base/file_util_win.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 "base/file_util.h"
   6
   7 #include <windows.h>
   8 #include <psapi.h>
   9 #include <shellapi.h>
  10 #include <shlobj.h>
  11 #include <time.h>
  12
  13 #include <algorithm>
  14 #include <limits>
  15 #include <string>
  16
  17 #include "base/files/file_path.h"
  18 #include "base/logging.h"
  19 #include "base/metrics/histogram.h"
  20 #include "base/process/process_handle.h"
  21 #include "base/rand_util.h"
  22 #include "base/strings/string_number_conversions.h"
  23 #include "base/strings/string_util.h"
  24 #include "base/strings/utf_string_conversions.h"
  25 #include "base/threading/thread_restrictions.h"
  26 #include "base/time/time.h"
  27 #include "base/win/scoped_handle.h"
  28 #include "base/win/windows_version.h"
  29
  30 namespace base {
  31
  32 namespace {
  33
  34 const DWORD kFileShareAll =
  35     FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE;
  36
  37 bool ShellCopy(const FilePath& from_path,
  38                const FilePath& to_path,
  39                bool recursive) {
  40   // WinXP SHFileOperation doesn't like trailing separators.
  41   FilePath stripped_from = from_path.StripTrailingSeparators();
  42   FilePath stripped_to = to_path.StripTrailingSeparators();
  43
  44   ThreadRestrictions::AssertIOAllowed();
  45
  46   // NOTE: I suspect we could support longer paths, but that would involve
  47   // analyzing all our usage of files.
  48   if (stripped_from.value().length() >= MAX_PATH ||
  49       stripped_to.value().length() >= MAX_PATH) {
  50     return false;
  51   }
  52
  53   // SHFILEOPSTRUCT wants the path to be terminated with two NULLs,
  54   // so we have to use wcscpy because wcscpy_s writes non-NULLs
  55   // into the rest of the buffer.
  56   wchar_t double_terminated_path_from[MAX_PATH + 1] = {0};
  57   wchar_t double_terminated_path_to[MAX_PATH + 1] = {0};
  58 #pragma warning(suppress:4996)  // don't complain about wcscpy deprecation
  59   wcscpy(double_terminated_path_from, stripped_from.value().c_str());
  60 #pragma warning(suppress:4996)  // don't complain about wcscpy deprecation
  61   wcscpy(double_terminated_path_to, stripped_to.value().c_str());
  62
  63   SHFILEOPSTRUCT file_operation = {0};
  64   file_operation.wFunc = FO_COPY;
  65   file_operation.pFrom = double_terminated_path_from;
  66   file_operation.pTo = double_terminated_path_to;
  67   file_operation.fFlags = FOF_NOERRORUI | FOF_SILENT | FOF_NOCONFIRMATION |
  68                           FOF_NOCONFIRMMKDIR;
  69   if (!recursive)
  70     file_operation.fFlags |= FOF_NORECURSION | FOF_FILESONLY;
  71
  72   return (SHFileOperation(&file_operation) == 0);
  73 }
  74
  75 }  // namespace
  76
  77 FilePath MakeAbsoluteFilePath(const FilePath& input) {
  78   ThreadRestrictions::AssertIOAllowed();
  79   wchar_t file_path[MAX_PATH];
  80   if (!_wfullpath(file_path, input.value().c_str(), MAX_PATH))
  81     return FilePath();
  82   return FilePath(file_path);
  83 }
  84
  85 bool DeleteFile(const FilePath& path, bool recursive) {
  86   ThreadRestrictions::AssertIOAllowed();
  87
  88   if (path.value().length() >= MAX_PATH)
  89     return false;
  90
  91   if (!recursive) {
  92     // If not recursing, then first check to see if |path| is a directory.
  93     // If it is, then remove it with RemoveDirectory.
  94     PlatformFileInfo file_info;
  95     if (file_util::GetFileInfo(path, &file_info) && file_info.is_directory)
  96       return RemoveDirectory(path.value().c_str()) != 0;
  97
  98     // Otherwise, it's a file, wildcard or non-existant. Try DeleteFile first
  99     // because it should be faster. If DeleteFile fails, then we fall through
 100     // to SHFileOperation, which will do the right thing.
