extensions/common/features/simple_feature.cc

   1 // Copyright 2014 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 "extensions/common/features/simple_feature.h"
   6
   7 #include <algorithm>
   8 #include <map>
   9 #include <vector>
  10
  11 #include "base/bind.h"
  12 #include "base/command_line.h"
  13 #include "base/macros.h"
  14 #include "base/sha1.h"
  15 #include "base/stl_util.h"
  16 #include "base/strings/string_number_conversions.h"
  17 #include "base/strings/string_util.h"
  18 #include "base/strings/stringprintf.h"
  19 #include "components/crx_file/id_util.h"
  20 #include "extensions/common/extension_api.h"
  21 #include "extensions/common/features/feature_provider.h"
  22 #include "extensions/common/features/feature_util.h"
  23 #include "extensions/common/switches.h"
  24
  25 using crx_file::id_util::HashedIdInHex;
  26
  27 namespace extensions {
  28
  29 namespace {
  30
  31 // A singleton copy of the --whitelisted-extension-id so that we don't need to
  32 // copy it from the CommandLine each time.
  33 std::string* g_whitelisted_extension_id = NULL;
  34
  35 Feature::Availability IsAvailableToManifestForBind(
  36     const std::string& extension_id,
  37     Manifest::Type type,
  38     Manifest::Location location,
  39     int manifest_version,
  40     Feature::Platform platform,
  41     const Feature* feature) {
  42   return feature->IsAvailableToManifest(
  43       extension_id, type, location, manifest_version, platform);
  44 }
  45
  46 Feature::Availability IsAvailableToContextForBind(const Extension* extension,
  47                                                   Feature::Context context,
  48                                                   const GURL& url,
  49                                                   Feature::Platform platform,
  50                                                   const Feature* feature) {
  51   return feature->IsAvailableToContext(extension, context, url, platform);
  52 }
  53
  54 // TODO(aa): Can we replace all this manual parsing with JSON schema stuff?
  55
  56 void ParseVector(const base::Value* value,
  57                  std::vector<std::string>* vector) {
  58   const base::ListValue* list_value = NULL;
  59   if (!value->GetAsList(&list_value))
  60     return;
  61
  62   vector->clear();
  63   size_t list_size = list_value->GetSize();
  64   vector->reserve(list_size);
  65   for (size_t i = 0; i < list_size; ++i) {
  66     std::string str_val;
  67     CHECK(list_value->GetString(i, &str_val));
  68     vector->push_back(str_val);
  69   }
  70   std::sort(vector->begin(), vector->end());
  71 }
  72
  73 template<typename T>
  74 void ParseEnum(const std::string& string_value,
  75                T* enum_value,
  76                const std::map<std::string, T>& mapping) {
  77   const auto& iter = mapping.find(string_value);
  78   if (iter == mapping.end())
  79     CRASH_WITH_MINIDUMP("Enum value not found: " + string_value);
  80   *enum_value = iter->second;
  81 }
  82
  83 template<typename T>
  84 void ParseEnum(const base::DictionaryValue* value,
  85                const std::string& property,
  86                T* enum_value,
  87                const std::map<std::string, T>& mapping) {
  88   std::string string_value;
  89   if (!value->GetString(property, &string_value))
  90     return;
  91
  92   ParseEnum(string_value, enum_value, mapping);
  93 }
  94
  95 template<typename T>
  96 void ParseEnumVector(const base::Value* value,
  97                      std::vector<T>* enum_vector,
  98                      const std::map<std::string, T>& mapping) {
  99   enum_vector->clear();
 100   std::string property_string;
 101   if (value->GetAsString(&property_string)) {
 102     if (property_string == "all") {
