third_party/chromium/media/base/key_systems.cc

// Copyright 2013 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 "media/base/key_systems.h"

#include <stddef.h>

#include <memory>
#include <unordered_map>

#include "base/cxx17_backports.h"
#include "base/logging.h"
#include "base/no_destructor.h"
#include "base/notreached.h"
#include "base/strings/string_util.h"
#include "base/threading/thread_checker.h"
#include "base/time/time.h"
#include "build/build_config.h"
#include "media/base/key_system_names.h"
#include "media/base/key_system_properties.h"
#include "media/base/media.h"
#include "media/base/media_client.h"
#include "media/base/media_switches.h"
#include "media/base/mime_util.h"
#include "media/media_buildflags.h"
#include "third_party/widevine/cdm/widevine_cdm_common.h"

namespace media {

const char kClearKeyKeySystem[] = "org.w3.clearkey";

// These names are used by UMA. Do not change them!
const char kClearKeyKeySystemNameForUMA[] = "ClearKey";
const char kUnknownKeySystemNameForUMA[] = "Unknown";

enum KeySystemForUkm {
  // These values reported to UKM. Do not change their ordinal values.
  kUnknownKeySystemForUkm = 0,
  kClearKeyKeySystemForUkm,
  kWidevineKeySystemForUkm,
};

struct MimeTypeToCodecs {
  const char* mime_type;
  SupportedCodecs codecs;
};

// Mapping between containers and their codecs.
// Only audio codecs can belong to a "audio/*" mime_type, and only video codecs
// can belong to a "video/*" mime_type.
static const MimeTypeToCodecs kMimeTypeToCodecsMap[] = {
    {"audio/webm", EME_CODEC_WEBM_AUDIO_ALL},
    {"video/webm", EME_CODEC_WEBM_VIDEO_ALL},
    {"audio/mp4", EME_CODEC_MP4_AUDIO_ALL},
    {"video/mp4", EME_CODEC_MP4_VIDEO_ALL},
#if BUILDFLAG(USE_PROPRIETARY_CODECS)
#if BUILDFLAG(ENABLE_MSE_MPEG2TS_STREAM_PARSER)
    {"video/mp2t", EME_CODEC_MP2T_VIDEO_ALL},
#endif  // BUILDFLAG(ENABLE_MSE_MPEG2TS_STREAM_PARSER)
#endif  // BUILDFLAG(USE_PROPRIETARY_CODECS)
};      // namespace media

EmeCodec ToAudioEmeCodec(AudioCodec codec) {
  switch (codec) {
    case AudioCodec::kAAC:
      return EME_CODEC_AAC;
    case AudioCodec::kVorbis:
      return EME_CODEC_VORBIS;
    case AudioCodec::kFLAC:
      return EME_CODEC_FLAC;
    case AudioCodec::kOpus:
      return EME_CODEC_OPUS;
    case AudioCodec::kEAC3:
      return EME_CODEC_EAC3;
    case AudioCodec::kAC3:
      return EME_CODEC_AC3;
    case AudioCodec::kMpegHAudio:
      return EME_CODEC_MPEG_H_AUDIO;
    default:
      DVLOG(1) << "Unsupported AudioCodec " << codec;
      return EME_CODEC_NONE;
  }
}

