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diff --git a/security/manager/ssl/DataStorage.h b/security/manager/ssl/DataStorage.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_DataStorage_h
+#define mozilla_DataStorage_h
+
+#include "mozilla/Atomics.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/Monitor.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/StaticPtr.h"
+#include "nsCOMPtr.h"
+#include "nsTHashMap.h"
+#include "nsIObserver.h"
+#include "nsITimer.h"
+#include "nsRefPtrHashtable.h"
+#include "nsString.h"
+
+class psm_DataStorageTest;
+
+namespace mozilla {
+class DataStorageMemoryReporter;
+class TaskQueue;
+
+/**
+ * DataStorage is a threadsafe, generic, narrow string-based hash map that
+ * persists data on disk and additionally handles temporary and private data.
+ * However, if used in a context where there is no profile directory, data
+ * will not be persisted.
+ *
+ * Its lifecycle is as follows:
+ * - Allocate with a filename (this is or will eventually be a file in the
+ *   profile directory, if the profile exists).
+ * - Call Init() from the main thread. This spins off an asynchronous read
+ *   of the backing file.
+ * - Eventually observers of the topic "data-storage-ready" will be notified
+ *   with the backing filename as the data in the notification when this
+ *   has completed.
+ * - Should the profile directory not be available, (e.g. in xpcshell),
+ *   DataStorage will not initially read any persistent data. The
+ *   "data-storage-ready" event will still be emitted. This follows semantics
+ *   similar to the permission manager and allows tests that test unrelated
+ *   components to proceed without a profile.
+ * - A timer periodically fires on a background thread that checks if any
+ *   persistent data has changed, and if so writes all persistent data to the
+ *   backing file. When this happens, observers will be notified with the
+ *   topic "data-storage-written" and the backing filename as the data.
+ *   It is possible to receive a "data-storage-written" event while there exist
+ *   pending persistent data changes. However, those changes will eventually be
+ *   written when the timer fires again, and eventually another
+ *   "data-storage-written" event will be sent.
+ * - When a DataStorage instance observes the topic "profile-before-change" in
+ *   anticipation of shutdown, all persistent data for that DataStorage is
+ *   written to the backing file (this blocks the main thread). In the process
+ *   of doing this, the background serial event target responsible for these
+ *   writes is then shut down to prevent further writes to that file (the
+ *   background timer is also cancelled when this happens).
+ *   If "profile-before-change" is not observed, this happens upon observing
+ *   "xpcom-shutdown-threads".
+ * - For testing purposes, the preference "test.datastorage.write_timer_ms" can
+ *   be set to cause the asynchronous writing of data to happen more quickly.
+ * - To prevent unbounded memory and disk use, the number of entries in each
+ *   table is limited to 1024. Evictions are handled in by a modified LRU scheme
+ *   (see implementation comments).
+ * - NB: Instances of DataStorage have long lifetimes because they are strong
+ *   observers of events and won't go away until the observer service does.
+ *
+ * For each key/value:
+ * - The key must be a non-empty string containing no instances of '\t' or '\n'
+ *   (this is a limitation of how the data is stored and will be addressed in
+ *   the future).
+ * - The key must have a length no more than 256.
+ * - The value must not contain '\n' and must have a length no more than 1024.
+ *   (the length limits are to prevent unbounded disk and memory usage)
+ */
+
+/**
+ * Data that is DataStorage_Persistent is saved on disk. DataStorage_Temporary
+ * and DataStorage_Private are not saved. DataStorage_Private is meant to
+ * only be set and accessed from private contexts. It will be cleared upon
+ * observing the event "last-pb-context-exited".
+ */
+enum DataStorageType {
+  DataStorage_Persistent,
+  DataStorage_Temporary,
+  DataStorage_Private
+};
+
+struct DataStorageItem final {
+  nsCString key;
+  nsCString value;
+  DataStorageType type;
+};
+
+enum class DataStorageClass {
+#define DATA_STORAGE(_) _,
+#include "mozilla/DataStorageList.h"
+#undef DATA_STORAGE
+};
+
+class DataStorage : public nsIObserver {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  // If there is a profile directory, there is or will eventually be a file
+  // by the name specified by aFilename there.
+  static already_AddRefed<DataStorage> Get(DataStorageClass aFilename);
+
+  // Initializes the DataStorage. Must be called before using.
+  nsresult Init();
+
+  // Given a key and a type of data, returns a value. Returns an empty string if
+  // the key is not present for that type of data. If Get is called before the
+  // "data-storage-ready" event is observed, it will block. NB: It is not
+  // currently possible to differentiate between missing data and data that is
+  // the empty string.
