[Sync] Store the past 10 traffic records in memory.

sync/engine/traffic_recorder.h

Index: sync/engine/traffic_recorder.h
diff --git a/sync/engine/traffic_recorder.h b/sync/engine/traffic_recorder.h
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index 0000000000000000000000000000000000000000..0903ee676e81cd4c0be212602f354ca43f658fbd
--- /dev/null
+++ b/sync/engine/traffic_recorder.h
@@ -0,0 +1,74 @@
+// Copyright (c) 2012 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 CHROME_BROWSER_SYNC_ENGINE_TRAFFIC_RECORDER_H_
+#define CHROME_BROWSER_SYNC_ENGINE_TRAFFIC_RECORDER_H_
+#pragma once
+
+#include <deque>
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/gtest_prod_util.h"
+#include "sync/protocol/sync.pb.h"
+
+namespace sync_pb {
+class ClientToServerResponse;
+class ClientToServerMessage;
+}
+
+namespace browser_sync {
+
+class TrafficRecorder {
+ public:
+  enum TrafficMessageType {
+    CLIENT_TO_SERVER_MESSAGE,
+    CLIENT_TO_SERVER_RESPONSE,

[rlarocque, 2012/03/29 17:56:21]

Shouldn't at least one of these be SERVER_TO_CLIENT?

[lipalani1, 2012/03/29 18:39:29]

Ideally yes. But the proto is named this way and there is too much stuff built
around this name.
On 2012/03/29 17:56:21, rlarocque wrote:

+    UNKNOWN_MESSAGE_TYPE
+  };
+
+  struct TrafficRecord {
+    // The serialized message.
+    std::string message;
+    TrafficMessageType message_type;
+    // If the message is too big to be kept in memory then it should be
+    // truncated. For now the entire message is omitted if it is too big.
+    // TODO(lipalani): Truncate the specifics to fit with in size.

[rlarocque, 2012/03/29 17:56:21]

nit: s/with in/within/

[lipalani1, 2012/03/29 18:39:29]

Done.

+    bool truncated;
+
+    TrafficRecord(const std::string& message,
+                  TrafficMessageType message_type,
+                  bool truncated);
+    TrafficRecord();
+    ~TrafficRecord();
+  };
+
+  TrafficRecorder(unsigned int max_messages, unsigned int max_message_size);
+  ~TrafficRecorder();
+
+  void RecordClientToServerMessage(const sync_pb::ClientToServerMessage& msg);
+  void RecordClientToServerResponse(
+      const sync_pb::ClientToServerResponse& response);
+
+  const std::deque<TrafficRecord>& records() {
+    return records_;
+  }
+
+ private:
+  void AddTrafficToQueue(const TrafficRecord& record);
+  void StoreProtoInQueue(const ::google::protobuf::MessageLite& msg,
+                         TrafficMessageType type);
+
+  // Maximum number of messages stored in the queue.
+  unsigned int max_messages_;
+
+  // Maximum size of each message.
+  unsigned int max_message_size_;
+  std::deque<TrafficRecord> records_;

[rlarocque, 2012/03/29 17:56:21]

I normally try to avoid premature optimization, but this is a bit excessive even
by my standards.  

Is it really necessary to copy construct these large strings every time we push
or pop an item?

[lipalani1, 2012/03/29 18:39:29]

answered in the next comment. Bottom line this would involve only one extra
copying.
On 2012/03/29 17:56:21, rlarocque wrote:

+  DISALLOW_COPY_AND_ASSIGN(TrafficRecorder);
+};
+
+}  // namespace browser_sync
+
+#endif  // CHROME_BROWSER_SYNC_ENGINE_TRAFFIC_RECORDER_H_