 103       enum_vector->reserve(mapping.size());
 104       for (const auto& it : mapping)
 105         enum_vector->push_back(it.second);
 106     }
 107     std::sort(enum_vector->begin(), enum_vector->end());
 108     return;
 109   }
 110
 111   std::vector<std::string> string_vector;
 112   ParseVector(value, &string_vector);
 113   enum_vector->reserve(string_vector.size());
 114   for (const auto& str : string_vector) {
 115     T enum_value = static_cast<T>(0);
 116     ParseEnum(str, &enum_value, mapping);
 117     enum_vector->push_back(enum_value);
 118   }
 119   std::sort(enum_vector->begin(), enum_vector->end());
 120 }
 121
 122 void ParseURLPatterns(const base::DictionaryValue* value,
 123                       const std::string& key,
 124                       URLPatternSet* set) {
 125   const base::ListValue* matches = NULL;
 126   if (value->GetList(key, &matches)) {
 127     set->ClearPatterns();
 128     for (size_t i = 0; i < matches->GetSize(); ++i) {
 129       std::string pattern;
 130       CHECK(matches->GetString(i, &pattern));
 131       set->AddPattern(URLPattern(URLPattern::SCHEME_ALL, pattern));
 132     }
 133   }
 134 }
 135
 136 // Gets a human-readable name for the given extension type, suitable for giving
 137 // to developers in an error message.
 138 std::string GetDisplayName(Manifest::Type type) {
 139   switch (type) {
 140     case Manifest::TYPE_UNKNOWN:
 141       return "unknown";
 142     case Manifest::TYPE_EXTENSION:
 143       return "extension";
 144     case Manifest::TYPE_HOSTED_APP:
 145       return "hosted app";
 146     case Manifest::TYPE_LEGACY_PACKAGED_APP:
 147       return "legacy packaged app";
 148     case Manifest::TYPE_PLATFORM_APP:
 149       return "packaged app";
 150     case Manifest::TYPE_THEME:
 151       return "theme";
 152     case Manifest::TYPE_USER_SCRIPT:
 153       return "user script";
 154     case Manifest::TYPE_SHARED_MODULE:
 155       return "shared module";
 156     case Manifest::NUM_LOAD_TYPES:
 157       NOTREACHED();
 158   }
 159   NOTREACHED();
 160   return "";
 161 }
 162
 163 // Gets a human-readable name for the given context type, suitable for giving
 164 // to developers in an error message.
 165 std::string GetDisplayName(Feature::Context context) {
 166   switch (context) {
 167     case Feature::UNSPECIFIED_CONTEXT:
 168       return "unknown";
 169     case Feature::BLESSED_EXTENSION_CONTEXT:
 170       // "privileged" is vague but hopefully the developer will understand that
 171       // means background or app window.
 172       return "privileged page";
 173     case Feature::UNBLESSED_EXTENSION_CONTEXT:
 174       // "iframe" is a bit of a lie/oversimplification, but that's the most
 175       // common unblessed context.
 176       return "extension iframe";
 177     case Feature::CONTENT_SCRIPT_CONTEXT:
 178       return "content script";
 179     case Feature::WEB_PAGE_CONTEXT:
 180       return "web page";
 181     case Feature::BLESSED_WEB_PAGE_CONTEXT:
 182       return "hosted app";
 183     case Feature::WEBUI_CONTEXT:
 184       return "webui";
 185     case Feature::SERVICE_WORKER_CONTEXT:
 186       return "service worker";
 187   }
 188   NOTREACHED();
 189   return "";
 190 }
 191
 192 // Gets a human-readable list of the display names (pluralized, comma separated
 193 // with the "and" in the correct place) for each of |enum_types|.
 194 template <typename EnumType>
 195 std::string ListDisplayNames(const std::vector<EnumType>& enum_types) {
 196   std::string display_name_list;
 197   for (size_t i = 0; i < enum_types.size(); ++i) {
 198     // Pluralize type name.
 199     display_name_list += GetDisplayName(enum_types[i]) + "s";
 200     // Comma-separate entries, with an Oxford comma if there is more than 2
 201     // total entries.
