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/numerics/safe_conversions.h"
  20 #include "base/strings/string_number_conversions.h"
  21 #include "base/strings/string_util.h"
  22 #include "base/task_runner.h"
  23 #include "base/task_runner_util.h"
  24 #include "base/threading/thread.h"
  25 #include "base/time/time.h"
  26
  27 namespace base {
  28
  29 namespace {
  30
  31 const int kDefaultCommitIntervalMs = 10000;
  32
  33 // This enum is used to define the buckets for an enumerated UMA histogram.
  34 // Hence,
  35 //   (a) existing enumerated constants should never be deleted or reordered, and
  36 //   (b) new constants should only be appended at the end of the enumeration.
  37 enum TempFileFailure {
  38   FAILED_CREATING,
  39   FAILED_OPENING,
  40   FAILED_CLOSING,  // Unused.
  41   FAILED_WRITING,
  42   FAILED_RENAMING,
  43   FAILED_FLUSHING,
  44   TEMP_FILE_FAILURE_MAX
  45 };
  46
  47 void LogFailure(const FilePath& path, TempFileFailure failure_code,
  48                 const std::string& message) {
  49   UMA_HISTOGRAM_ENUMERATION("ImportantFile.TempFileFailures", failure_code,
  50                             TEMP_FILE_FAILURE_MAX);
  51   DPLOG(WARNING) << "temp file failure: " << path.value() << " : " << 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   strlcpy(file_info.path, path.value().c_str(), arraysize(file_info.path));
  76   debug::Alias(&file_info);
  77 #endif
  78
  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 (!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 fails in the wild, something really bad is going on.
  96   const int data_length = checked_cast<int32_t>(data.length());
  97   int bytes_written = tmp_file.Write(0, data.data(), data_length);
  98   bool flush_success = tmp_file.Flush();
  99   tmp_file.Close();
 100
 101   if (bytes_written < data_length) {
 102     LogFailure(path, FAILED_WRITING, "error writing, bytes_written=" +
 103                IntToString(bytes_written));
 104     DeleteFile(tmp_file_path, false);
 105     return false;
 106   }
 107
 108   if (!flush_success) {
 109     LogFailure(path, FAILED_FLUSHING, "error flushing");
 110     DeleteFile(tmp_file_path, false);
 111     return false;
 112   }
 113
 114   if (!ReplaceFile(tmp_file_path, path, nullptr)) {
 115     LogFailure(path, FAILED_RENAMING, "could not rename temporary file");
 116     DeleteFile(tmp_file_path, false);
 117     return false;
 118   }
 119
 120   return true;
 121 }
 122
 123 ImportantFileWriter::ImportantFileWriter(
 124     const FilePath& path,
 125     const scoped_refptr<SequencedTaskRunner>& task_runner)
 126     : ImportantFileWriter(
 127         path,
 128         task_runner,
 129         TimeDelta::FromMilliseconds(kDefaultCommitIntervalMs)) {
 130 }
 131
 132 ImportantFileWriter::ImportantFileWriter(
 133     const FilePath& path,
 134     const scoped_refptr<SequencedTaskRunner>& task_runner,
 135     TimeDelta interval)
 136     : path_(path),
 137       task_runner_(task_runner),
 138       serializer_(nullptr),
 139       commit_interval_(interval),
 140       weak_factory_(this) {
 141   DCHECK(CalledOnValidThread());
 142   DCHECK(task_runner_);
 143 }
 144
 145 ImportantFileWriter::~ImportantFileWriter() {
 146   // We're usually a member variable of some other object, which also tends
 147   // to be our serializer. It may not be safe to call back to the parent object
 148   // being destructed.
 149   DCHECK(!HasPendingWrite());
 150 }
 151
 152 bool ImportantFileWriter::HasPendingWrite() const {
 153   DCHECK(CalledOnValidThread());
 154   return timer_.IsRunning();
 155 }
 156
 157 void ImportantFileWriter::WriteNow(scoped_ptr<std::string> data) {
 158   DCHECK(CalledOnValidThread());
 159   if (!IsValueInRangeForNumericType<int32_t>(data->length())) {
 160     NOTREACHED();
 161     return;
 162   }
 163
 164   if (HasPendingWrite())
 165     timer_.Stop();
 166
 167   auto task = Bind(&WriteScopedStringToFileAtomically, path_, Passed(&data));
 168   if (!PostWriteTask(task)) {
 169     // Posting the task to background message loop is not expected
 170     // to fail, but if it does, avoid losing data and just hit the disk
 171     // on the current thread.
 172     NOTREACHED();
 173
 174     task.Run();
 175   }
 176 }
 177
 178 void ImportantFileWriter::ScheduleWrite(DataSerializer* serializer) {
 179   DCHECK(CalledOnValidThread());
 180
 181   DCHECK(serializer);
 182   serializer_ = serializer;
 183
 184   if (!timer_.IsRunning()) {
 185     timer_.Start(FROM_HERE, commit_interval_, this,
 186                  &ImportantFileWriter::DoScheduledWrite);
 187   }
 188 }
 189
 190 void ImportantFileWriter::DoScheduledWrite() {
 191   DCHECK(serializer_);
 192   scoped_ptr<std::string> data(new std::string);
 193   if (serializer_->SerializeData(data.get())) {
 194     WriteNow(data.Pass());
 195   } else {
 196     DLOG(WARNING) << "failed to serialize data to be saved in "
 197                   << path_.value();
 198   }
 199   serializer_ = nullptr;
 200 }
 201
 202 void ImportantFileWriter::RegisterOnNextSuccessfulWriteCallback(
 203     const Closure& on_next_successful_write) {
 204   DCHECK(on_next_successful_write_.is_null());
 205   on_next_successful_write_ = on_next_successful_write;
 206 }
 207
 208 bool ImportantFileWriter::PostWriteTask(const Callback<bool()>& task) {
 209   // TODO(gab): This code could always use PostTaskAndReplyWithResult and let
 210   // ForwardSuccessfulWrite() no-op if |on_next_successful_write_| is null, but
 211   // PostTaskAndReply causes memory leaks in tests (crbug.com/371974) and
 212   // suppressing all of those is unrealistic hence we avoid most of them by
 213   // using PostTask() in the typical scenario below.
 214   if (!on_next_successful_write_.is_null()) {
 215     return PostTaskAndReplyWithResult(
 216         task_runner_.get(),
 217         FROM_HERE,
 218         MakeCriticalClosure(task),
 219         Bind(&ImportantFileWriter::ForwardSuccessfulWrite,
 220              weak_factory_.GetWeakPtr()));
 221   }
 222   return task_runner_->PostTask(
 223       FROM_HERE,
 224       MakeCriticalClosure(Bind(IgnoreResult(task))));
 225 }
 226
 227 void ImportantFileWriter::ForwardSuccessfulWrite(bool result) {
 228   DCHECK(CalledOnValidThread());
 229   if (result && !on_next_successful_write_.is_null()) {
 230     on_next_successful_write_.Run();
 231     on_next_successful_write_.Reset();
 232   }
 233 }
 234
 235 }  // namespace base