EmeCodec ToVideoEmeCodec(VideoCodec codec, VideoCodecProfile profile) {
  switch (codec) {
    case VideoCodec::kH264:
      return EME_CODEC_AVC1;
    case VideoCodec::kVP8:
      return EME_CODEC_VP8;
    case VideoCodec::kVP9:
      // ParseVideoCodecString() returns VIDEO_CODEC_PROFILE_UNKNOWN for "vp9"
      // and "vp9.0". Since these codecs are essentially the same as profile 0,
      // return EME_CODEC_VP9_PROFILE0.
      if (profile == VP9PROFILE_PROFILE0 ||
          profile == VIDEO_CODEC_PROFILE_UNKNOWN) {
        return EME_CODEC_VP9_PROFILE0;
      } else if (profile == VP9PROFILE_PROFILE2) {
        return EME_CODEC_VP9_PROFILE2;
      } else {
        // Profile 1 and 3 not supported by EME. See https://crbug.com/898298.
        return EME_CODEC_NONE;
      }
    case VideoCodec::kHEVC:
      // Only handle Main and Main10 profiles for HEVC.
      if (profile == HEVCPROFILE_MAIN)
        return EME_CODEC_HEVC_PROFILE_MAIN;
      if (profile == HEVCPROFILE_MAIN10)
        return EME_CODEC_HEVC_PROFILE_MAIN10;
      return EME_CODEC_NONE;
    case VideoCodec::kDolbyVision:
      // Only profiles 0, 4, 5, 7, 8, 9 are valid. Profile 0 and 9 are encoded
      // based on AVC while profile 4, 5, 7 and 8 are based on HEVC.
      if (profile == DOLBYVISION_PROFILE0 || profile == DOLBYVISION_PROFILE9) {
        return EME_CODEC_DOLBY_VISION_AVC;
      } else if (profile == DOLBYVISION_PROFILE4 ||
                 profile == DOLBYVISION_PROFILE5 ||
                 profile == DOLBYVISION_PROFILE7 ||
                 profile == DOLBYVISION_PROFILE8) {
        return EME_CODEC_DOLBY_VISION_HEVC;
      } else {
        return EME_CODEC_NONE;
      }
    case VideoCodec::kAV1:
      return EME_CODEC_AV1;
    default:
      DVLOG(1) << "Unsupported VideoCodec " << codec;
      return EME_CODEC_NONE;
  }
}

class ClearKeyProperties : public KeySystemProperties {
 public:
  std::string GetKeySystemName() const override { return kClearKeyKeySystem; }

  bool IsSupportedInitDataType(EmeInitDataType init_data_type) const override {
    return init_data_type == EmeInitDataType::CENC ||
           init_data_type == EmeInitDataType::WEBM ||
           init_data_type == EmeInitDataType::KEYIDS;
  }

  media::EmeConfigRule GetEncryptionSchemeConfigRule(
      media::EncryptionScheme encryption_scheme) const override {
    switch (encryption_scheme) {
      case media::EncryptionScheme::kCenc:
      case media::EncryptionScheme::kCbcs:
        return media::EmeConfigRule::SUPPORTED;
      case media::EncryptionScheme::kUnencrypted:
        break;
    }
    NOTREACHED();
    return media::EmeConfigRule::NOT_SUPPORTED;
  }

  SupportedCodecs GetSupportedCodecs() const override {
    // On Android, Vorbis, VP8, AAC and AVC1 are supported in MediaCodec:
    // http://developer.android.com/guide/appendix/media-formats.html
    // VP9 support is device dependent.
    return EME_CODEC_WEBM_ALL | EME_CODEC_MP4_ALL;
  }

  EmeConfigRule GetRobustnessConfigRule(
      EmeMediaType media_type,
      const std::string& requested_robustness,
      const bool* /*hw_secure_requirement*/) const override {
    return requested_robustness.empty() ? EmeConfigRule::SUPPORTED
                                        : EmeConfigRule::NOT_SUPPORTED;
  }

  EmeSessionTypeSupport GetPersistentLicenseSessionSupport() const override {
    return EmeSessionTypeSupport::NOT_SUPPORTED;
  }

  EmeFeatureSupport GetPersistentStateSupport() const override {
    return EmeFeatureSupport::NOT_SUPPORTED;
  }

  EmeFeatureSupport GetDistinctiveIdentifierSupport() const override {
    return EmeFeatureSupport::NOT_SUPPORTED;
  }

  bool UseAesDecryptor() const override { return true; }
};

// Returns whether the |key_system| is known to Chromium and is thus likely to
// be implemented in an interoperable way.
// True is always returned for a |key_system| that begins with "x-".
//
// As with other web platform features, advertising support for a key system
// implies that it adheres to a defined and interoperable specification.
//
// To ensure interoperability, implementations of a specific |key_system| string
// must conform to a specification for that identifier that defines
// key system-specific behaviors not fully defined by the EME specification.
// That specification should be provided by the owner of the domain that is the
// reverse of the |key_system| string.
// This involves more than calling a library, SDK, or platform API.
// KeySystemsImpl must be populated appropriately, and there will likely be glue
// code to adapt to the API of the library, SDK, or platform API.
//
// Chromium mainline contains this data and glue code for specific key systems,
// which should help ensure interoperability with other implementations using
// these key systems.
//
// If you need to add support for other key systems, ensure that you have
// obtained the specification for how to integrate it with EME, implemented the
// appropriate glue/adapter code, and added all the appropriate data to
// KeySystemsImpl. Only then should you change this function.
static bool IsPotentiallySupportedKeySystem(const std::string& key_system) {
  // Known and supported key systems.
  if (key_system == kWidevineKeySystem)
    return true;
  if (key_system == kClearKeyKeySystem)
    return true;

