bluetooth: readValue Blink implementation

Source/modules/bluetooth/BluetoothArrayBuffer.h

+// Copyright 2015 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.
+
+#ifndef BluetoothArrayBuffer_h
+#define BluetoothArrayBuffer_h
+
+#include "core/dom/DOMArrayBuffer.h"
+#include "platform/heap/Handle.h"
+#include "public/platform/WebVector.h"

[haraken, 2015/06/11 01:13:13]

WebVector will work for your purpose, but wouldn't it be better for content/ to
use WebArrayBuffer? As I commented in blink-dev@, you can let content/ use
WebArrayBuffer by doing something like:

- content/ calls web/ (which can use WebArrayBuffer)
- web/ converts WebArrayBuffer into DOMArrayBuffer
- web/ calls modules/ (which can use DOMArrayBuffer)

[Jeffrey Yasskin, 2015/06/11 01:30:36]

I'm not an expert on Promises in Blink, but that's not the flow for any of the
uses I can find. Specifically, content isn't calling into modules; modules is
calling into content through an interface defined in
platform/modules/bluetooth/WebBluetooth.h. The response comes back through the
same channel (defined by a CallbackPromiseAdapter created in the call), not
through the entirely separate channel a pre-Promises implementation might have
used.

Do you know of an example that uses Promises in a flow like what you want?

[haraken, 2015/06/11 01:42:20]

Ah, thanks; now I understand the flow you want. In that case, it is common to
put things in platform/modules/ and call it from content/. Then you cannot use
WebArrayBuffer (which is in web/) easily. If you really need to use
WebArrayBuffer for some reason, we can do that by implementing a couple of proxy
classes, but if WebVector works, that would be the easiest solution.

+
+namespace blink {
+
+class ScriptPromiseResolver;
+
+// BluetoothArrayBuffer is used with CallbackPromiseAdapter to receive
+// WebVector responses. See CallbackPromiseAdapter class comments.
+class BluetoothArrayBuffer {
+    WTF_MAKE_NONCOPYABLE(BluetoothArrayBuffer);
+public:
+    // Interface required by CallbackPromiseAdapter:
+    typedef WebVector<uint8_t> WebType;
+    static PassRefPtr<DOMArrayBuffer> take(ScriptPromiseResolver*, WebVector<uint8_t>*);
+    static void dispose(WebVector<uint8_t>*);
+
+private:
+    BluetoothArrayBuffer() = delete;
+};
+
+} // namespace blink
+
+#endif // BluetoothArrayBuffer_h