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// Copyright (c) 2011 The Chromium Embedded Framework Authors.
// Portions copyright (c) 2011 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.
#include "browser_persistent_cookie_store.h"
#include "cef_thread.h"
#include <list>
#include <map>
#include <set>
#include <utility>
#include "base/basictypes.h"
#include "base/bind.h"
#include "base/file_path.h"
#include "base/file_util.h"
#include "base/logging.h"
#include "base/memory/ref_counted.h"
#include "base/memory/scoped_ptr.h"
#include "base/metrics/histogram.h"
#include "base/string_util.h"
#include "base/synchronization/lock.h"
#include "base/threading/thread.h"
#include "base/threading/thread_restrictions.h"
#include "googleurl/src/gurl.h"
#include "net/base/registry_controlled_domain.h"
#include "sql/meta_table.h"
#include "sql/statement.h"
#include "sql/transaction.h"
using base::Time;
// This class is designed to be shared between any calling threads and the
// database thread. It batches operations and commits them on a timer.
//
// BrowserPersistentCookieStore::Load is called to load all cookies. It
// delegates to Backend::Load, which posts a Backend::LoadAndNotifyOnDBThread
// task to the DB thread. This task calls Backend::ChainLoadCookies(), which
// repeatedly posts itself to the DB thread to load each eTLD+1's cookies in
// separate tasks. When this is complete, Backend::NotifyOnIOThread is posted
// to the IO thread, which notifies the caller of BrowserPersistentCookieStore::
// Load that the load is complete.
//
// If a priority load request is invoked via BrowserPersistentCookieStore::
// LoadCookiesForKey, it is delegated to Backend::LoadCookiesForKey, which posts
// Backend::LoadKeyAndNotifyOnDBThread to the DB thread. That routine loads just
// that single domain key (eTLD+1)'s cookies, and posts a Backend::
// NotifyOnIOThread to the IO thread to notify the caller of
// BrowserPersistentCookieStore::LoadCookiesForKey that that load is complete.
//
// Subsequent to loading, mutations may be queued by any thread using
// AddCookie, UpdateCookieAccessTime, and DeleteCookie. These are flushed to
// disk on the DB thread every 30 seconds, 512 operations, or call to Flush(),
// whichever occurs first.
class BrowserPersistentCookieStore::Backend
: public base::RefCountedThreadSafe<BrowserPersistentCookieStore::Backend> {
public:
explicit Backend(const FilePath& path)
: path_(path),
db_(NULL),
num_pending_(0),
clear_local_state_on_exit_(false),
initialized_(false) {
}
// Creates or loads the SQLite database.
void Load(const LoadedCallback& loaded_callback);
// Loads cookies for the domain key (eTLD+1).
void LoadCookiesForKey(const std::string& domain,
const LoadedCallback& loaded_callback);
// Batch a cookie addition.
void AddCookie(const net::CookieMonster::CanonicalCookie& cc);
// Batch a cookie access time update.
void UpdateCookieAccessTime(const net::CookieMonster::CanonicalCookie& cc);
// Batch a cookie deletion.
void DeleteCookie(const net::CookieMonster::CanonicalCookie& cc);
// Commit pending operations as soon as possible.
void Flush(Task* completion_task);
// Commit any pending operations and close the database. This must be called
// before the object is destructed.
void Close();
void SetClearLocalStateOnExit(bool clear_local_state);
private:
friend class base::RefCountedThreadSafe<BrowserPersistentCookieStore::Backend>;
// You should call Close() before destructing this object.
~Backend() {
DCHECK(!db_.get()) << "Close should have already been called.";
DCHECK(num_pending_ == 0 && pending_.empty());
}
// Database upgrade statements.
bool EnsureDatabaseVersion();
class PendingOperation {
public:
typedef enum {
COOKIE_ADD,
COOKIE_UPDATEACCESS,
COOKIE_DELETE,
} OperationType;
PendingOperation(OperationType op,
const net::CookieMonster::CanonicalCookie& cc)
: op_(op), cc_(cc) { }
OperationType op() const { return op_; }
const net::CookieMonster::CanonicalCookie& cc() const { return cc_; }
private:
OperationType op_;
net::CookieMonster::CanonicalCookie cc_;
};
private:
// Creates or loads the SQLite database on DB thread.
