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Refactor bloom filter calculations out of PeerGroup into a separate F…
…ilterMerger class.
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core/src/main/java/com/google/bitcoin/net/FilterMerger.java
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| package com.google.bitcoin.net; | ||
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| import com.google.bitcoin.core.BloomFilter; | ||
| import com.google.bitcoin.core.PeerFilterProvider; | ||
| import com.google.common.collect.ImmutableList; | ||
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| // This code is unit tested by the PeerGroup tests. | ||
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| /** | ||
| * <p>A reusable object that will calculate, given a list of {@link com.google.bitcoin.core.PeerFilterProvider}s, a merged | ||
| * {@link com.google.bitcoin.core.BloomFilter} and earliest key time for all of them. | ||
| * Used by the {@link com.google.bitcoin.core.PeerGroup} class internally.</p> | ||
| * | ||
| * <p>Thread safety: this class tracks the element count of the last filter it calculated and so must be synchronised | ||
| * externally or used from only one thread. It will acquire a lock on each filter in turn before performing the | ||
| * calculation because the providers may be mutated in other threads in parallel, but global consistency is required | ||
| * to produce a merged filter.</p> | ||
| */ | ||
| public class FilterMerger { | ||
| // We use a constant tweak to avoid giving up privacy when we regenerate our filter with new keys | ||
| private final long bloomFilterTweak = (long) (Math.random() * Long.MAX_VALUE); | ||
| private double bloomFilterFPRate; | ||
| private int lastBloomFilterElementCount; | ||
| private BloomFilter lastFilter; | ||
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| public FilterMerger(double bloomFilterFPRate) { | ||
| this.bloomFilterFPRate = bloomFilterFPRate; | ||
| } | ||
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| public static class Result { | ||
| public BloomFilter filter; | ||
| public long earliestKeyTimeSecs; | ||
| public boolean changed; | ||
| } | ||
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| public Result calculate(ImmutableList<PeerFilterProvider> providers) { | ||
| Result result = new Result(); | ||
| result.earliestKeyTimeSecs = Long.MAX_VALUE; | ||
| int elements = 0; | ||
| boolean requiresUpdateAll = false; | ||
| for (PeerFilterProvider p : providers) { | ||
| result.earliestKeyTimeSecs = Math.min(result.earliestKeyTimeSecs, p.getEarliestKeyCreationTime()); | ||
| elements += p.getBloomFilterElementCount(); | ||
| requiresUpdateAll = requiresUpdateAll || p.isRequiringUpdateAllBloomFilter(); | ||
| } | ||
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| if (elements > 0) { | ||
| // We stair-step our element count so that we avoid creating a filter with different parameters | ||
| // as much as possible as that results in a loss of privacy. | ||
| // The constant 100 here is somewhat arbitrary, but makes sense for small to medium wallets - | ||
| // it will likely mean we never need to create a filter with different parameters. | ||
| lastBloomFilterElementCount = elements > lastBloomFilterElementCount ? elements + 100 : lastBloomFilterElementCount; | ||
| BloomFilter.BloomUpdate bloomFlags = | ||
| requiresUpdateAll ? BloomFilter.BloomUpdate.UPDATE_ALL : BloomFilter.BloomUpdate.UPDATE_P2PUBKEY_ONLY; | ||
| BloomFilter filter = new BloomFilter(lastBloomFilterElementCount, bloomFilterFPRate, bloomFilterTweak, bloomFlags); | ||
| for (PeerFilterProvider p : providers) | ||
| filter.merge(p.getBloomFilter(lastBloomFilterElementCount, bloomFilterFPRate, bloomFilterTweak)); | ||
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| result.changed = !filter.equals(lastFilter); | ||
| result.filter = lastFilter = filter; | ||
| } | ||
| // Now adjust the earliest key time backwards by a week to handle the case of clock drift. This can occur | ||
| // both in block header timestamps and if the users clock was out of sync when the key was first created | ||
| // (to within a small amount of tolerance). | ||
| result.earliestKeyTimeSecs -= 86400 * 7; | ||
| return result; | ||
| } | ||
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| public void setBloomFilterFPRate(double bloomFilterFPRate) { | ||
| this.bloomFilterFPRate = bloomFilterFPRate; | ||
| } | ||
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| public double getBloomFilterFPRate() { | ||
| return bloomFilterFPRate; | ||
| } | ||
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| public BloomFilter getLastFilter() { | ||
| return lastFilter; | ||
| } | ||
| } |