media: Refactor supported CDM version check

- Convert runtime DCHECK to compile time static_assert.
- Add helper function to simplify the check logic.
- Use CDM interface version as CdmWrapperImpl template argument to
  simplify some code and check logic.

Bug: 799169,733821
Test: No functionality change.
Change-Id: I2a97be9a507db853eb91b739bf26511492665eee
Reviewed-on: https://chromium-review.googlesource.com/1018144
Reviewed-by: John Rummell <jrummell@chromium.org>
Commit-Queue: Xiaohan Wang <xhwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552070}

media/cdm/cdm_adapter.cc

@@ -412,21 +412,9 @@ void* GetCdmHost(int host_interface_version, void* user_data) {
     return nullptr;
 
   static_assert(
-      cdm::ContentDecryptionModule::Host::kVersion == cdm::Host_9::kVersion,
-      "update the code below");
-
-  // Ensure IsSupportedCdmHostVersion matches implementation of this function.
-  // Always update this DCHECK when updating this function.
-  // If this check fails, update this function and DCHECK or update
-  // IsSupportedCdmHostVersion.
-
-  // TODO(xhwang): Static assert these at compile time.
-  const int kMinVersion = cdm::ContentDecryptionModule_9::kVersion;
-  const int kMaxVersion = cdm::ContentDecryptionModule_10::kVersion;
-  DCHECK(!IsSupportedCdmInterfaceVersion(kMinVersion - 1));
-  for (int version = kMinVersion; version <= kMaxVersion; ++version)
-    DCHECK(IsSupportedCdmInterfaceVersion(version));
-  DCHECK(!IsSupportedCdmInterfaceVersion(kMaxVersion + 1));
+      CheckSupportedCdmHostVersions(9, 10),
+      "Mismatch between GetCdmHost() and IsSupportedCdmHostVersion()");
+
   DCHECK(IsSupportedCdmHostVersion(host_interface_version));
 
   CdmAdapter* cdm_adapter = static_cast<CdmAdapter*>(user_data);

media/cdm/cdm_wrapper.h

@@ -171,30 +171,49 @@ class CdmWrapper {
   DISALLOW_COPY_AND_ASSIGN(CdmWrapper);
 };
 
+// Traits for CDM Interfaces
+template <int CdmInterfaceVersion>
+struct CdmInterfaceTraits {};
+
+template <>
+struct CdmInterfaceTraits<9> {
+  using CdmInterface = cdm::ContentDecryptionModule_9;
+};
+
+template <>
+struct CdmInterfaceTraits<10> {
+  using CdmInterface = cdm::ContentDecryptionModule_10;
+};
+
 // Template class that does the CdmWrapper -> CdmInterface conversion. Default
 // implementations are provided. Any methods that need special treatment should
 // be specialized.
-template <class CdmInterface>
+template <int CdmInterfaceVersion>
 class CdmWrapperImpl : public CdmWrapper {
  public:
+  using CdmInterface =
+      typename CdmInterfaceTraits<CdmInterfaceVersion>::CdmInterface;
+  static_assert(CdmInterfaceVersion == CdmInterface::kVersion,
+                "CDM interface version mismatch.");
+
   static CdmWrapper* Create(CreateCdmFunc create_cdm_func,
                             const char* key_system,
                             uint32_t key_system_size,
                             GetCdmHostFunc get_cdm_host_func,
                             void* user_data) {
     void* cdm_instance =
-        create_cdm_func(CdmInterface::kVersion, key_system, key_system_size,
+        create_cdm_func(CdmInterfaceVersion, key_system, key_system_size,
                         get_cdm_host_func, user_data);
     if (!cdm_instance)
       return nullptr;
 
-    return new CdmWrapperImpl<CdmInterface>(
+    return new CdmWrapperImpl<CdmInterfaceVersion>(
         static_cast<CdmInterface*>(cdm_instance));
   }
 
