android/libwvdrmengine/cdm/core/src/cdm_engine.cpp

// Copyright 2013 Google Inc. All Rights Reserved.

#include "cdm_engine.h"

#include <iostream>
#include <sstream>

#include "buffer_reader.h"
#include "cdm_session.h"
#include "crypto_engine.h"
#include "device_files.h"
#include "license_protocol.pb.h"
#include "log.h"
#include "properties.h"
#include "string_conversions.h"
#include "wv_cdm_constants.h"
#include "wv_cdm_event_listener.h"

#ifndef CDM_POLICY_TIMER_DURATION_SECONDS
#define CDM_POLICY_TIMER_DURATION_SECONDS 1
#endif

namespace {
const std::string kDefaultProvisioningServerUrl =
  "https://www.googleapis.com/"
  "certificateprovisioning/v1/devicecertificates/create"
  "?key=AIzaSyB-5OLKTx2iU5mko18DfdwK5611JIjbUhE";
}

namespace wvcdm {

// Protobuf generated classes.
using video_widevine_server::sdk::ClientIdentification;
using video_widevine_server::sdk::ProvisioningRequest;
using video_widevine_server::sdk::ProvisioningResponse;
using video_widevine_server::sdk::SignedProvisioningMessage;

typedef std::map<CdmSessionId,CdmSession*>::const_iterator CdmSessionIter;

CdmEngine::CdmEngine() : provisioning_session_(NULL) {
  Properties::Init();
}

CdmEngine::~CdmEngine() {
  CancelSessions();

  CdmSessionMap::iterator i(sessions_.begin());
  for (; i != sessions_.end(); ++i)
    delete i->second;
  sessions_.clear();
}

CdmResponseType CdmEngine::OpenSession(
    const CdmKeySystem& key_system,
    CdmSessionId* session_id) {
  LOGI("CdmEngine::OpenSession");

  if (!ValidateKeySystem(key_system)) {
    LOGI("CdmEngine::OpenSession: invalid key_system = %s", key_system.c_str());
    return KEY_ERROR;
  }

  if (!session_id) {
    LOGE("CdmEngine::OpenSession: no session ID destination provided");
    return KEY_ERROR;
  }

  // TODO(edwinwong, rfrias): Save key_system in session for validation checks
  CdmSession* new_session = new CdmSession();
  if (!new_session) {
    return KEY_ERROR;
  }

  if (new_session->session_id().empty()) {
    LOGE("CdmEngine::OpenSession: failure to generate session ID");
    delete(new_session);
    return UNKNOWN_ERROR;
  }

  CdmSessionId new_session_id = new_session->session_id();

  CdmResponseType sts = new_session->Init();
  if (sts != NO_ERROR) {
    LOGE("CdmEngine::OpenSession: bad session init");
    delete(new_session);
    return sts;
  }

  sessions_[new_session_id] = new_session;
  *session_id = new_session_id;
  return NO_ERROR;
}

CdmResponseType CdmEngine::CloseSession(const CdmSessionId& session_id) {
  LOGI("CdmEngine::CloseSession");

  CdmSessionIter iter = sessions_.find(session_id);
  if (iter == sessions_.end()) {
    LOGE("CdmEngine::CloseSession: session not found = %s", session_id.c_str());
    return KEY_ERROR;
  }

  sessions_.erase(session_id);
  if (sessions_.size() == 0)
    DisablePolicyTimer();
  iter->second->DestroySession();
  delete iter->second;
  return NO_ERROR;
}

CdmResponseType CdmEngine::GenerateKeyRequest(
    const CdmSessionId& session_id,
    bool is_key_system_present,
    const CdmKeySystem& key_system,
    const CdmInitData& init_data,
    const CdmLicenseType license_type,
    CdmAppParameterMap& app_parameters,
    CdmKeyMessage* key_request,
    std::string* server_url) {
  LOGI("CdmEngine::GenerateKeyRequest");

