The Tor Browser / file revision

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.

 // Use of this source code is governed by a BSD-style license that can be

 // found in the LICENSE file.

 #include "base/file_util.h"

 #include <windows.h>

 #include <psapi.h>

 #include <shellapi.h>

 #include <shlobj.h>

 #include <time.h>

 #include <algorithm>

 #include <limits>

 #include <string>

 #include "base/files/file_path.h"

 #include "base/logging.h"

 #include "base/metrics/histogram.h"

 #include "base/process/process_handle.h"

 #include "base/rand_util.h"

 #include "base/strings/string_number_conversions.h"

 #include "base/strings/string_util.h"

 #include "base/strings/utf_string_conversions.h"

 #include "base/threading/thread_restrictions.h"

 #include "base/time/time.h"

 #include "base/win/scoped_handle.h"

 #include "base/win/windows_version.h"

 namespace base {

 namespace {

 const DWORD kFileShareAll =

     FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE;

 bool ShellCopy(const FilePath& from_path,

                const FilePath& to_path,

                bool recursive) {

   // WinXP SHFileOperation doesn't like trailing separators.

   FilePath stripped_from = from_path.StripTrailingSeparators();

   FilePath stripped_to = to_path.StripTrailingSeparators();

   ThreadRestrictions::AssertIOAllowed();

   // NOTE: I suspect we could support longer paths, but that would involve

   // analyzing all our usage of files.

   if (stripped_from.value().length() >= MAX_PATH ||

       stripped_to.value().length() >= MAX_PATH) {

     return false;

   }

   // SHFILEOPSTRUCT wants the path to be terminated with two NULLs,

   // so we have to use wcscpy because wcscpy_s writes non-NULLs

   // into the rest of the buffer.

   wchar_t double_terminated_path_from[MAX_PATH + 1] = {0};

   wchar_t double_terminated_path_to[MAX_PATH + 1] = {0};

 #pragma warning(suppress:4996)  // don't complain about wcscpy deprecation

   wcscpy(double_terminated_path_from, stripped_from.value().c_str());

 #pragma warning(suppress:4996)  // don't complain about wcscpy deprecation

   wcscpy(double_terminated_path_to, stripped_to.value().c_str());

   SHFILEOPSTRUCT file_operation = {0};

   file_operation.wFunc = FO_COPY;

   file_operation.pFrom = double_terminated_path_from;

   file_operation.pTo = double_terminated_path_to;

   file_operation.fFlags = FOF_NOERRORUI | FOF_SILENT | FOF_NOCONFIRMATION |

                           FOF_NOCONFIRMMKDIR;

   if (!recursive)

     file_operation.fFlags |= FOF_NORECURSION | FOF_FILESONLY;

   return (SHFileOperation(&file_operation) == 0);

 }

 }  // namespace

 FilePath MakeAbsoluteFilePath(const FilePath& input) {

   ThreadRestrictions::AssertIOAllowed();

   wchar_t file_path[MAX_PATH];

   if (!_wfullpath(file_path, input.value().c_str(), MAX_PATH))

     return FilePath();

   return FilePath(file_path);

 }

 bool DeleteFile(const FilePath& path, bool recursive) {

   ThreadRestrictions::AssertIOAllowed();

   if (path.value().length() >= MAX_PATH)

     return false;

   if (!recursive) {

     // If not recursing, then first check to see if |path| is a directory.

     // If it is, then remove it with RemoveDirectory.

     PlatformFileInfo file_info;

     if (file_util::GetFileInfo(path, &file_info) && file_info.is_directory)

       return RemoveDirectory(path.value().c_str()) != 0;

     // Otherwise, it's a file, wildcard or non-existant. Try DeleteFile first

     // because it should be faster. If DeleteFile fails, then we fall through

     // to SHFileOperation, which will do the right thing.

     if (::DeleteFile(path.value().c_str()) != 0)

       return true;

   }

   // SHFILEOPSTRUCT wants the path to be terminated with two NULLs,

   // so we have to use wcscpy because wcscpy_s writes non-NULLs

   // into the rest of the buffer.