 101     if (::DeleteFile(path.value().c_str()) != 0)
 102       return true;
 103   }
 104
 105   // SHFILEOPSTRUCT wants the path to be terminated with two NULLs,
 106   // so we have to use wcscpy because wcscpy_s writes non-NULLs
 107   // into the rest of the buffer.
 108   wchar_t double_terminated_path[MAX_PATH + 1] = {0};
 109 #pragma warning(suppress:4996)  // don't complain about wcscpy deprecation
 110   if (g_bug108724_debug)
 111     LOG(WARNING) << "copying ";
 112   wcscpy(double_terminated_path, path.value().c_str());
 113
 114   SHFILEOPSTRUCT file_operation = {0};
 115   file_operation.wFunc = FO_DELETE;
 116   file_operation.pFrom = double_terminated_path;
 117   file_operation.fFlags = FOF_NOERRORUI | FOF_SILENT | FOF_NOCONFIRMATION;
 118   if (!recursive)
 119     file_operation.fFlags |= FOF_NORECURSION | FOF_FILESONLY;
 120   if (g_bug108724_debug)
 121     LOG(WARNING) << "Performing shell operation";
 122   int err = SHFileOperation(&file_operation);
 123   if (g_bug108724_debug)
 124     LOG(WARNING) << "Done: " << err;
 125
 126   // Since we're passing flags to the operation telling it to be silent,
 127   // it's possible for the operation to be aborted/cancelled without err
 128   // being set (although MSDN doesn't give any scenarios for how this can
 129   // happen).  See MSDN for SHFileOperation and SHFILEOPTSTRUCT.
 130   if (file_operation.fAnyOperationsAborted)
 131     return false;
 132
 133   // Some versions of Windows return ERROR_FILE_NOT_FOUND (0x2) when deleting
 134   // an empty directory and some return 0x402 when they should be returning
 135   // ERROR_FILE_NOT_FOUND. MSDN says Vista and up won't return 0x402.
 136   return (err == 0 || err == ERROR_FILE_NOT_FOUND || err == 0x402);
 137 }
 138
 139 bool DeleteFileAfterReboot(const FilePath& path) {
 140   ThreadRestrictions::AssertIOAllowed();
 141
 142   if (path.value().length() >= MAX_PATH)
 143     return false;
 144
 145   return MoveFileEx(path.value().c_str(), NULL,
 146                     MOVEFILE_DELAY_UNTIL_REBOOT |
 147                         MOVEFILE_REPLACE_EXISTING) != FALSE;
 148 }
 149
 150 bool ReplaceFile(const FilePath& from_path,
 151                  const FilePath& to_path,
 152                  PlatformFileError* error) {
 153   ThreadRestrictions::AssertIOAllowed();
 154   // Try a simple move first.  It will only succeed when |to_path| doesn't
 155   // already exist.
 156   if (::MoveFile(from_path.value().c_str(), to_path.value().c_str()))
 157     return true;
 158   // Try the full-blown replace if the move fails, as ReplaceFile will only
 159   // succeed when |to_path| does exist. When writing to a network share, we may
 160   // not be able to change the ACLs. Ignore ACL errors then
 161   // (REPLACEFILE_IGNORE_MERGE_ERRORS).
 162   if (::ReplaceFile(to_path.value().c_str(), from_path.value().c_str(), NULL,
 163                     REPLACEFILE_IGNORE_MERGE_ERRORS, NULL, NULL)) {
 164     return true;
 165   }
 166   if (error)
 167     *error = LastErrorToPlatformFileError(GetLastError());
 168   return false;
 169 }
 170
 171 bool CopyDirectory(const FilePath& from_path, const FilePath& to_path,
 172                    bool recursive) {
 173   ThreadRestrictions::AssertIOAllowed();
 174
 175   if (recursive)
 176     return ShellCopy(from_path, to_path, true);
 177
 178   // The following code assumes that from path is a directory.
