From 72b2192950f3c775226e6d4ca58f45b148aa0b75 Mon Sep 17 00:00:00 2001
From: Simon <simon@bitcartel.com>
Date: Tue, 20 Feb 2018 11:03:40 -0800
Subject: [PATCH] Overwinter peer management and network handshaking.

Implements ZIP 201.
---
 src/main.cpp  | 29 +++++++++++++++++++++++++++++
 src/net.cpp   | 29 +++++++++++++++++++++++++++++
 src/net.h     |  2 ++
 src/version.h |  2 +-
 4 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/src/main.cpp b/src/main.cpp
index 9e41d9c4e..5d45a29ff 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -4721,6 +4721,19 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             return false;
         }
 
+        // When Overwinter is active, reject incoming connections from non-Overwinter nodes
+        const Consensus::Params& params = Params().GetConsensus();
+        if (NetworkUpgradeActive(GetHeight(), params, Consensus::UPGRADE_OVERWINTER)
+            && pfrom->nVersion < params.vUpgrades[Consensus::UPGRADE_OVERWINTER].nProtocolVersion)
+        {
+            LogPrintf("peer=%d using obsolete version %i; disconnecting\n", pfrom->id, pfrom->nVersion);
+            pfrom->PushMessage("reject", strCommand, REJECT_OBSOLETE,
+                            strprintf("Version must be %d or greater",
+                            params.vUpgrades[Consensus::UPGRADE_OVERWINTER].nProtocolVersion));
+            pfrom->fDisconnect = true;
+            return false;
+        }
+
         if (pfrom->nVersion == 10300)
             pfrom->nVersion = 300;
         if (!vRecv.empty())
@@ -4839,6 +4852,22 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
+    // Disconnect existing peer connection when:
+    // 1. The version message has been received
+    // 2. Overwinter is active
+    // 3. Peer version is pre-Overwinter
+    else if (NetworkUpgradeActive(GetHeight(), chainparams.GetConsensus(), Consensus::UPGRADE_OVERWINTER)
+            && (pfrom->nVersion < chainparams.GetConsensus().vUpgrades[Consensus::UPGRADE_OVERWINTER].nProtocolVersion))
+    {
+        LogPrintf("peer=%d using obsolete version %i; disconnecting\n", pfrom->id, pfrom->nVersion);
+        pfrom->PushMessage("reject", strCommand, REJECT_OBSOLETE,
+                            strprintf("Version must be %d or greater",
+                            chainparams.GetConsensus().vUpgrades[Consensus::UPGRADE_OVERWINTER].nProtocolVersion));
+        pfrom->fDisconnect = true;
+        return false;
+    }
+
+
     else if (strCommand == "addr")
     {
         vector<CAddress> vAddr;
diff --git a/src/net.cpp b/src/net.cpp
index 05f427707..72ef82d5a 100644
--- a/src/net.cpp
+++ b/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;
diff --git a/src/net.h b/src/net.h
index 6fd49536d..55190baa5 100644
--- a/src/net.h
+++ b/src/net.h
@@ -57,6 +57,8 @@ static const size_t MAPASKFOR_MAX_SZ = MAX_INV_SZ;
 static const size_t SETASKFOR_MAX_SZ = 2 * MAX_INV_SZ;
 /** The maximum number of peer connections to maintain. */
 static const unsigned int DEFAULT_MAX_PEER_CONNECTIONS = 125;
+/** The period before a network upgrade activates, where connections to upgrading peers are preferred (in blocks). */
+static const int NETWORK_UPGRADE_PEER_PREFERENCE_BLOCK_PERIOD = 24 * 24 * 3;
 
 unsigned int ReceiveFloodSize();
 unsigned int SendBufferSize();
diff --git a/src/version.h b/src/version.h
index b68bafc87..25527895d 100644
--- a/src/version.h
+++ b/src/version.h
@@ -9,7 +9,7 @@
  * network protocol versioning
  */
 
-static const int PROTOCOL_VERSION = 170002;
+static const int PROTOCOL_VERSION = 170003;
 
 //! initial proto version, to be increased after version/verack negotiation
 static const int INIT_PROTO_VERSION = 209;