use iterators for getHeight.

lib/bcoin/blockdb.js

@@ -955,29 +955,39 @@ BlockDB.prototype.isSpent = function isSpent(hash, index, callback) {
 BlockDB.prototype.getHeight = function getHeight(callback) {
   var self = this;
   var maxHeight = -1;
-  var stream;
+  var iter;
 
-  callback = utils.asyncify(callback);
-
-  stream = this.index.createKeyStream({
-    start: 'b/h',
-    end: 'b/h~'
+  iter = this.index.db.iterator({
+    gte: 'b/h',
+    lte: 'b/h~',
+    keys: true,
+    values: false,
+    fillCache: false,
+    keyAsBuffer: false
   });
 
-  stream.on('data', function(key) {
-    var parts = key.split('/').slice(2);
-    var height = +parts[0];
-    if (height > maxHeight)
-      maxHeight = height;
-  });
+  (function next() {
+    iter.next(function(err, key, value) {
+      var parts, height;
 
-  stream.on('error', function(err) {
-    return callback(err);
-  });
+      if (err) {
+        return iter.end(function() {
+          return callback(err);
+        });
+      }
 
-  stream.on('end', function() {
-    return callback(null, maxHeight);
-  });
+      // iter.end() here?
+      if (!key)
+        return callback(null, maxHeight);
+
+      parts = key.split('/').slice(2);
+      height = +parts[0];
+      if (height > maxHeight)
+        maxHeight = height;
+
+      next();
+    });
+  })();
 };
 
 BlockDB.prototype.resetHeight = function resetHeight(height, callback, emit) {