Expose an API on ArrayBufferView to copy out content w/o changing the buffer

test/cctest/test-typedarrays.cc

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <stdlib.h>
+
+#include "src/v8.h"
+#include "test/cctest/cctest.h"
+
+#include "src/api.h"
+#include "src/heap/heap.h"
+#include "src/objects.h"
+
+using namespace v8::internal;
+
+void TestArrayBufferViewContents(LocalContext& env) {
+  v8::Local<v8::Object> obj_a =
+      v8::Local<v8::Object>::Cast(env->Global()->Get(v8_str("a")));
+  CHECK(obj_a->IsArrayBufferView());
+  v8::Local<v8::ArrayBufferView> array_buffer_view =
+      v8::Local<v8::ArrayBufferView>::Cast(obj_a);
+  Handle<JSArrayBufferView> internal_view(
+      v8::Utils::OpenHandle(*array_buffer_view));
+  bool has_buffer = true;
+  if (internal_view->IsJSTypedArray()) {
+    Handle<JSTypedArray> typed_array(JSTypedArray::cast(*internal_view));
+    has_buffer = !typed_array->buffer()->IsSmi();
+  }
+  unsigned char contents[4] = {23, 23, 23, 23};
+  CHECK_EQ(sizeof(contents),
+           array_buffer_view->CopyContents(contents, sizeof(contents)));
+  if (!has_buffer) {
+    CHECK(internal_view->IsJSTypedArray());
+    Handle<JSTypedArray> typed_array(JSTypedArray::cast(*internal_view));
+    CHECK(typed_array->buffer()->IsSmi());
+  }
+  for (size_t i = 0; i < sizeof(contents); ++i) {
+    CHECK_EQ(i, contents[i]);
+  }
+}
+
+
+TEST(CopyContentsTypedArray) {
+  LocalContext env;
+  v8::HandleScope scope(env->GetIsolate());
+  CompileRun(
+      "var a = new Uint8Array(4);"

[jochen (gone - plz use gerrit), 2015/03/31 16:40:27]

this is actually the only case that creates an on-v8-heap typed array

+      "a[0] = 0;"
+      "a[1] = 1;"
+      "a[2] = 2;"
+      "a[3] = 3;");
+  TestArrayBufferViewContents(env);
+}
+
+
+TEST(CopyContentsArray) {
+  LocalContext env;
+  v8::HandleScope scope(env->GetIsolate());
+  CompileRun("var a = new Uint8Array([0, 1, 2, 3]);");
+  TestArrayBufferViewContents(env);
+}
+
+
+TEST(CopyContentsView) {
+  LocalContext env;
+  v8::HandleScope scope(env->GetIsolate());
+  CompileRun(
+      "var b = new ArrayBuffer(6);"
+      "var c = new Uint8Array(b);"
+      "c[0] = -1;"
+      "c[1] = -1;"
+      "c[2] = 0;"
+      "c[3] = 1;"
+      "c[4] = 2;"
+      "c[5] = 3;"
+      "var a = new DataView(b, 2);");
+  TestArrayBufferViewContents(env);
+}