mozStorageService.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: sw=2 ts=2 et lcs=trail\:.,tab\:>~ :
 * 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 "mozilla/Attributes.h"
#include "mozilla/DebugOnly.h"

#include "mozStorageService.h"
#include "mozStorageConnection.h"
#include "nsAutoPtr.h"
#include "nsCollationCID.h"
#include "nsComponentManagerUtils.h"
#include "nsEmbedCID.h"
#include "nsExceptionHandler.h"
#include "nsThreadUtils.h"
#include "mozStoragePrivateHelpers.h"
#include "nsIObserverService.h"
#include "nsIPropertyBag2.h"
#include "mozilla/Services.h"
#include "mozilla/Preferences.h"
#include "mozilla/LateWriteChecks.h"
#include "mozIStorageCompletionCallback.h"
#include "mozIStoragePendingStatement.h"

#include "sqlite3.h"
#include "mozilla/AutoSQLiteLifetime.h"

#ifdef XP_WIN
// "windows.h" was included and it can #define lots of things we care about...
#  undef CompareString
#endif

////////////////////////////////////////////////////////////////////////////////
//// Defines

#define PREF_TS_SYNCHRONOUS "toolkit.storage.synchronous"
#define PREF_TS_SYNCHRONOUS_DEFAULT 1

#define PREF_TS_PAGESIZE "toolkit.storage.pageSize"

// This value must be kept in sync with the value of SQLITE_DEFAULT_PAGE_SIZE in
// third_party/sqlite3/src/Makefile.in.
#define PREF_TS_PAGESIZE_DEFAULT 32768

namespace mozilla {
namespace storage {

////////////////////////////////////////////////////////////////////////////////
//// Memory Reporting

#ifdef MOZ_DMD
mozilla::Atomic<size_t> gSqliteMemoryUsed;
#endif

static int64_t StorageSQLiteDistinguishedAmount() {
  return ::sqlite3_memory_used();
}

/**
 * Passes a single SQLite memory statistic to a memory reporter callback.
 *
 * @param aHandleReport
 *        The callback.
 * @param aData
 *        The data for the callback.
 * @param aConn
 *        The SQLite connection.
 * @param aPathHead
 *        Head of the path for the memory report.
 * @param aKind
 *        The memory report statistic kind, one of "stmt", "cache" or
 *        "schema".
 * @param aDesc
 *        The memory report description.
 * @param aOption
 *        The SQLite constant for getting the measurement.
 * @param aTotal
 *        The accumulator for the measurement.
 */
static void ReportConn(nsIHandleReportCallback* aHandleReport,
                       nsISupports* aData, Connection* aConn,
                       const nsACString& aPathHead, const nsACString& aKind,
                       const nsACString& aDesc, int32_t aOption,
                       size_t* aTotal) {
  nsCString path(aPathHead);
  path.Append(aKind);
  path.AppendLiteral("-used");

  int32_t val = aConn->getSqliteRuntimeStatus(aOption);
  aHandleReport->Callback(EmptyCString(), path, nsIMemoryReporter::KIND_HEAP,
                          nsIMemoryReporter::UNITS_BYTES, int64_t(val), aDesc,
                          aData);
  *aTotal += val;
}

// Warning: To get a Connection's measurements requires holding its lock.
// There may be a delay getting the lock if another thread is accessing the
// Connection.  This isn't very nice if CollectReports is called from the main
// thread!  But at the time of writing this function is only called when
// about:memory is loaded (not, for example, when telemetry pings occur) and
// any delays in that case aren't so bad.
NS_IMETHODIMP
Service::CollectReports(nsIHandleReportCallback* aHandleReport,
                        nsISupports* aData, bool aAnonymize) {
  size_t totalConnSize = 0;
  {
    nsTArray<RefPtr<Connection>> connections;
    getConnections(connections);

    for (uint32_t i = 0; i < connections.Length(); i++) {
      RefPtr<Connection>& conn = connections[i];