 202     if (enum_types.size() > 2) {
 203       if (i < enum_types.size() - 2)
 204         display_name_list += ", ";
 205       else if (i == enum_types.size() - 2)
 206         display_name_list += ", and ";
 207     } else if (enum_types.size() == 2 && i == 0) {
 208       display_name_list += " and ";
 209     }
 210   }
 211   return display_name_list;
 212 }
 213
 214 bool IsCommandLineSwitchEnabled(const std::string& switch_name) {
 215   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
 216   if (command_line->HasSwitch(switch_name + "=1"))
 217     return true;
 218   if (command_line->HasSwitch(std::string("enable-") + switch_name))
 219     return true;
 220   return false;
 221 }
 222
 223 bool IsWhitelistedForTest(const std::string& extension_id) {
 224   // TODO(jackhou): Delete the commandline whitelisting mechanism.
 225   // Since it is only used it tests, ideally it should not be set via the
 226   // commandline. At the moment the commandline is used as a mechanism to pass
 227   // the id to the renderer process.
 228   if (!g_whitelisted_extension_id) {
 229     g_whitelisted_extension_id = new std::string(
 230         base::CommandLine::ForCurrentProcess()->GetSwitchValueASCII(
 231             switches::kWhitelistedExtensionID));
 232   }
 233   return !g_whitelisted_extension_id->empty() &&
 234          *g_whitelisted_extension_id == extension_id;
 235 }
 236
 237 }  // namespace
 238
 239 SimpleFeature::ScopedWhitelistForTest::ScopedWhitelistForTest(
 240     const std::string& id)
 241     : previous_id_(g_whitelisted_extension_id) {
 242   g_whitelisted_extension_id = new std::string(id);
 243 }
 244
 245 SimpleFeature::ScopedWhitelistForTest::~ScopedWhitelistForTest() {
 246   delete g_whitelisted_extension_id;
 247   g_whitelisted_extension_id = previous_id_;
 248 }
 249
 250 struct SimpleFeature::Mappings {
 251   Mappings() {
 252     extension_types["extension"] = Manifest::TYPE_EXTENSION;
 253     extension_types["theme"] = Manifest::TYPE_THEME;
 254     extension_types["legacy_packaged_app"] = Manifest::TYPE_LEGACY_PACKAGED_APP;
 255     extension_types["hosted_app"] = Manifest::TYPE_HOSTED_APP;
 256     extension_types["platform_app"] = Manifest::TYPE_PLATFORM_APP;
 257     extension_types["shared_module"] = Manifest::TYPE_SHARED_MODULE;
 258
 259     contexts["blessed_extension"] = Feature::BLESSED_EXTENSION_CONTEXT;
 260     contexts["unblessed_extension"] = Feature::UNBLESSED_EXTENSION_CONTEXT;
 261     contexts["content_script"] = Feature::CONTENT_SCRIPT_CONTEXT;
 262     contexts["web_page"] = Feature::WEB_PAGE_CONTEXT;
 263     contexts["blessed_web_page"] = Feature::BLESSED_WEB_PAGE_CONTEXT;
 264     contexts["webui"] = Feature::WEBUI_CONTEXT;
 265
 266     locations["component"] = SimpleFeature::COMPONENT_LOCATION;
 267     locations["external_component"] =
 268         SimpleFeature::EXTERNAL_COMPONENT_LOCATION;
 269     locations["policy"] = SimpleFeature::POLICY_LOCATION;
 270
 271     platforms["chromeos"] = Feature::CHROMEOS_PLATFORM;
 272     platforms["linux"] = Feature::LINUX_PLATFORM;
 273     platforms["mac"] = Feature::MACOSX_PLATFORM;
 274     platforms["win"] = Feature::WIN_PLATFORM;
 275   }
 276
 277   std::map<std::string, Manifest::Type> extension_types;
 278   std::map<std::string, Feature::Context> contexts;
 279   std::map<std::string, SimpleFeature::Location> locations;
 280   std::map<std::string, Feature::Platform> platforms;
 281 };
 282
 283 SimpleFeature::SimpleFeature()
 284     : location_(UNSPECIFIED_LOCATION),
 285       min_manifest_version_(0),
 286       max_manifest_version_(0),
