base/files/important_file_writer.cc

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "base/files/important_file_writer.h"
   6
   7 #include <stdio.h>
   8
   9 #include <string>
  10
  11 #include "base/bind.h"
  12 #include "base/critical_closure.h"
  13 #include "base/debug/alias.h"
  14 #include "base/files/file.h"
  15 #include "base/files/file_path.h"
  16 #include "base/files/file_util.h"
  17 #include "base/logging.h"
  18 #include "base/metrics/histogram.h"
  19 #include "base/strings/string_number_conversions.h"
  20 #include "base/strings/string_util.h"
  21 #include "base/task_runner.h"
  22 #include "base/task_runner_util.h"
  23 #include "base/threading/thread.h"
  24 #include "base/time/time.h"
  25
  26 namespace base {
  27
  28 namespace {
  29
  30 const int kDefaultCommitIntervalMs = 10000;
  31
  32 // This enum is used to define the buckets for an enumerated UMA histogram.
  33 // Hence,
  34 //   (a) existing enumerated constants should never be deleted or reordered, and
  35 //   (b) new constants should only be appended at the end of the enumeration.
  36 enum TempFileFailure {
  37   FAILED_CREATING,
  38   FAILED_OPENING,
  39   FAILED_CLOSING,  // Unused.
  40   FAILED_WRITING,
  41   FAILED_RENAMING,
  42   FAILED_FLUSHING,
  43   TEMP_FILE_FAILURE_MAX
  44 };
  45
  46 void LogFailure(const FilePath& path, TempFileFailure failure_code,
  47                 const std::string& message) {
  48   UMA_HISTOGRAM_ENUMERATION("ImportantFile.TempFileFailures", failure_code,
  49                             TEMP_FILE_FAILURE_MAX);
  50   DPLOG(WARNING) << "temp file failure: " << path.value().c_str()
  51                  << " : " << message;
  52 }
  53
  54 // Helper function to call WriteFileAtomically() with a scoped_ptr<std::string>.
  55 bool WriteScopedStringToFileAtomically(const FilePath& path,
  56                                        scoped_ptr<std::string> data) {
  57   return ImportantFileWriter::WriteFileAtomically(path, *data);
  58 }
  59
  60 }  // namespace
  61
  62 // static
  63 bool ImportantFileWriter::WriteFileAtomically(const FilePath& path,
  64                                               const std::string& data) {
  65 #if defined(OS_CHROMEOS)
  66   // On Chrome OS, chrome gets killed when it cannot finish shutdown quickly,
  67   // and this function seems to be one of the slowest shutdown steps.
  68   // Include some info to the report for investigation. crbug.com/418627
  69   // TODO(hashimoto): Remove this.
  70   struct {
  71     size_t data_size;
  72     char path[128];
  73   } file_info;
  74   file_info.data_size = data.size();
  75   base::strlcpy(file_info.path, path.value().c_str(),
  76                 arraysize(file_info.path));
  77   base::debug::Alias(&file_info);
  78 #endif
  79   // Write the data to a temp file then rename to avoid data loss if we crash
  80   // while writing the file. Ensure that the temp file is on the same volume
  81   // as target file, so it can be moved in one step, and that the temp file
  82   // is securely created.
  83   FilePath tmp_file_path;
  84   if (!base::CreateTemporaryFileInDir(path.DirName(), &tmp_file_path)) {
  85     LogFailure(path, FAILED_CREATING, "could not create temporary file");
  86     return false;
  87   }
  88
  89   File tmp_file(tmp_file_path, File::FLAG_OPEN | File::FLAG_WRITE);
  90   if (!tmp_file.IsValid()) {
  91     LogFailure(path, FAILED_OPENING, "could not open temporary file");
  92     return false;
  93   }
  94
  95   // If this happens in the wild something really bad is going on.
