Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 842 insertions, 0 deletions

diff --git a/security/manager/ssl/DataStorage.cpp b/security/manager/ssl/DataStorage.cpp
new file mode 100644
index 0000000000..44c5bbbabb
--- /dev/null
+++ b/security/manager/ssl/DataStorage.cpp
@@ -0,0 +1,842 @@
+/* -*- 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/. */
+
+#include "DataStorage.h"
+
+#include "mozilla/Assertions.h"
+#include "mozilla/AppShutdown.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/FileUtils.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/Services.h"
+#include "mozilla/StaticMutex.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/TaskQueue.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/Unused.h"
+#include "nsAppDirectoryServiceDefs.h"
+#include "nsDirectoryServiceUtils.h"
+#include "nsIFileStreams.h"
+#include "nsIMemoryReporter.h"
+#include "nsIObserverService.h"
+#include "nsISerialEventTarget.h"
+#include "nsITimer.h"
+#include "nsIThread.h"
+#include "nsNetUtil.h"
+#include "nsPrintfCString.h"
+#include "nsStreamUtils.h"
+#include "nsThreadUtils.h"
+#include "private/pprio.h"
+
+#if defined(XP_WIN)
+#  include "nsILocalFileWin.h"
+#endif
+
+// NB: Read DataStorage.h first.
+
+// The default time between data changing and a write, in milliseconds.
+static const uint32_t sDataStorageDefaultTimerDelay = 5u * 60u * 1000u;
+// The maximum score an entry can have (prevents overflow)
+static const uint32_t sMaxScore = UINT32_MAX;
+// The maximum number of entries per type of data (limits resource use)
+static const uint32_t sMaxDataEntries = 1024;
+static const int64_t sOneDayInMicroseconds =
+    int64_t(24 * 60 * 60) * PR_USEC_PER_SEC;
+
+namespace mozilla {
+
+class DataStorageMemoryReporter final : public nsIMemoryReporter {
+  MOZ_DEFINE_MALLOC_SIZE_OF(MallocSizeOf)
+  ~DataStorageMemoryReporter() = default;
+
+ public:
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD CollectReports(nsIHandleReportCallback* aHandleReport,
+                            nsISupports* aData, bool aAnonymize) final {
+    nsTArray<nsString> fileNames;
+#define DATA_STORAGE(_) \
+  fileNames.AppendElement(NS_LITERAL_STRING_FROM_CSTRING(#_ ".txt"));
+#include "mozilla/DataStorageList.h"
+#undef DATA_STORAGE
+    for (const auto& file : fileNames) {
+      RefPtr<DataStorage> ds = DataStorage::GetFromRawFileName(file);
+      size_t amount = ds->SizeOfIncludingThis(MallocSizeOf);
+      nsPrintfCString path("explicit/data-storage/%s",
+                           NS_ConvertUTF16toUTF8(file).get());
+      Unused << aHandleReport->Callback(
+          ""_ns, path, KIND_HEAP, UNITS_BYTES, amount,
+          "Memory used by PSM data storage cache."_ns, aData);
+    }
+    return NS_OK;
+  }
+};
+
+NS_IMPL_ISUPPORTS(DataStorageMemoryReporter, nsIMemoryReporter)
+
+NS_IMPL_ISUPPORTS(DataStorage, nsIObserver)
+
+mozilla::StaticAutoPtr<DataStorage::DataStorages> DataStorage::sDataStorages;
+
+DataStorage::DataStorage(const nsString& aFilename)
+    : mMutex("DataStorage::mMutex"),
+      mPendingWrite(false),
+      mShuttingDown(false),
+      mInitCalled(false),
+      mReadyMonitor("DataStorage::mReadyMonitor"),
+      mReady(false),
+      mFilename(aFilename) {}
+
+// static
+already_AddRefed<DataStorage> DataStorage::Get(DataStorageClass aFilename) {
+  switch (aFilename) {
+#define DATA_STORAGE(_)     \
+  case DataStorageClass::_: \
+    return GetFromRawFileName(NS_LITERAL_STRING_FROM_CSTRING(#_ ".txt"));
+#include "mozilla/DataStorageList.h"
+#undef DATA_STORAGE
+    default:
+      MOZ_ASSERT_UNREACHABLE("Invalid DataStorage type passed?");
+      return nullptr;
+  }
+}
+
+// static
+already_AddRefed<DataStorage> DataStorage::GetFromRawFileName(
+    const nsString& aFilename) {
+  MOZ_ASSERT(NS_IsMainThread());
+  if (!sDataStorages) {
+    sDataStorages = new DataStorages();
+    ClearOnShutdown(&sDataStorages);
+  }
+  return do_AddRef(sDataStorages->LookupOrInsertWith(
+      aFilename, [&] { return RefPtr{new DataStorage(aFilename)}; }));
+}
+
+size_t DataStorage::SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) {
+  MutexAutoLock lock(mMutex);
+  size_t sizeOfExcludingThis =
+      mPersistentDataTable.ShallowSizeOfExcludingThis(aMallocSizeOf) +
+      mTemporaryDataTable.ShallowSizeOfExcludingThis(aMallocSizeOf) +
+      mPrivateDataTable.ShallowSizeOfExcludingThis(aMallocSizeOf) +
+      mFilename.SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+  return aMallocSizeOf(this) + sizeOfExcludingThis;
+}
+
+nsresult DataStorage::Init() {
+  // Don't access the observer service or preferences off the main thread.
