From 09f449167f01221209b4d55b0e0aea091bd7d58c Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Thu, 17 Nov 2016 04:12:25 -0800
Subject: [PATCH] chain: comments.

---
 lib/chain/chain.js | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/lib/chain/chain.js b/lib/chain/chain.js
index 267f4f4e..5ece74e7 100644
--- a/lib/chain/chain.js
+++ b/lib/chain/chain.js
@@ -315,7 +315,8 @@ Chain.prototype.verify = co(function* verify(block, prev) {
   if (this.options.spv)
     return this.state;
 
-  // Skip any blocks below the last checkpoint.
+  // Skip any blocks below the
+  // last checkpoint.
   if (!this.options.witness) {
     // We can't skip this with segwit
     // enabled since the block may have
@@ -330,7 +331,7 @@ Chain.prototype.verify = co(function* verify(block, prev) {
   ancestors = yield prev.getRetargetAncestors();
   medianTime = prev.getMedianTime(ancestors);
 
-  // Ensure the timestamp is correct
+  // Ensure the timestamp is correct.
   if (block.ts <= medianTime) {
     throw new VerifyError(block,
       'invalid',
@@ -338,6 +339,7 @@ Chain.prototype.verify = co(function* verify(block, prev) {
       0);
   }
 
+  // Ensure the POW is what we expect.
   if (block.bits !== this.getTarget(block, prev, ancestors)) {
     throw new VerifyError(block,
       'invalid',
@@ -345,9 +347,11 @@ Chain.prototype.verify = co(function* verify(block, prev) {
       100);
   }
 
+  // Get the new deployment state.
   state = yield this.getDeployments(block, prev);
 
-  // Make sure the height contained in the coinbase is correct.
+  // Make sure the height contained
+  // in the coinbase is correct.
   if (state.hasBIP34()) {
     if (block.getCoinbaseHeight() !== height) {
       throw new VerifyError(block,
@@ -412,12 +416,11 @@ Chain.prototype.verify = co(function* verify(block, prev) {
   // Get timestamp for tx.isFinal().
   ts = state.hasMTP() ? medianTime : block.ts;
 
-  // Check all transactions
+  // Transactions must be finalized with
+  // regards to nSequence and nLockTime.
   for (i = 0; i < block.txs.length; i++) {
     tx = block.txs[i];
 
-    // Transactions must be finalized with
-    // regards to nSequence and nLockTime.
     if (!tx.isFinal(height, ts)) {
       throw new VerifyError(block,
         'invalid',
@@ -478,14 +481,14 @@ Chain.prototype.getDeployments = co(function* getDeployments(block, prev) {
       throw new VerifyError(block, 'obsolete', 'bad-version', 0);
   }
 
-  // Make sure the height contained in the coinbase is correct.
+  // Coinbase heights are now enforced (bip34).
   if (height >= this.network.block.bip34height) {
     state.bip34 = true;
     if (!this.state.hasBIP34())
       this.logger.warning('BIP34 has been activated.');
   }
 
-  // Signature validation is now enforced (bip66)
+  // Signature validation is now enforced (bip66).
   if (height >= this.network.block.bip66height) {
     state.flags |= constants.flags.VERIFY_DERSIG;
     if (!this.state.hasBIP66())
@@ -708,10 +711,12 @@ Chain.prototype.verifyInputs = co(function* verifyInputs(block, prev, state) {
  */
 
 Chain.prototype.checkHeight = function checkHeight(hash) {
-  if (this.db.hasCache(hash))
-    return this.db.getCache(hash).height;
+  var entry = this.db.getCache(hash);
 
-  return -1;
+  if (!entry)
+    return -1;
+
+  return entry.height;
 };
 
 /**
@@ -849,7 +854,6 @@ Chain.prototype.disconnect = co(function* disconnect(entry) {
 
   this.tip = prev;
   this.height = prev.height;
-
   this.bestHeight = prev.height;
 
   this.emit('tip', prev);
@@ -895,7 +899,6 @@ Chain.prototype.reconnect = co(function* reconnect(entry) {
   this.tip = entry;
   this.height = entry.height;
   this.state = result.state;
-
   this.bestHeight = entry.height;
 
   this.emit('tip', entry);