From 1a4268544f309340a960aa5a932aa06fabee3e4b Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Tue, 1 Aug 2017 01:38:04 -0700
Subject: [PATCH] chain: better checkpoint handling.

---
 lib/blockchain/chain.js | 20 ++++++++++++++------
 lib/net/pool.js         |  6 +++---
 lib/node/fullnode.js    |  1 +
 lib/node/spvnode.js     |  1 +
 4 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/lib/blockchain/chain.js b/lib/blockchain/chain.js
index b57fde6a..695e5799 100644
--- a/lib/blockchain/chain.js
+++ b/lib/blockchain/chain.js
@@ -1469,7 +1469,10 @@ Chain.prototype.logStatus = function logStatus(start, block, entry) {
  */
 
 Chain.prototype.verifyCheckpoint = function verifyCheckpoint(prev, hash) {
-  if (!this.checkpoints)
+  if (!this.options.checkpoints)
+    return true;
+
+  if (!this.checkpoints && !this.options.enforceCheckpoints)
     return true;
 
   const height = prev.height + 1;
@@ -1799,11 +1802,10 @@ Chain.prototype.maybeSync = function maybeSync() {
     return;
 
   if (this.checkpoints) {
-    if (this.tip.height < this.network.lastCheckpoint)
-      return;
-
-    this.logger.info('Last checkpoint reached. Disabling checkpoints.');
-    this.checkpoints = false;
+    if (this.tip.height >= this.network.lastCheckpoint || this.hasChainwork()) {
+      this.logger.info('Last checkpoint reached. Disabling checkpoints.');
+      this.checkpoints = false;
+    }
   }
 
   if (this.tip.time < util.now() - this.network.block.maxTipAge)
@@ -2404,6 +2406,7 @@ function ChainOptions(options) {
   this.entryCache = 5000;
   this.maxOrphans = 20;
   this.checkpoints = true;
+  this.enforceCheckpoints = false;
 
   if (options)
     this.fromOptions(options);
@@ -2518,6 +2521,11 @@ ChainOptions.prototype.fromOptions = function fromOptions(options) {
     this.checkpoints = options.checkpoints;
   }
 
+  if (options.enforceCheckpoints != null) {
+    assert(typeof options.enforceCheckpoints === 'boolean');
+    this.enforceCheckpoints = options.enforceCheckpoints;
+  }
+
   return this;
 };
 
diff --git a/lib/net/pool.js b/lib/net/pool.js
index f8c99870..e5a1338d 100644
--- a/lib/net/pool.js
+++ b/lib/net/pool.js
@@ -242,8 +242,6 @@ Pool.prototype._open = async function _open() {
  */
 
 Pool.prototype.resetChain = function resetChain() {
-  const tip = this.chain.tip;
-
   if (!this.options.checkpoints)
     return;
 
@@ -253,7 +251,9 @@ Pool.prototype.resetChain = function resetChain() {
   this.headerChain.reset();
   this.headerNext = null;
 
-  if (tip.height < this.network.lastCheckpoint) {
+  const tip = this.chain.tip;
+
+  if (tip.height < this.network.lastCheckpoint && !this.chain.hasChainwork()) {
     this.checkpoints = true;
     this.chain.checkpoints = true;
     this.headerTip = this.getNextTip(tip.height);
diff --git a/lib/node/fullnode.js b/lib/node/fullnode.js
index 68b66dc0..2cb03b42 100644
--- a/lib/node/fullnode.js
+++ b/lib/node/fullnode.js
@@ -61,6 +61,7 @@ function FullNode(options) {
     bip148: this.config.bool('bip148'),
     prune: this.config.bool('prune'),
     checkpoints: this.config.bool('checkpoints'),
+    enforceCheckpoints: this.config.bool('enforce-checkpoints'),
     coinCache: this.config.mb('coin-cache'),
     entryCache: this.config.num('entry-cache'),
     indexTX: this.config.bool('index-tx'),
diff --git a/lib/node/spvnode.js b/lib/node/spvnode.js
index 966dce16..ba4710f0 100644
--- a/lib/node/spvnode.js
+++ b/lib/node/spvnode.js
@@ -54,6 +54,7 @@ function SPVNode(options) {
     entryCache: this.config.num('entry-cache'),
     forceFlags: this.config.bool('force-flags'),
     checkpoints: this.config.bool('checkpoints'),
+    enforceCheckpoints: this.config.bool('enforce-checkpoints'),
     bip91: this.config.bool('bip91'),
     bip148: this.config.bool('bip148'),
     spv: true