  // External Clear Key is known and supports suffixes for testing.
  if (IsExternalClearKey(key_system))
    return true;

  // Chromecast defines behaviors for Cast clients within its reverse domain.
  const char kChromecastRoot[] = "com.chromecast";
  if (IsSubKeySystemOf(key_system, kChromecastRoot))
    return true;

  // Implementations that do not have a specification or appropriate glue code
  // can use the "x-" prefix to avoid conflicting with and advertising support
  // for real key system names. Use is discouraged.
  const char kExcludedPrefix[] = "x-";
  return base::StartsWith(key_system, kExcludedPrefix,
                          base::CompareCase::SENSITIVE);
}

class KeySystemsImpl : public KeySystems {
 public:
  static KeySystemsImpl* GetInstance();

  // These two functions are for testing purpose only.
  void AddCodecMaskForTesting(EmeMediaType media_type,
                              const std::string& codec,
                              uint32_t mask);
  void AddMimeTypeCodecMaskForTesting(const std::string& mime_type,
                                      uint32_t mask);

  // Implementation of KeySystems interface.
  void UpdateIfNeeded() override;

  bool IsSupportedKeySystem(const std::string& key_system) const override;

  bool CanUseAesDecryptor(const std::string& key_system) const override;

  bool IsSupportedInitDataType(const std::string& key_system,
                               EmeInitDataType init_data_type) const override;

  EmeConfigRule GetEncryptionSchemeConfigRule(
      const std::string& key_system,
      EncryptionScheme encryption_scheme) const override;

  EmeConfigRule GetContentTypeConfigRule(
      const std::string& key_system,
      EmeMediaType media_type,
      const std::string& container_mime_type,
      const std::vector<std::string>& codecs) const override;

  EmeConfigRule GetRobustnessConfigRule(
      const std::string& key_system,
      EmeMediaType media_type,
      const std::string& requested_robustness,
      const bool* hw_secure_requirement) const override;

  EmeSessionTypeSupport GetPersistentLicenseSessionSupport(
      const std::string& key_system) const override;

  EmeFeatureSupport GetPersistentStateSupport(
      const std::string& key_system) const override;

  EmeFeatureSupport GetDistinctiveIdentifierSupport(
      const std::string& key_system) const override;

 private:
  friend class base::NoDestructor<KeySystemsImpl>;

  KeySystemsImpl();
  ~KeySystemsImpl() override;

  void InitializeUMAInfo();

  void UpdateSupportedKeySystems();

  void AddSupportedKeySystems(
      std::vector<std::unique_ptr<KeySystemProperties>> key_systems);

  void RegisterMimeType(const std::string& mime_type, SupportedCodecs codecs);
  bool IsValidMimeTypeCodecsCombination(const std::string& mime_type,
                                        SupportedCodecs codecs) const;

  typedef std::unordered_map<std::string, std::unique_ptr<KeySystemProperties>>
      KeySystemPropertiesMap;
  typedef std::unordered_map<std::string, SupportedCodecs> MimeTypeToCodecsMap;
  typedef std::unordered_map<std::string, EmeCodec> CodecMap;
  typedef std::unordered_map<std::string, EmeInitDataType> InitDataTypesMap;

  // TODO(sandersd): Separate container enum from codec mask value.
  // http://crbug.com/417440
  // Potentially pass EmeMediaType and a container enum.
  SupportedCodecs GetCodecMaskForMimeType(
      const std::string& container_mime_type) const;

  // Converts a full |codec_string| (e.g. vp09.02.10.10) to an EmeCodec. Returns
  // EME_CODEC_NONE is the |codec_string| is invalid or not supported by EME.
  EmeCodec GetEmeCodecForString(EmeMediaType media_type,
                                const std::string& container_mime_type,
                                const std::string& codec_string) const;

