shaka-player/tutorials/network.html

<!--
 Copyright 2015 Google Inc.

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
 You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
-->

<h3 class="tutorial-heading">
License Request Pre-processing and License Response Post-processing.
</h3>

<p>
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.
</p>

<p>
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.
</p>

<p>
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:

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

License response format:
  {"app_data": app_data_string,
   "license": base64_license_string}
</pre>

where 'app_data' is some arbitrary application-specific data.
</p>

Below we show a {@link shaka.player.DashVideoSource#ContentProtectionCallback}
that interprets the Widevine ContentProtection element and provides pre and
post processors for our hypothetical license server.
</p>

<pre class="prettyprint source"><code id="network_sample1">/**
 * @param {string} schemeIdUri The ContentProtection's scheme ID URI.
 * @param {!Element} contentProtection The ContentProtection element.
 * @return {!Array.&lt;shaka.player.DrmInfo.Config&gt;} 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
  }];
}

</code></pre>

<p>
For more information and more examples, see
{@link shaka.player.DashVideoSource.ContentProtectionCallback},
{@link shaka.player.DrmInfo.Config},
{@link shaka.player.DrmInfo.LicensePostProcessor},
{@link shaka.player.DrmInfo.LicenseRequestInfo}, and
{@link shaka.player.DrmInfo.LicensePreProcessor}.
</p>