base/win/registry.cc - chromium/src.git - Git at Google

 // 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/win/registry.h"

 #include <stddef.h>

 #include <algorithm>
 #include <string>
 #include <utility>

 #include "base/logging.h"
 #include "base/stl_util.h"
 #include "base/strings/string_util.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/win/shlwapi.h"
 #include "base/win/windows_version.h"

 namespace base {
 namespace win {

 namespace {

 // RegEnumValue() reports the number of characters from the name that were
 // written to the buffer, not how many there are. This constant is the maximum
 // name size, such that a buffer with this size should read any name.
 const DWORD MAX_REGISTRY_NAME_SIZE = 16384;

 // Registry values are read as BYTE* but can have wchar_t* data whose last
 // wchar_t is truncated. This function converts the reported |byte_size| to
 // a size in wchar_t that can store a truncated wchar_t if necessary.
 inline DWORD to_wchar_size(DWORD byte_size) {
   return (byte_size + sizeof(wchar_t) - 1) / sizeof(wchar_t);
 }

 // Mask to pull WOW64 access flags out of REGSAM access.
 const REGSAM kWow64AccessMask = KEY_WOW64_32KEY | KEY_WOW64_64KEY;

 }  // namespace

 // Watches for modifications to a key.
 class RegKey::Watcher : public ObjectWatcher::Delegate {
  public:
   Watcher() {}
   ~Watcher() override {}

   bool StartWatching(HKEY key, ChangeCallback callback);

   // Implementation of ObjectWatcher::Delegate.
   void OnObjectSignaled(HANDLE object) override {
     DCHECK(watch_event_.IsValid() && watch_event_.Get() == object);
     std::move(callback_).Run();
   }

  private:
   ScopedHandle watch_event_;
   ObjectWatcher object_watcher_;
   ChangeCallback callback_;
   DISALLOW_COPY_AND_ASSIGN(Watcher);
 };

 bool RegKey::Watcher::StartWatching(HKEY key, ChangeCallback callback) {
   DCHECK(key);
   DCHECK(callback_.is_null());

   if (!watch_event_.IsValid())
     watch_event_.Set(CreateEvent(NULL, TRUE, FALSE, NULL));

   if (!watch_event_.IsValid())
     return false;

   DWORD filter = REG_NOTIFY_CHANGE_NAME |
                  REG_NOTIFY_CHANGE_ATTRIBUTES |
                  REG_NOTIFY_CHANGE_LAST_SET |
                  REG_NOTIFY_CHANGE_SECURITY;

   // Watch the registry key for a change of value.
   LONG result = RegNotifyChangeKeyValue(key, TRUE, filter, watch_event_.Get(),
                                         TRUE);
   if (result != ERROR_SUCCESS) {
     watch_event_.Close();
     return false;
   }

   callback_ = std::move(callback);
   return object_watcher_.StartWatchingOnce(watch_event_.Get(), this);
 }

 // RegKey ----------------------------------------------------------------------

 RegKey::RegKey() : key_(NULL), wow64access_(0) {
 }

 RegKey::RegKey(HKEY key) : key_(key), wow64access_(0) {
 }

 RegKey::RegKey(HKEY rootkey, const char16* subkey, REGSAM access)
     : key_(NULL), wow64access_(0) {
   if (rootkey) {
     if (access & (KEY_SET_VALUE | KEY_CREATE_SUB_KEY | KEY_CREATE_LINK))
       Create(rootkey, subkey, access);
     else
       Open(rootkey, subkey, access);
   } else {
     DCHECK(!subkey);
     wow64access_ = access & kWow64AccessMask;
   }
 }

 RegKey::~RegKey() {
   Close();
 }

 LONG RegKey::Create(HKEY rootkey, const char16* subkey, REGSAM access) {
   DWORD disposition_value;
   return CreateWithDisposition(rootkey, subkey, &disposition_value, access);
 }

 LONG RegKey::CreateWithDisposition(HKEY rootkey,
                                    const char16* subkey,
                                    DWORD* disposition,
                                    REGSAM access) {
   DCHECK(rootkey && subkey && access && disposition);
   HKEY subhkey = NULL;
   LONG result = RegCreateKeyEx(rootkey, as_wcstr(subkey), 0, NULL,
                                REG_OPTION_NON_VOLATILE, access, NULL, &subhkey,
                                disposition);
   if (result == ERROR_SUCCESS) {
     Close();
     key_ = subhkey;
     wow64access_ = access & kWow64AccessMask;
   }

   return result;
 }

 LONG RegKey::CreateKey(const char16* name, REGSAM access) {
   DCHECK(name && access);
   // After the application has accessed an alternate registry view using one of
   // the [KEY_WOW64_32KEY / KEY_WOW64_64KEY] flags, all subsequent operations
   // (create, delete, or open) on child registry keys must explicitly use the
   // same flag. Otherwise, there can be unexpected behavior.
   // http://msdn.microsoft.com/en-us/library/windows/desktop/aa384129.aspx.
   if ((access & kWow64AccessMask) != wow64access_) {
     NOTREACHED();
     return ERROR_INVALID_PARAMETER;
   }
   HKEY subkey = NULL;
   LONG result =
       RegCreateKeyEx(key_, as_wcstr(name), 0, NULL, REG_OPTION_NON_VOLATILE,
                      access, NULL, &subkey, NULL);
   if (result == ERROR_SUCCESS) {
     Close();
     key_ = subkey;
     wow64access_ = access & kWow64AccessMask;
   }

   return result;
 }

 LONG RegKey::Open(HKEY rootkey, const char16* subkey, REGSAM access) {
   DCHECK(rootkey && subkey && access);
   HKEY subhkey = NULL;

