[GCM] Add connection factory for creating MCS connections

google_apis/gcm/engine/connection_factory.h

+// Copyright 2013 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 GOOGLE_APIS_GCM_ENGINE_CONNECTION_FACTORY_H_
+#define GOOGLE_APIS_GCM_ENGINE_CONNECTION_FACTORY_H_
+
+#include "base/time/time.h"
+#include "google_apis/gcm/base/gcm_export.h"
+#include "google_apis/gcm/engine/connection_handler.h"
+
+namespace mcs_proto {
+class LoginRequest;
+}
+
+namespace gcm {
+
+// Factory for creating a ConnectionHandler and maintaining its connection.
+// The factory retains ownership of the ConnectionHandler and will enforce
+// backoff policies when attempting connections.
+class GCM_EXPORT ConnectionFactory {
+ public:
+  ConnectionFactory();
+  virtual ~ConnectionFactory();
+
+  // Create a new uninitialized connection handler. Should only be called once.
+  // The factory will retain ownership of the connection handler.
+  // |read_callback| will be invoked with the contents of any received protobuf
+  // message.
+  // |write_callback| will be invoked anytime a message has been successfully
+  // sent. Note: this just means the data was sent to the wire, not that the
+  // other end received it.
+  virtual ConnectionHandler* BuildConnectionHandler(
+      const ConnectionHandler::ProtoReceivedCallback& read_callback,

[akalin, 2013/11/21 04:13:09]

having two callbacks passed in together indicates that perhaps a delegate class
would be better suited. Have you considered that? (I'm not sure if it will
actually be better, since there are pros/cons for both approaches, but wanna
make sure you thought about it).

[Nicolas Zea, 2013/11/22 05:39:18]

Yeah, given that I don't expect this to be reused outside of the MCS client
implementation, and that the callbacks are the two fundamental actions
associated with the handler, I felt leaving it like this was simpler.

+      const ConnectionHandler::ProtoSentCallback& write_callback) = 0;
+
+  // Opens a new connection for use by the locally owned connection handler
+  // (created via BuildConnectionHandler), and initiates login handshake using
+  // |login_request|. Upon completion of the handshake, |read_callback|
+  // will be invoked with a valid mcs_proto::LoginResponse.
+  // Note: BuildConnectionHandler must have already been invoked.
+  virtual void Connect(const mcs_proto::LoginRequest& login_request) = 0;
+
+  // Whether or not the MCS endpoint is currently reachable with an active
+  // connection.
+  virtual bool IsEndpointReachable() const = 0;
+
+  // If in backoff, the time at which the next retry will be made. Otherwise,
+  // a null time, indicating either no attempt to connect has been made or no
+  // backoff is in progress.
+  virtual base::TimeTicks NextRetryAttempt() const = 0;
+};
+
+}  // namespace gcm
+
+#endif  // GOOGLE_APIS_GCM_ENGINE_CONNECTION_FACTORY_H_