  // Map from key system string to KeySystemProperties instance.
  KeySystemPropertiesMap key_system_properties_map_;

  // This member should only be modified by RegisterMimeType().
  MimeTypeToCodecsMap mime_type_to_codecs_map_;

  // For unit test only.
  CodecMap codec_map_for_testing_;

  SupportedCodecs audio_codec_mask_;
  SupportedCodecs video_codec_mask_;

  // Makes sure all methods are called from the same thread.
  base::ThreadChecker thread_checker_;

  DISALLOW_COPY_AND_ASSIGN(KeySystemsImpl);
};

KeySystemsImpl* KeySystemsImpl::GetInstance() {
  static base::NoDestructor<KeySystemsImpl> key_systems;
  key_systems->UpdateIfNeeded();
  return key_systems.get();
}

// Because we use a thread-safe static, the key systems info must be populated
// when the instance is constructed.
KeySystemsImpl::KeySystemsImpl()
    : audio_codec_mask_(EME_CODEC_AUDIO_ALL),
      video_codec_mask_(EME_CODEC_VIDEO_ALL) {
  for (size_t i = 0; i < base::size(kMimeTypeToCodecsMap); ++i) {
    RegisterMimeType(kMimeTypeToCodecsMap[i].mime_type,
                     kMimeTypeToCodecsMap[i].codecs);
  }

  // Always update supported key systems during construction.
  UpdateSupportedKeySystems();
}

KeySystemsImpl::~KeySystemsImpl() = default;

SupportedCodecs KeySystemsImpl::GetCodecMaskForMimeType(
    const std::string& container_mime_type) const {
  auto iter = mime_type_to_codecs_map_.find(container_mime_type);
  if (iter == mime_type_to_codecs_map_.end())
    return EME_CODEC_NONE;

  DCHECK(IsValidMimeTypeCodecsCombination(container_mime_type, iter->second));
  return iter->second;
}

EmeCodec KeySystemsImpl::GetEmeCodecForString(
    EmeMediaType media_type,
    const std::string& container_mime_type,
    const std::string& codec_string) const {
  // Per spec, we should already reject empty mime types in
  // GetSupportedCapabilities().
  DCHECK(!container_mime_type.empty());

  // This is not checked because MimeUtil declares "vp9" and "vp9.0" as
  // ambiguous, but they have always been supported by EME.
  // TODO(xhwang): Find out whether we should fix MimeUtil about these cases.
  bool is_ambiguous = true;

  // For testing only.
  auto iter = codec_map_for_testing_.find(codec_string);
  if (iter != codec_map_for_testing_.end())
    return iter->second;

  if (media_type == EmeMediaType::AUDIO) {
    AudioCodec audio_codec = AudioCodec::kUnknown;
    ParseAudioCodecString(container_mime_type, codec_string, &is_ambiguous,
                          &audio_codec);
    DVLOG(3) << "Audio codec = " << audio_codec;
    return ToAudioEmeCodec(audio_codec);
  }

  DCHECK_EQ(media_type, EmeMediaType::VIDEO);

  // In general EmeCodec doesn't care about codec profiles and assumes the same
  // level of profile support as Chromium, which is checked in
  // KeySystemConfigSelector::IsSupportedContentType(). However, there are a few
  // exceptions where we need to know the profile. For example, for VP9, there
  // are older CDMs only supporting profile 0, hence EmeCodec differentiate
  // between VP9 profile 0 and higher profiles.
  VideoCodec video_codec = VideoCodec::kUnknown;
  VideoCodecProfile profile = VIDEO_CODEC_PROFILE_UNKNOWN;
  uint8_t level = 0;
  VideoColorSpace color_space;
  ParseVideoCodecString(container_mime_type, codec_string, &is_ambiguous,
                        &video_codec, &profile, &level, &color_space);
  DVLOG(3) << "Video codec = " << video_codec << ", profile = " << profile;
  return ToVideoEmeCodec(video_codec, profile);
}

void KeySystemsImpl::UpdateIfNeeded() {
  if (GetMediaClient() && GetMediaClient()->IsKeySystemsUpdateNeeded())
    UpdateSupportedKeySystems();
}

void KeySystemsImpl::UpdateSupportedKeySystems() {
  DCHECK(thread_checker_.CalledOnValidThread());
  key_system_properties_map_.clear();

  std::vector<std::unique_ptr<KeySystemProperties>> key_systems_properties;