      // Someone may have closed the Connection, in which case we skip it.
      // Note that we have consumers of the synchronous API that are off the
      // main-thread, like the DOM Cache and IndexedDB, and as such we must be
      // sure that we have a connection.
      MutexAutoLock lockedAsyncScope(conn->sharedAsyncExecutionMutex);
      if (!conn->connectionReady()) {
        continue;
      }

      nsCString pathHead("explicit/storage/sqlite/");
      // This filename isn't privacy-sensitive, and so is never anonymized.
      pathHead.Append(conn->getFilename());
      pathHead.Append('/');

      SQLiteMutexAutoLock lockedScope(conn->sharedDBMutex);

      NS_NAMED_LITERAL_CSTRING(
          stmtDesc,
          "Memory (approximate) used by all prepared statements used by "
          "connections to this database.");
      ReportConn(aHandleReport, aData, conn, pathHead,
                 NS_LITERAL_CSTRING("stmt"), stmtDesc,
                 SQLITE_DBSTATUS_STMT_USED, &totalConnSize);

      NS_NAMED_LITERAL_CSTRING(
          cacheDesc,
          "Memory (approximate) used by all pager caches used by connections "
          "to this database.");
      ReportConn(aHandleReport, aData, conn, pathHead,
                 NS_LITERAL_CSTRING("cache"), cacheDesc,
                 SQLITE_DBSTATUS_CACHE_USED_SHARED, &totalConnSize);

      NS_NAMED_LITERAL_CSTRING(
          schemaDesc,
          "Memory (approximate) used to store the schema for all databases "
          "associated with connections to this database.");
      ReportConn(aHandleReport, aData, conn, pathHead,
                 NS_LITERAL_CSTRING("schema"), schemaDesc,
                 SQLITE_DBSTATUS_SCHEMA_USED, &totalConnSize);
    }

#ifdef MOZ_DMD
    if (::sqlite3_memory_used() != int64_t(gSqliteMemoryUsed)) {
      NS_WARNING(
          "memory consumption reported by SQLite doesn't match "
          "our measurements");
    }
#endif
  }

  int64_t other = ::sqlite3_memory_used() - totalConnSize;

  MOZ_COLLECT_REPORT("explicit/storage/sqlite/other", KIND_HEAP, UNITS_BYTES,
                     other, "All unclassified sqlite memory.");

  return NS_OK;
}

////////////////////////////////////////////////////////////////////////////////
//// Service

NS_IMPL_ISUPPORTS(Service, mozIStorageService, nsIObserver, nsIMemoryReporter)

Service* Service::gService = nullptr;

already_AddRefed<Service> Service::getSingleton() {
  if (gService) {
    return do_AddRef(gService);
  }

  // The first reference to the storage service must be obtained on the
  // main thread.
  NS_ENSURE_TRUE(NS_IsMainThread(), nullptr);
  RefPtr<Service> service = new Service();
  if (NS_SUCCEEDED(service->initialize())) {
    // Note: This is cleared in the Service destructor.
    gService = service.get();
    return service.forget();
  }

  return nullptr;
}

int32_t Service::sSynchronousPref;

// static
int32_t Service::getSynchronousPref() { return sSynchronousPref; }

int32_t Service::sDefaultPageSize = PREF_TS_PAGESIZE_DEFAULT;

Service::Service()
    : mMutex("Service::mMutex"),
      mSqliteVFS(nullptr),
      mRegistrationMutex("Service::mRegistrationMutex"),
      mConnections() {}

Service::~Service() {
  mozilla::UnregisterWeakMemoryReporter(this);
  mozilla::UnregisterStorageSQLiteDistinguishedAmount();

  int rc = sqlite3_vfs_unregister(mSqliteVFS);
  if (rc != SQLITE_OK) NS_WARNING("Failed to unregister sqlite vfs wrapper.");

  gService = nullptr;
  delete mSqliteVFS;
  mSqliteVFS = nullptr;
}

void Service::registerConnection(Connection* aConnection) {
  mRegistrationMutex.AssertNotCurrentThreadOwns();
  MutexAutoLock mutex(mRegistrationMutex);
  (void)mConnections.AppendElement(aConnection);
}

