Implement Windows GPO support for "dlpref" in component updater.

chrome/installer/util/google_update_settings.cc

 // 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 "chrome/installer/util/google_update_settings.h"
 
 #include <stdint.h>
 
 #include <algorithm>
 #include <limits>
+#include <vector>
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/path_service.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/time/time.h"
 #include "base/win/registry.h"
 #include "base/win/win_util.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/installer/util/app_registration_data.h"
 #include "chrome/installer/util/browser_distribution.h"
 #include "chrome/installer/util/channel_info.h"
 #include "chrome/installer/util/google_update_constants.h"
 #include "chrome/installer/util/install_util.h"
 #include "chrome/installer/util/installation_state.h"
 #include "chrome/installer/util/product.h"
 
 using base::win::RegKey;
 using installer::InstallationState;
 
 const wchar_t GoogleUpdateSettings::kPoliciesKey[] =
     L"SOFTWARE\\Policies\\Google\\Update";
 const wchar_t GoogleUpdateSettings::kUpdatePolicyValue[] = L"UpdateDefault";
+const wchar_t GoogleUpdateSettings::kDownloadPreferencePolicyValue[] =
+    L"DownloadPreference";
 const wchar_t GoogleUpdateSettings::kUpdateOverrideValuePrefix[] = L"Update";
 const wchar_t GoogleUpdateSettings::kCheckPeriodOverrideMinutes[] =
     L"AutoUpdateCheckPeriodMinutes";
 
 // Don't allow update periods longer than six weeks.
 const int GoogleUpdateSettings::kCheckPeriodOverrideMinutesMax =
     60 * 24 * 7 * 6;
 
 const GoogleUpdateSettings::UpdatePolicy
 GoogleUpdateSettings::kDefaultUpdatePolicy =
@@ skipping 714 matching lines @@
     // permissions to make changes (the most likely reason is that there is no
     // policy set). Simply return whether or not we think updates are enabled.
     return AreAutoupdatesEnabled();
   }
 
 #endif
   // Non Google Chrome isn't going to autoupdate.
   return true;
 }
 
+// Reads and sanitizes the value of
+// "HKLM\SOFTWARE\Policies\Google\Update\DownloadPreference". A valid
+// group policy option must be a single alpha numeric word of up to 32
+// characters.
+base::string16 GoogleUpdateSettings::GetDownloadPreference() {
+  RegKey policy_key;
+  base::string16 value;
+  if (policy_key.Open(HKEY_LOCAL_MACHINE, kPoliciesKey, KEY_QUERY_VALUE) ==
+          ERROR_SUCCESS &&
+      policy_key.ReadValue(kDownloadPreferencePolicyValue, &value) ==
+          ERROR_SUCCESS) {
+    // Validates that |value| matches `[a-zA-z]{0-32}`.
+    const size_t kMaxValueLength = 32;
+    if (value.size() > kMaxValueLength)
+      return base::string16();
+    for (auto ch : value) {
+      if (!base::IsAsciiAlpha(ch))
+        return base::string16();
+    }
+    return value;
+  }
+  return base::string16();
+}
+
 void GoogleUpdateSettings::RecordChromeUpdatePolicyHistograms() {
   const bool is_multi_install = InstallUtil::IsMultiInstall(
       BrowserDistribution::GetDistribution(), IsSystemInstall());
   const base::string16 app_guid =
       BrowserDistribution::GetSpecificDistribution(
           is_multi_install ? BrowserDistribution::CHROME_BINARIES :
                              BrowserDistribution::CHROME_BROWSER)->GetAppGuid();
 
   bool is_overridden = false;
   const UpdatePolicy update_policy = GetAppUpdatePolicy(app_guid,
@@ skipping 188 matching lines @@
   }
 
   // If the key or value was not present, return the empty string.
   if (result == ERROR_FILE_NOT_FOUND || result == ERROR_PATH_NOT_FOUND) {
     experiment_labels->clear();
     return true;
   }
 
   return result == ERROR_SUCCESS;
 }