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Make CRollingBloomFilter set nTweak for you

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.
tags/v0.15.1
Peter Todd 5 years ago
parent
commit
d2d7ee0e86
5 changed files with 29 additions and 12 deletions
  1. 15
    4
      src/bloom.cpp
  2. 9
    3
      src/bloom.h
  3. 1
    1
      src/main.cpp
  4. 1
    1
      src/net.cpp
  5. 3
    3
      src/test/bloom_tests.cpp

+ 15
- 4
src/bloom.cpp View File

@@ -8,6 +8,7 @@
#include "hash.h"
#include "script/script.h"
#include "script/standard.h"
#include "random.h"
#include "streams.h"

#include <math.h>
@@ -121,6 +122,12 @@ void CBloomFilter::clear()
isEmpty = true;
}

void CBloomFilter::reset(unsigned int nNewTweak)
{
clear();
nTweak = nNewTweak;
}

bool CBloomFilter::IsWithinSizeConstraints() const
{
return vData.size() <= MAX_BLOOM_FILTER_SIZE && nHashFuncs <= MAX_HASH_FUNCS;
@@ -217,7 +224,8 @@ CRollingBloomFilter::CRollingBloomFilter(unsigned int nElements, double fpRate,
// inserted, so at least one always contains the last nElements
// inserted.
nBloomSize = nElements * 2;
nInsertions = 0;

reset(nTweak);
}

void CRollingBloomFilter::insert(const std::vector<unsigned char>& vKey)
@@ -254,9 +262,12 @@ bool CRollingBloomFilter::contains(const uint256& hash) const
return contains(data);
}

void CRollingBloomFilter::clear()
void CRollingBloomFilter::reset(unsigned int nNewTweak)
{
b1.clear();
b2.clear();
if (!nNewTweak)
nNewTweak = GetRand(std::numeric_limits<unsigned int>::max());

b1.reset(nNewTweak);
b2.reset(nNewTweak);
nInsertions = 0;
}

+ 9
- 3
src/bloom.h View File

@@ -89,6 +89,7 @@ public:
bool contains(const uint256& hash) const;

void clear();
void reset(unsigned int nNewTweak);

//! 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)
@@ -103,7 +104,11 @@ public:

/**
* RollingBloomFilter is a probabilistic "keep track of most recently inserted" set.
* Construct it with the number of items to keep track of, and a false-positive rate.
* Construct it with the number of items to keep track of, and a false-positive
* rate. Unlike CBloomFilter, by default nTweak is set to a cryptographically
* secure random value for you. Similarly rather than clear() the method
* reset() is provided, which also changes nTweak to decrease the impact of
* false-positives.
*
* contains(item) will always return true if item was one of the last N things
* insert()'ed ... but may also return true for items that were not inserted.
@@ -111,14 +116,15 @@ public:
class CRollingBloomFilter
{
public:
CRollingBloomFilter(unsigned int nElements, double nFPRate, unsigned int nTweak);
CRollingBloomFilter(unsigned int nElements, double nFPRate,
unsigned int nTweak = 0);

void insert(const std::vector<unsigned char>& vKey);
void insert(const uint256& hash);
bool contains(const std::vector<unsigned char>& vKey) const;
bool contains(const uint256& hash) const;

void clear();
void reset(unsigned int nNewTweak = 0);

private:
unsigned int nBloomSize;

+ 1
- 1
src/main.cpp View File

@@ -4812,7 +4812,7 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
{
// Periodically clear addrKnown to allow refresh broadcasts
if (nLastRebroadcast)
pnode->addrKnown.clear();
pnode->addrKnown.reset();

// Rebroadcast our address
AdvertizeLocal(pnode);

+ 1
- 1
src/net.cpp View File

@@ -2060,7 +2060,7 @@ unsigned int SendBufferSize() { return 1000*GetArg("-maxsendbuffer", 1*1000); }

CNode::CNode(SOCKET hSocketIn, const CAddress& addrIn, const std::string& addrNameIn, bool fInboundIn) :
ssSend(SER_NETWORK, INIT_PROTO_VERSION),
addrKnown(5000, 0.001, insecure_rand()),
addrKnown(5000, 0.001),
setInventoryKnown(SendBufferSize() / 1000)
{
nServices = 0;

+ 3
- 3
src/test/bloom_tests.cpp View File

@@ -469,7 +469,7 @@ static std::vector<unsigned char> RandomData()
BOOST_AUTO_TEST_CASE(rolling_bloom)
{
// last-100-entry, 1% false positive:
CRollingBloomFilter rb1(100, 0.01, 0);
CRollingBloomFilter rb1(100, 0.01, 1);

// Overfill:
static const int DATASIZE=399;
@@ -500,7 +500,7 @@ BOOST_AUTO_TEST_CASE(rolling_bloom)
BOOST_CHECK(nHits < 175);

BOOST_CHECK(rb1.contains(data[DATASIZE-1]));
rb1.clear();
rb1.reset(1);
BOOST_CHECK(!rb1.contains(data[DATASIZE-1]));

// Now roll through data, make sure last 100 entries
@@ -527,7 +527,7 @@ BOOST_AUTO_TEST_CASE(rolling_bloom)
BOOST_CHECK(nHits < 100);

// last-1000-entry, 0.01% false positive:
CRollingBloomFilter rb2(1000, 0.001, 0);
CRollingBloomFilter rb2(1000, 0.001, 1);
for (int i = 0; i < DATASIZE; i++) {
rb2.insert(data[i]);
}

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