   LONG result = RegOpenKeyEx(rootkey, as_wcstr(subkey), 0, access, &subhkey);
   if (result == ERROR_SUCCESS) {
     Close();
     key_ = subhkey;
     wow64access_ = access & kWow64AccessMask;
   }

   return result;
 }

 LONG RegKey::OpenKey(const char16* relative_key_name, REGSAM access) {
   DCHECK(relative_key_name && access);
   // After the application has accessed an alternate registry view using one of
   // the [KEY_WOW64_32KEY / KEY_WOW64_64KEY] flags, all subsequent operations
   // (create, delete, or open) on child registry keys must explicitly use the
   // same flag. Otherwise, there can be unexpected behavior.
   // http://msdn.microsoft.com/en-us/library/windows/desktop/aa384129.aspx.
   if ((access & kWow64AccessMask) != wow64access_) {
     NOTREACHED();
     return ERROR_INVALID_PARAMETER;
   }
   HKEY subkey = NULL;
   LONG result =
       RegOpenKeyEx(key_, as_wcstr(relative_key_name), 0, access, &subkey);

   // We have to close the current opened key before replacing it with the new
   // one.
   if (result == ERROR_SUCCESS) {
     Close();
     key_ = subkey;
     wow64access_ = access & kWow64AccessMask;
   }
   return result;
 }

 void RegKey::Close() {
   if (key_) {
     ::RegCloseKey(key_);
     key_ = NULL;
     wow64access_ = 0;
   }
 }

 // TODO(wfh): Remove this and other unsafe methods. See http://crbug.com/375400
 void RegKey::Set(HKEY key) {
   if (key_ != key) {
     Close();
     key_ = key;
   }
 }

 HKEY RegKey::Take() {
   DCHECK_EQ(wow64access_, 0u);
   HKEY key = key_;
   key_ = NULL;
   return key;
 }

 bool RegKey::HasValue(const char16* name) const {
   return RegQueryValueEx(key_, as_wcstr(name), 0, NULL, NULL, NULL) ==
          ERROR_SUCCESS;
 }

 DWORD RegKey::GetValueCount() const {
   DWORD count = 0;
   LONG result = RegQueryInfoKey(key_, NULL, 0, NULL, NULL, NULL, NULL, &count,
                                 NULL, NULL, NULL, NULL);
   return (result == ERROR_SUCCESS) ? count : 0;
 }

 LONG RegKey::GetValueNameAt(int index, string16* name) const {
   char16 buf[256];
   DWORD bufsize = size(buf);
   LONG r = ::RegEnumValue(key_, index, as_writable_wcstr(buf), &bufsize, NULL,
                           NULL, NULL, NULL);
   if (r == ERROR_SUCCESS)
     name->assign(buf, bufsize);

   return r;
 }

 LONG RegKey::DeleteKey(const char16* name) {
   DCHECK(key_);
   DCHECK(name);
   HKEY subkey = NULL;

   // Verify the key exists before attempting delete to replicate previous
   // behavior.
   LONG result = RegOpenKeyEx(key_, as_wcstr(name), 0,
                              READ_CONTROL | wow64access_, &subkey);
   if (result != ERROR_SUCCESS)
     return result;
   RegCloseKey(subkey);

   return RegDelRecurse(key_, name, wow64access_);
 }

 LONG RegKey::DeleteEmptyKey(const char16* name) {
   DCHECK(key_);
   DCHECK(name);

   HKEY target_key = NULL;
   LONG result = RegOpenKeyEx(key_, as_wcstr(name), 0, KEY_READ | wow64access_,
                              &target_key);

   if (result != ERROR_SUCCESS)
     return result;

   DWORD count = 0;
   result = RegQueryInfoKey(target_key, NULL, 0, NULL, NULL, NULL, NULL, &count,
                            NULL, NULL, NULL, NULL);

   RegCloseKey(target_key);

   if (result != ERROR_SUCCESS)
     return result;

   if (count == 0)
     return RegDeleteKeyExWrapper(key_, name, wow64access_, 0);

   return ERROR_DIR_NOT_EMPTY;
 }

 LONG RegKey::DeleteValue(const char16* value_name) {
   DCHECK(key_);
   LONG result = RegDeleteValue(key_, as_wcstr(value_name));
   return result;
 }

 LONG RegKey::ReadValueDW(const char16* name, DWORD* out_value) const {
   DCHECK(out_value);
   DWORD type = REG_DWORD;
   DWORD size = sizeof(DWORD);
   DWORD local_value = 0;
   LONG result = ReadValue(name, &local_value, &size, &type);
   if (result == ERROR_SUCCESS) {
     if ((type == REG_DWORD || type == REG_BINARY) && size == sizeof(DWORD))
       *out_value = local_value;
     else
       result = ERROR_CANTREAD;
   }

   return result;
 }

 LONG RegKey::ReadInt64(const char16* name, int64_t* out_value) const {
   DCHECK(out_value);
   DWORD type = REG_QWORD;
   int64_t local_value = 0;
   DWORD size = sizeof(local_value);
   LONG result = ReadValue(name, &local_value, &size, &type);
   if (result == ERROR_SUCCESS) {
     if ((type == REG_QWORD || type == REG_BINARY) &&
         size == sizeof(local_value))
       *out_value = local_value;
     else
       result = ERROR_CANTREAD;
   }

   return result;
 }

 LONG RegKey::ReadValue(const char16* name, string16* out_value) const {
   DCHECK(out_value);
   const size_t kMaxStringLength = 1024;  // This is after expansion.
   // Use the one of the other forms of ReadValue if 1024 is too small for you.
   char16 raw_value[kMaxStringLength];
   DWORD type = REG_SZ, size = sizeof(raw_value);
   LONG result = ReadValue(name, as_writable_wcstr(raw_value), &size, &type);
   if (result == ERROR_SUCCESS) {
     if (type == REG_SZ) {
       *out_value = raw_value;
     } else if (type == REG_EXPAND_SZ) {
       char16 expanded[kMaxStringLength];
       size = ExpandEnvironmentStrings(
           as_wcstr(raw_value), as_writable_wcstr(expanded), kMaxStringLength);
       // Success: returns the number of wchar_t's copied
       // Fail: buffer too small, returns the size required
       // Fail: other, returns 0
       if (size == 0 || size > kMaxStringLength) {
         result = ERROR_MORE_DATA;
       } else {
         *out_value = expanded;
       }
     } else {
       // Not a string. Oops.
       result = ERROR_CANTREAD;
     }
   }

   return result;
 }

 LONG RegKey::ReadValue(const char16* name,
                        void* data,
                        DWORD* dsize,
                        DWORD* dtype) const {
   LONG result = RegQueryValueEx(key_, as_wcstr(name), 0, dtype,
                                 reinterpret_cast<LPBYTE>(data), dsize);
   return result;
 }

