From a96868ff8e195cafd319cebf6f5fe8a155b16ca7 Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Sat, 4 Mar 2017 15:40:59 -0800
Subject: [PATCH] pool: track peer heights.

---
 lib/http/rpc.js |  2 ++
 lib/net/peer.js |  3 +++
 lib/net/pool.js | 61 +++++++++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 64 insertions(+), 2 deletions(-)

diff --git a/lib/http/rpc.js b/lib/http/rpc.js
index 3a44bb2c..2fbc8ebd 100644
--- a/lib/http/rpc.js
+++ b/lib/http/rpc.js
@@ -538,6 +538,8 @@ RPC.prototype.getpeerinfo = co(function* getpeerinfo(args, help) {
       subver: peer.agent,
       inbound: !peer.outbound,
       startingheight: peer.height,
+      besthash: peer.bestHash,
+      bestheight: peer.bestHeight,
       banscore: peer.banScore,
       inflight: peer.requestMap.keys().map(util.revHex),
       whitelisted: false
diff --git a/lib/net/peer.js b/lib/net/peer.js
index 527bc01f..15bf0b4b 100644
--- a/lib/net/peer.js
+++ b/lib/net/peer.js
@@ -125,6 +125,9 @@ function Peer(options) {
   this.minPing = -1;
   this.blockTime = -1;
 
+  this.bestHash = null;
+  this.bestHeight = -1;
+
   this.connectTimeout = null;
   this.pingTimer = null;
   this.invTimer = null;
diff --git a/lib/net/pool.js b/lib/net/pool.js
index 9d5e926c..57c8cf5f 100644
--- a/lib/net/pool.js
+++ b/lib/net/pool.js
@@ -699,6 +699,30 @@ Pool.prototype.resolveHeaders = function resolveHeaders(peer) {
   this.getBlock(peer, items);
 };
 
+/**
+ * Update all peer heights by their best hash.
+ * @param {Hash} hash
+ * @param {Number} height
+ */
+
+Pool.prototype.resolveHeight = function resolveHeight(hash, height) {
+  var total = 0;
+  var peer;
+
+  for (peer = this.peers.head(); peer; peer = peer.next) {
+    if (peer.bestHash !== hash)
+      continue;
+
+    if (peer.bestHeight !== height) {
+      peer.bestHeight = height;
+      total++;
+    }
+  }
+
+  if (total > 0)
+    this.logger.debug('Resolved height for %d peers.', total);
+};
+
 /**
  * Find the next checkpoint.
  * @private
@@ -1427,13 +1451,19 @@ Pool.prototype._handleInv = co(function* handleInv(peer, packet) {
 
 Pool.prototype.handleBlockInv = co(function* handleBlockInv(peer, hashes) {
   var items = [];
-  var i, hash;
+  var i, hash, exists, height;
 
   assert(hashes.length > 0);
 
   if (!this.syncing)
     return;
 
+  // Always keep track of the peer's best hash.
+  if (!peer.loader || this.chain.synced) {
+    hash = hashes[hashes.length - 1];
+    peer.bestHash = hash;
+  }
+
   // Ignore for now if we're still syncing
   if (!this.chain.synced && !peer.loader)
     return;
@@ -1466,6 +1496,8 @@ Pool.prototype.handleBlockInv = co(function* handleBlockInv(peer, hashes) {
       continue;
     }
 
+    exists = hash;
+
     // Normally we request the hashContinue.
     // In the odd case where we already have
     // it, we can do one of two things: either
@@ -1479,6 +1511,14 @@ Pool.prototype.handleBlockInv = co(function* handleBlockInv(peer, hashes) {
     }
   }
 
+  // Attempt to update the peer's best height
+  // with the last existing hash we know of.
+  if (exists && this.chain.synced) {
+    height = yield this.chain.db.getHeight(exists);
+    if (height !== -1)
+      peer.bestHeight = height;
+  }
+
   this.getBlock(peer, items);
 });
 
@@ -1973,7 +2013,7 @@ Pool.prototype.addBlock = co(function* addBlock(peer, block, flags) {
 
 Pool.prototype._addBlock = co(function* addBlock(peer, block, flags) {
   var hash = block.hash('hex');
-  var entry;
+  var entry, height;
 
   if (!this.syncing)
     return;
@@ -2008,6 +2048,17 @@ Pool.prototype._addBlock = co(function* addBlock(peer, block, flags) {
       return;
     }
 
+    // During a getblocks sync, peers send
+    // their best tip frequently. We can grab
+    // the height commitment from the coinbase.
+    height = block.getCoinbaseHeight();
+
+    if (height !== -1) {
+      peer.bestHash = hash;
+      peer.bestHeight = height;
+      this.resolveHeight(hash, height);
+    }
+
     this.logger.debug('Peer sent an orphan block. Resolving.');
 
     yield this.resolveOrphan(peer, hash);
@@ -2015,6 +2066,12 @@ Pool.prototype._addBlock = co(function* addBlock(peer, block, flags) {
     return;
   }
 
+  if (this.chain.synced) {
+    peer.bestHash = entry.hash;
+    peer.bestHeight = entry.height;
+    this.resolveHeight(entry.hash, entry.height);
+  }
+
   this.logStatus(block);
 
   yield this.resolveChain(peer, hash);