base/win/registry.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/win/registry.h"
   6
   7 #include <shlwapi.h>
   8 #include <algorithm>
   9
  10 #include "base/logging.h"
  11 #include "base/strings/string_util.h"
  12 #include "base/threading/thread_restrictions.h"
  13 #include "base/win/windows_version.h"
  14
  15 namespace base {
  16 namespace win {
  17
  18 namespace {
  19
  20 // RegEnumValue() reports the number of characters from the name that were
  21 // written to the buffer, not how many there are. This constant is the maximum
  22 // name size, such that a buffer with this size should read any name.
  23 const DWORD MAX_REGISTRY_NAME_SIZE = 16384;
  24
  25 // Registry values are read as BYTE* but can have wchar_t* data whose last
  26 // wchar_t is truncated. This function converts the reported |byte_size| to
  27 // a size in wchar_t that can store a truncated wchar_t if necessary.
  28 inline DWORD to_wchar_size(DWORD byte_size) {
  29   return (byte_size + sizeof(wchar_t) - 1) / sizeof(wchar_t);
  30 }
  31
  32 // Mask to pull WOW64 access flags out of REGSAM access.
  33 const REGSAM kWow64AccessMask = KEY_WOW64_32KEY | KEY_WOW64_64KEY;
  34
  35 }  // namespace
  36
  37 // Watches for modifications to a key.
  38 class RegKey::Watcher : public ObjectWatcher::Delegate {
  39  public:
  40   explicit Watcher(RegKey* owner) : owner_(owner) {}
  41   ~Watcher() {}
  42
  43   bool StartWatching(HKEY key, const ChangeCallback& callback);
  44
  45   // Implementation of ObjectWatcher::Delegate.
  46   void OnObjectSignaled(HANDLE object) override {
  47     DCHECK(watch_event_.IsValid() && watch_event_.Get() == object);
  48     ChangeCallback callback = callback_;
  49     callback_.Reset();
  50     callback.Run();
  51   }
  52
  53  private:
  54   RegKey* owner_;
  55   ScopedHandle watch_event_;
  56   ObjectWatcher object_watcher_;
  57   ChangeCallback callback_;
  58   DISALLOW_COPY_AND_ASSIGN(Watcher);
  59 };
  60
  61 bool RegKey::Watcher::StartWatching(HKEY key, const ChangeCallback& callback) {
  62   DCHECK(key);
  63   DCHECK(callback_.is_null());
  64
  65   if (!watch_event_.IsValid())
  66     watch_event_.Set(CreateEvent(NULL, TRUE, FALSE, NULL));
  67
  68   if (!watch_event_.IsValid())
  69     return false;
  70
  71   DWORD filter = REG_NOTIFY_CHANGE_NAME |
  72                  REG_NOTIFY_CHANGE_ATTRIBUTES |
  73                  REG_NOTIFY_CHANGE_LAST_SET |
  74                  REG_NOTIFY_CHANGE_SECURITY;
  75
  76   // Watch the registry key for a change of value.