   ~CdmWrapperImpl() override { cdm_->Destroy(); }
 
-  int GetInterfaceVersion() override { return CdmInterface::kVersion; }
+  int GetInterfaceVersion() override { return CdmInterfaceVersion; }
 
   bool Initialize(bool allow_distinctive_identifier,
                   bool allow_persistent_state,
@@ -320,17 +339,15 @@ class CdmWrapperImpl : public CdmWrapper {
 // TODO(crbug.com/799219): Remove when CDM_9 no longer supported.
 
 template <>
-bool CdmWrapperImpl<cdm::ContentDecryptionModule_9>::Initialize(
-    bool allow_distinctive_identifier,
-    bool allow_persistent_state,
-    bool /* use_hw_secure_codecs*/) {
+bool CdmWrapperImpl<9>::Initialize(bool allow_distinctive_identifier,
+                                   bool allow_persistent_state,
+                                   bool /* use_hw_secure_codecs*/) {
   cdm_->Initialize(allow_distinctive_identifier, allow_persistent_state);
   return false;
 }
 
 template <>
-cdm::Status
-CdmWrapperImpl<cdm::ContentDecryptionModule_9>::InitializeAudioDecoder(
+cdm::Status CdmWrapperImpl<9>::InitializeAudioDecoder(
     const cdm::AudioDecoderConfig_2& audio_decoder_config) {
   if (!IsEncryptionSchemeSupportedByLegacyCdms(
           audio_decoder_config.encryption_scheme))
@@ -341,8 +358,7 @@ CdmWrapperImpl<cdm::ContentDecryptionModule_9>::InitializeAudioDecoder(
 }
 
 template <>
-cdm::Status
-CdmWrapperImpl<cdm::ContentDecryptionModule_9>::InitializeVideoDecoder(
+cdm::Status CdmWrapperImpl<9>::InitializeVideoDecoder(
     const cdm::VideoDecoderConfig_2& video_decoder_config) {
   if (!IsEncryptionSchemeSupportedByLegacyCdms(
           video_decoder_config.encryption_scheme))
@@ -353,7 +369,7 @@ CdmWrapperImpl<cdm::ContentDecryptionModule_9>::InitializeVideoDecoder(
 }
 
 template <>
-cdm::Status CdmWrapperImpl<cdm::ContentDecryptionModule_9>::Decrypt(
+cdm::Status CdmWrapperImpl<9>::Decrypt(
     const cdm::InputBuffer_2& encrypted_buffer,
     cdm::DecryptedBlock* decrypted_buffer) {
   if (!IsEncryptionSchemeSupportedByLegacyCdms(
@@ -364,8 +380,7 @@ cdm::Status CdmWrapperImpl<cdm::ContentDecryptionModule_9>::Decrypt(
 }
 
 template <>
-cdm::Status
-CdmWrapperImpl<cdm::ContentDecryptionModule_9>::DecryptAndDecodeFrame(
+cdm::Status CdmWrapperImpl<9>::DecryptAndDecodeFrame(
     const cdm::InputBuffer_2& encrypted_buffer,
     cdm::VideoFrame* video_frame) {
   if (!IsEncryptionSchemeSupportedByLegacyCdms(
@@ -377,8 +392,7 @@ CdmWrapperImpl<cdm::ContentDecryptionModule_9>::DecryptAndDecodeFrame(
 }
 