void Service::unregisterConnection(Connection* aConnection) {
  // If this is the last Connection it might be the only thing keeping Service
  // alive.  So ensure that Service is destroyed only after the Connection is
  // cleanly unregistered and destroyed.
  RefPtr<Service> kungFuDeathGrip(this);
  RefPtr<Connection> forgettingRef;
  {
    mRegistrationMutex.AssertNotCurrentThreadOwns();
    MutexAutoLock mutex(mRegistrationMutex);

    for (uint32_t i = 0; i < mConnections.Length(); ++i) {
      if (mConnections[i] == aConnection) {
        // Because dropping the final reference can potentially result in
        // spinning a nested event loop if the connection was not properly
        // shutdown, we want to do that outside this loop so that we can finish
        // mutating the array and drop our mutex.
        forgettingRef = std::move(mConnections[i]);
        mConnections.RemoveElementAt(i);
        break;
      }
    }
  }

  MOZ_ASSERT(forgettingRef,
             "Attempt to unregister unknown storage connection!");

  // Do not proxy the release anywhere, just let this reference drop here.  (We
  // previously did proxy the release, but that was because we invoked Close()
  // in the destructor and Close() likes to complain if it's not invoked on the
  // opener thread, so it was essential that the last reference be dropped on
  // the opener thread.  We now enqueue Close() inside our caller, Release(), so
  // it doesn't actually matter what thread our reference drops on.)
}

void Service::getConnections(
    /* inout */ nsTArray<RefPtr<Connection>>& aConnections) {
  mRegistrationMutex.AssertNotCurrentThreadOwns();
  MutexAutoLock mutex(mRegistrationMutex);
  aConnections.Clear();
  aConnections.AppendElements(mConnections);
}

void Service::minimizeMemory() {
  nsTArray<RefPtr<Connection>> connections;
  getConnections(connections);

  for (uint32_t i = 0; i < connections.Length(); i++) {
    RefPtr<Connection> conn = connections[i];
    // For non-main-thread owning/opening threads, we may be racing against them
    // closing their connection or their thread.  That's okay, see below.
    if (!conn->connectionReady()) {
      continue;
    }

    NS_NAMED_LITERAL_CSTRING(shrinkPragma, "PRAGMA shrink_memory");
    bool onOpenedThread = false;

    if (!conn->operationSupported(Connection::SYNCHRONOUS)) {
      // This is a mozIStorageAsyncConnection, it can only be used on the main
      // thread, so we can do a straight API call.
      nsCOMPtr<mozIStoragePendingStatement> ps;
      DebugOnly<nsresult> rv = conn->ExecuteSimpleSQLAsync(
          shrinkPragma, nullptr, getter_AddRefs(ps));
      MOZ_ASSERT(NS_SUCCEEDED(rv), "Should have purged sqlite caches");
    } else if (NS_SUCCEEDED(
                   conn->threadOpenedOn->IsOnCurrentThread(&onOpenedThread)) &&
               onOpenedThread) {
      if (conn->isAsyncExecutionThreadAvailable()) {
        nsCOMPtr<mozIStoragePendingStatement> ps;
        DebugOnly<nsresult> rv = conn->ExecuteSimpleSQLAsync(
            shrinkPragma, nullptr, getter_AddRefs(ps));
        MOZ_ASSERT(NS_SUCCEEDED(rv), "Should have purged sqlite caches");
      } else {
        conn->ExecuteSimpleSQL(shrinkPragma);
      }
    } else {
      // We are on the wrong thread, the query should be executed on the
      // opener thread, so we must dispatch to it.
      // It's possible the connection is already closed or will be closed by the
      // time our runnable runs.  ExecuteSimpleSQL will safely return with a
      // failure in that case.  If the thread is shutting down or shut down, the
      // dispatch will fail and that's okay.
      nsCOMPtr<nsIRunnable> event = NewRunnableMethod<const nsCString>(
          "Connection::ExecuteSimpleSQL", conn, &Connection::ExecuteSimpleSQL,
          shrinkPragma);
      Unused << conn->threadOpenedOn->Dispatch(event, NS_DISPATCH_NORMAL);
    }
  }
}