 287       component_extensions_auto_granted_(true) {}
 288
 289 SimpleFeature::~SimpleFeature() {}
 290
 291 bool SimpleFeature::HasDependencies() const {
 292   return !dependencies_.empty();
 293 }
 294
 295 void SimpleFeature::AddFilter(scoped_ptr<SimpleFeatureFilter> filter) {
 296   filters_.push_back(filter.Pass());
 297 }
 298
 299 std::string SimpleFeature::Parse(const base::DictionaryValue* dictionary) {
 300   static base::LazyInstance<SimpleFeature::Mappings> mappings =
 301       LAZY_INSTANCE_INITIALIZER;
 302
 303   no_parent_ = false;
 304   for (base::DictionaryValue::Iterator it(*dictionary);
 305       !it.IsAtEnd();
 306       it.Advance()) {
 307     std::string key = it.key();
 308     const base::Value* value = &it.value();
 309     if (key == "matches") {
 310       ParseURLPatterns(dictionary, "matches", &matches_);
 311     } else if (key == "blacklist") {
 312       ParseVector(value, &blacklist_);
 313     } else if (key == "whitelist") {
 314       ParseVector(value, &whitelist_);
 315     } else if (key == "dependencies") {
 316       ParseVector(value, &dependencies_);
 317     } else if (key == "extension_types") {
 318       ParseEnumVector<Manifest::Type>(value, &extension_types_,
 319                                       mappings.Get().extension_types);
 320     } else if (key == "contexts") {
 321       ParseEnumVector<Context>(value, &contexts_,
 322                                mappings.Get().contexts);
 323     } else if (key == "location") {
 324       ParseEnum<Location>(dictionary, "location", &location_,
 325                           mappings.Get().locations);
 326     } else if (key == "platforms") {
 327       ParseEnumVector<Platform>(value, &platforms_,
 328                                 mappings.Get().platforms);
 329     } else if (key == "min_manifest_version") {
 330       dictionary->GetInteger("min_manifest_version", &min_manifest_version_);
 331     } else if (key == "max_manifest_version") {
 332       dictionary->GetInteger("max_manifest_version", &max_manifest_version_);
 333     } else if (key == "noparent") {
 334       dictionary->GetBoolean("noparent", &no_parent_);
 335     } else if (key == "component_extensions_auto_granted") {
 336       dictionary->GetBoolean("component_extensions_auto_granted",
 337                              &component_extensions_auto_granted_);
 338     } else if (key == "command_line_switch") {
 339       dictionary->GetString("command_line_switch", &command_line_switch_);
 340     }
 341   }
 342
 343   // NOTE: ideally we'd sanity check that "matches" can be specified if and
 344   // only if there's a "web_page" or "webui" context, but without
 345   // (Simple)Features being aware of their own heirarchy this is impossible.
 346   //
 347   // For example, we might have feature "foo" available to "web_page" context
 348   // and "matches" google.com/*. Then a sub-feature "foo.bar" might override
 349   // "matches" to be chromium.org/*. That sub-feature doesn't need to specify
 350   // "web_page" context because it's inherited, but we don't know that here.
 351
 352   std::string result;
 353   for (const auto& filter : filters_) {
 354     result = filter->Parse(dictionary);
 355     if (!result.empty())
 356       break;
 357   }
 358
 359   return result;
 360 }
 361
 362 Feature::Availability SimpleFeature::IsAvailableToManifest(
 363     const std::string& extension_id,
 364     Manifest::Type type,
 365     Manifest::Location location,
 366     int manifest_version,
 367     Platform platform) const {
 368   // Check extension type first to avoid granting platform app permissions
 369   // to component extensions.