 179   DCHECK(DirectoryExists(from_path));
 180
 181   // Instead of creating a new directory, we copy the old one to include the
 182   // security information of the folder as part of the copy.
 183   if (!PathExists(to_path)) {
 184     // Except that Vista fails to do that, and instead do a recursive copy if
 185     // the target directory doesn't exist.
 186     if (base::win::GetVersion() >= base::win::VERSION_VISTA)
 187       file_util::CreateDirectory(to_path);
 188     else
 189       ShellCopy(from_path, to_path, false);
 190   }
 191
 192   FilePath directory = from_path.Append(L"*.*");
 193   return ShellCopy(directory, to_path, false);
 194 }
 195
 196 bool PathExists(const FilePath& path) {
 197   ThreadRestrictions::AssertIOAllowed();
 198   return (GetFileAttributes(path.value().c_str()) != INVALID_FILE_ATTRIBUTES);
 199 }
 200
 201 bool PathIsWritable(const FilePath& path) {
 202   ThreadRestrictions::AssertIOAllowed();
 203   HANDLE dir =
 204       CreateFile(path.value().c_str(), FILE_ADD_FILE, kFileShareAll,
 205                  NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
 206
 207   if (dir == INVALID_HANDLE_VALUE)
 208     return false;
 209
 210   CloseHandle(dir);
 211   return true;
 212 }
 213
 214 bool DirectoryExists(const FilePath& path) {
 215   ThreadRestrictions::AssertIOAllowed();
 216   DWORD fileattr = GetFileAttributes(path.value().c_str());
 217   if (fileattr != INVALID_FILE_ATTRIBUTES)
 218     return (fileattr & FILE_ATTRIBUTE_DIRECTORY) != 0;
 219   return false;
 220 }
 221
 222 }  // namespace base
 223
 224 // -----------------------------------------------------------------------------
 225
 226 namespace file_util {
 227
 228 using base::DirectoryExists;
 229 using base::FilePath;
 230 using base::kFileShareAll;
 231
 232 bool GetTempDir(FilePath* path) {
 233   base::ThreadRestrictions::AssertIOAllowed();
 234
 235   wchar_t temp_path[MAX_PATH + 1];
 236   DWORD path_len = ::GetTempPath(MAX_PATH, temp_path);
 237   if (path_len >= MAX_PATH || path_len <= 0)
 238     return false;
 239   // TODO(evanm): the old behavior of this function was to always strip the
 240   // trailing slash.  We duplicate this here, but it shouldn't be necessary
 241   // when everyone is using the appropriate FilePath APIs.
 242   *path = FilePath(temp_path).StripTrailingSeparators();
 243   return true;
 244 }
 245
 246 bool GetShmemTempDir(FilePath* path, bool executable) {
 247   return GetTempDir(path);
 248 }
 249
 250 bool CreateTemporaryFile(FilePath* path) {
 251   base::ThreadRestrictions::AssertIOAllowed();
 252
 253   FilePath temp_file;
 254
 255   if (!GetTempDir(path))
 256     return false;
 257
 258   if (CreateTemporaryFileInDir(*path, &temp_file)) {
 259     *path = temp_file;
 260     return true;
 261   }
 262
 263   return false;
 264 }
 265
 266 FILE* CreateAndOpenTemporaryShmemFile(FilePath* path, bool executable) {
 267   base::ThreadRestrictions::AssertIOAllowed();
 268   return CreateAndOpenTemporaryFile(path);
 269 }
 270
 271 // On POSIX we have semantics to create and open a temporary file
 272 // atomically.
 273 // TODO(jrg): is there equivalent call to use on Windows instead of
 274 // going 2-step?
 275 FILE* CreateAndOpenTemporaryFileInDir(const FilePath& dir, FilePath* path) {
 276   base::ThreadRestrictions::AssertIOAllowed();
 277   if (!CreateTemporaryFileInDir(dir, path)) {
 278     return NULL;
 279   }
 280   // Open file in binary mode, to avoid problems with fwrite. On Windows
 281   // it replaces \n's with \r\n's, which may surprise you.