  CdmSessionIter iter = sessions_.find(session_id);
  if (iter == sessions_.end()) {
    LOGE("CdmEngine::GenerateKeyRequest: session_id not found = %s", session_id.c_str());
    return KEY_ERROR;
  }

  if (is_key_system_present) {
    // TODO(edwinwong, rfrias): validate key_system has not changed
  }

  if (!key_request) {
    LOGE("CdmEngine::GenerateKeyRequest: no key request destination provided");
    return KEY_ERROR;
  }

  key_request->clear();

  // TODO(edwinwong, rfrias): need to pass in license type and app parameters
  CdmResponseType sts = iter->second->GenerateKeyRequest(init_data,
                                                         license_type,
                                                         app_parameters,
                                                         key_request,
                                                         server_url);

  if (KEY_MESSAGE != sts) {
    LOGE("CdmEngine::GenerateKeyRequest: key request generation failed, sts=%d",
         (int)sts);
    return sts;
  }

  // TODO(edwinwong, rfrias): persist init_data, license_type, app_parameters
  //                          in session

  return KEY_MESSAGE;
}

CdmResponseType CdmEngine::AddKey(
    const CdmSessionId& session_id,
    const CdmKeyResponse& key_data) {
  LOGI("CdmEngine::AddKey");

  CdmSessionIter iter = sessions_.find(session_id);
  if (iter == sessions_.end()) {
    LOGE("CdmEngine::AddKey: session_id not found = %s", session_id.c_str());
    return KEY_ERROR;
  }

  if (key_data.empty()) {
    LOGE("CdmEngine::AddKey: no key_data");
    return KEY_ERROR;
  }

  CdmResponseType sts = iter->second->AddKey(key_data);
  if (KEY_ADDED != sts) {
    LOGE("CdmEngine::AddKey: keys not added, result = %d", (int)sts);
  }
  EnablePolicyTimer();
  return sts;
}

CdmResponseType CdmEngine::CancelKeyRequest(
    const CdmSessionId& session_id,
    bool is_key_system_present,
    const CdmKeySystem& key_system) {
  LOGI("CdmEngine::CancelKeyRequest");

  //TODO(gmorgan): Issue: what is semantics of canceling a key request. Should
  //this call cancel all keys for the session?
  // TODO(jfore): We should disable the policy timer here if there are no
  // active sessions. Sessions are currently not being destroyed here. We can
  // add this logic once the semantics of canceling the key is worked out.

  CdmSessionIter iter = sessions_.find(session_id);
  if (iter == sessions_.end()) {
    LOGE("CdmEngine::CancelKeyRequest: session_id not found = %s", session_id.c_str());
    return KEY_ERROR;
  }

  if (is_key_system_present) {
    // TODO(edwinwong, rfrias): validate key_system has not changed
  }

  // TODO(edwinwong, rfrias): unload keys here
  DisablePolicyTimer();
  return NO_ERROR;
}

CdmResponseType CdmEngine::GenerateRenewalRequest(
    const CdmSessionId& session_id,
    CdmKeyMessage* key_request,
    std::string* server_url) {
  LOGI("CdmEngine::GenerateRenewalRequest");

  CdmSessionIter iter = sessions_.find(session_id);
  if (iter == sessions_.end()) {
    LOGE("CdmEngine::GenerateRenewalRequest: session_id not found = %s", session_id.c_str());
    return KEY_ERROR;
  }

  if (!key_request) {
    LOGE("CdmEngine::GenerateRenewalRequest: no key request destination provided");
    return KEY_ERROR;
  }

  key_request->clear();

  CdmResponseType sts = iter->second->GenerateRenewalRequest(key_request,
                                                             server_url);

  if (KEY_MESSAGE != sts) {
    LOGE("CdmEngine::GenerateRenewalRequest: key request generation failed, sts=%d",
         (int)sts);
    return sts;
  }

  return KEY_MESSAGE;
}

CdmResponseType CdmEngine::RenewKey(
    const CdmSessionId& session_id,
    const CdmKeyResponse& key_data) {
  LOGI("CdmEngine::RenewKey");

