Blimp: create MessageDispatcher class.

blimp/common/net/message_dispatcher.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 BLIMP_COMMON_NET_MESSAGE_DISPATCHER_H_
+#define BLIMP_COMMON_NET_MESSAGE_DISPATCHER_H_
+
+#include <map>
+
+#include "base/threading/thread_checker.h"
+#include "blimp/common/blimp_common_export.h"
+#include "blimp/common/proto/blimp_message.pb.h"
+
+namespace blimp {
+
+// Routes BlimpMessages to feature-specific handlers according to the messages'
+// types.
+class BLIMP_COMMON_EXPORT MessageDispatcher {

[Wez, 2015/10/02 01:10:29]

nit: BlimpMessageDispatcher, for consistency w/ BlimpMessage?

+ public:
+  class Handler {
+   public:
+    // Returns true if |this| is capable of handling |message|.
+    virtual bool Validate(const BlimpMessage& message) const = 0;

[Wez, 2015/10/02 01:10:29]

What's the value in keeping this and OnMessage separate; surely you can just
have OnMessage return |true| if it handles the message, and let the handler
implementation break validation into a separate sub-routine if necessary?

+
+    // Receives |message| for processing.
+    // Validate() is guaranteed to be called prior to this call to OnMessage().
+    // The handler is responsible for routing the call through the appropriate
+    // thread.
+    virtual void OnMessage(const BlimpMessage& message) = 0;

[Wez, 2015/10/02 01:10:29]

nit: OnBlimpMessage?

+  };
+
+  MessageDispatcher();
+  ~MessageDispatcher();
+
+  // Registers a message dispatcher handler which will process all messages
+  // with the type |type|.
+  // Only one handler may be added per type.
+  //
+  // The caller must ensure that the lifetime of |handler| exceeds the lifetime
+  // of |this|.
+  void AddHandler(BlimpMessage::Type type, Handler* handler);
+
+  // Takes a BlimpMessage and dispatches it to the appropriate tab and
+  // feature-specific handler, based on the value of |message.type|.
+  //
+  // Logs an error if there is no Handler registered for
+  // |message.type|, or if the Handler failed to validate the message.
+  void Dispatch(const BlimpMessage& message) const;
+
+ private:
+  std::map<BlimpMessage::Type, Handler*> feature_handler_map_;
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(MessageDispatcher);
+};
+
+}  // namespace blimp
+
+#endif  // BLIMP_COMMON_NET_MESSAGE_DISPATCHER_H_