void LoadAndNotifyOnDBThread(const LoadedCallback& loaded_callback);
// Loads cookies for the domain key (eTLD+1) on DB thread.
void LoadKeyAndNotifyOnDBThread(const std::string& domains,
const LoadedCallback& loaded_callback);
// Notifies the CookieMonster when loading completes for a specific domain key
// or for all domain keys. Triggers the callback and passes it all cookies
// that have been loaded from DB since last IO notification.
void NotifyOnIOThread(
const LoadedCallback& loaded_callback,
bool load_success);
// Initialize the data base.
bool InitializeDatabase();
// Loads cookies for the next domain key from the DB, then either reschedules
// itself or schedules the provided callback to run on the IO thread (if all
// domains are loaded).
void ChainLoadCookies(const LoadedCallback& loaded_callback);
// Load all cookies for a set of domains/hosts
bool LoadCookiesForDomains(const std::set<std::string>& key);
// Batch a cookie operation (add or delete)
void BatchOperation(PendingOperation::OperationType op,
const net::CookieMonster::CanonicalCookie& cc);
// Commit our pending operations to the database.
void Commit();
// Close() executed on the background thread.
void InternalBackgroundClose();
FilePath path_;
scoped_ptr<sql::Connection> db_;
sql::MetaTable meta_table_;
typedef std::list<PendingOperation*> PendingOperationsList;
PendingOperationsList pending_;
PendingOperationsList::size_type num_pending_;
// True if the persistent store should be deleted upon destruction.
bool clear_local_state_on_exit_;
// Guard |cookies_|, |pending_|, |num_pending_|, |clear_local_state_on_exit_|
base::Lock lock_;
// Temporary buffer for cookies loaded from DB. Accumulates cookies to reduce
// the number of messages sent to the IO thread. Sent back in response to
// individual load requests for domain keys or when all loading completes.
std::vector<net::CookieMonster::CanonicalCookie*> cookies_;
// Map of domain keys(eTLD+1) to domains/hosts that are to be loaded from DB.
std::map<std::string, std::set<std::string> > keys_to_load_;
// Indicates if DB has been initialized.
bool initialized_;
DISALLOW_COPY_AND_ASSIGN(Backend);
};
// Version number of the database. In version 4, we migrated the time epoch.
// If you open the DB with an older version on Mac or Linux, the times will
// look wonky, but the file will likely be usable. On Windows version 3 and 4
// are the same.
//
// Version 3 updated the database to include the last access time, so we can
// expire them in decreasing order of use when we've reached the maximum
// number of cookies.
static const int kCurrentVersionNumber = 4;
static const int kCompatibleVersionNumber = 3;
namespace {
// Initializes the cookies table, returning true on success.
bool InitTable(sql::Connection* db) {
if (!db->DoesTableExist("cookies")) {
if (!db->Execute("CREATE TABLE cookies ("
"creation_utc INTEGER NOT NULL UNIQUE PRIMARY KEY,"
"host_key TEXT NOT NULL,"
"name TEXT NOT NULL,"
"value TEXT NOT NULL,"
"path TEXT NOT NULL,"
// We only store persistent, so we know it expires
"expires_utc INTEGER NOT NULL,"
"secure INTEGER NOT NULL,"
"httponly INTEGER NOT NULL,"
"last_access_utc INTEGER NOT NULL)"))
return false;
}
// Try to create the index every time. Older versions did not have this index,
// so we want those people to get it. Ignore errors, since it may exist.
db->Execute("CREATE INDEX IF NOT EXISTS cookie_times ON cookies"
" (creation_utc)");
db->Execute("CREATE INDEX IF NOT EXISTS domain ON cookies(host_key)");
return true;
}
} // namespace
void BrowserPersistentCookieStore::Backend::Load(
const LoadedCallback& loaded_callback) {
// This function should be called only once per instance.