   wchar_t double_terminated_path[MAX_PATH + 1] = {0};

 #pragma warning(suppress:4996)  // don't complain about wcscpy deprecation

   if (g_bug108724_debug)

     LOG(WARNING) << "copying ";

   wcscpy(double_terminated_path, path.value().c_str());

   SHFILEOPSTRUCT file_operation = {0};

   file_operation.wFunc = FO_DELETE;

   file_operation.pFrom = double_terminated_path;

   file_operation.fFlags = FOF_NOERRORUI | FOF_SILENT | FOF_NOCONFIRMATION;

   if (!recursive)

     file_operation.fFlags |= FOF_NORECURSION | FOF_FILESONLY;

   if (g_bug108724_debug)

     LOG(WARNING) << "Performing shell operation";

   int err = SHFileOperation(&file_operation);

   if (g_bug108724_debug)

     LOG(WARNING) << "Done: " << err;

   // Since we're passing flags to the operation telling it to be silent,

   // it's possible for the operation to be aborted/cancelled without err

   // being set (although MSDN doesn't give any scenarios for how this can

   // happen).  See MSDN for SHFileOperation and SHFILEOPTSTRUCT.

   if (file_operation.fAnyOperationsAborted)

     return false;

   // Some versions of Windows return ERROR_FILE_NOT_FOUND (0x2) when deleting

   // an empty directory and some return 0x402 when they should be returning

   // ERROR_FILE_NOT_FOUND. MSDN says Vista and up won't return 0x402.

   return (err == 0 || err == ERROR_FILE_NOT_FOUND || err == 0x402);

 }

 bool DeleteFileAfterReboot(const FilePath& path) {

   ThreadRestrictions::AssertIOAllowed();

   if (path.value().length() >= MAX_PATH)

     return false;

   return MoveFileEx(path.value().c_str(), NULL,

                     MOVEFILE_DELAY_UNTIL_REBOOT |

                         MOVEFILE_REPLACE_EXISTING) != FALSE;

 }

 bool ReplaceFile(const FilePath& from_path,

                  const FilePath& to_path,

                  PlatformFileError* error) {

   ThreadRestrictions::AssertIOAllowed();

   // Try a simple move first.  It will only succeed when |to_path| doesn't

   // already exist.

   if (::MoveFile(from_path.value().c_str(), to_path.value().c_str()))

     return true;

   // Try the full-blown replace if the move fails, as ReplaceFile will only

   // succeed when |to_path| does exist. When writing to a network share, we may

   // not be able to change the ACLs. Ignore ACL errors then

   // (REPLACEFILE_IGNORE_MERGE_ERRORS).

   if (::ReplaceFile(to_path.value().c_str(), from_path.value().c_str(), NULL,

                     REPLACEFILE_IGNORE_MERGE_ERRORS, NULL, NULL)) {

     return true;

   }

   if (error)

     *error = LastErrorToPlatformFileError(GetLastError());

   return false;

 }

 bool CopyDirectory(const FilePath& from_path, const FilePath& to_path,

                    bool recursive) {

   ThreadRestrictions::AssertIOAllowed();

   if (recursive)

     return ShellCopy(from_path, to_path, true);

   // The following code assumes that from path is a directory.

   DCHECK(DirectoryExists(from_path));

   // Instead of creating a new directory, we copy the old one to include the

   // security information of the folder as part of the copy.

   if (!PathExists(to_path)) {

     // Except that Vista fails to do that, and instead do a recursive copy if

     // the target directory doesn't exist.

     if (base::win::GetVersion() >= base::win::VERSION_VISTA)

       file_util::CreateDirectory(to_path);

     else

       ShellCopy(from_path, to_path, false);

   }

   FilePath directory = from_path.Append(L"*.*");

   return ShellCopy(directory, to_path, false);

 }

 bool PathExists(const FilePath& path) {

   ThreadRestrictions::AssertIOAllowed();

   return (GetFileAttributes(path.value().c_str()) != INVALID_FILE_ATTRIBUTES);

 }

 bool PathIsWritable(const FilePath& path) {

   ThreadRestrictions::AssertIOAllowed();

