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/file_util.h"
  14 #include "base/files/file.h"
  15 #include "base/files/file_path.h"
  16 #include "base/logging.h"
  17 #include "base/metrics/histogram.h"
  18 #include "base/strings/string_number_conversions.h"
  19 #include "base/task_runner.h"
  20 #include "base/task_runner_util.h"
  21 #include "base/threading/thread.h"
  22 #include "base/time/time.h"
  23
  24 namespace base {
  25
  26 namespace {
  27
  28 const int kDefaultCommitIntervalMs = 10000;
  29
  30 enum TempFileFailure {
  31   FAILED_CREATING,
  32   FAILED_OPENING,
  33   FAILED_CLOSING,
  34   FAILED_WRITING,
  35   FAILED_RENAMING,
  36   TEMP_FILE_FAILURE_MAX
  37 };
  38
  39 void LogFailure(const FilePath& path, TempFileFailure failure_code,
  40                 const std::string& message) {
  41   UMA_HISTOGRAM_ENUMERATION("ImportantFile.TempFileFailures", failure_code,
  42                             TEMP_FILE_FAILURE_MAX);
  43   DPLOG(WARNING) << "temp file failure: " << path.value().c_str()
  44                  << " : " << message;
  45 }
  46
  47 }  // namespace
  48
  49 // static
  50 bool ImportantFileWriter::WriteFileAtomically(const FilePath& path,
  51                                               const std::string& data) {
  52   // Write the data to a temp file then rename to avoid data loss if we crash
  53   // while writing the file. Ensure that the temp file is on the same volume
  54   // as target file, so it can be moved in one step, and that the temp file
  55   // is securely created.
  56   FilePath tmp_file_path;
  57   if (!base::CreateTemporaryFileInDir(path.DirName(), &tmp_file_path)) {
  58     LogFailure(path, FAILED_CREATING, "could not create temporary file");
  59     return false;
  60   }
  61
  62   File tmp_file(tmp_file_path, File::FLAG_OPEN | File::FLAG_WRITE);
  63   if (!tmp_file.IsValid()) {
  64     LogFailure(path, FAILED_OPENING, "could not open temporary file");
  65     return false;
  66   }
  67
  68   // If this happens in the wild something really bad is going on.
  69   CHECK_LE(data.length(), static_cast<size_t>(kint32max));
  70   int bytes_written = tmp_file.Write(0, data.data(),
  71                                      static_cast<int>(data.length()));
  72   tmp_file.Flush();  // Ignore return value.
  73   tmp_file.Close();
  74
  75   if (bytes_written < static_cast<int>(data.length())) {
  76     LogFailure(path, FAILED_WRITING, "error writing, bytes_written=" +
  77                IntToString(bytes_written));
  78     base::DeleteFile(tmp_file_path, false);
  79     return false;
  80   }
  81
  82   if (!base::ReplaceFile(tmp_file_path, path, NULL)) {
  83     LogFailure(path, FAILED_RENAMING, "could not rename temporary file");
  84     base::DeleteFile(tmp_file_path, false);
  85     return false;
  86   }
  87
  88   return true;
  89 }
  90
  91 ImportantFileWriter::ImportantFileWriter(const FilePath& path,
  92                                          base::SequencedTaskRunner* task_runner)
  93     : path_(path),
  94       task_runner_(task_runner),
  95       serializer_(NULL),
  96       commit_interval_(TimeDelta::FromMilliseconds(kDefaultCommitIntervalMs)),
  97       weak_factory_(this) {
  98   DCHECK(CalledOnValidThread());
  99   DCHECK(task_runner_.get());
 100 }
 101
 102 ImportantFileWriter::~ImportantFileWriter() {
 103   // We're usually a member variable of some other object, which also tends
 104   // to be our serializer. It may not be safe to call back to the parent object
 105   // being destructed.
 106   DCHECK(!HasPendingWrite());
 107 }
 108
 109 bool ImportantFileWriter::HasPendingWrite() const {
 110   DCHECK(CalledOnValidThread());
 111   return timer_.IsRunning();
 112 }
 113
 114 void ImportantFileWriter::WriteNow(const std::string& data) {
 115   DCHECK(CalledOnValidThread());
 116   if (data.length() > static_cast<size_t>(kint32max)) {
 117     NOTREACHED();
 118     return;
 119   }
 120
 121   if (HasPendingWrite())
 122     timer_.Stop();
 123
 124   if (!PostWriteTask(data)) {
 125     // Posting the task to background message loop is not expected
 126     // to fail, but if it does, avoid losing data and just hit the disk
 127     // on the current thread.
 128     NOTREACHED();
 129
 130     WriteFileAtomically(path_, data);
 131   }
 132 }
 133
 134 void ImportantFileWriter::ScheduleWrite(DataSerializer* serializer) {
 135   DCHECK(CalledOnValidThread());
 136
 137   DCHECK(serializer);
 138   serializer_ = serializer;
 139
 140   if (!timer_.IsRunning()) {
 141     timer_.Start(FROM_HERE, commit_interval_, this,
 142                  &ImportantFileWriter::DoScheduledWrite);
 143   }
 144 }
 145
 146 void ImportantFileWriter::DoScheduledWrite() {
 147   DCHECK(serializer_);
 148   std::string data;
 149   if (serializer_->SerializeData(&data)) {
 150     WriteNow(data);
 151   } else {
 152     DLOG(WARNING) << "failed to serialize data to be saved in "
 153                   << path_.value().c_str();
 154   }
 155   serializer_ = NULL;
 156 }
 157
 158 void ImportantFileWriter::RegisterOnNextSuccessfulWriteCallback(
 159     const base::Closure& on_next_successful_write) {
 160   DCHECK(on_next_successful_write_.is_null());
 161   on_next_successful_write_ = on_next_successful_write;
 162 }
 163
 164 bool ImportantFileWriter::PostWriteTask(const std::string& data) {
 165   // TODO(gab): This code could always use PostTaskAndReplyWithResult and let
 166   // ForwardSuccessfulWrite() no-op if |on_next_successful_write_| is null, but
 167   // PostTaskAndReply causes memory leaks in tests (crbug.com/371974) and
 168   // suppressing all of those is unrealistic hence we avoid most of them by
 169   // using PostTask() in the typical scenario below.
 170   if (!on_next_successful_write_.is_null()) {
 171     return base::PostTaskAndReplyWithResult(
 172         task_runner_,
 173         FROM_HERE,
 174         MakeCriticalClosure(
 175             Bind(&ImportantFileWriter::WriteFileAtomically, path_, data)),
 176         Bind(&ImportantFileWriter::ForwardSuccessfulWrite,
 177              weak_factory_.GetWeakPtr()));
 178   }
 179   return task_runner_->PostTask(
 180       FROM_HERE,
 181       MakeCriticalClosure(
 182           Bind(IgnoreResult(&ImportantFileWriter::WriteFileAtomically),
 183                path_, data)));
 184 }
 185
 186 void ImportantFileWriter::ForwardSuccessfulWrite(bool result) {
 187   DCHECK(CalledOnValidThread());
 188   if (result && !on_next_successful_write_.is_null()) {
 189     on_next_successful_write_.Run();
 190     on_next_successful_write_.Reset();
 191   }
 192 }
 193
 194 }  // namespace base