DCHECK(!db_.get());
CefThread::PostTask(
CefThread::FILE, FROM_HERE,
base::Bind(&Backend::LoadAndNotifyOnDBThread, this, loaded_callback));
}
void BrowserPersistentCookieStore::Backend::LoadCookiesForKey(
const std::string& key,
const LoadedCallback& loaded_callback) {
CefThread::PostTask(
CefThread::FILE, FROM_HERE,
base::Bind(&Backend::LoadKeyAndNotifyOnDBThread, this,
key,
loaded_callback));
}
void BrowserPersistentCookieStore::Backend::LoadAndNotifyOnDBThread(
const LoadedCallback& loaded_callback) {
DCHECK(CefThread::CurrentlyOn(CefThread::FILE));
if (!InitializeDatabase()) {
CefThread::PostTask(
CefThread::IO, FROM_HERE,
base::Bind(&BrowserPersistentCookieStore::Backend::NotifyOnIOThread,
this, loaded_callback, false));
} else {
ChainLoadCookies(loaded_callback);
}
}
void BrowserPersistentCookieStore::Backend::LoadKeyAndNotifyOnDBThread(
const std::string& key,
const LoadedCallback& loaded_callback) {
DCHECK(CefThread::CurrentlyOn(CefThread::FILE));
bool success = false;
if (InitializeDatabase()) {
std::map<std::string, std::set<std::string> >::iterator
it = keys_to_load_.find(key);
if (it != keys_to_load_.end()) {
success = LoadCookiesForDomains(it->second);
keys_to_load_.erase(it);
} else {
success = true;
}
}
CefThread::PostTask(
CefThread::IO, FROM_HERE,
base::Bind(&BrowserPersistentCookieStore::Backend::NotifyOnIOThread,
this, loaded_callback, success));
}
void BrowserPersistentCookieStore::Backend::NotifyOnIOThread(
const LoadedCallback& loaded_callback,
bool load_success) {
DCHECK(CefThread::CurrentlyOn(CefThread::IO));
std::vector<net::CookieMonster::CanonicalCookie*> cookies;
{
base::AutoLock locked(lock_);
cookies.swap(cookies_);
}
loaded_callback.Run(cookies);
}
bool BrowserPersistentCookieStore::Backend::InitializeDatabase() {
DCHECK(CefThread::CurrentlyOn(CefThread::FILE));
if (initialized_) {
return true;
}
const FilePath dir = path_.DirName();
if (!file_util::PathExists(dir) && !file_util::CreateDirectory(dir)) {
return false;
}
db_.reset(new sql::Connection);
if (!db_->Open(path_)) {
NOTREACHED() << "Unable to open cookie DB.";
db_.reset();
return false;
}
//db_->set_error_delegate(GetErrorHandlerForCookieDb());
if (!EnsureDatabaseVersion() || !InitTable(db_.get())) {
NOTREACHED() << "Unable to open cookie DB.";
db_.reset();
return false;
}
db_->Preload();
// Retrieve all the domains
sql::Statement smt(db_->GetUniqueStatement(
"SELECT DISTINCT host_key FROM cookies"));
if (!smt) {
NOTREACHED() << "select statement prep failed";
db_.reset();
return false;
}
// Build a map of domain keys (always eTLD+1) to domains.
while (smt.Step()) {
std::string domain = smt.ColumnString(0);
std::string key =
net::RegistryControlledDomainService::GetDomainAndRegistry(domain);
std::map<std::string, std::set<std::string> >::iterator it =
keys_to_load_.find(key);
if (it == keys_to_load_.end())
it = keys_to_load_.insert(std::make_pair
(key, std::set<std::string>())).first;
it->second.insert(domain);
}
initialized_ = true;
return true;
}
void BrowserPersistentCookieStore::Backend::ChainLoadCookies(
const LoadedCallback& loaded_callback) {
DCHECK(CefThread::CurrentlyOn(CefThread::FILE));
bool load_success = true;
if (keys_to_load_.size() > 0) {
// Load cookies for the first domain key.
std::map<std::string, std::set<std::string> >::iterator
it = keys_to_load_.begin();
load_success = LoadCookiesForDomains(it->second);
keys_to_load_.erase(it);
}
// If load is successful and there are more domain keys to be loaded,
// then post a DB task to continue chain-load;
// Otherwise notify on IO thread.