   HANDLE dir =

       CreateFile(path.value().c_str(), FILE_ADD_FILE, kFileShareAll,

                  NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);

   if (dir == INVALID_HANDLE_VALUE)

     return false;

   CloseHandle(dir);

   return true;

 }

 bool DirectoryExists(const FilePath& path) {

   ThreadRestrictions::AssertIOAllowed();

   DWORD fileattr = GetFileAttributes(path.value().c_str());

   if (fileattr != INVALID_FILE_ATTRIBUTES)

     return (fileattr & FILE_ATTRIBUTE_DIRECTORY) != 0;

   return false;

 }

 }  // namespace base

 // -----------------------------------------------------------------------------

 namespace file_util {

 using base::DirectoryExists;

 using base::FilePath;

 using base::kFileShareAll;

 bool GetTempDir(FilePath* path) {

   base::ThreadRestrictions::AssertIOAllowed();

   wchar_t temp_path[MAX_PATH + 1];

   DWORD path_len = ::GetTempPath(MAX_PATH, temp_path);

   if (path_len >= MAX_PATH || path_len <= 0)

     return false;

   // TODO(evanm): the old behavior of this function was to always strip the

   // trailing slash.  We duplicate this here, but it shouldn't be necessary

   // when everyone is using the appropriate FilePath APIs.

   *path = FilePath(temp_path).StripTrailingSeparators();

   return true;

 }

 bool GetShmemTempDir(FilePath* path, bool executable) {

   return GetTempDir(path);

 }

 bool CreateTemporaryFile(FilePath* path) {

   base::ThreadRestrictions::AssertIOAllowed();

   FilePath temp_file;

   if (!GetTempDir(path))

     return false;

   if (CreateTemporaryFileInDir(*path, &temp_file)) {

     *path = temp_file;

     return true;

   }

   return false;

 }

 FILE* CreateAndOpenTemporaryShmemFile(FilePath* path, bool executable) {

   base::ThreadRestrictions::AssertIOAllowed();

   return CreateAndOpenTemporaryFile(path);

 }

 // On POSIX we have semantics to create and open a temporary file

 // atomically.

 // TODO(jrg): is there equivalent call to use on Windows instead of

 // going 2-step?

 FILE* CreateAndOpenTemporaryFileInDir(const FilePath& dir, FilePath* path) {

   base::ThreadRestrictions::AssertIOAllowed();

   if (!CreateTemporaryFileInDir(dir, path)) {

     return NULL;

   }

   // Open file in binary mode, to avoid problems with fwrite. On Windows

   // it replaces \n's with \r\n's, which may surprise you.

   // Reference: http://msdn.microsoft.com/en-us/library/h9t88zwz(VS.71).aspx

   return OpenFile(*path, "wb+");

 }

 bool CreateTemporaryFileInDir(const FilePath& dir,

                               FilePath* temp_file) {

   base::ThreadRestrictions::AssertIOAllowed();

   wchar_t temp_name[MAX_PATH + 1];

   if (!GetTempFileName(dir.value().c_str(), L"", 0, temp_name)) {

     DPLOG(WARNING) << "Failed to get temporary file name in " << dir.value();

     return false;

   }

   wchar_t long_temp_name[MAX_PATH + 1];

   DWORD long_name_len = GetLongPathName(temp_name, long_temp_name, MAX_PATH);

   if (long_name_len > MAX_PATH || long_name_len == 0) {

     // GetLongPathName() failed, but we still have a temporary file.

     *temp_file = FilePath(temp_name);

     return true;

   }

   FilePath::StringType long_temp_name_str;

   long_temp_name_str.assign(long_temp_name, long_name_len);

   *temp_file = FilePath(long_temp_name_str);

   return true;

 }

 bool CreateTemporaryDirInDir(const FilePath& base_dir,

                              const FilePath::StringType& prefix,

                              FilePath* new_dir) {

   base::ThreadRestrictions::AssertIOAllowed();

   FilePath path_to_create;

   for (int count = 0; count < 50; ++count) {

     // Try create a new temporary directory with random generated name. If

     // the one exists, keep trying another path name until we reach some limit.