 LONG RegKey::ReadValues(const char16* name, std::vector<string16>* values) {
   values->clear();

   DWORD type = REG_MULTI_SZ;
   DWORD size = 0;
   LONG result = ReadValue(name, NULL, &size, &type);
   if (result != ERROR_SUCCESS || size == 0)
     return result;

   if (type != REG_MULTI_SZ)
     return ERROR_CANTREAD;

   std::vector<char16> buffer(size / sizeof(char16));
   result = ReadValue(name, as_writable_wcstr(buffer.data()), &size, NULL);
   if (result != ERROR_SUCCESS || size == 0)
     return result;

   // Parse the double-null-terminated list of strings.
   // Note: This code is paranoid to not read outside of |buf|, in the case where
   // it may not be properly terminated.
   auto entry = buffer.cbegin();
   auto buffer_end = buffer.cend();
   while (entry < buffer_end && *entry != '\0') {
     auto entry_end = std::find(entry, buffer_end, '\0');
     values->emplace_back(entry, entry_end);
     entry = entry_end + 1;
   }
   return 0;
 }

 LONG RegKey::WriteValue(const char16* name, DWORD in_value) {
   return WriteValue(
       name, &in_value, static_cast<DWORD>(sizeof(in_value)), REG_DWORD);
 }

 LONG RegKey::WriteValue(const char16* name, const char16* in_value) {
   return WriteValue(
       name, in_value,
       static_cast<DWORD>(sizeof(*in_value) *
                          (std::char_traits<char16>::length(in_value) + 1)),
       REG_SZ);
 }

 LONG RegKey::WriteValue(const char16* name,
                         const void* data,
                         DWORD dsize,
                         DWORD dtype) {
   DCHECK(data || !dsize);

   LONG result =
       RegSetValueEx(key_, as_wcstr(name), 0, dtype,
                     reinterpret_cast<LPBYTE>(const_cast<void*>(data)), dsize);
   return result;
 }

 bool RegKey::StartWatching(ChangeCallback callback) {
   if (!key_watcher_)
     key_watcher_.reset(new Watcher());

   if (!key_watcher_->StartWatching(key_, std::move(callback)))
     return false;

   return true;
 }

 // static
 LONG RegKey::RegDeleteKeyExWrapper(HKEY hKey,
                                    const char16* lpSubKey,
                                    REGSAM samDesired,
                                    DWORD Reserved) {
   typedef LSTATUS(WINAPI* RegDeleteKeyExPtr)(HKEY, LPCWSTR, REGSAM, DWORD);

   RegDeleteKeyExPtr reg_delete_key_ex_func =
       reinterpret_cast<RegDeleteKeyExPtr>(
           GetProcAddress(GetModuleHandleA("advapi32.dll"), "RegDeleteKeyExW"));

   if (reg_delete_key_ex_func)
     return reg_delete_key_ex_func(hKey, as_wcstr(lpSubKey), samDesired,
                                   Reserved);

   // Windows XP does not support RegDeleteKeyEx, so fallback to RegDeleteKey.
   return RegDeleteKey(hKey, as_wcstr(lpSubKey));
 }

 // static
 LONG RegKey::RegDelRecurse(HKEY root_key, const char16* name, REGSAM access) {
   // First, see if the key can be deleted without having to recurse.
   LONG result = RegDeleteKeyExWrapper(root_key, name, access, 0);
   if (result == ERROR_SUCCESS)
     return result;

   HKEY target_key = NULL;
   result = RegOpenKeyEx(root_key, as_wcstr(name), 0,
                         KEY_ENUMERATE_SUB_KEYS | access, &target_key);

   if (result == ERROR_FILE_NOT_FOUND)
     return ERROR_SUCCESS;
   if (result != ERROR_SUCCESS)
     return result;

   string16 subkey_name(name);

   // Check for an ending slash and add one if it is missing.
   if (!subkey_name.empty() && subkey_name.back() != '\\')
     subkey_name.push_back('\\');

   // Enumerate the keys
   result = ERROR_SUCCESS;
   const DWORD kMaxKeyNameLength = MAX_PATH;
   const size_t base_key_length = subkey_name.length();
   string16 key_name;
   while (result == ERROR_SUCCESS) {
     DWORD key_size = kMaxKeyNameLength;
     result =
         RegEnumKeyEx(target_key, 0,
                      as_writable_wcstr(WriteInto(&key_name, kMaxKeyNameLength)),
                      &key_size, NULL, NULL, NULL, NULL);

     if (result != ERROR_SUCCESS)
       break;

     key_name.resize(key_size);
     subkey_name.resize(base_key_length);
     subkey_name += key_name;

     if (RegDelRecurse(root_key, subkey_name.c_str(), access) != ERROR_SUCCESS)
       break;
   }

   RegCloseKey(target_key);

   // Try again to delete the key.
   result = RegDeleteKeyExWrapper(root_key, name, access, 0);

   return result;
 }

 // RegistryValueIterator ------------------------------------------------------

 RegistryValueIterator::RegistryValueIterator(HKEY root_key,
                                              const char16* folder_key,
                                              REGSAM wow64access)
     : name_(MAX_PATH, '\0'), value_(MAX_PATH, '\0') {
   Initialize(root_key, folder_key, wow64access);
 }