+  nsCString Get(const nsCString& aKey, DataStorageType aType);
+  // Give a key, value, and type of data, adds an entry as appropriate.
+  // Updates existing entries.
+  nsresult Put(const nsCString& aKey, const nsCString& aValue,
+               DataStorageType aType);
+  // Given a key and type of data, removes an entry if present.
+  void Remove(const nsCString& aKey, DataStorageType aType);
+  // Removes all entries of all types of data.
+  nsresult Clear();
+
+  // Read all of the data items.
+  void GetAll(nsTArray<DataStorageItem>* aItems);
+
+  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf);
+
+  // Return true if this data storage is ready to be used.
+  bool IsReady();
+
+  void ArmTimer(const MutexAutoLock& aProofOfLock);
+  void ShutdownTimer();
+
+ private:
+  explicit DataStorage(const nsString& aFilename);
+  virtual ~DataStorage() = default;
+
+  static already_AddRefed<DataStorage> GetFromRawFileName(
+      const nsString& aFilename);
+
+  friend class ::psm_DataStorageTest;
+  friend class mozilla::DataStorageMemoryReporter;
+
+  class Writer;
+  class Reader;
+
+  class Entry {
+   public:
+    Entry();
+    bool UpdateScore();
+
+    uint32_t mScore;
+    int32_t mLastAccessed;  // the last accessed time in days since the epoch
+    nsCString mValue;
+  };
+
+  // Utility class for scanning tables for an entry to evict.
+  class KeyAndEntry {
+   public:
+    nsCString mKey;
+    Entry mEntry;
+  };
+
+  typedef nsTHashMap<nsCStringHashKey, Entry> DataStorageTable;
+  typedef nsRefPtrHashtable<nsStringHashKey, DataStorage> DataStorages;
+
+  void WaitForReady();
+  nsresult AsyncWriteData(const MutexAutoLock& aProofOfLock);
+  nsresult AsyncReadData(const MutexAutoLock& aProofOfLock);
+
+  static nsresult ValidateKeyAndValue(const nsCString& aKey,
+                                      const nsCString& aValue);
+  static void TimerCallback(nsITimer* aTimer, void* aClosure);
+  void NotifyObservers(const char* aTopic);
+
+  bool GetInternal(const nsCString& aKey, Entry* aEntry, DataStorageType aType,
+                   const MutexAutoLock& aProofOfLock);
+  nsresult PutInternal(const nsCString& aKey, Entry& aEntry,
+                       DataStorageType aType,
+                       const MutexAutoLock& aProofOfLock);
+  void MaybeEvictOneEntry(DataStorageType aType,
+                          const MutexAutoLock& aProofOfLock);
+  DataStorageTable& GetTableForType(DataStorageType aType,
+                                    const MutexAutoLock& aProofOfLock);
+
+  void ReadAllFromTable(DataStorageType aType,
+                        nsTArray<DataStorageItem>* aItems,
+                        const MutexAutoLock& aProofOfLock);
+
+  Mutex mMutex;  // This mutex protects access to the following members:
+  DataStorageTable mPersistentDataTable MOZ_GUARDED_BY(mMutex);
+  DataStorageTable mTemporaryDataTable MOZ_GUARDED_BY(mMutex);
+  DataStorageTable mPrivateDataTable MOZ_GUARDED_BY(mMutex);
+  nsCOMPtr<nsIFile> mBackingFile MOZ_GUARDED_BY(mMutex);
+  bool mPendingWrite MOZ_GUARDED_BY(
+      mMutex);  // true if a write is needed but hasn't been dispatched
+  bool mTimerArmed MOZ_GUARDED_BY(mMutex);
+  bool mShuttingDown MOZ_GUARDED_BY(mMutex);
+  RefPtr<TaskQueue> mBackgroundTaskQueue MOZ_GUARDED_BY(mMutex);
+  // (End list of members protected by mMutex)
+
+  nsCOMPtr<nsITimer> mTimer;
+
+  mozilla::Atomic<bool> mInitCalled;  // Indicates that Init() has been called.
+  uint32_t mTimerDelayMS;
+
+  Monitor mReadyMonitor;  // Do not acquire this at the same time as mMutex.
+  bool mReady MOZ_GUARDED_BY(mReadyMonitor);  // Indicates that saved data has
+                                              // been read and Get can proceed.
+
+  const nsString mFilename;
+
+  static StaticAutoPtr<DataStorages> sDataStorages;
+};
+
+}  // namespace mozilla
+
+#endif  // mozilla_DataStorage_h