     string16 new_dir_name;

     new_dir_name.assign(prefix);

     new_dir_name.append(base::IntToString16(::base::GetCurrentProcId()));

     new_dir_name.push_back('_');

     new_dir_name.append(base::IntToString16(base::RandInt(0, kint16max)));

     path_to_create = base_dir.Append(new_dir_name);

     if (::CreateDirectory(path_to_create.value().c_str(), NULL)) {

       *new_dir = path_to_create;

       return true;

     }

   }

   return false;

 }

 bool CreateNewTempDirectory(const FilePath::StringType& prefix,

                             FilePath* new_temp_path) {

   base::ThreadRestrictions::AssertIOAllowed();

   FilePath system_temp_dir;

   if (!GetTempDir(&system_temp_dir))

     return false;

   return CreateTemporaryDirInDir(system_temp_dir, prefix, new_temp_path);

 }

 bool CreateDirectoryAndGetError(const FilePath& full_path,

                                 base::PlatformFileError* error) {

   base::ThreadRestrictions::AssertIOAllowed();

   // If the path exists, we've succeeded if it's a directory, failed otherwise.

   const wchar_t* full_path_str = full_path.value().c_str();

   DWORD fileattr = ::GetFileAttributes(full_path_str);

   if (fileattr != INVALID_FILE_ATTRIBUTES) {

     if ((fileattr & FILE_ATTRIBUTE_DIRECTORY) != 0) {

       DVLOG(1) << "CreateDirectory(" << full_path_str << "), "

                << "directory already exists.";

       return true;

     }

     DLOG(WARNING) << "CreateDirectory(" << full_path_str << "), "

                   << "conflicts with existing file.";

     if (error) {

       *error = base::PLATFORM_FILE_ERROR_NOT_A_DIRECTORY;

     }

     return false;

   }

   // Invariant:  Path does not exist as file or directory.

   // Attempt to create the parent recursively.  This will immediately return

   // true if it already exists, otherwise will create all required parent

   // directories starting with the highest-level missing parent.

   FilePath parent_path(full_path.DirName());

   if (parent_path.value() == full_path.value()) {

     if (error) {

       *error = base::PLATFORM_FILE_ERROR_NOT_FOUND;

     }

     return false;

   }

   if (!CreateDirectoryAndGetError(parent_path, error)) {

     DLOG(WARNING) << "Failed to create one of the parent directories.";

     if (error) {

       DCHECK(*error != base::PLATFORM_FILE_OK);

     }

     return false;

   }

   if (!::CreateDirectory(full_path_str, NULL)) {

     DWORD error_code = ::GetLastError();

     if (error_code == ERROR_ALREADY_EXISTS && DirectoryExists(full_path)) {

       // This error code ERROR_ALREADY_EXISTS doesn't indicate whether we

       // were racing with someone creating the same directory, or a file

       // with the same path.  If DirectoryExists() returns true, we lost the

       // race to create the same directory.

       return true;

     } else {

       if (error)

         *error = base::LastErrorToPlatformFileError(error_code);

       DLOG(WARNING) << "Failed to create directory " << full_path_str

                     << ", last error is " << error_code << ".";

       return false;

     }

   } else {

     return true;

   }

 }

 // TODO(rkc): Work out if we want to handle NTFS junctions here or not, handle

 // them if we do decide to.

 bool IsLink(const FilePath& file_path) {

   return false;

 }

 bool GetFileInfo(const FilePath& file_path, base::PlatformFileInfo* results) {

   base::ThreadRestrictions::AssertIOAllowed();

   WIN32_FILE_ATTRIBUTE_DATA attr;

   if (!GetFileAttributesEx(file_path.value().c_str(),

                            GetFileExInfoStandard, &attr)) {

     return false;

   }

   ULARGE_INTEGER size;

   size.HighPart = attr.nFileSizeHigh;

   size.LowPart = attr.nFileSizeLow;

   results->size = size.QuadPart;

   results->is_directory =

       (attr.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) != 0;

   results->last_modified = base::Time::FromFileTime(attr.ftLastWriteTime);

   results->last_accessed = base::Time::FromFileTime(attr.ftLastAccessTime);

   results->creation_time = base::Time::FromFileTime(attr.ftCreationTime);

   return true;