+  if (!NS_IsMainThread()) {
+    MOZ_ASSERT_UNREACHABLE("DataStorage::Init called off main thread");
+    return NS_ERROR_NOT_SAME_THREAD;
+  }
+
+  if (!XRE_IsParentProcess()) {
+    MOZ_ASSERT_UNREACHABLE("DataStorage used in non-parent process");
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  if (AppShutdown::IsInOrBeyond(ShutdownPhase::AppShutdownConfirmed)) {
+    // Reject new DataStorage instances if the browser is shutting down. There
+    // is no guarantee that DataStorage writes will be able to be persisted if
+    // we init during shutdown, so we return an error here to hopefully make
+    // this more explicit and consistent.
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  MutexAutoLock lock(mMutex);
+
+  // Ignore attempts to initialize several times.
+  if (mInitCalled) {
+    return NS_OK;
+  }
+
+  mInitCalled = true;
+
+  static bool memoryReporterRegistered = false;
+  if (!memoryReporterRegistered) {
+    nsresult rv = RegisterStrongMemoryReporter(new DataStorageMemoryReporter());
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+    memoryReporterRegistered = true;
+  }
+
+  nsCOMPtr<nsISerialEventTarget> target;
+  nsresult rv = NS_CreateBackgroundTaskQueue(
+      "DataStorage::mBackgroundTaskQueue", getter_AddRefs(target));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  mBackgroundTaskQueue = TaskQueue::Create(target.forget(), "PSM DataStorage");
+
+  // For test purposes, we can set the write timer to be very fast.
+  uint32_t timerDelayMS = Preferences::GetInt("test.datastorage.write_timer_ms",
+                                              sDataStorageDefaultTimerDelay);
+  rv = NS_NewTimerWithFuncCallback(
+      getter_AddRefs(mTimer), DataStorage::TimerCallback, this, timerDelayMS,
+      nsITimer::TYPE_REPEATING_SLACK_LOW_PRIORITY, "DataStorageTimer",
+      mBackgroundTaskQueue);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = AsyncReadData(lock);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  nsCOMPtr<nsIObserverService> os = services::GetObserverService();
+  if (NS_WARN_IF(!os)) {
+    return NS_ERROR_FAILURE;
+  }
+  // Clear private data as appropriate.
+  os->AddObserver(this, "last-pb-context-exited", false);
+  // Observe shutdown; save data and prevent any further writes.
+  // We need to write to the profile directory, so we should listen for
+  // profile-before-change so that we can safely write to the profile.
+  os->AddObserver(this, "profile-before-change", false);
+  // This is a backstop for xpcshell and other cases where
+  // profile-before-change might not get sent.
+  os->AddObserver(this, "xpcom-shutdown-threads", false);
+  // On mobile, if the app is backgrounded, it may be killed. Observe this
+  // notification to kick off an asynchronous write to avoid losing data.
+  os->AddObserver(this, "application-background", false);
+
+  return NS_OK;
+}
+
+class DataStorage::Reader : public Runnable {
+ public:
+  explicit Reader(DataStorage* aDataStorage)
+      : Runnable("DataStorage::Reader"), mDataStorage(aDataStorage) {}
+  ~Reader();
+
+ private:
+  NS_DECL_NSIRUNNABLE
+
+  static nsresult ParseLine(nsDependentCSubstring& aLine, nsCString& aKeyOut,
+                            Entry& aEntryOut);
+
+  RefPtr<DataStorage> mDataStorage;
+};
+
+DataStorage::Reader::~Reader() {
+  // Notify that calls to Get can proceed.
