Fix PlayReady on IE and Edge

We broke PlayReady on IE and Edge in #815 when we fixed PlayReady for
Tizen.  This should work for both, but will still need to be tested on
Tizen after merging.

Closes #837

Change-Id: Iff41845ae6a4b369e8f21a80623ebb2cb5475fd6

Author: joeyparrish

lib/media/drm_engine.js

@@ -1119,23 +1119,9 @@ shaka.media.DrmEngine.prototype.sendLicenseRequest_ = function(event) {
  * @private
  */
 shaka.media.DrmEngine.prototype.unpackPlayReadyRequest_ = function(request) {
-  // 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
-  // request) and any HttpHeader elements (sent as request headers).
+  // On IE and Edge, the raw license message is UTF-16-encoded XML.  We need to
+  // unpack the Challenge element (base64-encoded string containing the actual
+  // license request) and any HttpHeader elements (sent as request headers).
 
   // Example XML:
 
@@ -1155,8 +1141,18 @@ shaka.media.DrmEngine.prototype.unpackPlayReadyRequest_ = function(request) {
   //   </LicenseAcquisition>
   // </PlayReadyKeyMessage>
 
-  xml = shaka.util.StringUtils.fromUTF16(
-      request.body, true /* littleEndian */);
+  var xml = shaka.util.StringUtils.fromUTF16(
+      request.body, true /* littleEndian */, true /* noThrow */);
+  if (xml.indexOf('PlayReadyKeyMessage') == -1) {
+    // This does not appear to be a wrapped message as on IE and Edge.  Some
+    // clients do not need this unwrapping, so we will assume this is one of
+    // them.  Note that "xml" at this point probably looks like random garbage,
+    // since we interpreted UTF-8 as UTF-16.
+    shaka.log.debug('PlayReady request is already unwrapped.');
+    request.headers['Content-Type'] = 'text/xml; charset=utf-8';
+    return;
+  }
+  shaka.log.debug('Unwrapping PlayReady request.');
   var dom = new DOMParser().parseFromString(xml, 'application/xml');
 
   // Set request headers.

lib/util/string_utils.js

@@ -70,14 +70,17 @@ shaka.util.StringUtils.fromUTF8 = function(data) {
  *
  * @param {?BufferSource} data
  * @param {boolean} littleEndian true to read little endian, false to read big.
+ * @param {boolean=} opt_noThrow true to avoid throwing in cases where we may
+ *     expect invalid input.  If noThrow is true and the data has an odd length,
+ *     it will be truncated.
  * @return {string}
  * @throws {shaka.util.Error}
  * @export
  */
-shaka.util.StringUtils.fromUTF16 = function(data, littleEndian) {
+shaka.util.StringUtils.fromUTF16 = function(data, littleEndian, opt_noThrow) {
   if (!data) return '';
 
-  if (data.byteLength % 2 != 0) {
+  if (!opt_noThrow && data.byteLength % 2 != 0) {
     shaka.log.error('Data has an incorrect length, must be even.');
     throw new shaka.util.Error(
         shaka.util.Error.Severity.CRITICAL, shaka.util.Error.Category.TEXT,
@@ -98,7 +101,7 @@ shaka.util.StringUtils.fromUTF16 = function(data, littleEndian) {
   }
 
   // Use a DataView to ensure correct endianness.
-  var length = data.byteLength / 2;
+  var length = Math.floor(data.byteLength / 2);
   var arr = new Uint16Array(length);
   var dataView = new DataView(buffer);
   for (var i = 0; i < length; i++) {

test/media/drm_engine_integration.js

@@ -247,9 +247,8 @@ describe('DrmEngine', function() {
   });  // describe('basic flow')
 
   function checkKeySystems() {
-    // TODO: re-enable these tests for PlayReady (b/38496036)
     // Our test asset for this suite can use any of these key systems:
-    if (!support['com.widevine.alpha']) {
+    if (!support['com.widevine.alpha'] && !support['com.microsoft.playready']) {
       // pending() throws a special exception that Jasmine uses to skip a test.
       // It can only be used from inside it(), not describe() or beforeEach().
       pending('Skipping DrmEngine tests.');