 RegistryValueIterator::RegistryValueIterator(HKEY root_key,
                                              const char16* folder_key)
     : name_(MAX_PATH, '\0'), value_(MAX_PATH, '\0') {
   Initialize(root_key, folder_key, 0);
 }

 void RegistryValueIterator::Initialize(HKEY root_key,
                                        const char16* folder_key,
                                        REGSAM wow64access) {
   DCHECK_EQ(wow64access & ~kWow64AccessMask, static_cast<REGSAM>(0));
   LONG result = RegOpenKeyEx(root_key, as_wcstr(folder_key), 0,
                              KEY_READ | wow64access, &key_);
   if (result != ERROR_SUCCESS) {
     key_ = NULL;
   } else {
     DWORD count = 0;
     result = ::RegQueryInfoKey(key_, NULL, 0, NULL, NULL, NULL, NULL, &count,
                                NULL, NULL, NULL, NULL);

     if (result != ERROR_SUCCESS) {
       ::RegCloseKey(key_);
       key_ = NULL;
     } else {
       index_ = count - 1;
     }
   }

   Read();
 }

 RegistryValueIterator::~RegistryValueIterator() {
   if (key_)
     ::RegCloseKey(key_);
 }

 DWORD RegistryValueIterator::ValueCount() const {
   DWORD count = 0;
   LONG result = ::RegQueryInfoKey(key_, NULL, 0, NULL, NULL, NULL, NULL,
                                   &count, NULL, NULL, NULL, NULL);
   if (result != ERROR_SUCCESS)
     return 0;

   return count;
 }

 bool RegistryValueIterator::Valid() const {
   return key_ != NULL && index_ >= 0;
 }

 void RegistryValueIterator::operator++() {
   --index_;
   Read();
 }

 bool RegistryValueIterator::Read() {
   if (Valid()) {
     DWORD capacity = static_cast<DWORD>(name_.capacity());
     DWORD name_size = capacity;
     // |value_size_| is in bytes. Reserve the last character for a NUL.
     static_assert(sizeof(wchar_t) == sizeof(char16),
                   "wchar_t is not the same size as base::char16");
     value_size_ = static_cast<DWORD>((value_.size() - 1) * sizeof(wchar_t));
     LONG result = ::RegEnumValue(
         key_, index_, as_writable_wcstr(WriteInto(&name_, name_size)),
         &name_size, NULL, &type_, reinterpret_cast<BYTE*>(value_.data()),
         &value_size_);

     if (result == ERROR_MORE_DATA) {
       // Registry key names are limited to 255 characters and fit within
       // MAX_PATH (which is 260) but registry value names can use up to 16,383
       // characters and the value itself is not limited
       // (from http://msdn.microsoft.com/en-us/library/windows/desktop/
       // ms724872(v=vs.85).aspx).
       // Resize the buffers and retry if their size caused the failure.
       DWORD value_size_in_wchars = to_wchar_size(value_size_);
       if (value_size_in_wchars + 1 > value_.size())
         value_.resize(value_size_in_wchars + 1, '\0');
       value_size_ = static_cast<DWORD>((value_.size() - 1) * sizeof(wchar_t));
       name_size = name_size == capacity ? MAX_REGISTRY_NAME_SIZE : capacity;
       result = ::RegEnumValue(
           key_, index_, as_writable_wcstr(WriteInto(&name_, name_size)),
           &name_size, NULL, &type_, reinterpret_cast<BYTE*>(value_.data()),
           &value_size_);
     }

     if (result == ERROR_SUCCESS) {
       DCHECK_LT(to_wchar_size(value_size_), value_.size());
       value_[to_wchar_size(value_size_)] = '\0';
       return true;
     }
   }

   name_[0] = '\0';
   value_[0] = '\0';
   value_size_ = 0;
   return false;
 }

 // RegistryKeyIterator --------------------------------------------------------

 RegistryKeyIterator::RegistryKeyIterator(HKEY root_key,
                                          const char16* folder_key) {
   Initialize(root_key, folder_key, 0);
 }

 RegistryKeyIterator::RegistryKeyIterator(HKEY root_key,
                                          const char16* folder_key,
                                          REGSAM wow64access) {
   Initialize(root_key, folder_key, wow64access);
 }

 RegistryKeyIterator::~RegistryKeyIterator() {
   if (key_)
     ::RegCloseKey(key_);
 }

 DWORD RegistryKeyIterator::SubkeyCount() const {
   DWORD count = 0;
   LONG result = ::RegQueryInfoKey(key_, NULL, 0, NULL, &count, NULL, NULL,
                                   NULL, NULL, NULL, NULL, NULL);
   if (result != ERROR_SUCCESS)
     return 0;

   return count;
 }

 bool RegistryKeyIterator::Valid() const {
   return key_ != NULL && index_ >= 0;
 }

 void RegistryKeyIterator::operator++() {
   --index_;
   Read();
 }

 bool RegistryKeyIterator::Read() {
   if (Valid()) {
     DWORD ncount = static_cast<DWORD>(size(name_));
     FILETIME written;
     LONG r = ::RegEnumKeyEx(key_, index_, as_writable_wcstr(name_), &ncount,
                             NULL, NULL, NULL, &written);
     if (ERROR_SUCCESS == r)
       return true;
   }

   name_[0] = '\0';
   return false;
 }

 void RegistryKeyIterator::Initialize(HKEY root_key,
                                      const char16* folder_key,
                                      REGSAM wow64access) {
   DCHECK_EQ(wow64access & ~kWow64AccessMask, static_cast<REGSAM>(0));
   LONG result = RegOpenKeyEx(root_key, as_wcstr(folder_key), 0,
                              KEY_READ | wow64access, &key_);
   if (result != ERROR_SUCCESS) {
     key_ = NULL;
   } else {
     DWORD count = 0;
     result = ::RegQueryInfoKey(key_, NULL, 0, NULL, &count, NULL, NULL, NULL,
                                NULL, NULL, NULL, NULL);

     if (result != ERROR_SUCCESS) {
       ::RegCloseKey(key_);
       key_ = NULL;
     } else {
       index_ = count - 1;
     }
   }

