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/files/file.h"
  14 #include "base/files/file_path.h"
  15 #include "base/files/file_util.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 // This enum is used to define the buckets for an enumerated UMA histogram.
  31 // Hence,
  32 //   (a) existing enumerated constants should never be deleted or reordered, and
  33 //   (b) new constants should only be appended at the end of the enumeration.
  34 enum TempFileFailure {
  35   FAILED_CREATING,
  36   FAILED_OPENING,
  37   FAILED_CLOSING,  // Unused.
  38   FAILED_WRITING,
  39   FAILED_RENAMING,
  40   FAILED_FLUSHING,
  41   TEMP_FILE_FAILURE_MAX
  42 };
  43
  44 void LogFailure(const FilePath& path, TempFileFailure failure_code,
  45                 const std::string& message) {
  46   UMA_HISTOGRAM_ENUMERATION("ImportantFile.TempFileFailures", failure_code,
  47                             TEMP_FILE_FAILURE_MAX);
  48   DPLOG(WARNING) << "temp file failure: " << path.value().c_str()
  49                  << " : " << message;
  50 }
  51
  52 }  // namespace
  53
  54 // static
  55 bool ImportantFileWriter::WriteFileAtomically(const FilePath& path,
  56                                               const std::string& data) {
  57   // Write the data to a temp file then rename to avoid data loss if we crash
  58   // while writing the file. Ensure that the temp file is on the same volume
  59   // as target file, so it can be moved in one step, and that the temp file
  60   // is securely created.
  61   FilePath tmp_file_path;
  62   if (!base::CreateTemporaryFileInDir(path.DirName(), &tmp_file_path)) {
  63     LogFailure(path, FAILED_CREATING, "could not create temporary file");
  64     return false;
  65   }
  66
  67   File tmp_file(tmp_file_path, File::FLAG_OPEN | File::FLAG_WRITE);
  68   if (!tmp_file.IsValid()) {
  69     LogFailure(path, FAILED_OPENING, "could not open temporary file");
  70     return false;
  71   }
  72
  73   // If this happens in the wild something really bad is going on.
  74   CHECK_LE(data.length(), static_cast<size_t>(kint32max));
  75   int bytes_written = tmp_file.Write(0, data.data(),
  76                                      static_cast<int>(data.length()));
  77   bool flush_success = tmp_file.Flush();
  78   tmp_file.Close();
  79
  80   if (bytes_written < static_cast<int>(data.length())) {
  81     LogFailure(path, FAILED_WRITING, "error writing, bytes_written=" +
  82                IntToString(bytes_written));
  83     base::DeleteFile(tmp_file_path, false);
  84     return false;
  85   }
  86
  87   if (!flush_success) {
  88     LogFailure(path, FAILED_FLUSHING, "error flushing");
  89     base::DeleteFile(tmp_file_path, false);
  90     return false;
  91   }
  92
  93   if (!base::ReplaceFile(tmp_file_path, path, NULL)) {
  94     LogFailure(path, FAILED_RENAMING, "could not rename temporary file");
  95     base::DeleteFile(tmp_file_path, false);
  96     return false;
  97   }
  98
  99   return true;
 100 }
 101
 102 ImportantFileWriter::ImportantFileWriter(
 103     const FilePath& path,
 104     const scoped_refptr<base::SequencedTaskRunner>& task_runner)
 105     : path_(path),
 106       task_runner_(task_runner),
 107       serializer_(NULL),
 108       commit_interval_(TimeDelta::FromMilliseconds(kDefaultCommitIntervalMs)),
 109       weak_factory_(this) {
 110   DCHECK(CalledOnValidThread());
 111   DCHECK(task_runner_.get());
 112 }
 113
 114 ImportantFileWriter::~ImportantFileWriter() {
 115   // We're usually a member variable of some other object, which also tends
 116   // to be our serializer. It may not be safe to call back to the parent object
 117   // being destructed.
 118   DCHECK(!HasPendingWrite());
 119 }
 120
 121 bool ImportantFileWriter::HasPendingWrite() const {
 122   DCHECK(CalledOnValidThread());
 123   return timer_.IsRunning();
 124 }
 125
 126 void ImportantFileWriter::WriteNow(const std::string& data) {
 127   DCHECK(CalledOnValidThread());
 128   if (data.length() > static_cast<size_t>(kint32max)) {
 129     NOTREACHED();
 130     return;
 131   }
 132
 133   if (HasPendingWrite())
 134     timer_.Stop();
 135
 136   if (!PostWriteTask(data)) {
 137     // Posting the task to background message loop is not expected
 138     // to fail, but if it does, avoid losing data and just hit the disk
 139     // on the current thread.
 140     NOTREACHED();
 141
 142     WriteFileAtomically(path_, data);
 143   }
 144 }
 145
 146 void ImportantFileWriter::ScheduleWrite(DataSerializer* serializer) {
 147   DCHECK(CalledOnValidThread());
 148
 149   DCHECK(serializer);
 150   serializer_ = serializer;
 151
 152   if (!timer_.IsRunning()) {
 153     timer_.Start(FROM_HERE, commit_interval_, this,
 154                  &ImportantFileWriter::DoScheduledWrite);
 155   }
 156 }
 157
 158 void ImportantFileWriter::DoScheduledWrite() {
 159   DCHECK(serializer_);
 160   std::string data;
 161   if (serializer_->SerializeData(&data)) {
 162     WriteNow(data);
 163   } else {
 164     DLOG(WARNING) << "failed to serialize data to be saved in "
 165                   << path_.value().c_str();
 166   }
 167   serializer_ = NULL;
 168 }
 169
 170 void ImportantFileWriter::RegisterOnNextSuccessfulWriteCallback(
 171     const base::Closure& on_next_successful_write) {
 172   DCHECK(on_next_successful_write_.is_null());
 173   on_next_successful_write_ = on_next_successful_write;
 174 }
 175
 176 bool ImportantFileWriter::PostWriteTask(const std::string& data) {
 177   // TODO(gab): This code could always use PostTaskAndReplyWithResult and let
 178   // ForwardSuccessfulWrite() no-op if |on_next_successful_write_| is null, but
 179   // PostTaskAndReply causes memory leaks in tests (crbug.com/371974) and
 180   // suppressing all of those is unrealistic hence we avoid most of them by
 181   // using PostTask() in the typical scenario below.
 182   if (!on_next_successful_write_.is_null()) {
 183     return base::PostTaskAndReplyWithResult(
 184         task_runner_.get(),
 185         FROM_HERE,
 186         MakeCriticalClosure(
 187             Bind(&ImportantFileWriter::WriteFileAtomically, path_, data)),
 188         Bind(&ImportantFileWriter::ForwardSuccessfulWrite,
 189              weak_factory_.GetWeakPtr()));
 190   }
 191   return task_runner_->PostTask(
 192       FROM_HERE,
 193       MakeCriticalClosure(
 194           Bind(IgnoreResult(&ImportantFileWriter::WriteFileAtomically),
 195                path_, data)));
 196 }
 197
 198 void ImportantFileWriter::ForwardSuccessfulWrite(bool result) {
 199   DCHECK(CalledOnValidThread());
 200   if (result && !on_next_successful_write_.is_null()) {
 201     on_next_successful_write_.Run();
 202     on_next_successful_write_.Reset();
 203   }
 204 }
 205
 206 }  // namespace base