  // Add key systems supported by the MediaClient implementation.
  if (GetMediaClient()) {
    GetMediaClient()->AddSupportedKeySystems(&key_systems_properties);
  } else {
    DVLOG(1) << __func__ << " No media client to provide key systems";
  }

  // Clear Key is always supported.
  key_systems_properties.emplace_back(new ClearKeyProperties());

  AddSupportedKeySystems(std::move(key_systems_properties));
}

// Returns whether distinctive identifiers and persistent state can be reliably
// blocked for |properties| (and therefore be safely configurable).
static bool CanBlock(const KeySystemProperties& properties) {
  // When AesDecryptor is used, we are sure we can block.
  if (properties.UseAesDecryptor())
    return true;

  // For External Clear Key, it is either implemented as a library CDM (Clear
  // Key CDM), which is covered above, or by using AesDecryptor remotely, e.g.
  // via MojoCdm. In both cases, we can block. This is only used for testing.
  if (base::FeatureList::IsEnabled(media::kExternalClearKeyForTesting) &&
      IsExternalClearKey(properties.GetKeySystemName()))
    return true;

#if BUILDFLAG(ENABLE_LIBRARY_CDMS)
  // When library CDMs are enabled, we are either using AesDecryptor, or using
  // the library CDM hosted in a sandboxed process. In both cases distinctive
  // identifiers and persistent state can be reliably blocked.
  return true;
#else
  // For other platforms assume the CDM can and will do anything. So we cannot
  // block.
  return false;
#endif
}

void KeySystemsImpl::AddSupportedKeySystems(
    std::vector<std::unique_ptr<KeySystemProperties>> key_systems) {
  DCHECK(thread_checker_.CalledOnValidThread());
  DCHECK(key_system_properties_map_.empty());

  for (auto& properties : key_systems) {
    DCHECK(!properties->GetKeySystemName().empty());
    DCHECK(properties->GetPersistentLicenseSessionSupport() !=
           EmeSessionTypeSupport::INVALID);
    DCHECK(properties->GetPersistentStateSupport() !=
           EmeFeatureSupport::INVALID);
    DCHECK(properties->GetDistinctiveIdentifierSupport() !=
           EmeFeatureSupport::INVALID);

    if (!IsPotentiallySupportedKeySystem(properties->GetKeySystemName())) {
      // If you encounter this path, see the comments for the function above.
      DLOG(ERROR) << "Unsupported name '" << properties->GetKeySystemName()
                  << "'. See code comments.";
      continue;
    }

    // Supporting persistent state is a prerequisite for supporting persistent
    // sessions.
    if (properties->GetPersistentStateSupport() ==
        EmeFeatureSupport::NOT_SUPPORTED) {
      DCHECK(properties->GetPersistentLicenseSessionSupport() ==
             EmeSessionTypeSupport::NOT_SUPPORTED);
    }

    // If distinctive identifiers are not supported, then no other features can
    // require them.
    if (properties->GetDistinctiveIdentifierSupport() ==
        EmeFeatureSupport::NOT_SUPPORTED) {
      DCHECK(properties->GetPersistentLicenseSessionSupport() !=
             EmeSessionTypeSupport::SUPPORTED_WITH_IDENTIFIER);
    }

    if (!CanBlock(*properties)) {
      DCHECK(properties->GetDistinctiveIdentifierSupport() ==
             EmeFeatureSupport::ALWAYS_ENABLED);
      DCHECK(properties->GetPersistentStateSupport() ==
             EmeFeatureSupport::ALWAYS_ENABLED);
    }

    DCHECK_EQ(key_system_properties_map_.count(properties->GetKeySystemName()),
              0u)
        << "Key system '" << properties->GetKeySystemName()
        << "' already registered";

#if defined(OS_ANDROID)
    // Ensure that the renderer can access the decoders necessary to use the
    // key system.
    if (!properties->UseAesDecryptor() && !HasPlatformDecoderSupport()) {
      DLOG(WARNING) << properties->GetKeySystemName() << " not registered";
      continue;
    }
#endif  // defined(OS_ANDROID)