   Read();
 }

 }  // namespace win
 }  // namespace base
	// 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/win/registry.h"

	#include <stddef.h>

	#include <algorithm>
	#include <string>
	#include <utility>

	#include "base/logging.h"
	#include "base/stl_util.h"
	#include "base/strings/string_util.h"
	#include "base/threading/thread_restrictions.h"
	#include "base/win/shlwapi.h"
	#include "base/win/windows_version.h"

	namespace base {
	namespace win {

	namespace {

	// RegEnumValue() reports the number of characters from the name that were
	// written to the buffer, not how many there are. This constant is the maximum
	// name size, such that a buffer with this size should read any name.
	const DWORD MAX_REGISTRY_NAME_SIZE = 16384;

	// Registry values are read as BYTE* but can have wchar_t* data whose last
	// wchar_t is truncated. This function converts the reported \|byte_size\| to
	// a size in wchar_t that can store a truncated wchar_t if necessary.
	inline DWORD to_wchar_size(DWORD byte_size) {
	return (byte_size + sizeof(wchar_t) - 1) / sizeof(wchar_t);
	}

	// Mask to pull WOW64 access flags out of REGSAM access.
	const REGSAM kWow64AccessMask = KEY_WOW64_32KEY \| KEY_WOW64_64KEY;

	} // namespace

	// Watches for modifications to a key.
	class RegKey::Watcher : public ObjectWatcher::Delegate {
	public:
	Watcher() {}
	~Watcher() override {}

	bool StartWatching(HKEY key, ChangeCallback callback);

	// Implementation of ObjectWatcher::Delegate.
	void OnObjectSignaled(HANDLE object) override {
	DCHECK(watch_event_.IsValid() && watch_event_.Get() == object);
	std::move(callback_).Run();
	}

	private:
	ScopedHandle watch_event_;
	ObjectWatcher object_watcher_;
	ChangeCallback callback_;
	DISALLOW_COPY_AND_ASSIGN(Watcher);
	};

	bool RegKey::Watcher::StartWatching(HKEY key, ChangeCallback callback) {
	DCHECK(key);
	DCHECK(callback_.is_null());

	if (!watch_event_.IsValid())
	watch_event_.Set(CreateEvent(NULL, TRUE, FALSE, NULL));

	if (!watch_event_.IsValid())
	return false;

	DWORD filter = REG_NOTIFY_CHANGE_NAME \|
	REG_NOTIFY_CHANGE_ATTRIBUTES \|
	REG_NOTIFY_CHANGE_LAST_SET \|
	REG_NOTIFY_CHANGE_SECURITY;

	// Watch the registry key for a change of value.
	LONG result = RegNotifyChangeKeyValue(key, TRUE, filter, watch_event_.Get(),
	TRUE);
	if (result != ERROR_SUCCESS) {
	watch_event_.Close();
	return false;
	}

	callback_ = std::move(callback);
	return object_watcher_.StartWatchingOnce(watch_event_.Get(), this);
	}

	// RegKey ----------------------------------------------------------------------

	RegKey::RegKey() : key_(NULL), wow64access_(0) {
	}

	RegKey::RegKey(HKEY key) : key_(key), wow64access_(0) {
	}

	RegKey::RegKey(HKEY rootkey, const char16* subkey, REGSAM access)
	: key_(NULL), wow64access_(0) {
	if (rootkey) {
	if (access & (KEY_SET_VALUE \| KEY_CREATE_SUB_KEY \| KEY_CREATE_LINK))
	Create(rootkey, subkey, access);
	else
	Open(rootkey, subkey, access);
	} else {
	DCHECK(!subkey);
	wow64access_ = access & kWow64AccessMask;
	}
	}

	RegKey::~RegKey() {
	Close();
	}

	LONG RegKey::Create(HKEY rootkey, const char16* subkey, REGSAM access) {
	DWORD disposition_value;
	return CreateWithDisposition(rootkey, subkey, &disposition_value, access);
	}

	LONG RegKey::CreateWithDisposition(HKEY rootkey,
	const char16* subkey,
	DWORD* disposition,
	REGSAM access) {
	DCHECK(rootkey && subkey && access && disposition);
	HKEY subhkey = NULL;
	LONG result = RegCreateKeyEx(rootkey, as_wcstr(subkey), 0, NULL,
	REG_OPTION_NON_VOLATILE, access, NULL, &subhkey,
	disposition);
	if (result == ERROR_SUCCESS) {
	Close();
	key_ = subhkey;
	wow64access_ = access & kWow64AccessMask;
	}

	return result;
	}

	LONG RegKey::CreateKey(const char16* name, REGSAM access) {
	DCHECK(name && access);
	// After the application has accessed an alternate registry view using one of
	// the [KEY_WOW64_32KEY / KEY_WOW64_64KEY] flags, all subsequent operations
	// (create, delete, or open) on child registry keys must explicitly use the
	// same flag. Otherwise, there can be unexpected behavior.
	// http://msdn.microsoft.com/en-us/library/windows/desktop/aa384129.aspx.
	if ((access & kWow64AccessMask) != wow64access_) {
	NOTREACHED();
	return ERROR_INVALID_PARAMETER;
	}
	HKEY subkey = NULL;
	LONG result =
	RegCreateKeyEx(key_, as_wcstr(name), 0, NULL, REG_OPTION_NON_VOLATILE,
	access, NULL, &subkey, NULL);
	if (result == ERROR_SUCCESS) {
	Close();
	key_ = subkey;
	wow64access_ = access & kWow64AccessMask;
	}

	return result;
	}

	LONG RegKey::Open(HKEY rootkey, const char16* subkey, REGSAM access) {
	DCHECK(rootkey && subkey && access);
	HKEY subhkey = NULL;