  CdmSessionIter iter = sessions_.find(session_id);
  if (iter == sessions_.end()) {
    LOGE("CdmEngine::RenewKey: session_id not found = %s", session_id.c_str());
    return KEY_ERROR;
  }

  if (key_data.empty()) {
    LOGE("CdmEngine::RenewKey: no key_data");
    return KEY_ERROR;
  }

  CdmResponseType sts = iter->second->RenewKey(key_data);
  if (KEY_ADDED != sts) {
    LOGE("CdmEngine::RenewKey: keys not added, sts=%d", (int)sts);
    return sts;
  }

  return KEY_ADDED;
}

CdmResponseType CdmEngine::QueryStatus(CdmQueryMap* key_info) {
  LOGI("CdmEngine::QueryStatus");
  CryptoEngine* crypto_engine = CryptoEngine::GetInstance();
  if (!crypto_engine) {
    return KEY_ERROR;
  }

  switch (crypto_engine->GetSecurityLevel()) {
    case CryptoEngine::kSecurityLevelL1:
      (*key_info)[QUERY_KEY_SECURITY_LEVEL] = QUERY_VALUE_SECURITY_LEVEL_L1;
      break;
    case CryptoEngine::kSecurityLevelL2:
      (*key_info)[QUERY_KEY_SECURITY_LEVEL] = QUERY_VALUE_SECURITY_LEVEL_L2;
      break;
    case CryptoEngine::kSecurityLevelL3:
      (*key_info)[QUERY_KEY_SECURITY_LEVEL] = QUERY_VALUE_SECURITY_LEVEL_L3;
      break;
    case CryptoEngine::kSecurityLevelUnknown:
      (*key_info)[QUERY_KEY_SECURITY_LEVEL] = QUERY_VALUE_SECURITY_LEVEL_Unknown;
      break;
    default:
      return KEY_ERROR;
  }

  std::string deviceId;
  bool success = crypto_engine->GetDeviceUniqueId(&deviceId);
  if (success) {
    (*key_info)[QUERY_KEY_DEVICE_ID] = deviceId;
  }

  uint32_t system_id;
  success = crypto_engine->GetSystemId(&system_id);
  if (success) {
    std::ostringstream system_id_stream;
    system_id_stream << system_id;
    (*key_info)[QUERY_KEY_SYSTEM_ID] = system_id_stream.str();
  }

  return NO_ERROR;
}

CdmResponseType CdmEngine::QueryKeyStatus(
    const CdmSessionId& session_id,
    CdmQueryMap* key_info) {
  LOGI("CdmEngine::QueryKeyStatus");
  CdmSessionIter iter = sessions_.find(session_id);
  if (iter == sessions_.end()) {
    LOGE("CdmEngine::QueryKeyStatus: session_id not found = %s", session_id.c_str());
    return KEY_ERROR;
  }
  return iter->second->QueryKeyStatus(key_info);
}

CdmResponseType CdmEngine::QueryKeyControlInfo(
    const CdmSessionId& session_id,
    CdmQueryMap* key_info) {
  LOGI("CdmEngine::QueryKeyControlInfo");
  CdmSessionIter iter = sessions_.find(session_id);
  if (iter == sessions_.end()) {
    LOGE("CdmEngine::QueryKeyControlInfo: session_id not found = %s", session_id.c_str());
    return KEY_ERROR;
  }
  return iter->second->QueryKeyControlInfo(key_info);
}

/*
 * The certificate provisioning process creates a cdm and a crypto session.
 * The lives of these sessions are short and therefore, not added to the
 * CdmSessionMap. We need to explicitly delete these objects when error occurs
 * or when we are done with provisioning.
 */
void CdmEngine::CleanupProvisioningSession() {
  if (provisioning_session_) {
    CryptoEngine* crypto_engine = CryptoEngine::GetInstance();
    if (crypto_engine) {
      CdmSessionId cdm_session_id = provisioning_session_->session_id();
      CryptoSession* crypto_session =
          crypto_engine->FindSession(cdm_session_id);
      if (crypto_session) {
        LOGV("delete crypto session for id=%s", cdm_session_id.c_str());
        delete crypto_session;
      } else {
        LOGE("CleanupProvisioningSession: cannot find crypto_session");
      }
    }
    delete provisioning_session_;
    provisioning_session_ = NULL;
  }
}