if (load_success && keys_to_load_.size() > 0) {
CefThread::PostTask(
CefThread::FILE, FROM_HERE,
base::Bind(&Backend::ChainLoadCookies, this, loaded_callback));
} else {
CefThread::PostTask(
CefThread::IO, FROM_HERE,
base::Bind(&BrowserPersistentCookieStore::Backend::NotifyOnIOThread,
this, loaded_callback, load_success));
}
}
bool BrowserPersistentCookieStore::Backend::LoadCookiesForDomains(
const std::set<std::string>& domains) {
DCHECK(CefThread::CurrentlyOn(CefThread::FILE));
sql::Statement smt(db_->GetCachedStatement(SQL_FROM_HERE,
"SELECT creation_utc, host_key, name, value, path, expires_utc, secure, "
"httponly, last_access_utc FROM cookies WHERE host_key = ?"));
if (!smt) {
NOTREACHED() << "select statement prep failed";
db_.reset();
return false;
}
std::vector<net::CookieMonster::CanonicalCookie*> cookies;
std::set<std::string>::const_iterator it = domains.begin();
for (; it != domains.end(); ++it) {
smt.BindString(0, *it);
while (smt.Step()) {
scoped_ptr<net::CookieMonster::CanonicalCookie> cc(
new net::CookieMonster::CanonicalCookie(
// The "source" URL is not used with persisted cookies.
GURL(), // Source
smt.ColumnString(2), // name
smt.ColumnString(3), // value
smt.ColumnString(1), // domain
smt.ColumnString(4), // path
std::string(), // TODO(abarth): Persist mac_key
std::string(), // TODO(abarth): Persist mac_algorithm
Time::FromInternalValue(smt.ColumnInt64(0)), // creation_utc
Time::FromInternalValue(smt.ColumnInt64(5)), // expires_utc
Time::FromInternalValue(smt.ColumnInt64(8)), // last_access_utc
smt.ColumnInt(6) != 0, // secure
smt.ColumnInt(7) != 0, // httponly
true, // has_expires
true)); // is_persistent
DLOG_IF(WARNING,
cc->CreationDate() > Time::Now()) << L"CreationDate too recent";
cookies.push_back(cc.release());
}
smt.Reset();
}
{
base::AutoLock locked(lock_);
cookies_.insert(cookies_.end(), cookies.begin(), cookies.end());
}
return true;
}
bool BrowserPersistentCookieStore::Backend::EnsureDatabaseVersion() {
// Version check.
if (!meta_table_.Init(
db_.get(), kCurrentVersionNumber, kCompatibleVersionNumber)) {
return false;
}
if (meta_table_.GetCompatibleVersionNumber() > kCurrentVersionNumber) {
LOG(WARNING) << "Cookie database is too new.";
return false;
}
int cur_version = meta_table_.GetVersionNumber();
if (cur_version == 2) {
sql::Transaction transaction(db_.get());
if (!transaction.Begin())
return false;
if (!db_->Execute("ALTER TABLE cookies ADD COLUMN last_access_utc "
"INTEGER DEFAULT 0") ||
!db_->Execute("UPDATE cookies SET last_access_utc = creation_utc")) {
LOG(WARNING) << "Unable to update cookie database to version 3.";
return false;
}
++cur_version;
meta_table_.SetVersionNumber(cur_version);
meta_table_.SetCompatibleVersionNumber(
std::min(cur_version, kCompatibleVersionNumber));
transaction.Commit();
}
if (cur_version == 3) {
// The time epoch changed for Mac & Linux in this version to match Windows.
// This patch came after the main epoch change happened, so some
// developers have "good" times for cookies added by the more recent
// versions. So we have to be careful to only update times that are under
// the old system (which will appear to be from before 1970 in the new
// system). The magic number used below is 1970 in our time units.
sql::Transaction transaction(db_.get());
transaction.Begin();
#if !defined(OS_WIN)
db_->Execute(
"UPDATE cookies "
"SET creation_utc = creation_utc + 11644473600000000 "
"WHERE rowid IN "
"(SELECT rowid FROM cookies WHERE "
"creation_utc > 0 AND creation_utc < 11644473600000000)");
db_->Execute(
"UPDATE cookies "
"SET expires_utc = expires_utc + 11644473600000000 "
"WHERE rowid IN "
"(SELECT rowid FROM cookies WHERE "
"expires_utc > 0 AND expires_utc < 11644473600000000)");
db_->Execute(
"UPDATE cookies "
"SET last_access_utc = last_access_utc + 11644473600000000 "
"WHERE rowid IN "
"(SELECT rowid FROM cookies WHERE "
"last_access_utc > 0 AND last_access_utc < 11644473600000000)");
#endif
++cur_version;
meta_table_.SetVersionNumber(cur_version);
transaction.Commit();
}
// Put future migration cases here.