 }

 FILE* OpenFile(const FilePath& filename, const char* mode) {

   base::ThreadRestrictions::AssertIOAllowed();

   std::wstring w_mode = ASCIIToWide(std::string(mode));

   return _wfsopen(filename.value().c_str(), w_mode.c_str(), _SH_DENYNO);

 }

 FILE* OpenFile(const std::string& filename, const char* mode) {

   base::ThreadRestrictions::AssertIOAllowed();

   return _fsopen(filename.c_str(), mode, _SH_DENYNO);

 }

 int ReadFile(const FilePath& filename, char* data, int size) {

   base::ThreadRestrictions::AssertIOAllowed();

   base::win::ScopedHandle file(CreateFile(filename.value().c_str(),

                                           GENERIC_READ,

                                           FILE_SHARE_READ | FILE_SHARE_WRITE,

                                           NULL,

                                           OPEN_EXISTING,

                                           FILE_FLAG_SEQUENTIAL_SCAN,

                                           NULL));

   if (!file)

     return -1;

   DWORD read;

   if (::ReadFile(file, data, size, &read, NULL) &&

       static_cast<int>(read) == size)

     return read;

   return -1;

 }

 int WriteFile(const FilePath& filename, const char* data, int size) {

   base::ThreadRestrictions::AssertIOAllowed();

   base::win::ScopedHandle file(CreateFile(filename.value().c_str(),

                                           GENERIC_WRITE,

                                           0,

                                           NULL,

                                           CREATE_ALWAYS,

                                           0,

                                           NULL));

   if (!file) {

     DLOG_GETLASTERROR(WARNING) << "CreateFile failed for path "

                                << filename.value();

     return -1;

   }

   DWORD written;

   BOOL result = ::WriteFile(file, data, size, &written, NULL);

   if (result && static_cast<int>(written) == size)

     return written;

   if (!result) {

     // WriteFile failed.

     DLOG_GETLASTERROR(WARNING) << "writing file " << filename.value()

                                << " failed";

   } else {

     // Didn't write all the bytes.

     DLOG(WARNING) << "wrote" << written << " bytes to "

                   << filename.value() << " expected " << size;

   }

   return -1;

 }

 int AppendToFile(const FilePath& filename, const char* data, int size) {

   base::ThreadRestrictions::AssertIOAllowed();

   base::win::ScopedHandle file(CreateFile(filename.value().c_str(),

                                           FILE_APPEND_DATA,

                                           0,

                                           NULL,

                                           OPEN_EXISTING,

                                           0,

                                           NULL));

   if (!file) {

     DLOG_GETLASTERROR(WARNING) << "CreateFile failed for path "

                                << filename.value();

     return -1;

   }

   DWORD written;

   BOOL result = ::WriteFile(file, data, size, &written, NULL);

   if (result && static_cast<int>(written) == size)

     return written;

   if (!result) {

     // WriteFile failed.

     DLOG_GETLASTERROR(WARNING) << "writing file " << filename.value()

                                << " failed";

   } else {

     // Didn't write all the bytes.

     DLOG(WARNING) << "wrote" << written << " bytes to "

                   << filename.value() << " expected " << size;

   }

   return -1;

 }

 // Gets the current working directory for the process.

 bool GetCurrentDirectory(FilePath* dir) {

   base::ThreadRestrictions::AssertIOAllowed();

   wchar_t system_buffer[MAX_PATH];

   system_buffer[0] = 0;

   DWORD len = ::GetCurrentDirectory(MAX_PATH, system_buffer);

   if (len == 0 || len > MAX_PATH)

     return false;

   // TODO(evanm): the old behavior of this function was to always strip the

   // trailing slash.  We duplicate this here, but it shouldn't be necessary

   // when everyone is using the appropriate FilePath APIs.

   std::wstring dir_str(system_buffer);

   *dir = FilePath(dir_str).StripTrailingSeparators();

   return true;

 }

 // Sets the current working directory for the process.

