src/chrome/browser/sessions/session_backend.cc

   1 // Copyright (c) 2012 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 "chrome/browser/sessions/session_backend.h"
   6
   7 #include <limits>
   8
   9 #include "base/file_util.h"
  10 #include "base/files/file.h"
  11 #include "base/memory/scoped_vector.h"
  12 #include "base/metrics/histogram.h"
  13 #include "base/threading/thread_restrictions.h"
  14
  15 using base::TimeTicks;
  16
  17 // File version number.
  18 static const int32 kFileCurrentVersion = 1;
  19
  20 // The signature at the beginning of the file = SSNS (Sessions).
  21 static const int32 kFileSignature = 0x53534E53;
  22
  23 namespace {
  24
  25 // The file header is the first bytes written to the file,
  26 // and is used to identify the file as one written by us.
  27 struct FileHeader {
  28   int32 signature;
  29   int32 version;
  30 };
  31
  32 // SessionFileReader ----------------------------------------------------------
  33
  34 // SessionFileReader is responsible for reading the set of SessionCommands that
  35 // describe a Session back from a file. SessionFileRead does minimal error
  36 // checking on the file (pretty much only that the header is valid).
  37
  38 class SessionFileReader {
  39  public:
  40   typedef SessionCommand::id_type id_type;
  41   typedef SessionCommand::size_type size_type;
  42
  43   explicit SessionFileReader(const base::FilePath& path)
  44       : errored_(false),
  45         buffer_(SessionBackend::kFileReadBufferSize, 0),
  46         buffer_position_(0),
  47         available_count_(0) {
  48     file_.reset(new base::File(
  49         path, base::File::FLAG_OPEN | base::File::FLAG_READ));
  50   }
  51   // Reads the contents of the file specified in the constructor, returning
  52   // true on success. It is up to the caller to free all SessionCommands
  53   // added to commands.
  54   bool Read(BaseSessionService::SessionType type,
  55             std::vector<SessionCommand*>* commands);
  56
  57  private:
  58   // Reads a single command, returning it. A return value of NULL indicates
  59   // either there are no commands, or there was an error. Use errored_ to
  60   // distinguish the two. If NULL is returned, and there is no error, it means
  61   // the end of file was successfully reached.
  62   SessionCommand* ReadCommand();
  63
  64   // Shifts the unused portion of buffer_ to the beginning and fills the
  65   // remaining portion with data from the file. Returns false if the buffer
  66   // couldn't be filled. A return value of false only signals an error if
  67   // errored_ is set to true.
  68   bool FillBuffer();
  69
  70   // Whether an error condition has been detected (
  71   bool errored_;
  72
  73   // As we read from the file, data goes here.
  74   std::string buffer_;
  75
  76   // The file.
  77   scoped_ptr<base::File> file_;
  78
  79   // Position in buffer_ of the data.
  80   size_t buffer_position_;
  81
  82   // Number of available bytes; relative to buffer_position_.
  83   size_t available_count_;
  84
  85   DISALLOW_COPY_AND_ASSIGN(SessionFileReader);
  86 };
  87
  88 bool SessionFileReader::Read(BaseSessionService::SessionType type,
  89                              std::vector<SessionCommand*>* commands) {
  90   if (!file_->IsValid())
  91     return false;
  92   FileHeader header;
  93   int read_count;
  94   TimeTicks start_time = TimeTicks::Now();
  95   read_count = file_->ReadAtCurrentPos(reinterpret_cast<char*>(&header),
  96                                        sizeof(header));
  97   if (read_count != sizeof(header) || header.signature != kFileSignature ||
  98       header.version != kFileCurrentVersion)
  99     return false;
 100
 101   ScopedVector<SessionCommand> read_commands;
 102   for (SessionCommand* command = ReadCommand(); command && !errored_;
 103        command = ReadCommand())
 104     read_commands.push_back(command);
 105   if (!errored_)
 106     read_commands.swap(*commands);
 107   if (type == BaseSessionService::TAB_RESTORE) {
 108     UMA_HISTOGRAM_TIMES("TabRestore.read_session_file_time",
 109                         TimeTicks::Now() - start_time);
 110   } else {
 111     UMA_HISTOGRAM_TIMES("SessionRestore.read_session_file_time",
 112                         TimeTicks::Now() - start_time);
 113   }
 114   return !errored_;
 115 }
 116
 117 SessionCommand* SessionFileReader::ReadCommand() {
 118   // Make sure there is enough in the buffer for the size of the next command.