+  {
+    MonitorAutoLock readyLock(mDataStorage->mReadyMonitor);
+    mDataStorage->mReady = true;
+    mDataStorage->mReadyMonitor.NotifyAll();
+  }
+
+  // This is for tests.
+  nsCOMPtr<nsIRunnable> job = NewRunnableMethod<const char*>(
+      "DataStorage::NotifyObservers", mDataStorage,
+      &DataStorage::NotifyObservers, "data-storage-ready");
+  nsresult rv = NS_DispatchToMainThread(job, NS_DISPATCH_NORMAL);
+  Unused << NS_WARN_IF(NS_FAILED(rv));
+}
+
+NS_IMETHODIMP
+DataStorage::Reader::Run() {
+  nsresult rv;
+  // Concurrent operations on nsIFile objects are not guaranteed to be safe,
+  // so we clone the file while holding the lock and then release the lock.
+  // At that point, we can safely operate on the clone.
+  nsCOMPtr<nsIFile> file;
+  {
+    MutexAutoLock lock(mDataStorage->mMutex);
+    // If we don't have a profile, bail.
+    if (!mDataStorage->mBackingFile) {
+      return NS_OK;
+    }
+    rv = mDataStorage->mBackingFile->Clone(getter_AddRefs(file));
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+  nsCOMPtr<nsIInputStream> fileInputStream;
+  rv = NS_NewLocalFileInputStream(getter_AddRefs(fileInputStream), file);
+  // If we failed for some reason other than the file doesn't exist, bail.
+  if (NS_WARN_IF(NS_FAILED(rv) && rv != NS_ERROR_FILE_NOT_FOUND)) {
+    return rv;
+  }
+
+  // If there is a file with data in it, read it. If there isn't,
+  // we'll essentially fall through to notifying that we're good to go.
+  nsCString data;
+  if (fileInputStream) {
+    // Limit to 2MB of data, but only store sMaxDataEntries entries.
+    rv = NS_ConsumeStream(fileInputStream, 1u << 21, data);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  // Atomically parse the data and insert the entries read.
+  // Don't clear existing entries - they may have been inserted between when
+  // this read was kicked-off and when it was run.
+  {
+    MutexAutoLock lock(mDataStorage->mMutex);
+    // The backing file consists of a list of
+    //   <key>\t<score>\t<last accessed time>\t<value>\n
+    // The final \n is not optional; if it is not present the line is assumed
+    // to be corrupt.
+    int32_t currentIndex = 0;
+    int32_t newlineIndex = 0;
+    do {
+      newlineIndex = data.FindChar('\n', currentIndex);
+      // If there are no more newlines or the data table has too many
+      // entries, we are done.
+      if (newlineIndex < 0 ||
+          mDataStorage->mPersistentDataTable.Count() >= sMaxDataEntries) {
+        break;
+      }
+
+      nsDependentCSubstring line(data, currentIndex,
+                                 newlineIndex - currentIndex);
+      currentIndex = newlineIndex + 1;
+      nsCString key;
+      Entry entry;
+      nsresult parseRV = ParseLine(line, key, entry);
+      if (NS_SUCCEEDED(parseRV)) {
+        // It could be the case that a newer entry was added before
+        // we got around to reading the file. Don't overwrite new entries.
+        mDataStorage->mPersistentDataTable.LookupOrInsert(key,
+                                                          std::move(entry));
+      }
+    } while (true);
+
+    Telemetry::Accumulate(Telemetry::DATA_STORAGE_ENTRIES,
+                          mDataStorage->mPersistentDataTable.Count());
+  }
+
+  return NS_OK;
+}
+
+// The key must be a non-empty string containing no instances of '\t' or '\n',
+// and 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 memory and disk usage.
+/* static */
+nsresult DataStorage::ValidateKeyAndValue(const nsCString& aKey,
+                                          const nsCString& aValue) {
+  if (aKey.IsEmpty()) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  if (aKey.Length() > 256) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  int32_t delimiterIndex = aKey.FindChar('\t', 0);
+  if (delimiterIndex >= 0) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  delimiterIndex = aKey.FindChar('\n', 0);
+  if (delimiterIndex >= 0) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  delimiterIndex = aValue.FindChar('\n', 0);
+  if (delimiterIndex >= 0) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  if (aValue.Length() > 1024) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  return NS_OK;
+}
+
+// Each line is: <key>\t<score>\t<last accessed time>\t<value>
+// Where <score> is a uint32_t as a string, <last accessed time> is a
+// int32_t as a string, and the rest are strings.