/*
 * This function converts SignedProvisioningRequest into base64 string.
 * It then wraps it in JSON format expected by the Apiary frontend.
 * Apiary requires the base64 encoding to replace '+' with minus '-',
 * and '/' with underscore '_'; opposite to stubby's.
 *
 * Returns the JSON formated string in *request. The JSON string will be
 * appended as a query parameter, i.e. signedRequest=<base 64 encoded
 * SignedProvisioningRequest>. All base64 '=' padding chars must be removed.
 *
 * The JSON formated request takes the following format:
 *
 * base64 encoded message
 */
void CdmEngine::ComposeJsonRequestAsQueryString(
    const std::string& message,
    CdmProvisioningRequest* request) {

  // performs base64 encoding for message
  std::vector<uint8_t> message_vector(message.begin(), message.end());
  std::string message_b64 = Base64SafeEncode(message_vector);

  // removes trailing '=' padding characters;
  // the encoded string can have at most 2 '=' padding chars, so start
  // searching at the end minus four characters
  size_t found_pos = message_b64.find("=", message_b64.size() - 4);
  if (std::string::npos != found_pos) {
    message_b64.resize(found_pos);
  }
  request->assign(message_b64);
}

/*
 * Composes a device provisioning request and output the request in JSON format
 * in *request. It also returns the default url for the provisioning server
 * in *default_url.
 *
 * Returns NO_ERROR for success and UNKNOWN_ERROR if fails.
 */
CdmResponseType CdmEngine::GetProvisioningRequest(
    CdmProvisioningRequest* request,
    std::string* default_url) {
  if (!request || !default_url) {
    LOGE("GetProvisioningRequest: invalid input parameters");
    return UNKNOWN_ERROR;
  }

  default_url->assign(kDefaultProvisioningServerUrl);

  if (provisioning_session_) {
    CleanupProvisioningSession();
  }

  //
  //---------------------------------------------------------------------------
  // This function can be called before a cdm session is created.
  // First creates a cdm session, then creates a crypto session.
  //
  CdmSession* cdm_session = new CdmSession();
  if (!cdm_session) {
    LOGE("GetProvisioningRequest: fails to create a cdm session");
    return UNKNOWN_ERROR;
  }

  if (cdm_session->session_id().empty()) {
    LOGE("GetProvisioningRequest: fails to generate session ID");
    delete cdm_session;
    return UNKNOWN_ERROR;
  }

  CryptoEngine* crypto_engine = CryptoEngine::GetInstance();
  if (!crypto_engine) {
    LOGE("GetProvisioningRequest: fails to create a crypto engine");
    delete cdm_session;
    return UNKNOWN_ERROR;
  }

  CdmSessionId cdm_session_id = cdm_session->session_id();
  CryptoSession* crypto_session = crypto_engine->CreateSession(cdm_session_id);
  if (!crypto_session) {
    LOGE("GetProvisioningRequest: fails to create a crypto session");
    delete cdm_session;
    return UNKNOWN_ERROR;
  }

  // TODO(edwinwong): replace this cdm session pointer with crypto session
  // pointer if feasible
  provisioning_session_ = cdm_session;
  LOGV("provisioning session id=%s", cdm_session_id.c_str());

