Mojo C++ bindings: make String16 and gfx::Size available in Blink

third_party/WebKit/Source/platform/mojo/CommonCustomTypesStructTraits.cpp

+// Copyright 2016 The Chromium 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 "platform/mojo/CommonCustomTypesStructTraits.h"
+
+#include "mojo/public/cpp/bindings/array_traits_wtf_vector.h"
+#include "wtf/text/StringImpl.h"
+#include "wtf/text/WTFString.h"
+#include <cstring>
+
+namespace mojo {
+
+// static
+WTF::Vector<uint16_t>
+StructTraits<mojo::common::mojom::String16DataView, ::blink::WebString>::data(

[Ken Rockot(use gerrit already), 2016/10/04 18:20:29]

This is called twice during serialization. You should use SetUpContext and
TearDownContext if you need to do non-trivial setup to get data in a useful
form.

In this case though, I'm not sure it's needed. I don't think we should allow for
accidental use of an 8-bit WebString for a 16-bit string field, so you should
DCHECK(!strView.is8Bit). We should really avoid ever accidentally doing
transcoding for callers.

In the valid 16-bit case, I think we could add a mojo::ConstCArray<T> type (see
src/mojo/public/cpp/bindings/array_traits_carray.h) with the necessary subset of
ArrayTraits defined. Then you can simply return something like:

  return mojo::ConstCArray<uint16_t>(
      reinterpret_cast<const uint16_t*>(strView.characters16()),
      strView.length());

Then there's no need for extra copying or setup.

[Zhiqiang Zhang (Slow), 2016/10/04 20:06:22]

Thanks! Done.
BTW, I saw your other comment, and tried using mojo::CArray<const uint16_t> but
there's a static assert, so I'm adding mojo::ConstCArray.

The static assert is:
/array_serialization.h:119:3: error: static_assert failed "Incorrect array
serializer"

+    const ::blink::WebString& str) {
+  DCHECK(!str.isNull())
+      << "mojo::common::mojom::String16 only accepts non-null blink::WebString";
+  WTF::Vector<uint16_t> rawData(str.length());
+  WTF::StringView strView = str;
+  if (strView.is8Bit()) {
+    WTF::StringImpl::copyChars(reinterpret_cast<UChar*>(rawData.data()),
+                               strView.characters8(), strView.length());
+  } else {
+    memcpy(rawData.data(), strView.characters16(), strView.length());
+  }
+  return rawData;
+}
+
+// static
+bool StructTraits<mojo::common::mojom::String16DataView, ::blink::WebString>::
+    Read(mojo::common::mojom::String16DataView data, ::blink::WebString* out) {
+  mojo::ArrayDataView<uint16_t> view;
+  data.GetDataDataView(&view);
+  if (view.is_null())
+    return false;
+  *out = ::blink::WebString(
+      reinterpret_cast<const ::blink::WebUChar*>(view.data()), view.size());
+  return true;
+}
+
+}  // namespace mojo