 370   // HACK(kalman): user script -> extension. Solve this in a more generic way
 371   // when we compile feature files.
 372   Manifest::Type type_to_check = (type == Manifest::TYPE_USER_SCRIPT) ?
 373       Manifest::TYPE_EXTENSION : type;
 374   if (!extension_types_.empty() &&
 375       !ContainsValue(extension_types_, type_to_check)) {
 376     return CreateAvailability(INVALID_TYPE, type);
 377   }
 378
 379   if (IsIdInBlacklist(extension_id))
 380     return CreateAvailability(FOUND_IN_BLACKLIST, type);
 381
 382   // TODO(benwells): don't grant all component extensions.
 383   // See http://crbug.com/370375 for more details.
 384   // Component extensions can access any feature.
 385   // NOTE: Deliberately does not match EXTERNAL_COMPONENT.
 386   if (component_extensions_auto_granted_ && location == Manifest::COMPONENT)
 387     return CreateAvailability(IS_AVAILABLE, type);
 388
 389   if (!whitelist_.empty() && !IsIdInWhitelist(extension_id) &&
 390       !IsWhitelistedForTest(extension_id)) {
 391     return CreateAvailability(NOT_FOUND_IN_WHITELIST, type);
 392   }
 393
 394   if (!MatchesManifestLocation(location))
 395     return CreateAvailability(INVALID_LOCATION, type);
 396
 397   if (!platforms_.empty() && !ContainsValue(platforms_, platform))
 398     return CreateAvailability(INVALID_PLATFORM, type);
 399
 400   if (min_manifest_version_ != 0 && manifest_version < min_manifest_version_)
 401     return CreateAvailability(INVALID_MIN_MANIFEST_VERSION, type);
 402
 403   if (max_manifest_version_ != 0 && manifest_version > max_manifest_version_)
 404     return CreateAvailability(INVALID_MAX_MANIFEST_VERSION, type);
 405
 406   if (!command_line_switch_.empty() &&
 407       !IsCommandLineSwitchEnabled(command_line_switch_)) {
 408     return CreateAvailability(MISSING_COMMAND_LINE_SWITCH, type);
 409   }
 410
 411   for (const auto& filter : filters_) {
 412     Availability availability = filter->IsAvailableToManifest(
 413         extension_id, type, location, manifest_version, platform);
 414     if (!availability.is_available())
 415       return availability;
 416   }
 417
 418   return CheckDependencies(base::Bind(&IsAvailableToManifestForBind,
 419                                       extension_id,
 420                                       type,
 421                                       location,
 422                                       manifest_version,
 423                                       platform));
 424 }
 425
 426 Feature::Availability SimpleFeature::IsAvailableToContext(
 427     const Extension* extension,
 428     SimpleFeature::Context context,
 429     const GURL& url,
 430     SimpleFeature::Platform platform) const {
 431   if (extension) {
 432     Availability result = IsAvailableToManifest(extension->id(),
 433                                                 extension->GetType(),
 434                                                 extension->location(),
 435                                                 extension->manifest_version(),
 436                                                 platform);
 437     if (!result.is_available())
 438       return result;
 439   }
 440
 441   if (!contexts_.empty() && !ContainsValue(contexts_, context))
 442     return CreateAvailability(INVALID_CONTEXT, context);
 443
 444   // TODO(kalman): Consider checking |matches_| regardless of context type.
 445   // Fewer surprises, and if the feature configuration wants to isolate
 446   // "matches" from say "blessed_extension" then they can use complex features.
