buffer: allow Uint8Array input to methods

Allow all methods on `buffer` and `Buffer` to take `Uint8Array`
arguments where it makes sense. On the native side, there is
effectively no difference, and as a bonus the `isUint8Array`
check is faster than `instanceof Buffer`.

PR-URL: https://github.com/nodejs/node/pull/10236
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>

lib/buffer.js

@@ -2,7 +2,8 @@
 'use strict';
 
 const binding = process.binding('buffer');
-const { isArrayBuffer, isSharedArrayBuffer } = process.binding('util');
+const { isArrayBuffer, isSharedArrayBuffer, isUint8Array } =
+    process.binding('util');
 const bindingObj = {};
 const internalUtil = require('internal/util');
 
@@ -251,13 +252,13 @@ function fromArrayBuffer(obj, byteOffset, length) {
 }
 
 function fromObject(obj) {
-  if (obj instanceof Buffer) {
+  if (isUint8Array(obj)) {
     const b = allocate(obj.length);
 
     if (b.length === 0)
       return b;
 
-    obj.copy(b, 0, 0, obj.length);
+    binding.copy(obj, b, 0, 0, obj.length);
     return b;
   }
 
@@ -287,9 +288,8 @@ Buffer.isBuffer = function isBuffer(b) {
 
 
 Buffer.compare = function compare(a, b) {
-  if (!(a instanceof Buffer) ||
-      !(b instanceof Buffer)) {
-    throw new TypeError('Arguments must be Buffers');
+  if (!isUint8Array(a) || !isUint8Array(b)) {
+    throw new TypeError('Arguments must be Buffers or Uint8Arrays');
   }
 
   if (a === b) {
@@ -306,10 +306,13 @@ Buffer.isEncoding = function(encoding) {
 };
 Buffer[internalUtil.kIsEncodingSymbol] = Buffer.isEncoding;
 
+const kConcatErrMsg = '"list" argument must be an Array ' +
+                      'of Buffer or Uint8Array instances';
+
 Buffer.concat = function(list, length) {
   var i;
   if (!Array.isArray(list))
-    throw new TypeError('"list" argument must be an Array of Buffers');
+    throw new TypeError(kConcatErrMsg);
 
   if (list.length === 0)
     return new FastBuffer();
@@ -326,9 +329,9 @@ Buffer.concat = function(list, length) {
   var pos = 0;
   for (i = 0; i < list.length; i++) {
     var buf = list[i];
-    if (!Buffer.isBuffer(buf))
-      throw new TypeError('"list" argument must be an Array of Buffers');
-    buf.copy(buffer, pos);
+    if (!isUint8Array(buf))
+      throw new TypeError(kConcatErrMsg);
+    binding.copy(buf, buffer, pos);
     pos += buf.length;
   }
 
@@ -495,6 +498,9 @@ function slowToString(encoding, start, end) {
   }
 }
 
+Buffer.prototype.copy = function(target, targetStart, sourceStart, sourceEnd) {
+  return binding.copy(this, target, targetStart, sourceStart, sourceEnd);
+};
 
 Buffer.prototype.toString = function() {
   let result;
@@ -510,8 +516,8 @@ Buffer.prototype.toString = function() {
 
 
 Buffer.prototype.equals = function equals(b) {
-  if (!(b instanceof Buffer))
-    throw new TypeError('Argument must be a Buffer');
+  if (!isUint8Array(b))
+    throw new TypeError('Argument must be a Buffer or Uint8Array');
 
   if (this === b)
     return true;
@@ -539,8 +545,8 @@ Buffer.prototype.compare = function compare(target,
                                             thisStart,
                                             thisEnd) {
 
-  if (!(target instanceof Buffer))
-    throw new TypeError('Argument must be a Buffer');
+  if (!isUint8Array(target))
+    throw new TypeError('Argument must be a Buffer or Uint8Array');
 
   if (start === undefined)
     start = 0;
@@ -604,13 +610,14 @@ function bidirectionalIndexOf(buffer, val, byteOffset, encoding, dir) {
       return binding.indexOfString(buffer, val, byteOffset, encoding, dir);
     }
     return slowIndexOf(buffer, val, byteOffset, encoding, dir);
-  } else if (val instanceof Buffer) {
+  } else if (isUint8Array(val)) {
     return binding.indexOfBuffer(buffer, val, byteOffset, encoding, dir);
   } else if (typeof val === 'number') {
     return binding.indexOfNumber(buffer, val, byteOffset, dir);
   }
 
-  throw new TypeError('"val" argument must be string, number or Buffer');
+  throw new TypeError('"val" argument must be string, number, Buffer ' +
+                      'or Uint8Array');
 }
 
 
@@ -1037,8 +1044,8 @@ Buffer.prototype.readDoubleBE = function readDoubleBE(offset, noAssert) {
 
 
 function checkInt(buffer, value, offset, ext, max, min) {
-  if (!(buffer instanceof Buffer))
-    throw new TypeError('"buffer" argument must be a Buffer instance');
+  if (!isUint8Array(buffer))
+    throw new TypeError('"buffer" argument must be a Buffer or Uint8Array');
   if (value > max || value < min)
     throw new TypeError('"value" argument is out of bounds');
   if (offset + ext > buffer.length)