From 37c6389c5a0ca63ae3573440ecdfe95d28ad8f07 Mon Sep 17 00:00:00 2001
From: Gregory Maxwell <greg@xiph.org>
Date: Sun, 18 Aug 2013 20:21:06 -0700
Subject: [PATCH] Performance optimization for bloom filters.

This reduces a peer's ability to attack network resources by
 using a full bloom filter, but without reducing the usability
 of bloom filters.  It sets a default match everything filter
 for peers and it generalizes a prior optimization to
 cover more cases.
---
 src/bloom.cpp | 26 ++++++++++++++++++++++++--
 src/bloom.h   |  9 ++++++---
 src/main.cpp  |  3 ++-
 src/net.h     |  2 +-
 4 files changed, 33 insertions(+), 7 deletions(-)

diff --git a/src/bloom.cpp b/src/bloom.cpp
index b6799e143..8e8d8fa06 100644
--- a/src/bloom.cpp
+++ b/src/bloom.cpp
@@ -23,6 +23,8 @@ vData(min((unsigned int)(-1  / LN2SQUARED * nElements * log(nFPRate)), MAX_BLOOM
 // 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 http://en.wikipedia.org/wiki/Bloom_filter for an explanation of these formulas
+isFull(false),
+isEmpty(false),
 nHashFuncs(min((unsigned int)(vData.size() * 8 / nElements * LN2), MAX_HASH_FUNCS)),
 nTweak(nTweakIn),
 nFlags(nFlagsIn)
@@ -37,7 +39,7 @@ inline unsigned int CBloomFilter::Hash(unsigned int nHashNum, const std::vector<
 
 void CBloomFilter::insert(const vector<unsigned char>& vKey)
 {
-    if (vData.size() == 1 && vData[0] == 0xff)
+    if (isFull)
         return;
     for (unsigned int i = 0; i < nHashFuncs; i++)
     {
@@ -45,6 +47,7 @@ void CBloomFilter::insert(const vector<unsigned char>& vKey)
         // Sets bit nIndex of vData
         vData[nIndex >> 3] |= bit_mask[7 & nIndex];
     }
+    isEmpty = false;
 }
 
 void CBloomFilter::insert(const COutPoint& outpoint)
@@ -63,8 +66,10 @@ void CBloomFilter::insert(const uint256& hash)
 
 bool CBloomFilter::contains(const vector<unsigned char>& vKey) const
 {
-    if (vData.size() == 1 && vData[0] == 0xff)
+    if (isFull)
         return true;
+    if (isEmpty)
+        return false;
     for (unsigned int i = 0; i < nHashFuncs; i++)
     {
         unsigned int nIndex = Hash(i, vKey);
@@ -99,6 +104,10 @@ bool CBloomFilter::IsRelevantAndUpdate(const CTransaction& tx, const uint256& ha
     bool fFound = false;
     // Match if the filter contains the hash of tx
     //  for finding tx when they appear in a block
+    if (isFull)
+        return true;
+    if (isEmpty)
+        return false;
     if (contains(hash))
         fFound = true;
 
@@ -158,3 +167,16 @@ bool CBloomFilter::IsRelevantAndUpdate(const CTransaction& tx, const uint256& ha
 
     return false;
 }
+
+void CBloomFilter::UpdateEmptyFull()
+{
+    bool full = true;
+    bool empty = true;
+    for (unsigned int i = 0; i < vData.size(); i++)
+    {
+        full &= vData[i] == 0xff;
+        empty &= vData[i] == 0;
+    }
+    isFull = full;
+    isEmpty = empty;
+}
diff --git a/src/bloom.h b/src/bloom.h
index 389ae748e..f482bfcc1 100644
--- a/src/bloom.h
+++ b/src/bloom.h
@@ -42,6 +42,8 @@ class CBloomFilter
 {
 private:
     std::vector<unsigned char> vData;
+    bool isFull;
+    bool isEmpty;
     unsigned int nHashFuncs;
     unsigned int nTweak;
     unsigned char nFlags;
@@ -57,9 +59,7 @@ public:
     // 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)
     CBloomFilter(unsigned int nElements, double nFPRate, unsigned int nTweak, unsigned char nFlagsIn);
-    // Using a filter initialized with this results in undefined behavior
-    // Should only be used for deserialization
-    CBloomFilter() {}
+    CBloomFilter() : isFull(true) {}
 
     IMPLEMENT_SERIALIZE
     (
@@ -83,6 +83,9 @@ public:
 
     // Also adds any outputs which match the filter to the filter (to match their spending txes)
     bool IsRelevantAndUpdate(const CTransaction& tx, const uint256& hash);
+
+    // Checks for empty and full filters to avoid wasting cpu
+    void UpdateEmptyFull();
 };
 
 #endif /* BITCOIN_BLOOM_H */
diff --git a/src/main.cpp b/src/main.cpp
index 2ccd5131d..b62f107b4 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -3893,6 +3893,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv)
             LOCK(pfrom->cs_filter);
             delete pfrom->pfilter;
             pfrom->pfilter = new CBloomFilter(filter);
+            filter.UpdateEmptyFull();
         }
         pfrom->fRelayTxes = true;
     }
@@ -3922,7 +3923,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv)
     {
         LOCK(pfrom->cs_filter);
         delete pfrom->pfilter;
-        pfrom->pfilter = NULL;
+        pfrom->pfilter = new CBloomFilter();
         pfrom->fRelayTxes = true;
     }
 
diff --git a/src/net.h b/src/net.h
index e75fe48f6..686861fbe 100644
--- a/src/net.h
+++ b/src/net.h
@@ -267,7 +267,7 @@ public:
         nMisbehavior = 0;
         fRelayTxes = false;
         setInventoryKnown.max_size(SendBufferSize() / 1000);
-        pfilter = NULL;
+        pfilter = new CBloomFilter();
 
         // Be shy and don't send version until we hear
         if (hSocket != INVALID_SOCKET && !fInbound)