Make SDCH dictionaries persistent across browser restart.

net/sdch/sdch_owner.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 NET_SDCH_SDCH_OWNER_H_
 #define NET_SDCH_SDCH_OWNER_H_
 
+#include <map>
 #include <string>
 
 #include "base/memory/memory_pressure_listener.h"
+#include "base/prefs/pref_store.h"
 #include "net/base/sdch_observer.h"
 #include "net/url_request/sdch_dictionary_fetcher.h"
 
 class GURL;
+class PersistentPrefStore;
+class ValueMapPrefStore;
+class WriteablePrefStore;
 
 namespace base {
 class Clock;
 }
 
 namespace net {
 class SdchManager;
 class URLRequestContext;
 
 // This class owns the SDCH objects not owned as part of URLRequestContext, and
 // exposes interface for setting SDCH policy.  It should be instantiated by
 // the net/ embedder.
 // TODO(rdsmith): Implement dictionary prioritization.
-class NET_EXPORT SdchOwner : public net::SdchObserver {
+class NET_EXPORT SdchOwner : public net::SdchObserver,
+                             public PrefStore::Observer {
  public:
   static const size_t kMaxTotalDictionarySize;
   static const size_t kMinSpaceForDictionaryFetch;
 
   // Consumer must guarantee that |sdch_manager| and |context| outlive
   // this object.
   SdchOwner(net::SdchManager* sdch_manager, net::URLRequestContext* context);
   ~SdchOwner() override;
 
+  // Preference name used by this class in PersistentPrefStore
+  // argument to EnablePersistentStorage().
+  static std::string PreferenceName();

[mmenke, 2015/02/04 21:14:39]

Should we just make this a static const char[]?  Or get rid of it, per my
PrefRegistry suggestion.

[Elly Fong-Jones, 2015/02/05 23:03:12]

Done.

+
+  // Enables use of pref persistence.  Note that |pref_store| is owned
+  // by the caller, but must be guaranteed to outlive SdchOwner.  The
+  // actual mechanisms by which the WriteablePrefStore are persisted
+  // are the responsibility of the caller.  This routine may only be
+  // called once per SdchOwner instance.
+  void EnablePersistentStorage(PersistentPrefStore* pref_store);
+
   // Defaults to kMaxTotalDictionarySize.
   void SetMaxTotalDictionarySize(size_t max_total_dictionary_size);
 
   // Defaults to kMinSpaceForDictionaryFetch.
   void SetMinSpaceForDictionaryFetch(size_t min_space_for_dictionary_fetch);
 
   // SdchObserver implementation.
   void OnDictionaryUsed(SdchManager* manager,
                         const std::string& server_hash) override;
   void OnGetDictionary(net::SdchManager* manager,
                        const GURL& request_url,
                        const GURL& dictionary_url) override;
   void OnClearDictionaries(net::SdchManager* manager) override;
 
-  // Implementation detail--this is the pathway through which the
-  // fetcher informs the SdchOwner that it's gotten the dictionary.
+  // PrefStore::Observer implementation.
+  void OnPrefValueChanged(const std::string& key) override;
+  void OnInitializationCompleted(bool succeeded) override;
+
+  // Implementation detail--this is the function callback by the callback
+  // passed to the fetcher through which the fetcher informs the SdchOwner
+  // that it's gotten the dictionary.  The first two arguments are
+  // bound locally.
   // Public for testing.
-  void OnDictionaryFetched(const std::string& dictionary_text,
+  void OnDictionaryFetched(base::Time last_used,
+                           int use_count,
+                           const std::string& dictionary_text,
                            const GURL& dictionary_url,
                            const net::BoundNetLog& net_log);
 
   void SetClockForTesting(scoped_ptr<base::Clock> clock);
 
  private:
   // For each active dictionary, stores local info.
-  // Indexed by server hash.
+  // Indexed by the server hash of the dictionary.
   struct DictionaryInfo {
     base::Time last_used;
     int use_count;
     size_t size;
 
     DictionaryInfo() : use_count(0), size(0) {}
     DictionaryInfo(const base::Time& last_used, size_t size)
         : last_used(last_used), use_count(0), size(size) {}
     DictionaryInfo(const DictionaryInfo& rhs) = default;
     DictionaryInfo& operator=(const DictionaryInfo& rhs) = default;
   };
 
   void OnMemoryPressure(
       base::MemoryPressureListener::MemoryPressureLevel level);
 
+  // Schedule loading of all dictionaries described in |persisted_info|.
+  // Returns false if the persisted_info has a bad format.
+  bool SchedulePersistedDictionaryLoads(
+      const base::DictionaryValue& persisted_info);
+
   net::SdchManager* manager_;
   net::SdchDictionaryFetcher fetcher_;
 
-  std::map<std::string, DictionaryInfo> local_dictionary_info_;
   size_t total_dictionary_bytes_;
 
   scoped_ptr<base::Clock> clock_;
 
   size_t max_total_dictionary_size_;
   size_t min_space_for_dictionary_fetch_;
 
+  // Dictionary persistence machinery.
+  // * |in_memory_pref_store_| is created on construction and used in
+  //   the absence of any call to EnablePersistentStorage().
+  // * |external_pref_store_| holds the preference store specified
+  //   by EnablePersistentStorage() (if any), while it is being read in.
+  //   it is only set while the external pref store is being observed.
+  //   A non-null value here signals that the SdchOwner is observing
+  //   the pref store; when read-in completes and observation is no longer
+  //   needed, the pointer is set to null.  This is to avoid lots of
+  //   extra irrelevant function calls; the only observer interface this
+  //   class is interested in is OnInitializationCompleted().
+  // * |pref_store_| holds an unowned pointer to the currently
+  //   active pref store (one of the preceding two).
+  scoped_refptr<ValueMapPrefStore> in_memory_pref_store_;
+  PersistentPrefStore* external_pref_store_;
+
+  WriteablePrefStore* pref_store_;
+
   base::MemoryPressureListener memory_pressure_listener_;
 
   DISALLOW_COPY_AND_ASSIGN(SdchOwner);
 };
 
 }  // namespace net
 
 #endif  // NET_SDCH_SDCH_OWNER_H_