// When the version is too old, we just try to continue anyway, there should
// not be a released product that makes a database too old for us to handle.
LOG_IF(WARNING, cur_version < kCurrentVersionNumber) <<
"Cookie database version " << cur_version << " is too old to handle.";
return true;
}
void BrowserPersistentCookieStore::Backend::AddCookie(
const net::CookieMonster::CanonicalCookie& cc) {
BatchOperation(PendingOperation::COOKIE_ADD, cc);
}
void BrowserPersistentCookieStore::Backend::UpdateCookieAccessTime(
const net::CookieMonster::CanonicalCookie& cc) {
BatchOperation(PendingOperation::COOKIE_UPDATEACCESS, cc);
}
void BrowserPersistentCookieStore::Backend::DeleteCookie(
const net::CookieMonster::CanonicalCookie& cc) {
BatchOperation(PendingOperation::COOKIE_DELETE, cc);
}
void BrowserPersistentCookieStore::Backend::BatchOperation(
PendingOperation::OperationType op,
const net::CookieMonster::CanonicalCookie& cc) {
// Commit every 30 seconds.
static const int kCommitIntervalMs = 30 * 1000;
// Commit right away if we have more than 512 outstanding operations.
static const size_t kCommitAfterBatchSize = 512;
DCHECK(!CefThread::CurrentlyOn(CefThread::FILE));
// We do a full copy of the cookie here, and hopefully just here.
scoped_ptr<PendingOperation> po(new PendingOperation(op, cc));
PendingOperationsList::size_type num_pending;
{
base::AutoLock locked(lock_);
pending_.push_back(po.release());
num_pending = ++num_pending_;
}
if (num_pending == 1) {
// We've gotten our first entry for this batch, fire off the timer.
CefThread::PostDelayedTask(
CefThread::FILE, FROM_HERE,
base::Bind(&Backend::Commit, this), kCommitIntervalMs);
} else if (num_pending == kCommitAfterBatchSize) {
// We've reached a big enough batch, fire off a commit now.
CefThread::PostTask(
CefThread::FILE, FROM_HERE,
base::Bind(&Backend::Commit, this));
}
}
void BrowserPersistentCookieStore::Backend::Commit() {
DCHECK(CefThread::CurrentlyOn(CefThread::FILE));
PendingOperationsList ops;
{
base::AutoLock locked(lock_);
pending_.swap(ops);
num_pending_ = 0;
}
// Maybe an old timer fired or we are already Close()'ed.
if (!db_.get() || ops.empty())
return;
sql::Statement add_smt(db_->GetCachedStatement(SQL_FROM_HERE,
"INSERT INTO cookies (creation_utc, host_key, name, value, path, "
"expires_utc, secure, httponly, last_access_utc) "
"VALUES (?,?,?,?,?,?,?,?,?)"));
if (!add_smt) {
NOTREACHED();
return;
}
sql::Statement update_access_smt(db_->GetCachedStatement(SQL_FROM_HERE,
"UPDATE cookies SET last_access_utc=? WHERE creation_utc=?"));
if (!update_access_smt) {
NOTREACHED();
return;
}
sql::Statement del_smt(db_->GetCachedStatement(SQL_FROM_HERE,
"DELETE FROM cookies WHERE creation_utc=?"));
if (!del_smt) {
NOTREACHED();
return;
}
sql::Transaction transaction(db_.get());
if (!transaction.Begin()) {
NOTREACHED();
return;
}
for (PendingOperationsList::iterator it = ops.begin();
it != ops.end(); ++it) {
// Free the cookies as we commit them to the database.