 template <>
-cdm::Status
-CdmWrapperImpl<cdm::ContentDecryptionModule_9>::DecryptAndDecodeSamples(
+cdm::Status CdmWrapperImpl<9>::DecryptAndDecodeSamples(
     const cdm::InputBuffer_2& encrypted_buffer,
     cdm::AudioFrames* audio_frames) {
   if (!IsEncryptionSchemeSupportedByLegacyCdms(
@@ -395,53 +409,32 @@ CdmWrapper* CdmWrapper::Create(CreateCdmFunc create_cdm_func,
                                uint32_t key_system_size,
                                GetCdmHostFunc get_cdm_host_func,
                                void* user_data) {
-  // cdm::ContentDecryptionModule::kVersion is always the latest stable version.
-  static_assert(cdm::ContentDecryptionModule::kVersion ==
-                    cdm::ContentDecryptionModule_9::kVersion,
-                "update the code below");
-
-  // Ensure IsSupportedCdmInterfaceVersion() matches this implementation.
-  // Always update this DCHECK when updating this function.
-  // If this check fails, update this function and DCHECK or update
-  // IsSupportedCdmInterfaceVersion().
-  // TODO(xhwang): Static assert these at compile time.
-  const int kMinVersion = cdm::ContentDecryptionModule_9::kVersion;
-  const int kMaxVersion = cdm::ContentDecryptionModule_10::kVersion;
-  DCHECK(!IsSupportedCdmInterfaceVersion(kMinVersion - 1));
-  for (int version = kMinVersion; version <= kMaxVersion; ++version)
-    DCHECK(IsSupportedCdmInterfaceVersion(version));
-  DCHECK(!IsSupportedCdmInterfaceVersion(kMaxVersion + 1));
+  static_assert(CheckSupportedCdmInterfaceVersions(9, 10),
+                "Mismatch between CdmWrapper::Create() and "
+                "IsSupportedCdmInterfaceVersion()");
 
   // Try to create the CDM using the latest CDM interface version.
   // This is only attempted if requested.
   CdmWrapper* cdm_wrapper = nullptr;
 
   // TODO(xhwang): Check whether we can use static loops to simplify this code.
   if (IsExperimentalCdmInterfaceSupported()) {
-    cdm_wrapper = CdmWrapperImpl<cdm::ContentDecryptionModule_10>::Create(
-        create_cdm_func, key_system, key_system_size, get_cdm_host_func,
-        user_data);
+    cdm_wrapper =
+        CdmWrapperImpl<10>::Create(create_cdm_func, key_system, key_system_size,
+                                   get_cdm_host_func, user_data);
   }
 
   // If |cdm_wrapper| is NULL, try to create the CDM using older supported
   // versions of the CDM interface here.
   if (!cdm_wrapper) {
-    cdm_wrapper = CdmWrapperImpl<cdm::ContentDecryptionModule_9>::Create(
-        create_cdm_func, key_system, key_system_size, get_cdm_host_func,
-        user_data);
+    cdm_wrapper =
+        CdmWrapperImpl<9>::Create(create_cdm_func, key_system, key_system_size,
+                                  get_cdm_host_func, user_data);
   }
 
   return cdm_wrapper;
 }
 
-// When updating the CdmAdapter, ensure you've updated the CdmWrapper to contain
-// stub implementations for new or modified methods that the older CDM interface
-// does not have.
-// Also update supported_cdm_versions.h.
-static_assert(cdm::ContentDecryptionModule::kVersion ==
-                  cdm::ContentDecryptionModule_9::kVersion,
-              "ensure cdm wrapper templates have old version support");
-
 }  // namespace media
 
 #endif  // MEDIA_CDM_CDM_WRAPPER_H_

media/cdm/supported_cdm_versions.cc

@@ -4,8 +4,6 @@
 
 #include "media/cdm/supported_cdm_versions.h"
 
-#include "media/cdm/api/content_decryption_module.h"
-
 namespace media {
 
 bool IsSupportedCdmModuleVersion(int version) {
@@ -18,32 +16,4 @@ bool IsSupportedCdmModuleVersion(int version) {
   }
 }
 