 282   // Reference: http://msdn.microsoft.com/en-us/library/h9t88zwz(VS.71).aspx
 283   return OpenFile(*path, "wb+");
 284 }
 285
 286 bool CreateTemporaryFileInDir(const FilePath& dir,
 287                               FilePath* temp_file) {
 288   base::ThreadRestrictions::AssertIOAllowed();
 289
 290   wchar_t temp_name[MAX_PATH + 1];
 291
 292   if (!GetTempFileName(dir.value().c_str(), L"", 0, temp_name)) {
 293     DPLOG(WARNING) << "Failed to get temporary file name in " << dir.value();
 294     return false;
 295   }
 296
 297   wchar_t long_temp_name[MAX_PATH + 1];
 298   DWORD long_name_len = GetLongPathName(temp_name, long_temp_name, MAX_PATH);
 299   if (long_name_len > MAX_PATH || long_name_len == 0) {
 300     // GetLongPathName() failed, but we still have a temporary file.
 301     *temp_file = FilePath(temp_name);
 302     return true;
 303   }
 304
 305   FilePath::StringType long_temp_name_str;
 306   long_temp_name_str.assign(long_temp_name, long_name_len);
 307   *temp_file = FilePath(long_temp_name_str);
 308   return true;
 309 }
 310
 311 bool CreateTemporaryDirInDir(const FilePath& base_dir,
 312                              const FilePath::StringType& prefix,
 313                              FilePath* new_dir) {
 314   base::ThreadRestrictions::AssertIOAllowed();
 315
 316   FilePath path_to_create;
 317
 318   for (int count = 0; count < 50; ++count) {
 319     // Try create a new temporary directory with random generated name. If
 320     // the one exists, keep trying another path name until we reach some limit.
 321     string16 new_dir_name;
 322     new_dir_name.assign(prefix);
 323     new_dir_name.append(base::IntToString16(::base::GetCurrentProcId()));
 324     new_dir_name.push_back('_');
 325     new_dir_name.append(base::IntToString16(base::RandInt(0, kint16max)));
 326
 327     path_to_create = base_dir.Append(new_dir_name);
 328     if (::CreateDirectory(path_to_create.value().c_str(), NULL)) {
 329       *new_dir = path_to_create;
 330       return true;
 331     }
 332   }
 333
 334   return false;
 335 }
 336
 337 bool CreateNewTempDirectory(const FilePath::StringType& prefix,
 338                             FilePath* new_temp_path) {
 339   base::ThreadRestrictions::AssertIOAllowed();
 340
 341   FilePath system_temp_dir;
 342   if (!GetTempDir(&system_temp_dir))
 343     return false;
 344
 345   return CreateTemporaryDirInDir(system_temp_dir, prefix, new_temp_path);
 346 }
 347
 348 bool CreateDirectoryAndGetError(const FilePath& full_path,
 349                                 base::PlatformFileError* error) {
 350   base::ThreadRestrictions::AssertIOAllowed();
 351
 352   // If the path exists, we've succeeded if it's a directory, failed otherwise.
 353   const wchar_t* full_path_str = full_path.value().c_str();
 354   DWORD fileattr = ::GetFileAttributes(full_path_str);
 355   if (fileattr != INVALID_FILE_ATTRIBUTES) {
 356     if ((fileattr & FILE_ATTRIBUTE_DIRECTORY) != 0) {
 357       DVLOG(1) << "CreateDirectory(" << full_path_str << "), "
 358                << "directory already exists.";
 359       return true;
 360     }
 361     DLOG(WARNING) << "CreateDirectory(" << full_path_str << "), "
 362                   << "conflicts with existing file.";
 363     if (error) {
 364       *error = base::PLATFORM_FILE_ERROR_NOT_A_DIRECTORY;
 365     }
 366     return false;
 367   }
 368
 369   // Invariant:  Path does not exist as file or directory.
 370
 371   // Attempt to create the parent recursively.  This will immediately return
 372   // true if it already exists, otherwise will create all required parent
 373   // directories starting with the highest-level missing parent.