 bool SetCurrentDirectory(const FilePath& directory) {

   base::ThreadRestrictions::AssertIOAllowed();

   BOOL ret = ::SetCurrentDirectory(directory.value().c_str());

   return ret != 0;

 }

 bool NormalizeFilePath(const FilePath& path, FilePath* real_path) {

   base::ThreadRestrictions::AssertIOAllowed();

   FilePath mapped_file;

   if (!NormalizeToNativeFilePath(path, &mapped_file))

     return false;

   // NormalizeToNativeFilePath() will return a path that starts with

   // "\Device\Harddisk...".  Helper DevicePathToDriveLetterPath()

   // will find a drive letter which maps to the path's device, so

   // that we return a path starting with a drive letter.

   return DevicePathToDriveLetterPath(mapped_file, real_path);

 }

 bool DevicePathToDriveLetterPath(const FilePath& nt_device_path,

                                  FilePath* out_drive_letter_path) {

   base::ThreadRestrictions::AssertIOAllowed();

   // Get the mapping of drive letters to device paths.

   const int kDriveMappingSize = 1024;

   wchar_t drive_mapping[kDriveMappingSize] = {'\0'};

   if (!::GetLogicalDriveStrings(kDriveMappingSize - 1, drive_mapping)) {

     DLOG(ERROR) << "Failed to get drive mapping.";

     return false;

   }

   // The drive mapping is a sequence of null terminated strings.

   // The last string is empty.

   wchar_t* drive_map_ptr = drive_mapping;

   wchar_t device_path_as_string[MAX_PATH];

   wchar_t drive[] = L" :";

   // For each string in the drive mapping, get the junction that links

   // to it.  If that junction is a prefix of |device_path|, then we

   // know that |drive| is the real path prefix.

   while (*drive_map_ptr) {

     drive[0] = drive_map_ptr[0];  // Copy the drive letter.

     if (QueryDosDevice(drive, device_path_as_string, MAX_PATH)) {

       FilePath device_path(device_path_as_string);

       if (device_path == nt_device_path ||

           device_path.IsParent(nt_device_path)) {

         *out_drive_letter_path = FilePath(drive +

             nt_device_path.value().substr(wcslen(device_path_as_string)));

         return true;

       }

     }

     // Move to the next drive letter string, which starts one

     // increment after the '\0' that terminates the current string.

     while (*drive_map_ptr++);

   }

   // No drive matched.  The path does not start with a device junction

   // that is mounted as a drive letter.  This means there is no drive

   // letter path to the volume that holds |device_path|, so fail.

   return false;

 }

 bool NormalizeToNativeFilePath(const FilePath& path, FilePath* nt_path) {

   base::ThreadRestrictions::AssertIOAllowed();

   // In Vista, GetFinalPathNameByHandle() would give us the real path

   // from a file handle.  If we ever deprecate XP, consider changing the

   // code below to a call to GetFinalPathNameByHandle().  The method this

   // function uses is explained in the following msdn article:

   // http://msdn.microsoft.com/en-us/library/aa366789(VS.85).aspx

   base::win::ScopedHandle file_handle(

       ::CreateFile(path.value().c_str(),

                    GENERIC_READ,

                    kFileShareAll,

                    NULL,

                    OPEN_EXISTING,

                    FILE_ATTRIBUTE_NORMAL,

                    NULL));

   if (!file_handle)

     return false;

   // Create a file mapping object.  Can't easily use MemoryMappedFile, because

   // we only map the first byte, and need direct access to the handle. You can

   // not map an empty file, this call fails in that case.

   base::win::ScopedHandle file_map_handle(

       ::CreateFileMapping(file_handle.Get(),

                           NULL,

                           PAGE_READONLY,

                           0,

                           1,  // Just one byte.  No need to look at the data.

                           NULL));

   if (!file_map_handle)

     return false;

   // Use a view of the file to get the path to the file.

   void* file_view = MapViewOfFile(file_map_handle.Get(),

                                   FILE_MAP_READ, 0, 0, 1);

   if (!file_view)

     return false;

   // The expansion of |path| into a full path may make it longer.