sqlite3_vfs* ConstructTelemetryVFS();
const char* GetVFSName();

static const char* sObserverTopics[] = {"memory-pressure",
                                        "xpcom-shutdown-threads"};

nsresult Service::initialize() {
  MOZ_ASSERT(NS_IsMainThread(), "Must be initialized on the main thread");

  int rc = AutoSQLiteLifetime::getInitResult();
  if (rc != SQLITE_OK) return convertResultCode(rc);

  mSqliteVFS = ConstructTelemetryVFS();
  if (mSqliteVFS) {
    rc = sqlite3_vfs_register(mSqliteVFS, 0);
    if (rc != SQLITE_OK) return convertResultCode(rc);
  } else {
    NS_WARNING("Failed to register telemetry VFS");
  }

  nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();
  NS_ENSURE_TRUE(os, NS_ERROR_FAILURE);

  for (size_t i = 0; i < ArrayLength(sObserverTopics); ++i) {
    nsresult rv = os->AddObserver(this, sObserverTopics[i], false);
    if (NS_WARN_IF(NS_FAILED(rv))) {
      return rv;
    }
  }

  // We need to obtain the toolkit.storage.synchronous preferences on the main
  // thread because the preference service can only be accessed there.  This
  // is cached in the service for all future Open[Unshared]Database calls.
  sSynchronousPref =
      Preferences::GetInt(PREF_TS_SYNCHRONOUS, PREF_TS_SYNCHRONOUS_DEFAULT);

  // We need to obtain the toolkit.storage.pageSize preferences on the main
  // thread because the preference service can only be accessed there.  This
  // is cached in the service for all future Open[Unshared]Database calls.
  sDefaultPageSize =
      Preferences::GetInt(PREF_TS_PAGESIZE, PREF_TS_PAGESIZE_DEFAULT);

  mozilla::RegisterWeakMemoryReporter(this);
  mozilla::RegisterStorageSQLiteDistinguishedAmount(
      StorageSQLiteDistinguishedAmount);

  return NS_OK;
}

int Service::localeCompareStrings(const nsAString& aStr1,
                                  const nsAString& aStr2,
                                  int32_t aComparisonStrength) {
  // The implementation of nsICollation.CompareString() is platform-dependent.
  // On Linux it's not thread-safe.  It may not be on Windows and OS X either,
  // but it's more difficult to tell.  We therefore synchronize this method.
  MutexAutoLock mutex(mMutex);

  nsICollation* coll = getLocaleCollation();
  if (!coll) {
    NS_ERROR("Storage service has no collation");
    return 0;
  }

  int32_t res;
  nsresult rv = coll->CompareString(aComparisonStrength, aStr1, aStr2, &res);
  if (NS_FAILED(rv)) {
    NS_ERROR("Collation compare string failed");
    return 0;
  }

  return res;
}

nsICollation* Service::getLocaleCollation() {
  mMutex.AssertCurrentThreadOwns();

  if (mLocaleCollation) return mLocaleCollation;

  nsCOMPtr<nsICollationFactory> collFact =
      do_CreateInstance(NS_COLLATIONFACTORY_CONTRACTID);
  if (!collFact) {
    NS_WARNING("Could not create collation factory");
    return nullptr;
  }

  nsresult rv = collFact->CreateCollation(getter_AddRefs(mLocaleCollation));
  if (NS_FAILED(rv)) {
    NS_WARNING("Could not create collation");
    return nullptr;
  }

  return mLocaleCollation;
}

////////////////////////////////////////////////////////////////////////////////
//// mozIStorageService

NS_IMETHODIMP
Service::OpenSpecialDatabase(const char* aStorageKey,
                             mozIStorageConnection** _connection) {
  nsresult rv;

  nsCOMPtr<nsIFile> storageFile;
  if (::strcmp(aStorageKey, "memory") == 0) {
    // just fall through with nullptr storageFile, this will cause the storage
    // connection to use a memory DB.
  } else {
    return NS_ERROR_INVALID_ARG;
  }