    DVLOG(1) << __func__
             << ": Adding key system:" << properties->GetKeySystemName();
    key_system_properties_map_[properties->GetKeySystemName()] =
        std::move(properties);
  }
}

// Adds the MIME type with the codec mask after verifying the validity.
// Only this function should modify |mime_type_to_codecs_map_|.
void KeySystemsImpl::RegisterMimeType(const std::string& mime_type,
                                      SupportedCodecs codecs) {
  DCHECK(thread_checker_.CalledOnValidThread());
  DCHECK(!mime_type_to_codecs_map_.count(mime_type));
  DCHECK(IsValidMimeTypeCodecsCombination(mime_type, codecs))
      << ": mime_type = " << mime_type << ", codecs = " << codecs;

  mime_type_to_codecs_map_[mime_type] = codecs;
}

// Returns whether |mime_type| follows a valid format and the specified codecs
// are of the correct type based on |*_codec_mask_|.
// Only audio/ or video/ MIME types with their respective codecs are allowed.
bool KeySystemsImpl::IsValidMimeTypeCodecsCombination(
    const std::string& mime_type,
    SupportedCodecs codecs) const {
  DCHECK(thread_checker_.CalledOnValidThread());
  if (codecs == EME_CODEC_NONE)
    return true;

  if (base::StartsWith(mime_type, "audio/", base::CompareCase::SENSITIVE))
    return !(codecs & ~audio_codec_mask_);
  if (base::StartsWith(mime_type, "video/", base::CompareCase::SENSITIVE))
    return !(codecs & ~video_codec_mask_);

  return false;
}

bool KeySystemsImpl::IsSupportedInitDataType(
    const std::string& key_system,
    EmeInitDataType init_data_type) const {
  DCHECK(thread_checker_.CalledOnValidThread());

  auto key_system_iter = key_system_properties_map_.find(key_system);
  if (key_system_iter == key_system_properties_map_.end()) {
    NOTREACHED();
    return false;
  }
  return key_system_iter->second->IsSupportedInitDataType(init_data_type);
}

EmeConfigRule KeySystemsImpl::GetEncryptionSchemeConfigRule(
    const std::string& key_system,
    EncryptionScheme encryption_scheme) const {
  DCHECK(thread_checker_.CalledOnValidThread());

  auto key_system_iter = key_system_properties_map_.find(key_system);
  if (key_system_iter == key_system_properties_map_.end()) {
    NOTREACHED();
    return EmeConfigRule::NOT_SUPPORTED;
  }
  return key_system_iter->second->GetEncryptionSchemeConfigRule(
      encryption_scheme);
}

void KeySystemsImpl::AddCodecMaskForTesting(EmeMediaType media_type,
                                            const std::string& codec,
                                            uint32_t mask) {
  DCHECK(thread_checker_.CalledOnValidThread());
  DCHECK(!codec_map_for_testing_.count(codec));
  codec_map_for_testing_[codec] = static_cast<EmeCodec>(mask);
  if (media_type == EmeMediaType::AUDIO) {
    audio_codec_mask_ |= mask;
  } else {
    video_codec_mask_ |= mask;
  }
}

void KeySystemsImpl::AddMimeTypeCodecMaskForTesting(
    const std::string& mime_type,
    uint32_t codecs_mask) {
  RegisterMimeType(mime_type, static_cast<EmeCodec>(codecs_mask));
}

bool KeySystemsImpl::IsSupportedKeySystem(const std::string& key_system) const {
  DCHECK(thread_checker_.CalledOnValidThread());

  if (!key_system_properties_map_.count(key_system))
    return false;

  return true;
}

bool KeySystemsImpl::CanUseAesDecryptor(const std::string& key_system) const {
  DCHECK(thread_checker_.CalledOnValidThread());

  auto key_system_iter = key_system_properties_map_.find(key_system);
  if (key_system_iter == key_system_properties_map_.end()) {
    DLOG(ERROR) << key_system << " is not a known key system";
    return false;
  }
  return key_system_iter->second->UseAesDecryptor();
}

EmeConfigRule KeySystemsImpl::GetContentTypeConfigRule(
    const std::string& key_system,
    EmeMediaType media_type,
    const std::string& container_mime_type,
    const std::vector<std::string>& codecs) const {
  DCHECK(thread_checker_.CalledOnValidThread());

