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      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 "chrome/browser/sessions/session_backend.h"
      6 
      7 #include <limits>
      8 
      9 #include "base/file_util.h"
     10 #include "base/memory/scoped_vector.h"
     11 #include "base/metrics/histogram.h"
     12 #include "net/base/file_stream.h"
     13 #include "net/base/net_errors.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 FilePath& path)
     44       : errored_(false),
     45         buffer_(SessionBackend::kFileReadBufferSize, 0),
     46         buffer_position_(0),
     47         available_count_(0) {
     48     file_.reset(new net::FileStream());
     49     file_->Open(path, base::PLATFORM_FILE_OPEN | base::PLATFORM_FILE_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<net::FileStream> 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_->IsOpen())
     91     return false;
     92   FileHeader header;
     93   int read_count;
     94   TimeTicks start_time = TimeTicks::Now();
     95   read_count = file_->ReadUntilComplete(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   SessionCommand* command;
    103   while ((command = ReadCommand()) && !errored_)
    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       // Still couldn't read a valid size for the command, assume write was
    124       // incomplete and return NULL.
    125       return NULL;
    126     }
    127   }
    128   // Get the size of the command.
    129   size_type command_size;
    130   memcpy(&command_size, &(buffer_[buffer_position_]), sizeof(command_size));
    131   buffer_position_ += sizeof(command_size);
    132   available_count_ -= sizeof(command_size);
    133 
    134   if (command_size == 0) {
    135     // Empty command. Shouldn't happen if write was successful, fail.
    136     return NULL;
    137   }
    138 
    139   // Make sure buffer has the complete contents of the command.
    140   if (command_size > available_count_) {
    141     if (command_size > buffer_.size())
    142       buffer_.resize((command_size / 1024 + 1) * 1024, 0);
    143     if (!FillBuffer() || command_size > available_count_) {
    144       // Again, assume the file was ok, and just the last chunk was lost.
    145       return NULL;
    146     }
    147   }
    148   const id_type command_id = buffer_[buffer_position_];
    149   // NOTE: command_size includes the size of the id, which is not part of
    150   // the contents of the SessionCommand.
    151   SessionCommand* command =
    152       new SessionCommand(command_id, command_size - sizeof(id_type));
    153   if (command_size > sizeof(id_type)) {
    154     memcpy(command->contents(),
    155            &(buffer_[buffer_position_ + sizeof(id_type)]),
    156            command_size - sizeof(id_type));
    157   }
    158   buffer_position_ += command_size;
    159   available_count_ -= command_size;
    160   return command;
    161 }
    162 
    163 bool SessionFileReader::FillBuffer() {
    164   if (available_count_ > 0 && buffer_position_ > 0) {
    165     // Shift buffer to beginning.
    166     memmove(&(buffer_[0]), &(buffer_[buffer_position_]), available_count_);
    167   }
    168   buffer_position_ = 0;
    169   DCHECK(buffer_position_ + available_count_ < buffer_.size());
    170   int to_read = static_cast<int>(buffer_.size() - available_count_);
    171   int read_count = file_->ReadUntilComplete(&(buffer_[available_count_]),
    172                                             to_read);
    173   if (read_count < 0) {
    174     errored_ = true;
    175     return false;
    176   }
    177   if (read_count == 0)
    178     return false;
    179   available_count_ += read_count;
    180   return true;
    181 }
    182 
    183 }  // namespace
    184 
    185 // SessionBackend -------------------------------------------------------------
    186 
    187 // File names (current and previous) for a type of TAB.
    188 static const char* kCurrentTabSessionFileName = "Current Tabs";
    189 static const char* kLastTabSessionFileName = "Last Tabs";
    190 
    191 // File names (current and previous) for a type of SESSION.
    192 static const char* kCurrentSessionFileName = "Current Session";
    193 static const char* kLastSessionFileName = "Last Session";
    194 
    195 // static
    196 const int SessionBackend::kFileReadBufferSize = 1024;
    197 
    198 SessionBackend::SessionBackend(BaseSessionService::SessionType type,
    199                                const FilePath& path_to_dir)
    200     : type_(type),
    201       path_to_dir_(path_to_dir),
    202       last_session_valid_(false),
    203       inited_(false),
    204       empty_file_(true) {
    205   // NOTE: this is invoked on the main thread, don't do file access here.