  77   LONG result = RegNotifyChangeKeyValue(key, TRUE, filter, watch_event_.Get(),
  78                                         TRUE);
  79   if (result != ERROR_SUCCESS) {
  80     watch_event_.Close();
  81     return false;
  82   }
  83
  84   callback_ = callback;
  85   return object_watcher_.StartWatching(watch_event_.Get(), this);
  86 }
  87
  88 // RegKey ----------------------------------------------------------------------
  89
  90 RegKey::RegKey() : key_(NULL), wow64access_(0) {
  91 }
  92
  93 RegKey::RegKey(HKEY key) : key_(key), wow64access_(0) {
  94 }
  95
  96 RegKey::RegKey(HKEY rootkey, const wchar_t* subkey, REGSAM access)
  97     : key_(NULL),
  98       wow64access_(0) {
  99   if (rootkey) {
 100     if (access & (KEY_SET_VALUE | KEY_CREATE_SUB_KEY | KEY_CREATE_LINK))
 101       Create(rootkey, subkey, access);
 102     else
 103       Open(rootkey, subkey, access);
 104   } else {
 105     DCHECK(!subkey);
 106     wow64access_ = access & kWow64AccessMask;
 107   }
 108 }
 109
 110 RegKey::~RegKey() {
 111   Close();
 112 }
 113
 114 LONG RegKey::Create(HKEY rootkey, const wchar_t* subkey, REGSAM access) {
 115   DWORD disposition_value;
 116   return CreateWithDisposition(rootkey, subkey, &disposition_value, access);
 117 }
 118
 119 LONG RegKey::CreateWithDisposition(HKEY rootkey, const wchar_t* subkey,
 120                                    DWORD* disposition, REGSAM access) {
 121   DCHECK(rootkey && subkey && access && disposition);
 122   HKEY subhkey = NULL;
 123   LONG result = RegCreateKeyEx(rootkey, subkey, 0, NULL,
 124                                REG_OPTION_NON_VOLATILE, access, NULL, &subhkey,
 125                                disposition);
 126   if (result == ERROR_SUCCESS) {
 127     Close();
 128     key_ = subhkey;
 129     wow64access_ = access & kWow64AccessMask;
 130   }
 131
 132   return result;
 133 }
 134
 135 LONG RegKey::CreateKey(const wchar_t* name, REGSAM access) {
 136   DCHECK(name && access);
 137   // After the application has accessed an alternate registry view using one of
 138   // the [KEY_WOW64_32KEY / KEY_WOW64_64KEY] flags, all subsequent operations
 139   // (create, delete, or open) on child registry keys must explicitly use the
 140   // same flag. Otherwise, there can be unexpected behavior.
 141   // http://msdn.microsoft.com/en-us/library/windows/desktop/aa384129.aspx.
 142   if ((access & kWow64AccessMask) != wow64access_) {
 143     NOTREACHED();
 144     return ERROR_INVALID_PARAMETER;
 145   }
 146   HKEY subkey = NULL;
 147   LONG result = RegCreateKeyEx(key_, name, 0, NULL, REG_OPTION_NON_VOLATILE,
 148                                access, NULL, &subkey, NULL);
 149   if (result == ERROR_SUCCESS) {
 150     Close();
 151     key_ = subkey;
 152     wow64access_ = access & kWow64AccessMask;
 153   }
 154
 155   return result;
 156 }
 157
 158 LONG RegKey::Open(HKEY rootkey, const wchar_t* subkey, REGSAM access) {
 159   DCHECK(rootkey && subkey && access);
 160   HKEY subhkey = NULL;
 161
 162   LONG result = RegOpenKeyEx(rootkey, subkey, 0, access, &subhkey);
 163   if (result == ERROR_SUCCESS) {
 164     Close();
 165     key_ = subhkey;
 166     wow64access_ = access & kWow64AccessMask;
 167   }
 168
 169   return result;
 170 }
 171
 172 LONG RegKey::OpenKey(const wchar_t* relative_key_name, REGSAM access) {
 173   DCHECK(relative_key_name && access);
 174   // After the application has accessed an alternate registry view using one of
 175   // the [KEY_WOW64_32KEY / KEY_WOW64_64KEY] flags, all subsequent operations
 176   // (create, delete, or open) on child registry keys must explicitly use the
 177   // same flag. Otherwise, there can be unexpected behavior.
 178   // http://msdn.microsoft.com/en-us/library/windows/desktop/aa384129.aspx.
 179   if ((access & kWow64AccessMask) != wow64access_) {
 180     NOTREACHED();
 181     return ERROR_INVALID_PARAMETER;
 182   }
 183   HKEY subkey = NULL;
 184   LONG result = RegOpenKeyEx(key_, relative_key_name, 0, access, &subkey);
 185
 186   // We have to close the current opened key before replacing it with the new
 187   // one.