	LONG result = RegOpenKeyEx(rootkey, as_wcstr(subkey), 0, access, &subhkey);
	if (result == ERROR_SUCCESS) {
	Close();
	key_ = subhkey;
	wow64access_ = access & kWow64AccessMask;
	}

	return result;
	}

	LONG RegKey::OpenKey(const char16* relative_key_name, REGSAM access) {
	DCHECK(relative_key_name && access);
	// After the application has accessed an alternate registry view using one of
	// the [KEY_WOW64_32KEY / KEY_WOW64_64KEY] flags, all subsequent operations
	// (create, delete, or open) on child registry keys must explicitly use the
	// same flag. Otherwise, there can be unexpected behavior.
	// http://msdn.microsoft.com/en-us/library/windows/desktop/aa384129.aspx.
	if ((access & kWow64AccessMask) != wow64access_) {
	NOTREACHED();
	return ERROR_INVALID_PARAMETER;
	}
	HKEY subkey = NULL;
	LONG result =
	RegOpenKeyEx(key_, as_wcstr(relative_key_name), 0, access, &subkey);

	// We have to close the current opened key before replacing it with the new
	// one.
	if (result == ERROR_SUCCESS) {
	Close();
	key_ = subkey;
	wow64access_ = access & kWow64AccessMask;
	}
	return result;
	}

	void RegKey::Close() {
	if (key_) {
	::RegCloseKey(key_);
	key_ = NULL;
	wow64access_ = 0;
	}
	}

	// TODO(wfh): Remove this and other unsafe methods. See http://crbug.com/375400
	void RegKey::Set(HKEY key) {
	if (key_ != key) {
	Close();
	key_ = key;
	}
	}

	HKEY RegKey::Take() {
	DCHECK_EQ(wow64access_, 0u);
	HKEY key = key_;
	key_ = NULL;
	return key;
	}

	bool RegKey::HasValue(const char16* name) const {
	return RegQueryValueEx(key_, as_wcstr(name), 0, NULL, NULL, NULL) ==
	ERROR_SUCCESS;
	}

	DWORD RegKey::GetValueCount() const {
	DWORD count = 0;
	LONG result = RegQueryInfoKey(key_, NULL, 0, NULL, NULL, NULL, NULL, &count,
	NULL, NULL, NULL, NULL);
	return (result == ERROR_SUCCESS) ? count : 0;
	}

	LONG RegKey::GetValueNameAt(int index, string16* name) const {
	char16 buf[256];
	DWORD bufsize = size(buf);
	LONG r = ::RegEnumValue(key_, index, as_writable_wcstr(buf), &bufsize, NULL,
	NULL, NULL, NULL);
	if (r == ERROR_SUCCESS)
	name->assign(buf, bufsize);

	return r;
	}

	LONG RegKey::DeleteKey(const char16* name) {
	DCHECK(key_);
	DCHECK(name);
	HKEY subkey = NULL;

	// Verify the key exists before attempting delete to replicate previous
	// behavior.
	LONG result = RegOpenKeyEx(key_, as_wcstr(name), 0,
	READ_CONTROL \| wow64access_, &subkey);
	if (result != ERROR_SUCCESS)
	return result;
	RegCloseKey(subkey);

	return RegDelRecurse(key_, name, wow64access_);
	}

	LONG RegKey::DeleteEmptyKey(const char16* name) {
	DCHECK(key_);
	DCHECK(name);

	HKEY target_key = NULL;
	LONG result = RegOpenKeyEx(key_, as_wcstr(name), 0, KEY_READ \| wow64access_,
	&target_key);

	if (result != ERROR_SUCCESS)
	return result;

	DWORD count = 0;
	result = RegQueryInfoKey(target_key, NULL, 0, NULL, NULL, NULL, NULL, &count,
	NULL, NULL, NULL, NULL);

	RegCloseKey(target_key);

	if (result != ERROR_SUCCESS)
	return result;

	if (count == 0)
	return RegDeleteKeyExWrapper(key_, name, wow64access_, 0);

	return ERROR_DIR_NOT_EMPTY;
	}

	LONG RegKey::DeleteValue(const char16* value_name) {
	DCHECK(key_);
	LONG result = RegDeleteValue(key_, as_wcstr(value_name));
	return result;
	}

	LONG RegKey::ReadValueDW(const char16* name, DWORD* out_value) const {
	DCHECK(out_value);
	DWORD type = REG_DWORD;
	DWORD size = sizeof(DWORD);
	DWORD local_value = 0;
	LONG result = ReadValue(name, &local_value, &size, &type);
	if (result == ERROR_SUCCESS) {
	if ((type == REG_DWORD \|\| type == REG_BINARY) && size == sizeof(DWORD))
	*out_value = local_value;
	else
	result = ERROR_CANTREAD;
	}

	return result;
	}

	LONG RegKey::ReadInt64(const char16* name, int64_t* out_value) const {
	DCHECK(out_value);
	DWORD type = REG_QWORD;
	int64_t local_value = 0;
	DWORD size = sizeof(local_value);
	LONG result = ReadValue(name, &local_value, &size, &type);
	if (result == ERROR_SUCCESS) {
	if ((type == REG_QWORD \|\| type == REG_BINARY) &&
	size == sizeof(local_value))
	*out_value = local_value;
	else
	result = ERROR_CANTREAD;
	}

	return result;
	}

	LONG RegKey::ReadValue(const char16* name, string16* out_value) const {
	DCHECK(out_value);
	const size_t kMaxStringLength = 1024; // This is after expansion.
	// Use the one of the other forms of ReadValue if 1024 is too small for you.
	char16 raw_value[kMaxStringLength];
	DWORD type = REG_SZ, size = sizeof(raw_value);
	LONG result = ReadValue(name, as_writable_wcstr(raw_value), &size, &type);
	if (result == ERROR_SUCCESS) {
	if (type == REG_SZ) {
	*out_value = raw_value;
	} else if (type == REG_EXPAND_SZ) {
	char16 expanded[kMaxStringLength];
	size = ExpandEnvironmentStrings(
	as_wcstr(raw_value), as_writable_wcstr(expanded), kMaxStringLength);
	// Success: returns the number of wchar_t's copied
	// Fail: buffer too small, returns the size required
	// Fail: other, returns 0
	if (size == 0 \|\| size > kMaxStringLength) {
	result = ERROR_MORE_DATA;
	} else {
	*out_value = expanded;
	}
	} else {
	// Not a string. Oops.
	result = ERROR_CANTREAD;
	}
	}

	return result;
	}

	LONG RegKey::ReadValue(const char16* name,
	void* data,
	DWORD* dsize,
	DWORD* dtype) const {
	LONG result = RegQueryValueEx(key_, as_wcstr(name), 0, dtype,
	reinterpret_cast<LPBYTE>(data), dsize);
	return result;
	}