 447   if ((context == WEB_PAGE_CONTEXT || context == WEBUI_CONTEXT) &&
 448       !matches_.MatchesURL(url)) {
 449     return CreateAvailability(INVALID_URL, url);
 450   }
 451
 452   for (const auto& filter : filters_) {
 453     Availability availability =
 454         filter->IsAvailableToContext(extension, context, url, platform);
 455     if (!availability.is_available())
 456       return availability;
 457   }
 458
 459   // TODO(kalman): Assert that if the context was a webpage or WebUI context
 460   // then at some point a "matches" restriction was checked.
 461   return CheckDependencies(base::Bind(
 462       &IsAvailableToContextForBind, extension, context, url, platform));
 463 }
 464
 465 std::string SimpleFeature::GetAvailabilityMessage(
 466     AvailabilityResult result,
 467     Manifest::Type type,
 468     const GURL& url,
 469     Context context) const {
 470   switch (result) {
 471     case IS_AVAILABLE:
 472       return std::string();
 473     case NOT_FOUND_IN_WHITELIST:
 474     case FOUND_IN_BLACKLIST:
 475       return base::StringPrintf(
 476           "'%s' is not allowed for specified extension ID.",
 477           name().c_str());
 478     case INVALID_URL:
 479       return base::StringPrintf("'%s' is not allowed on %s.",
 480                                 name().c_str(), url.spec().c_str());
 481     case INVALID_TYPE:
 482       return base::StringPrintf(
 483           "'%s' is only allowed for %s, but this is a %s.",
 484           name().c_str(),
 485           ListDisplayNames(std::vector<Manifest::Type>(
 486               extension_types_.begin(), extension_types_.end())).c_str(),
 487           GetDisplayName(type).c_str());
 488     case INVALID_CONTEXT:
 489       return base::StringPrintf(
 490           "'%s' is only allowed to run in %s, but this is a %s",
 491           name().c_str(),
 492           ListDisplayNames(std::vector<Context>(
 493               contexts_.begin(), contexts_.end())).c_str(),
 494           GetDisplayName(context).c_str());
 495     case INVALID_LOCATION:
 496       return base::StringPrintf(
 497           "'%s' is not allowed for specified install location.",
 498           name().c_str());
 499     case INVALID_PLATFORM:
 500       return base::StringPrintf(
 501           "'%s' is not allowed for specified platform.",
 502           name().c_str());
 503     case INVALID_MIN_MANIFEST_VERSION:
 504       return base::StringPrintf(
 505           "'%s' requires manifest version of at least %d.",
 506           name().c_str(),
 507           min_manifest_version_);
 508     case INVALID_MAX_MANIFEST_VERSION:
 509       return base::StringPrintf(
 510           "'%s' requires manifest version of %d or lower.",
 511           name().c_str(),
 512           max_manifest_version_);
 513     case NOT_PRESENT:
 514       return base::StringPrintf(
 515           "'%s' requires a different Feature that is not present.",
 516           name().c_str());
 517     case UNSUPPORTED_CHANNEL:
 518       return base::StringPrintf(
 519           "'%s' is unsupported in this version of the platform.",
 520           name().c_str());
 521     case MISSING_COMMAND_LINE_SWITCH:
 522       return base::StringPrintf(
 523           "'%s' requires the '%s' command line switch to be enabled.",
 524           name().c_str(), command_line_switch_.c_str());
 525   }
 526
 527   NOTREACHED();
 528   return std::string();
 529 }
 530
 531 Feature::Availability SimpleFeature::CreateAvailability(
 532     AvailabilityResult result) const {
 533   return Availability(
 534       result, GetAvailabilityMessage(result, Manifest::TYPE_UNKNOWN, GURL(),
 535                                      UNSPECIFIED_CONTEXT));
 536 }
 537
 538 Feature::Availability SimpleFeature::CreateAvailability(
 539     AvailabilityResult result, Manifest::Type type) const {
