Overwinter peer management and network handshaking.

Implements ZIP 201.

src/net.cpp

@@ -7,6 +7,7 @@
 #include "config/bitcoin-config.h"
 #endif
 
+#include "main.h"
 #include "net.h"
 
 #include "addrman.h"
@@ -812,6 +813,34 @@ static bool AttemptToEvictConnection(bool fPreferNewConnection) {
 
     // Protect connections with certain characteristics
 
+    // Check version of eviction candidates and prioritize nodes which do not support network upgrade.
+    std::vector<CNodeRef> vTmpEvictionCandidates;
+    int height;
+    {
+        LOCK(cs_main);
+        height = chainActive.Height();
+    }
+
+    const Consensus::Params& params = Params().GetConsensus();
+    int nActivationHeight = params.vUpgrades[Consensus::UPGRADE_OVERWINTER].nActivationHeight;
+
+    if (nActivationHeight > 0 &&
+        height < nActivationHeight &&
+        height >= nActivationHeight - NETWORK_UPGRADE_PEER_PREFERENCE_BLOCK_PERIOD)
+    {
+        // Find any nodes which don't support Overwinter protocol version
+        BOOST_FOREACH(const CNodeRef &node, vEvictionCandidates) {
+            if (node->nVersion < params.vUpgrades[Consensus::UPGRADE_OVERWINTER].nProtocolVersion) {
+                vTmpEvictionCandidates.push_back(node);
+            }
+        }
+
+        // Prioritize these nodes by replacing eviction set with them
+        if (vTmpEvictionCandidates.size() > 0) {
+            vEvictionCandidates = vTmpEvictionCandidates;
+        }
+    }
+
     // Deterministically select 4 peers to protect by netgroup.
     // An attacker cannot predict which netgroups will be protected.
     static CompareNetGroupKeyed comparerNetGroupKeyed;