+// <value> can contain anything but a newline.
+// Returns a successful status if the line can be decoded into a key and entry.
+// Otherwise, an error status is returned and the values assigned to the
+// output parameters are in an undefined state.
+/* static */
+nsresult DataStorage::Reader::ParseLine(nsDependentCSubstring& aLine,
+                                        nsCString& aKeyOut, Entry& aEntryOut) {
+  // First find the indices to each part of the line.
+  int32_t scoreIndex;
+  scoreIndex = aLine.FindChar('\t', 0) + 1;
+  if (scoreIndex <= 0) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  int32_t accessedIndex = aLine.FindChar('\t', scoreIndex) + 1;
+  if (accessedIndex <= 0) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  int32_t valueIndex = aLine.FindChar('\t', accessedIndex) + 1;
+  if (valueIndex <= 0) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  // Now make substrings based on where each part is.
+  nsDependentCSubstring keyPart(aLine, 0, scoreIndex - 1);
+  nsDependentCSubstring scorePart(aLine, scoreIndex,
+                                  accessedIndex - scoreIndex - 1);
+  nsDependentCSubstring accessedPart(aLine, accessedIndex,
+                                     valueIndex - accessedIndex - 1);
+  nsDependentCSubstring valuePart(aLine, valueIndex);
+
+  nsresult rv;
+  rv = DataStorage::ValidateKeyAndValue(nsCString(keyPart),
+                                        nsCString(valuePart));
+  if (NS_FAILED(rv)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  // Now attempt to decode the score part as a uint32_t.
+  // XXX nsDependentCSubstring doesn't support ToInteger
+  int32_t integer = nsCString(scorePart).ToInteger(&rv);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  if (integer < 0) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  aEntryOut.mScore = (uint32_t)integer;
+
+  integer = nsCString(accessedPart).ToInteger(&rv);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+  if (integer < 0) {
+    return NS_ERROR_UNEXPECTED;
+  }
+  aEntryOut.mLastAccessed = integer;
+
+  // Now set the key and value.
+  aKeyOut.Assign(keyPart);
+  aEntryOut.mValue.Assign(valuePart);
+
+  return NS_OK;
+}
+
+nsresult DataStorage::AsyncReadData(const MutexAutoLock& /*aProofOfLock*/) {
+  mMutex.AssertCurrentThreadOwns();
+  // Allocate a Reader so that even if it isn't dispatched,
+  // the data-storage-ready notification will be fired and Get
+  // will be able to proceed (this happens in its destructor).
+  nsCOMPtr<nsIRunnable> job(new Reader(this));
+  nsresult rv;
+  // If we don't have a profile directory, this will fail.
+  // That's okay - it just means there is no persistent state.
+  rv = NS_GetSpecialDirectory(NS_APP_USER_PROFILE_50_DIR,
+                              getter_AddRefs(mBackingFile));
+  if (NS_FAILED(rv)) {
+    mBackingFile = nullptr;
+    return NS_OK;
+  }
+
+  rv = mBackingFile->Append(mFilename);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = mBackgroundTaskQueue->Dispatch(job.forget());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+bool DataStorage::IsReady() {
+  MonitorAutoLock readyLock(mReadyMonitor);
+  return mReady;
+}
+
+void DataStorage::WaitForReady() {
+  MOZ_DIAGNOSTIC_ASSERT(mInitCalled, "Waiting before Init() has been called?");
+
+  MonitorAutoLock readyLock(mReadyMonitor);
+  while (!mReady) {
+    readyLock.Wait();
+  }
+  MOZ_ASSERT(mReady);
+}
+
+nsCString DataStorage::Get(const nsCString& aKey, DataStorageType aType) {
+  WaitForReady();
+  MutexAutoLock lock(mMutex);
+
+  Entry entry;
+  bool foundValue = GetInternal(aKey, &entry, aType, lock);
+  if (!foundValue) {
+    return ""_ns;
+  }
+
+  // If we're here, we found a value. Maybe update its score.
