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

sync/engine/traffic_logger.cc

 // 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.
 
 #include "sync/engine/traffic_logger.h"
 
+#include <queue>
 #include <string>
 
 #include "base/json/json_writer.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/values.h"
 #include "sync/protocol/proto_value_conversions.h"
 #include "sync/protocol/sync.pb.h"
+#include "sync/sessions/sync_session.h"
 
 namespace browser_sync {
 
+using sessions::SyncSession;
+
+TrafficRecord::TrafficRecord(const std::string& message,
+                             TrafficMessageType message_type,
+                             bool truncated) :
+    message(message),
+    message_type(message_type),
+    truncated(truncated) {
+}
+
+TrafficRecord::TrafficRecord()
+    : message_type(UNKNOWN_MESSAGE_TYPE),
+      truncated(false) {
+}
+
+TrafficRecord::~TrafficRecord() {
+}
+
+static const unsigned int kMaxMessages = 10;
+static const unsigned int kMaxMessageSize = 5 * 1024;
 namespace {
 template <class T>
 void LogData(const T& data,
              DictionaryValue* (*to_dictionary_value)(const T&, bool),
              const std::string& description) {
   if (::logging::DEBUG_MODE && VLOG_IS_ON(1)) {
     scoped_ptr<DictionaryValue> value(
         (*to_dictionary_value)(data, true /* include_specifics */));
     std::string message;
     base::JSONWriter::WriteWithOptions(value.get(),
         base::JSONWriter::OPTIONS_PRETTY_PRINT,
         &message);
     DVLOG(1) << "\n" << description << "\n" << message << "\n";
   }
 }
+
+void AddTrafficToQueue(std::queue<TrafficRecord>* traffic_recorder,
+                       const TrafficRecord& record) {
+  while (traffic_recorder->size() > kMaxMessages) {

[akalin, 2012/03/23 00:58:50]

actually, I think >= was correct.  It's just confusing because usually you want
to maintain invariants *after* you do an operation which may violate it.  So

// May violate the size invariant.
traffic_recorder->push(record);
// Maintain size invariant.
while (traffic_recorder->size() > kMaxMessages) {
  traffic_record->pop();
}

would be clearer than

// Maintain a condition just similar enough to the invariant to be confusing.
while (traffic_recorder->size() >= kMaxMessages) {
  traffic_record->pop();
}
// This maintains the invariant, but you have to reason about the previous line
to see it.
traffic_recorder->push(record);

[lipalani1, 2012/03/26 21:25:21]

Done.

+    traffic_recorder->pop();
+  }
+
+  traffic_recorder->push(record);
+}
+
+void StoreProtoInQueue(const ::google::protobuf::MessageLite& msg,
+                       TrafficMessageType type,
+                       SyncSession* session) {
+  bool truncated = false;
+  std::string message;
+  if (msg.ByteSize() >= kMaxMessageSize) {
+    // TODO(lipalani): Trim the specifics to fit in size.
+    truncated = true;
+  } else {
+    msg.SerializeToString(&message);
+  }
+
+  TrafficRecord record(message, type, truncated);
+  AddTrafficToQueue(session->context()->traffic_recorder(), record);
+}
+
 }  // namespace
 
-void LogClientToServerMessage(const sync_pb::ClientToServerMessage& msg) {
+void LogClientToServerMessage(const sync_pb::ClientToServerMessage& msg,
+                              SyncSession* session) {
   LogData(msg, &ClientToServerMessageToValue,
           "******Client To Server Message******");
-  // TODO(lipalani) : Store the data (minus specifics)
-  // in a circular buffer in memory.
+
+  StoreProtoInQueue(msg, CLIENT_TO_SERVER_MESSAGE, session);
 }
 
 void LogClientToServerResponse(
-    const sync_pb::ClientToServerResponse& response) {
+    const sync_pb::ClientToServerResponse& response,
+    SyncSession* session) {
   LogData(response, &ClientToServerResponseToValue,
           "******Server Response******");
-  // TODO(lipalani) : Store the data (minus specifics)
-  // in a circular buffer in memory.
+
+  StoreProtoInQueue(response, CLIENT_TO_SERVER_RESPONSE, session);
 }
 
 }  // namespace browser_sync