  //
  //---------------------------------------------------------------------------
  // Prepares device provisioning request.
  //
  ProvisioningRequest provisioning_request;
  ClientIdentification* client_id = provisioning_request.mutable_client_id();
  client_id->set_type(ClientIdentification::KEYBOX);
  std::string token;
  if (!crypto_engine->GetToken(&token)) {
    LOGE("GetProvisioningRequest: fails to get token");
    CleanupProvisioningSession();
    return UNKNOWN_ERROR;
  }
  client_id->set_token(token);

  uint32_t nonce;
  if (!crypto_session->GenerateNonce(&nonce)) {
    LOGE("GetProvisioningRequest: fails to generate a nonce");
    CleanupProvisioningSession();
    return UNKNOWN_ERROR;
  }

  // The provisioning server does not convert the nonce to uint32_t, it just
  // passes the binary data to the response message.
  std::string the_nonce(reinterpret_cast<char*>(&nonce), sizeof(nonce));
  provisioning_request.set_nonce(the_nonce);

  std::string serialized_message;
  provisioning_request.SerializeToString(&serialized_message);

  // Derives signing and encryption keys and constructs signature.
  std::string request_signature;
  if (!crypto_session->PrepareRequest(serialized_message,
                                      &request_signature, true)) {
    request->clear();
    CleanupProvisioningSession();
    return UNKNOWN_ERROR;
  }
  if (request_signature.empty()) {
     request->clear();
     CleanupProvisioningSession();
     return UNKNOWN_ERROR;
  }

  SignedProvisioningMessage signed_provisioning_msg;
  signed_provisioning_msg.set_message(serialized_message);
  signed_provisioning_msg.set_signature(request_signature);

  std::string serialized_request;
  signed_provisioning_msg.SerializeToString(&serialized_request);

  // converts request into JSON string
  ComposeJsonRequestAsQueryString(serialized_request, request);

  return NO_ERROR;
}

/*
 * Parses the input json_str and locates substring using start_substr and
 * end_stubstr. The found base64 substring is then decoded and returns
 * in *result.
 *
 * Returns true for success and false if fails.
 */
bool CdmEngine::ParseJsonResponse(
    const CdmProvisioningResponse& json_str,
    const std::string& start_substr,
    const std::string& end_substr,
    std::string* result) {
  std::string b64_string;
  size_t start = json_str.find(start_substr);
  if (start == json_str.npos) {
    LOGE("ParseJsonResponse: cannot find start substring");
    return false;
  } else {
    size_t end = json_str.find(end_substr, start + start_substr.length());
    if (end == json_str.npos) {
      LOGE("ParseJsonResponse cannot locate end substring");
      return false;
    }

    size_t b64_string_size = end - start - start_substr.length();
    b64_string.assign(json_str, start + start_substr.length(), b64_string_size);
  }

  // Decodes base64 substring and returns it in *result
  std::vector<uint8_t> result_vector = Base64SafeDecode(b64_string);
  result->assign(result_vector.begin(), result_vector.end());

  return true;
}

/*
 * The response message consists of a device certificate and the device RSA key.
 * The device RSA key is stored in the T.E.E. The device certificate is stored
 * in the device.
 *
 * Returns NO_ERROR for success and UNKNOWN_ERROR if fails.
 */
CdmResponseType CdmEngine::HandleProvisioningResponse(
    CdmProvisioningResponse& response) {
  if (response.empty()) {
    LOGE("Empty provisioning response.");
    return UNKNOWN_ERROR;
  }

  //---------------------------------------------------------------------------
  // Extracts signed response from JSON string, decodes base64 signed response
  const std::string kMessageStart = "\"signedResponse\": \"";
  const std::string kMessageEnd = "\"";
  std::string serialized_signed_response;
  if (!ParseJsonResponse(response, kMessageStart, kMessageEnd,
                         &serialized_signed_response)) {
    LOGE("Fails to extract signed serialized response from JSON response");
    return UNKNOWN_ERROR;
  }

  //
  //---------------------------------------------------------------------------
  // Creates a crypto session using provisioning_session_.
  //
  if (!provisioning_session_) {
    LOGE("HandleProvisioningResponse: invalid provisioning session");
    return UNKNOWN_ERROR;
  }