 119   if (available_count_ < sizeof(size_type)) {
 120     if (!FillBuffer())
 121       return NULL;
 122     if (available_count_ < sizeof(size_type)) {
 123       VLOG(1) << "SessionFileReader::ReadCommand, file incomplete";
 124       // Still couldn't read a valid size for the command, assume write was
 125       // incomplete and return NULL.
 126       return NULL;
 127     }
 128   }
 129   // Get the size of the command.
 130   size_type command_size;
 131   memcpy(&command_size, &(buffer_[buffer_position_]), sizeof(command_size));
 132   buffer_position_ += sizeof(command_size);
 133   available_count_ -= sizeof(command_size);
 134
 135   if (command_size == 0) {
 136     VLOG(1) << "SessionFileReader::ReadCommand, empty command";
 137     // Empty command. Shouldn't happen if write was successful, fail.
 138     return NULL;
 139   }
 140
 141   // Make sure buffer has the complete contents of the command.
 142   if (command_size > available_count_) {
 143     if (command_size > buffer_.size())
 144       buffer_.resize((command_size / 1024 + 1) * 1024, 0);
 145     if (!FillBuffer() || command_size > available_count_) {
 146       // Again, assume the file was ok, and just the last chunk was lost.
 147       VLOG(1) << "SessionFileReader::ReadCommand, last chunk lost";
 148       return NULL;
 149     }
 150   }
 151   const id_type command_id = buffer_[buffer_position_];
 152   // NOTE: command_size includes the size of the id, which is not part of
 153   // the contents of the SessionCommand.
 154   SessionCommand* command =
 155       new SessionCommand(command_id, command_size - sizeof(id_type));
 156   if (command_size > sizeof(id_type)) {
 157     memcpy(command->contents(),
 158            &(buffer_[buffer_position_ + sizeof(id_type)]),
 159            command_size - sizeof(id_type));
 160   }
 161   buffer_position_ += command_size;
 162   available_count_ -= command_size;
 163   return command;
 164 }
 165
 166 bool SessionFileReader::FillBuffer() {
 167   if (available_count_ > 0 && buffer_position_ > 0) {
 168     // Shift buffer to beginning.
 169     memmove(&(buffer_[0]), &(buffer_[buffer_position_]), available_count_);
 170   }
 171   buffer_position_ = 0;
 172   DCHECK(buffer_position_ + available_count_ < buffer_.size());
 173   int to_read = static_cast<int>(buffer_.size() - available_count_);
 174   int read_count = file_->ReadAtCurrentPos(&(buffer_[available_count_]),
 175                                            to_read);
 176   if (read_count < 0) {
 177     errored_ = true;
 178     return false;
 179   }
 180   if (read_count == 0)
 181     return false;
 182   available_count_ += read_count;
 183   return true;
 184 }
 185
 186 }  // namespace
 187
 188 // SessionBackend -------------------------------------------------------------
 189
 190 // File names (current and previous) for a type of TAB.
 191 static const char* kCurrentTabSessionFileName = "Current Tabs";
 192 static const char* kLastTabSessionFileName = "Last Tabs";
 193
 194 // File names (current and previous) for a type of SESSION.
 195 static const char* kCurrentSessionFileName = "Current Session";
 196 static const char* kLastSessionFileName = "Last Session";
 197
 198 // static
 199 const int SessionBackend::kFileReadBufferSize = 1024;
 200
 201 SessionBackend::SessionBackend(BaseSessionService::SessionType type,
 202                                const base::FilePath& path_to_dir)
 203     : type_(type),
 204       path_to_dir_(path_to_dir),
 205       last_session_valid_(false),
 206       inited_(false),
 207       empty_file_(true) {
 208   // NOTE: this is invoked on the main thread, don't do file access here.
