use median filter for peer-reported reported number of blocks

- fixes problem that one misconfigured or malicious node can mess up progress bar
- implementation in src/util.h
- testcase in src/test/util_tests.cpp

src/main.cpp

@@ -32,7 +32,6 @@ uint256 hashGenesisBlock("0x000000000019d6689c085ae165831e934ff763ae46a2a6c172b3
 static CBigNum bnProofOfWorkLimit(~uint256(0) >> 32);
 const int nTotalBlocksEstimate = 140700; // Conservative estimate of total nr of blocks on main chain
 const int nInitialBlockThreshold = 120; // Regard blocks up until N-threshold as "initial download"
-int nMaxBlocksOfPeers = 0; // Amount of blocks that other nodes claim to have
 CBlockIndex* pindexGenesisBlock = NULL;
 int nBestHeight = -1;
 CBigNum bnBestChainWork = 0;
@@ -41,6 +40,8 @@ uint256 hashBestChain = 0;
 CBlockIndex* pindexBest = NULL;
 int64 nTimeBestReceived = 0;
 
+CMedianFilter<int> cPeerBlockCounts(5, 0); // Amount of blocks that other nodes claim to have
+
 map<uint256, CBlock*> mapOrphanBlocks;
 multimap<uint256, CBlock*> mapOrphanBlocksByPrev;
 
@@ -65,11 +66,6 @@ int fUseUPnP = false;
 #endif
 
 
-
-
-
-
-
 //////////////////////////////////////////////////////////////////////////////
 //
 // dispatching functions
@@ -730,7 +726,7 @@ int GetTotalBlocksEstimate()
 // Return maximum amount of blocks that other nodes claim to have
 int GetNumBlocksOfPeers()
 {
-    return std::max(nMaxBlocksOfPeers, GetTotalBlocksEstimate());
+    return std::max(cPeerBlockCounts.median(), GetTotalBlocksEstimate());
 }
 
 bool IsInitialBlockDownload()
@@ -1847,10 +1843,8 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv)
         pfrom->fSuccessfullyConnected = true;
 
         printf("version message: version %d, blocks=%d\n", pfrom->nVersion, pfrom->nStartingHeight);
-        if(pfrom->nStartingHeight > nMaxBlocksOfPeers)
-        {
-            nMaxBlocksOfPeers = pfrom->nStartingHeight;
-        }
+
+        cPeerBlockCounts.input(pfrom->nStartingHeight);
     }