-bool IsSupportedCdmInterfaceVersion(int version) {
-  static_assert(cdm::ContentDecryptionModule::kVersion ==
-                    cdm::ContentDecryptionModule_9::kVersion,
-                "update the code below");
-  switch (version) {
-    // Supported versions in decreasing order.
-    case cdm::ContentDecryptionModule_10::kVersion:
-    case cdm::ContentDecryptionModule_9::kVersion:
-      return true;
-    default:
-      return false;
-  }
-}
-
-bool IsSupportedCdmHostVersion(int version) {
-  static_assert(cdm::ContentDecryptionModule::Host::kVersion ==
-                    cdm::ContentDecryptionModule_9::Host::kVersion,
-                "update the code below");
-  switch (version) {
-    // Supported versions in decreasing order.
-    case cdm::Host_10::kVersion:
-    case cdm::Host_9::kVersion:
-      return true;
-    default:
-      return false;
-  }
-}
-
 }  // namespace media

media/cdm/supported_cdm_versions.h

@@ -6,14 +6,91 @@
 #define MEDIA_CDM_SUPPORTED_CDM_VERSIONS_H_
 
 #include "media/base/media_export.h"
+#include "media/cdm/api/content_decryption_module.h"
 
 namespace media {
 
+namespace {
+
+typedef bool (*VersionCheckFunc)(int version);
+
+// Returns true if all versions in the range [min_version, max_version] and no
+// versions outside the range are supported, and false otherwise.
+constexpr bool CheckSupportedVersions(VersionCheckFunc check_func,
+                                      int min_version,
+                                      int max_version) {
+  // For simplicity, only check one version out of the range boundary.
+  if (check_func(min_version - 1) || check_func(max_version + 1))
+    return false;
+
+  for (int version = min_version; version <= max_version; ++version) {
+    if (!check_func(version))
+      return false;
+  }
+
+  return true;
+}
+
+}  // namespace
+
 MEDIA_EXPORT bool IsSupportedCdmModuleVersion(int version);
 
-MEDIA_EXPORT bool IsSupportedCdmInterfaceVersion(int version);
+constexpr bool IsSupportedCdmInterfaceVersion(int version) {
+  static_assert(cdm::ContentDecryptionModule::kVersion ==
+                    cdm::ContentDecryptionModule_9::kVersion,
+                "update the code below");
+  switch (version) {
+    // Supported versions in decreasing order.
+    case cdm::ContentDecryptionModule_10::kVersion:
+    case cdm::ContentDecryptionModule_9::kVersion:
+      return true;
+    default:
+      return false;
+  }
+}
+
+constexpr bool IsSupportedCdmHostVersion(int version) {
+  static_assert(cdm::ContentDecryptionModule::Host::kVersion ==
+                    cdm::ContentDecryptionModule_9::Host::kVersion,
+                "update the code below");
+  switch (version) {
+    // Supported versions in decreasing order.
+    case cdm::Host_10::kVersion:
+    case cdm::Host_9::kVersion:
+      return true;
+    default:
+      return false;
+  }
+}
+
+// Ensures CDM interface versions in and only in the range [min_version,
+// max_version] are supported.
+constexpr bool CheckSupportedCdmInterfaceVersions(int min_version,
+                                                  int max_version) {
+  // The latest stable CDM interface should always be supported.
+  int latest_stable_version = cdm::ContentDecryptionModule::kVersion;
+  if (latest_stable_version < min_version ||
+      latest_stable_version > max_version) {
+    return false;
+  }
+
+  return CheckSupportedVersions(IsSupportedCdmInterfaceVersion, min_version,
+                                max_version);
+}
+
+// Ensures CDM host interface versions in and only in the range [min_version,
+// max_version] are supported.
+constexpr bool CheckSupportedCdmHostVersions(int min_version, int max_version) {
+  // The latest stable CDM Host interface should always be supported.
+  int latest_stable_version = cdm::ContentDecryptionModule::Host::kVersion;
+  if (latest_stable_version < min_version ||
+      latest_stable_version > max_version) {
+    return false;
+  }
 
-MEDIA_EXPORT bool IsSupportedCdmHostVersion(int version);
+  return CheckSupportedVersions(IsSupportedCdmHostVersion, min_version,
+                                max_version);
+}
 
 }  // namespace media