	LONG RegKey::ReadValues(const char16* name, std::vector<string16>* values) {
	values->clear();

	DWORD type = REG_MULTI_SZ;
	DWORD size = 0;
	LONG result = ReadValue(name, NULL, &size, &type);
	if (result != ERROR_SUCCESS \|\| size == 0)
	return result;

	if (type != REG_MULTI_SZ)
	return ERROR_CANTREAD;

	std::vector<char16> buffer(size / sizeof(char16));
	result = ReadValue(name, as_writable_wcstr(buffer.data()), &size, NULL);
	if (result != ERROR_SUCCESS \|\| size == 0)
	return result;

	// Parse the double-null-terminated list of strings.
	// Note: This code is paranoid to not read outside of \|buf\|, in the case where
	// it may not be properly terminated.
	auto entry = buffer.cbegin();
	auto buffer_end = buffer.cend();
	while (entry < buffer_end && *entry != '\0') {
	auto entry_end = std::find(entry, buffer_end, '\0');
	values->emplace_back(entry, entry_end);
	entry = entry_end + 1;
	}
	return 0;
	}

	LONG RegKey::WriteValue(const char16* name, DWORD in_value) {
	return WriteValue(
	name, &in_value, static_cast<DWORD>(sizeof(in_value)), REG_DWORD);
	}

	LONG RegKey::WriteValue(const char16* name, const char16* in_value) {
	return WriteValue(
	name, in_value,
	static_cast<DWORD>(sizeof(in_value)
	(std::char_traits<char16>::length(in_value) + 1)),
	REG_SZ);
	}

	LONG RegKey::WriteValue(const char16* name,
	const void* data,
	DWORD dsize,
	DWORD dtype) {
	DCHECK(data \|\| !dsize);

	LONG result =
	RegSetValueEx(key_, as_wcstr(name), 0, dtype,
	reinterpret_cast<LPBYTE>(const_cast<void*>(data)), dsize);
	return result;
	}

	bool RegKey::StartWatching(ChangeCallback callback) {
	if (!key_watcher_)
	key_watcher_.reset(new Watcher());

	if (!key_watcher_->StartWatching(key_, std::move(callback)))
	return false;

	return true;
	}

	// static
	LONG RegKey::RegDeleteKeyExWrapper(HKEY hKey,
	const char16* lpSubKey,
	REGSAM samDesired,
	DWORD Reserved) {
	typedef LSTATUS(WINAPI* RegDeleteKeyExPtr)(HKEY, LPCWSTR, REGSAM, DWORD);

	RegDeleteKeyExPtr reg_delete_key_ex_func =
	reinterpret_cast<RegDeleteKeyExPtr>(
	GetProcAddress(GetModuleHandleA("advapi32.dll"), "RegDeleteKeyExW"));

	if (reg_delete_key_ex_func)
	return reg_delete_key_ex_func(hKey, as_wcstr(lpSubKey), samDesired,
	Reserved);

	// Windows XP does not support RegDeleteKeyEx, so fallback to RegDeleteKey.
	return RegDeleteKey(hKey, as_wcstr(lpSubKey));
	}

	// static
	LONG RegKey::RegDelRecurse(HKEY root_key, const char16* name, REGSAM access) {
	// First, see if the key can be deleted without having to recurse.
	LONG result = RegDeleteKeyExWrapper(root_key, name, access, 0);
	if (result == ERROR_SUCCESS)
	return result;

	HKEY target_key = NULL;
	result = RegOpenKeyEx(root_key, as_wcstr(name), 0,
	KEY_ENUMERATE_SUB_KEYS \| access, &target_key);

	if (result == ERROR_FILE_NOT_FOUND)
	return ERROR_SUCCESS;
	if (result != ERROR_SUCCESS)
	return result;

	string16 subkey_name(name);

	// Check for an ending slash and add one if it is missing.
	if (!subkey_name.empty() && subkey_name.back() != '\\')
	subkey_name.push_back('\\');

	// Enumerate the keys
	result = ERROR_SUCCESS;
	const DWORD kMaxKeyNameLength = MAX_PATH;
	const size_t base_key_length = subkey_name.length();
	string16 key_name;
	while (result == ERROR_SUCCESS) {
	DWORD key_size = kMaxKeyNameLength;
	result =
	RegEnumKeyEx(target_key, 0,
	as_writable_wcstr(WriteInto(&key_name, kMaxKeyNameLength)),
	&key_size, NULL, NULL, NULL, NULL);

	if (result != ERROR_SUCCESS)
	break;

	key_name.resize(key_size);
	subkey_name.resize(base_key_length);
	subkey_name += key_name;

	if (RegDelRecurse(root_key, subkey_name.c_str(), access) != ERROR_SUCCESS)
	break;
	}

	RegCloseKey(target_key);

	// Try again to delete the key.
	result = RegDeleteKeyExWrapper(root_key, name, access, 0);

	return result;
	}

	// RegistryValueIterator ------------------------------------------------------

	RegistryValueIterator::RegistryValueIterator(HKEY root_key,
	const char16* folder_key,
	REGSAM wow64access)
	: name_(MAX_PATH, '\0'), value_(MAX_PATH, '\0') {
	Initialize(root_key, folder_key, wow64access);
	}