  RefPtr<Connection> msc =
      new Connection(this, SQLITE_OPEN_READWRITE, Connection::SYNCHRONOUS);

  rv = storageFile ? msc->initialize(storageFile) : msc->initialize();
  NS_ENSURE_SUCCESS(rv, rv);

  msc.forget(_connection);
  return NS_OK;
}

namespace {

class AsyncInitDatabase final : public Runnable {
 public:
  AsyncInitDatabase(Connection* aConnection, nsIFile* aStorageFile,
                    int32_t aGrowthIncrement,
                    mozIStorageCompletionCallback* aCallback)
      : Runnable("storage::AsyncInitDatabase"),
        mConnection(aConnection),
        mStorageFile(aStorageFile),
        mGrowthIncrement(aGrowthIncrement),
        mCallback(aCallback) {
    MOZ_ASSERT(NS_IsMainThread());
  }

  NS_IMETHOD Run() override {
    MOZ_ASSERT(!NS_IsMainThread());
    nsresult rv = mConnection->initializeOnAsyncThread(mStorageFile);
    if (NS_FAILED(rv)) {
      return DispatchResult(rv, nullptr);
    }

    if (mGrowthIncrement >= 0) {
      // Ignore errors. In the future, we might wish to log them.
      (void)mConnection->SetGrowthIncrement(mGrowthIncrement, EmptyCString());
    }

    return DispatchResult(
        NS_OK, NS_ISUPPORTS_CAST(mozIStorageAsyncConnection*, mConnection));
  }

 private:
  nsresult DispatchResult(nsresult aStatus, nsISupports* aValue) {
    RefPtr<CallbackComplete> event =
        new CallbackComplete(aStatus, aValue, mCallback.forget());
    return NS_DispatchToMainThread(event);
  }

  ~AsyncInitDatabase() {
    NS_ReleaseOnMainThreadSystemGroup("AsyncInitDatabase::mStorageFile",
                                      mStorageFile.forget());
    NS_ReleaseOnMainThreadSystemGroup("AsyncInitDatabase::mConnection",
                                      mConnection.forget());

    // Generally, the callback will be released by CallbackComplete.
    // However, if for some reason Run() is not executed, we still
    // need to ensure that it is released here.
    NS_ReleaseOnMainThreadSystemGroup("AsyncInitDatabase::mCallback",
                                      mCallback.forget());
  }

  RefPtr<Connection> mConnection;
  nsCOMPtr<nsIFile> mStorageFile;
  int32_t mGrowthIncrement;
  RefPtr<mozIStorageCompletionCallback> mCallback;
};

}  // namespace

NS_IMETHODIMP
Service::OpenAsyncDatabase(nsIVariant* aDatabaseStore,
                           nsIPropertyBag2* aOptions,
                           mozIStorageCompletionCallback* aCallback) {
  if (!NS_IsMainThread()) {
    return NS_ERROR_NOT_SAME_THREAD;
  }
  NS_ENSURE_ARG(aDatabaseStore);
  NS_ENSURE_ARG(aCallback);

  nsresult rv;
  bool shared = false;
  bool readOnly = false;
  bool ignoreLockingMode = false;
  int32_t growthIncrement = -1;

#define FAIL_IF_SET_BUT_INVALID(rv)                    \
  if (NS_FAILED(rv) && rv != NS_ERROR_NOT_AVAILABLE) { \
    return NS_ERROR_INVALID_ARG;                       \
  }

  // Deal with options first:
  if (aOptions) {
    rv = aOptions->GetPropertyAsBool(NS_LITERAL_STRING("readOnly"), &readOnly);
    FAIL_IF_SET_BUT_INVALID(rv);

    rv = aOptions->GetPropertyAsBool(NS_LITERAL_STRING("ignoreLockingMode"),
                                     &ignoreLockingMode);
    FAIL_IF_SET_BUT_INVALID(rv);
    // Specifying ignoreLockingMode will force use of the readOnly flag:
    if (ignoreLockingMode) {
      readOnly = true;
    }

    rv = aOptions->GetPropertyAsBool(NS_LITERAL_STRING("shared"), &shared);
    FAIL_IF_SET_BUT_INVALID(rv);

