buffer: optimize buffer.concat performance

lib/buffer.js

@@ -608,31 +608,57 @@ Buffer[kIsEncodingSymbol] = Buffer.isEncoding;
 Buffer.concat = function concat(list, length) {
   validateArray(list, 'list');
 
-  if (list.length === 0)
+  const listLen = list.length;
+  if (listLen === 0)
     return new FastBuffer();
 
   if (length === undefined) {
     length = 0;
-    for (let i = 0; i < list.length; i++) {
-      if (list[i].length) {
-        length += list[i].length;
+    for (let i = 0; i < listLen; i++) {
+      const buf = list[i];
+      if (!isUint8Array(buf)) {
+        // TODO(BridgeAR): This should not be of type ERR_INVALID_ARG_TYPE.
+        // Instead, find the proper error code for this.
+        throw new ERR_INVALID_ARG_TYPE(
+          `list[${i}]`, ['Buffer', 'Uint8Array'], buf);
       }
+      length += buf.length;
     }
-  } else {
-    validateOffset(length, 'length');
+
+    const buffer = allocate(length);
+    let pos = 0;
+    for (let i = 0; i < listLen; i++) {
+      const buf = list[i];
+      TypedArrayPrototypeSet(buffer, buf, pos);
+      pos += buf.length;
+    }
+
+    if (pos < length) {
+      TypedArrayPrototypeFill(buffer, 0, pos, length);
+    }
+    return buffer;
   }
 
-  const buffer = Buffer.allocUnsafe(length);
+  validateOffset(length, 'length');
+  const buffer = allocate(length);
   let pos = 0;
-  for (let i = 0; i < list.length; i++) {
+  for (let i = 0; i < listLen; i++) {
     const buf = list[i];
     if (!isUint8Array(buf)) {
       // TODO(BridgeAR): This should not be of type ERR_INVALID_ARG_TYPE.
       // Instead, find the proper error code for this.
       throw new ERR_INVALID_ARG_TYPE(
-        `list[${i}]`, ['Buffer', 'Uint8Array'], list[i]);
+        `list[${i}]`, ['Buffer', 'Uint8Array'], buf);
+    }
+    if (pos + buf.length > length) {
+      TypedArrayPrototypeSet(buffer,
+                             TypedArrayPrototypeSlice(buf, 0, length - pos),
+                             pos);
+      pos = length;
+      break;
     }
-    pos += _copyActual(buf, buffer, pos, 0, buf.length, true);
+    TypedArrayPrototypeSet(buffer, buf, pos);
+    pos += buf.length;
   }
 
   // Note: `length` is always equal to `buffer.length` at this point