chain: determine sync state using last checkpoint's chainwork.

lib/blockchain/chain.js

@@ -1802,10 +1802,11 @@ Chain.prototype.maybeSync = function maybeSync() {
     return;
 
   if (this.checkpoints) {
-    if (this.tip.height >= this.network.lastCheckpoint || this.hasChainwork()) {
+    if (!this.hasCheckpoints())
-      this.logger.info('Last checkpoint reached. Disabling checkpoints.');
+      return;
-      this.checkpoints = false;
+
-    }
+    this.logger.info('Last checkpoint reached. Disabling checkpoints.');
+    this.checkpoints = false;
   }
 
   if (this.tip.time < util.now() - this.network.block.maxTipAge)
@@ -1829,6 +1830,17 @@ Chain.prototype.hasChainwork = function hasChainwork() {
   return this.tip.chainwork.cmp(this.network.pow.chainwork) >= 0;
 };
 
+/**
+ * Test the chain to see if it has the
+ * minimum required chainwork for the
+ * last checkpointed block.
+ * @returns {Boolean}
+ */
+
+Chain.prototype.hasCheckpoints = function hasCheckpoints() {
+  return this.tip.chainwork.cmp(this.network.lastChainwork) >= 0;
+};
+
 /**
  * Get the fill percentage.
  * @returns {Number} percent - Ranges from 0.0 to 1.0.

lib/net/pool.js

@@ -251,9 +251,8 @@ Pool.prototype.resetChain = function resetChain() {
   this.headerChain.reset();
   this.headerNext = null;
 
-  const tip = this.chain.tip;
+  if (!this.chain.hasCheckpoints()) {
-
+    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);

lib/protocol/network.js

@@ -32,6 +32,7 @@ function Network(options) {
   this.port = options.port;
   this.checkpointMap = options.checkpointMap;
   this.lastCheckpoint = options.lastCheckpoint;
+  this.lastChainwork = options.lastChainwork;
   this.checkpoints = [];
   this.halvingInterval = options.halvingInterval;
   this.genesis = options.genesis;

lib/protocol/networks.js

@@ -112,6 +112,17 @@ main.checkpointMap = {
 
 main.lastCheckpoint = 470000;
 
+/**
+ * Last checkpoint chainwork.
+ * @const {BN}
+ * @default
+ */
+
+main.lastChainwork = new BN(
+  '0000000000000000000000000000000000000000005dcc420d5bcce89a5d0d04',
+  'hex'
+);
+
 /**
  * @const {Number}
  * @default
@@ -513,6 +524,10 @@ testnet.checkpointMap = {
 };
 
 testnet.lastCheckpoint = 1050000;
+testnet.lastChainwork = new BN(
+  '00000000000000000000000000000000000000000000001a461538dc48da1a06',
+  'hex'
+);
 
 testnet.halvingInterval = 210000;
 
@@ -674,6 +689,10 @@ regtest.port = 48444;
 
 regtest.checkpointMap = {};
 regtest.lastCheckpoint = 0;
+regtest.lastChainwork = new BN(
+  '0000000000000000000000000000000000000000000000000000000000000002',
+  'hex'
+);
 
 regtest.halvingInterval = 150;
 
@@ -836,6 +855,10 @@ simnet.port = 18555;
 simnet.checkpointMap = {};
 
 simnet.lastCheckpoint = 0;
+simnet.lastChainwork = new BN(
+  '0000000000000000000000000000000000000000000000000000000000000002',
+  'hex'
+);
 
 simnet.halvingInterval = 210000;