  // Make sure the container MIME type matches |media_type|.
  switch (media_type) {
    case EmeMediaType::AUDIO:
      if (!base::StartsWith(container_mime_type, "audio/",
                            base::CompareCase::SENSITIVE))
        return EmeConfigRule::NOT_SUPPORTED;
      break;
    case EmeMediaType::VIDEO:
      if (!base::StartsWith(container_mime_type, "video/",
                            base::CompareCase::SENSITIVE))
        return EmeConfigRule::NOT_SUPPORTED;
      break;
  }

  // Double check whether the key system is supported.
  auto key_system_iter = key_system_properties_map_.find(key_system);
  if (key_system_iter == key_system_properties_map_.end()) {
    NOTREACHED()
        << "KeySystemConfigSelector should've checked key system support";
    return EmeConfigRule::NOT_SUPPORTED;
  }

  // Look up the key system's supported codecs and secure codecs.
  SupportedCodecs key_system_codec_mask =
      key_system_iter->second->GetSupportedCodecs();
  SupportedCodecs key_system_hw_secure_codec_mask =
      key_system_iter->second->GetSupportedHwSecureCodecs();

  // Check that the container is supported by the key system. (This check is
  // necessary because |codecs| may be empty.)
  SupportedCodecs mime_type_codec_mask =
      GetCodecMaskForMimeType(container_mime_type);
  if ((key_system_codec_mask & mime_type_codec_mask) == 0) {
    DVLOG(2) << "Container " << container_mime_type << " not supported by "
             << key_system;
    return EmeConfigRule::NOT_SUPPORTED;
  }

  // Check that the codecs are supported by the key system and container based
  // on the following rule:
  // SupportedCodecs  | SupportedSecureCodecs  | Result
  //       yes        |         yes            | SUPPORTED
  //       yes        |         no             | HW_SECURE_CODECS_NOT_ALLOWED
  //       no         |         yes            | HW_SECURE_CODECS_REQUIRED
  //       no         |         no             | NOT_SUPPORTED
  EmeConfigRule support = EmeConfigRule::SUPPORTED;
  for (size_t i = 0; i < codecs.size(); i++) {
    EmeCodec codec =
        GetEmeCodecForString(media_type, container_mime_type, codecs[i]);
    if (codec == EME_CODEC_NONE) {
      DVLOG(2) << "Unsupported codec string \"" << codecs[i] << "\"";
      return EmeConfigRule::NOT_SUPPORTED;
    }

    // Currently all EmeCodecs only have one bit set. In case there could be
    // codecs with multiple bits set, e.g. to cover multiple profiles, we check
    // (codec & mask) == codec instead of (codec & mask) != 0 to make sure all
    // bits are set. Same below.
    if ((codec & key_system_codec_mask & mime_type_codec_mask) != codec &&
        (codec & key_system_hw_secure_codec_mask & mime_type_codec_mask) !=
            codec) {
      DVLOG(2) << "Container/codec pair (" << container_mime_type << " / "
               << codecs[i] << ") not supported by " << key_system;
      return EmeConfigRule::NOT_SUPPORTED;
    }

    // Check whether the codec supports a hardware-secure mode (any level).
    if ((codec & key_system_hw_secure_codec_mask) != codec) {
      DCHECK_EQ(codec & key_system_codec_mask, codec);
      if (support == EmeConfigRule::HW_SECURE_CODECS_REQUIRED)
        return EmeConfigRule::NOT_SUPPORTED;
      support = EmeConfigRule::HW_SECURE_CODECS_NOT_ALLOWED;
    }

    // Check whether the codec requires a hardware-secure mode (any level).
    if ((codec & key_system_codec_mask) != codec) {
      DCHECK_EQ(codec & key_system_hw_secure_codec_mask, codec);
      if (support == EmeConfigRule::HW_SECURE_CODECS_NOT_ALLOWED)
        return EmeConfigRule::NOT_SUPPORTED;
      support = EmeConfigRule::HW_SECURE_CODECS_REQUIRED;
    }
  }

  return support;
}

EmeConfigRule KeySystemsImpl::GetRobustnessConfigRule(
    const std::string& key_system,
    EmeMediaType media_type,
    const std::string& requested_robustness,
    const bool* hw_secure_requirement) const {
  DCHECK(thread_checker_.CalledOnValidThread());

  auto key_system_iter = key_system_properties_map_.find(key_system);
  if (key_system_iter == key_system_properties_map_.end()) {
    NOTREACHED();
    return EmeConfigRule::NOT_SUPPORTED;
  }
  return key_system_iter->second->GetRobustnessConfigRule(
      media_type, requested_robustness, hw_secure_requirement);
}

