ppapi: PPB_VpnProvider: Implement Resource Stub

ppapi/shared_impl/vpn_provider_util.h

+// 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.
+
+#ifndef PPAPI_SHAERD_IMPL_VPN_PROVIDER_UTIL_H_
+#define PPAPI_SHAERD_IMPL_VPN_PROVIDER_UTIL_H_
+
+#include <memory>
+
+#include "base/memory/shared_memory.h"
+#include "ppapi/shared_impl/ppapi_shared_export.h"
+
+namespace ppapi {
+
+class PPAPI_SHARED_EXPORT VpnProviderSharedBuffer {
+ public:
+  VpnProviderSharedBuffer(uint32_t capacity,
+                          uint32_t packet_size,
+                          std::unique_ptr<base::SharedMemory> shm);
+  ~VpnProviderSharedBuffer();
+
+  bool GetAvailable(uint32_t* id);
+  void SetAvailable(uint32_t id, bool value);
+  void* GetBuffer(uint32_t id);
+  base::SharedMemoryHandle GetHandle();

[bbudge, 2016/05/17 09:50:12]

This doesn't seem to be used yet. It seems undesirable to expose the underlying
shm buffer. Is it necessary?

[adrian.belgun, 2016/05/17 11:05:29]

This class is used by both the Resource and the Resource Host. 
This method is used in the Resource Host's Bind() flow to pass the handle to the
Resource.

context.params.AppendHandle(ppapi::proxy::SerializedHandle(
    send_packet_buffer_->GetHandle(),
    kMaxQueuedPackets * kMaxPacketSizeInBytes));

https://codereview.chromium.org/1735473002/diff/240001/content/browser/render...

[bbudge, 2016/05/17 13:34:39]

But the host has access to that handle already (to construct the shared buffer).

[adrian.belgun, 2016/05/17 15:25:29]

The issue is that this API is tied to the chrome.vpnProvider JS API. 
A connection is bound after it has connected. If the connection gets
disconnected it will also get unbound. Thus, in the app's lifetime, Bind() can
be called multiple times - on every reconnect.

The proposed implementation keeps the shm handle inside the shared buffer class.
Thus, on ulterior Bind() calls, the shm will be retrieved from cache.

The shm will be cleared when the resource gets destroyed. 

+
+ private:
+  uint32_t capacity_;
+  uint32_t packet_size_;
+  std::unique_ptr<base::SharedMemory> shm_;
+  std::unique_ptr<bool[]> available_;

[bbudge, 2016/05/17 09:50:12]

std::vector<bool> is a little tricky to use but should work here.

[adrian.belgun, 2016/05/17 11:05:29]

Done.

+};
+
+}  // namespace ppapi
+
+#endif  // PPAPI_SHAERD_IMPL_VPN_PROVIDER_UTIL_H_