d2d7ee0e86
While CBloomFilter is usually used with an explicitly set nTweak, CRollingBloomFilter is only used internally. Requiring every caller to set nTweak is error-prone and redundant; better to have the class handle that for you with a high-quality randomness source. Additionally when clearing the filter it makes sense to change nTweak as well to recover from a bad setting, e.g. due to insufficient randomness at initialization, so the clear() method is replaced by a reset() method that sets a new, random, nTweak value.
137 lines
4.8 KiB
C++
137 lines
4.8 KiB
C++
// Copyright (c) 2012-2014 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#ifndef BITCOIN_BLOOM_H
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#define BITCOIN_BLOOM_H
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#include "serialize.h"
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#include <vector>
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class COutPoint;
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class CTransaction;
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class uint256;
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//! 20,000 items with fp rate < 0.1% or 10,000 items and <0.0001%
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static const unsigned int MAX_BLOOM_FILTER_SIZE = 36000; // bytes
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static const unsigned int MAX_HASH_FUNCS = 50;
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/**
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* First two bits of nFlags control how much IsRelevantAndUpdate actually updates
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* The remaining bits are reserved
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*/
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enum bloomflags
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{
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BLOOM_UPDATE_NONE = 0,
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BLOOM_UPDATE_ALL = 1,
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// Only adds outpoints to the filter if the output is a pay-to-pubkey/pay-to-multisig script
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BLOOM_UPDATE_P2PUBKEY_ONLY = 2,
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BLOOM_UPDATE_MASK = 3,
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};
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/**
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* BloomFilter is a probabilistic filter which SPV clients provide
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* so that we can filter the transactions we send them.
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*
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* This allows for significantly more efficient transaction and block downloads.
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*
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* Because bloom filters are probabilistic, a SPV node can increase the false-
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* positive rate, making us send it transactions which aren't actually its,
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* allowing clients to trade more bandwidth for more privacy by obfuscating which
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* keys are controlled by them.
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*/
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class CBloomFilter
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{
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private:
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std::vector<unsigned char> vData;
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bool isFull;
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bool isEmpty;
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unsigned int nHashFuncs;
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unsigned int nTweak;
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unsigned char nFlags;
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unsigned int Hash(unsigned int nHashNum, const std::vector<unsigned char>& vDataToHash) const;
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// Private constructor for CRollingBloomFilter, no restrictions on size
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CBloomFilter(unsigned int nElements, double nFPRate, unsigned int nTweak);
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friend class CRollingBloomFilter;
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public:
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/**
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* Creates a new bloom filter which will provide the given fp rate when filled with the given number of elements
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* Note that if the given parameters will result in a filter outside the bounds of the protocol limits,
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* the filter created will be as close to the given parameters as possible within the protocol limits.
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* This will apply if nFPRate is very low or nElements is unreasonably high.
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* nTweak is a constant which is added to the seed value passed to the hash function
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* It should generally always be a random value (and is largely only exposed for unit testing)
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* nFlags should be one of the BLOOM_UPDATE_* enums (not _MASK)
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*/
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CBloomFilter(unsigned int nElements, double nFPRate, unsigned int nTweak, unsigned char nFlagsIn);
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CBloomFilter() : isFull(true), isEmpty(false), nHashFuncs(0), nTweak(0), nFlags(0) {}
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ADD_SERIALIZE_METHODS;
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template <typename Stream, typename Operation>
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inline void SerializationOp(Stream& s, Operation ser_action, int nType, int nVersion) {
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READWRITE(vData);
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READWRITE(nHashFuncs);
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READWRITE(nTweak);
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READWRITE(nFlags);
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}
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void insert(const std::vector<unsigned char>& vKey);
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void insert(const COutPoint& outpoint);
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void insert(const uint256& hash);
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bool contains(const std::vector<unsigned char>& vKey) const;
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bool contains(const COutPoint& outpoint) const;
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bool contains(const uint256& hash) const;
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void clear();
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void reset(unsigned int nNewTweak);
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//! True if the size is <= MAX_BLOOM_FILTER_SIZE and the number of hash functions is <= MAX_HASH_FUNCS
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//! (catch a filter which was just deserialized which was too big)
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bool IsWithinSizeConstraints() const;
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//! Also adds any outputs which match the filter to the filter (to match their spending txes)
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bool IsRelevantAndUpdate(const CTransaction& tx);
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//! Checks for empty and full filters to avoid wasting cpu
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void UpdateEmptyFull();
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};
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/**
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* RollingBloomFilter is a probabilistic "keep track of most recently inserted" set.
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* Construct it with the number of items to keep track of, and a false-positive
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* rate. Unlike CBloomFilter, by default nTweak is set to a cryptographically
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* secure random value for you. Similarly rather than clear() the method
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* reset() is provided, which also changes nTweak to decrease the impact of
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* false-positives.
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*
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* contains(item) will always return true if item was one of the last N things
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* insert()'ed ... but may also return true for items that were not inserted.
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*/
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class CRollingBloomFilter
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{
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public:
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CRollingBloomFilter(unsigned int nElements, double nFPRate,
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unsigned int nTweak = 0);
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void insert(const std::vector<unsigned char>& vKey);
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void insert(const uint256& hash);
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bool contains(const std::vector<unsigned char>& vKey) const;
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bool contains(const uint256& hash) const;
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void reset(unsigned int nNewTweak = 0);
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private:
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unsigned int nBloomSize;
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unsigned int nInsertions;
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CBloomFilter b1, b2;
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};
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#endif // BITCOIN_BLOOM_H
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