scoped_ptr<PendingOperation> po(*it);
switch (po->op()) {
case PendingOperation::COOKIE_ADD:
add_smt.Reset();
add_smt.BindInt64(0, po->cc().CreationDate().ToInternalValue());
add_smt.BindString(1, po->cc().Domain());
add_smt.BindString(2, po->cc().Name());
add_smt.BindString(3, po->cc().Value());
add_smt.BindString(4, po->cc().Path());
add_smt.BindInt64(5, po->cc().ExpiryDate().ToInternalValue());
add_smt.BindInt(6, po->cc().IsSecure());
add_smt.BindInt(7, po->cc().IsHttpOnly());
add_smt.BindInt64(8, po->cc().LastAccessDate().ToInternalValue());
if (!add_smt.Run())
NOTREACHED() << "Could not add a cookie to the DB.";
break;
case PendingOperation::COOKIE_UPDATEACCESS:
update_access_smt.Reset();
update_access_smt.BindInt64(0,
po->cc().LastAccessDate().ToInternalValue());
update_access_smt.BindInt64(1,
po->cc().CreationDate().ToInternalValue());
if (!update_access_smt.Run())
NOTREACHED() << "Could not update cookie last access time in the DB.";
break;
case PendingOperation::COOKIE_DELETE:
del_smt.Reset();
del_smt.BindInt64(0, po->cc().CreationDate().ToInternalValue());
if (!del_smt.Run())
NOTREACHED() << "Could not delete a cookie from the DB.";
break;
default:
NOTREACHED();
break;
}
}
transaction.Commit();
}
void BrowserPersistentCookieStore::Backend::Flush(Task* completion_task) {
DCHECK(!CefThread::CurrentlyOn(CefThread::FILE));
CefThread::PostTask(
CefThread::FILE, FROM_HERE, base::Bind(&Backend::Commit, this));
if (completion_task) {
// We want the completion task to run immediately after Commit() returns.
// Posting it from here means there is less chance of another task getting
// onto the message queue first, than if we posted it from Commit() itself.
CefThread::PostTask(CefThread::FILE, FROM_HERE, completion_task);
}
}
// Fire off a close message to the background thread. We could still have a
// pending commit timer that will be holding a reference on us, but if/when
// this fires we will already have been cleaned up and it will be ignored.
void BrowserPersistentCookieStore::Backend::Close() {
if (CefThread::CurrentlyOn(CefThread::FILE)) {
InternalBackgroundClose();
} else {
// Must close the backend on the background thread.
CefThread::PostTask(
CefThread::FILE, FROM_HERE,
base::Bind(&Backend::InternalBackgroundClose, this));
}
}
void BrowserPersistentCookieStore::Backend::InternalBackgroundClose() {
DCHECK(CefThread::CurrentlyOn(CefThread::FILE));
// Commit any pending operations
Commit();
db_.reset();
if (clear_local_state_on_exit_)
file_util::Delete(path_, false);
}
void BrowserPersistentCookieStore::Backend::SetClearLocalStateOnExit(
bool clear_local_state) {
base::AutoLock locked(lock_);
clear_local_state_on_exit_ = clear_local_state;
}
BrowserPersistentCookieStore::BrowserPersistentCookieStore(const FilePath& path)
: backend_(new Backend(path)) {
}
BrowserPersistentCookieStore::~BrowserPersistentCookieStore() {
if (backend_.get()) {
backend_->Close();
// Release our reference, it will probably still have a reference if the
// background thread has not run Close() yet.
backend_ = NULL;
}
}
void BrowserPersistentCookieStore::Load(const LoadedCallback& loaded_callback) {
backend_->Load(loaded_callback);
}
void BrowserPersistentCookieStore::LoadCookiesForKey(
const std::string& key,
const LoadedCallback& loaded_callback) {
backend_->LoadCookiesForKey(key, loaded_callback);
}
void BrowserPersistentCookieStore::AddCookie(
const net::CookieMonster::CanonicalCookie& cc) {
if (backend_.get())
backend_->AddCookie(cc);
}
void BrowserPersistentCookieStore::UpdateCookieAccessTime(
const net::CookieMonster::CanonicalCookie& cc) {
if (backend_.get())
backend_->UpdateCookieAccessTime(cc);
}
void BrowserPersistentCookieStore::DeleteCookie(
const net::CookieMonster::CanonicalCookie& cc) {
if (backend_.get())
backend_->DeleteCookie(cc);
}
void BrowserPersistentCookieStore::SetClearLocalStateOnExit(
bool clear_local_state) {
if (backend_.get())
backend_->SetClearLocalStateOnExit(clear_local_state);
}
void BrowserPersistentCookieStore::Flush(Task* completion_task) {
if (backend_.get())
backend_->Flush(completion_task);
else if (completion_task)
MessageLoop::current()->PostTask(FROM_HERE, completion_task);
}