Blimp: define HeliumTransport/HeliumStream interfaces.

blimp/net/helium/helium_stream.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 BLIMP_NET_HELIUM_HELIUM_STREAM_H_
+#define BLIMP_NET_HELIUM_HELIUM_STREAM_H_
+
+#include <memory>
+
+#include "base/callback.h"
+#include "blimp/net/helium/helium_result.h"
+
+namespace blimp {
+
+class HeliumMessage;
+
+// Abstract base class for HeliumMessage-oriented transport streams.
+// Details about how the HeliumStream is bound to the network layer are handled
+// by subclasses of HeliumStream.
+class HeliumStream {
+ public:
+  class Delegate {
+   public:
+    // Invoked when the HeliumStream is disconnected.
+    //
+    // An observer which owns |this| may delete the HeliumStream in response to
+    // receiving an OnStreamDisconnected() notification. The deletion method
+    // must be asynchronously posted to occur *after* the OnStreamDisconnected()
+    // handler, not during.
+    virtual void OnStreamDisconnected(HeliumStream* stream) = 0;
+
+    // Called when a message is read from the HeliumStream.
+    virtual void OnMessageReceived(std::unique_ptr<HeliumMessage> message) = 0;
+  };
+
+  HeliumStream();
+  virtual ~HeliumStream();
+
+  // Sends |helium_message| over the Stream. |callback| is invoked when the
+  // message is sent (or otherwise moved to the low-level write buffers),
+  // which signals the caller that it is clear to send another message.
+  //
+  // The caller is responsible for ensuring that only one outstanding
+  // SendMessage() call is made at a time.
+  virtual void SendMessage(
+      std::unique_ptr<HeliumMessage> helium_message,
+      const base::Callback<void(HeliumResult)>& callback) = 0;
+
+  void SetDelegate(std::unique_ptr<Delegate> delegate);

[perumaal, 2016/10/06 00:02:11]

nit: Delegates in general (IMO) are better off being WeakPtrs.
Specifically, given that the caller of HeliumStream would need to somehow add
'itself' or an object it owns....

[Kevin M, 2016/10/06 00:44:32]

Not sure if I agree. WeakPtrs are definitely good when destruction order is
indeterminate. However, since the SyncManager is the both recipient of delegate
events AND the owner of HeliumStreams, we can guarantee that the Stream will be
torn down before the target Delegate.

+
+ protected:
+  Delegate* delegate() { return delegate_.get(); }
+
+ private:
+  std::unique_ptr<Delegate> delegate_;
+
+  DISALLOW_COPY_AND_ASSIGN(HeliumStream);
+};
+
+}  // namespace blimp
+
+#endif  // BLIMP_NET_HELIUM_HELIUM_STREAM_H_