chaindb: add forceWitness option.

lib/chain/chaindb.js

@@ -229,9 +229,10 @@ ChainDB.prototype._open = co(function* open() {
   if (options) {
     // Verify the options haven't changed.
     this.options.verify(options);
-    this.options = options;
+    if (this.options.forceWitness)
+      yield this.saveOptions();
   } else {
-    yield this.db.put(layout.O, this.options.toRaw());
+    yield this.saveOptions();
   }
 
   if (state) {
@@ -1611,6 +1612,15 @@ ChainDB.prototype.pruneBlock = co(function* pruneBlock(block) {
   this.del(layout.u(hash));
 });
 
+/**
+ * Save database options.
+ * @returns {Promise}
+ */
+
+ChainDB.prototype.saveOptions = function saveOptions() {
+  return this.db.put(layout.O, this.options.toRaw());
+};
+
 /**
  * Chain Options
  * @constructor
@@ -1626,6 +1636,8 @@ function ChainOptions(options) {
   this.indexTX = false;
   this.indexAddress = false;
 
+  this.forceWitness = false;
+
   if (options)
     this.fromOptions(options);
 }
@@ -1656,6 +1668,11 @@ ChainOptions.prototype.fromOptions = function fromOptions(options) {
     this.indexAddress = options.indexAddress;
   }
 
+  if (options.forceWitness != null) {
+    assert(typeof options.forceWitness === 'boolean');
+    this.forceWitness = options.forceWitness;
+  }
+
   return this;
 };
 
@@ -1670,11 +1687,13 @@ ChainOptions.prototype.verify = function verify(options) {
   if (!this.spv && options.spv)
     throw new Error('Cannot retroactively disable SPV.');
 
-  if (this.witness && !options.witness)
+  if (!this.forceWitness) {
-    throw new Error('Cannot retroactively enable witness.');
+    if (this.witness && !options.witness)
+      throw new Error('Cannot retroactively enable witness.');
 
-  if (!this.witness && options.witness)
+    if (!this.witness && options.witness)
-    throw new Error('Cannot retroactively disable witness.');
+      throw new Error('Cannot retroactively disable witness.');
+  }
 
   if (this.prune && !options.prune)
     throw new Error('Cannot retroactively prune.');

lib/node/config.js

@@ -157,6 +157,7 @@ config.parseData = function parseData(data, prefix, dirname) {
 
   // Chain
   options.witness = bool(data.witness);
+  options.forceWitness = bool(data.forcewitness);
   options.prune = bool(data.prune);
   options.useCheckpoints = bool(data.usecheckpoints);
   options.coinCache = bool(data.coincache);

lib/node/fullnode.js

@@ -74,6 +74,7 @@ function Fullnode(options) {
     preload: false,
     spv: false,
     witness: this.options.witness,
+    forceWitness: this.options.forceWitness,
     prune: this.options.prune,
     useCheckpoints: this.options.useCheckpoints,
     coinCache: this.options.coinCache,

lib/node/spvnode.js

@@ -56,6 +56,7 @@ function SPVNode(options) {
     db: this.options.db,
     location: this.location('spvchain'),
     witness: this.options.witness,
+    forceWitness: this.options.forceWitness,
     useCheckpoints: this.options.useCheckpoints,
     maxFiles: this.options.maxFiles,
     spv: true