add getAsync.

lib/bcoin/chain.js

@@ -756,6 +756,9 @@ ChainDB.prototype.getBuffer = function(size) {
   if (!this._bufferPool[size])
     this._bufferPool[size] = new Buffer(size);
 
+  // if (this._bufferPool[size].__used)
+  //   return new Buffer(size);
+
   return this._bufferPool[size];
 };
 
@@ -828,6 +831,46 @@ ChainDB.prototype.get = function get(height) {
   return entry;
 };
 
+ChainDB.prototype.getAsync = function getAsync(height, callback) {
+  var self = this;
+
+  callback = utils.asyncify(callback);
+
+  if (this._cache[height])
+    return callback(null, this._cache[height]);
+
+  if (this._queue[height])
+    return callback(null, this._queue[height]);
+
+  if (height < 0 || height == null)
+    return callback();
+
+  if ((height + 1) * BLOCK_SIZE > this.size)
+    return callback();
+
+  this._readAsync(BLOCK_SIZE, height * BLOCK_SIZE, function(err, data) {
+    var entry;
+
+    if (err)
+      return callback(err);
+
+    if (!data)
+      return callback();
+
+    // Ignore if it is a null block.
+    if (utils.read32(data, 0) === 0)
+      return callback();
+
+    entry = ChainBlock.fromRaw(self.chain, height, data);
+
+    // Cache the past 1001 blocks in memory
+    // (necessary for isSuperMajority)
+    self.cache(entry);
+
+    return callback(null, entry);
+  });
+};
+
 ChainDB.prototype.save = function save(entry) {
   var self = this;
   var raw, offset;
@@ -843,7 +886,7 @@ ChainDB.prototype.save = function save(entry) {
 };
 
 // This causes weird race conditions with size/count/tip.
-ChainDB.prototype.saveAsync = function save(entry, callback) {
+ChainDB.prototype.saveAsync = function saveAsync(entry, callback) {
   var self = this;
   var raw, offset;
 
@@ -953,6 +996,32 @@ ChainDB.prototype._read = function _read(size, offset) {
   }
 };
 
+ChainDB.prototype._readAsync = function _read(size, offset) {
+  var self = this;
+  var data = new Buffer(size);
+  var index = 0;
+  var bytes;
+
+  if (offset < 0 || offset == null)
+    return false;
+
+  (function callee() {
+    fs.read(self.fd, data, index, size, offset, function(err, bytes) {
+      if (err)
+        return callback(err);
+
+      index += bytes;
+      size -= bytes;
+      offset += bytes;
+
+      if (index === data.length)
+        return callback(null, data);
+
+      callee();
+    });
+  })();
+};
+
 ChainDB.prototype._writeAsync = function _writeAsync(data, offset, callback) {
   var self = this;
   var added = Math.max(0, (offset + data.length) - this.size);