    206 }
    207 
    208 void SessionBackend::Init() {
    209   if (inited_)
    210     return;
    211 
    212   inited_ = true;
    213 
    214   // Create the directory for session info.
    215   file_util::CreateDirectory(path_to_dir_);
    216 
    217   MoveCurrentSessionToLastSession();
    218 }
    219 
    220 void SessionBackend::AppendCommands(
    221     std::vector<SessionCommand*>* commands,
    222     bool reset_first) {
    223   Init();
    224   // Make sure and check current_session_file_, if opening the file failed
    225   // current_session_file_ will be NULL.
    226   if ((reset_first && !empty_file_) || !current_session_file_.get() ||
    227       !current_session_file_->IsOpen()) {
    228     ResetFile();
    229   }
    230   // Need to check current_session_file_ again, ResetFile may fail.
    231   if (current_session_file_.get() && current_session_file_->IsOpen() &&
    232       !AppendCommandsToFile(current_session_file_.get(), *commands)) {
    233     current_session_file_.reset(NULL);
    234   }
    235   empty_file_ = false;
    236   STLDeleteElements(commands);
    237   delete commands;
    238 }
    239 
    240 void SessionBackend::ReadLastSessionCommands(
    241     scoped_refptr<BaseSessionService::InternalGetCommandsRequest> request) {
    242   if (request->canceled())
    243     return;
    244   Init();
    245   ReadLastSessionCommandsImpl(&(request->commands));
    246   request->ForwardResult(
    247       BaseSessionService::InternalGetCommandsRequest::TupleType(
    248           request->handle(), request));
    249 }
    250 
    251 bool SessionBackend::ReadLastSessionCommandsImpl(
    252     std::vector<SessionCommand*>* commands) {
    253   Init();
    254   SessionFileReader file_reader(GetLastSessionPath());
    255   return file_reader.Read(type_, commands);
    256 }
    257 
    258 void SessionBackend::DeleteLastSession() {
    259   Init();
    260   file_util::Delete(GetLastSessionPath(), false);
    261 }
    262 
    263 void SessionBackend::MoveCurrentSessionToLastSession() {
    264   Init();
    265   current_session_file_.reset(NULL);
    266 
    267   const FilePath current_session_path = GetCurrentSessionPath();
    268   const FilePath last_session_path = GetLastSessionPath();
    269   if (file_util::PathExists(last_session_path))
    270     file_util::Delete(last_session_path, false);
    271   if (file_util::PathExists(current_session_path)) {
    272     int64 file_size;
    273     if (file_util::GetFileSize(current_session_path, &file_size)) {
    274       if (type_ == BaseSessionService::TAB_RESTORE) {
    275         UMA_HISTOGRAM_COUNTS("TabRestore.last_session_file_size",
    276                              static_cast<int>(file_size / 1024));
    277       } else {
    278         UMA_HISTOGRAM_COUNTS("SessionRestore.last_session_file_size",
    279                              static_cast<int>(file_size / 1024));
    280       }
    281     }
    282     last_session_valid_ = file_util::Move(current_session_path,
    283                                           last_session_path);
    284   }
    285 
    286   if (file_util::PathExists(current_session_path))
    287     file_util::Delete(current_session_path, false);
    288 
    289   // Create and open the file for the current session.
