buffer: fix Buffer::HasInstance() check

It was returning true for typed arrays. Check that the object was
instantiated with the Buffer constructor.

src/node.js

@@ -165,6 +165,7 @@
     global.GLOBAL = global;
     global.root = global;
     global.Buffer = NativeModule.require('buffer').Buffer;
+    process.binding('buffer').setFastBufferConstructor(global.Buffer);
   };
 
   startup.globalTimeouts = function() {

src/node_buffer.cc

@@ -61,6 +61,7 @@ using namespace v8;
 static Persistent<String> length_symbol;
 static Persistent<String> chars_written_sym;
 static Persistent<String> write_sym;
+static Persistent<Function> fast_buffer_constructor;
 Persistent<FunctionTemplate> Buffer::constructor_template;
 
 
@@ -913,14 +914,23 @@ bool Buffer::HasInstance(Handle<Value> val) {
   if (!val->IsObject()) return false;
   Local<Object> obj = val->ToObject();
 
-  if (obj->GetIndexedPropertiesExternalArrayDataType() == kExternalUnsignedByteArray)
-    return true;
+  ExternalArrayType type = obj->GetIndexedPropertiesExternalArrayDataType();
+  if (type != kExternalUnsignedByteArray)
+    return false;
 
   // Also check for SlowBuffers that are empty.
   if (constructor_template->HasInstance(obj))
     return true;
 
-  return false;
+  assert(!fast_buffer_constructor.IsEmpty());
+  return obj->GetConstructor()->StrictEquals(fast_buffer_constructor);
+}
+
+
+Handle<Value> SetFastBufferConstructor(const Arguments& args) {
+  assert(args[0]->IsFunction());
+  fast_buffer_constructor = Persistent<Function>::New(args[0].As<Function>());
+  return Undefined();
 }
 
 
@@ -1036,6 +1046,8 @@ void Buffer::Initialize(Handle<Object> target) {
                   Buffer::MakeFastBuffer);
 
   target->Set(String::NewSymbol("SlowBuffer"), constructor_template->GetFunction());
+  target->Set(String::NewSymbol("setFastBufferConstructor"),
+              FunctionTemplate::New(SetFastBufferConstructor)->GetFunction());
 
   HeapProfiler::DefineWrapperClass(BUFFER_CLASS_ID, WrapperInfo);
 }

test/simple/test-typed-arrays.js

@@ -201,3 +201,41 @@ assert.throws(function() {
   view.setUint16(0, 1);
   assert.equal(view.getUint16(0), 1);
 })();
+
+(function() {
+  // Backing store should not be shared.
+  var a = new Uint8Array(1);
+  var b = new Uint8Array(a);
+  a[0] = 0;
+  b[0] = 1;
+  assert.equal(a[0], 0);
+  assert.equal(b[0], 1);
+  assert.notEqual(a, b.buffer);
+  assert.notEqual(a.buffer, b.buffer);
+})();
+
+(function() {
+  // Backing store should not be shared.
+  var a = new Uint8Array(2);
+  var b = new Uint16Array(a);
+  a[0] = 0;
+  a[1] = 0;
+  b[0] = 257;
+  assert.equal(a[0], 0);
+  assert.equal(a[1], 0);
+  assert.equal(b[0], 257);
+  assert.notEqual(a, b.buffer);
+  assert.notEqual(a.buffer, b.buffer);
+})();
+
+(function() {
+  // Backing store should be shared.
+  var abuf = new ArrayBuffer(32);
+  var a = new Uint8Array(abuf);
+  var b = new Uint8Array(abuf);
+  a[0] = 0;
+  b[0] = 1;
+  assert.equal(a[0], 1);
+  assert.equal(b[0], 1);
+  assert.equal(a.buffer, b.buffer);
+})();