Check if PlayReady license message is wrapped (#815)

Closes #814

CONTRIBUTORS

@@ -24,6 +24,7 @@
 
 Andy Hochhaus <ahochhaus@samegoal.com>
 Chad Assareh <assareh@google.com>
+Chris Fillmore <fillmore.chris@gmail.com>
 Costel Madalin Grecu <madalin.grecu@adswizz.com>
 Donato Borrello <donato@jwplayer.com>
 Duc Pham <duc.pham@edgeware.tv>

lib/media/drm_engine.js

@@ -1106,9 +1106,19 @@ shaka.media.DrmEngine.prototype.sendLicenseRequest_ = function(event) {
  * @private
  */
 shaka.media.DrmEngine.prototype.unpackPlayReadyRequest_ = function(request) {
-  // The PlayReady license message as it comes from the CDM can't be directly
-  // delivered to a license server.  Other CDMs do not seem to need this kind
-  // of special handling.
+  // PlayReady CDMs in some clients (e.g. IE11, Edge) wrap the license message
+  // in UTF-16 encoded XML which can't be directly delivered to a license
+  // server. However, not all clients exhibit this behaviour. The Tizen
+  // PlayReady CDM message is UTF-8 encoded and can be passed to the license
+  // server as-is. Other CDMs do not seem to need this kind of special
+  // handling.
+  var xml = String.fromCharCode.apply(null, new Uint8Array(request.body));
+
+  if (xml.indexOf('<PlayReadyKeyMessage') !== 0) {
+    // The message is not wrapped.
+    request.headers['Content-Type'] = 'text/xml; charset=utf-8';
+    return;
+  }
 
   // The raw license message is UTF-16-encoded XML.  We need to unpack the
   // Challenge element (base64-encoded string containing the actual license
@@ -1132,7 +1142,7 @@ shaka.media.DrmEngine.prototype.unpackPlayReadyRequest_ = function(request) {
   //   </LicenseAcquisition>
   // </PlayReadyKeyMessage>
 
-  var xml = shaka.util.StringUtils.fromUTF16(
+  xml = shaka.util.StringUtils.fromUTF16(
       request.body, true /* littleEndian */);
   var dom = new DOMParser().parseFromString(xml, 'application/xml');