CBloomFilter Class Reference

BloomFilter is a probabilistic filter which SPV clients provide so that we can filter the transactions we send them. More...

#include <bloom.h>

Public Member Functions
	CBloomFilter (unsigned int nElements, double nFPRate, unsigned int nTweak, unsigned char nFlagsIn)
	Creates a new bloom filter which will provide the given fp rate when filled with the given number of elements Note that if the given parameters will result in a filter outside the bounds of the protocol limits, the filter created will be as close to the given parameters as possible within the protocol limits.
	CBloomFilter ()
	SERIALIZE_METHODS (CBloomFilter, obj)
void	insert (std::span< const unsigned char > vKey)
void	insert (const COutPoint &outpoint)
bool	contains (std::span< const unsigned char > vKey) const
bool	contains (const COutPoint &outpoint) const
bool	IsWithinSizeConstraints () const
	True if the size is <= MAX_BLOOM_FILTER_SIZE and the number of hash functions is <= MAX_HASH_FUNCS (catch a filter which was just deserialized which was too big)
bool	IsRelevantAndUpdate (const CTransaction &tx)
	Also adds any outputs which match the filter to the filter (to match their spending txes)

Private Member Functions
unsigned int	Hash (unsigned int nHashNum, std::span< const unsigned char > vDataToHash) const

Private Attributes
std::vector< unsigned char >	vData
unsigned int	nHashFuncs
unsigned int	nTweak
unsigned char	nFlags

Detailed Description

BloomFilter is a probabilistic filter which SPV clients provide so that we can filter the transactions we send them.

This allows for significantly more efficient transaction and block downloads.

Because bloom filters are probabilistic, a SPV node can increase the false- positive rate, making us send it transactions which aren't actually its, allowing clients to trade more bandwidth for more privacy by obfuscating which keys are controlled by them.

Definition at line 44 of file bloom.h.

Constructor & Destructor Documentation

CBloomFilter() [1/2]

CBloomFilter::CBloomFilter	(	unsigned int	nElements,
		double	nFPRate,
		unsigned int	nTweak,
		unsigned char	nFlagsIn )

Creates a new bloom filter which will provide the given fp rate when filled with the given number of elements Note that if the given parameters will result in a filter outside the bounds of the protocol limits, the filter created will be as close to the given parameters as possible within the protocol limits.

The ideal size for a bloom filter with a given number of elements and false positive rate is:

This will apply if nFPRate is very low or nElements is unreasonably high. nTweak is a constant which is added to the seed value passed to the hash function It should generally always be a random value (and is largely only exposed for unit testing) nFlags should be one of the BLOOM_UPDATE_* enums (not _MASK)

• nElements * log(fp rate) / ln(2)^2 We ignore filter parameters which will create a bloom filter larger than the protocol limits The ideal number of hash functions is filter size * ln(2) / number of elements Again, we ignore filter parameters which will create a bloom filter with more hash functions than the protocol limits See https://en.wikipedia.org/wiki/Bloom_filter for an explanation of these formulas

Definition at line 25 of file bloom.cpp.

CBloomFilter() [2/2]

CBloomFilter::CBloomFilter ( )

inline

Definition at line 65 of file bloom.h.

Member Function Documentation

contains() [1/2]

bool CBloomFilter::contains

(

const COutPoint &

outpoint

)

const

Definition at line 82 of file bloom.cpp.

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contains() [2/2]

bool CBloomFilter::contains

(

std::span< const unsigned char >

vKey

)

const

Definition at line 68 of file bloom.cpp.

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Hash()

unsigned int CBloomFilter::Hash ( unsigned int nHashNum, std::span< const unsigned char > vDataToHash ) const

inlineprivate

Definition at line 43 of file bloom.cpp.

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insert() [1/2]

void CBloomFilter::insert

(

const COutPoint &

outpoint

)

Definition at line 61 of file bloom.cpp.

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insert() [2/2]

void CBloomFilter::insert

(

std::span< const unsigned char >

vKey

)

Definition at line 49 of file bloom.cpp.

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IsRelevantAndUpdate()

bool CBloomFilter::IsRelevantAndUpdate

(

const CTransaction &

tx

)

Also adds any outputs which match the filter to the filter (to match their spending txes)

Definition at line 94 of file bloom.cpp.

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IsWithinSizeConstraints()

bool CBloomFilter::IsWithinSizeConstraints

(

)

const

True if the size is <= MAX_BLOOM_FILTER_SIZE and the number of hash functions is <= MAX_HASH_FUNCS (catch a filter which was just deserialized which was too big)

Definition at line 89 of file bloom.cpp.

SERIALIZE_METHODS()

CBloomFilter::SERIALIZE_METHODS ( CBloomFilter , obj  )

inline

Definition at line 67 of file bloom.h.

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Member Data Documentation

nFlags

unsigned char CBloomFilter::nFlags

private

Definition at line 50 of file bloom.h.

nHashFuncs

unsigned int CBloomFilter::nHashFuncs

private

Definition at line 48 of file bloom.h.

nTweak

unsigned int CBloomFilter::nTweak

private

Definition at line 49 of file bloom.h.

vData

std::vector<unsigned char> CBloomFilter::vData

private

Definition at line 47 of file bloom.h.

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The documentation for this class was generated from the following files:

• src/common/bloom.h
• src/common/bloom.cpp