  CryptoEngine* crypto_engine = CryptoEngine::GetInstance();
  if (!crypto_engine) {
    LOGE("HandleProvisioningResponse: fails to create a crypto engine");
    return UNKNOWN_ERROR;
  }

  CdmSessionId cdm_session_id = provisioning_session_->session_id();
  CryptoSession* crypto_session = crypto_engine->FindSession(cdm_session_id);
  if (!crypto_session) {
    LOGE("HandleProvisioningResponse: fails to find %s",
         cdm_session_id.c_str());
    return UNKNOWN_ERROR;
  }

  //---------------------------------------------------------------------------
  // Authenticates provisioning response using D1s (server key derived from
  // the provisioing request's input). Validate provisioning response and
  // stores private device RSA key and certificate.
  SignedProvisioningMessage signed_response;
  if (!signed_response.ParseFromString(serialized_signed_response)) {
    LOGE("Fails to parse signed serialized response");
    CleanupProvisioningSession();
    return UNKNOWN_ERROR;
  }

  if (!signed_response.has_signature() || !signed_response.has_message()) {
    LOGE("Invalid response - signature or message not found");
    CleanupProvisioningSession();
    return UNKNOWN_ERROR;
  }

  const std::string& signed_message = signed_response.message();
  ProvisioningResponse provisioning_response;

  if (!provisioning_response.ParseFromString(signed_message)) {
    LOGE("Fails to parse signed message");
    CleanupProvisioningSession();
    return UNKNOWN_ERROR;
  }

  if (!provisioning_response.has_device_rsa_key()) {
    LOGE("Invalid response - key not found");
    CleanupProvisioningSession();
    return UNKNOWN_ERROR;
  }

  const std::string& enc_rsa_key = provisioning_response.device_rsa_key();
  const std::string& nonce = provisioning_response.nonce();
  const std::string& rsa_key_iv = provisioning_response.device_rsa_key_iv();
  const std::string& signature = signed_response.signature();

  std::string wrapped_rsa_key;
  if (!crypto_session->RewrapDeviceRSAKey(signed_message,
                                          signature,
                                          nonce.data(),
                                          enc_rsa_key,
                                          enc_rsa_key.size(),
                                          rsa_key_iv,
                                          &wrapped_rsa_key)) {
    LOGE("HandleProvisioningResponse: RewrapDeviceRSAKey fails");
    CleanupProvisioningSession();
    return UNKNOWN_ERROR;
  }

  const std::string&  device_certificate = provisioning_response.device_certificate();
  DeviceFiles::StoreCertificate(device_certificate, wrapped_rsa_key);

  //
  //---------------------------------------------------------------------------
  // Deletes cdm and crypto sessions created for provisioning.
  //
  CleanupProvisioningSession();
  return NO_ERROR;
}

CdmResponseType CdmEngine::GetSecureStops(
    CdmSecureStops* secure_stops) {
  // TODO(edwinwong, rfrias): add implementation
  return NO_ERROR;
}

CdmResponseType CdmEngine::ReleaseSecureStops(
    const CdmSecureStopReleaseMessage& message) {
  // TODO(edwinwong, rfrias): add implementation
  return NO_ERROR;
}

CdmResponseType CdmEngine::Decrypt(
    const CdmSessionId& session_id,
    bool is_encrypted,
    bool is_secure,
    const KeyId& key_id,
    const uint8_t* encrypt_buffer,
    size_t encrypt_length,
    const std::vector<uint8_t>& iv,
    size_t block_offset,
    void* decrypt_buffer,
    size_t decrypt_buffer_offset,
    bool is_video) {
  CdmSessionIter iter = sessions_.find(session_id);
  if (iter == sessions_.end()) {
    LOGW("CdmEngine::Decrypt: session_id not found = %s", session_id.c_str());
    return KEY_ERROR;
  }

  return iter->second->Decrypt(is_encrypted, is_secure, key_id, encrypt_buffer,
                               encrypt_length, iv, block_offset,
                               decrypt_buffer, decrypt_buffer_offset,
                               is_video);
}

bool CdmEngine::IsKeyValid(const KeyId& key_id) {
  for (CdmSessionIter iter = sessions_.begin();
       iter != sessions_.end(); ++iter) {
    if (iter->second->IsKeyValid(key_id)) {
      return true;
    }
  }
  return false;
}

bool CdmEngine::AttachEventListener(
    const CdmSessionId& session_id,
    WvCdmEventListener* listener) {

