147    //! Compute the filter header given the previous one.
148    uint256 ComputeHeader(const uint256& prev_header) const;
149
150    template <typename Stream>
151    void Serialize(Stream& s) const {
152        s << static_cast<uint8_t>(m_filter_type)
153          << m_block_hash
154          << m_filter.GetEncoded();
155    }
156
157    template <typename Stream>
158    void Unserialize(Stream& s) {
159        std::vector<unsigned char> encoded_filter;
160        uint8_t filter_type;
161
162        s >> filter_type
163          >> m_block_hash
164          >> encoded_filter;
165
166        m_filter_type = static_cast<BlockFilterType>(filter_type);
167
168        GCSFilter::Params params;
169        if (!BuildParams(params)) {
170            throw std::ios_base::failure("unknown filter_type");
171        }
172        m_filter = GCSFilter(params, std::move(encoded_filter), /*skip_decode_check=*/false);
173    }
174};
175
176#endif // BITCOIN_BLOCKFILTER_H
177