+  if (entry.UpdateScore()) {
+    PutInternal(aKey, entry, aType, lock);
+  }
+
+  return entry.mValue;
+}
+
+bool DataStorage::GetInternal(const nsCString& aKey, Entry* aEntry,
+                              DataStorageType aType,
+                              const MutexAutoLock& aProofOfLock) {
+  DataStorageTable& table = GetTableForType(aType, aProofOfLock);
+  bool foundValue = table.Get(aKey, aEntry);
+  return foundValue;
+}
+
+DataStorage::DataStorageTable& DataStorage::GetTableForType(
+    DataStorageType aType, const MutexAutoLock& /*aProofOfLock*/) {
+  switch (aType) {
+    case DataStorage_Persistent:
+      return mPersistentDataTable;
+    case DataStorage_Temporary:
+      return mTemporaryDataTable;
+    case DataStorage_Private:
+      return mPrivateDataTable;
+  }
+
+  MOZ_CRASH("given bad DataStorage storage type");
+}
+
+void DataStorage::ReadAllFromTable(DataStorageType aType,
+                                   nsTArray<DataStorageItem>* aItems,
+                                   const MutexAutoLock& aProofOfLock) {
+  for (auto iter = GetTableForType(aType, aProofOfLock).Iter(); !iter.Done();
+       iter.Next()) {
+    DataStorageItem* item = aItems->AppendElement();
+    item->key = iter.Key();
+    item->value = iter.Data().mValue;
+    item->type = aType;
+  }
+}
+
+void DataStorage::GetAll(nsTArray<DataStorageItem>* aItems) {
+  WaitForReady();
+  MutexAutoLock lock(mMutex);
+
+  aItems->SetCapacity(mPersistentDataTable.Count() +
+                      mTemporaryDataTable.Count() + mPrivateDataTable.Count());
+  ReadAllFromTable(DataStorage_Persistent, aItems, lock);
+  ReadAllFromTable(DataStorage_Temporary, aItems, lock);
+  ReadAllFromTable(DataStorage_Private, aItems, lock);
+}
+
+// Limit the number of entries per table. This is to prevent unbounded
+// resource use. The eviction strategy is as follows:
+// - An entry's score is incremented once for every day it is accessed.
+// - Evict an entry with score no more than any other entry in the table
+//   (this is the same as saying evict the entry with the lowest score,
+//    except for when there are multiple entries with the lowest score,
+//    in which case one of them is evicted - which one is not specified).
+void DataStorage::MaybeEvictOneEntry(DataStorageType aType,
+                                     const MutexAutoLock& aProofOfLock) {
+  DataStorageTable& table = GetTableForType(aType, aProofOfLock);
+  if (table.Count() >= sMaxDataEntries) {
+    KeyAndEntry toEvict;
+    // If all entries have score sMaxScore, this won't actually remove
+    // anything. This will never happen, however, because having that high
+    // a score either means someone tampered with the backing file or every
+    // entry has been accessed once a day for ~4 billion days.
+    // The worst that will happen is there will be 1025 entries in the
+    // persistent data table, with the 1025th entry being replaced every time
+    // data with a new key is inserted into the table. This is bad but
+    // ultimately not that concerning, considering that if an attacker can
+    // modify data in the profile, they can cause much worse harm.
