From 6ff3aa6a4a40f33fcb00926dc8f3a25b870aca84 Mon Sep 17 00:00:00 2001
From: Brian White <mscdex@mscdex.net>
Date: Sun, 26 Jan 2020 10:01:21 -0500
Subject: [PATCH] buffer: improve concat() performance

---
 benchmark/buffers/buffer-concat-fill.js | 23 +++++++++++++++++++++++
 lib/buffer.js                           |  9 ++++++---
 test/benchmark/test-benchmark-buffer.js |  1 +
 3 files changed, 30 insertions(+), 3 deletions(-)
 create mode 100644 benchmark/buffers/buffer-concat-fill.js

diff --git a/benchmark/buffers/buffer-concat-fill.js b/benchmark/buffers/buffer-concat-fill.js
new file mode 100644
index 00000000000000..8fb389fe6c8639
--- /dev/null
+++ b/benchmark/buffers/buffer-concat-fill.js
@@ -0,0 +1,23 @@
+'use strict';
+const common = require('../common.js');
+
+const bench = common.createBenchmark(main, {
+  extraSize: [1, 256, 4 * 256],
+  n: [8e5]
+});
+
+function main({ n, extraSize }) {
+  const pieces = 4;
+  const pieceSize = 256;
+
+  const list = Array.from({ length: pieces })
+    .fill(Buffer.allocUnsafe(pieceSize));
+
+  const totalLength = (pieces * pieceSize) + extraSize;
+
+  bench.start();
+  for (let i = 0; i < n; i++) {
+    Buffer.concat(list, totalLength);
+  }
+  bench.end(n);
+}
diff --git a/lib/buffer.js b/lib/buffer.js
index 5a6b75c33e5be6..bf7ae972eff6e5 100644
--- a/lib/buffer.js
+++ b/lib/buffer.js
@@ -238,6 +238,10 @@ function _copy(source, target, targetStart, sourceStart, sourceEnd) {
                                sourceStart);
   }
 
+  return _copyActual(source, target, targetStart, sourceStart, sourceEnd);
+}
+
+function _copyActual(source, target, targetStart, sourceStart, sourceEnd) {
   if (sourceEnd - sourceStart > target.length - targetStart)
     sourceEnd = sourceStart + target.length - targetStart;
 
@@ -568,8 +572,7 @@ Buffer.concat = function concat(list, length) {
       throw new ERR_INVALID_ARG_TYPE(
         `list[${i}]`, ['Buffer', 'Uint8Array'], list[i]);
     }
-    _copy(buf, buffer, pos);
-    pos += buf.length;
+    pos += _copyActual(buf, buffer, pos, 0, buf.length);
   }
 
   // Note: `length` is always equal to `buffer.length` at this point
@@ -577,7 +580,7 @@ Buffer.concat = function concat(list, length) {
     // Zero-fill the remaining bytes if the specified `length` was more than
     // the actual total length, i.e. if we have some remaining allocated bytes
     // there were not initialized.
-    buffer.fill(0, pos, length);
+    TypedArrayFill.call(buffer, 0, pos, length);
   }
 
   return buffer;
diff --git a/test/benchmark/test-benchmark-buffer.js b/test/benchmark/test-benchmark-buffer.js
index 6ce0e542a93474..57130ffb08ba3d 100644
--- a/test/benchmark/test-benchmark-buffer.js
+++ b/test/benchmark/test-benchmark-buffer.js
@@ -15,6 +15,7 @@ runBenchmark('buffers',
                'difflen=false',
                'encoding=utf8',
                'endian=BE',
+               'extraSize=1',
                'len=256',
                'linesCount=1',
                'method=',