   // GetMappedFileName() will fail if the result is longer than MAX_PATH.

   // Pad a bit to be safe.  If kMaxPathLength is ever changed to be less

   // than MAX_PATH, it would be nessisary to test that GetMappedFileName()

   // not return kMaxPathLength.  This would mean that only part of the

   // path fit in |mapped_file_path|.

   const int kMaxPathLength = MAX_PATH + 10;

   wchar_t mapped_file_path[kMaxPathLength];

   bool success = false;

   HANDLE cp = GetCurrentProcess();

   if (::GetMappedFileNameW(cp, file_view, mapped_file_path, kMaxPathLength)) {

     *nt_path = FilePath(mapped_file_path);

     success = true;

   }

   ::UnmapViewOfFile(file_view);

   return success;

 }

 int GetMaximumPathComponentLength(const FilePath& path) {

   base::ThreadRestrictions::AssertIOAllowed();

   wchar_t volume_path[MAX_PATH];

   if (!GetVolumePathNameW(path.NormalizePathSeparators().value().c_str(),

                           volume_path,

                           arraysize(volume_path))) {

     return -1;

   }

   DWORD max_length = 0;

   if (!GetVolumeInformationW(volume_path, NULL, 0, NULL, &max_length, NULL,

                              NULL, 0)) {

     return -1;

   }

   // Length of |path| with path separator appended.

   size_t prefix = path.StripTrailingSeparators().value().size() + 1;

   // The whole path string must be shorter than MAX_PATH. That is, it must be

   // prefix + component_length < MAX_PATH (or equivalently, <= MAX_PATH - 1).

   int whole_path_limit = std::max(0, MAX_PATH - 1 - static_cast<int>(prefix));

   return std::min(whole_path_limit, static_cast<int>(max_length));

 }

 }  // namespace file_util

 namespace base {

 namespace internal {

 bool MoveUnsafe(const FilePath& from_path, const FilePath& to_path) {

   ThreadRestrictions::AssertIOAllowed();

   // NOTE: I suspect we could support longer paths, but that would involve

   // analyzing all our usage of files.

   if (from_path.value().length() >= MAX_PATH ||

       to_path.value().length() >= MAX_PATH) {

     return false;

   }

   if (MoveFileEx(from_path.value().c_str(), to_path.value().c_str(),

                  MOVEFILE_COPY_ALLOWED | MOVEFILE_REPLACE_EXISTING) != 0)

     return true;

   // Keep the last error value from MoveFileEx around in case the below

   // fails.

   bool ret = false;

   DWORD last_error = ::GetLastError();

   if (DirectoryExists(from_path)) {

     // MoveFileEx fails if moving directory across volumes. We will simulate

     // the move by using Copy and Delete. Ideally we could check whether

     // from_path and to_path are indeed in different volumes.

     ret = internal::CopyAndDeleteDirectory(from_path, to_path);

   }

   if (!ret) {

     // Leave a clue about what went wrong so that it can be (at least) picked

     // up by a PLOG entry.

     ::SetLastError(last_error);

   }

   return ret;

 }

 bool CopyFileUnsafe(const FilePath& from_path, const FilePath& to_path) {

   ThreadRestrictions::AssertIOAllowed();

   // NOTE: I suspect we could support longer paths, but that would involve

   // analyzing all our usage of files.

   if (from_path.value().length() >= MAX_PATH ||

       to_path.value().length() >= MAX_PATH) {

     return false;

   }

   return (::CopyFile(from_path.value().c_str(), to_path.value().c_str(),

                      false) != 0);

 }

 bool CopyAndDeleteDirectory(const FilePath& from_path,

                             const FilePath& to_path) {

   ThreadRestrictions::AssertIOAllowed();

   if (CopyDirectory(from_path, to_path, true)) {

     if (DeleteFile(from_path, true))

       return true;

     // Like Move, this function is not transactional, so we just

     // leave the copied bits behind if deleting from_path fails.

     // If to_path exists previously then we have already overwritten

     // it by now, we don't get better off by deleting the new bits.

   }

   return false;

 }

 }  // namespace internal

 }  // namespace base