 188   if (result == ERROR_SUCCESS) {
 189     Close();
 190     key_ = subkey;
 191     wow64access_ = access & kWow64AccessMask;
 192   }
 193   return result;
 194 }
 195
 196 void RegKey::Close() {
 197   if (key_) {
 198     ::RegCloseKey(key_);
 199     key_ = NULL;
 200     wow64access_ = 0;
 201   }
 202 }
 203
 204 // TODO(wfh): Remove this and other unsafe methods. See http://crbug.com/375400
 205 void RegKey::Set(HKEY key) {
 206   if (key_ != key) {
 207     Close();
 208     key_ = key;
 209   }
 210 }
 211
 212 HKEY RegKey::Take() {
 213   DCHECK(wow64access_ == 0);
 214   HKEY key = key_;
 215   key_ = NULL;
 216   return key;
 217 }
 218
 219 bool RegKey::HasValue(const wchar_t* name) const {
 220   return RegQueryValueEx(key_, name, 0, NULL, NULL, NULL) == ERROR_SUCCESS;
 221 }
 222
 223 DWORD RegKey::GetValueCount() const {
 224   DWORD count = 0;
 225   LONG result = RegQueryInfoKey(key_, NULL, 0, NULL, NULL, NULL, NULL, &count,
 226                                 NULL, NULL, NULL, NULL);
 227   return (result == ERROR_SUCCESS) ? count : 0;
 228 }
 229
 230 LONG RegKey::GetValueNameAt(int index, std::wstring* name) const {
 231   wchar_t buf[256];
 232   DWORD bufsize = arraysize(buf);
 233   LONG r = ::RegEnumValue(key_, index, buf, &bufsize, NULL, NULL, NULL, NULL);
 234   if (r == ERROR_SUCCESS)
 235     *name = buf;
 236
 237   return r;
 238 }
 239
 240 LONG RegKey::DeleteKey(const wchar_t* name) {
 241   DCHECK(key_);
 242   DCHECK(name);
 243   HKEY subkey = NULL;
 244
 245   // Verify the key exists before attempting delete to replicate previous
 246   // behavior.
 247   LONG result =
 248       RegOpenKeyEx(key_, name, 0, READ_CONTROL | wow64access_, &subkey);
 249   if (result != ERROR_SUCCESS)
 250     return result;
 251   RegCloseKey(subkey);
 252
 253   return RegDelRecurse(key_, std::wstring(name), wow64access_);
 254 }
 255
 256 LONG RegKey::DeleteEmptyKey(const wchar_t* name) {
 257   DCHECK(key_);
 258   DCHECK(name);
 259
 260   HKEY target_key = NULL;
 261   LONG result = RegOpenKeyEx(key_, name, 0, KEY_READ | wow64access_,
 262                              &target_key);
 263
 264   if (result != ERROR_SUCCESS)
 265     return result;
 266
 267   DWORD count = 0;
 268   result = RegQueryInfoKey(target_key, NULL, 0, NULL, NULL, NULL, NULL, &count,
 269                            NULL, NULL, NULL, NULL);
 270
 271   RegCloseKey(target_key);
 272
 273   if (result != ERROR_SUCCESS)
 274     return result;
 275
 276   if (count == 0)
 277     return RegDeleteKeyExWrapper(key_, name, wow64access_, 0);
 278
 279   return ERROR_DIR_NOT_EMPTY;
 280 }
 281
 282 LONG RegKey::DeleteValue(const wchar_t* value_name) {
 283   DCHECK(key_);
 284   LONG result = RegDeleteValue(key_, value_name);
 285   return result;
 286 }
 287
 288 LONG RegKey::ReadValueDW(const wchar_t* name, DWORD* out_value) const {
 289   DCHECK(out_value);
 290   DWORD type = REG_DWORD;
 291   DWORD size = sizeof(DWORD);
 292   DWORD local_value = 0;
 293   LONG result = ReadValue(name, &local_value, &size, &type);
 294   if (result == ERROR_SUCCESS) {
 295     if ((type == REG_DWORD || type == REG_BINARY) && size == sizeof(DWORD))
 296       *out_value = local_value;
 297     else
 298       result = ERROR_CANTREAD;
 299   }
 300
 301   return result;
 302 }
 303
 304 LONG RegKey::ReadInt64(const wchar_t* name, int64* out_value) const {
 305   DCHECK(out_value);
 306   DWORD type = REG_QWORD;
 307   int64 local_value = 0;
 308   DWORD size = sizeof(local_value);
 309   LONG result = ReadValue(name, &local_value, &size, &type);
 310   if (result == ERROR_SUCCESS) {
 311     if ((type == REG_QWORD || type == REG_BINARY) &&
 312         size == sizeof(local_value))
 313       *out_value = local_value;
 314     else
 315       result = ERROR_CANTREAD;
 316   }
 317
 318   return result;
 319 }
 320
 321 LONG RegKey::ReadValue(const wchar_t* name, std::wstring* out_value) const {
 322   DCHECK(out_value);
 323   const size_t kMaxStringLength = 1024;  // This is after expansion.
