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 enum TempFileFailure {
  31   FAILED_CREATING,
  32   FAILED_OPENING,
  33   FAILED_CLOSING,
  34   FAILED_WRITING,
  35   FAILED_RENAMING,
  36   FAILED_FLUSHING,
  37   TEMP_FILE_FAILURE_MAX
  38 };
  39
  40 void LogFailure(const FilePath& path, TempFileFailure failure_code,
  41                 const std::string& message) {
  42   UMA_HISTOGRAM_ENUMERATION("ImportantFile.TempFileFailures", failure_code,
  43                             TEMP_FILE_FAILURE_MAX);
  44   DPLOG(WARNING) << "temp file failure: " << path.value().c_str()
  45                  << " : " << message;
  46 }
  47
  48 }  // namespace
  49
  50 // static
  51 bool ImportantFileWriter::WriteFileAtomically(const FilePath& path,
  52                                               const std::string& data) {
  53   // Write the data to a temp file then rename to avoid data loss if we crash
  54   // while writing the file. Ensure that the temp file is on the same volume
  55   // as target file, so it can be moved in one step, and that the temp file
  56   // is securely created.
  57   FilePath tmp_file_path;
  58   if (!base::CreateTemporaryFileInDir(path.DirName(), &tmp_file_path)) {
  59     LogFailure(path, FAILED_CREATING, "could not create temporary file");
  60     return false;
  61   }
  62
  63   File tmp_file(tmp_file_path, File::FLAG_OPEN | File::FLAG_WRITE);
  64   if (!tmp_file.IsValid()) {
  65     LogFailure(path, FAILED_OPENING, "could not open temporary file");
  66     return false;
  67   }
  68
  69   // If this happens in the wild something really bad is going on.
  70   CHECK_LE(data.length(), static_cast<size_t>(kint32max));
  71   int bytes_written = tmp_file.Write(0, data.data(),
  72                                      static_cast<int>(data.length()));
  73   bool flush_success = tmp_file.Flush();
  74   tmp_file.Close();
  75
  76   if (bytes_written < static_cast<int>(data.length())) {
  77     LogFailure(path, FAILED_WRITING, "error writing, bytes_written=" +
  78                IntToString(bytes_written));
  79     base::DeleteFile(tmp_file_path, false);
  80     return false;
  81   }
  82
  83   if (!flush_success) {
  84     LogFailure(path, FAILED_FLUSHING, "error flushing");
  85     base::DeleteFile(tmp_file_path, false);
  86     return false;
  87   }
  88
  89   if (!base::ReplaceFile(tmp_file_path, path, NULL)) {
  90     LogFailure(path, FAILED_RENAMING, "could not rename temporary file");
  91     base::DeleteFile(tmp_file_path, false);
  92     return false;
  93   }
  94
  95   return true;
  96 }
  97
  98 ImportantFileWriter::ImportantFileWriter(
  99     const FilePath& path,
 100     const scoped_refptr<base::SequencedTaskRunner>& task_runner)
 101     : path_(path),
 102       task_runner_(task_runner),
 103       serializer_(NULL),
 104       commit_interval_(TimeDelta::FromMilliseconds(kDefaultCommitIntervalMs)),
 105       weak_factory_(this) {
 106   DCHECK(CalledOnValidThread());
 107   DCHECK(task_runner_.get());
 108 }
 109
 110 ImportantFileWriter::~ImportantFileWriter() {
 111   // We're usually a member variable of some other object, which also tends
 112   // to be our serializer. It may not be safe to call back to the parent object
 113   // being destructed.
 114   DCHECK(!HasPendingWrite());
 115 }
 116
 117 bool ImportantFileWriter::HasPendingWrite() const {
 118   DCHECK(CalledOnValidThread());
 119   return timer_.IsRunning();
 120 }
 121
 122 void ImportantFileWriter::WriteNow(const std::string& data) {
 123   DCHECK(CalledOnValidThread());
 124   if (data.length() > static_cast<size_t>(kint32max)) {
 125     NOTREACHED();
 126     return;
 127   }
 128
 129   if (HasPendingWrite())
 130     timer_.Stop();
 131
 132   if (!PostWriteTask(data)) {
 133     // Posting the task to background message loop is not expected
 134     // to fail, but if it does, avoid losing data and just hit the disk
 135     // on the current thread.
 136     NOTREACHED();
 137
 138     WriteFileAtomically(path_, data);
 139   }
 140 }
 141
 142 void ImportantFileWriter::ScheduleWrite(DataSerializer* serializer) {
 143   DCHECK(CalledOnValidThread());
 144
 145   DCHECK(serializer);
 146   serializer_ = serializer;
 147
 148   if (!timer_.IsRunning()) {
 149     timer_.Start(FROM_HERE, commit_interval_, this,
 150                  &ImportantFileWriter::DoScheduledWrite);
 151   }
 152 }
 153
 154 void ImportantFileWriter::DoScheduledWrite() {
 155   DCHECK(serializer_);
 156   std::string data;
 157   if (serializer_->SerializeData(&data)) {
 158     WriteNow(data);
 159   } else {
 160     DLOG(WARNING) << "failed to serialize data to be saved in "
 161                   << path_.value().c_str();
 162   }
 163   serializer_ = NULL;
 164 }
 165
 166 void ImportantFileWriter::RegisterOnNextSuccessfulWriteCallback(
 167     const base::Closure& on_next_successful_write) {
 168   DCHECK(on_next_successful_write_.is_null());
 169   on_next_successful_write_ = on_next_successful_write;
 170 }
 171
 172 bool ImportantFileWriter::PostWriteTask(const std::string& data) {
 173   // TODO(gab): This code could always use PostTaskAndReplyWithResult and let
 174   // ForwardSuccessfulWrite() no-op if |on_next_successful_write_| is null, but
 175   // PostTaskAndReply causes memory leaks in tests (crbug.com/371974) and
 176   // suppressing all of those is unrealistic hence we avoid most of them by
 177   // using PostTask() in the typical scenario below.
 178   if (!on_next_successful_write_.is_null()) {
 179     return base::PostTaskAndReplyWithResult(
 180         task_runner_.get(),
 181         FROM_HERE,
 182         MakeCriticalClosure(
 183             Bind(&ImportantFileWriter::WriteFileAtomically, path_, data)),
 184         Bind(&ImportantFileWriter::ForwardSuccessfulWrite,
 185              weak_factory_.GetWeakPtr()));
 186   }
 187   return task_runner_->PostTask(
 188       FROM_HERE,
 189       MakeCriticalClosure(
 190           Bind(IgnoreResult(&ImportantFileWriter::WriteFileAtomically),
 191                path_, data)));
 192 }
 193
 194 void ImportantFileWriter::ForwardSuccessfulWrite(bool result) {
 195   DCHECK(CalledOnValidThread());
 196   if (result && !on_next_successful_write_.is_null()) {
 197     on_next_successful_write_.Run();
 198     on_next_successful_write_.Reset();
 199   }
 200 }
 201
 202 }  // namespace base