	RegistryValueIterator::RegistryValueIterator(HKEY root_key,
	const char16* folder_key)
	: name_(MAX_PATH, '\0'), value_(MAX_PATH, '\0') {
	Initialize(root_key, folder_key, 0);
	}

	void RegistryValueIterator::Initialize(HKEY root_key,
	const char16* folder_key,
	REGSAM wow64access) {
	DCHECK_EQ(wow64access & ~kWow64AccessMask, static_cast<REGSAM>(0));
	LONG result = RegOpenKeyEx(root_key, as_wcstr(folder_key), 0,
	KEY_READ \| wow64access, &key_);
	if (result != ERROR_SUCCESS) {
	key_ = NULL;
	} else {
	DWORD count = 0;
	result = ::RegQueryInfoKey(key_, NULL, 0, NULL, NULL, NULL, NULL, &count,
	NULL, NULL, NULL, NULL);

	if (result != ERROR_SUCCESS) {
	::RegCloseKey(key_);
	key_ = NULL;
	} else {
	index_ = count - 1;
	}
	}

	Read();
	}

	RegistryValueIterator::~RegistryValueIterator() {
	if (key_)
	::RegCloseKey(key_);
	}

	DWORD RegistryValueIterator::ValueCount() const {
	DWORD count = 0;
	LONG result = ::RegQueryInfoKey(key_, NULL, 0, NULL, NULL, NULL, NULL,
	&count, NULL, NULL, NULL, NULL);
	if (result != ERROR_SUCCESS)
	return 0;

	return count;
	}

	bool RegistryValueIterator::Valid() const {
	return key_ != NULL && index_ >= 0;
	}

	void RegistryValueIterator::operator++() {
	--index_;
	Read();
	}

	bool RegistryValueIterator::Read() {
	if (Valid()) {
	DWORD capacity = static_cast<DWORD>(name_.capacity());
	DWORD name_size = capacity;
	// \|value_size_\| is in bytes. Reserve the last character for a NUL.
	static_assert(sizeof(wchar_t) == sizeof(char16),
	"wchar_t is not the same size as base::char16");
	value_size_ = static_cast<DWORD>((value_.size() - 1) * sizeof(wchar_t));
	LONG result = ::RegEnumValue(
	key_, index_, as_writable_wcstr(WriteInto(&name_, name_size)),
	&name_size, NULL, &type_, reinterpret_cast<BYTE*>(value_.data()),
	&value_size_);

	if (result == ERROR_MORE_DATA) {
	// Registry key names are limited to 255 characters and fit within
	// MAX_PATH (which is 260) but registry value names can use up to 16,383
	// characters and the value itself is not limited
	// (from http://msdn.microsoft.com/en-us/library/windows/desktop/
	// ms724872(v=vs.85).aspx).
	// Resize the buffers and retry if their size caused the failure.
	DWORD value_size_in_wchars = to_wchar_size(value_size_);
	if (value_size_in_wchars + 1 > value_.size())
	value_.resize(value_size_in_wchars + 1, '\0');
	value_size_ = static_cast<DWORD>((value_.size() - 1) * sizeof(wchar_t));
	name_size = name_size == capacity ? MAX_REGISTRY_NAME_SIZE : capacity;
	result = ::RegEnumValue(
	key_, index_, as_writable_wcstr(WriteInto(&name_, name_size)),
	&name_size, NULL, &type_, reinterpret_cast<BYTE*>(value_.data()),
	&value_size_);
	}

	if (result == ERROR_SUCCESS) {
	DCHECK_LT(to_wchar_size(value_size_), value_.size());
	value_[to_wchar_size(value_size_)] = '\0';
	return true;
	}
	}

	name_[0] = '\0';
	value_[0] = '\0';
	value_size_ = 0;
	return false;
	}

	// RegistryKeyIterator --------------------------------------------------------

	RegistryKeyIterator::RegistryKeyIterator(HKEY root_key,
	const char16* folder_key) {
	Initialize(root_key, folder_key, 0);
	}

	RegistryKeyIterator::RegistryKeyIterator(HKEY root_key,
	const char16* folder_key,
	REGSAM wow64access) {
	Initialize(root_key, folder_key, wow64access);
	}

	RegistryKeyIterator::~RegistryKeyIterator() {
	if (key_)
	::RegCloseKey(key_);
	}

	DWORD RegistryKeyIterator::SubkeyCount() const {
	DWORD count = 0;
	LONG result = ::RegQueryInfoKey(key_, NULL, 0, NULL, &count, NULL, NULL,
	NULL, NULL, NULL, NULL, NULL);
	if (result != ERROR_SUCCESS)
	return 0;

	return count;
	}

	bool RegistryKeyIterator::Valid() const {
	return key_ != NULL && index_ >= 0;
	}

	void RegistryKeyIterator::operator++() {
	--index_;
	Read();
	}

	bool RegistryKeyIterator::Read() {
	if (Valid()) {
	DWORD ncount = static_cast<DWORD>(size(name_));
	FILETIME written;
	LONG r = ::RegEnumKeyEx(key_, index_, as_writable_wcstr(name_), &ncount,
	NULL, NULL, NULL, &written);
	if (ERROR_SUCCESS == r)
	return true;
	}

	name_[0] = '\0';
	return false;
	}

	void RegistryKeyIterator::Initialize(HKEY root_key,
	const char16* folder_key,
	REGSAM wow64access) {
	DCHECK_EQ(wow64access & ~kWow64AccessMask, static_cast<REGSAM>(0));
	LONG result = RegOpenKeyEx(root_key, as_wcstr(folder_key), 0,
	KEY_READ \| wow64access, &key_);
	if (result != ERROR_SUCCESS) {
	key_ = NULL;
	} else {
	DWORD count = 0;
	result = ::RegQueryInfoKey(key_, NULL, 0, NULL, &count, NULL, NULL, NULL,
	NULL, NULL, NULL, NULL);

	if (result != ERROR_SUCCESS) {
	::RegCloseKey(key_);
	key_ = NULL;
	} else {
	index_ = count - 1;
	}
	}

	Read();
	}

	} // namespace win
	} // namespace base