  96   CHECK_LE(data.length(), static_cast<size_t>(kint32max));
  97   int bytes_written = tmp_file.Write(0, data.data(),
  98                                      static_cast<int>(data.length()));
  99   bool flush_success = tmp_file.Flush();
 100   tmp_file.Close();
 101
 102   if (bytes_written < static_cast<int>(data.length())) {
 103     LogFailure(path, FAILED_WRITING, "error writing, bytes_written=" +
 104                IntToString(bytes_written));
 105     base::DeleteFile(tmp_file_path, false);
 106     return false;
 107   }
 108
 109   if (!flush_success) {
 110     LogFailure(path, FAILED_FLUSHING, "error flushing");
 111     base::DeleteFile(tmp_file_path, false);
 112     return false;
 113   }
 114
 115   if (!base::ReplaceFile(tmp_file_path, path, NULL)) {
 116     LogFailure(path, FAILED_RENAMING, "could not rename temporary file");
 117     base::DeleteFile(tmp_file_path, false);
 118     return false;
 119   }
 120
 121   return true;
 122 }
 123
 124 ImportantFileWriter::ImportantFileWriter(
 125     const FilePath& path,
 126     const scoped_refptr<base::SequencedTaskRunner>& task_runner)
 127     : path_(path),
 128       task_runner_(task_runner),
 129       serializer_(NULL),
 130       commit_interval_(TimeDelta::FromMilliseconds(kDefaultCommitIntervalMs)),
 131       weak_factory_(this) {
 132   DCHECK(CalledOnValidThread());
 133   DCHECK(task_runner_);
 134 }
 135
 136 ImportantFileWriter::~ImportantFileWriter() {
 137   // We're usually a member variable of some other object, which also tends
 138   // to be our serializer. It may not be safe to call back to the parent object
 139   // being destructed.
 140   DCHECK(!HasPendingWrite());
 141 }
 142
 143 bool ImportantFileWriter::HasPendingWrite() const {
 144   DCHECK(CalledOnValidThread());
 145   return timer_.IsRunning();
 146 }
 147
 148 void ImportantFileWriter::WriteNow(scoped_ptr<std::string> data) {
 149   DCHECK(CalledOnValidThread());
 150   if (data->length() > static_cast<size_t>(kint32max)) {
 151     NOTREACHED();
 152     return;
 153   }
 154
 155   if (HasPendingWrite())
 156     timer_.Stop();
 157
 158   auto task = Bind(&WriteScopedStringToFileAtomically, path_, Passed(&data));
 159   if (!PostWriteTask(task)) {
 160     // Posting the task to background message loop is not expected
 161     // to fail, but if it does, avoid losing data and just hit the disk
 162     // on the current thread.
 163     NOTREACHED();
 164
 165     task.Run();
 166   }
 167 }
 168
 169 void ImportantFileWriter::ScheduleWrite(DataSerializer* serializer) {
 170   DCHECK(CalledOnValidThread());
 171
 172   DCHECK(serializer);
 173   serializer_ = serializer;
 174
 175   if (!timer_.IsRunning()) {
 176     timer_.Start(FROM_HERE, commit_interval_, this,
 177                  &ImportantFileWriter::DoScheduledWrite);
 178   }
 179 }
 180
 181 void ImportantFileWriter::DoScheduledWrite() {
 182   DCHECK(serializer_);
 183   scoped_ptr<std::string> data(new std::string);
 184   if (serializer_->SerializeData(data.get())) {
 185     WriteNow(data.Pass());
 186   } else {
 187     DLOG(WARNING) << "failed to serialize data to be saved in "
 188                   << path_.value().c_str();
 189   }
 190   serializer_ = NULL;
 191 }
 192
 193 void ImportantFileWriter::RegisterOnNextSuccessfulWriteCallback(
 194     const base::Closure& on_next_successful_write) {
 195   DCHECK(on_next_successful_write_.is_null());
 196   on_next_successful_write_ = on_next_successful_write;
 197 }
 198
 199 bool ImportantFileWriter::PostWriteTask(const Callback<bool()>& task) {
 200   // TODO(gab): This code could always use PostTaskAndReplyWithResult and let
 201   // ForwardSuccessfulWrite() no-op if |on_next_successful_write_| is null, but
 202   // PostTaskAndReply causes memory leaks in tests (crbug.com/371974) and
 203   // suppressing all of those is unrealistic hence we avoid most of them by
 204   // using PostTask() in the typical scenario below.
 205   if (!on_next_successful_write_.is_null()) {
 206     return base::PostTaskAndReplyWithResult(
 207         task_runner_.get(),
 208         FROM_HERE,
 209         MakeCriticalClosure(task),
 210         Bind(&ImportantFileWriter::ForwardSuccessfulWrite,
 211              weak_factory_.GetWeakPtr()));
 212   }
 213   return task_runner_->PostTask(
 214       FROM_HERE,
 215       MakeCriticalClosure(base::Bind(IgnoreResult(task))));
 216 }
 217
 218 void ImportantFileWriter::ForwardSuccessfulWrite(bool result) {
 219   DCHECK(CalledOnValidThread());
 220   if (result && !on_next_successful_write_.is_null()) {
 221     on_next_successful_write_.Run();
 222     on_next_successful_write_.Reset();
 223   }
 224 }
 225
 226 }  // namespace base