 540   return Availability(result, GetAvailabilityMessage(result, type, GURL(),
 541                                                      UNSPECIFIED_CONTEXT));
 542 }
 543
 544 Feature::Availability SimpleFeature::CreateAvailability(
 545     AvailabilityResult result,
 546     const GURL& url) const {
 547   return Availability(
 548       result, GetAvailabilityMessage(result, Manifest::TYPE_UNKNOWN, url,
 549                                      UNSPECIFIED_CONTEXT));
 550 }
 551
 552 Feature::Availability SimpleFeature::CreateAvailability(
 553     AvailabilityResult result,
 554     Context context) const {
 555   return Availability(
 556       result, GetAvailabilityMessage(result, Manifest::TYPE_UNKNOWN, GURL(),
 557                                      context));
 558 }
 559
 560 bool SimpleFeature::IsInternal() const {
 561   return false;
 562 }
 563
 564 bool SimpleFeature::IsIdInBlacklist(const std::string& extension_id) const {
 565   return IsIdInList(extension_id, blacklist_);
 566 }
 567
 568 bool SimpleFeature::IsIdInWhitelist(const std::string& extension_id) const {
 569   return IsIdInList(extension_id, whitelist_);
 570 }
 571
 572 // static
 573 bool SimpleFeature::IsIdInArray(const std::string& extension_id,
 574                                 const char* const array[],
 575                                 size_t array_length) {
 576   if (!IsValidExtensionId(extension_id))
 577     return false;
 578
 579   const char* const* start = array;
 580   const char* const* end = array + array_length;
 581
 582   return ((std::find(start, end, extension_id) != end) ||
 583           (std::find(start, end, HashedIdInHex(extension_id)) != end));
 584 }
 585
 586 // static
 587 bool SimpleFeature::IsIdInList(const std::string& extension_id,
 588                                const std::vector<std::string>& list) {
 589   if (!IsValidExtensionId(extension_id))
 590     return false;
 591
 592   return (ContainsValue(list, extension_id) ||
 593           ContainsValue(list, HashedIdInHex(extension_id)));
 594 }
 595
 596 bool SimpleFeature::MatchesManifestLocation(
 597     Manifest::Location manifest_location) const {
 598   switch (location_) {
 599     case SimpleFeature::UNSPECIFIED_LOCATION:
 600       return true;
 601     case SimpleFeature::COMPONENT_LOCATION:
 602       return manifest_location == Manifest::COMPONENT;
 603     case SimpleFeature::EXTERNAL_COMPONENT_LOCATION:
 604       return manifest_location == Manifest::EXTERNAL_COMPONENT;
 605     case SimpleFeature::POLICY_LOCATION:
 606       return manifest_location == Manifest::EXTERNAL_POLICY ||
 607              manifest_location == Manifest::EXTERNAL_POLICY_DOWNLOAD;
 608   }
 609   NOTREACHED();
 610   return false;
 611 }
 612
 613 Feature::Availability SimpleFeature::CheckDependencies(
 614     const base::Callback<Availability(const Feature*)>& checker) const {
 615   for (const auto& dep_name : dependencies_) {
 616     Feature* dependency =
 617         ExtensionAPI::GetSharedInstance()->GetFeatureDependency(dep_name);
 618     if (!dependency)
 619       return CreateAvailability(NOT_PRESENT);
 620     Availability dependency_availability = checker.Run(dependency);
 621     if (!dependency_availability.is_available())
 622       return dependency_availability;
 623   }
 624   return CreateAvailability(IS_AVAILABLE);
 625 }
 626
 627 // static
 628 bool SimpleFeature::IsValidExtensionId(const std::string& extension_id) {
 629   // Belt-and-suspenders philosophy here. We should be pretty confident by this
 630   // point that we've validated the extension ID format, but in case something
 631   // slips through, we avoid a class of attack where creative ID manipulation
 632   // leads to hash collisions.
 633   // 128 bits / 4 = 32 mpdecimal characters
 634   return (extension_id.length() == 32);
 635 }
 636
 637 }  // namespace extensions