 374   FilePath parent_path(full_path.DirName());
 375   if (parent_path.value() == full_path.value()) {
 376     if (error) {
 377       *error = base::PLATFORM_FILE_ERROR_NOT_FOUND;
 378     }
 379     return false;
 380   }
 381   if (!CreateDirectoryAndGetError(parent_path, error)) {
 382     DLOG(WARNING) << "Failed to create one of the parent directories.";
 383     if (error) {
 384       DCHECK(*error != base::PLATFORM_FILE_OK);
 385     }
 386     return false;
 387   }
 388
 389   if (!::CreateDirectory(full_path_str, NULL)) {
 390     DWORD error_code = ::GetLastError();
 391     if (error_code == ERROR_ALREADY_EXISTS && DirectoryExists(full_path)) {
 392       // This error code ERROR_ALREADY_EXISTS doesn't indicate whether we
 393       // were racing with someone creating the same directory, or a file
 394       // with the same path.  If DirectoryExists() returns true, we lost the
 395       // race to create the same directory.
 396       return true;
 397     } else {
 398       if (error)
 399         *error = base::LastErrorToPlatformFileError(error_code);
 400       DLOG(WARNING) << "Failed to create directory " << full_path_str
 401                     << ", last error is " << error_code << ".";
 402       return false;
 403     }
 404   } else {
 405     return true;
 406   }
 407 }
 408
 409 // TODO(rkc): Work out if we want to handle NTFS junctions here or not, handle
 410 // them if we do decide to.
 411 bool IsLink(const FilePath& file_path) {
 412   return false;
 413 }
 414
 415 bool GetFileInfo(const FilePath& file_path, base::PlatformFileInfo* results) {
 416   base::ThreadRestrictions::AssertIOAllowed();
 417
 418   WIN32_FILE_ATTRIBUTE_DATA attr;
 419   if (!GetFileAttributesEx(file_path.value().c_str(),
 420                            GetFileExInfoStandard, &attr)) {
 421     return false;
 422   }
 423
 424   ULARGE_INTEGER size;
 425   size.HighPart = attr.nFileSizeHigh;
 426   size.LowPart = attr.nFileSizeLow;
 427   results->size = size.QuadPart;
 428
 429   results->is_directory =
 430       (attr.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) != 0;
 431   results->last_modified = base::Time::FromFileTime(attr.ftLastWriteTime);
 432   results->last_accessed = base::Time::FromFileTime(attr.ftLastAccessTime);
 433   results->creation_time = base::Time::FromFileTime(attr.ftCreationTime);
 434
 435   return true;
 436 }
 437
 438 FILE* OpenFile(const FilePath& filename, const char* mode) {
 439   base::ThreadRestrictions::AssertIOAllowed();
 440   std::wstring w_mode = ASCIIToWide(std::string(mode));
 441   return _wfsopen(filename.value().c_str(), w_mode.c_str(), _SH_DENYNO);
 442 }
 443
 444 FILE* OpenFile(const std::string& filename, const char* mode) {
 445   base::ThreadRestrictions::AssertIOAllowed();
 446   return _fsopen(filename.c_str(), mode, _SH_DENYNO);
 447 }
 448
 449 int ReadFile(const FilePath& filename, char* data, int size) {
 450   base::ThreadRestrictions::AssertIOAllowed();
 451   base::win::ScopedHandle file(CreateFile(filename.value().c_str(),
 452                                           GENERIC_READ,
 453                                           FILE_SHARE_READ | FILE_SHARE_WRITE,
 454                                           NULL,
 455                                           OPEN_EXISTING,
 456                                           FILE_FLAG_SEQUENTIAL_SCAN,
 457                                           NULL));
 458   if (!file)
 459     return -1;
 460
 461   DWORD read;
 462   if (::ReadFile(file, data, size, &read, NULL) &&
 463       static_cast<int>(read) == size)
 464     return read;
 465   return -1;
 466 }
 467
 468 int WriteFile(const FilePath& filename, const char* data, int size) {
 469   base::ThreadRestrictions::AssertIOAllowed();
 470   base::win::ScopedHandle file(CreateFile(filename.value().c_str(),
 471                                           GENERIC_WRITE,
 472                                           0,
 473                                           NULL,
 474                                           CREATE_ALWAYS,
 475                                           0,
 476                                           NULL));
 477   if (!file) {
 478     DLOG_GETLASTERROR(WARNING) << "CreateFile failed for path "
 479                                << filename.value();
 480     return -1;
 481   }
 482
 483   DWORD written;
 484   BOOL result = ::WriteFile(file, data, size, &written, NULL);
 485   if (result && static_cast<int>(written) == size)
 486     return written;
 487
 488   if (!result) {
 489     // WriteFile failed.