    // NB: we re-set to -1 if we don't have a storage file later on.
    rv = aOptions->GetPropertyAsInt32(NS_LITERAL_STRING("growthIncrement"),
                                      &growthIncrement);
    FAIL_IF_SET_BUT_INVALID(rv);
  }
  int flags = readOnly ? SQLITE_OPEN_READONLY : SQLITE_OPEN_READWRITE;

  nsCOMPtr<nsIFile> storageFile;
  nsCOMPtr<nsISupports> dbStore;
  rv = aDatabaseStore->GetAsISupports(getter_AddRefs(dbStore));
  if (NS_SUCCEEDED(rv)) {
    // Generally, aDatabaseStore holds the database nsIFile.
    storageFile = do_QueryInterface(dbStore, &rv);
    if (NS_FAILED(rv)) {
      return NS_ERROR_INVALID_ARG;
    }

    nsCOMPtr<nsIFile> cloned;
    rv = storageFile->Clone(getter_AddRefs(cloned));
    MOZ_ASSERT(NS_SUCCEEDED(rv));
    storageFile = std::move(cloned);

    if (!readOnly) {
      // Ensure that SQLITE_OPEN_CREATE is passed in for compatibility reasons.
      flags |= SQLITE_OPEN_CREATE;
    }

    // Apply the shared-cache option.
    flags |= shared ? SQLITE_OPEN_SHAREDCACHE : SQLITE_OPEN_PRIVATECACHE;
  } else {
    // Sometimes, however, it's a special database name.
    nsAutoCString keyString;
    rv = aDatabaseStore->GetAsACString(keyString);
    if (NS_FAILED(rv) || !keyString.EqualsLiteral("memory")) {
      return NS_ERROR_INVALID_ARG;
    }

    // Just fall through with nullptr storageFile, this will cause the storage
    // connection to use a memory DB.
  }

  if (!storageFile && growthIncrement >= 0) {
    return NS_ERROR_INVALID_ARG;
  }

  // Create connection on this thread, but initialize it on its helper thread.
  RefPtr<Connection> msc =
      new Connection(this, flags, Connection::ASYNCHRONOUS, ignoreLockingMode);
  nsCOMPtr<nsIEventTarget> target = msc->getAsyncExecutionTarget();
  MOZ_ASSERT(target,
             "Cannot initialize a connection that has been closed already");

  RefPtr<AsyncInitDatabase> asyncInit =
      new AsyncInitDatabase(msc, storageFile, growthIncrement, aCallback);
  return target->Dispatch(asyncInit, nsIEventTarget::DISPATCH_NORMAL);
}

NS_IMETHODIMP
Service::OpenDatabase(nsIFile* aDatabaseFile,
                      mozIStorageConnection** _connection) {
  NS_ENSURE_ARG(aDatabaseFile);

  // Always ensure that SQLITE_OPEN_CREATE is passed in for compatibility
  // reasons.
  int flags =
      SQLITE_OPEN_READWRITE | SQLITE_OPEN_SHAREDCACHE | SQLITE_OPEN_CREATE;
  RefPtr<Connection> msc = new Connection(this, flags, Connection::SYNCHRONOUS);

  nsresult rv = msc->initialize(aDatabaseFile);
  NS_ENSURE_SUCCESS(rv, rv);

  msc.forget(_connection);
  return NS_OK;
}

NS_IMETHODIMP
Service::OpenUnsharedDatabase(nsIFile* aDatabaseFile,
                              mozIStorageConnection** _connection) {
  NS_ENSURE_ARG(aDatabaseFile);

  // Always ensure that SQLITE_OPEN_CREATE is passed in for compatibility
  // reasons.
  int flags =
      SQLITE_OPEN_READWRITE | SQLITE_OPEN_PRIVATECACHE | SQLITE_OPEN_CREATE;
  RefPtr<Connection> msc = new Connection(this, flags, Connection::SYNCHRONOUS);

  nsresult rv = msc->initialize(aDatabaseFile);
  NS_ENSURE_SUCCESS(rv, rv);

  msc.forget(_connection);
  return NS_OK;
}

NS_IMETHODIMP
Service::OpenDatabaseWithFileURL(nsIFileURL* aFileURL,
                                 mozIStorageConnection** _connection) {
  NS_ENSURE_ARG(aFileURL);