 209 }
 210
 211 void SessionBackend::Init() {
 212   if (inited_)
 213     return;
 214
 215   inited_ = true;
 216
 217   // Create the directory for session info.
 218   base::CreateDirectory(path_to_dir_);
 219
 220   MoveCurrentSessionToLastSession();
 221 }
 222
 223 void SessionBackend::AppendCommands(
 224     std::vector<SessionCommand*>* commands,
 225     bool reset_first) {
 226   Init();
 227   // Make sure and check current_session_file_, if opening the file failed
 228   // current_session_file_ will be NULL.
 229   if ((reset_first && !empty_file_) || !current_session_file_.get() ||
 230       !current_session_file_->IsValid()) {
 231     ResetFile();
 232   }
 233   // Need to check current_session_file_ again, ResetFile may fail.
 234   if (current_session_file_.get() && current_session_file_->IsValid() &&
 235       !AppendCommandsToFile(current_session_file_.get(), *commands)) {
 236     current_session_file_.reset(NULL);
 237   }
 238   empty_file_ = false;
 239   STLDeleteElements(commands);
 240   delete commands;
 241 }
 242
 243 void SessionBackend::ReadLastSessionCommands(
 244     const base::CancelableTaskTracker::IsCanceledCallback& is_canceled,
 245     const BaseSessionService::InternalGetCommandsCallback& callback) {
 246   if (is_canceled.Run())
 247     return;
 248
 249   Init();
 250
 251   ScopedVector<SessionCommand> commands;
 252   ReadLastSessionCommandsImpl(&(commands.get()));
 253   callback.Run(commands.Pass());
 254 }
 255
 256 bool SessionBackend::ReadLastSessionCommandsImpl(
 257     std::vector<SessionCommand*>* commands) {
 258   Init();
 259   SessionFileReader file_reader(GetLastSessionPath());
 260   return file_reader.Read(type_, commands);
 261 }
 262
 263 void SessionBackend::DeleteLastSession() {
 264   Init();
 265   base::DeleteFile(GetLastSessionPath(), false);
 266 }
 267
 268 void SessionBackend::MoveCurrentSessionToLastSession() {
 269   Init();
 270   current_session_file_.reset(NULL);
 271
 272   const base::FilePath current_session_path = GetCurrentSessionPath();
 273   const base::FilePath last_session_path = GetLastSessionPath();
 274   if (base::PathExists(last_session_path))
 275     base::DeleteFile(last_session_path, false);
 276   if (base::PathExists(current_session_path)) {
 277     int64 file_size;
 278     if (base::GetFileSize(current_session_path, &file_size)) {
 279       if (type_ == BaseSessionService::TAB_RESTORE) {
 280         UMA_HISTOGRAM_COUNTS("TabRestore.last_session_file_size",
 281                              static_cast<int>(file_size / 1024));
 282       } else {
 283         UMA_HISTOGRAM_COUNTS("SessionRestore.last_session_file_size",
 284                              static_cast<int>(file_size / 1024));
 285       }
 286     }
 287     last_session_valid_ = base::Move(current_session_path, last_session_path);
 288   }
 289
 290   if (base::PathExists(current_session_path))
 291     base::DeleteFile(current_session_path, false);
 292
 293   // Create and open the file for the current session.