 490     DLOG_GETLASTERROR(WARNING) << "writing file " << filename.value()
 491                                << " failed";
 492   } else {
 493     // Didn't write all the bytes.
 494     DLOG(WARNING) << "wrote" << written << " bytes to "
 495                   << filename.value() << " expected " << size;
 496   }
 497   return -1;
 498 }
 499
 500 int AppendToFile(const FilePath& filename, const char* data, int size) {
 501   base::ThreadRestrictions::AssertIOAllowed();
 502   base::win::ScopedHandle file(CreateFile(filename.value().c_str(),
 503                                           FILE_APPEND_DATA,
 504                                           0,
 505                                           NULL,
 506                                           OPEN_EXISTING,
 507                                           0,
 508                                           NULL));
 509   if (!file) {
 510     DLOG_GETLASTERROR(WARNING) << "CreateFile failed for path "
 511                                << filename.value();
 512     return -1;
 513   }
 514
 515   DWORD written;
 516   BOOL result = ::WriteFile(file, data, size, &written, NULL);
 517   if (result && static_cast<int>(written) == size)
 518     return written;
 519
 520   if (!result) {
 521     // WriteFile failed.
 522     DLOG_GETLASTERROR(WARNING) << "writing file " << filename.value()
 523                                << " failed";
 524   } else {
 525     // Didn't write all the bytes.
 526     DLOG(WARNING) << "wrote" << written << " bytes to "
 527                   << filename.value() << " expected " << size;
 528   }
 529   return -1;
 530 }
 531
 532 // Gets the current working directory for the process.
 533 bool GetCurrentDirectory(FilePath* dir) {
 534   base::ThreadRestrictions::AssertIOAllowed();
 535
 536   wchar_t system_buffer[MAX_PATH];
 537   system_buffer[0] = 0;
 538   DWORD len = ::GetCurrentDirectory(MAX_PATH, system_buffer);
 539   if (len == 0 || len > MAX_PATH)
 540     return false;
 541   // TODO(evanm): the old behavior of this function was to always strip the
 542   // trailing slash.  We duplicate this here, but it shouldn't be necessary
 543   // when everyone is using the appropriate FilePath APIs.
 544   std::wstring dir_str(system_buffer);
 545   *dir = FilePath(dir_str).StripTrailingSeparators();
 546   return true;
 547 }
 548
 549 // Sets the current working directory for the process.
 550 bool SetCurrentDirectory(const FilePath& directory) {
 551   base::ThreadRestrictions::AssertIOAllowed();
 552   BOOL ret = ::SetCurrentDirectory(directory.value().c_str());
 553   return ret != 0;
 554 }
 555
 556 bool NormalizeFilePath(const FilePath& path, FilePath* real_path) {
 557   base::ThreadRestrictions::AssertIOAllowed();
 558   FilePath mapped_file;
 559   if (!NormalizeToNativeFilePath(path, &mapped_file))
 560     return false;
 561   // NormalizeToNativeFilePath() will return a path that starts with
 562   // "\Device\Harddisk...".  Helper DevicePathToDriveLetterPath()
 563   // will find a drive letter which maps to the path's device, so
 564   // that we return a path starting with a drive letter.
 565   return DevicePathToDriveLetterPath(mapped_file, real_path);
 566 }
 567
 568 bool DevicePathToDriveLetterPath(const FilePath& nt_device_path,
 569                                  FilePath* out_drive_letter_path) {
 570   base::ThreadRestrictions::AssertIOAllowed();
 571
 572   // Get the mapping of drive letters to device paths.