 324   // Use the one of the other forms of ReadValue if 1024 is too small for you.
 325   wchar_t raw_value[kMaxStringLength];
 326   DWORD type = REG_SZ, size = sizeof(raw_value);
 327   LONG result = ReadValue(name, raw_value, &size, &type);
 328   if (result == ERROR_SUCCESS) {
 329     if (type == REG_SZ) {
 330       *out_value = raw_value;
 331     } else if (type == REG_EXPAND_SZ) {
 332       wchar_t expanded[kMaxStringLength];
 333       size = ExpandEnvironmentStrings(raw_value, expanded, kMaxStringLength);
 334       // Success: returns the number of wchar_t's copied
 335       // Fail: buffer too small, returns the size required
 336       // Fail: other, returns 0
 337       if (size == 0 || size > kMaxStringLength) {
 338         result = ERROR_MORE_DATA;
 339       } else {
 340         *out_value = expanded;
 341       }
 342     } else {
 343       // Not a string. Oops.
 344       result = ERROR_CANTREAD;
 345     }
 346   }
 347
 348   return result;
 349 }
 350
 351 LONG RegKey::ReadValue(const wchar_t* name,
 352                        void* data,
 353                        DWORD* dsize,
 354                        DWORD* dtype) const {
 355   LONG result = RegQueryValueEx(key_, name, 0, dtype,
 356                                 reinterpret_cast<LPBYTE>(data), dsize);
 357   return result;
 358 }
 359
 360 LONG RegKey::ReadValues(const wchar_t* name,
 361                         std::vector<std::wstring>* values) {
 362   values->clear();
 363
 364   DWORD type = REG_MULTI_SZ;
 365   DWORD size = 0;
 366   LONG result = ReadValue(name, NULL, &size, &type);
 367   if (FAILED(result) || size == 0)
 368     return result;
 369
 370   if (type != REG_MULTI_SZ)
 371     return ERROR_CANTREAD;
 372
 373   std::vector<wchar_t> buffer(size / sizeof(wchar_t));
 374   result = ReadValue(name, &buffer[0], &size, NULL);
 375   if (FAILED(result) || size == 0)
 376     return result;
 377
 378   // Parse the double-null-terminated list of strings.
 379   // Note: This code is paranoid to not read outside of |buf|, in the case where
 380   // it may not be properly terminated.