    290   ResetFile();
    291 }
    292 
    293 void SessionBackend::ReadCurrentSessionCommands(
    294     scoped_refptr<BaseSessionService::InternalGetCommandsRequest> request) {
    295   if (request->canceled())
    296     return;
    297   Init();
    298   ReadCurrentSessionCommandsImpl(&(request->commands));
    299   request->ForwardResult(
    300       BaseSessionService::InternalGetCommandsRequest::TupleType(
    301           request->handle(), request));
    302 }
    303 
    304 bool SessionBackend::ReadCurrentSessionCommandsImpl(
    305     std::vector<SessionCommand*>* commands) {
    306   Init();
    307   SessionFileReader file_reader(GetCurrentSessionPath());
    308   return file_reader.Read(type_, commands);
    309 }
    310 
    311 bool SessionBackend::AppendCommandsToFile(net::FileStream* file,
    312     const std::vector<SessionCommand*>& commands) {
    313   for (std::vector<SessionCommand*>::const_iterator i = commands.begin();
    314        i != commands.end(); ++i) {
    315     int wrote;
    316     const size_type content_size = static_cast<size_type>((*i)->size());
    317     const size_type total_size =  content_size + sizeof(id_type);
    318     if (type_ == BaseSessionService::TAB_RESTORE)
    319       UMA_HISTOGRAM_COUNTS("TabRestore.command_size", total_size);
    320     else
    321       UMA_HISTOGRAM_COUNTS("SessionRestore.command_size", total_size);
    322     wrote = file->Write(reinterpret_cast<const char*>(&total_size),
    323                         sizeof(total_size), NULL);
    324     if (wrote != sizeof(total_size)) {
    325       NOTREACHED() << "error writing";
    326       return false;
    327     }
    328     id_type command_id = (*i)->id();
    329     wrote = file->Write(reinterpret_cast<char*>(&command_id),
    330                         sizeof(command_id), NULL);
    331     if (wrote != sizeof(command_id)) {
    332       NOTREACHED() << "error writing";
    333       return false;
    334     }
    335     if (content_size > 0) {
    336       wrote = file->Write(reinterpret_cast<char*>((*i)->contents()),
    337                           content_size, NULL);
    338       if (wrote != content_size) {
    339         NOTREACHED() << "error writing";
    340         return false;
    341       }
    342     }
    343   }
    344   file->Flush();
    345   return true;
    346 }
    347 
    348 SessionBackend::~SessionBackend() {
    349 }
    350 
    351 void SessionBackend::ResetFile() {
    352   DCHECK(inited_);
    353   if (current_session_file_.get()) {
    354     // File is already open, truncate it. We truncate instead of closing and
    355     // reopening to avoid the possibility of scanners locking the file out
    356     // from under us once we close it. If truncation fails, we'll try to
    357     // recreate.
    358     const int header_size = static_cast<int>(sizeof(FileHeader));
    359     if (current_session_file_->Truncate(header_size) != header_size)
    360       current_session_file_.reset(NULL);
    361   }
    362   if (!current_session_file_.get())
    363     current_session_file_.reset(OpenAndWriteHeader(GetCurrentSessionPath()));
    364   empty_file_ = true;
    365 }
    366 
    367 net::FileStream* SessionBackend::OpenAndWriteHeader(const FilePath& path) {
    368   DCHECK(!path.empty());
    369   scoped_ptr<net::FileStream> file(new net::FileStream());
    370   if (file->Open(path, base::PLATFORM_FILE_CREATE_ALWAYS |
    371       base::PLATFORM_FILE_WRITE | base::PLATFORM_FILE_EXCLUSIVE_WRITE |
    372       base::PLATFORM_FILE_EXCLUSIVE_READ) != net::OK)
    373     return NULL;
    374   FileHeader header;
    375   header.signature = kFileSignature;
    376   header.version = kFileCurrentVersion;
    377   int wrote = file->Write(reinterpret_cast<char*>(&header),
    378                           sizeof(header), NULL);
    379   if (wrote != sizeof(header))
    380     return NULL;
    381   return file.release();
    382 }
    383 
    384 FilePath SessionBackend::GetLastSessionPath() {
    385   FilePath path = path_to_dir_;
    386   if (type_ == BaseSessionService::TAB_RESTORE)
    387     path = path.AppendASCII(kLastTabSessionFileName);
    388   else
    389     path = path.AppendASCII(kLastSessionFileName);
    390   return path;
    391 }
    392 
    393 FilePath SessionBackend::GetCurrentSessionPath() {
    394   FilePath path = path_to_dir_;
    395   if (type_ == BaseSessionService::TAB_RESTORE)
    396     path = path.AppendASCII(kCurrentTabSessionFileName);
    397   else
    398     path = path.AppendASCII(kCurrentSessionFileName);
    399   return path;
    400 }
    401