Headers-first synchronization

Many changes:
* Do not use 'getblocks', but 'getheaders', and use it to build a headers tree.
* Blocks are fetched in parallel from all available outbound peers, using a
  limited moving window. When one peer stalls the movement of the window, it is
  disconnected.
* No more orphan blocks. At all. We only ever request a block for which we have
  verified the headers, and store it to disk immediately. This means that a
  disk-fill attack would require PoW.
* Require protocol version 31800 for every peer (released in december 2010).
* No more syncnode (we sync from everyone we can, though limited to 1 during
  initial *headers* sync).
* Introduce some extra named constants, comments and asserts.

1 files changed, 0 insertions, 50 deletions

diff --git a/src/net.cpp b/src/net.cpp
index dd5cb480cc..50b435cf14 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -73,7 +73,6 @@ map<CNetAddr, LocalServiceInfo> mapLocalHost;
 static bool vfReachable[NET_MAX] = {};
 static bool vfLimited[NET_MAX] = {};
 static CNode* pnodeLocalHost = NULL;
-static CNode* pnodeSync = NULL;
 uint64_t nLocalHostNonce = 0;
 static std::vector<ListenSocket> vhListenSocket;
 CAddrMan addrman;
@@ -519,10 +518,6 @@ void CNode::CloseSocketDisconnect()
     TRY_LOCK(cs_vRecvMsg, lockRecv);
     if (lockRecv)
         vRecvMsg.clear();
-
-    // if this was the sync node, we'll need a new one
-    if (this == pnodeSync)
-        pnodeSync = NULL;
 }
 
 void CNode::PushVersion()
@@ -615,7 +610,6 @@ void CNode::copyStats(CNodeStats &stats)
     X(nSendBytes);
     X(nRecvBytes);
     X(fWhitelisted);
-    stats.fSyncNode = (this == pnodeSync);
 
     // It is common for nodes with good ping times to suddenly become lagged,
     // due to a new block arriving or other large transfer.
@@ -1487,61 +1481,20 @@ bool OpenNetworkConnection(const CAddress& addrConnect, CSemaphoreGrant *grantOu
 }
 
 
-// for now, use a very simple selection metric: the node from which we received
-// most recently
-static int64_t NodeSyncScore(const CNode *pnode) {
-    return pnode->nLastRecv;
-}
-
-void static StartSync(const vector<CNode*> &vNodes) {
-    CNode *pnodeNewSync = NULL;
-    int64_t nBestScore = 0;
-
-    int nBestHeight = g_signals.GetHeight().get_value_or(0);
-
-    // Iterate over all nodes
-    BOOST_FOREACH(CNode* pnode, vNodes) {
-        // check preconditions for allowing a sync
-        if (!pnode->fClient && !pnode->fOneShot &&
-            !pnode->fDisconnect && pnode->fSuccessfullyConnected &&
-            (pnode->nStartingHeight > (nBestHeight - 144)) &&
-            (pnode->nVersion < NOBLKS_VERSION_START || pnode->nVersion >= NOBLKS_VERSION_END)) {
-            // if ok, compare node's score with the best so far
-            int64_t nScore = NodeSyncScore(pnode);
-            if (pnodeNewSync == NULL || nScore > nBestScore) {
-                pnodeNewSync = pnode;
-                nBestScore = nScore;
-            }
-        }
-    }
-    // if a new sync candidate was found, start sync!
-    if (pnodeNewSync) {
-        pnodeNewSync->fStartSync = true;
-        pnodeSync = pnodeNewSync;
-    }
-}
-
 void ThreadMessageHandler()
 {
     SetThreadPriority(THREAD_PRIORITY_BELOW_NORMAL);
     while (true)
     {
-        bool fHaveSyncNode = false;
-
         vector<CNode*> vNodesCopy;
         {
             LOCK(cs_vNodes);
             vNodesCopy = vNodes;
             BOOST_FOREACH(CNode* pnode, vNodesCopy) {
                 pnode->AddRef();
-                if (pnode == pnodeSync)
-                    fHaveSyncNode = true;
             }
         }
 
-        if (!fHaveSyncNode)
-            StartSync(vNodesCopy);
-
         // Poll the connected nodes for messages
         CNode* pnodeTrickle = NULL;
         if (!vNodesCopy.empty())
@@ -2078,10 +2031,7 @@ CNode::CNode(SOCKET hSocketIn, CAddress addrIn, std::string addrNameIn, bool fIn
     nSendSize = 0;
     nSendOffset = 0;
     hashContinue = 0;
-    pindexLastGetBlocksBegin = 0;
-    hashLastGetBlocksEnd = 0;
     nStartingHeight = -1;
-    fStartSync = false;
     fGetAddr = false;
     fRelayTxes = false;
     setInventoryKnown.max_size(SendBufferSize() / 1000);