buffer: speed up concat via TypedArray#set

lib/buffer.js

@@ -240,7 +240,7 @@ function copyImpl(source, target, targetStart, sourceStart, sourceEnd) {
   return _copyActual(source, target, targetStart, sourceStart, sourceEnd);
 }
 
-function _copyActual(source, target, targetStart, sourceStart, sourceEnd) {
+function _copyActual(source, target, targetStart, sourceStart, sourceEnd, isUint8Copy = false) {
   if (sourceEnd - sourceStart > target.byteLength - targetStart)
     sourceEnd = sourceStart + target.byteLength - targetStart;
 
@@ -252,7 +252,11 @@ function _copyActual(source, target, targetStart, sourceStart, sourceEnd) {
   if (nb <= 0)
     return 0;
 
-  _copy(source, target, targetStart, sourceStart, nb);
+  if (sourceStart === 0 && nb === sourceLen && (isUint8Copy || isUint8Array(target))) {
+    TypedArrayPrototypeSet(target, source, targetStart);
+  } else {
+    _copy(source, target, targetStart, sourceStart, nb);
+  }
 
   return nb;
 }
@@ -600,7 +604,7 @@ Buffer.concat = function concat(list, length) {
       throw new ERR_INVALID_ARG_TYPE(
         `list[${i}]`, ['Buffer', 'Uint8Array'], list[i]);
     }
-    pos += _copyActual(buf, buffer, pos, 0, buf.length);
+    pos += _copyActual(buf, buffer, pos, 0, buf.length, true);
   }
 
   // Note: `length` is always equal to `buffer.length` at this point

test/parallel/test-buffer-concat.js

@@ -76,6 +76,13 @@ assert.throws(() => {
 const random10 = common.hasCrypto ?
   require('crypto').randomBytes(10) :
   Buffer.alloc(10, 1);
+const derived18 = Buffer.alloc(18);
+for (let i = 0, j = 0; i < 18; i++) {
+  if (i < 10)
+    derived18[i] = random10[i];
+  else
+    derived18[i] = random10[j++];
+}
 const empty = Buffer.alloc(0);
 
 assert.notDeepStrictEqual(random10, empty);
@@ -85,6 +92,7 @@ assert.deepStrictEqual(Buffer.concat([], 100), empty);
 assert.deepStrictEqual(Buffer.concat([random10], 0), empty);
 assert.deepStrictEqual(Buffer.concat([random10], 10), random10);
 assert.deepStrictEqual(Buffer.concat([random10, random10], 10), random10);
+assert.deepStrictEqual(Buffer.concat([random10, random10], 18), derived18);
 assert.deepStrictEqual(Buffer.concat([empty, random10]), random10);
 assert.deepStrictEqual(Buffer.concat([random10, empty, empty]), random10);
 

test/parallel/test-buffer-copy.js

@@ -226,6 +226,23 @@ b.copy(c, 'not a valid offset');
 // Make sure this acted like a regular copy with `0` offset.
 assert.deepStrictEqual(c, b.slice(0, c.length));
 
+// Copy into a Uint16Array target; bytes are packed into 16-bit elements.
+{
+  const x = new Uint16Array(4);
+  const buf = Buffer.of(1, 2, 3, 4);
+  const copied = buf.copy(x);
+  assert.strictEqual(copied, 4);
+  assert.ok(x instanceof Uint16Array);
+  const bytes = new Uint8Array(x.buffer, x.byteOffset, 4);
+  assert.deepStrictEqual(Array.from(bytes), [1, 2, 3, 4]);
+  const remaining = new Uint8Array(
+    x.buffer,
+    x.byteOffset + 4,
+    x.byteLength - 4
+  );
+  assert.ok(remaining.every((b) => b === 0));
+}
+
 {
   c.fill('C');
   assert.throws(() => {