Make MetricsService save compressed logs to local state.

components/metrics/persisted_logs.h

 // Copyright 2014 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 COMPONENTS_METRICS_PERSISTED_LOGS_H_
 #define COMPONENTS_METRICS_PERSISTED_LOGS_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 24 matching lines @@
     DEPRECATED_XML_PROTO_MISMATCH,  // The XML and protobuf logs have
                                     // inconsistent data.
     END_RECALL_STATUS       // Number of bins to use to create the histogram.
   };
 
   enum StoreType {
     NORMAL_STORE,       // A standard store operation.
     PROVISIONAL_STORE,  // A store operation that can be easily reverted later.
   };
 
-  // Constructs a PersistedLogs that stores data in |local_state| under
-  // the preference |pref_name|.  Calling code is responsible for ensuring that
-  // the lifetime of |local_state| is longer than the lifetime of PersistedLogs.
-  // When saving logs to disk, we will store either the first |min_log_count|
-  // logs, or at least |min_log_bytes| bytes of logs, whichever is more.
-  // If the optional max_log_size parameter is non-zero, all logs larger than
+  // Constructs a PersistedLogs that stores data in |local_state| under the
+  // preference |pref_name| and also reads from legacy pref |old_pref_name|.
+  // Calling code is responsible for ensuring that the lifetime of |local_state|
+  // is longer than the lifetime of PersistedLogs.
+  //
+  // When saving logs to disk, stores either the first |min_log_count| logs, or
+  // at least |min_log_bytes| bytes of logs, whichever is greater.
+  //
+  // If the optional |max_log_size| parameter is non-zero, all logs larger than
   // that limit will be dropped before logs are written to disk.
   PersistedLogs(PrefService* local_state,
                 const char* pref_name,
+                const char* old_pref_name,
                 size_t min_log_count,
                 size_t min_log_bytes,
                 size_t max_log_size);
   ~PersistedLogs();
 
   // Write list to storage.
   void SerializeLogs();
 
   // Reads the list from the preference.
   LogReadStatus DeserializeLogs();
 
-  // Adds a log to the list.  |input| will be swapped with an empty string.
-  void StoreLog(std::string* input);
+  // Adds a log to the list.
+  void StoreLog(const std::string& log_data);
 
   // Stages the most recent log.  The staged_log will remain the same even if
   // additional logs are added.
   void StageLog();
 
   // Remove the staged log.
   void DiscardStagedLog();
 
   // Saves the staged log, then clears staged_log().
   // If |store_type| is PROVISIONAL_STORE, it can be dropped from storage with
   // a later call to DiscardLastProvisionalStore (if it hasn't already been
   // staged again).
   // This is intended to be used when logs are being saved while an upload is in
   // progress, in case the upload later succeeds.
   // This can only be called if has_staged_log() is true.
   void StoreStagedLogAsUnsent(StoreType store_type);
 
   // Discards the last log stored with StoreStagedLogAsUnsent with |store_type|
   // set to PROVISIONAL_STORE, as long as it hasn't already been re-staged. If
   // the log is no longer present, this is a no-op.
   void DiscardLastProvisionalStore();
 
   // True if a log has been staged.
-  bool has_staged_log() const { return !staged_log_.log.empty(); };
+  bool has_staged_log() const {
+    return !staged_log_.compressed_log_data.empty();
+  }
 
   // Returns the element in the front of the list.
   const std::string& staged_log() const {
     DCHECK(has_staged_log());
-    return staged_log_.log;
+    return staged_log_.compressed_log_data;
   }
 
   // Returns the element in the front of the list.
   const std::string& staged_log_hash() const {
     DCHECK(has_staged_log());
     return staged_log_.hash;
   }
 
   // The number of elements currently stored.
   size_t size() const { return list_.size(); }
 
   // True if there are no stored logs.
   bool empty() const { return list_.empty(); }
 
  private:
   // Writes the list to the ListValue.
   void WriteLogsToPrefList(base::ListValue* list);
 
   // Reads the list from the ListValue.
   LogReadStatus ReadLogsFromPrefList(const base::ListValue& list);
 
+  // Reads the list from the old pref's ListValue.
+  // TODO(asvitkine): Remove the old pref in M39.
+  LogReadStatus ReadLogsFromOldPrefList(const base::ListValue& list);
+
   // A weak pointer to the PrefService object to read and write the preference
   // from.  Calling code should ensure this object continues to exist for the
   // lifetime of the PersistedLogs object.
   PrefService* local_state_;
 
-  // The name of the preference this object stores logs in.
+  // The name of the preference to serialize logs to/from.
   const char* pref_name_;
 
+  // The name of the preference to serialize logs from.
+  // TODO(asvitkine): Remove the old pref in M39.
+  const char* old_pref_name_;
+
   // We will keep at least this |min_log_count_| logs or |min_log_bytes_| bytes
   // of logs, whichever is greater, when writing to disk.  These apply after
   // skipping logs greater than |max_log_size_|.
   const size_t min_log_count_;
   const size_t min_log_bytes_;
 
   // Logs greater than this size will not be written to disk.
   const size_t max_log_size_;
 
   struct LogHashPair {
     // Raw log text, typically a serialized protobuf.

[Ilya Sherman, 2014/06/09 23:17:00]

nit: Please update this comment.

[Alexei Svitkine (slow), 2014/06/10 17:01:15]

Done.

-    std::string log;
+    std::string compressed_log_data;
+
     // The SHA1 hash of log, stored to catch errors from memory corruption.
     std::string hash;
-    // Swap the content of input into log and update the hash.
-    void SwapLog(std::string* input);
+
+    // Initializes the members based on uncompressed |log_data|.
+    void Init(const std::string& log_data);
+
+    // Clears the struct members.
+    void Clear();
+
     // Swap both log and hash from another LogHashPair.
     void Swap(LogHashPair* input);

[Ilya Sherman, 2014/06/09 23:17:00]

nit: Member variables should come below methods.  (I know this isn't newly
introduced by your CL, but might as well clean this up while we're here.)

[Alexei Svitkine (slow), 2014/06/10 17:01:15]

Done.

   };
   // A list of all of the stored logs, stored with SHA1 hashes to check for
   // corruption while they are stored in memory.
   std::vector<LogHashPair> list_;
 
   // The log staged for upload.
   LogHashPair staged_log_;
 
   // The index and type of the last provisional store. If nothing has been
   // provisionally stored, or the last provisional store has already been
   // re-staged, the index will be -1;
   // This is necessary because during an upload there are two logs (staged
   // and current) and a client might store them in either order, so it's
   // not necessarily the case that the provisional store is the last store.
   int last_provisional_store_index_;
 
   DISALLOW_COPY_AND_ASSIGN(PersistedLogs);
 };
 
 }  // namespace metrics
 
 #endif  // COMPONENTS_METRICS_PERSISTED_LOGS_H_