  // Always ensure that SQLITE_OPEN_CREATE is passed in for compatibility
  // reasons.
  int flags = SQLITE_OPEN_READWRITE | SQLITE_OPEN_SHAREDCACHE |
              SQLITE_OPEN_CREATE | SQLITE_OPEN_URI;
  RefPtr<Connection> msc = new Connection(this, flags, Connection::SYNCHRONOUS);

  nsresult rv = msc->initialize(aFileURL);
  NS_ENSURE_SUCCESS(rv, rv);

  msc.forget(_connection);
  return NS_OK;
}

NS_IMETHODIMP
Service::BackupDatabaseFile(nsIFile* aDBFile, const nsAString& aBackupFileName,
                            nsIFile* aBackupParentDirectory, nsIFile** backup) {
  nsresult rv;
  nsCOMPtr<nsIFile> parentDir = aBackupParentDirectory;
  if (!parentDir) {
    // This argument is optional, and defaults to the same parent directory
    // as the current file.
    rv = aDBFile->GetParent(getter_AddRefs(parentDir));
    NS_ENSURE_SUCCESS(rv, rv);
  }

  nsCOMPtr<nsIFile> backupDB;
  rv = parentDir->Clone(getter_AddRefs(backupDB));
  NS_ENSURE_SUCCESS(rv, rv);

  rv = backupDB->Append(aBackupFileName);
  NS_ENSURE_SUCCESS(rv, rv);

  rv = backupDB->CreateUnique(nsIFile::NORMAL_FILE_TYPE, 0600);
  NS_ENSURE_SUCCESS(rv, rv);

  nsAutoString fileName;
  rv = backupDB->GetLeafName(fileName);
  NS_ENSURE_SUCCESS(rv, rv);

  rv = backupDB->Remove(false);
  NS_ENSURE_SUCCESS(rv, rv);

  backupDB.forget(backup);

  return aDBFile->CopyTo(parentDir, fileName);
}

////////////////////////////////////////////////////////////////////////////////
//// nsIObserver

NS_IMETHODIMP
Service::Observe(nsISupports*, const char* aTopic, const char16_t*) {
  if (strcmp(aTopic, "memory-pressure") == 0) {
    minimizeMemory();
  } else if (strcmp(aTopic, "xpcom-shutdown-threads") == 0) {
    // The Service is kept alive by our strong observer references and
    // references held by Connection instances.  Since we're about to remove the
    // former and then wait for the latter ones to go away, it behooves us to
    // hold a strong reference to ourselves so our calls to getConnections() do
    // not happen on a deleted object.
    RefPtr<Service> kungFuDeathGrip = this;

    nsCOMPtr<nsIObserverService> os = mozilla::services::GetObserverService();

    for (size_t i = 0; i < ArrayLength(sObserverTopics); ++i) {
      (void)os->RemoveObserver(this, sObserverTopics[i]);
    }

    SpinEventLoopUntil([&]() -> bool {
      // We must wait until all the closing connections are closed.
      nsTArray<RefPtr<Connection>> connections;
      getConnections(connections);
      for (auto& conn : connections) {
        if (conn->isClosing()) {
          return false;
        }
      }
      return true;
    });

#ifdef DEBUG
    nsTArray<RefPtr<Connection>> connections;
    getConnections(connections);
    for (uint32_t i = 0, n = connections.Length(); i < n; i++) {
      if (!connections[i]->isClosed()) {
        // getFilename is only the leaf name for the database file,
        // so it shouldn't contain privacy-sensitive information.
        CrashReporter::AnnotateCrashReport(
            CrashReporter::Annotation::StorageConnectionNotClosed,
            connections[i]->getFilename());
        printf_stderr("Storage connection not closed: %s",
                      connections[i]->getFilename().get());
        MOZ_CRASH();
      }
    }
#endif
  }

  return NS_OK;
}

}  // namespace storage
}  // namespace mozilla