add version error to ldb.

lib/bcoin/chaindb.js

@@ -239,7 +239,7 @@ ChainDB.prototype._open = function open(callback) {
 
     bcoin.debug('Chain successfully loaded.');
 
-    callback();
+    self.db.checkVersion('V', 0, callback);
   }
 
   this.db.open(function(err) {

lib/bcoin/lowlevelup.js

@@ -10,6 +10,7 @@
 var utils = require('./utils');
 var assert = utils.assert;
 var AsyncObject = require('./async');
+var VERSION_ERROR;
 
 /**
  * Extremely low-level version of levelup.
@@ -376,6 +377,33 @@ LowlevelUp.prototype.lookup = function lookup(options, callback) {
   });
 };
 
+/**
+ * Write and assert a version number for the database.
+ * @param {Number} version
+ * @param {Function} callback
+ */
+
+LowlevelUp.prototype.checkVersion = function checkVersion(key, version, callback) {
+  var self = this;
+  this.get(key, function(err, data) {
+    if (err)
+      return callback(err);
+
+    if (!data) {
+      data = new Buffer(4);
+      data.writeUInt32LE(version, 0, true);
+      return self.put(key, data, callback);
+    }
+
+    data = data.readUInt32LE(0, true);
+
+    if (data !== version)
+      return callback(new Error(VERSION_ERROR));
+
+    return callback();
+  });
+};
+
 /*
  * Helpers
  */
@@ -389,6 +417,14 @@ function isNotFound(err) {
     || /not\s*found/i.test(err.message);
 }
 
+VERSION_ERROR = 'Warning:'
+  + ' Your database does not match the current database version.'
+  + ' This is likely because the database layout or serialization'
+  + ' format has changed drastically. If you want to dump your'
+  + ' data, downgrade to your previous version first. If you do'
+  + ' not think you should be seeing this error, post an issue on'
+  + ' the repo.'
+
 /*
  * Expose
  */

lib/bcoin/walletdb.js

@@ -132,7 +132,12 @@ WalletDB.prototype._open = function open(callback) {
     if (err)
       return callback(err);
 
-    self.tx._loadFilter(callback);
+    self.db.checkVersion('V', 0, function(err) {
+      if (err)
+        return callback(err);
+
+      self.tx._loadFilter(callback);
+    });
   });
 };