Tutorial: Custom Request and Response Processing

License Request Pre-processing and License Response Post-processing.

Shaka Player supports pre-processing license requests and post-processing license responses. Applications may require pre and post processing when interacting with certain license servers.

By default Shaka Player assumes the license server accepts raw license request messages from the key system and assumes the license server responds with raw licenses that Shaka Player can pass directly to the key system. If your license server does not work this way then you must provide a license request pre-processor, a license request post-processor, or both.

Suppose your application uses the Widevine key system, but the license server has a front-end which expects a JSON-based request and responds with a JSON-based response, as defined below:

License request format:
  {"app_data": app_data_string,
   "message": base64_message_string}

License response format:
  {"app_data": app_data_string,
   "license": base64_license_string}

/**
 * @param {string} schemeIdUri The ContentProtection's scheme ID URI.
 * @param {!Element} contentProtection The ContentProtection element.
 * @return {!Array.<shaka.player.DrmInfo.Config>} An array of Config
 *     objects or null if the element is not understood by this application.
 */
function interpretContentProtection(schemeIdUri, contentProtection) {
  // edash-packager uses this UUID to represent the Widevine key system.
  // This is the only scheme we are expecting for this application.
  if (schemeIdUri != 'urn:uuid:edef8ba9-79d6-4ace-a3c8-27dcd51d21ed') {
    console.warn('Unrecognized scheme: ' + schemeIdUri);
    return null;
  }

  /**
   * @param {!shaka.player.DrmInfo.LicenseRequestInfo} requestInfo
   */
  var preProcessor = function(requestInfo) {
    // Encode the license request message as base64.
    var message = window.btoa(
        String.fromCharCode.apply(null, new Uint8Array(requestInfo.body)));

    // Encode the payload as JSON.
    var obj = {
      'app_data': App.clientData,  // Provide some arbitrary data.
      'message': message
    };
    requestInfo.body = JSON.stringify(obj);
  };

  /**
   * @param {!Uint8Array} serverResponse
   * @return {!Uint8Array}
   */
  var postProcessor = function(serverResponse) {
    // serverResponse is a Uint8Array, so decode it into an object.
    var json = String.fromCharCode.apply(null, serverResponse);
    var obj = JSON.parse(json);

    // Update our arbitrary data.
    App.clientData = obj['app_data'];

    // obj['license'] is base64, so decode it into a string and then encode it
    // into a Uint8Array.
    var licenseString = window.atob(obj['license']);
    var license = new Uint8Array(licenseString.split('').map(
        function(ch) { return ch.charCodeAt(0); }));
    return license;
  };

  return [{
    'keySystem': 'com.widevine.alpha',
    'licenseServerUrl': App.LICENSE_SERVER_URL,
    'licensePreProcessor': preProcessor,
    'licensePostProcessor': postProcessor
  }];
}

For more information and more examples, see shaka.player.DashVideoSource.ContentProtectionCallback, shaka.player.DrmInfo.Config, shaka.player.DrmInfo.LicensePostProcessor, shaka.player.DrmInfo.LicenseRequestInfo, and shaka.player.DrmInfo.LicensePreProcessor.