 573   const int kDriveMappingSize = 1024;
 574   wchar_t drive_mapping[kDriveMappingSize] = {'\0'};
 575   if (!::GetLogicalDriveStrings(kDriveMappingSize - 1, drive_mapping)) {
 576     DLOG(ERROR) << "Failed to get drive mapping.";
 577     return false;
 578   }
 579
 580   // The drive mapping is a sequence of null terminated strings.
 581   // The last string is empty.
 582   wchar_t* drive_map_ptr = drive_mapping;
 583   wchar_t device_path_as_string[MAX_PATH];
 584   wchar_t drive[] = L" :";
 585
 586   // For each string in the drive mapping, get the junction that links
 587   // to it.  If that junction is a prefix of |device_path|, then we
 588   // know that |drive| is the real path prefix.
 589   while (*drive_map_ptr) {
 590     drive[0] = drive_map_ptr[0];  // Copy the drive letter.
 591
 592     if (QueryDosDevice(drive, device_path_as_string, MAX_PATH)) {
 593       FilePath device_path(device_path_as_string);
 594       if (device_path == nt_device_path ||
 595           device_path.IsParent(nt_device_path)) {
 596         *out_drive_letter_path = FilePath(drive +
 597             nt_device_path.value().substr(wcslen(device_path_as_string)));
 598         return true;
 599       }
 600     }
 601     // Move to the next drive letter string, which starts one
 602     // increment after the '\0' that terminates the current string.
 603     while (*drive_map_ptr++);
 604   }
 605
 606   // No drive matched.  The path does not start with a device junction
 607   // that is mounted as a drive letter.  This means there is no drive
 608   // letter path to the volume that holds |device_path|, so fail.
 609   return false;
 610 }
 611
 612 bool NormalizeToNativeFilePath(const FilePath& path, FilePath* nt_path) {
 613   base::ThreadRestrictions::AssertIOAllowed();
 614   // In Vista, GetFinalPathNameByHandle() would give us the real path
 615   // from a file handle.  If we ever deprecate XP, consider changing the
 616   // code below to a call to GetFinalPathNameByHandle().  The method this
 617   // function uses is explained in the following msdn article:
 618   // http://msdn.microsoft.com/en-us/library/aa366789(VS.85).aspx
 619   base::win::ScopedHandle file_handle(
 620       ::CreateFile(path.value().c_str(),
 621                    GENERIC_READ,
 622                    kFileShareAll,
 623                    NULL,
 624                    OPEN_EXISTING,
 625                    FILE_ATTRIBUTE_NORMAL,
 626                    NULL));
 627   if (!file_handle)
 628     return false;
 629
 630   // Create a file mapping object.  Can't easily use MemoryMappedFile, because
 631   // we only map the first byte, and need direct access to the handle. You can
 632   // not map an empty file, this call fails in that case.
 633   base::win::ScopedHandle file_map_handle(
 634       ::CreateFileMapping(file_handle.Get(),
 635                           NULL,
 636                           PAGE_READONLY,
 637                           0,
 638                           1,  // Just one byte.  No need to look at the data.
 639                           NULL));
 640   if (!file_map_handle)
 641     return false;
 642
 643   // Use a view of the file to get the path to the file.
 644   void* file_view = MapViewOfFile(file_map_handle.Get(),
 645                                   FILE_MAP_READ, 0, 0, 1);
 646   if (!file_view)
 647     return false;
 648
 649   // The expansion of |path| into a full path may make it longer.
 650   // GetMappedFileName() will fail if the result is longer than MAX_PATH.
 651   // Pad a bit to be safe.  If kMaxPathLength is ever changed to be less
 652   // than MAX_PATH, it would be nessisary to test that GetMappedFileName()
 653   // not return kMaxPathLength.  This would mean that only part of the
 654   // path fit in |mapped_file_path|.
