Remove unnecessary buffer copies when receiving large packets

Author: dougwilson

Changes.md

@@ -12,6 +12,7 @@ you spot any mistakes.
 * Add new error codes up to MySQL 5.7.17
 * Fix edge cases when determing Query result packets #1547
 * Fix memory leak when using long-running domains #1619 #1620
+* Remove unnecessary buffer copies when receiving large packets
 * Update `bignumber.js` to 3.1.2
 * Use a simple buffer list to improve performance #566 #1590
 

lib/protocol/Parser.js

@@ -100,20 +100,47 @@ Parser.prototype.append = function append(chunk) {
     return;
   }
 
-  var buffer      = chunk;
+  // Calculate slice ranges
   var sliceEnd    = this._buffer.length;
   var sliceStart  = this._packetOffset === null
     ? this._offset
     : this._packetOffset;
   var sliceLength = sliceEnd - sliceStart;
 
+  // Get chunk data
+  var buffer = null;
+  var chunks = !(chunk instanceof Array || Array.isArray(chunk)) ? [chunk] : chunk;
+  var length = 0;
+  var offset = 0;
+
+  for (var i = 0; i < chunks.length; i++) {
+    length += chunks[i].length;
+  }
+
   if (sliceLength !== 0) {
     // Create a new Buffer
-    buffer = new Buffer(sliceLength + chunk.length);
+    buffer = new Buffer(sliceLength + length);
+    offset = 0;
+
+    // Copy data slice
+    offset += this._buffer.copy(buffer, 0, sliceStart, sliceEnd);
 
-    // Copy data
-    this._buffer.copy(buffer, 0, sliceStart, sliceEnd);
-    chunk.copy(buffer, sliceLength);
+    // Copy chunks
+    for (var i = 0; i < chunks.length; i++) {
+      offset += chunks[i].copy(buffer, offset);
+    }
+  } else if (chunks.length > 1) {
+    // Create a new Buffer
+    buffer = new Buffer(length);
+    offset = 0;
+
+    // Copy chunks
+    for (var i = 0; i < chunks.length; i++) {
+      offset += chunks[i].copy(buffer, offset);
+    }
+  } else {
+    // Buffer is the only chunk
+    buffer = chunks[0];
   }
 
   // Adjust data-tracking pointers
@@ -384,19 +411,27 @@ Parser.prototype.packetLength = function packetLength() {
 };
 
 Parser.prototype._combineNextBuffers = function _combineNextBuffers(bytes) {
-  if ((this._buffer.length - this._offset) >= bytes) {
+  var length = this._buffer.length - this._offset;
+
+  if (length >= bytes) {
     return true;
   }
 
-  if (!this._nextBuffers.size) {
+  if ((length + this._nextBuffers.size) < bytes) {
     return false;
   }
 
-  while (this._nextBuffers.size && (this._buffer.length - this._offset) < bytes) {
-    this.append(this._nextBuffers.shift());
+  var buffers     = [];
+  var bytesNeeded = bytes - length;
+
+  while (bytesNeeded > 0) {
+    var buffer = this._nextBuffers.shift();
+    buffers.push(buffer);
+    bytesNeeded -= buffer.length;
   }
 
-  return (this._buffer.length - this._offset) >= bytes;
+  this.append(buffers);
+  return true;
 };
 
 Parser.prototype._combineLongPacketBuffers = function _combineLongPacketBuffers() {