+    toEvict.mEntry.mScore = sMaxScore;
+
+    for (auto iter = table.Iter(); !iter.Done(); iter.Next()) {
+      Entry entry = iter.UserData();
+      if (entry.mScore < toEvict.mEntry.mScore) {
+        toEvict.mKey = iter.Key();
+        toEvict.mEntry = entry;
+      }
+    }
+
+    table.Remove(toEvict.mKey);
+  }
+}
+
+nsresult DataStorage::Put(const nsCString& aKey, const nsCString& aValue,
+                          DataStorageType aType) {
+  WaitForReady();
+  MutexAutoLock lock(mMutex);
+
+  nsresult rv;
+  rv = ValidateKeyAndValue(aKey, aValue);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  Entry entry;
+  bool exists = GetInternal(aKey, &entry, aType, lock);
+  if (exists) {
+    entry.UpdateScore();
+  } else {
+    MaybeEvictOneEntry(aType, lock);
+  }
+  entry.mValue = aValue;
+  return PutInternal(aKey, entry, aType, lock);
+}
+
+nsresult DataStorage::PutInternal(const nsCString& aKey, Entry& aEntry,
+                                  DataStorageType aType,
+                                  const MutexAutoLock& aProofOfLock) {
+  mMutex.AssertCurrentThreadOwns();
+  DataStorageTable& table = GetTableForType(aType, aProofOfLock);
+  table.InsertOrUpdate(aKey, aEntry);
+
+  if (aType == DataStorage_Persistent) {
+    mPendingWrite = true;
+  }
+
+  return NS_OK;
+}
+
+void DataStorage::Remove(const nsCString& aKey, DataStorageType aType) {
+  WaitForReady();
+  MutexAutoLock lock(mMutex);
+
+  DataStorageTable& table = GetTableForType(aType, lock);
+  table.Remove(aKey);
+
+  if (aType == DataStorage_Persistent) {
+    mPendingWrite = true;
+  }
+}
+
+class DataStorage::Writer final : public Runnable {
+ public:
+  Writer(nsCString& aData, DataStorage* aDataStorage)
+      : Runnable("DataStorage::Writer"),
+        mData(aData),
+        mDataStorage(aDataStorage) {}
+
+ protected:
+  NS_DECL_NSIRUNNABLE
+
+  nsCString mData;
+  RefPtr<DataStorage> mDataStorage;
+};
+
+NS_IMETHODIMP
+DataStorage::Writer::Run() {
+  nsresult rv;
+  // Concurrent operations on nsIFile objects are not guaranteed to be safe,
+  // so we clone the file while holding the lock and then release the lock.
+  // At that point, we can safely operate on the clone.
+  nsCOMPtr<nsIFile> file;
+  {
+    MutexAutoLock lock(mDataStorage->mMutex);
+    // If we don't have a profile, bail.
+    if (!mDataStorage->mBackingFile) {
+      return NS_OK;
+    }
+    rv = mDataStorage->mBackingFile->Clone(getter_AddRefs(file));
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  nsCOMPtr<nsIOutputStream> outputStream;
+  rv =
+      NS_NewSafeLocalFileOutputStream(getter_AddRefs(outputStream), file,
+                                      PR_CREATE_FILE | PR_TRUNCATE | PR_WRONLY);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  // When the output stream is null, it means we don't have a profile.
+  if (!outputStream) {
+    return NS_OK;
+  }
+
+  const char* ptr = mData.get();
+  uint32_t remaining = mData.Length();
+  uint32_t written = 0;
+  while (remaining > 0) {
+    rv = outputStream->Write(ptr, remaining, &written);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+    remaining -= written;
+    ptr += written;
+  }
+
+  nsCOMPtr<nsISafeOutputStream> safeOutputStream =
+      do_QueryInterface(outputStream);
+  if (!safeOutputStream) {
+    return NS_ERROR_FAILURE;
+  }
+  rv = safeOutputStream->Finish();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // Observed by tests.
+  nsCOMPtr<nsIRunnable> job = NewRunnableMethod<const char*>(
+      "DataStorage::NotifyObservers", mDataStorage,
+      &DataStorage::NotifyObservers, "data-storage-written");
+  rv = NS_DispatchToMainThread(job, NS_DISPATCH_NORMAL);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+nsresult DataStorage::AsyncWriteData(const MutexAutoLock& /*aProofOfLock*/) {
+  mMutex.AssertCurrentThreadOwns();
+  if (!mPendingWrite || mShuttingDown || !mBackingFile) {
+    return NS_OK;
+  }
+
+  nsCString output;
+  for (auto iter = mPersistentDataTable.Iter(); !iter.Done(); iter.Next()) {
+    Entry entry = iter.UserData();
+    output.Append(iter.Key());
+    output.Append('\t');
+    output.AppendInt(entry.mScore);
+    output.Append('\t');
+    output.AppendInt(entry.mLastAccessed);
+    output.Append('\t');
+    output.Append(entry.mValue);
+    output.Append('\n');
+  }
+
+  nsCOMPtr<nsIRunnable> job(new Writer(output, this));
+  nsresult rv = mBackgroundTaskQueue->Dispatch(job.forget());
+  mPendingWrite = false;
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+nsresult DataStorage::Clear() {
+  WaitForReady();
+  MutexAutoLock lock(mMutex);
+  mPersistentDataTable.Clear();
+  mTemporaryDataTable.Clear();
+  mPrivateDataTable.Clear();
+  mPendingWrite = true;
+
+  // Asynchronously clear the file. This is similar to the permission manager
+  // in that it doesn't wait to synchronously remove the data from its backing
+  // storage either.