 381   const wchar_t* entry = &buffer[0];
 382   const wchar_t* buffer_end = entry + (size / sizeof(wchar_t));
 383   while (entry < buffer_end && entry[0] != '\0') {
 384     const wchar_t* entry_end = std::find(entry, buffer_end, L'\0');
 385     values->push_back(std::wstring(entry, entry_end));
 386     entry = entry_end + 1;
 387   }
 388   return 0;
 389 }
 390
 391 LONG RegKey::WriteValue(const wchar_t* name, DWORD in_value) {
 392   return WriteValue(
 393       name, &in_value, static_cast<DWORD>(sizeof(in_value)), REG_DWORD);
 394 }
 395
 396 LONG RegKey::WriteValue(const wchar_t * name, const wchar_t* in_value) {
 397   return WriteValue(name, in_value,
 398       static_cast<DWORD>(sizeof(*in_value) * (wcslen(in_value) + 1)), REG_SZ);
 399 }
 400
 401 LONG RegKey::WriteValue(const wchar_t* name,
 402                         const void* data,
 403                         DWORD dsize,
 404                         DWORD dtype) {
 405   DCHECK(data || !dsize);
 406
 407   LONG result = RegSetValueEx(key_, name, 0, dtype,
 408       reinterpret_cast<LPBYTE>(const_cast<void*>(data)), dsize);
 409   return result;
 410 }
 411
 412 bool RegKey::StartWatching(const ChangeCallback& callback) {
 413   if (!key_watcher_)
 414     key_watcher_.reset(new Watcher(this));
 415
 416   if (!key_watcher_.get()->StartWatching(key_, callback))
 417     return false;
 418
 419   return true;
 420 }
 421
 422 // static
 423 LONG RegKey::RegDeleteKeyExWrapper(HKEY hKey,
 424                                    const wchar_t* lpSubKey,
 425                                    REGSAM samDesired,
 426                                    DWORD Reserved) {
 427   typedef LSTATUS(WINAPI* RegDeleteKeyExPtr)(HKEY, LPCWSTR, REGSAM, DWORD);
 428
 429   RegDeleteKeyExPtr reg_delete_key_ex_func =
 430       reinterpret_cast<RegDeleteKeyExPtr>(
 431           GetProcAddress(GetModuleHandleA("advapi32.dll"), "RegDeleteKeyExW"));
 432
 433   if (reg_delete_key_ex_func)
 434     return reg_delete_key_ex_func(hKey, lpSubKey, samDesired, Reserved);
 435
 436   // Windows XP does not support RegDeleteKeyEx, so fallback to RegDeleteKey.
 437   return RegDeleteKey(hKey, lpSubKey);
 438 }
 439
 440 // static
 441 LONG RegKey::RegDelRecurse(HKEY root_key,
 442                            const std::wstring& name,
 443                            REGSAM access) {
 444   // First, see if the key can be deleted without having to recurse.
 445   LONG result = RegDeleteKeyExWrapper(root_key, name.c_str(), access, 0);
 446   if (result == ERROR_SUCCESS)
 447     return result;
 448
 449   HKEY target_key = NULL;
 450   result = RegOpenKeyEx(
 451       root_key, name.c_str(), 0, KEY_ENUMERATE_SUB_KEYS | access, &target_key);
 452
 453   if (result == ERROR_FILE_NOT_FOUND)
 454     return ERROR_SUCCESS;
 455   if (result != ERROR_SUCCESS)
 456     return result;
 457
 458   std::wstring subkey_name(name);
 459
 460   // Check for an ending slash and add one if it is missing.
 461   if (!name.empty() && subkey_name[name.length() - 1] != L'\\')
 462     subkey_name += L"\\";
 463
 464   // Enumerate the keys
 465   result = ERROR_SUCCESS;
 466   const DWORD kMaxKeyNameLength = MAX_PATH;
 467   const size_t base_key_length = subkey_name.length();
 468   std::wstring key_name;
 469   while (result == ERROR_SUCCESS) {
 470     DWORD key_size = kMaxKeyNameLength;
 471     result = RegEnumKeyEx(target_key,
 472                           0,
 473                           WriteInto(&key_name, kMaxKeyNameLength),
 474                           &key_size,
 475                           NULL,
 476                           NULL,
 477                           NULL,
 478                           NULL);
 479
 480     if (result != ERROR_SUCCESS)
 481       break;
 482
 483     key_name.resize(key_size);
 484     subkey_name.resize(base_key_length);
 485     subkey_name += key_name;
 486
 487     if (RegDelRecurse(root_key, subkey_name, access) != ERROR_SUCCESS)
 488       break;
 489   }
 490
 491   RegCloseKey(target_key);
 492
 493   // Try again to delete the key.