  CdmSessionIter iter = sessions_.find(session_id);
  if (iter == sessions_.end()) {
    return false;
  }

  return iter->second->AttachEventListener(listener);
}

bool CdmEngine::DetachEventListener(
    const CdmSessionId& session_id,
    WvCdmEventListener* listener) {

  CdmSessionIter iter = sessions_.find(session_id);
  if (iter == sessions_.end()) {
    return false;
  }

  return iter->second->DetachEventListener(listener);
}

bool CdmEngine::ValidateKeySystem(const CdmKeySystem& key_system) {
  return (key_system.find("widevine") != std::string::npos);
}

bool CdmEngine::CancelSessions() {
  // TODO(gmorgan) Implement CancelSessions()
  return true;
}

// Parse a blob of multiple concatenated PSSH atoms to extract the first
// widevine pssh
// TODO(kqyang): temporary workaround - remove after b/7928472 is resolved
bool CdmEngine::ExtractWidevinePssh(
    const CdmInitData& init_data, CdmInitData* output) {

  BufferReader reader(
      reinterpret_cast<const uint8_t*>(init_data.data()), init_data.length());

  // TODO(kqyang): Extracted from an actual init_data;
  // Need to find out where it comes from.
  static const uint8_t kWidevineSystemId[] = {
      0xED, 0xEF, 0x8B, 0xA9, 0x79, 0xD6, 0x4A, 0xCE,
      0xA3, 0xC8, 0x27, 0xDC, 0xD5, 0x1D, 0x21, 0xED,
  };

  // one PSSH blob consists of:
  // 4 byte size of the PSSH atom, inclusive
  // "pssh"
  // 4 byte flags, value 0
  // 16 byte system id
  // 4 byte size of PSSH data, exclusive
  while (1) {
    // size of PSSH atom, used for skipping
    uint32_t size;
    if (!reader.Read4(&size)) return false;

    // "pssh"
    std::vector<uint8_t> pssh;
    if (!reader.ReadVec(&pssh, 4)) return false;
    if (memcmp(&pssh[0], "pssh", 4)) return false;

    // flags
    uint32_t flags;
    if (!reader.Read4(&flags)) return false;
    if (flags != 0) return false;

    // system id
    std::vector<uint8_t> system_id;
    if (!reader.ReadVec(&system_id, sizeof(kWidevineSystemId))) return false;

    if (memcmp(&system_id[0], kWidevineSystemId,
               sizeof(kWidevineSystemId))) {
      // skip the remaining contents of the atom,
      // after size field, atom name, flags and system id
      if (!reader.SkipBytes(
          size - 4 - 4 - 4 - sizeof(kWidevineSystemId))) return false;
      continue;
    }

    // size of PSSH box
    uint32_t pssh_length;
    if (!reader.Read4(&pssh_length)) return false;

    output->clear();
    if (!reader.ReadString(output, pssh_length)) return false;

    return true;
  }

  // we did not find a matching record
  return false;
}

void CdmEngine::EnablePolicyTimer() {

  if (!policy_timer_.IsRunning())
    policy_timer_.Start(this, CDM_POLICY_TIMER_DURATION_SECONDS);
}

void CdmEngine::DisablePolicyTimer() {

  if (policy_timer_.IsRunning())
    policy_timer_.Stop();
}

void CdmEngine::OnTimerEvent() {

  for (CdmSessionIter iter = sessions_.begin();
       iter != sessions_.end(); ++iter) {
    iter->second->OnTimerEvent();
  }
}

}  // namespace wvcdm