+  return AsyncWriteData(lock);
+}
+
+/* static */
+void DataStorage::TimerCallback(nsITimer* aTimer, void* aClosure) {
+  RefPtr<DataStorage> aDataStorage = (DataStorage*)aClosure;
+  MutexAutoLock lock(aDataStorage->mMutex);
+  Unused << aDataStorage->AsyncWriteData(lock);
+}
+
+void DataStorage::NotifyObservers(const char* aTopic) {
+  // Don't access the observer service off the main thread.
+  if (!NS_IsMainThread()) {
+    MOZ_ASSERT_UNREACHABLE(
+        "DataStorage::NotifyObservers called off main thread");
+    return;
+  }
+
+  nsCOMPtr<nsIObserverService> os = services::GetObserverService();
+  if (os) {
+    os->NotifyObservers(nullptr, aTopic, mFilename.get());
+  }
+}
+
+void DataStorage::ShutdownTimer() {
+  MOZ_ASSERT(NS_IsMainThread());
+  if (mTimer) {
+    nsresult rv = mTimer->Cancel();
+    Unused << NS_WARN_IF(NS_FAILED(rv));
+    mTimer = nullptr;
+  }
+}
+
+//------------------------------------------------------------
+// DataStorage::nsIObserver
+//------------------------------------------------------------
+
+NS_IMETHODIMP
+DataStorage::Observe(nsISupports* /*aSubject*/, const char* aTopic,
+                     const char16_t* /*aData*/) {
+  if (!NS_IsMainThread()) {
+    MOZ_ASSERT_UNREACHABLE("DataStorage::Observe called off main thread");
+    return NS_ERROR_NOT_SAME_THREAD;
+  }
+
+  if (strcmp(aTopic, "last-pb-context-exited") == 0) {
+    MutexAutoLock lock(mMutex);
+    mPrivateDataTable.Clear();
+    return NS_OK;
+  }
+
+  if (strcmp(aTopic, "profile-before-change") == 0 ||
+      strcmp(aTopic, "xpcom-shutdown-threads") == 0) {
+    RefPtr<TaskQueue> taskQueueToAwait;
+    {
+      MutexAutoLock lock(mMutex);
+      if (!mShuttingDown) {
+        nsresult rv = AsyncWriteData(lock);
+        Unused << NS_WARN_IF(NS_FAILED(rv));
+        mShuttingDown = true;
+        mBackgroundTaskQueue->BeginShutdown();
+        taskQueueToAwait = mBackgroundTaskQueue;
+      }
+    }
+    // Tasks on the background queue may take the lock, so it can't be held
+    // while waiting for them to finish.
+    if (taskQueueToAwait) {
+      taskQueueToAwait->AwaitShutdownAndIdle();
+    }
+    ShutdownTimer();
+  }
+
+  // On mobile, if the app is backgrounded, it may be killed. Kick off an
+  // asynchronous write to avoid losing data.
+  if (strcmp(aTopic, "application-background") == 0) {
+    MutexAutoLock lock(mMutex);
+    if (!mShuttingDown) {
+      nsresult rv = AsyncWriteData(lock);
+      Unused << NS_WARN_IF(NS_FAILED(rv));
+    }
+  }
+
+  return NS_OK;
+}
+
+DataStorage::Entry::Entry()
+    : mScore(0), mLastAccessed((int32_t)(PR_Now() / sOneDayInMicroseconds)) {}
+
+// Updates this entry's score. Returns true if the score has actually changed.
+// If it's been less than a day since this entry has been accessed, the score
+// does not change. Otherwise, the score increases by 1.
+// The default score is 0. The maximum score is the maximum value that can
+// be represented by an unsigned 32 bit integer.
+// This is to handle evictions from our tables, which in turn is to prevent
+// unbounded resource use.
+bool DataStorage::Entry::UpdateScore() {
+  int32_t nowInDays = (int32_t)(PR_Now() / sOneDayInMicroseconds);
+  int32_t daysSinceAccessed = (nowInDays - mLastAccessed);
+
+  // Update the last accessed time.
+  mLastAccessed = nowInDays;
+
+  // If it's been less than a day since we've been accessed,
+  // the score isn't updated.
+  if (daysSinceAccessed < 1) {
+    return false;
+  }
+
+  // Otherwise, increment the score (but don't overflow).
+  if (mScore < sMaxScore) {
+    mScore++;
+  }
+  return true;
+}
+
+}  // namespace mozilla