 494   result = RegDeleteKeyExWrapper(root_key, name.c_str(), access, 0);
 495
 496   return result;
 497 }
 498
 499 // RegistryValueIterator ------------------------------------------------------
 500
 501 RegistryValueIterator::RegistryValueIterator(HKEY root_key,
 502                                              const wchar_t* folder_key,
 503                                              REGSAM wow64access)
 504     : name_(MAX_PATH, L'\0'),
 505       value_(MAX_PATH, L'\0') {
 506   Initialize(root_key, folder_key, wow64access);
 507 }
 508
 509 RegistryValueIterator::RegistryValueIterator(HKEY root_key,
 510                                              const wchar_t* folder_key)
 511     : name_(MAX_PATH, L'\0'),
 512       value_(MAX_PATH, L'\0') {
 513   Initialize(root_key, folder_key, 0);
 514 }
 515
 516 void RegistryValueIterator::Initialize(HKEY root_key,
 517                                        const wchar_t* folder_key,
 518                                        REGSAM wow64access) {
 519   DCHECK_EQ(wow64access & ~kWow64AccessMask, static_cast<REGSAM>(0));
 520   LONG result =
 521       RegOpenKeyEx(root_key, folder_key, 0, KEY_READ | wow64access, &key_);
 522   if (result != ERROR_SUCCESS) {
 523     key_ = NULL;
 524   } else {
 525     DWORD count = 0;
 526     result = ::RegQueryInfoKey(key_, NULL, 0, NULL, NULL, NULL, NULL, &count,
 527                                NULL, NULL, NULL, NULL);
 528
 529     if (result != ERROR_SUCCESS) {
 530       ::RegCloseKey(key_);
 531       key_ = NULL;
 532     } else {
 533       index_ = count - 1;
 534     }
 535   }
 536
 537   Read();
 538 }
 539
 540 RegistryValueIterator::~RegistryValueIterator() {
 541   if (key_)
 542     ::RegCloseKey(key_);
 543 }
 544
 545 DWORD RegistryValueIterator::ValueCount() const {
 546   DWORD count = 0;
 547   LONG result = ::RegQueryInfoKey(key_, NULL, 0, NULL, NULL, NULL, NULL,
 548                                   &count, NULL, NULL, NULL, NULL);
 549   if (result != ERROR_SUCCESS)
 550     return 0;
 551
 552   return count;
 553 }
 554
 555 bool RegistryValueIterator::Valid() const {
 556   return key_ != NULL && index_ >= 0;
 557 }
 558
 559 void RegistryValueIterator::operator++() {
 560   --index_;
 561   Read();
 562 }
 563
 564 bool RegistryValueIterator::Read() {
 565   if (Valid()) {
 566     DWORD capacity = static_cast<DWORD>(name_.capacity());
 567     DWORD name_size = capacity;
 568     // |value_size_| is in bytes. Reserve the last character for a NUL.
 569     value_size_ = static_cast<DWORD>((value_.size() - 1) * sizeof(wchar_t));
 570     LONG result = ::RegEnumValue(
 571         key_, index_, WriteInto(&name_, name_size), &name_size, NULL, &type_,
 572         reinterpret_cast<BYTE*>(vector_as_array(&value_)), &value_size_);
 573
 574     if (result == ERROR_MORE_DATA) {
 575       // Registry key names are limited to 255 characters and fit within
 576       // MAX_PATH (which is 260) but registry value names can use up to 16,383
 577       // characters and the value itself is not limited
 578       // (from http://msdn.microsoft.com/en-us/library/windows/desktop/
 579       // ms724872(v=vs.85).aspx).