 294   ResetFile();
 295 }
 296
 297 bool SessionBackend::ReadCurrentSessionCommandsImpl(
 298     std::vector<SessionCommand*>* commands) {
 299   Init();
 300   SessionFileReader file_reader(GetCurrentSessionPath());
 301   return file_reader.Read(type_, commands);
 302 }
 303
 304 bool SessionBackend::AppendCommandsToFile(base::File* file,
 305     const std::vector<SessionCommand*>& commands) {
 306   for (std::vector<SessionCommand*>::const_iterator i = commands.begin();
 307        i != commands.end(); ++i) {
 308     int wrote;
 309     const size_type content_size = static_cast<size_type>((*i)->size());
 310     const size_type total_size =  content_size + sizeof(id_type);
 311     if (type_ == BaseSessionService::TAB_RESTORE)
 312       UMA_HISTOGRAM_COUNTS("TabRestore.command_size", total_size);
 313     else
 314       UMA_HISTOGRAM_COUNTS("SessionRestore.command_size", total_size);
 315     wrote = file->WriteAtCurrentPos(reinterpret_cast<const char*>(&total_size),
 316                                     sizeof(total_size));
 317     if (wrote != sizeof(total_size)) {
 318       NOTREACHED() << "error writing";
 319       return false;
 320     }
 321     id_type command_id = (*i)->id();
 322     wrote = file->WriteAtCurrentPos(reinterpret_cast<char*>(&command_id),
 323                                     sizeof(command_id));
 324     if (wrote != sizeof(command_id)) {
 325       NOTREACHED() << "error writing";
 326       return false;
 327     }
 328     if (content_size > 0) {
 329       wrote = file->WriteAtCurrentPos(reinterpret_cast<char*>((*i)->contents()),
 330                                       content_size);
 331       if (wrote != content_size) {
 332         NOTREACHED() << "error writing";
 333         return false;
 334       }
 335     }
 336   }
 337 #if defined(OS_CHROMEOS)
 338   file->Flush();
 339 #endif
 340   return true;
 341 }
 342
 343 SessionBackend::~SessionBackend() {
 344   if (current_session_file_.get()) {
 345     // Destructor performs file IO because file is open in sync mode.
 346     // crbug.com/112512.
 347     base::ThreadRestrictions::ScopedAllowIO allow_io;
 348     current_session_file_.reset();
 349   }
 350 }
 351
 352 void SessionBackend::ResetFile() {
 353   DCHECK(inited_);
 354   if (current_session_file_.get()) {
 355     // File is already open, truncate it. We truncate instead of closing and
 356     // reopening to avoid the possibility of scanners locking the file out
 357     // from under us once we close it. If truncation fails, we'll try to
 358     // recreate.
 359     const int header_size = static_cast<int>(sizeof(FileHeader));
 360     if (current_session_file_->Seek(
 361             base::File::FROM_BEGIN, header_size) != header_size ||
 362         !current_session_file_->SetLength(header_size))
 363       current_session_file_.reset(NULL);
 364   }
 365   if (!current_session_file_.get())
 366     current_session_file_.reset(OpenAndWriteHeader(GetCurrentSessionPath()));
 367   empty_file_ = true;
 368 }
 369
 370 base::File* SessionBackend::OpenAndWriteHeader(const base::FilePath& path) {
 371   DCHECK(!path.empty());
 372   scoped_ptr<base::File> file(new base::File(
 373       path,
 374       base::File::FLAG_CREATE_ALWAYS | base::File::FLAG_WRITE |
 375       base::File::FLAG_EXCLUSIVE_WRITE | base::File::FLAG_EXCLUSIVE_READ));
 376   if (!file->IsValid())
 377     return NULL;
 378   FileHeader header;
 379   header.signature = kFileSignature;
 380   header.version = kFileCurrentVersion;
 381   int wrote = file->WriteAtCurrentPos(reinterpret_cast<char*>(&header),
 382                                       sizeof(header));
 383   if (wrote != sizeof(header))
 384     return NULL;
 385   return file.release();
 386 }
 387
 388 base::FilePath SessionBackend::GetLastSessionPath() {
 389   base::FilePath path = path_to_dir_;
 390   if (type_ == BaseSessionService::TAB_RESTORE)
 391     path = path.AppendASCII(kLastTabSessionFileName);
 392   else
 393     path = path.AppendASCII(kLastSessionFileName);
 394   return path;
 395 }
 396
 397 base::FilePath SessionBackend::GetCurrentSessionPath() {
 398   base::FilePath path = path_to_dir_;
 399   if (type_ == BaseSessionService::TAB_RESTORE)
 400     path = path.AppendASCII(kCurrentTabSessionFileName);
 401   else
 402     path = path.AppendASCII(kCurrentSessionFileName);
 403   return path;
 404 }