 655   const int kMaxPathLength = MAX_PATH + 10;
 656   wchar_t mapped_file_path[kMaxPathLength];
 657   bool success = false;
 658   HANDLE cp = GetCurrentProcess();
 659   if (::GetMappedFileNameW(cp, file_view, mapped_file_path, kMaxPathLength)) {
 660     *nt_path = FilePath(mapped_file_path);
 661     success = true;
 662   }
 663   ::UnmapViewOfFile(file_view);
 664   return success;
 665 }
 666
 667 int GetMaximumPathComponentLength(const FilePath& path) {
 668   base::ThreadRestrictions::AssertIOAllowed();
 669
 670   wchar_t volume_path[MAX_PATH];
 671   if (!GetVolumePathNameW(path.NormalizePathSeparators().value().c_str(),
 672                           volume_path,
 673                           arraysize(volume_path))) {
 674     return -1;
 675   }
 676
 677   DWORD max_length = 0;
 678   if (!GetVolumeInformationW(volume_path, NULL, 0, NULL, &max_length, NULL,
 679                              NULL, 0)) {
 680     return -1;
 681   }
 682
 683   // Length of |path| with path separator appended.
 684   size_t prefix = path.StripTrailingSeparators().value().size() + 1;
 685   // The whole path string must be shorter than MAX_PATH. That is, it must be
 686   // prefix + component_length < MAX_PATH (or equivalently, <= MAX_PATH - 1).
 687   int whole_path_limit = std::max(0, MAX_PATH - 1 - static_cast<int>(prefix));
 688   return std::min(whole_path_limit, static_cast<int>(max_length));
 689 }
 690
 691 }  // namespace file_util
 692
 693 namespace base {
 694 namespace internal {
 695
 696 bool MoveUnsafe(const FilePath& from_path, const FilePath& to_path) {
 697   ThreadRestrictions::AssertIOAllowed();
 698
 699   // NOTE: I suspect we could support longer paths, but that would involve
 700   // analyzing all our usage of files.
 701   if (from_path.value().length() >= MAX_PATH ||
 702       to_path.value().length() >= MAX_PATH) {
 703     return false;
 704   }
 705   if (MoveFileEx(from_path.value().c_str(), to_path.value().c_str(),
 706                  MOVEFILE_COPY_ALLOWED | MOVEFILE_REPLACE_EXISTING) != 0)
 707     return true;
 708
 709   // Keep the last error value from MoveFileEx around in case the below
 710   // fails.
 711   bool ret = false;
 712   DWORD last_error = ::GetLastError();
 713
 714   if (DirectoryExists(from_path)) {
 715     // MoveFileEx fails if moving directory across volumes. We will simulate
 716     // the move by using Copy and Delete. Ideally we could check whether
 717     // from_path and to_path are indeed in different volumes.
 718     ret = internal::CopyAndDeleteDirectory(from_path, to_path);
 719   }
 720
 721   if (!ret) {
 722     // Leave a clue about what went wrong so that it can be (at least) picked
 723     // up by a PLOG entry.
 724     ::SetLastError(last_error);
 725   }
 726
 727   return ret;
 728 }
 729
 730 bool CopyFileUnsafe(const FilePath& from_path, const FilePath& to_path) {
 731   ThreadRestrictions::AssertIOAllowed();
 732
 733   // NOTE: I suspect we could support longer paths, but that would involve
 734   // analyzing all our usage of files.
 735   if (from_path.value().length() >= MAX_PATH ||
 736       to_path.value().length() >= MAX_PATH) {
 737     return false;
 738   }
 739   return (::CopyFile(from_path.value().c_str(), to_path.value().c_str(),
 740                      false) != 0);
 741 }
 742
 743 bool CopyAndDeleteDirectory(const FilePath& from_path,
 744                             const FilePath& to_path) {
 745   ThreadRestrictions::AssertIOAllowed();
 746   if (CopyDirectory(from_path, to_path, true)) {
 747     if (DeleteFile(from_path, true))
 748       return true;
 749
 750     // Like Move, this function is not transactional, so we just
 751     // leave the copied bits behind if deleting from_path fails.
 752     // If to_path exists previously then we have already overwritten
 753     // it by now, we don't get better off by deleting the new bits.
 754   }
 755   return false;
 756 }
 757
 758 }  // namespace internal
 759 }  // namespace base