 580       // Resize the buffers and retry if their size caused the failure.
 581       DWORD value_size_in_wchars = to_wchar_size(value_size_);
 582       if (value_size_in_wchars + 1 > value_.size())
 583         value_.resize(value_size_in_wchars + 1, L'\0');
 584       value_size_ = static_cast<DWORD>((value_.size() - 1) * sizeof(wchar_t));
 585       name_size = name_size == capacity ? MAX_REGISTRY_NAME_SIZE : capacity;
 586       result = ::RegEnumValue(
 587           key_, index_, WriteInto(&name_, name_size), &name_size, NULL, &type_,
 588           reinterpret_cast<BYTE*>(vector_as_array(&value_)), &value_size_);
 589     }
 590
 591     if (result == ERROR_SUCCESS) {
 592       DCHECK_LT(to_wchar_size(value_size_), value_.size());
 593       value_[to_wchar_size(value_size_)] = L'\0';
 594       return true;
 595     }
 596   }
 597
 598   name_[0] = L'\0';
 599   value_[0] = L'\0';
 600   value_size_ = 0;
 601   return false;
 602 }
 603
 604 // RegistryKeyIterator --------------------------------------------------------
 605
 606 RegistryKeyIterator::RegistryKeyIterator(HKEY root_key,
 607                                          const wchar_t* folder_key) {
 608   Initialize(root_key, folder_key, 0);
 609 }
 610
 611 RegistryKeyIterator::RegistryKeyIterator(HKEY root_key,
 612                                          const wchar_t* folder_key,
 613                                          REGSAM wow64access) {
 614   Initialize(root_key, folder_key, wow64access);
 615 }
 616
 617 RegistryKeyIterator::~RegistryKeyIterator() {
 618   if (key_)
 619     ::RegCloseKey(key_);
 620 }
 621
 622 DWORD RegistryKeyIterator::SubkeyCount() const {
 623   DWORD count = 0;
 624   LONG result = ::RegQueryInfoKey(key_, NULL, 0, NULL, &count, NULL, NULL,
 625                                   NULL, NULL, NULL, NULL, NULL);
 626   if (result != ERROR_SUCCESS)
 627     return 0;
 628
 629   return count;
 630 }
 631
 632 bool RegistryKeyIterator::Valid() const {
 633   return key_ != NULL && index_ >= 0;
 634 }
 635
 636 void RegistryKeyIterator::operator++() {
 637   --index_;
 638   Read();
 639 }
 640
 641 bool RegistryKeyIterator::Read() {
 642   if (Valid()) {
 643     DWORD ncount = arraysize(name_);
 644     FILETIME written;
 645     LONG r = ::RegEnumKeyEx(key_, index_, name_, &ncount, NULL, NULL,
 646                             NULL, &written);
 647     if (ERROR_SUCCESS == r)
 648       return true;
 649   }
 650
 651   name_[0] = '\0';
 652   return false;
 653 }
 654
 655 void RegistryKeyIterator::Initialize(HKEY root_key,
 656                                      const wchar_t* folder_key,
 657                                      REGSAM wow64access) {
 658   DCHECK_EQ(wow64access & ~kWow64AccessMask, static_cast<REGSAM>(0));
 659   LONG result =
 660       RegOpenKeyEx(root_key, folder_key, 0, KEY_READ | wow64access, &key_);
 661   if (result != ERROR_SUCCESS) {
 662     key_ = NULL;
 663   } else {
 664     DWORD count = 0;
 665     LONG result = ::RegQueryInfoKey(key_, NULL, 0, NULL, &count, NULL, NULL,
 666                                     NULL, NULL, NULL, NULL, NULL);
 667
 668     if (result != ERROR_SUCCESS) {
 669       ::RegCloseKey(key_);
 670       key_ = NULL;
 671     } else {
 672       index_ = count - 1;
 673     }
 674   }
 675
 676   Read();
 677 }
 678
 679 }  // namespace win
 680 }  // namespace base