EmeSessionTypeSupport KeySystemsImpl::GetPersistentLicenseSessionSupport(
    const std::string& key_system) const {
  DCHECK(thread_checker_.CalledOnValidThread());

  auto key_system_iter = key_system_properties_map_.find(key_system);
  if (key_system_iter == key_system_properties_map_.end()) {
    NOTREACHED();
    return EmeSessionTypeSupport::INVALID;
  }
  return key_system_iter->second->GetPersistentLicenseSessionSupport();
}

EmeFeatureSupport KeySystemsImpl::GetPersistentStateSupport(
    const std::string& key_system) const {
  DCHECK(thread_checker_.CalledOnValidThread());

  auto key_system_iter = key_system_properties_map_.find(key_system);
  if (key_system_iter == key_system_properties_map_.end()) {
    NOTREACHED();
    return EmeFeatureSupport::INVALID;
  }
  return key_system_iter->second->GetPersistentStateSupport();
}

EmeFeatureSupport KeySystemsImpl::GetDistinctiveIdentifierSupport(
    const std::string& key_system) const {
  DCHECK(thread_checker_.CalledOnValidThread());

  auto key_system_iter = key_system_properties_map_.find(key_system);
  if (key_system_iter == key_system_properties_map_.end()) {
    NOTREACHED();
    return EmeFeatureSupport::INVALID;
  }
  return key_system_iter->second->GetDistinctiveIdentifierSupport();
}

KeySystems* KeySystems::GetInstance() {
  return KeySystemsImpl::GetInstance();
}

//------------------------------------------------------------------------------

bool IsSupportedKeySystemWithInitDataType(const std::string& key_system,
                                          EmeInitDataType init_data_type) {
  return KeySystemsImpl::GetInstance()->IsSupportedInitDataType(key_system,
                                                                init_data_type);
}

std::string GetKeySystemNameForUMA(const std::string& key_system) {
  // Here we maintain a short list of known key systems to facilitate UMA
  // reporting. Mentioned key systems are not necessarily supported by
  // the current platform.
  if (key_system == kWidevineKeySystem)
    return kWidevineKeySystemNameForUMA;

  if (key_system == kClearKeyKeySystem)
    return kClearKeyKeySystemNameForUMA;

  return kUnknownKeySystemNameForUMA;
}

int GetKeySystemIntForUKM(const std::string& key_system) {
  if (key_system == kWidevineKeySystem)
    return KeySystemForUkm::kWidevineKeySystemForUkm;

  if (key_system == kClearKeyKeySystem)
    return KeySystemForUkm::kClearKeyKeySystemForUkm;

  return KeySystemForUkm::kUnknownKeySystemForUkm;
}

bool CanUseAesDecryptor(const std::string& key_system) {
  return KeySystemsImpl::GetInstance()->CanUseAesDecryptor(key_system);
}

// These two functions are for testing purpose only. The declaration in the
// header file is guarded by "#if defined(UNIT_TEST)" so that they can be used
// by tests but not non-test code. However, this .cc file is compiled as part of
// "media" where "UNIT_TEST" is not defined. So we need to specify
// "MEDIA_EXPORT" here again so that they are visible to tests.

MEDIA_EXPORT void AddCodecMaskForTesting(EmeMediaType media_type,
                                         const std::string& codec,
                                         uint32_t mask) {
  KeySystemsImpl::GetInstance()->AddCodecMaskForTesting(media_type, codec,
                                                        mask);
}

MEDIA_EXPORT void AddMimeTypeCodecMaskForTesting(const std::string& mime_type,
                                                 uint32_t mask) {
  KeySystemsImpl::GetInstance()->AddMimeTypeCodecMaskForTesting(mime_type,
                                                                mask);
}

}  // namespace media