3 files changed, 48 insertions, 0 deletions

diff --git a/src/main.cpp b/src/main.cpp
index 336a5a9a86..dc68431282 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -207,6 +207,10 @@ struct CNodeState {
     std::string name;
     // List of asynchronously-determined block rejections to notify this peer about.
     std::vector<CBlockReject> rejects;
+    // The best known block we know this peer has announced.
+    CBlockIndex *pindexBestKnownBlock;
+    // The hash of the last unknown block this peer has announced.
+    uint256 hashLastUnknownBlock;
     list<QueuedBlock> vBlocksInFlight;
     int nBlocksInFlight;
     list<uint256> vBlocksToDownload;
@@ -217,6 +221,8 @@ struct CNodeState {
     CNodeState() {
         nMisbehavior = 0;
         fShouldBan = false;
+        pindexBestKnownBlock = NULL;
+        hashLastUnknownBlock = uint256(0);
         nBlocksToDownload = 0;
         nBlocksInFlight = 0;
         nLastBlockReceive = 0;
@@ -313,6 +319,39 @@ void MarkBlockAsInFlight(NodeId nodeid, const uint256 &hash) {
     mapBlocksInFlight[hash] = std::make_pair(nodeid, it);
 }
 
+/** Check whether the last unknown block a peer advertized is not yet known. */
+void ProcessBlockAvailability(NodeId nodeid) {
+    CNodeState *state = State(nodeid);
+    assert(state != NULL);
+
+    if (state->hashLastUnknownBlock != 0) {
+        map<uint256, CBlockIndex*>::iterator itOld = mapBlockIndex.find(state->hashLastUnknownBlock);
+        if (itOld != mapBlockIndex.end() && itOld->second->nChainWork > 0) {
+            if (state->pindexBestKnownBlock == NULL || itOld->second->nChainWork >= state->pindexBestKnownBlock->nChainWork)
+                state->pindexBestKnownBlock = itOld->second;
+            state->hashLastUnknownBlock = uint256(0);
+        }
+    }
+}
+
+/** Update tracking information about which blocks a peer is assumed to have. */
+void UpdateBlockAvailability(NodeId nodeid, const uint256 &hash) {
+    CNodeState *state = State(nodeid);
+    assert(state != NULL);
+
+    ProcessBlockAvailability(nodeid);
+
+    map<uint256, CBlockIndex*>::iterator it = mapBlockIndex.find(hash);
+    if (it != mapBlockIndex.end() && it->second->nChainWork > 0) {
+        // An actually better block was announced.
+        if (state->pindexBestKnownBlock == NULL || it->second->nChainWork >= state->pindexBestKnownBlock->nChainWork)
+            state->pindexBestKnownBlock = it->second;
+    } else {
+        // An unknown block was announced; just assume that the latest one is the best one.
+        state->hashLastUnknownBlock = hash;
+    }
+}
+
 } // anon namespace
 
 bool GetNodeStateStats(NodeId nodeid, CNodeStateStats &stats) {
@@ -321,6 +360,7 @@ bool GetNodeStateStats(NodeId nodeid, CNodeStateStats &stats) {
     if (state == NULL)
         return false;
     stats.nMisbehavior = state->nMisbehavior;
+    stats.nSyncHeight = state->pindexBestKnownBlock ? state->pindexBestKnownBlock->nHeight : -1;
     return true;
 }
 
@@ -3613,6 +3653,9 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv)
                 PushGetBlocks(pfrom, chainActive.Tip(), GetOrphanRoot(inv.hash));
             }
 
+            if (inv.type == MSG_BLOCK)
+                UpdateBlockAvailability(pfrom->GetId(), inv.hash);
+
             // Track requests for our stuff
             g_signals.Inventory(inv.hash);
         }
@@ -4359,6 +4402,9 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
             pto->fDisconnect = true;
         }
 
+        // Update knowledge of peer's block availability.
+        ProcessBlockAvailability(pto->GetId());
+
         //
         // Message: getdata (blocks)
         //
diff --git a/src/main.h b/src/main.h
index 0332db2163..9487078b74 100644
--- a/src/main.h
+++ b/src/main.h
@@ -185,6 +185,7 @@ bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransa
 
 struct CNodeStateStats {
     int nMisbehavior;
+    int nSyncHeight;
 };
 
 struct CDiskBlockPos
diff --git a/src/rpcnet.cpp b/src/rpcnet.cpp
index a54872ccc4..2d7abb2d58 100644
--- a/src/rpcnet.cpp
+++ b/src/rpcnet.cpp
@@ -134,6 +134,7 @@ Value getpeerinfo(const Array& params, bool fHelp)
         obj.push_back(Pair("startingheight", stats.nStartingHeight));
         if (fStateStats) {
             obj.push_back(Pair("banscore", statestats.nMisbehavior));
+            obj.push_back(Pair("syncheight", statestats.nSyncHeight));
         }
         obj.push_back(Pair("syncnode", stats.fSyncNode));